''Elaeophora schneideri'' (arterial worm; carotid worm; cause of elaeophorosis, aka "filarial dermatitis" or "sorehead" in sheep; or "clear-eyed" blindness in elk) is a

nematode The nematodes ( or ; ; ), roundworms or eelworms constitute the phylum Nematoda. Species in the phylum inhabit a broad range of environments. Most species are free-living, feeding on microorganisms, but many are parasitic. Parasitic worms (h ...

which infests several mammalian hosts in North America. It is transmitted by

horse-flies Horse flies and deer flies are true flies in the family Tabanidae in the insect order Diptera. The adults are often large and agile in flight. Only females bite land vertebrates, including humans, to obtain blood. They prefer to fly in sunli ...

. Infection in the normal definitive hosts,

mule deer The mule deer (''Odocoileus hemionus'') is a deer indigenous to western North America; it is named for its ears, which are large like those of the mule. Two subspecies of mule deer are grouped into the black-tailed deer. Unlike the related whit ...

black-tailed deer Black-tailed deer or blacktail deer occupy coastal regions of western North America. There are two subspecies, the Columbian black-tailed deer (''Odocoileus hemionus columbianus'') which ranges from the Pacific Northwest of the United States and ...

, seldom produces clinical symptoms. In other hosts, such as

sheep Sheep (: sheep) or domestic sheep (''Ovis aries'') are a domesticated, ruminant mammal typically kept as livestock. Although the term ''sheep'' can apply to other species in the genus '' Ovis'', in everyday usage it almost always refers to d ...

elk The elk (: ''elk'' or ''elks''; ''Cervus canadensis'') or wapiti, is the second largest species within the deer family, Cervidae, and one of the largest terrestrial mammals in its native range of North America and Central and East Asia. ...

moose The moose (: 'moose'; used in North America) or elk (: 'elk' or 'elks'; used in Eurasia) (''Alces alces'') is the world's tallest, largest and heaviest extant species of deer and the only species in the genus ''Alces''. It is also the tal ...

, and

goat The goat or domestic goat (''Capra hircus'') is a species of Caprinae, goat-antelope that is mostly kept as livestock. It was domesticated from the wild goat (''C. aegagrus'') of Southwest Asia and Eastern Europe. The goat is a member of the ...

s, infection with ''E. schneideri'' leads to elaeophorosis. Symptoms of elaeophorosis include necrosis of the muzzle, ears, and optic nerves; lack of coordination (

ataxia Ataxia (from Greek α- negative prefix+ -τάξις rder= "lack of order") is a neurological sign consisting of lack of voluntary coordination of muscle movements that can include gait abnormality, speech changes, and abnormalities in e ...

); facial or lower limb

dermatitis Dermatitis is a term used for different types of skin inflammation, typically characterized by itchiness, redness and a rash. In cases of short duration, there may be small blisters, while in long-term cases the skin may become thickened ...

; horn deformities; blindness; and death.

Discovery

Symptoms of elaeophorosis were first observed in 1933, in sheep (New Mexico) and mule deer (Utah) infested by an unknown nematode worm. Specimens were first described as ''Macdonaldius'' sp. in 1934, and later revised to ''Elaeophora schneideri'' Wehr and Dikmans, 1935. A more complete description of adults from elk, sheep and deer was published in 1968.

Description

The female adults are 60–120 mm long and 56-89 μm wide, while males are 55–85 mm long and 40-68 μm wide. The

microfilaria The microfilaria (plural microfilariae, sometimes abbreviated mf) is an early stage in the life cycle of certain parasitic nematodes in the family Onchocercidae. In these species, the adults live in a tissue or the circulatory system of vertebr ...

e are 239-279 μm long and 11-15 μm wide.

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 The white-tailed deer (''Odocoileus virginianus''), also known Common name, commonly as the whitetail and the Virginia deer, is a medium-sized species of deer native to North America, North, Central America, Central and South America. It is the ...

