Spatial and temporal patterns of gray wolf exposure to vector-borne diseases in Wisconsin, USA
Lyme disease, anaplasmosis, ehrlichiosis and heartworm are diseases that affect canids, but their prevalence in wild wolves (Canis lupus) has not been systematically assessed. While all of them affect dogs (Canis familiaris) and have also been found in humans, Lyme disease and anaplasmosis are most frequently diagnosed in the United States. In Wisconsin, the incidence of human Lyme disease and anaplasmosis has been steadily increasing over time; however, true incidence could be much higher due to underreporting of the disease. It is useful to study vector-borne infections in wolves not only to better understand their health threats, but also because wolves might serve as a sentinel species for human and domestic dog health. Our objectives were to assess the potential risk of wolf exposure to the pathogens causing these diseases, identify areas with higher risks of infection, and compare these patterns to those of dogs and humans in Wisconsin. We tested 379 gray wolf serum or blood samples collected in Wisconsin between 1985 and 2011, using the SNAP® 4Dx® Test (IDEXX Laboratories, Westbrook, ME). Data on human incidence of Lyme disease was provided by the Wisconsin Department of Health Services. Dog data was provided by IDEXX and retrieved from literature.
The prevalences of wolf exposure were: Borrelia burgdorferi (Lyme disease) 65.6%, Anaplasias phagocytophilum (anaplasmosis) 47.2%, Ehrlichia canis (ehrlichiosis) 5.9%, and Dirofilaria immitis (heartworm) 8.8%. Adults had higher exposure to B. burgdorferi, A. phagocytophilum, and E. canis than pups. There was a significant temporal increase during the study period in the prevalence of exposure to B. burgdorferi, which corresponds to changes in the incidence of human Lyme disease. Prevalence of exposure to the four pathogens was significantly higher in wolves than dogs. There is a cluster of wolf exposure to B. burgdorferi in northwestern Wisconsin that is contained within dog and human clusters for the same pathogen. The high prevalence of wolf exposure to these pathogens, particularly those causing Lyme disease and anaplasmosis, suggests a potential health risk to wolf populations, although further information on the effects of these diseases in wolves is required. During the study period, the estimated winter population grew from 14 to 782 wolves in Wisconsin; thus, it does not appear that diseases interfered with the population growth of the state’s wolves. Compared to dogs, wolves might better reflect the natural patterns of infection risk because wolves have higher contact with vectors that transmit these diseases.