1. (:OMP.

PATH.

1978.

\‘ot.

167

88.

INTERACTIOX BETWEEN A HOG CHOLERA STRAIX AND PASTEURELLA ,lIUL7-OCIDA PRODUCTIOK OF PORCINE PXEUMONIA

C.

PIJOAN

and G.

Escuela aVacional de Estudios Projkionales

VACCINE IN THE

OCHOA

Cuautitldn,

N&ico

INTRODUCTION

Porcine pneumonia, due to a variety of infective agents, is a serious disease of pigs raised under intensive conditions. In Mexico, approximately 10 peg cent of pigs killed at a central slaughterhouse had pneumonia (Pijoan, Ochoa and Trigo, 1975) ; a large number of bacteria were isolated, but only Pasteurella multocida showed a statistically significant relationship with the presence of severe macroscopic and microscopic lesions (Pijoan et al., 1975). In these lungs an inverse relationship between hletastrong$us apri and pneumonia was shown (Pijoan and Dominguez, 1975) as well as the presence of specific immunofluorescence against hog cholera virus (Pijoan et al., 1975). This paper describes an investigation of the interaction between a live vaccine against hog cholera (swine Sever) and P. multocida in respiratory infection.

MATERIAL

AND

METHODS

Piqs< . Twenty-five Yorkshire pigs of both sexes, aged 8 to 10 weeks, were obtained from a local producer known to raise pigs free of neutralizing antibodies against hog cholera virus. The pigs were bled on arrival and the serum was tested hy tube agglutination against serotypes A, B, D, and E of P. multocida with negative results. The pigs were housed in isolation units with filtered air and a regulated temperature of about 20 “C. The pigs were divided randomly in 6 units, and 3 weeks later were inoculated as detailed in Table 1. Hog cholera vaccinations. The hog cholera vaccine was obtained through a retailer. and consisted of a live strain grown in porcine tissue culture. The dose (2 ml) and the inoculation route (intramuscular) were in accordance with the manufacturer’s instructions. P. multocida i@ction. Pigs were inoculated intratracheally with a dose of 3 ml of a suspension containing 5.6 x lo9 live organisms per ml. This large dose was necessary in view of the difficulty in producing experimental disease with this agent. The bacteria were 10 fresh isolates of P. multocida obtained from pneumonic lungs and passaged not more than 3 times in artificial media. The serotypes of the strains were not known. Erlaluation of the degree of pneumonia. All the pigs were assessed clinically for 12 days after the pasteurella inoculation. Coughing, difficult respiration or other abnormalities were noted, as well as rectal temperature. Fifteen days after inoculation the animals were killed. The degree of macroscopic pneumonia present was evaluated by means of an arbitrary scale of 0 to 5 points per lobe affected. In addition, 0 to 5 points were also awarded for the presence of pleurisy, pleural adhesions or both. In thi\

168

C.

PIJOAN

AND

G. OCHOA

scale system, 1 point was awarded for a very small lesion (of not more than 2 sq. cm), 2 points for a lesion not exceeding 4 sq. cm, 3 points for a lesion between 6 and 10 sq. cm, and 5 points for a lesion in excess of 10 sq. cm. The evaluation was made by the same observer. All the lungs were examined microscopically and bacteriologically by standard techniques. Bacteria isolated were identified in accordance with the characteristics in Cowan (1974). Th e results were subject to statistical analysis by Student’s t-test at P < 0.05 (Kreysig, 1975). RESULTS

Most of the animals of groups 1, 2 and 3, and one animal each of groups 4, 5 and 6 had temperatures above 39 “C up to the 12th day after infection with P. multocida. In addition, 2 pigs each of groups 1, 2 and 3 had temperatures in excess of 39 “C over the same period. Clinical signs correlated closely with rectal temperature. The mean scores of lesions for the 6 groups were 4.8, 7.8, 7.8, 0, 2.3 and 1.7 respectively. Groups 2 and 3 (hog cholera and P. multocida) had the highest count, and this difference was statistically significant when compared with groups 4, 5 and 6 but not with group 1, which also received hog cholera and P. multocida inoculations. Two of 3 pigs inoculated with

~OCULAT~ON

SCHEDULE

FOR THE 6 GROUPS

Intmal

G,-Otlp

Number animals

of

(days)

afterthe Pi,p

Pigs given hog cholem vaccine

OF PIGS

beginning of the e.u,beriment infected with Pasteurella Pigs multocida slaughtered

__---1

15 15 15 15

i 4 5 6

4

P. multocida alone (group 5), 2 of 4 untreated pigs (group 6), and none of 3 pigs that received hog cholera vaccine alone (group 4) had lesions. These lesions were not severe, a mean score of 2.5 compared with 7.2 in the hog cholera P. multocida groups. There was a correlation between macroscopic and microscopic lesions. The groups receiving both inoculations (1,2 and 3) showed extensive haemorrhages, congestion and polymorph infiltration, as well as large areas of collapsed lung tissue. The control groups (4, 5 and 6) showed much lesssevere lesions, or no lesions at all. P. multocidawas re-isolated from the lungs of 7 of the 18 pigs that were infected with this organism. DISCUSSION

