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FELINE DENTISTRY
ACUTE AND CHRONIC FAUCITIS OF DOMESTIC CATS A Feline Calicivirus-Induced Disease Gerhard H. Reubel, DrMedVet, Diane E. Hoffmann, BS, and Niels C. Pedersen, DVM, PhD
Inflammatory diseases of the oral cavity of domestic cats are of great importance to cat owners and veterinarians. One half to three fourths of randomly examined cats had some type of inflammatory lesion in the mouth. 16, 18 The most common inflammatory disease of the mouth is gingivitis, followed by periodontitis. More severe forms of oral cavity inflammation, usually termed stomatitis in the veterinary literature, are much less common. The selective use of the term stomatitis for severe oral diseases in cats suggests that feline stomatitis has a single clinical presentation and a single cause. Severe oral inflammation of cats, however, is diverse in both clinical expression and causeY One specific type of feline stomatitis has been called chronic plasma cell gingivitis and pharyngitis/ As originally described, plasma cell gingivitis and pharyngitis is a chronic ulceroproliferative disease centered around a specific region of the mouth, the oral fauces. Affected tissues are densely infiltrated with plasma cells and lymphocytes, hence the name. Some cats described in the literature as having chronic stomatitis appeared to have a disease similar to chronic plasma cell gingivitis and pharyngitis. 8, 17 The cause of plasma cell gingivitis and pharyngitis has not been determined, and attempts to cure the condition have been unsuccessful. Several events occurred over the last year that caused the authors to study inflammatory lesions in the oral fauces of cats. Outbreaks of a chronic ulceroproliferative faucitis were observed in multiple cats within several households. Chronic faucitis was also seen with increasing frequency among cats presented to the Veterinary Medical Teaching Hospital (VMTH), University of California, Davis, for oral cavity afflictions. The two observations led to the postulate that inflammatory faucial disease in cats might be a specific and infectious disease From the Department of Medicine, University of California, Davis, School of Veterinary Medicine, Davis, California VETERINARY CLINICS OF NORTH AMERICA: SMALL ANIMAL PRACTICE VOLUME 22 • NUMBER 6 • NOVEMBER 1992
1347
1348
REVBEL et al
entity. This study reports on the isolation of several different strains of feline calicivirus (FCV) from cats with both acute and chronic naturally occurring faucitis and the experimental recreation of acute faucitis with these isolates in specific pathogen free (SPF) cats. These studies indicate that FCV can cause acute faucitis in cats and that a proportion of acutely affected cats may go on to develop chronic faucitis. MATERIALS AND METHODS Field Studies
Field studies were conducted on pet cats presented to the VMTH, University of California, Davis. The first group consisted of 23 cats that were seen for oral cavity disease. The second group consisted of 140 cats randomly selected from cats seen at the VMTH for any reason (10 for oral disease); 134 of these 140 cats have been previously described.!6 The clinical diagnoses at the time of testing were taken from the animal's hospital records. Experimental Animals
SPF domestic cats were obtained from the breeding colony of the Feline Nutrition Laboratory of the School of Veterinary Medicine, University of California, Davis, and were housed in infectious disease isolation facilities provided by the Animal Resources Service at the same institution. Virus Isolation
The oral fauces of each animal were brushed with a sterile cotton-tipped swab and FCV isolated as previously described. '6 Feline Calicivirus Strains
Four FCV isolates were used for the experimental infection. FCV-Cook was isolated from the oral cavity of a privately owned 9-year-old cat (case no. 2S28-24) with severe, chronic gingivitis and faucitis. FCV-VMTH-1 was isolated from the oral cavity of a 6-year-old cat (case no. 2S-38-68) with chronic faucitis, FCV-VMTH-2 from a 9-year-old cat (case no. 2S-64-06) with chronic pharyngitis and faucitis, and FCV-SPCA from the oral cavity of a 2-year-old cat (case no. 2S-62-83) with severe faucitis and gingivitis. Experimental Infection
Cats were 6 to 9 months of age at the time of infection. Cats of four experimental groups (FCV-Cook, FCV-VMTH-1, FCV-VMTH-2, FCV-SPCA) were inoculated by mouth with 1075 tissue culture infectious dose-SO% (TCIDso ) per O.S mL of the different virus isolates. Cats in the fifth experimental group were infected with a similar amount of FCV-VMTH-1 by shallow injection along the gums and in the oral fauces as well as onto the mucous membranes. Cats
ACUTE AND CHRONIC FAUCITIS OF DOMESTIC CATS
1349
in the sixth experimental group were housed for 1 month together with two cats that were naturally infected with the Cook isolate of FCV. The naturally infected cats had chronic gingivitis, periodontitis, and u1ceroproliferative faucitis. Clinical Evaluation
Cats were monitored daily for the first week postinfection and weekly thereafter. In addition to routine physical examination, precise inspection of the oral cavity was performed. Rectal temperatures were taken daily for the first week postinfection of all cats except those infected through natural contact. Biopsy
Tissue samples were taken from the fauces of three cats with experimentally induced acute faucitis under ketamine hydrochloride/acepromazine anesthesia and fixed in 10% buffered formal-saline. Thin sections were stained with hematoxylin and eosin. Cells and Media
Crandell feline kidney cells (CrFK) were used as a substrate for virus isolation, virus titration, and detection of virus neutralizing antibodies. Cells were grown in a 1:1 dilution of Leibovitz's L 15 medium and Earle's minimum essential medium containing 10% fetal calf serum; penicillin, 100 IU/mL, streptomycin, 10 J..lg/mL; and gentamicin, 5 J..lg/mL. Serology
Sera for FCV neutralization were diluted serial twofold in cell culture media. Fifty microliters of diluted sera were mixed with 50 J..lL of virus solution containing 100 TCIDsJmL in 96-well microtiter plates and incubated for 90 minutes at 37°C. Thereafter 100J..lL of CrFK cell suspension were added to each well. Plates were monitored for FCV cytopathic effect (CPE) for 4 days. Antibody titers were expressed as the reciprocal of the highest serum dilution completely neutralizing CPE. Cross virus neutralization was performed with homologous and heterologous FCV isolates. Antisera used in the study were harvested 3 weeks following infection. Electron Microscopy
CrFK cells inoculated with FCV from cats infected with each of the four FCV isolates were fixed in 2% glutaraldehyde in cacodylate buffer and processed in a routine manner for electron microscopic examination. Statistical Analysis
The probability of FCV oral carriage in the different categories of the field cases was evaluated by contingency table chi square analysis using a computerized statistics package (Statview SE + Graphics, Abacus Concepts, CA).