, elk, moose,

bighorn sheep The bighorn sheep (''Ovis canadensis'') is a species of Ovis, sheep native to North America. It is named for its large Horn (anatomy), horns. A pair of horns may weigh up to ; the sheep typically weigh up to . Recent genetic testing indicates th ...

Barbary sheep The Barbary sheep (''Ammotragus lervia''), also known as aoudad (pronounced �ɑʊdæd, is a species of caprine native to rocky mountains in North Africa and parts of West Africa. While this is the only species in genus ''Ammotragus'', six sub ...

domestic sheep Sheep (: sheep) or domestic sheep (''Ovis aries'') are a domesticated, ruminant mammal typically kept as livestock. Although the term ''sheep'' can apply to other species in the genus '' Ovis'', in everyday usage it almost always refers to ...

. Infestation was also found in

sika deer The sika deer (''Cervus nippon''), also known as the northern spotted deer or the Japanese deer, is a species of deer native to much of East Asia and introduced to other parts of the world. Previously found from northern Vietnam in the south t ...

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 Horse flies and deer flies are true flies in the family Tabanidae in the insect order Diptera. The adults are often large and agile in flight. Only females bite land vertebrates, including humans, to obtain blood. They prefer to fly in sunli ...

, genera ''

Hybomitra ''Hybomitra'' is a genus of horse flies in the family Tabanidae Horse flies and deer flies are true flies in the family Tabanidae in the insect order Diptera. The adults are often large and agile in flight. Only females bite land vertebrat ...

'', '' Tabanus'', or Silvius.Pence, D.B. (1991) Elaeophorosis in wild ruminants. ''Bulletin of the Society for Vector Ecology'' 16(1):149-160. Life cycle. In the normal definitive host, ''E. schneideri''

e are found in the host's skin, particularly around the forehead and

poll Poll, polled, or polling may refer to: Forms of voting and counting * Poll, a formal election ** Election verification exit poll, a survey taken to verify election counts ** Polling, voting to make decisions or determine opinions ** Polling pla ...

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 Carotid artery may refer to: * Common carotid artery, often "carotids" or "carotid", an artery on each side of the neck which divides into the external carotid artery and internal carotid artery * External carotid artery, an artery on each side of ...

. 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.Hibler, C.P. and C.J. Metzger (1974
Morphology of the larval stages of ''Elaeophora schneideri'' in the intermediate and definitive hosts with some observations on their pathogenesis in abnormal definitive hosts
''Journal of Wildlife Diseases'' 10(4):361-369. 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

Distribution

In the United States, ''E. schneideri'' has been reported from various wild hosts in 19 states: Arizona, Arkansas, California, Colorado, Florida, Georgia, Louisiana, Missouri, Montana, Nebraska, New Mexico, North Dakota (in imported animals), Oklahoma, South Carolina, South Dakota, Texas, Utah, Washington and Wyoming.Pessier, A.P., V.T. Hamilton, W.J. Foreyt, S. Parish, and T.L. McElwain (1998
Probable elaeophorosis in a moose (''Alces alces'') from eastern Washington state
''Journal of Veterinary Diagnostic Investigation'' 10(1):82-84. It has also been reported from elk and black-tailed deer in Canada. Species of '' Elaeophora'' other than ''E. schneideri'' infest various mammals in Europe, Asia and Africa. One survey of Red Deer (''Cervus e. elaphus''), Fallow deer (''Dama dama''), as well as domestic sheep, cattle and goats in Czechoslovakia yielded no specimens of ''E. schneideri''.

Prevalence

Field surveys of wild mammal populations have shown wide variation in the percentage of animals infested with ''E. schneideri''. Surveys of all hosts in the southeastern United States generally indicate infection rates in the range of 2-15%. Prevalence rates as high as 50% in mule deer near Durango, Colorado; 78% in black tailed deer herd in Mendocino County, California, 90% in mule deer herds at high elevation sites in Arizona and New Mexico, and 100% (14 of 14 animals) in Texas mule deer have been reported. In areas of high abundance in definitive hosts, the fear of spread to commercial livestock is greatest.