The results suggested a synergistic effect between a live hog cholera vaccine strain and P. multocida. Roberts and Little (1970) stated that lesions experi-

PORCINE

PNEUMONIA

169

mentally produced by Mycoplasma hyopneumoniae alone arc much less scvcr( than those found in field conditions. Similar findings have been reported by C:artc.r (1970). Kasza, Hodges, Betts and Trcxlcr (1969) described the interaction between a porcine adenovirus and ,%I. hyopneumoniae, while Smith (1970) described an interaction between P. multocidu and .2&oplusmu h_vopnezlmonine Interaction between hog cholera virus and Pasteurella multocidu has bcc11 described previously (Hutyra, Marek, and Manningcr, 1936). Thcrc was a slight though non-significant difference between group 1 and groups 2 and 3, even though all received both hog cholera vaccine and P. mzrltocida. The reasons for this difference may reside in the time lapse betwcrn the hog cholera vaccination and the P. multocidu infection, which was grratrr i 14 days) for group 1 than for groups 2 and 3 (5 and 3 days respectivclyi. Similar results were reported by DegrC (1970) w 110 studied a parainflucnzahaemophilus interaction in mice. He found that previous infection with paraillflucnza virus enhanced the bacterial infection, l)ut this clrect was muc~11 grcatcr if the period between viral and bacterial infections was 4 days than if‘ it was 2 or 6 days. Respiratory tract interactions between vaccine virus strains and bacteria llavc I~cn described in other conditions, notably in chronic respiratory discaac in the chicken (Cortsvet and Sadler, 1966a,b). In \-ic\v of this it is not surprising to detect a similar interaction in pigs. T’11(* rcsl~lts indicate that care should be taken in the LISC of li\:c hog cholrra \-accinc~. SUMMARY

Twenty-five pigs in 6 groups and housed in isolation units were used to stud) the possible interaction between a live hog cholera vaccine strain and Parteurelln mrltocidu. Three groups were vaccinated against hog cholera, and then inoculatctl at different intervals with a large dose of P. mztltocidu. One group rrccivrd hog cholera vaccine only, one P. mzlltocidu only, and one remained untrcatcd. ;I11 animals were killed 15 days after the last inoculation and the lung lesions M’cr( c\-aluatcd by means of a scoring system. The groups ivhich received both hog cholera vaccine and P. mcdtocida had higllcr lesion scores than control groups which received only one agent? and chc diffcrcnces \vcrc statistically significant. The results suggest that vaccination \2-ith live strains of hog cholera virus may be a factor in the s\vinc pncumoni;l complc:.. REFERENCES

Carter, G. R. (1970). Pasteurellosis. In Disease oj‘Sz&np,H. W. Dunne, Ed., pp. 56% 670. Iowa State University Press. Corhtvet, R. E., and Sadler, W. W. (1966a). A4 comparative study of single and multiple respiratory infections in the chicken: multiple infection with A’f_ycoplusm~z galliseflticum, Newcastle disease,and infectious bronchitis virus. American Journal nj‘ Veterinary Research, 27, 1703% 1720. Corstvet. R. E., and Sadler, W. W. (196611).A comparative study of single and multiple respiratory infections in the chicken: single infections with n/Jvcoplasma gallise~ticumand Newcastle disease.American Journal of Veterinary Research, 27, 1721-1733.

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AND

G. OCHOA

Cowan, S. ‘I. (1974). Cowan and Steel’s Manual for the Identijcation qf Medical Bacteria, 2nd edit. Cambridge University Press,Cambridge. Degre, M. (1970). Synergistic effect in viral-bacterial infection. dcta pathologica et microbiologica scandinavica, Section B, 78, 4 l-50. Hutyra, E., Marek, J., and Manninger, R. (1936). Pasteurellosisof swine. In Special Pathology and Therapeutics of the Diseases of Domestic Animals, 4th English edit., J. Russell, Ed. Bailliere, Tindall and Cox, London. Kasza, L., Hodges, R. T., Betts, A. O., and Trexler, P. C. (1969). Pneumonia in gnotobiotic pigs produced by simultaneous inoculation of swine adenovirus and Mjcot!Jasma

hyopneumoniae.

Veterinary Record, 84, 262-267.

Kreysig, E. (1975). Introduccidn a la Estadistica Matemdtica Edicidn Limusa, p. 234. S. A. Wiley, Mexico. Pijoan, C., and Dominguez, J. L. (1975). Incidencia de Metastrongylus sp. en pulmones neumonicos y no neumonicos de cerdo. 7e’cnica Pecuaria en Mexico, 28, 38-39. Pijoan, C., Ochoa, G., and Trigo, F. (1975). Aislamiento de agentes infecciososde pulmones neumonicos de cerdo colectados en el rastro de Ferreria. Ttknica Pecuaria en Mexico,

29, 46-49.

Roberts, D. H., and Little, T. W. A. (1970). Serologic studiesin pigs with Mycoplasma hy~opneumoniae. Journal of Comparative Patholopv, 80, 2 1 I-220. Smith, I. M. (1970). Studies on the role of somemicro-organisms in the respiratory infections of the pig with special reference to the involvement of Pasteurella septica. Ph.D. Thesis, University of London. [Received for publication,

September 24th, 19761