Invasive Species Compendium

Detailed coverage of invasive species threatening livelihoods and the environment worldwide

Abstract

Elaeophorosis in wild ruminants.

Abstract

Elaeophorosis is an infection of domestic and wild ruminants with the filariid Elaeophora schneideri. Adult nematodes are mostly found in the cephalic arteries of the vertebrate host. Microfilariae (mff) are found in the skin, usually in the head region, of infected animals. Lesions caused by the nematodes in American elk (Cervus elaphus) and moose (Alces alces) include hyperplasia and occlusion of cephalic and other arteries, which can result in severe disease and mortality. In other species, arterial lesions are minimal or absent, but hypersensitivity to mff results in a severe dermatosis in the head of domestic sheep (Ovis aries), Barbary sheep (Ammotragus lervia) and sika deer (C. nippon). The disease is less severe in white-tailed deer (Odocoileus virginianus). Clinical signs of disease are absent in mule and black-tailed deer (O. hemionus), apparently the normal definitive hosts and reservoirs of infection in western North America. At least 16 species of horseflies of the genera Hybomitra and Tabanus are biological vectors of E. schneideri. The 1st to 3rd stage larvae develop in the horsefly. In the southwestern USA, the transmission of E. schneideri is limited to the period of high prevalence of adult tabanids, usually about 1 month in early summer. In this area, horsefly numbers appear to fluctuate considerably across years depending largely on local and regional weather patterns. Unanswered questions concerning the epizootiology of elaeophorosis include why the disease is no longer highly prevalent as a morbidity and mortality factor in certain elk herds in the western USA, the status of white-tailed deer as a reservoir of infection in the southeastern USA, and the prevalence of E. schneideri in sheep and the importance of these hosts as reservoirs of infection.