Elaeophora Schneideri - Hosts and Life Cycle

Hosts and Life Cycle

The normal definitive hosts for E. schneideri are the Mule deer and Black-tailed deer. It has also been found in several other wild mammalian hosts: White tailed deer, elk, moose, Bighorn sheep, Barbary sheep, Domestic sheep. Infestation was also found in sika deer on Texas ranches. Infestations of cattle, horses or humans have not been reported. The vectors of E. schneideri are blood-feeding Horse-flies of the family Tabanidae, genera Hybomitra, Tabanus, or Silvius.

Life cycle. In the normal definitive host, E. schneideri microfilariae are found in the host's skin, particularly around the forehead and poll areas. When a horse-fly feeds on an infected host, it ingests some of these microfilariae. Within a few weeks, the microfilariae develop into infective third-stage larvae (called L3) in the fly's fat body tissue and haemocoel. The mature L3 larvae migrate to the head and mouth-parts of the fly. When the fly feeds on another host, the L3 larvae enter the host's blood stream through the bite wound. They are carried throughout the host's circulatory system, and embed themselves in the walls of the leptomeningeal arteries. After a 2-week maturation period, they migrate to the carotid artery. About 4–6 months later they become sexually mature and begin to produce microfilariae. The adults live for 3–4 years. The microfilariae are released into the host's bloodstream, which carries them to the small capillaries of the skin in the head region. They become lodged in these narrow spaces, and await the next feeding horsefly.

In abnormal definitive hosts, such as sheep and elk, the adults may remain in the smaller arteries of the head and face region, instead of migrating to the carotid artery. In these smaller arteries, they obstruct blood flow to various parts of the head, face, and brain; which leads to the clinical symptoms of elaeophorosis (see below).