Trop. Anim. Hlth Prod. (1990) 22, 185-194

PERSISTENCE OF THE CAR~ER STATUS IN HAEMORRHAGIC SEPTICAEMIA (PASTEURELLA MULTOClDA SEROTYPE 6:B I N F E C T I O N ) I N BUFFALOES M. C. L. DE ALWIS, THULA G. WLIEWARDANA, ANOMA I. U. GOMIS and A. A. VIPULASIRI Veterinary Research Institute, Gannoruwa, Peradeniya, Sri Lanka SUMMARY

Fifty-seven young buffaloes were experimentally infected or naturally exposed to haemorrhagic septicaemia (HS). Of these animals 32 became immune carriers. They were observed in groups for periods up to 360 days to monitor the appearance of pasteurellae in the nasopharynx and antibody status. In most animals pasteurellae appeared in the nasopharynx for a short period initially and disappeared. The organism reappeared intermittently and the longest observed period of reappearance was 215 days after exposure. All animals showed rising antibody titres with a peak lasting for 150 to 180 days and declining thereafter. Pasteurellae persisted in the tonsils and were isolated from 20 out of 27 carriers after slaughter. The longest period when isolation was made after slaughter was 229 days. The organism lodged in the tonsils was unaffected by antibacterial therapy using drugs to which the organism displayed in vitro sensitivity. It is concluded that in HS, carrier animals exist in an active as well as a latent state, the former appearing for short intermittent periods between long latent periods, when pasteurellae continue to remain in the tonsils which constitute a long-term reservoir. INTRODUCTION

Haemorrhagic septicaemia (HS) is an acute, septicaemic highly fatal form of pasteurellosis affecting buffaloes and cattle in Asia and Africa. It is caused by specific serotypes of Pasteurella multocida the Asian serotype being designated 6: B (Namioka: Carter) or B :2 (Carter: Heddleston). In countries where the disease is endemic it is of considerable economic importance. The presence of carder animals in HS is well established (Singh, 1948; Mohan, Sinha, Singh and Gupta, 1968; Wijewanta and Kurunaratne, 1968; Mustafa, Ghalib and Shigidi, 1978; Farid, E1-Ghani, Khalil, EI-Ghawas and Kamel, 1980; Hiramune and de Alwis, 1982). Such animals are clinically normal but the causative organism can be isolated from the nasopharynx. It was believed that carder animals were the initiators of fresh outbreaks but their significance in the epidemiology of the disease was not fully understood. In different studies the percentage of carders detected has been at considerable variance and has ranged from less than 1% (Mohan et al., 1968) to as high as 44% (Mustafa et aL, 1978) of the animals tested. The evidence available was suggestive of a relationship between the percentage of carder animals detected and recent exposure to the disease (Gupta, 1962; Mustafa et al., 1978 and Hiramune and de Alwis, 1982). A relationship between the phenomenon of naturally acquired immunity and recent exposure to HS has also been observed (de Alwis, 1982; de Alwis and Sumanadasa, 1982). More recent studies have indicated the detection of a high percentage of carriers (12% to 40%) on repeated swabbing of the nasopharynx of 185

186

DE ALWIS, WEIEWARDANA, GOMIS AND VIPULASIRI

animals that survived and remained clinically normal during outbreaks of HS, and the development of antibody titres in an even higher percentage (80% to 100%) of these animals (de Alwis, Wijewardana, Sivaram and Vipulasiri, 1986). These observations also appeared to indicate that the presence of the organism in the nasopharynx of carder animals was transient and that in a few animals organisms reappeared after an interval. Closer observations in animals maintained under controlled conditions were necessary both to confirm these findings and to determine other sites of persistence of the HS organism when it disappeared from the naospharynx. It is known that survival of the organism outside the animal is very short lived. The investigations described in this paper were undertaken with a view to studying the persistence of the organism and the antibody status in carrier animals produced experimentally by controlled exposure to HS and maintained in laboratory premises. MATERIALS AND METHODS

