Routes of intraspecies transmission of Mycobacterium avium subsp. paratuberculosis in rabbits (Oryctolagus cuniculus): a field study

Rabbits have been increasingly linked to the persistence of paratuberculosis (Johne's disease) in domestic ruminants in the United Kingdom. The aims of this study were to determine the routes of intraspecies transmission of Mycobacterium avium subspecies paratuberculosis (MAP) in rabbits and to estimate the probability of transmission via each route, in order to gain understanding of the dynamics of MAP in this host. Rabbits were sampled from two sites where MAP had previously been isolated from the livestock and rabbit populations. No pathology was noted in any animals, but the overall prevalence of MAP in rabbits was high at both sites studied, 39.7% and 23.0%, respectively. MAP was isolated from the testes, uterus, placenta, fetuses, and milk. This is the first time that the bacterium has been isolated from any of these tissues in a nonruminant wildlife species. These results suggest that transmission may occur vertically, pseudovertically, and horizontally. Vertical, i.e., transplacental, and/or pseudo-vertical, i.e., through the ingestion of contaminated milk and/or feces, transmission occurred in 14% of offspring entering the population at 1 month of age. As infection via these routes is only possible from infected adult females, this equates to a probability of infection via this route of 0.326. Probability of infection via horizontal transmission (including interspecies transmission) occurred at up to 0.037 per month. The presence of these routes of transmission within natural rabbit populations will contribute to the maintenance of MAP infections within such populations and, therefore, the environment.