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REUBEL et al
RESULTS
Feline Calicivirus Isolations from Field Cases
FCV was isolated from oral swabs of 26 out of 140 randomly selected cats (19%) and from 14 out of 23 cats with a specific history of oral cavity disease (61 %) (Table 1). Eight of 23 cats admitted for oral cavity disease had a chronic ulceroproliferative faucitis (Color Plate 3, Figure 8), and one of 23 had an acute faucitis (Color Plate 3, Figure 9). One of the eight cats with chronic faucitis tested positive for feline immunodeficiency virus (FIV), and none were infected with feline leukemia virus (FeLV). The one kitten with acute faucitis tested negative for both FIV and FeLV. All of the cats that were presented witli faucitis (n = 9) were FCV positive, which was significantly higher than the incidence of FCV isolations from the 14 cats presented for oral cavity disease that did not have faucitis (P = 0.0082) or from the 140 randomly selected cats (P sO.OOOI). Electron Microscopy
Figure 1 shows crystalline arrays typical for caliciviruses that were seen in the cytoplasma of CrFK cells infected in vitro with the four strains of FCV Table 1. RESULTS OF FELINE CALICIVIRUS ISOLATIONS FROM ORAL SWABS OF 23 CATS PRESENTED TO THE VETERINARY MEDICAL TEACHING HOSPITAL WITH HISTORY OF ORAL CAVITY DISEASE
Cat#
Case#
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
24-42-93 25-4075 25-28-24 24-42-18 24-46-36 25-25-78 25-62-83 25-33-43 25-00-52 23-00-96 24-95-25 25-41-53 25-31-78 25-28-26 25-38-69 25-91-94 25-64-06 "boots horn" 25-79-72 25-94-11 25-72-73 25-82-31 25-90-68
Age (years) 2 adult 9 5 4 3 2 1 6 11 14 adult 15 1 6 adult 9 4 3 10 1 5 %
Clinical Diagnosis Mild chronic gingivitis Mild chronic gingivitis Mild chronic gingivitis Mild chronic gingivitis Mild chronic gingivitis Severe chronic gingivitis Severe chronic gingivitis Severe chronic gingivitis Severe chronic gingivitis Severe chronic gingivitis Severe chronic periodontitis Severe chronic periodontitis Chronic periodontitis Severe chronic stomatitis Chronic faucitis Severe chronic faucitis Chronic faucitis and pharyngitis Chronic faucitis and gingivitis Chronic faucitis and gingivitis Chronic faucitis and periodontitis Chronic faucitis and periodontitis Chronic bilateral faucitis Acute faucitis, palatitis, and limping
Feline Calicivirus Oral Carriage
+ + + + +
+ + + + + + + + +
ACUTE AND CHRONIC FAUCITIS OF DOMESTIC CATS
1351
Figure 1. Transmission electron photomicrograph of a Crandell feline kidney cell infected with the Cook strain of feline calicivirus. (Lead citrate and uranyl acetate stain; original magnification x 66.)
(Cook, VMTH-l, VMTH-2, SPCA) isolated from four cats with naturally occurring chronic ulceroproliferative faucitis. Clinical Evaluation-Experimentally
Infecte~
Cats
Clinical signs of illness appeared in all FCV-Cook, FCV-VMTH-l, FCVVMTH-2, and FCV-SPCA infected cats 2 to 3 days after experimental exposure by mouth and 7 to 14 days after natural contact exposure. The four FCV isolates induced a similar acute disease (Tables 2 and 3). Clinical signs of illness included depression, pyrexia, reduced appetite, inflammation along the gumlines (Color Plate 3,* Figure 10), ulcerations of the soft and hard palate, ulcerations on the tongue (Color Plate 3, Figure 11), and inflammation of the fauces (Color Plate 3, Figures 12 and 13). Twelve out of 19 cats had transient limping or stiffness. Mild rhinitis was observed in two of 25 cats and conjunctivitis in three of 25. Diarrhea was observed in one cat infected with the SPCA strain of FCV. Clinical signs lasted from a few days (fever, limping, diarrhea, rhinitis, conjunctivitis, and lingual and palatal ulcers) to several weeks (gingivitis, faucitis). No sign of chronic oral disease was observed in any of the cats as long as 7 months later. Feline Calicivirus Isolation from Experimentally Infected Cats
FCV was conSistently recovered from most of the experimentally FCVinfected cats for the first 4 weeks after inoculation. Virus was isolated only 'See color section in the beginning of this issue.
Table 2. DEVELOPMENT OF CLINICAL SIGNS IN SPECIFIC PATHOGEN FREE CATS (n FOUR ISOLATES OF FELINE CALICIVIRUS
=
19) AFTER EXPERIMENTAL INOCULATION WITH
Number of Cats Days after Infection
Weeks after Infection
Clinical Signs
3
5
7
2
Fever (>38SC) Limpinglsoreness Ulcers Tongue Palate Lip Nasal frenulum Gingivitis' Pharyngitis Faucitis Conjunctivitis Rhinitis Diarrhea
18/19 1/19
19/19 11/19
12/19 3119
5119 3/19
5
6
7
8
4/19 3/19 2/19
5/19 4/19 2/19 1/19 4/19
4/19
5/19 1/19
10/19 1/19
12/19 3/19
1/19
1/19
5/19 9/19 6/19 1/19 5/19 1/19 12/19 2/19 2/19 1/19
2/19 1/19
8/19
7/19 9/19 3/19 1/19 8/19
5/19
8/19
6/19
5/19
4/19
8119
6/19 1/19
8/19
2/19 1/19
1/19
1/19
1/19
1/19
1/19
1/19
1/19
1/19
1/19
3
4 1/19
'Cats were erupting their permanent dentition, and it was difficult to differentiate traumatic from viral·induced inflammation.
Table 3. DEVELOPMENT OF CLINICAL SIGNS IN SPECIFIC PATHOGEN FREE CATS (n = 6) AFTER CONTACT EXPOSURE TO TWO CATS NATURALLY INFECTED WITH THE COOK STRAIN OF FELINE CALICIVIRUS Number of Cats Weeks after Infection Clinical Signs
Fever (>38SC) Limping/soreness Ulcers Tongue Palate Lip Gingivitis" Pharyngitis Faucitis Conjunctivitis Rhinitis Diarrhea
nt' nt
3/6
2
3
4
5
6
7
B
9
10
13
15
17
19
nt nt
nt nt
nt nt
nt nt
nt nt
nt nt
nt nt
nt nt
nt nt
nt nt
nt nt
nt nt
nt nt
1/6 1/6 5/6
4/6
6/6
6/6
6/6
6/6
6/6
5/6
6/6
6/6
5/6
4/6
4/6
5/6 2/6 1/6
3/6
3/6
2/6
4/6
3/6
1/6
4/6 1/6 4/6
• Not tested. "Cats were erupting their permanent dentition, and it was difficult to differentiate traumatic from viral·induced inflammation.
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REUBEL et al
sporadically from single individuals thereafter (Table 4). None of the cats shed FCV later than 17 weeks after infection. Serology
Serum antibodies that neutralized the homologous virus were detectable in all cats as early as 2 weeks after infection (data not shown). Antisera against FCV-SPCA neutralized the homologous virus only. Antisera to FCV-VMTH-2 had weak neutralizing activity against heterologous strains, whereas antisera to FCV-Cook and FCV-VMTH-1 neutralized heterologous strains to similar degrees (Table 5). This pattern of homologous and heterologous reactivity . indicated that the four FCV isolates represented three distinct serotypes: (1) FCV-SPCA, (2) FCV-Cook and FCV-VMTH-1, and (3) FCV-VMTH-2. Biopsy
Similar lesions were seen in tissues taken by biopsy from the acutely inflamed fauces of three experimentally infected cats. Multifocal, multiloculated, vesicopustular lesions were observed in the stratum spino sum of the oral mucosa (Fig. 2). There was diffuse edema of the submucosa with an associated vasculitis involving small venules. The venulitis was characterized by infiltration and margination of the vascular wall with neutrophils and focal areas of endothelial cell degeneration. DISCUSSION
The finding that at least one form of severe oral inflammation might be caused by FCV is not new. Povey" made reference in passing to FCV and chronic gingivitis and pharyngitis in cats in 1976. The next reference to FCV infection and chronic gingivitis and pharyngitis was published by Australian researchers in 1984.17 An English study recently demonstrated that 50% to 92% of cats with chronic stomatitis were FCV shedders compared with 0 to 19% of nonaffected control groupS.8 According to the descriptions, at least some of the cats in these studies had faucial lesions. No one, however, has been able to recreate experimentally chronic oral lesions with FCV, even using isolates from cats that had chronic stomatitis. 9 Tenorio et a1'6 made a statistical comparison between persistent oral carriage of FCV, FeL V, and FlV and chronic inflammatory oral cavity lesions. No statistical linkage was found between FCV oral carriage and milder forms of chronic stomatitis, i.e., gingivitis. FlV infection was more often related to chronic oral cavity disease than could be accounted for by chance, especially as the severity of the oral cavity disease increased. This was supported by other studies that have linked FlV infection with oral cavity disease. s, 6, 8, 20 Although FCV carriage could not be linked to milder forms of inflammatory oral disease, there was a greater tendency for cats with more severe oral disease to be FCV shedders.16 This relationship was strongest for cats that were also coinfected with FeLV or FlV. The present study shows conclusively that acute faucitis is a FCV-induced lesion. The four field isolates of FCV used in these experiments produced similar types of lesions regardless of type of exposure. Inoculation of small
Table 4. RESULTS OF FCV ISOLATIONS FROM ORAL SWABS OF SPECIFIC PATHOGEN FREE CATS EXPERIMENTALLY INFECTED WITH FOUR DIFFERENT ISOLATES OF FELINE CALICIVIRUS Type of Exposure
Strain
Cook
Cook
>-'
w
r..n r..n
Contact
By mouth
VMTH-1
By mouth Local injection
VMTH-1
By mouth
VMTH-2
By mouth
SPCA
By mouth
'Not done.
