Haemonchus contortus

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Haemonchus contortus
Haemonchus contortus.jpg
Haemonchus contortus egg
Scientific classification
Kingdom: Animalia
Phylum: Nematoda
Class: Secernentea
Subclass: Rhabditia
Order: Strongylida
Family: Trichostrongylidae
Genus: Haemonchus
Species: H. contortus
Binomial name
Haemonchus contortus
(Rudolphi, 1803) Cobb, 1898

Haemonchus contortus, also known as red stomach worm, wire worm or barber's pole worm, is very common parasite and one of the most pathogenic nematodes of ruminants. Adult worms are attached to abomasal mucosa and feed on the blood. This parasite is responsible for anemia, bottle jaw, and death of infected sheep and goats, mainly during summer months in warm, humid climates.[1]

Females may lay over 10,000 eggs a day,[2] which are secreted from the host animal via the feces. After hatching from their eggs, H. contortus larvae molt several times, resulting in an L3 form that is infectious for the animals. They can take up these larvae when eating grass leaves. The L4 larvae, formed after another molt, suck blood in the abomasum of the animal, potentially giving rise to anaemia and oedema, which eventually can lead to death.[3]

The infection, called haemonchosis, causes large economic losses for farmers around the world, especially for those living in the warmer climates. Antihelminthics are used to combat these, and other, worm infections for a long time, but resistance of the parasites against these chemicals is growing.

Morphology[edit]

The oocyte is yellowish in color. The egg is approximately 70–85 μm long by 44 μm wide, and the early stages of cleavage contain between 16 and 32 cells. The adult female is 18–30 mm long and is easily recognized by its trademark "barber pole" coloration. The red and white appearance is because H. contortus is a blood feeder, and the white ovaries that coil around the intestines are filled with blood. The male adult worm is much smaller at 10–20 mm long, and displays the distinct feature of a well-developed copulatory bursa, containing an asymmetrical dorsal lobe and a Y-shaped dorsal ray.

Life cycle[edit]

The adult female worm can release between 5,000 and 10,000 eggs, which will be passed out in the feces. Eggs then develop in moist conditions in the feces and continue to develop into the L1 (rhabditiform), and L2 juvenile stages by feeding on bacteria in the dung. The L1 stage usually occurs within four to six days under the optimal conditions of 24–29 °C. The L2 rhabditform sheds its cuticle and then develops into the L3 filiariform infective larvae. The L3 form has a protective cuticle, but under dry, hot conditions will not survive long. The L3s then crawl up the blades of wet grass and wait to be ingested by a grazing animal. Sheep, goats and other ruminants become infected when they graze and eat grasses containing the L3 infecting larvae. The infecting larvae pass through the first three stomachs to reach the abomasum. There, the L3s shed their cuticles and burrow into the internal layer of the abomasum, where they develop into L4s, usually within 48 hours, or preadult larvae. The L4 larvae then molt and develop into the L5 adult form. The male and female adults mate and live in the abomasum, where they feed on blood.

Prevention[edit]

A common type of clover may be a preventative or palliative for the disease.[4] Joan Burke, a scientist at the ARS Dale Bumpers Small Farms Research Center in Booneville, Arkansas claimed they have patented formulations of food containing Sericea lespedeza, commonly referred to as Chinese bush clover, which will ameliorate the effects of the worms on sheep.[5] Some particular breeds of sheep, such as the Gulf Coast Native from the Southern United States, have been shown to have developed special resistance to H. contortus.[6][7] Targeted selective treatment methods such as the FAMACHA method can also be valuable in reducing the number of dosing intervals, selecting for more wireworm resistant sheep and increasing the percentage of parasites on pasture that is still susceptible to anthelmintics.

Pathogenicity[edit]

The nematodes piercing the abomasum cause a number of significant complications in the infected ruminants that can lead to death. They can display severe dehydration, diarrhea, unthrifty appearance, lethargy, depressed low-energy behavior, rough hair coats and uncoordinated movements. Furthermore, significantly reduced growth and poor reproductive performance has been observed. The accumulation of fluid in the abdomen, gut wall, thoracic cavity and submandibular tissue – a phenomenon commonly called "bottle jaw”, also is a common association with this infection. Severe blood loss, white mucous membranes, and anemia or low packed cell volumes are common complications of the infection.

References[edit]

Footnotes[edit]

Other sources[edit]

  1. Newton, S. 1995. Progress on vaccination of Haemonchus contortus. International Journal of Parasitology, 25: 1281–1289.
  2. Roberts, L., J. Janovy. 2000. Foundations of Parasitology. US: The McGraw Hill Companies, Inc..
  3. Fetterer, R., M. Rhoads. 1996. The role of the sheath in resistance of Haemonchus contortus infective stage larvae to proteolytic digestion. Veterinary Parasitology, 64: 267–276.
  4. Dorny, P., A. Batubara, M. Iskander, V. Pandey. 1996. Helminth infections of sheep in North Sumatra, Indonesia. Veterinary Parasitology, 61: 353–358.