Carder animals were produced either by direct experimental infection by intranasal or oral routes or by controlled natural exposure to experimentally infected animals. Intranasal infection was effected by spraying a broth culture into a polythene bag fastened around the muzzle. The amount of broth culture converted into aerosol with each stroke of the hand sprayer was predetermined. Oral infection was carried out by drenching with broth culture. Natural exposure to HS was accomplished by tying the subjects in the same pens as clinically affected buffaloes for regulated periods. The animals used were indigenous buffalo calves from four to 10 months of age and were from areas where no recent outbreaks of HS had been reported. Prior to purchase they were tested for the absence of HS antibodies by the indirect haemagglutination test (IHAT) and the passive mouse protection test (PMFF). The animals were housed in a shed 6 m by 3 m and 2-3 m high enclosed by a half wall and divided into three equal compartments with detachable partitions. Each compartment housed up to three animals. During the first 10 days after experimental infection or natural exposure the animals were housed all day and stall fed. Thereafter they were permitted eight hours of grazing in an enclosed field and given access ad lib. to cut grass and water while being housed. On admission to the shed all buffaloes were de-wormed with Rintal (Bayer) and sprayed with Asuntol (Bayer) to remove all ectoparasites. The medium used to culture the organism used in infecting animals was Casein-Sucrose-Yeast (CSY) broth and CSY blood agar prepared as described by Wijewardana, de Alwis and Bastiansz (1986b). The culture used to infect buffaloes was a streptomycin resistant strain developed from a virulent field isolate (strain 33, VRI Sri Lanka culture collection number 8406). Antibiotic resistance has not been Observed in any Sri Lankan isolates of P. mu/toc/da. This property therefore served as a useful marker to isolate and identify the strain in experimentally infected and ineontact animals. The field isolate was grown in CSY broth for six hours and heavily seeded on to CSY blood agar containing streptomycin at a concentration of 100/Jg/ml. The few colonies that grew were subcultured successively on to plates containing both 200/~g/ml and 400/tg/ml of streptomycin. At each subculture CSY plates without

CARRIERS IN HS

187

streptomycin were included to ensure that the colonies isolated were resistant and not streptomycin dependent. Finally the selected culture was tested for mouse virulence to ensure that its LDso was the same as that of the original field isolate. Monitoring of the carrier and antibody status From the day of infection or natural exposure nasopharyngeal swabs were collected daily for the first 10 days, and twice weekly (Monday and Thursday) thereafter, throughout the period of observation. Blood samples were collected on days 10, 20 and 30 and at monthly intervals thereafter. Some of the animals were slaughtered and attempts were made to isolate the infecting organism from 14 different sites namely the nasopharynx (swabbed directly after slaughter), tonsils, parotid, mandibular, retropharyngeal, cervical, axiUary, mediastinal and bronchial, mesenteric and hepatic lymph nodes, haemolymph nodes, spleen and the parotid and mandibular salivary glands. For swabbing sterile flexible wires of nickel-silver alloy, 35 cm long with cotton wool swabs at the end were used. The external nares were cleaned with methylated spirits and the swab inserted to a depth of 20 to 30 cm and the nasopharyngeal mucosa was swabbed by rotating the swab several times. The nasopharynx was swabbed through both external nares using the same swab. When swabbing after slaughter the nasopharynx was approached directly after the head was separated. Animals were bled by jugular puncture. Serum was separated and stored frozen at -20°C. Tissues for culture were dissected out immediately after slaughter. In the case of paired lymph nodes and salivary glands, portions from both sides were collected and pooled. Isolation and identification of the organism The swabs were washed into 3 ml volumes of broth. Approximately 2 g portions of each of the tissues were immersed in methylated spirits a n d surface sterilised by flaming. They were then finely crushed and transferred into bottles containing 3 ml of sterile broth and mixed thoroughly. Approximately 0-2ml volumes of the broth were inoculated into mice by the subcutaneous route. The heart blood of any mice that died were plated on to CSY blood agar containing 400 ~tg/ml of streptomycin. Suspicious colonies that appeared on the plate after 24 to 48 hours incubation were tested for rapid slide agglutination with P. multocida serotype 6:B hyperimmune rabbit antiserum. Two tests were used to assess the immune status. These were the I H A T and the PMPT. The IHAT was carried out by the method of Carter (1955) as modified by Wijewardana et al. (1986b) using sheep erythrocytes. The PMPT was carried out as described by Bain, de Alwis, Carter and Gupta (1982). Treatment of carriers with antibacterial agents Three groups of carrier animals were given three day courses of treatment with 10 mg/kg of oxytetracycline (Pfizer Ltd) or 20 mg/kg of chloramphenicol by the intramuscular route or 0.2 mi/kg of 33~% solution of sulphadimidine (TAD Pharmazeutisches Cnxhaven, West Germany) by the intramuscular route.. This course of treatment was given to animals clearly identified as carriers but during periods when nasopharyngeal swabs were negative. Approximately one week

