Haemonchus contortus

Haemonchus contortus
The tail ends of 11 Haemonchus contortus adult females. The worms were all taken from one sheep infected with a single strain of this worm species.
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 the barber's pole worm, is very common parasite and one of the most pathogenic nematodes of ruminants. Adult worms attach to abomasal mucosa and feed on the blood. This parasite is responsible for anemia, oedema, 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 pass from the host animal in the faeces. After hatching from their eggs, H. contortus larvae molt several times, resulting in an L3 form that is infectious for the animals. The host ingests these larvae when grazing. The L4 larvae, formed after another molt, and adult worms 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 warmer climates. Anthelminthics are used to prevent and treat these, and other, worm infections, but resistance of the parasites against these chemicals is growing. Some breeds, such as the West African Dwarf goat, are more resistant than other breeds of domestic goat to H. contortus (haemonchotolerance).^[4]

Morphology

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 can be seen coiled around the blood-filled intestine. 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

The adult female worm can release between 5,000 and 10,000 eggs, which are 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 survival is reduced. Sheep, goats and other ruminants become infected when they graze and ingest the L3 infecting larvae. The infecting larvae pass through the first three stomachs to reach the abomasum. There, the L3 shed their cuticles and burrow into the internal layer of the abomasum, where they develop into L4, 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.

Genetics

The H. contortus draft genome was published in 2013 .^[5] Further work to complete the reference genome is underway at the Wellcome Trust Sanger Institute ^[6] in collaboration with The University of Calgary, The University of Glasgow and the Moredun Research Institute. Developing genetic and genomic resources for this parasite will facilitate the identification of the genetic changes conferring anthelmintic resistance and may help design new drugs or vaccines to combat disease and improve animal health.

Pathogenicity

Clinical signs are largely due to blood loss. Sudden death may be the only observation in acute infection, other common clinical signs include pallor, anemia, oedema, ill thrift, lethargy and depression. The accumulation of fluid in the submandibular tissue, a phenomenon commonly called "bottle jaw”, may be seen. Growth and production are significantly reduced.

Prevention and Treatment

Prophylactic anthelmintic treatment necessary to prevent infection in endemic regions, but wherever possible, a reduction on reliance on chemical treatment is warranted given the rapid rise of anthelmintic resistance. Targeted selective treatment methods such as the FAMACHA method may be valuable in reducing the number of dosing intervals and thus reducing the percentage of surviving parasites that are resistant to anthelmintics. Fecal egg counts are used to track parasite infestation levels, individual animals' susceptibility, and anthelmintic effectiveness. Other management strategies include selective breeding for more parasite-resistant sheep or goats (e.g. by culling the most susceptible animals or by introducing parasite-resistant breeds such as Gulf Coast Native sheep); careful pasture management, such as managed intensive rotational grazing, especially during peak parasite season; and "cleaning" infested pastures by haying, tilling, or grazing with a non-susceptible species (e.g. swine or poultry).^[7]

References

Footnotes

1. Burke, Joan, Research Animal Scientist. Management of Barber pole Worm in Sheep and Goats in the Southern U.S. USDA, ARS, Dale Bumpers Small Farms Research Center, Booneville, AR.>
2. Barber's pole worm (Haemonchus contortus) at Australian Wool Limited.
3. "Haemonchus, Ostertagia, and Trichostrongylus spp". The Merck Veterinary Manual. 2006. Retrieved 2007-07-01.
4. Chiejina, Samuel N.; Behnke, Jerzy M.; Fakae, Barineme B. (2015). "Haemonchotolerance in West African Dwarf goats: contribution to sustainable, anthelmintics-free helminth control in traditionally managed Nigerian dwarf goats". Parasite 22: 7. doi:10.1051/parasite/2015006. ISSN 1776-1042.
5. Laing, Roz; Taisei Kikuchi, Axel Martinelli, Isheng J. Tsai, Robin N. Beech, Elizabeth Redman, Nancy Holroyd, David J. Bartley, Helen Beasley, Collette Britton, David Curran, Eileen Devaney, Aude Gilabert, Martin Hunt, Frank Jackson, Stephanie L. Johnston, Ivan Kryukov, Keyu Li, Alison A. Morrison, Adam J. Reid, Neil Sargison, Gary I. Saunders, James D. Wasmuth, Adrian Wolstenholme, Matthew Berriman, John S. Gilleard, James A. Cotton (2013-08-28). "The genome and transcriptome of Haemonchus contortus, a key model parasite for drug and vaccine discovery". Genome Biology 14 (8): R88. doi:10.1186/gb-2013-14-8-r88. ISSN 1465-6906. PMC 4054779. PMID 23985316. Retrieved 2014-11-25. Cite uses deprecated parameter |coauthors= (help)
6. https://www.sanger.ac.uk/resources/downloads/helminths/haemonchus-contortus.html
7. Anderson, Samuel. "Summary of Results: New England Small Ruminant Producer Survey." Northeast IPM Center, 2013. http://www.northeastipm.org/neipm/assets/File/New-England-Small-Ruminant-Survey-Results-2013.pdf

Other sources

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.