Weeks Postexposure
2
Cat 10 #
90-419 90-444 90-454 90-475 90-513 90-683 5054 5064 5077 5080 90-430 90-445 90-660 5060 5065 5076 5078 5079 90-777 90-795 90-826 91-006 90-831 91-003 91-025
+ + + + + + + + + + + + + + + + + + + + +
3
+
+
+
+ +
+ + + + + + + + + + + + + + + + + + + +
+ + + + + + + + + + + + + + +
4
+ + + + + + + + + + + + + + + + + + + + +
5
+ +
+ + + + + + + + +
+
6
7
+ + +
nd* nd nd nd nd nd nd nd nd nd
nd nd nd nd nd nd nd nd nd nd nd nd
+
nd nd nd nd nd
+
8
+
nd nd nd
9 nd nd nd nd nd nd
+
11
nd nd nd nd
15
17
19
+ + + nd nd nd nd
+
+
13
nd nd nd nd nd nd nd nd nd nd nd nd
+ nd nd nd nd
nd nd nd nd
nd nd nd nd
nd nd nd nd nd nd nd nd nd nd nd nd
nd nd nd nd nd nd nd nd nd nd nd nd
nd nd nd nd nd nd nd nd nd nd nd nd
nd nd nd nd nd nd nd nd nd nd nd nd nd nd nd nd nd nd nd
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REUBEL et al
Table 5. FELINE CALICIVIRUS NEUTRALIZING ANTIBODY RESPONSE (MEAN ± SD) IN SERA OF SPECIFIC PATHOGEN FREE CATS EXPERIMENTALLY INFECTED WITH FOUR DIFFERENT ISOLATES OF FELINE CALICIVIRUS 3 WEEKS POSTINFECTION
Feline Calicivirus Strain Cook VMTH·1 VMTH-2 SPCA
Serum Neutralizing Antibody Titers of Convalescent Feline Calicivirus Antisera against four Strains of Feline Calicivirus Cook
(n = 5)
38.4 256.0 6.0 0.0
(± 51 .0) (± 0.0) (±4.0) (±O.O)
VMTH-1 (n 3)
=
112.0 213.3 20.0 0.0
(±96.0) (± 73.9) (± 30.3) (±O.O)
VMTH-2
(n = 4)
128.0 16.0 112.0 0.0
(± 78.4) ( ± O.O) (±32.0) (±O.O)
SPCA
(n = 4)
48.0 28.0 2.0 106.7
( ± 45.3) (± 31.7) (±2.3) (± 37.0)
amounts of virus into the gums and fauces did not produce any different disease than seen in cats infected by dropping the virus onto the oral mucous membranes or that were infected by natural contact. The same was true for natural contact exposure versus direct infection by mouth . Clinical signs, however, took 1 to 2 weeks longer to appear after natural contact than direct exposure by mouth. The natural exposure studies demonstrated how efficiently and rapidly FeV could be transmitted between carrier and susceptible cats placed in intimate contact with each other. Acute faucitis was seen in a majority of cats that were infected with at least four different field isolates of FeV obtained from cats with chronic faucitis. Faucitis has not been previously reported as an acute lesion of FeV infection, although it is well known that the virus causes acute lingual and palatine
Figure 2. Photomicrograph of mucosal and submucosal tissue taken from the oral fauces of an experimentally feline calicivirus-infected cat with acutefaucitis. Multifocal, multiloculated, vesicopustular lesions were present in the stratum spinosum of the oral mucosa. The submucosa was edematous, and numerous polymorphonuclear leukocytes were marginating within and without of small venules. (Hematoxylin and eosin stain; original magnification x 300.)
ACUTE AND CHRONIC FAUCITIS OF DOMESTIC CATS
1357
ulcers, fever, and limping.JO, 13 It is possible that acute faucitis occurred during other experimental studies but that it was not detected. The acute faucitis was not always flamboyant in appearance, and identification of the lesion required a close inspection of the mouth and a familiarity with the normal appearance of the oral fauces. There has also been a tendency for previous FCV researchers to concentrate on the lesions that were of particular interest for them. For example, early FCV studies stressed the upper respiratory component of the infection and usually failed to mention limping and soreness. lO Acute faucitis was not just an experimental lesion because at least one cat observed at the VMTH also developed faucitis during a brief episode of classic FCV-induced disease. The faucial lesions in this cat were detected because the clinicians had been made aware of the lesion in experimentally infected cats. Feline calicivirus was isolated from the oral cavities of this naturally infected cat. The oral fauces as a site for FCV-induced lesions should have been anticipated. The tonsils and adjacent faucial mucosa are sites of virus replication in asymptomatic chronic FCV carrier cats.' FCV was reportedly replicating within cells of the stratum germinativum in healthy carrier cats, whereas lesions in acute FCV-induced faucitis reported here were in the stratum spinosum and in venules in the submucosa. Unfortunately no virus localization studies were done in the present study to see if lesional sites and sites of virus replication were the same. Chronic faucitis was not reproduced in this study with field isolates of FCV, so what is the evidence that chronic faucitis is FCV induced? The most critical evidence came from field cases that showed oral carriage of FCV by 100% of the cats with the lesion. This was significantly higher than the background carriage rate of 19% in randomly selected cats and 36% in cats with severe oral disease and no faucitis. The second piece of evidence was that a similar, although acute, type of faucitis could be induced with FCV strains isolated from cats with chronic faucitis. It would be unlikely for such an uncommon and specific lesion to be caused by entirely different agents. Finally, the oral fauces have been shown to be a site of persistent FCV replication! ConSidering what is known about FCV infection and oral cavity disease, what is the pathogenesis of chronic FCV-induced disease? We would propose that one or more of the following possible mechanisms or factors are involved in the disease: (1) Chronic faucitis is associated with specific strains of FCV; (2) chronic faucitis is associated with persistent FCV oral carriage, although FCV strains isolated from diseased mouths infrequently cause persistent infections (compared with other strains); (3) cofactors that enhance the likelihood of persistent FCV infection will increase the incidence of chronic faucitis; and (4) chronic faucitis may result from an uncommon and abnormal type of immune response to persistent FCV infection of the fauces. Evidence for the involvement of specific strains of FCV in chronic faucitis is conflicting. On one hand, past studies of experimentally induced FCV infection suggest that FCV manifestations can vary with the strain.'9 Some strains of FCV reportedly cause mainly upper respiratory-like illness and pneumonia, whereas other strains have been associated mainly with limping. lO Acute faucitis has not been previously reported, indicating that faucitis may be strain-specific. On the other hand, most strains of FCV will cause oral lesions to some degree, and it is likely that faucitis was just not recognized in previous studies. As an example, limping became a commonly recognized feature of Fev infection only after it was specifically brought to attention," Further, if chronic faucitis is caused by a specific strain of FCV, faucitis-inducing strains
1358
REUBEL et al
