ASPECTS OF THE EPIZOOTIOLOGY OF PARELAPHOSTRONGYLUS TENIUS IN A WHITE-TAILED DEER POPULATION

Abstract

Larvae of Parelaphostrongylus tenuis occurred in 44% of fecal samples from 832 known-age white-tailed deer (Odocoileus virginianus) killed by vehicles October, 1986 to September 1990 in northeastern Minnesota. The earliest a fawn was found passing larvae was 12 October. Prevalence of larvae in feces of fawns rose steadily through autumn and winter (Sept.-Feb.). Forty-six percent were passing larvae by the time they approached one year of age and 68% at 12-15 mth. The overall prevalence in deer older than one yr, was 58% and it did not vary with increasing age. Prevalence of larvae in feces varied between years (32%, 45%, 44%, 52%, in 1986-90, respectively) and with season; more deer passed larvae in spring (67%) than in autumn and winter (49 and 53%). Changes in prevalence were likely due to climatological factors affecting transmission from gastropods and not to changes in deer density. The mean number of larvae in feces was positively skewed (X̅=51.7+6.1/g fresh feces; range = 1-1250/g) and negatively correlated with age; fawns and yearlings passed the most. More larvae were passed in spring by deer of all ages than at other times of the year.

The prevalence of P. tenuis in a deer herd is seen as an easily measured yet comprehensive index of the many host and habitat factors that interact to determine the overall success of the parasite. As such, it may also be the best measure of the risk of P. tenuis being transmitted to sympatric moose. Prevalence measured by examining deer heads for adult worms will differ from that determined by examining feces for larvae.