Canine distemper virus (CDV) is a common pathogen in canids, hyaenids, mustelids, procyonids, and viverrids, but, until recently, was not thought to cause disease in felids. CDV outbreaks have devastated lion populations in Serengeti National Park, Africa and have caused deaths of large cats in North American zoos. Dogs and raccoons were believed to be the source of crossover infections in these cats. In order to understand the transmission of this agent and to develop strategies to protect susceptible captive carnivores, this study examined risk factors for CDV infection in zoo cats.
To determine prevalence of infection with CDV, we used banked and newly collected serum samples from 85 captive felids from Brookfield Zoo in Cook County, IL. These sera had been collected between 1984 and 1998. Sera were also collected from 59 raccoons captured within zoo grounds in 1995 and 1996. Serologic testing was done by Cornell University using the CDV serum neutralizing test. Geographic information systems (GIS; MapInfoR and ArcViewR) were used to create maps of Brookfield Zoo, overlay habitat information and link data on the age, sex, location, housing characteristics, and history of each cat. Accessibility of each exhibit to raccoons was also assessed through a survey of the exhibits and interviews with keepers. Risk factors were compared between seropositive and seronegative animals using contingency tables and multivariate logistic regression.
Seventy-three percent of raccoons and 32% of the cats were seropositive for CDV. This level of exposure among cats was considerably higher than that observed in zoo cats in other studies.1 Cats housed outdoors had a twenty-three times greater risk of being seropositive for CDV (p<0.01). Among the smaller felid species, cats housed outdoors had a forty times greater risk of being seropositive than cats housed indoors (p<0.01). Other significant risk factors included species, sex, and age. Large cats were three times more likely to be seropositive for CDV than small cats. Males were four times more likely to be seropositive for CDV than females (p<0.05), and there was a ten percent increase in risk with each increasing year of age for both sexes (p<0.01). The time span during which seroconversion occurred was identified in nine cats. We are currently examining keeper records and animal health records produced during these time periods to look for specific exposure opportunities and we are testing banked wild raccoon serum samples to identify disease status in the wildlife populations during these periods.
Zoos provide a unique opportunity to determine risk factors for disease transmission that are relevant to both captive and wild populations. The development of preventive medicine programs in zoos should balance the protection of individuals from disease with the potential for using exposure and disease data to understand disease risk and transmission.
The authors wish to thank the keeper staff and laboratory personnel who assisted in the gathering of these data and processing the serum samples; Mark Jocelyn, at the Illinois Natural History Survey, for GIS assistance; and the Howard Hughes Medical Institute for its support.
1. Appel MJG, Yates RA, Foley GL, Bernstein JJ, Santinelli S, Spelman LH, et al. Canine distemper epizootic in lions, tigers, and leopards in North America. J Vet Diag Invest. 1994;6:277–288.