Grand Teton National Park Report
The lungworm of elk, Dictyocaulus hadweni, is morphologically quite like the species in cattle but the parasite affects the two species of host animals in very different ways. In cattle, D. viviparus is usually found only in young animals. After a calf is exposed and makes antibody or cell mediated immunological responses to the parasite, the calf usually can not be reinfected. In the case of the parasite's invasion of elk tissue, some immunological response is apparently made during the late spring, summer and fall months so that very few elk are positive for lungworm from September-January. However, most elk (65-80%) are susceptible to infection or reinfection annually (Apri 1-May). It appears that the reinfection time coincides with the span of time in which the elk are at their physiological low. The April-May period may be the time when the physiological condition of the elk is at a seasonal low. Any biological factors which would decrease the numbers of infective Dictyocaulus larvae would benefit the elk.
Bergstrom, Robert C.
"Parasites of Ungulates in the Jackson Hole Area: Scarabaeoid Beetles Acting on Lungworm, Dictyocaulus hadweni, Larvae in Elk Feces, 1978,"
University of Wyoming National Park Service Research Center Annual Report: Vol. 2
, Article 3.
Available at: https://repository.uwyo.edu/uwnpsrc_reports/vol2/iss1/3