Understanding the Spread of Johne’s Disease in Zoo Animals: Who Should We Worry About?
1Wildlife Disease Laboratories, Institute for Conservation Research, San Diego Zoo Global, Escondido, CA, USA; 2Wildlife Health Center, School of Veterinary Medicine, University of California, Davis, CA, USA
Johne’s disease (caused by Mycobacterium avium subsp. paratuberculosis; MAP) is a chronic, progressive bacterial enteritis of ruminants which can cause serious losses of both livestock and exotic species.1 Disease risk in exotic ruminants has been shown to be associated with maternal infection status, but the effect of other herdmates on risk of infection is not well understood.2 A retrospective epidemiologic study was conducted to evaluate the association between Johne’s infection status and early-life exposure to infected herdmates. The study population included 1599 individuals representing 52 species housed within the San Diego Zoo facilities between 1991 and 2010. Pre- and post-mortem disease surveillance records were reviewed to identify the infection status of all individuals in the population. Early-life (<180 days) exposure was considered to have occurred when individuals were contemporaneously housed with infected herdmates. Herdmate infection status was further classified according to stage of infection, age, and whether diagnostic lesions were ultimately found at necropsy. Conditional maximum likelihood methods were used to estimate the effect of contact with infected herdmates while controlling for maternal exposure, differences in species susceptibility, and herd management. Herdmate contact was significantly associated with disease within some of the evaluated scenarios, but was less important as a disease risk than maternal infection status. Disease odds declined by approximately 20% per year during the study period, reflecting the effectiveness of the MAP control program. These findings may be used to improve the efficiency and effectiveness of MAP surveillance and control in zoo animals.
The authors thank the Ellen Browning Scripps Foundation for funding this study. The authors also thank Phil Kass (UC Davis) for advice on the analysis, P.J. Stanley Hamel for technical contributions, and the keepers, managers, veterinarians, and laboratory personnel for data acquisition and maintenance.
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2. Witte, C.L., L.L. Hungerford, and B.A. Rideout. 2009. Association between Mycobacterium avium subsp. Paratuberculosis infection among offspring and their dams in nondomestic ruminant species housed in a zoo. J Vet Diagn Invest. 12:40–47.