The objective of this
study was to investigate suitability of juvenile New Zealand white
rabbits as laboratory animal infection model and appropriateness of
various routes of inoculation for the study of pathogenesis of
paratuberculosis. Fifty-four 2-4 weeks old, rabbits were divided
into 3 groups viz., oral, intraperitoneal (I/P) and
intravenous (I/V) with 12 animals each, and their respective
control (uninfected) groups with 6 animals each. A bovine isolate
of M. a. paratuberculosis (MAP) was grown in Middlebrook 7H9
medium containing ADC supplement and mycobactin J. The bacterial
concentration was adjusted to 108( cfu/ml) in pasteurized
milk for oral (10 times) and 107 and 106 in
sterile saline for I/P and I/V inoculations (3 times),
respectively. The infection was sequentially monitored for a period
of 9 months after last inoculation by serological, immunological,
bacteriological, PCR and histopathological methods.
Most rabbits in all the 3
groups did not exhibit any clinical signs except rough hair coat,
depletion of perineal and mesenteric fat reserve, and emaciation
and decrease in the body weight at 9 MPI in I/V group. No gross
lesion suggestive of paratuberculosis infection was observed in any
group. Histologically, the I/V group had more pronounced lesions in
the organs such as ileum, sacculus rotundus, vermiform appendix and
mesenteric lymph nodes. Focal to multifocal granulomas were
observed in the lymphoid follicles of these organs. The oral and
I/P groups did not have significant differences in terms of type
and severity of the lesions which were produced in the ileum,
sacculus rotundus, mesenteric lymph nodes and vermiform appendix
but lesions were less pronounced than the I/V group. The acid-fast
bacilli were observed in the sacculus rotundus and mesenteric lymph
nodes of 2 rabbits from I/V group. There was rising antibody titres
in all the groups from 3 MPI onwards but was most prominently
observed in the I/V group. MAP was isolated from tissues of one
rabbit each at 3 and 6 MPI from I/V group. Faecal and tissue PCR
results were positive at 6 MPI for all the 3 groups. The results of
this study suggested that young rabbits could be used as laboratory
animal model for pathogenesis of paratuberculosis infection and I/V
route of inoculation was better than oral and I/P routes in terms
of severity of lesions