should be serologically distinct. The four faucitis-inducing strains that were reported herein belonged to three different serotypes based on cross virus neutralization tests. This amount of diversity among four random isolates was typical of what would have been expected for FCV isolates in general. 14 The second factor in the pathogenesis of chronic faucitis presumes that faucitis-inducing strains of FCV are different from other strains of FCV, i.e., they cause persistent infection in only a very small proportion in infected cats. Studies with FCV isolates from cats with chronic faucitis (reported herein) or chronic stomatitis9 support this presumption. At least five different FCV isolates from two widely different geographic locations were incapable of inducing a persistent oral carrier state in experimentally infected cats. In contrast, Wardley and Povey19 found that 16% to 20% of cats infected with two of three different FCV isolates shed virus from their oral cavities longer than 6 months. This carriage rate was identical to that observed in the field. It is important to note, however, that such studies are the exception; most experimentally FCV-infected cats cease shedding within 1 to 2 months. It is uncertain therefore whether or not persistent FCV carrier state is strain-dependent or if persistent infection is largely influenced by vagaries in experimental conditions. If it is the latter, there may be nothing unique about faucitis-inducing strains of FCV in terms of their ability to cause chronic infections. The third possible factor involved in the induction of chronic faucitis by FCV is the easiest to support scientifically. Dawson et aP induced protracted oral FCV carriage in cats that were either previously vaccinated against FCV or were in the primary stages of FlV infection. One of four FlV negative/FCV vaccinated cats was still shedding FCV after 5 months compared with none of four FlV negative/FCV nonvaccinated cats; among FlV infected cats, three of four FCV-vaccinated and three of four FCV-nonvaccinated cats (six of eight of all FlV-infected cats) were still shedding FCV after 5 months. One of the strains (LS015) used in the study of Dawson et aP was the same as one used by Knowles et aV i.e., an isolate from a cat with chronic stomatitis. This same strain did not cause persistent oral carriage in FIV-noninfected/FCV-nonvaccinated cats. These findings help to explain why 15% to 80%, depending on the study, of cats with chronic stomatitis are also infected with FlV.6. 8. 20 One of eight cats (13%) with chronic faucitis in the present study was FIV infected. The fourth mechanism, i.e., that chronic faucitis results from an abnormal immune response to persistent FCV infection, regardless of serotype, also has credence. There is evidence that persistent FCV infection, even with chronic stomatitis strains, is not sufficient by itself to induce chronic faucitis; chronic oral cavity disease was not observed in any of the seven cats reported to have protracted Fev oral carriage by Dawson et al. 3 The characteristic microscopic change observed in cats with chronic faucitis was a dense lymphocytic! plasmacytic infiltrate.' Such an infiltrate, in this location, is indicative of a chronic immune response to FeV. From 19% to 26% of healthy-appearing household pet cats, however, shed FCV from their oral cavities, and very few of them develop chronic faucitis. 16 Is it possible that asymptomatic FeV carrier cats are in a perfect host-parasite relationship? The establishment of such a perfect relationship after acute illness is not unique. Feline leukemia virus infection evokes a florid host response during the initial viremic stage, but this response is terminated by either complete recovery or the establishment of a chronic asymptomatic carrier state. 2 The same is true of FlV infection of cats.2l Such an all or none concept, however, must be modified to include an intermediate state of immunity: a state where the host attempts to rid the body of the parasite and in so doing injures itself. Such a state has been described
ACUTE AND CHRONIC FAUCITIS OF DOMESTIC CATS
1359
for another viral disease of cats, feline infectious peritonitis virus (FIPV) infection. FIPV infection occurs in three clinical forms: an asymptomatic carrier state, a generalized exudative serositis, and a systemic granulomatous disease. There is strong circumstantial evidence that the form of infection is directly related to the comparative strengths of humoral and cellular immuti.ityY Asymptomatic FlPV carriers have very strong cell-mediated immunity, cats with exudative serositis have no cellular immunity, whereas cats with granulomatous disease have partial cell-mediated immunity. In the same manner, chronic faucitis could occur in a small proportion of cats that respond immunologically to a persistent FeV oral carriage in an atypical manner. FlV infection could enhance FeV-induced disease not only by increasing the likelihood of a carrier state, but also by causing perturbations in the strength or type of FeV immunity. Acute gingivitis was an additional FCV-induced oral lesion observed in this study that has not heretofore been described. The gingivitis was quite florid in some animals, especially when it involved the incisor teeth. Lesions were also seen in the gums overlying or adjacent to premolars, molars, and canines that were erupting. Gingival lesions could have been enhanced in this study by mechanical trauma, thus allowing more fertile environment for the virus to infect and cause lesions. Whether acute FeV-induced gingivitis has a chronic counterpart is unknown. A recent large field study showed no relationship between the common type of gingivitis in cats and FCV infection. 16 There are, however, at least two anecdotal reports in the literature linking chronic gingivitis with persistent oral carriage of FeV.I. [9 The increasing incidence of chronic faucitis in cats is a reason for concern, especially if it is a property of all FeV strains that exist in the field. The lesion is very debilitating for affected animals and frequently leads to owners having their cat euthanized. The fact that more cats are currently oral carriers of FeV than before vaccination began almost 2 decades ago" is another reason to be concerned. Because faucitis with or without accompanying gingivitis or periodontitis appears to be a specific disease entity, it is proposed that this disorder be given a specific name and not lumped under the terms stomatitis and pharyngitis. A preferable name would be feline calicivirus induced acute (or chronic) ulceroproliferative faucitis. ACKNOWLEDGMENTS We would like to acknowledge Dr. Leigh West-Hyde, Department of Surgery, University of California, Davis, School of Veterinary Medicine, for helping to prOVide oral swabs and histories for cats presented to the VMTH for oral diseases; Mr. Robert Munn, Department of Pathology, University of California, Davis, School of Medicine, for the electron microscopy; Pro-Visions Corp., Checkerboard Square, St. Louis, MO, for providing cat food; and NIH (AI-25802-05) for funding.
References 1. August JR: Feline viral respiratory disease. The carrier state, vaccination, and control. Vet CIin North Am 14:1150-1121, 1984 2. Charreyre CE, Pedersen NC: Study of feline leukemia virus immunity. J Am Vet Med Assoc 199(10):1316-1324, 1991 3. Dawson S, Smyth NR, Bennett M, et al: Effect of primary-stage feline immunodefi-
1360
4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20.
21.
