''Habronema muscae'' is an internal

stomach The stomach is a muscular, hollow organ in the gastrointestinal tract of humans and many other animals, including several invertebrates. The stomach has a dilated structure and functions as a vital organ in the digestive system. The stomach i ...

parasite Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson has ...

that is most commonly found in

horse The horse (''Equus ferus caballus'') is a domesticated, one-toed, hoofed mammal. It belongs to the taxonomic family Equidae and is one of two extant subspecies of ''Equus ferus''. The horse has evolved over the past 45 to 55 million y ...

s. It is the most common cause of cutaneous ulcerative granulomas in the horse. It is in genus '' Habronema''.

Life cycle

Eggs

The

parasitic Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson has c ...

adult female worms lay

eggs Humans and human ancestors have scavenged and eaten animal eggs for millions of years. Humans in Southeast Asia had domesticated chickens and harvested their eggs for food by 1,500 BCE. The most widely consumed eggs are those of fowl, especial ...

within the horse's stomach. The eggs are later excreted through the

feces Feces ( or faeces), known colloquially and in slang as poo and poop, are the solid or semi-solid remains of food that was not digested in the small intestine, and has been broken down by bacteria in the large intestine. Feces contain a relati ...

. The eggs hatch out within the feces producing first stage larvae.

Larvae

After the eggs have hatched in the feces, the

larva A larva (; plural larvae ) is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle. The ...

e are ingested by the

maggot A maggot is the larva of a fly (order Diptera); it is applied in particular to the larvae of Brachycera flies, such as houseflies, cheese flies, and blowflies, rather than larvae of the Nematocera, such as mosquitoes and crane flies. ...

s of various

flies Flies are insects of the order Diptera, the name being derived from the Greek δι- ''di-'' "two", and πτερόν ''pteron'' "wing". Insects of this order use only a single pair of wings to fly, the hindwings having evolved into advanced ...

that lay their eggs in the feces (such as ''

Stomoxys ''Stomoxys'' is a genus of Fly, flies in the family (biology), family Muscidae. The genus is unusual among the Muscidae in that it includes species that are bloodsucking Parasitism, ectoparasites of mammals. The best-known species is ''stable fly ...

'' (the stable fly) or ''

Musca Musca () is a small constellation in the deep southern sky. It was one of 12 constellations created by Petrus Plancius from the observations of Pieter Dirkszoon Keyser and Frederick de Houtman, and it first appeared on a celestial globe in dia ...

'' (the house fly). The nematode larvae develop within the maggot for about one week (depending upon ambient temperature), as the maggots mature into the imago (adult)

fly Flies are insects of the Order (biology), order Diptera, the name being derived from the Ancient Greek, Greek δι- ''di-'' "two", and πτερόν ''pteron'' "wing". Insects of this order use only a single pair of wings to fly, the hindwing ...

. The infective larvae (L3 larval stage) migrate to the mouthparts of the fly, where they are passed on to the horse when they feed around the horse's moist areas such as

wound A wound is a rapid onset of injury that involves laceration, lacerated or puncture wound, punctured skin (an ''open'' wound), or a bruise, contusion (a ''closed'' wound) from blunt force physical trauma, trauma or compression. In pathology, a '' ...

nostril A nostril (or naris , plural ''nares'' ) is either of the two orifices of the nose. They enable the entry and exit of air and other gasses through the nasal cavities. In birds and mammals, they contain branched bones or cartilages called turbi ...

s, lips, and eyes. If the larvae are deposited into open wounds, or broken skin they can cause intense granulomatous reactions, producing an

ulcerated An ulcer is a discontinuity or break in a bodily membrane that impedes normal function of the affected organ. According to Robbins's pathology, "ulcer is the breach of the continuity of skin, epithelium or mucous membrane caused by sloughing o ...

irritation called Habronemiasis, or more commonly, " summer sores". They may also invade the eye and the eye membrane causing a persistent

conjunctivitis Conjunctivitis, also known as pink eye, is inflammation of the conjunctiva, outermost layer of the white part of the eye and the inner surface of the eyelid. It makes the eye appear pink or reddish. Pain, burning, scratchiness, or itchiness may ...

. If the larvae find their way up through the nose they can migrate into the

lung The lungs are the primary organs of the respiratory system in humans and most other animals, including some snails and a small number of fish. In mammals and most other vertebrates, two lungs are located near the backbone on either side of t ...

s and cause tiny

abscesses An abscess is a collection of pus that has built up within the tissue of the body. Signs and symptoms of abscesses include redness, pain, warmth, and swelling. The swelling may feel fluid-filled when pressed. The area of redness often extends b ...

around where they embed in the lung tissue.

Adults

When the larvae are licked and swallowed by the horse during grooming they travel to the stomach and embed themselves into the glandular part of the stomach close to the margo plicatus. A thick mucus is excreted by the stomach lining. The larvae mature into adults and females produce eggs to complete the life cycle. Larvae that invade skin or eye tissue do not develop into adults. Morphology: Adult has two lateral lips, dorsal and ventral lips may also be present. Buccal capsule cylindrical, chitinous. Oesophagous is divided into two parts, a short anterior muscular and long posterior glandular portion, intestine simple without any diverticula. Male:

spicules Spicules are any of various small needle-like anatomical structures occurring in organisms Spicule may also refer to: *Spicule (sponge), small skeletal elements of sea sponges *Spicule (nematode), reproductive structures found in male nematodes ( ...

unequal,

gubernaculum The paired gubernacula (from Ancient Greek κυβερνάω = pilot, steer) also called the caudal genital ligament, are embryonic structures which begin as undifferentiated mesenchyme attaching to the caudal end of the gonads (testes in male ...

present and bears 4 pairs of preanal, 1 pair adanal and 2 pairs of postanal pedunculated papillae, 3 pairs of sessile papillae also present, tail spirally twisted.A colour Atlas of Equine Parasites D.E. Jacobs 1986 Balliere Tindall London

Treatment

For most horses, the lesions will resolve by the end of summer. Topical or systemic treatment with

Ivermectin Ivermectin (, '' EYE-vər-MEK-tin'') is an antiparasitic drug. After its discovery in 1975, its first uses were in veterinary medicine to prevent and treat heartworm and acariasis. Approved for human use in 1987, today it is used to treat inf ...

is effective against Habronemiasis. Ivermectin or moxidectin can eliminate nematodes in the stomach. Glucocorticoids or antihistamines may be necessary to control inflammation, tissue proliferation, hypersensitivity, or pruritus. Surgical excision may be required to remove large masses.

Prevention

Prevention is primarily through regular deworming of the horse and good fly control systems, especially removal of manure. Environmental sprays and clean bedding also help.

References

{{Taxonbar, from=Q10515439 Spirurida Parasitic nematodes of mammals Parasites of equines Veterinary helminthology