Clinical signs

Symptoms of ''Elaeophora schneideri'' infestation vary among the different mammalian hosts. In the normal definitive hosts, mule deer and black-tailed deer, infestations are asymptomatic. In the white-tailed deer, infestation is also often asymptomatic. However, blockage and thickening of coronary, cephalic, brachial and femoral arteries and sublingual food impaction have been reported in this host. In both moose and elk, infestation can lead to fatality. Blockage of the carotid and other arteries of the head and face region by ''E. schneideri'' adults restricts local bloodflow, leading to

ischemic Ischemia or ischaemia is a restriction in blood supply to any tissue, muscle group, or organ of the body, causing a shortage of oxygen that is needed for cellular metabolism (to keep tissue alive). Ischemia is generally caused by problems ...

damage to the brain, optic nerve, ears, muzzle and other facial areas. The results are often blindness; walking in circles or poor coordination (

);

gangrene Gangrene is a type of tissue death caused by a lack of blood supply. Symptoms may include a change in skin color to red or black, numbness, swelling, pain, skin breakdown, and coolness. The feet and hands are most commonly affected. If the ga ...

of the ears, muzzle or nostrils; abnormal antler growth; or death. In the domestic sheep, Barbary sheep, bighorn sheep, goats, and sika deer, symptoms are typically dermatological, resulting from inflammatory responses to the microfilariae which accumulate under the skin of the face and ears. The resulting lesions have been described by various authors as "dermal encrustations", "tumorous masses", "raw, bloody dermatitis", or "crusty, scabby lesions" of the head and face.

Alopecia Hair loss, also known as alopecia or baldness, refers to a loss of hair from part of the head or body. Typically at least the head is involved. The severity of hair loss can vary from a small area to the entire body. Inflammation or scarring ...

blepharitis Blepharitis, sometimes known as granulated eyelids, is one of the most common ocular conditions characterized by inflammation, scaling, reddening, and crusting of the eyelid. This condition may also cause swelling, burning, itching, or a grainy ...

, and secondary

conjunctivitis Conjunctivitis, also known as pink eye or Madras eye, is inflammation of the conjunctiva, the thin, clear layer that covers the white surface of the eye and the inner eyelid. It makes the eye appear pink or reddish. Pain, burning, scratchiness ...

have also been observed in sheep. Arterial occulsion may also occur in sheep, but to a lesser degree than in moose and elk.

Diagnosis and treatment

Diagnosis involves recovering either adult worms from the arteries after the death of the infested host, or microcercariae from the skin of the face or head. Treatments have been reported for sheep. A combination of tartar emetic (

antimony potassium tartrate Antimony potassium tartrate, also known as potassium antimonyl tartrate, potassium antimontarterate, or tartar emetic, has the formula K2Sb2(C4H2O6)2. The compound has long been known as a powerful emetic, and was used in the treatment of schistoso ...

) and

emetine Emetine is a drug used as both an anti-protozoal and to induce vomiting. It is produced from the ipecac root. It takes its name from its emetic properties. Early preparations Mechanism of action of emetine was studied by François Magendie duri ...

hydrochloride healed the skin lesions. For elimination of the nematodes, fuadin (stibophen), diethylcarbamazine and piperazine hexahydrate have been suggested.Kemper, H.E. (1957) Filarial dermatosis of sheep. ''Journal of the American Veterinary Medical Association'' 130(5):220-224. However, repeated administration of diethylcarbamazine runs the risk of fatality due to accumulation of dead worms in the arteries.

References

{{Taxonbar, from=Q5353126 Spirurida Parasitic nematodes of mammals Ruminant diseases Veterinary helminthology Insect-borne diseases Nematodes described in 1935 Invertebrates of North America