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Cell culture

Conservation > Fish & Wildlife Diseases Arterial Worm

For questions/concerns about this disease in humans, please call your doctor or the Montana Department of Public Health and Human Services  (DPHHS).


For questions about this disease/parasite in wildlife, please call the FWP Wildlife Health Lab at 406-577-7882.


Arterial worm infection, or Elaeophorosis, is caused by the filarial nematode parasite, Elaeophora schneideri. The adult parasite is a long, pearly-white roundworm that inhabits the terminal branches of the common carotid arteries, generally at the angle of the jaw. The females are about the length and diameter of a paperclip. (Adrian, 1981).


In the United States, E. schneideri is endemic to much of the western and southwestern USA, but has also been identified in other focal areas including portions of the southeastern United States and areas of Minnesota (Merck Veterinary Manual).

Species affected

Mule deer and black-tailed deer are the normal definitive hosts for Elaeophora, and these deer species generally do not develop clinical disease as the result of infection. Infection does often result in disease in atypical hosts, which include elk, moose, domestic and wild sheep, sika deer, and Sambar deer (Merck Veterinary Manual).


The life cycle of E. schneideri involves a cervid host and biting a horse fly or deer fly. Mule deer and black-tailed deer are definitive hosts, and transmission occurs via the bite of the fly. These flies become infected when they ingest immature parasites called microfilariae in a blood meal. After metamorphosis in an infected fly, third-stage larvae migrate from the fly mouthparts into the new cervid host's circulatory system via the fly bite, and eventually migrate to the carotid arteries or leptomeningeal arteries (arteries that supply blood to tissues surrouding the brain) and matrue into adults. Microfilariae generally reside within the smaller capillaries of the head and neck, where they can be ingested by a feeding fly to compelte the parasite's life cycle (Grunenwald et. al, 2018). 


Although infections in the definitive hosts, mule deer and black-tailed deer, are generally subclinical, atypical hosts such as moose, white-tailed deer, elk, sheep, and goats can develop significant symptoms. The clinical condition is called Elaeophorosis. Elaeophorosis is a characterized by blood flow, damage to the lining of blood vessels, coagulation or clotting of blood, and tissue injury or deah, due to the presence of nematodes in the carotid and cephalic arterial system. This disruption in arterial circulation can lead to blindness; ischemic necrosis of the brain, ears, muzzle and other tissues of the head (cell death caused by lack of oxygen as a result of low blood flow); poor antler development; oral food impactions; and death (Grunenwald et. al, 2018). 

Public Health Concerns

No public health concern.


Adrian, W.J., editor. 1981. Manual of Common Wildlife Diseases in Colorado. Denver: Colorado Division of Wildlife.

Grunenwald CM, Butler E, W√ľnschmann A, et al. Emergence of the arterial worm Elaeophora schneideri in moose (Alces alces) and tabanid fly vectors in northeastern Minnesota, USA. Parasit Vectors. 2018;11(1):507. Published 2018 Sep 10. doi:10.1186/s13071-018-3077-0

Merck Veterinary Manual web site. Gerhold, R.W., Elaeophorosis in Animals. Accessed 1/12/22.

Western Wildlife Disease Workshop Notebook. 2009. Southeastern Cooperative Wildlife Disease Study. College of Veterinary Medicine, University of Georgia.