Epidemiology and pathogenesis of paratuberculosis

• Main Author: Beard, Philippa M.
• Published: University of Edinburgh 2001
• Subjects: 636.089
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.641423

Investigations into three aspects of the epidemiology and pathogenesis of paratuberculosis were undertaken - infection of wildlife with <i>Mycobacterium avium </i>subsp<i> paratuberculosis (M. a. paratuberculosis),</i> the early host immune response mounted against organism, and the influence of host genotype on susceptibility to the disease. The pathology of natural rabbit paratuberculosis was investigated and described, with rabbits exhibiting either mild or severe lesions. The changes noted in the severely affected rabbits included the presence of giant cells containing over 50 nuclei and many acid fast bacteria.<i> M. a. paratuberculosis</i> was cultured from the faeces and urine of the naturally infected rabbits, revealing two possible routes of interspecies transmission of the organism. To investigate the impact of natural rabbit paratuberculosis on the disease in ruminant livestock, young calves were inoculated orally with a strain of <i>M. a. paratuberculosis</i> isolated from a naturally infected rabbit. After an incubation period of six months, the organism was recovered from the intestinal tissues of seven out of eight inoculated calves, with three of these calves also exhibiting pathological changes consistent with chronic paratuberculosis, suggesting that <i>M.a.paratuberculosis</i> from rabbits is capable of causing paratuberculosis in cattle. In a parallel experiment, two groups of rabbits were inoculated with either a bovine or leporine derived strain of <i>M. a. paratuberculosis</i>, but no evidence of infection was noted after a six month incubation period, suggesting that further, as yet unidentified factors, are involved in the pathogenesis of paratuberculosis in rabbits. A large survey in rural Scotland revealed <i>M.a. paratuberculosis</i> infection of 10 species of wildlife - fox, stoat, weasel, crow, rook, jackdaw, rat, wood mouse, hare, and badger. The investigations into wildlife reservoirs of <i>M.a. paratuberculosis,</i> the influence of host genes on susceptibility to the disease, and the role of gd T cells in the initial response to <i>M.a. paratuberculosis</i> infection provide new information on the epidemiology and pathogenesis of this disease, and may have a role to play in creating more effective control measures against paratuberculosis.