188

DE ALWIS, WIJEWARDANA,GOMIS AND VIPULASIRI

after such treatment the animals were slaughtered and attempts made to isolate the organism from the 14 different sites. Sensitivity tests were carried out in vitro using oxytetracycline, chloramphenicol and sulphadimidine impregnated discs (Rosco Sensitabs) on MuellerHinton medium (Difco) by standard methods. RESULTS

Fifty-seven buffalo calves were used in these experiments in batches of four to nine animals. In the first experiment one animal was infected experimentally by the subcutaneous route and placed in contact with eight other animals. In all other subsequent experiments infection was carried out either by intranasal or oral routes. The dose used for subcutaneous inoculation was 107 viable organisms. For intranasal infection the viable count of the total volume of broth converted into aerosol ranged from 2.4 x 107 to 2-9 x 10 12 organisms, although the actual numbers inhaled could not be accurately determined. The dose used for oral infection was 6.6 x 10l° viable organsims for one animal and 2-6 x 1011 viable organsims for each of three animals. After experimental infection or natural exposure all animals were observed for 30 days. Those that developed an antibody titre or showed the presence of the organism in the nasopharynx on at least one occasion were retained for further observation for varying periods of time up to one year. A few animals that showed no response at all were also retained for comparison. The carrier status and antibody titres The results of the experiments are summarised in Table I. The animal infected by the subcutaneous route died of clinical HS. Of the 28 animals infected by the intranasal route, seven died of clinical HS, 19 became immune carriers while two animals showed no response at all. Of the four animals infected by the oral route, two died of clinical HS and the other two became immune carriers. Of the 24 animals subjected to natural exposure four died of clinical HS, 11 animals developed antibody titres and eight of these also displayed a carrier status by the presence of the organism in the nasopharynx. Eight animals showed no response at all. There was no evidence that the response in the animal was related to the infecting dose and in fact in the animal infected intranasally the actual number of organisms inhaled could not be ascertained. TAeLE I

The response of susceptible buffaloes experimentally infected with and naturally exposed to haemorrhagic septicaemia under controlled conditions Total Died number of HS Experimental infection by subcutaneous route Experimental infection by intranasal route Experimental infection by oral route Naturally exposed

Rising anU13ody + organsim in Rising antibody nasopharynx only

Died due No to other response causes

01

01

.

28

07

19

m

02

m

04 24

02

02

~

__

__

04

08

03

08

01

Figures indicate number of animals.

.

.

.

CARRIERS IN HS

189

In all experiments put together, a total of 32 animals developed an antibody response and 29 of these also showed the presence of the organism in the nasopharynx. Fourteen animals died of HS. Among the animals that became immune carders, some passed through a transient phase of temperature elevation but with no other signs of the disease. Investigations carried out on the animals that died will be reported elsewhere. Twenty-six animals were observed and their carrier and antibody status were monitored for periods ranging up to 100 days. All of these animals showed rising antibody titres which developed between 10 to 20 days after exposure and persisted throughout the period of observation. The highest IHA titres were 1/2560, whilst in most animals the peak was in the region of 1/320-1/640. After exposure the organism was detectable in the nasopharynx in most animals for an initial transient period ranging from less than 10 days to 48 days and then disappeared. In eight animals the organism reappeared on one or several occasions intermittently. The period for which the organism disappeared from the nasopharynx was variable but extended up to 41 days which corresponded to 11 consecutive nasopharyngeal swabs collected twice weekly. Six of the other animals in this category and two which showed no response were monitored for up to 180 to 360 days. The animals with no initial response continued to remain so throughout. The pattern of intermittent appearance of the organism in the nasopharynx and the IHA titres in these six animals is shown in Fig. 1. In animals number 5 and 6 intermittent appearance occurred on several

5!

