Brainworm, Parelaphostrongylus Tenuis, in White-tailed Deer (odocoileus Virginianus) of Eastern South Dakota: Implications for Western South Dakota

Diseases and parasites are important mortality factors affecting cervid populations. Meningeal worm (Parelaphostrongylus tenuis) is a nematode parasite found in white-tailed deer (Odocoileus virginianus) populations throughout eastern North America. To determine the distribution of meningeal worm in South Dakota, heads of hunter harvested deer were examined for P. tenuis from 1997-1999. A total of 2,848 deer were examined for the parasite. Prevalence of P. tenuis infection was significantly higher in deer examined in eastern (n=2,271) than in western South Dakota (n=577) (P < 0.0001). One in four deer (25.1%) harvested east of the Missouri River were found to be infected with P. tenuis while only 1.4% of the deer examined in western South Dakota were infected. Furthermore, 570 of 578 (98.6%) infected deer were harvested in eastern South Dakota. Infected deer were present in 37 of 44 counties in eastern South Dakota and in 3 of 22 counties in western South Dakota. Distribution of P. tenuis also is dependent of the presence of suitable terrestrial gastropod intermediate hosts. To determine the distribution, abundance, species composition, and involvement of terrestrial gastropods in transmission of P. tenuis to deer populations, gastropods also were collected during the summers of 1999 and 2000. A total of 4,062 terrestrial gastropods representing 14 species, five of which are known intermediate hosts for P. tenuis, was collected throughout South Dakota during the summers of 1999 and 2000. Total number of gastropods collected was significantly higher in eastern (n=3,221) than in western South Dakota (n=841) (P < 0.0001). Furthermore, five known gastropod intermediate host species were collected in eastern South Dakota while only two known intermediate hosts were collected in western South Dakota. The scarcity of infected deer in western South Dakota might indicate that the Missouri River represents a physical barrier to the western movement of the parasite. Furthermore, the semi-arid climate associated with western South Dakota may not be suitable for survival of viable first stage P. tenuis larvae or may not be wet enough for a time period long enough to permit development to an infective third stage in terrestrial gastropods. The accidental introduction and the consequences for native mule deer (O. hemionus) and elk (Cervus elaphus) populations that currently occur in western South Dakota is 374 Proceedings of the South Dakota Academy of Science, Vol. 80 (2001) potentially disastrous. In fact, if P. tenuis became established in white-tailed deer populations in western South Dakota following an accidental introduction, it would be virtually impossible to eliminate. Thus, as game managers we must be conservative in our management practices to ensure that we not find out the hard way if P. tenuis could become established in western South Dakota if accidentally introduced.