REUBEL et al
ciency virus infection on subsequent feline calicivirus vaccination and challenge in cats. AIDS 5:747-750, 1991 Dick CP, Johnson RP, Yamashiro S: Sites of persistence of feline calicivirus. Res Vet Sci 47(3):367-373, 1989 Hosie MJ, Robertson C, Jarrett 0: Prevalence of feline leukaemia virus and antibodies to feline immunodeficiency virus in cats in the United Kingdom. Vet Rec 125(11):293297, 1989 Ishida T, Washizu T, Toriyabe K, et al: Feline immunodeficiency virus infection in cats of Japan. J Am Vet Med Assoc 194(2):221-225, 1989 Johnessee J, Hurvitz A: Feline plasma cell gingivitis-pharyngitis. J Am Anim Hosp Assoc 19:179-181, 1983 Knowles JO, Gaskell RM, Gaskell q, et al: Prevalence of feline calicivirus, feline. leukaemia virus and antibodies to FlV in cats with chronic stomatitis. Vet Rec 124(13):336-338, 1989 Knowles JO, McArdle F, Dawson S, et al: Studies on the role of feline calicivirus in chronic stomatitis in cats. Vet Microbiol 27(3-4):205-219, 1991 Pedersen NC: Common infectious diseases of multiple-cat environments. In Feline Husbandry. Goleta, CA, American Veterinary Publications, 1991, pp 163-288 Pedersen NC: Inflammatory oral cavity diseases of the cat. Vet Clin North Am Small Anim Pract 1992; in press Pedersen NC, Floyd K: Experimental studies with three new strains of feline infectious peritonitis virus FlPV-UCD-2, FlPV-UCD-3 and FlPV-UCD-4. Compend Con tin Educ Pract Vet 7:1001-1011, 1985 Pedersen NC, Laliberte L, Ekman S: A transient febrile limping syndrome of kittens caused by two different strains of feline calicivirus. Feline Practice 13(1):26-35, 1983 Povey RC: Serological relationship among feline caliciviruses. Infect Immun 10:13071314, 1974 Povey RC: Viral diseases of cats: Current concepts. Vet Rec 98:293, 1976 Tenorio AP, Franti CE, Madewell BR, et al: Chronic oral infections of cats and their relationship to persistent oral carriage of feline calici-, immunodeficiency, or leukemia viruses. Vet Immunol Immunopathol 29(1-2):1-14, 1991 Thompson RR, Wilcox GE, Clark WT, et al: Association of calicivirus infection with chronic gingivitis and pharyngitis. J Small Anim Pract 25:207-210, 1984 Von Schlup D: Epidemiologische und morphologische Untersuchungen am Katzengebil3. I. Mitteilung: Epidemiologische Untersuchungen. Kleintierpraxis 27:87-94, 1982 Wardley RC, Povey RC: The clinical disease and patterns of excretion associated with three differertt strains of feline caliciviruses. Res Vet Sci 23:7-14, 1977 Yamamoto JK, Hansen H, Ho EW, et al: Epidemiologic and clinical aspects of feline immunodeficiency virus infection in cats from the continental United States and Canada and possible mode of transmission. J Am Vet Med Assoc 194(2):213-220, 1989 Yamamoto JK, Sparger E, Ho EW, et al: Pathogenesis of experimentally induced feline immunodeficiency virus infection in cats. Am J Vet Res 49(8):1246-1258, 1988
Address reprint requests to Gerhard H. Reubel, DrMedVet Department of Medicine University of California, Davis School of Veterinary Medicine Davis, CA 95616
FELINE DENTISTRY
ACUTE AND CHRONIC FAUCITIS OF DOMESTIC CATS A Feline Calicivirus-Induced Disease Gerhard H. Reubel, DrMedVet, Diane E. Hoffmann, BS, and Niels C. Pedersen, DVM, PhD
Inflammatory diseases of the oral cavity of domestic cats are of great importance to cat owners and veterinarians. One half to three fourths of randomly examined cats had some type of inflammatory lesion in the mouth. 16, 18 The most common inflammatory disease of the mouth is gingivitis, followed by periodontitis. More severe forms of oral cavity inflammation, usually termed stomatitis in the veterinary literature, are much less common. The selective use of the term stomatitis for severe oral diseases in cats suggests that feline stomatitis has a single clinical presentation and a single cause. Severe oral inflammation of cats, however, is diverse in both clinical expression and causeY One specific type of feline stomatitis has been called chronic plasma cell gingivitis and pharyngitis/ As originally described, plasma cell gingivitis and pharyngitis is a chronic ulceroproliferative disease centered around a specific region of the mouth, the oral fauces. Affected tissues are densely infiltrated with plasma cells and lymphocytes, hence the name. Some cats described in the literature as having chronic stomatitis appeared to have a disease similar to chronic plasma cell gingivitis and pharyngitis. 8, 17 The cause of plasma cell gingivitis and pharyngitis has not been determined, and attempts to cure the condition have been unsuccessful. Several events occurred over the last year that caused the authors to study inflammatory lesions in the oral fauces of cats. Outbreaks of a chronic ulceroproliferative faucitis were observed in multiple cats within several households. Chronic faucitis was also seen with increasing frequency among cats presented to the Veterinary Medical Teaching Hospital (VMTH), University of California, Davis, for oral cavity afflictions. The two observations led to the postulate that inflammatory faucial disease in cats might be a specific and infectious disease From the Department of Medicine, University of California, Davis, School of Veterinary Medicine, Davis, California VETERINARY CLINICS OF NORTH AMERICA: SMALL ANIMAL PRACTICE VOLUME 22 • NUMBER 6 • NOVEMBER 1992
1347
1348
REVBEL et al
entity. This study reports on the isolation of several different strains of feline calicivirus (FCV) from cats with both acute and chronic naturally occurring faucitis and the experimental recreation of acute faucitis with these isolates in specific pathogen free (SPF) cats. These studies indicate that FCV can cause acute faucitis in cats and that a proportion of acutely affected cats may go on to develop chronic faucitis. MATERIALS AND METHODS Field Studies
Field studies were conducted on pet cats presented to the VMTH, University of California, Davis. The first group consisted of 23 cats that were seen for oral cavity disease. The second group consisted of 140 cats randomly selected from cats seen at the VMTH for any reason (10 for oral disease); 134 of these 140 cats have been previously described.!6 The clinical diagnoses at the time of testing were taken from the animal's hospital records. Experimental Animals
SPF domestic cats were obtained from the breeding colony of the Feline Nutrition Laboratory of the School of Veterinary Medicine, University of California, Davis, and were housed in infectious disease isolation facilities provided by the Animal Resources Service at the same institution. Virus Isolation
The oral fauces of each animal were brushed with a sterile cotton-tipped swab and FCV isolated as previously described. '6 Feline Calicivirus Strains
Four FCV isolates were used for the experimental infection. FCV-Cook was isolated from the oral cavity of a privately owned 9-year-old cat (case no. 2S28-24) with severe, chronic gingivitis and faucitis. FCV-VMTH-1 was isolated from the oral cavity of a 6-year-old cat (case no. 2S-38-68) with chronic faucitis, FCV-VMTH-2 from a 9-year-old cat (case no. 2S-64-06) with chronic pharyngitis and faucitis, and FCV-SPCA from the oral cavity of a 2-year-old cat (case no. 2S-62-83) with severe faucitis and gingivitis. Experimental Infection
Cats were 6 to 9 months of age at the time of infection. Cats of four experimental groups (FCV-Cook, FCV-VMTH-1, FCV-VMTH-2, FCV-SPCA) were inoculated by mouth with 1075 tissue culture infectious dose-SO% (TCIDso ) per O.S mL of the different virus isolates. Cats in the fifth experimental group were infected with a similar amount of FCV-VMTH-1 by shallow injection along the gums and in the oral fauces as well as onto the mucous membranes. Cats
ACUTE AND CHRONIC FAUCITIS OF DOMESTIC CATS
1349
in the sixth experimental group were housed for 1 month together with two cats that were naturally infected with the Cook isolate of FCV. The naturally infected cats had chronic gingivitis, periodontitis, and u1ceroproliferative faucitis. Clinical Evaluation
Cats were monitored daily for the first week postinfection and weekly thereafter. In addition to routine physical examination, precise inspection of the oral cavity was performed. Rectal temperatures were taken daily for the first week postinfection of all cats except those infected through natural contact. Biopsy
Tissue samples were taken from the fauces of three cats with experimentally induced acute faucitis under ketamine hydrochloride/acepromazine anesthesia and fixed in 10% buffered formal-saline. Thin sections were stained with hematoxylin and eosin. Cells and Media
Crandell feline kidney cells (CrFK) were used as a substrate for virus isolation, virus titration, and detection of virus neutralizing antibodies. Cells were grown in a 1:1 dilution of Leibovitz's L 15 medium and Earle's minimum essential medium containing 10% fetal calf serum; penicillin, 100 IU/mL, streptomycin, 10 J..lg/mL; and gentamicin, 5 J..lg/mL. Serology
Sera for FCV neutralization were diluted serial twofold in cell culture media. Fifty microliters of diluted sera were mixed with 50 J..lL of virus solution containing 100 TCIDsJmL in 96-well microtiter plates and incubated for 90 minutes at 37°C. Thereafter 100J..lL of CrFK cell suspension were added to each well. Plates were monitored for FCV cytopathic effect (CPE) for 4 days. Antibody titers were expressed as the reciprocal of the highest serum dilution completely neutralizing CPE. Cross virus neutralization was performed with homologous and heterologous FCV isolates. Antisera used in the study were harvested 3 weeks following infection. Electron Microscopy
CrFK cells inoculated with FCV from cats infected with each of the four FCV isolates were fixed in 2% glutaraldehyde in cacodylate buffer and processed in a routine manner for electron microscopic examination. Statistical Analysis
The probability of FCV oral carriage in the different categories of the field cases was evaluated by contingency table chi square analysis using a computerized statistics package (Statview SE + Graphics, Abacus Concepts, CA).