,20

30

8o

to

2o

,o

lO

,o

20

20

10

lO

19 0 3 2 0 3 2 0 3 2 0

0

0

640

40

160

10

80

160

NT

320

0

10

40

0

20

80

40

80

10

20

0

FIG. 1. Detection o f infecting pasteurellae in the nasopharynx and tonsils and the antibody titres in buffaloes exposed to haemo~hagic septicaemia.

Numbers on the left hand side indicate the identity of the animals. Animal no. 23 was orally infected. All others were naturally exposed to HS. Each circle represents one week of observation. O indicates no pasteurellae detected in the nasopharynx. 4D or • indicates pasteurellae detected on one occasion. • indicates pasteurellae

detected on both occasions. The figures below the arrow indicate the reciprocal IHA titres at that time. NT denotes serum not tested. + o r - indicatesisolationor failure to isolate pasteurellae from the tonsilsafter slaughter.

190

DE ALWIS, WLIEWARDANA, GOMIS AND VIPULASIRI

occasions, up to 215 days and 131 days respectively. Their IHA titres remained high up to around 150 to 180 days and then declined but were still detectable at 360 days. In the other four animals the organism was detectable in the nasopharynx only during the first week or two after exposure with the I H A titres persisting in some but showing a rapid decline in others.

Recovery of the organism from sites other than the nasopharynx Thirty animals were slaughtered after initial exposure to the infection during periods when the organism was not detectable in the nasopharynx when swabbed through the external nares. The time of slaughter varied from 27 to 340 days post-exposure. Twenty-one of the 30 calves were infected experimentally while the rest were exposed to the disease naturally. Twenty-seven calves elicited an antibody response alone or coupled with the carrier state. In 10 of these animals the organism was isolated from more than one site (Table H). The tonsils were the only site of isolation of the organism in another 13 animals. The organism was not recovered from the remaining four animals nor from any of the three calves that showed no response to the infection. Two animals which had shown an antibody response alone without any pasteurellae being detected in the nasopharynx at any stage during life were shown after slaughter to have harboured the organism in several sites (calves no. 12 and no. 18, Table II). The most common site of recovery of the organism was the tonsils from where isolation was made from 20 animals. Effect of antibacterial therapy Four animals each received oxytetracycline (nos 36, 38, 39 and 51) and chloramphenicol (nos 42, 43, 45 and 50) while three others received sulphadimidine (nos 55, 59 and 60) treatment. After slaughter the infecting organism was recovered from all these animals, most consistently from the tonsils. Antibiotic sensitivity tests carded out on the infecting organism, as well as the isolates from the tonsils of each animal displayed their /n vitro sensitivity to oxytetracycline, chloramphenicol and sulphadimidine and confirmed their resistance to streptomycin. DISCUSSION

The observations of de Alwis et al. (1986) in an earlier investigation appeared to indicate that in buffaloes which survived exposure to HS, and remained clinically normal, the'causative organism continued to appear in the nasopharynx intermittently. The present investigation provides confirmatory evidence and proves beyond doubt the transient appearance of the organism in the nasopharynx following exposure to disease, and its intermittent reappearance thereafter, for a long period of time. The present study also provides further evidence of the antibody response following exposure reported earlier (de Alwis, 1982; de Alwis et al., 1986) and establishes a relationship between the antibody response and the carrier status. It is known from previous work that a high IHA titre is indicative of natural exposure and confers solid immunity (de Alwis, 1982; de Alwis and Sumanadasa, 1982), whereas the IHA response to vaccination is poor (de Alwis, Gunatillake and Wickramasingha, 1978). Hence the IHA test using Carter's antigen (56°C, 30 rain supernate) was employed as an index of immunity. For practical reasons only a few animals could be maintained for a long time

.

El

E1

El

E1

51

55

57

58

El

E!

50

60

El

48

El

El

45

59

EI

.

27

41 . 41

97

97

35.

35

35

71

71

71

50

50

64

64

50

183

229

64

50

50

78

78

No

Yes

Yes . Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

No

Yes

Yes

.

* =

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

Yes

.

+

+

+

.

