Disease Ecology of Wild and Domestic Carnivores in the Bolivian Chaco: Preliminary Results
Conservationists are becoming more concerned with the potential for diseases to negatively impact wildlife populations. Disease has caused population declines in a variety of free-ranging carnivore species, and domestic dogs are frequently suspected of being the origin of the agent in question. Because of the known susceptibility of wild carnivores to domestic carnivore diseases, and the lack of knowledge regarding carnivore diseases in South America, we are conducting a serosurvey of carnivores in Bolivia. We sampled domestic carnivores in villages near a national park, and wild carnivores at varying distances from the park. Data on canine demographics and contact rates with wild carnivores are being incorporated into an epidemiologic model to predict the risk of disease spread from domestic to wild populations. Our preliminary results indicate that most domestic dogs in this region have been exposed to canine distemper virus and canine parvovirus, both viruses of conservation concern. Results of serologic analyses of wild carnivores is pending and data collection is ongoing.
Infectious disease is increasingly being recognized as a threat to free-ranging carnivore populations.1,4-6,10,12,16 Some species, such as lions and Ethiopian wolves, have already experienced population declines due to disease outbreaks, and in selected cases, domestic animals have been implicated as the source.3,13 There is ample evidence that in both captivity and the wild, nondomestic canids and felids are susceptible to the diseases of domestic dogs and cats.2,7,8,13 However, little is known about the effects, or even the presence, of diseases on carnivore populations in South America. A major goal of our project is to use serology to quantify exposure to disease agents in the wild and domestic carnivore populations living in and near a national park in Bolivia.
A relatively new national park in Bolivia, the Kaa-Iya of the Gran Chaco, is a large protected area of tropical dry forest located in the southwestern part of the country. Its eastern border is approximately 40 km from a group of Izoceño-Guaraní villages.15 The Izoceños, indigenous people inhabiting these villages, use this “buffer zone” region (called the Integrated Management Area) between the park and the villages for subsistence hunting. Because hunting almost always involves dogs, there is potential for contact between domestic dogs and wild carnivores. This area has a high diversity of carnivores, despite the dry climate.15 Geoffroy’s cats (Oncifelis geoffroyi), pampas foxes (Pseudalopex gymnocercus), and crab-eating foxes (Cerdocyon thous) are seen frequently near the villages. Hunters commonly report seeing signs of pumas (Puma concolor), ocelots (Leopardus pardalis), jaguarundi (Herpailurus yagouarondi), and jaguar (Panthera onca), and sightings of the actual animals occur regularly. Most of these species are protected in part or all of their range, and are, therefore, of conservation concern.11,15
In an effort to assess the risk of disease transmission from domestic carnivores to free-ranging carnivores, we have begun a project that involves sampling domestic dogs and cats, sampling wild canids and felids, interviewing villagers about dog demographics, and finally, constructing an epidemiologic model of disease dynamics in these populations. Our hypothesis is that wild carnivores residing near human settlements have greater contact with domestic carnivores, and, therefore, will be more likely to be exposed to disease agents than are wild carnivores living in areas with little encroachment from humans.
Three villages were targeted for domestic animal sampling on the basis of ease of access and previous involvement with researchers. Dogs were identified for sampling by walking from house to house and asking residents if they had dogs or cats and were willing to participate. In exchange for participation, their pets were vaccinated against rabies and given antiparasitides. Sampling was basically opportunistic; no effort was made to randomize subjects. However, only animals 6 months of age and older were included, to avoid interference and false positive serologic results due to the presence of maternal antibodies. Blood, fecal, and tick specimens were taken from dogs with the aid of manual restraint and muzzles. Cats required chemical restraint; 10 mg of tiletamine-zolazepam (Telazol®, Fort Dodge Laboratories, IA, USA) given intramuscularly (IM) was used. Fecal samples were preserved in 10% buffered formalin, ectoparasites were preserved in 70% ethanol, and blood samples were spun down within 2 hours of collection so that the serum could be separated and frozen in liquid nitrogen.