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REUBEL et al
RESULTS
Feline Calicivirus Isolations from Field Cases
FCV was isolated from oral swabs of 26 out of 140 randomly selected cats (19%) and from 14 out of 23 cats with a specific history of oral cavity disease (61 %) (Table 1). Eight of 23 cats admitted for oral cavity disease had a chronic ulceroproliferative faucitis (Color Plate 3, Figure 8), and one of 23 had an acute faucitis (Color Plate 3, Figure 9). One of the eight cats with chronic faucitis tested positive for feline immunodeficiency virus (FIV), and none were infected with feline leukemia virus (FeLV). The one kitten with acute faucitis tested negative for both FIV and FeLV. All of the cats that were presented witli faucitis (n = 9) were FCV positive, which was significantly higher than the incidence of FCV isolations from the 14 cats presented for oral cavity disease that did not have faucitis (P = 0.0082) or from the 140 randomly selected cats (P sO.OOOI). Electron Microscopy
Figure 1 shows crystalline arrays typical for caliciviruses that were seen in the cytoplasma of CrFK cells infected in vitro with the four strains of FCV Table 1. RESULTS OF FELINE CALICIVIRUS ISOLATIONS FROM ORAL SWABS OF 23 CATS PRESENTED TO THE VETERINARY MEDICAL TEACHING HOSPITAL WITH HISTORY OF ORAL CAVITY DISEASE
Cat#
Case#
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
24-42-93 25-4075 25-28-24 24-42-18 24-46-36 25-25-78 25-62-83 25-33-43 25-00-52 23-00-96 24-95-25 25-41-53 25-31-78 25-28-26 25-38-69 25-91-94 25-64-06 "boots horn" 25-79-72 25-94-11 25-72-73 25-82-31 25-90-68
Age (years) 2 adult 9 5 4 3 2 1 6 11 14 adult 15 1 6 adult 9 4 3 10 1 5 %
Clinical Diagnosis Mild chronic gingivitis Mild chronic gingivitis Mild chronic gingivitis Mild chronic gingivitis Mild chronic gingivitis Severe chronic gingivitis Severe chronic gingivitis Severe chronic gingivitis Severe chronic gingivitis Severe chronic gingivitis Severe chronic periodontitis Severe chronic periodontitis Chronic periodontitis Severe chronic stomatitis Chronic faucitis Severe chronic faucitis Chronic faucitis and pharyngitis Chronic faucitis and gingivitis Chronic faucitis and gingivitis Chronic faucitis and periodontitis Chronic faucitis and periodontitis Chronic bilateral faucitis Acute faucitis, palatitis, and limping
Feline Calicivirus Oral Carriage
+ + + + +
+ + + + + + + + +
ACUTE AND CHRONIC FAUCITIS OF DOMESTIC CATS
1351
Figure 1. Transmission electron photomicrograph of a Crandell feline kidney cell infected with the Cook strain of feline calicivirus. (Lead citrate and uranyl acetate stain; original magnification x 66.)
(Cook, VMTH-l, VMTH-2, SPCA) isolated from four cats with naturally occurring chronic ulceroproliferative faucitis. Clinical Evaluation-Experimentally
Infecte~
Cats
Clinical signs of illness appeared in all FCV-Cook, FCV-VMTH-l, FCVVMTH-2, and FCV-SPCA infected cats 2 to 3 days after experimental exposure by mouth and 7 to 14 days after natural contact exposure. The four FCV isolates induced a similar acute disease (Tables 2 and 3). Clinical signs of illness included depression, pyrexia, reduced appetite, inflammation along the gumlines (Color Plate 3,* Figure 10), ulcerations of the soft and hard palate, ulcerations on the tongue (Color Plate 3, Figure 11), and inflammation of the fauces (Color Plate 3, Figures 12 and 13). Twelve out of 19 cats had transient limping or stiffness. Mild rhinitis was observed in two of 25 cats and conjunctivitis in three of 25. Diarrhea was observed in one cat infected with the SPCA strain of FCV. Clinical signs lasted from a few days (fever, limping, diarrhea, rhinitis, conjunctivitis, and lingual and palatal ulcers) to several weeks (gingivitis, faucitis). No sign of chronic oral disease was observed in any of the cats as long as 7 months later. Feline Calicivirus Isolation from Experimentally Infected Cats
FCV was conSistently recovered from most of the experimentally FCVinfected cats for the first 4 weeks after inoculation. Virus was isolated only 'See color section in the beginning of this issue.
Table 2. DEVELOPMENT OF CLINICAL SIGNS IN SPECIFIC PATHOGEN FREE CATS (n FOUR ISOLATES OF FELINE CALICIVIRUS
=
19) AFTER EXPERIMENTAL INOCULATION WITH
Number of Cats Days after Infection
Weeks after Infection
Clinical Signs
3
5
7
2
Fever (>38SC) Limpinglsoreness Ulcers Tongue Palate Lip Nasal frenulum Gingivitis' Pharyngitis Faucitis Conjunctivitis Rhinitis Diarrhea
18/19 1/19
19/19 11/19
12/19 3119
5119 3/19
5
6
7
8
4/19 3/19 2/19
5/19 4/19 2/19 1/19 4/19
4/19
5/19 1/19
10/19 1/19
12/19 3/19
1/19
1/19
5/19 9/19 6/19 1/19 5/19 1/19 12/19 2/19 2/19 1/19
2/19 1/19
8/19
7/19 9/19 3/19 1/19 8/19
5/19
8/19
6/19
5/19
4/19
8119
6/19 1/19
8/19
2/19 1/19
1/19
1/19
1/19
1/19
1/19
1/19
1/19
1/19
1/19
3
4 1/19
'Cats were erupting their permanent dentition, and it was difficult to differentiate traumatic from viral·induced inflammation.
Table 3. DEVELOPMENT OF CLINICAL SIGNS IN SPECIFIC PATHOGEN FREE CATS (n = 6) AFTER CONTACT EXPOSURE TO TWO CATS NATURALLY INFECTED WITH THE COOK STRAIN OF FELINE CALICIVIRUS Number of Cats Weeks after Infection Clinical Signs
Fever (>38SC) Limping/soreness Ulcers Tongue Palate Lip Gingivitis" Pharyngitis Faucitis Conjunctivitis Rhinitis Diarrhea
nt' nt
3/6
2
3
4
5
6
7
B
9
10
13
15
17
19
nt nt
nt nt
nt nt
nt nt
nt nt
nt nt
nt nt
nt nt
nt nt
nt nt
nt nt
nt nt
nt nt
1/6 1/6 5/6
4/6
6/6
6/6
6/6
6/6
6/6
5/6
6/6
6/6
5/6
4/6
4/6
5/6 2/6 1/6
3/6
3/6
2/6
4/6
3/6
1/6
4/6 1/6 4/6
• Not tested. "Cats were erupting their permanent dentition, and it was difficult to differentiate traumatic from viral·induced inflammation.