+

+

Retropharyngeal LN Cervical LN

+

+

AxUlary LN

+

Mediastinal & bronchial LN

+

+

Mesenteric LN

+

+

+ +

+ +

HaemoHepatic lymph LN nodes Spleen

Swabbed directly after slaughter; N E = Natural exposure; EI = Experimental infection.

.

+

Antibody Parotid Mandibtitre LN ularLN

LN -- Lymph node; S G = Salivary gland;

.

EI

43

El

37

42

EI

36

El

NE

El

NE

30

32

39

E1

23

38

HE

NE

NE

17

18

El

21

NE

13

Method Animal of Days post- Carrier number exposure exposure status

.....12

TABLE II

t

+

+

Pamttd SG

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

MandibNasoularSG Tonsils pharynx*

Isolation of pasteurellae after slaughter from buffaloes experimentally infected with and naturally exposed to haemorrhagic septicaemia

192

DE ALWIS, WIJEWARDANA, GOMIS AND VIPULASIRI

and among these the longest period after which pasturellae was detectable in nasopharyngeal swabs was 215 days after initial exposure. The longest interval after which a carrier animal was slaughtered was 229 days after exposure and pasteureUae were present in its tonsils. In this animal nasopharyngeal swabs showed pasteurellae only in the first week. The ~ antibody levels remained high around 150 to 180 days and waned thereafter. The antibody levels were considerably higher than those attained by vaccination and immunity was in evidence even after one year. The main site of persistence of pasteurellae appeared to be the tonsils. Whether detection in this tissue reflected the transient presence of the organism during the process of elimination by the natural defence mechanisms or a long-term reservoir of organisms is yet uncertain. The presence of HS pasteureUae in the tonsils of a healthy bovine has been reported earlier (Omar, Cheah and Shanta, 1962). Also in an abattoir survey isolation of HS organisms has been made from the retropharyngeal lymph nodes (Wijewardana, de Alwis, Athuraliya and Vipulasiri, 1986a). In the present study its detection at periods as long as 215 and 229 days after initial exposure seems to suggest that the tonsil could serve as a long term reservoir. The use of streptomycin resistance as a marker helped to trace the organism and ensure that what was isolated months later was the organism that was used for experimental infection. Furthermore, the use of a medium containing a 400/~g/ml concentration of streptomycin served as a selective medium for the isolation of the specific organism used for experimental infection. Mouse inoculation was used as a method of isolation as it is known that mice may be killed by ~10 HS pasteurellae and the LD~o of this streptomycin resistant strain was checked and found to remain unchanged before use. The virulence of the organisms isolated from carrier animals has been studied and reported elsewhere (Wijewardana et al., 1986b). If however, with long-term persistence in the tonsils, mouse virulence is lost, the method of isolation adopted by us could fail to detect the organisms. The findings of this study establishes the fact that the carrier animal in HS exists in two states. During the latent state, the organism persists in the tonsils whilst in the active state it also appears in the nasopharynx and is therefore shed in the nasal secretions. It appears, therefore, that during an outbreak of HS some animals develop a subclinical infection which leads to transient active carrier or shedder state, which is followed by a prolonged latent carrier state. During the latter state, however, short intermittent periods of the active state may appear apparently with diminishing frequency (Fig. 1). All such animals display IHA titres and this is therefore a reliable index for identifying a carrier animal. Conventional methods of detecting carriers adopted by past workers viz, swabbing of the nasopharynx through the external nares on one occasion would detect only those animals which are in the active state at the time of swabbing. Earlier studies have shown that in HS endemic areas a high proportion of animals acquired natural immunity particularly where recent outbreaks of disease had occurred (de Alwis and Sumanadasa, 1982; de Alwis et al., 1986). Coupled with the present findings it seems reasonable to conclude that in these areas all of the animals showing high IHA titres are latent carriers and are therefore a potential source of infection when converted to the active state. Organisms shed by active carrier animals can be expected to infect incontact susceptible animals. The antibacterial therapy was carried out in carriers with a

