Moose are well adapted to winter survival, whereas deer are not. They could not withstand the harsh winters in these regions of the northeastern United States and the southeastern provinces of Canada. Deer populations began to move into the southern portions of moose range in the early 1900s following changes in climate, logging, mining, forest fires, and increasing human development. High-quality deer habitat associated with these changes has led to dramatic increases in deer abundance in these regions. White-tailed deer are the normal host of the "P. tenuis" parasite and are immunologically adapted to its presence. Deer and "P. tenuis" have coadapted in an evolutionary arms race over time. Deer remain largely unaffected by the presence of "P. tenuis" because of the immunity they have built as a result of coadaptation. The prevalence and infection rate of "P. tenuis" in deer is density dependent; increased rates of infection by the parasite are the result of higher deer densities. Moose populations on the southern fringes of their range have recently experienced dramatic declines. As deer encroached upon the southern fringes of moose range, they introduced the parasite to a naïve host, the moose. Upon transmission of the pathogen into moose, the worm causes cerebrospinal nematodiasis, a disease of the nervous system that often results in death. "P. tenuis" may be one factor that has contributed to moose declines in southern portions of their range. This disruption of host-pathogen dynamics due to habitat alterations has promoted the spread of this parasite to a naïve host and has potentially contributed to declines in moose abundance and productivity in regions with high deer densities. Continued increase in deer abundance and density in the southern fringes of moose range are predicted to facilitate sustained transmission of "P. tenuis" to moose. Continued transmission of deer-related parasites, coupled with low productivity, habitat degradation, and a northward shift in the moose thermonuetral zone, leads to a troubling prognosis for southern moose populations. Murray et al. (2006) predict, if current trends continue, moose populations in these regions will not be viable and population declines will persist. Currently, there is no definitive treatment for "P. tenuis" in mammals, though research is still being conducted"." The use of anthelmintics (ivermectin and fenbendazole) have been attempted in white-tailed deer.