| Haemonchus contortus | |
|---|---|
| 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 |
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Haemonchus contortus, also known as red stomach worm, wire worm or Barber's pole worm, is very common parasite and one the most pathogenic nematode 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 animal via the faeces. 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.
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The oocyte is yellowish in color. The egg is approximately 70–85 μm long by 44 μm wide, and the early stages of cleavage containing between 16–32 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 due to the fact the Haemonchus contortus is a blood feeder and is due to the white ovaries that coil around the intestines which 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.
The adult female worm can release between 5,000 – 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 L-2 juvenile stages by feeding on bacteria in the dung. The L-1 stage usually occurs within 4–6 days under the optimal conditions of 24–29 °C. The L-2 rhabditform sheds its cuticle and then develops into the L-3 filiariform infective larvae. The L-3 have a protective cuticle, however under dry hot conditions will not survive long. The L-3 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 L-3 sheds its cuticle and burrows into the internal layer of the abomasum where they develop into L-4, usually within 48 hours, or pre-adult larvae. The L-4 larvae then molts and develops into the L-5 adult form. The male and female adults mate and live in the abomasum, where they feed upon the blood.
It is said that 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 Centre in Booneville, Arkansas claimed that 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]
The nematode piercing the abomasum causes a number of significant complications in the infected ruminants that can lead to death. The infected animals can display severe dehydration, diarrhea, unthrifty appearance, lethargy, depressed low energy behavior, rough hair coat 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/low PCV are common complications of the infection.