CARRIERS IN HS

193

view to determining whether the carrier state can be cleared by treatment. The persistence of pasteurellae in the tonsils despite treatment with antibacterial drugs to which the organism is sensitive in vitro suggest that the organisms within the tonsils are in a dormant state and are not in active multiplication. In the light of the present knowledge it is reasonable to postulate that at the end of an epidemic of HS in a given herd or village a high proportion of surviving animals that remain clinically normal become immune earners. The proportion of such animals could even reach 100 per cent. For a short transient period they will be shedding pasteurellae but will soon pass into the latent state when the organism persists in a dormant state in the tonsils. Such animals will have a high level of humoral immunity as evinced by detectable I H A antibody levels. Intermittently such latent carrier animals will become active and shed virulent pasteurellae and pass the infection on to incontact susceptible animals. Some of the latter animals may pass through a subclinical infection and become immune carriers. Others may develop clinical HS and the magnitude of the outbreak will depend on the proportion of immune to nonimmune animals in the herd at that time. The different patterns of morbidity reported by de Alwis (1981) in endemic and non-endemic areas is explained by the different proportions of immune animals present in these areas. What factors cause a latent carrier to become active is yet unknown. A popular belief exists that HS breaks out when animals are subjected to stress. It is now known that the disease can be experimentally produced in animals well fed and managed using pure cultures alone, without any concurrent, extraneous stress factors. Perhaps stress---a collective term used to describe a host of ill-defined factors may play a role in converting a latent carrier to an active state. The experimental infection studies, by what are likely to be the natural routes viz. oral and intranasal, gave some indication of the number of viable organisms required to set up clinical infection. As to how a susceptible incontact animal could pick up such a large infective dose from a shedding carrier remains to be understood. The apparent absence of a dose-response relationship suggests that the infective dose itself is a highly variable entity, presumably determined by the interaction of a variety of factors. The location of the organism within the tonsillar tissue has also yet to be determined. Whilst the findings of this work have thrown considerable light on the role of the carrier animal further investigations into those aspects discussed above are necessary to comprehend fully the true significance of the carrier animal in the epidemiology of HS. ACKNOWLEDGEMENTS The authors are grateful to the Swedish Agency for Research Co-operation (SAREC) for the research grant that made this work possible and to the Natural Resources, Energy and Science Authority of Sri Lanka (NARESA) for their assistance in operating the grant. Accepted for publication May 1989 REFERENCES BAIN, R. V. S., DE ALWlS, M. C. L., CARTER, G. R. & GUPTA, B. K. (1982). Haemorrhagic septicaemia. FAO Animal Production & Health paper No. 33, FAO, Rome. CARTER, G. R. (1955). American Journal of Veterinary Research, 16, 481-484.