1354
REUBEL et al
sporadically from single individuals thereafter (Table 4). None of the cats shed FCV later than 17 weeks after infection. Serology
Serum antibodies that neutralized the homologous virus were detectable in all cats as early as 2 weeks after infection (data not shown). Antisera against FCV-SPCA neutralized the homologous virus only. Antisera to FCV-VMTH-2 had weak neutralizing activity against heterologous strains, whereas antisera to FCV-Cook and FCV-VMTH-1 neutralized heterologous strains to similar degrees (Table 5). This pattern of homologous and heterologous reactivity . indicated that the four FCV isolates represented three distinct serotypes: (1) FCV-SPCA, (2) FCV-Cook and FCV-VMTH-1, and (3) FCV-VMTH-2. Biopsy
Similar lesions were seen in tissues taken by biopsy from the acutely inflamed fauces of three experimentally infected cats. Multifocal, multiloculated, vesicopustular lesions were observed in the stratum spino sum of the oral mucosa (Fig. 2). There was diffuse edema of the submucosa with an associated vasculitis involving small venules. The venulitis was characterized by infiltration and margination of the vascular wall with neutrophils and focal areas of endothelial cell degeneration. DISCUSSION
The finding that at least one form of severe oral inflammation might be caused by FCV is not new. Povey" made reference in passing to FCV and chronic gingivitis and pharyngitis in cats in 1976. The next reference to FCV infection and chronic gingivitis and pharyngitis was published by Australian researchers in 1984.17 An English study recently demonstrated that 50% to 92% of cats with chronic stomatitis were FCV shedders compared with 0 to 19% of nonaffected control groupS.8 According to the descriptions, at least some of the cats in these studies had faucial lesions. No one, however, has been able to recreate experimentally chronic oral lesions with FCV, even using isolates from cats that had chronic stomatitis. 9 Tenorio et a1'6 made a statistical comparison between persistent oral carriage of FCV, FeL V, and FlV and chronic inflammatory oral cavity lesions. No statistical linkage was found between FCV oral carriage and milder forms of chronic stomatitis, i.e., gingivitis. FlV infection was more often related to chronic oral cavity disease than could be accounted for by chance, especially as the severity of the oral cavity disease increased. This was supported by other studies that have linked FlV infection with oral cavity disease. s, 6, 8, 20 Although FCV carriage could not be linked to milder forms of inflammatory oral disease, there was a greater tendency for cats with more severe oral disease to be FCV shedders.16 This relationship was strongest for cats that were also coinfected with FeLV or FlV. The present study shows conclusively that acute faucitis is a FCV-induced lesion. The four field isolates of FCV used in these experiments produced similar types of lesions regardless of type of exposure. Inoculation of small
Table 4. RESULTS OF FCV ISOLATIONS FROM ORAL SWABS OF SPECIFIC PATHOGEN FREE CATS EXPERIMENTALLY INFECTED WITH FOUR DIFFERENT ISOLATES OF FELINE CALICIVIRUS Type of Exposure
Strain
Cook
Cook
>-'
w
r..n r..n
Contact
By mouth
VMTH-1
By mouth Local injection
VMTH-1
By mouth
VMTH-2
By mouth
SPCA
By mouth
'Not done.
Weeks Postexposure
2
Cat 10 #
90-419 90-444 90-454 90-475 90-513 90-683 5054 5064 5077 5080 90-430 90-445 90-660 5060 5065 5076 5078 5079 90-777 90-795 90-826 91-006 90-831 91-003 91-025
+ + + + + + + + + + + + + + + + + + + + +
3
+
+
+
+ +
+ + + + + + + + + + + + + + + + + + + +
+ + + + + + + + + + + + + + +
4
+ + + + + + + + + + + + + + + + + + + + +
5
+ +
+ + + + + + + + +
+
6
7
+ + +
nd* nd nd nd nd nd nd nd nd nd
nd nd nd nd nd nd nd nd nd nd nd nd
+
nd nd nd nd nd
+
8
+
nd nd nd
9 nd nd nd nd nd nd
+
11
nd nd nd nd
15
17
19
+ + + nd nd nd nd
+
+
13
nd nd nd nd nd nd nd nd nd nd nd nd
+ nd nd nd nd
nd nd nd nd
nd nd nd nd
nd nd nd nd nd nd nd nd nd nd nd nd
nd nd nd nd nd nd nd nd nd nd nd nd
nd nd nd nd nd nd nd nd nd nd nd nd
nd nd nd nd nd nd nd nd nd nd nd nd nd nd nd nd nd nd nd
1356
REUBEL et al
Table 5. FELINE CALICIVIRUS NEUTRALIZING ANTIBODY RESPONSE (MEAN ± SD) IN SERA OF SPECIFIC PATHOGEN FREE CATS EXPERIMENTALLY INFECTED WITH FOUR DIFFERENT ISOLATES OF FELINE CALICIVIRUS 3 WEEKS POSTINFECTION
Feline Calicivirus Strain Cook VMTH·1 VMTH-2 SPCA
Serum Neutralizing Antibody Titers of Convalescent Feline Calicivirus Antisera against four Strains of Feline Calicivirus Cook
(n = 5)
38.4 256.0 6.0 0.0
(± 51 .0) (± 0.0) (±4.0) (±O.O)
VMTH-1 (n 3)
=
112.0 213.3 20.0 0.0
(±96.0) (± 73.9) (± 30.3) (±O.O)
VMTH-2
(n = 4)
128.0 16.0 112.0 0.0
(± 78.4) ( ± O.O) (±32.0) (±O.O)
SPCA
(n = 4)
48.0 28.0 2.0 106.7
( ± 45.3) (± 31.7) (±2.3) (± 37.0)
amounts of virus into the gums and fauces did not produce any different disease than seen in cats infected by dropping the virus onto the oral mucous membranes or that were infected by natural contact. The same was true for natural contact exposure versus direct infection by mouth . Clinical signs, however, took 1 to 2 weeks longer to appear after natural contact than direct exposure by mouth. The natural exposure studies demonstrated how efficiently and rapidly FeV could be transmitted between carrier and susceptible cats placed in intimate contact with each other. Acute faucitis was seen in a majority of cats that were infected with at least four different field isolates of FeV obtained from cats with chronic faucitis. Faucitis has not been previously reported as an acute lesion of FeV infection, although it is well known that the virus causes acute lingual and palatine
Figure 2. Photomicrograph of mucosal and submucosal tissue taken from the oral fauces of an experimentally feline calicivirus-infected cat with acutefaucitis. Multifocal, multiloculated, vesicopustular lesions were present in the stratum spinosum of the oral mucosa. The submucosa was edematous, and numerous polymorphonuclear leukocytes were marginating within and without of small venules. (Hematoxylin and eosin stain; original magnification x 300.)