Wild carnivores were captured using cage-style box traps (Tomahawk Livetrap Comp., Tomahawk, WI, USA and Havahart Traps, Woodstream Corp., Lititz, PA, USA) modified to house a live chicken.
Baited traps were placed along roads and trails about 200 m apart in four general sites:
1. Within 1–2 km of a village
2. At a site frequently used by hunters and their dogs, about 28 km from the nearest village
3. At a site 40 km from the nearest village, where hunters rarely venture
4. At a site within the National Park, about 200 km from the village
Traps were checked once or twice daily.
Trapped canids were immobilized with Telazol® at 5 mg/kg given IM. Felids were immobilized with a combination of ketamine (5 mg/kg) and medetomidine (Pfizer Corp., New York, NY, USA) (0.05 mg/kg); the latter was reversed with an equal volume of atipamezole (Pfizer Corp., New York, NY, USA) when all procedures were complete. Heart rate, pulse, respiratory rate, temperature, and oxygen saturation were monitored throughout anesthesia. Animals were weighed, measured, given a complete physical exam, photographed, ear tagged, and sampled for blood, feces, ectoparasites, and hair. Once recovered, animals were released at the site of capture. Specimens were processed similarly to the domestic carnivore samples.
Serologic analysis and parasite identification were performed at the Cornell University Veterinary Diagnostic Laboratory.
Domestic felids were tested for exposure to:
- Feline leukemia virus
- Feline immunodeficiency virus
- Feline calicivirus
- Feline panleukopenia virus
- Feline herpesvirus
- Feline coronavirus
- Toxoplasma gondii
- Leptospira interrogans
- Heartworm disease
Wild felids were tested for the above as well as canine distemper virus.
Domestic and wild canids were tested for exposure to:
- Canine distemper virus
- Canine parvovirus
- Canine herpesvirus
- Canine adenovirus
- Canine coronavirus
- T. gondii
- L. interrogans
- Heartworm disease
In addition to wild carnivore sampling, data on domestic dog demographics and contact rates with wild carnivores were collected. Villagers were interviewed and questioned about dog ownership, dog mortality, birth rates, and vaccination rates. Hunters in the communities were given data sheets and asked to keep track of wild carnivore sightings and signs. Data on frequency and location of hunting were available from previous studies. This information is being incorporated into a model developed by May and Anderson.9 By using a model, we can predict whether—and how fast—a given disease will spread from the domestic to the wild carnivore population.
Results and Discussion
Our results thus far are preliminary, but we have found that domestic dogs in the villages have a very high neonatal mortality rate, and based on serologic tests, many infectious diseases are maintained in the population. For example, the prevalence of antibodies to canine distemper virus and canine parvovirus in the dogs is greater than 90% (n=28), and the prevalence of antibodies to feline panleukopenia in cats is 100% (n=5). In the dogs, antibodies against canine herpesvirus, canine adenovirus, canine coronavirus, and T. gondii were also found. In addition, several dogs were positive for Dirofilaria immitis antigen. Sarcoptic mange also appears to be common based on physical examinations. Serologic tests are still pending on additional domestic dogs and cats, and on several wild carnivores (representing four species), but sarcoptic mange has been confirmed in one species, the pampas fox (Pseudalopex gymnocercus).7
To date, all the wild carnivores we have sampled were trapped in an area between five and fifteen km from the park boundary. In the future, we will be sampling wildlife close to the villages, in order to test the hypothesis that wild carnivores living adjacent to human settlements are more likely to have been exposed to domestic carnivore diseases than wild carnivores living more distant from humans. In addition, information on seroprevalence of diseases in domestic carnivores, coupled with estimates of contact rates between domestic and wild carnivores, will be used to construct an epidemiologic model to predict the likelihood of disease transmission to the wildlife species.
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