A serological survey of infectious disease in Yellowstone National Park's canid community

Abstract

Background: Gray wolves (Canis lupus) were reintroduced into Yellowstone National Park (YNP) after a >70 year absence, and as part of recovery efforts, the population has been closely monitored. In 1999 and 2005, pup survival was significantly reduced, suggestive of disease outbreaks.

Methodology/principal findings: We analyzed sympatric wolf, coyote (Canis latrans), and red fox (Vulpes vulpes) serologic data from YNP, spanning 1991-2007, to identify long-term patterns of pathogen exposure, identify associated risk factors, and examine evidence for disease-induced mortality among wolves for which there were survival data. We found high, constant exposure to canine parvovirus (wolf seroprevalence: 100%; coyote: 94%), canine adenovirus-1 (wolf pups [0.5-0.9 yr]: 91%, adults [>or=1 yr]: 96%; coyote juveniles [0.5-1.5 yrs]: 18%, adults [>or=1.6 yrs]: 83%), and canine herpesvirus (wolf: 87%; coyote juveniles: 23%, young adults [1.6-4.9 yrs]: 51%, old adults [>or=5 yrs]: 87%) suggesting that these pathogens were enzootic within YNP wolves and coyotes. An average of 50% of wolves exhibited exposure to the protozoan parasite, Neospora caninum, although individuals' odds of exposure tended to increase with age and was temporally variable. Wolf, coyote, and fox exposure to canine distemper virus (CDV) was temporally variable, with evidence for distinct multi-host outbreaks in 1999 and 2005, and perhaps a smaller, isolated outbreak among wolves in the interior of YNP in 2002. The years of high wolf-pup mortality in 1999 and 2005 in the northern region of the park were correlated with peaks in CDV seroprevalence, suggesting that CDV contributed to the observed mortality.

Conclusions/significance: Of the pathogens we examined, none appear to jeopardize the long-term population of canids in YNP. However, CDV appears capable of causing short-term population declines. Additional information on how and where CDV is maintained and the frequency with which future epizootics might be expected might be useful for future management of the Northern Rocky Mountain wolf population.

Figure 1. Annual canine distemper virus seroprevalence among wolves and coyotes in Yellowstone National Park, 1991–2007.

Among wolves, data are divided by location (Northern Range [NR] and Interior), whereas coyotes were sampled only on the NR. Sample sizes are displayed above seroprevalences (see Table S3 for number of packs sampled and 95% CIs). Where points overlap, the top number refers to NR, the bottom to Interior.

Figure 2. Neospora caninum seroprevalence among wolves in Yellowstone National Park, 1997–2007.

Data are divided by age class: juvenile (0.5–1.9 yrs), young adult (2–4.9 yrs), and old adult (≥5 yrs). Sample sizes are displayed above seroprevalences. Where points overlap, numbers refer to juveniles, young adults and old adults, respectively.

Figure 3. Annual wolf-pup survival in Yellowstone National Park by location (Northern Range [NR] and Interior), 1995–2007.

Error bars are 95% confidence intervals and the numbers at the bottom of the graph represent the number of pups monitored/the number of packs observed (NR listed on top).