ACUTE AND CHRONIC FAUCITIS OF DOMESTIC CATS
1357
ulcers, fever, and limping.JO, 13 It is possible that acute faucitis occurred during other experimental studies but that it was not detected. The acute faucitis was not always flamboyant in appearance, and identification of the lesion required a close inspection of the mouth and a familiarity with the normal appearance of the oral fauces. There has also been a tendency for previous FCV researchers to concentrate on the lesions that were of particular interest for them. For example, early FCV studies stressed the upper respiratory component of the infection and usually failed to mention limping and soreness. lO Acute faucitis was not just an experimental lesion because at least one cat observed at the VMTH also developed faucitis during a brief episode of classic FCV-induced disease. The faucial lesions in this cat were detected because the clinicians had been made aware of the lesion in experimentally infected cats. Feline calicivirus was isolated from the oral cavities of this naturally infected cat. The oral fauces as a site for FCV-induced lesions should have been anticipated. The tonsils and adjacent faucial mucosa are sites of virus replication in asymptomatic chronic FCV carrier cats.' FCV was reportedly replicating within cells of the stratum germinativum in healthy carrier cats, whereas lesions in acute FCV-induced faucitis reported here were in the stratum spinosum and in venules in the submucosa. Unfortunately no virus localization studies were done in the present study to see if lesional sites and sites of virus replication were the same. Chronic faucitis was not reproduced in this study with field isolates of FCV, so what is the evidence that chronic faucitis is FCV induced? The most critical evidence came from field cases that showed oral carriage of FCV by 100% of the cats with the lesion. This was significantly higher than the background carriage rate of 19% in randomly selected cats and 36% in cats with severe oral disease and no faucitis. The second piece of evidence was that a similar, although acute, type of faucitis could be induced with FCV strains isolated from cats with chronic faucitis. It would be unlikely for such an uncommon and specific lesion to be caused by entirely different agents. Finally, the oral fauces have been shown to be a site of persistent FCV replication! ConSidering what is known about FCV infection and oral cavity disease, what is the pathogenesis of chronic FCV-induced disease? We would propose that one or more of the following possible mechanisms or factors are involved in the disease: (1) Chronic faucitis is associated with specific strains of FCV; (2) chronic faucitis is associated with persistent FCV oral carriage, although FCV strains isolated from diseased mouths infrequently cause persistent infections (compared with other strains); (3) cofactors that enhance the likelihood of persistent FCV infection will increase the incidence of chronic faucitis; and (4) chronic faucitis may result from an uncommon and abnormal type of immune response to persistent FCV infection of the fauces. Evidence for the involvement of specific strains of FCV in chronic faucitis is conflicting. On one hand, past studies of experimentally induced FCV infection suggest that FCV manifestations can vary with the strain.'9 Some strains of FCV reportedly cause mainly upper respiratory-like illness and pneumonia, whereas other strains have been associated mainly with limping. lO Acute faucitis has not been previously reported, indicating that faucitis may be strain-specific. On the other hand, most strains of FCV will cause oral lesions to some degree, and it is likely that faucitis was just not recognized in previous studies. As an example, limping became a commonly recognized feature of Fev infection only after it was specifically brought to attention," Further, if chronic faucitis is caused by a specific strain of FCV, faucitis-inducing strains
1358
REUBEL et al
should be serologically distinct. The four faucitis-inducing strains that were reported herein belonged to three different serotypes based on cross virus neutralization tests. This amount of diversity among four random isolates was typical of what would have been expected for FCV isolates in general. 14 The second factor in the pathogenesis of chronic faucitis presumes that faucitis-inducing strains of FCV are different from other strains of FCV, i.e., they cause persistent infection in only a very small proportion in infected cats. Studies with FCV isolates from cats with chronic faucitis (reported herein) or chronic stomatitis9 support this presumption. At least five different FCV isolates from two widely different geographic locations were incapable of inducing a persistent oral carrier state in experimentally infected cats. In contrast, Wardley and Povey19 found that 16% to 20% of cats infected with two of three different FCV isolates shed virus from their oral cavities longer than 6 months. This carriage rate was identical to that observed in the field. It is important to note, however, that such studies are the exception; most experimentally FCV-infected cats cease shedding within 1 to 2 months. It is uncertain therefore whether or not persistent FCV carrier state is strain-dependent or if persistent infection is largely influenced by vagaries in experimental conditions. If it is the latter, there may be nothing unique about faucitis-inducing strains of FCV in terms of their ability to cause chronic infections. The third possible factor involved in the induction of chronic faucitis by FCV is the easiest to support scientifically. Dawson et aP induced protracted oral FCV carriage in cats that were either previously vaccinated against FCV or were in the primary stages of FlV infection. One of four FlV negative/FCV vaccinated cats was still shedding FCV after 5 months compared with none of four FlV negative/FCV nonvaccinated cats; among FlV infected cats, three of four FCV-vaccinated and three of four FCV-nonvaccinated cats (six of eight of all FlV-infected cats) were still shedding FCV after 5 months. One of the strains (LS015) used in the study of Dawson et aP was the same as one used by Knowles et aV i.e., an isolate from a cat with chronic stomatitis. This same strain did not cause persistent oral carriage in FIV-noninfected/FCV-nonvaccinated cats. These findings help to explain why 15% to 80%, depending on the study, of cats with chronic stomatitis are also infected with FlV.6. 8. 20 One of eight cats (13%) with chronic faucitis in the present study was FIV infected. The fourth mechanism, i.e., that chronic faucitis results from an abnormal immune response to persistent FCV infection, regardless of serotype, also has credence. There is evidence that persistent FCV infection, even with chronic stomatitis strains, is not sufficient by itself to induce chronic faucitis; chronic oral cavity disease was not observed in any of the seven cats reported to have protracted Fev oral carriage by Dawson et al. 3 The characteristic microscopic change observed in cats with chronic faucitis was a dense lymphocytic! plasmacytic infiltrate.' Such an infiltrate, in this location, is indicative of a chronic immune response to FeV. From 19% to 26% of healthy-appearing household pet cats, however, shed FCV from their oral cavities, and very few of them develop chronic faucitis. 16 Is it possible that asymptomatic FeV carrier cats are in a perfect host-parasite relationship? The establishment of such a perfect relationship after acute illness is not unique. Feline leukemia virus infection evokes a florid host response during the initial viremic stage, but this response is terminated by either complete recovery or the establishment of a chronic asymptomatic carrier state. 2 The same is true of FlV infection of cats.2l Such an all or none concept, however, must be modified to include an intermediate state of immunity: a state where the host attempts to rid the body of the parasite and in so doing injures itself. Such a state has been described
ACUTE AND CHRONIC FAUCITIS OF DOMESTIC CATS
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for another viral disease of cats, feline infectious peritonitis virus (FIPV) infection. FIPV infection occurs in three clinical forms: an asymptomatic carrier state, a generalized exudative serositis, and a systemic granulomatous disease. There is strong circumstantial evidence that the form of infection is directly related to the comparative strengths of humoral and cellular immuti.ityY Asymptomatic FlPV carriers have very strong cell-mediated immunity, cats with exudative serositis have no cellular immunity, whereas cats with granulomatous disease have partial cell-mediated immunity. In the same manner, chronic faucitis could occur in a small proportion of cats that respond immunologically to a persistent FeV oral carriage in an atypical manner. FlV infection could enhance FeV-induced disease not only by increasing the likelihood of a carrier state, but also by causing perturbations in the strength or type of FeV immunity. Acute gingivitis was an additional FCV-induced oral lesion observed in this study that has not heretofore been described. The gingivitis was quite florid in some animals, especially when it involved the incisor teeth. Lesions were also seen in the gums overlying or adjacent to premolars, molars, and canines that were erupting. Gingival lesions could have been enhanced in this study by mechanical trauma, thus allowing more fertile environment for the virus to infect and cause lesions. Whether acute FeV-induced gingivitis has a chronic counterpart is unknown. A recent large field study showed no relationship between the common type of gingivitis in cats and FCV infection. 16 There are, however, at least two anecdotal reports in the literature linking chronic gingivitis with persistent oral carriage of FeV.I. [9 The increasing incidence of chronic faucitis in cats is a reason for concern, especially if it is a property of all FeV strains that exist in the field. The lesion is very debilitating for affected animals and frequently leads to owners having their cat euthanized. The fact that more cats are currently oral carriers of FeV than before vaccination began almost 2 decades ago" is another reason to be concerned. Because faucitis with or without accompanying gingivitis or periodontitis appears to be a specific disease entity, it is proposed that this disorder be given a specific name and not lumped under the terms stomatitis and pharyngitis. A preferable name would be feline calicivirus induced acute (or chronic) ulceroproliferative faucitis. ACKNOWLEDGMENTS We would like to acknowledge Dr. Leigh West-Hyde, Department of Surgery, University of California, Davis, School of Veterinary Medicine, for helping to prOVide oral swabs and histories for cats presented to the VMTH for oral diseases; Mr. Robert Munn, Department of Pathology, University of California, Davis, School of Medicine, for the electron microscopy; Pro-Visions Corp., Checkerboard Square, St. Louis, MO, for providing cat food; and NIH (AI-25802-05) for funding.
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Address reprint requests to Gerhard H. Reubel, DrMedVet Department of Medicine University of California, Davis School of Veterinary Medicine Davis, CA 95616