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DE ALWIS, M. C. L. (1981). TropicalAnimal Health and Production, 13, 195-202. D~ ALWlS, M. C. L. (1982). TropicalAnimal Health and Production, 14, 29-30. DE ALWIS,M. C. L., GUNATILLAKE,A. A. P. & WICKRAMASINGHA,W. A. T. (1978). Ceylon Veterinary .Iournal, 26, 35-41. DE ALWIS, M. C. L. & SUMANADASA,M. A. (1982). Tropical Animal Health and Production, 14, 27-28. DE ALWlS, M. C. L., Wm~WARDANA,THULA G., SIVARAM,A. & VIPULASIRI,A. A. (1986). Sri Lanka Veterinary Journal, 34, 33-42. FARID, A., ELoGHANI, M. A., KHALIL, A., EL-GHAWAS,A. & KAMEL, A. (1980). Agricultural Research Review, 58(7), 107-115. GUFrA, B. K. (I962). Studies on the carrier problem in haemorrhagic septicaemia. Thesis. Punjab University, Chandigar, India. HIRAMUNE,T. & DE ALWIS,M. C. L. (1982). Tropical Animal Health and Production, 14, 91-92. MOHAN, K., StNHA, M. N., SiNGH,R. P. & GUPTA,G. M. (1968). Veterinary Record, 83, 155-156. MUSTAFA,A. A., GHALIB,H. W. & SHIGIDI,M. T. (1978). British Veterinary Journal, 134, 375-378. OMAR, A. R., CHEAH,P. P. & SHASTA,C. S. (1962). British Veterinary Yournal, 118, 71-73. SINGH, M. (1948). Indian Journal of Veterinary Science and Animal Husbandry, 18, 77-80. WIJEWANTA,E. A. ,¢" KARUNARATNE,K. G. (1968). Cornell Veterinarian, 58, 462-465. WIJEWARDANA,THULAG., DE ALWIS, M. C. L., ATHURELIYA,D. S. • VIPULASIRI,A. A. (1986a). Sri Lanka Veterinary Journal, 34, 16-23. WIJEWARDANA, 'I~LA G., DE ALWIS, M. C. L. ~; BASTIAIqSZ,H. L. G. (1986b). Sri Lanka Veterinary Journal, 34, 43-57. PERSISTANCE DE LA SITUATION DE PORTEUR CHEZ DES BUFFLES ATTEINTS DE SEPTICEMIE HEMORRAGIQUE A PASTEURELIM MULTOCIDA, SEROTYPE 6:B Rq~nu~-Cinquante sept jeunes buflles ont ~te infect~ exl~rimentalement ou naturellement exposes la septic~mie hemorragique (HS). Parmi eux, 32 sont devenus des porteurs immuns. Ils ont ~t~ suivis par groupes pendant des p~riodes allant jusqu'a 360 jours pour deceler I'apparition de pasteurelles dam le nasopharynx et caracteriser leurs taux d'anticorps. Chez la plupart des animanx, les pasteurelles sont apparues darts le nasopharynx pendant une courte p~riode initiale puis ont disparu mais elles sont r~apparues par intermittence et la p~riode de presence la plus longue a et~ de 215 jours apr~s le contact infectieux. Tousles animaux ont relev~ des titres croissants d'anticorps avec un pic d'une dur~e de 150 ~ 180 jours suivi d'un d~clin ult6rieur, l.as pasteurelles ont persist6 dans les amygdales et ont et6 isolees sur 20 des 27 porteurs apr~s abatage. La p~riode la plus longue pendant laqueile l'isolement a pu etre r~alis~ apr~ abattage a et~ de 229 jours. L'organisme heberg6 dans les amygdales a rc~sist~ a une th~rapie antibacterienne avec des m~dicaments anxquels il se revelait sensible in vitro. En conclusion, darts la septic~mie hemorragique, il reste des porteurs "actifs" aussi bien que "latents". Les premiers apparaissent par intermittence pendant des episodes de courte dur~e, entre de longues periodes de latence, alors que les pasteurelles restent presentes dans les amygdales. Celles-ci jouent de ce fait le r61e d'un r(:servoir ~t long terme. PERSISTENCIA DEL ESTADO DE PORTADOR DE SEPTICEMIA HEMORRAGICA (INFECCION CON PASTEURELLA MULTOCIDA SEROTIPO 6:B) BUFALOS Remmea--Cincuenta y siete bttfalos j6venes fueron infectados experimentalmente o expuestos naturalmente a septicemia hemomigica (SH). Treinta y dos de estos animales se volvieron portadores inmunes. Los bdfalos fueron observados en grupos por periodos de hasta 360 dias, para detectar ta aparici6n de la pasteurela en la nasofaringe y de anticuerpos. En la mayorla de los animales la pasteurela apareci6 en la nasofaringe pot un peflodo initial corto y desapareci6. E! organismo reapareci6 intermitentemente y el perfodo m~s largo observado rue 215 d~nsdespu~s de la exposici6n. Todos los animales tuvieron un aumento de anticuerpos, con un pico que dur6 de 150 a 180 dias, declinando despu(:s. La pasteurela persisti6 en las tonsilas y rue aislada eta 20 de 27 portadores despu~s del sacrifido. El peHodo m~s largo de aislamiento, despu~s del sacrifido, rite de 229 dias. El organismo alojado en las tonsilas, no fue afectado por terapia antibacterial, utilizando drogas alas cuales la bacteria rue sensitiva/n v/fro. Se concluye queen SH, los animales portadores existen en estado "activo" y "latente', apareciendo el primero pot periodes intermitentes cortos, entre largos periodos latentes, coando pasteurela se aloja en las tonsilas, las cuales constituyen un reservario permanente.

Persistence of the carrier status in haemorrhagic septicaemia (Pasteurella multocida serotype 6:B infection) in buffaloes.

Fifty-seven young buffaloes were experimentally infected or naturally exposed to haemorrhagic septicaemia (HS). Of these animals 32 became immune carr...
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