''Haemonchus contortus'', also known as the

barber's pole A barber's pole is a type of sign used by barbers to signify the place or shop where they perform their craft. The trade sign is, by a tradition dating back to the Middle Ages, a staff or pole with a helix of colored stripes (often red and whi ...

worm, is a very common parasite and one of the most pathogenic

nematode The nematodes ( or grc-gre, Νηματώδη; la, Nematoda) or roundworms constitute the phylum Nematoda (also called Nemathelminthes), with plant-Parasitism, parasitic nematodes also known as eelworms. They are a diverse animal phylum inhab ...

s of

ruminant Ruminants (suborder Ruminantia) are ungulate, hoofed herbivorous grazing or browsing mammals that are able to acquire nutrients from plant-based food by Enteric fermentation, fermenting it in a specialized stomach prior to digestion, principally ...

s. Adult worms attach to abomasal mucosa and feed on the blood. This parasite is responsible for

anemia Anemia or anaemia (British English) is a blood disorder in which the blood has a reduced ability to carry oxygen due to a lower than normal number of red blood cells, or a reduction in the amount of hemoglobin. When anemia comes on slowly, th ...

oedema Edema, also spelled oedema, and also known as fluid retention, dropsy, hydropsy and swelling, is the build-up of fluid in the body's tissue. Most commonly, the legs or arms are affected. Symptoms may include skin which feels tight, the area ma ...

, and death of infected

sheep Sheep or domestic sheep (''Ovis aries'') are domesticated, ruminant mammals 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 domesticated s ...

and

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

, mainly during summer in warm, humid climates. Females may lay over 10,000 eggs a day, which pass from the host animal in the

faeces 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 ...

. After hatching from their eggs, ''H. contortus''

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 ...

molt In biology, moulting (British English), or molting (American English), also known as sloughing, shedding, or in many invertebrates, ecdysis, is the manner in which an animal routinely casts off a part of its body (often, but not always, an outer ...

several times, resulting in an L3 form that is

infectious An infection is the invasion of tissues by pathogens, their multiplication, and the reaction of host tissues to the infectious agent and the toxins they produce. An infectious disease, also known as a transmissible disease or communicable dise ...

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. The infection, called haemonchosis, causes large economic losses for farmers around the world, especially for those living in warmer climates.

Anthelminthics Anthelmintics or antihelminthics are a group of antiparasitic drugs that expel parasitic worms (helminths) and other internal parasites from the body by either stunning or killing them and without causing significant damage to the host. They may ...

are used to prevent and treat these, and other, worm infections, but resistance of the

parasites Parasitism is a Symbiosis, close relationship between species, where one organism, the parasite, lives on or inside another organism, the Host (biology), host, causing it some harm, and is Adaptation, adapted structurally to this way of lif ...

against these

chemicals A chemical substance is a form of matter having constant chemical composition and characteristic properties. Some references add that chemical substance cannot be separated into its constituent elements by physical separation methods, i.e., wit ...

is growing. Some breeds, such as the West African Dwarf goat and N'Dama cattle, are more resistant than other breeds to ''H. contortus'' (haemonchotolerance).

Morphology

The ova is yellowish in color. The egg is about 70–85 μm long by 44 μm wide, and the early stages of cleavage contain between 16 and 32 cells. The adult female is 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 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 faeces. Eggs then develop in moist conditions in the faeces 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 . 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 infective larvae. The infective larvae pass through the first three stomach chambers 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. Further work to complete the reference genome is underway at the

Wellcome Trust Sanger Institute The Wellcome Sanger Institute, previously known as The Sanger Centre and Wellcome Trust Sanger Institute, is a non-profit British genomics and genetics research institute, primarily funded by the Wellcome Trust. It is located on the Wellcome G ...

in collaboration with the University of Calgary, the University of Glasgow, and the

Moredun Research Institute The Moredun Research Institute is a scientific research institution based at the Pentlands Science Park, in the Bush Estate area of Midlothian, Scotland. It conducts research into diseases of farm livestock and the promotion of animal health and ...

. 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

vaccine A vaccine is a biological Dosage form, preparation that provides active acquired immunity to a particular infectious disease, infectious or cancer, malignant disease. The safety and effectiveness of vaccines has been widely studied and verifie ...

s 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, while 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. A commercial vaccine known as Barbervax in Australia or Wirevax in South Africa has become available in recent years. This works mainly by reducing egg output and hence pasture contamination. The vaccine contains proteins from the lining of the intestines of the Barber's Pole worm. The animal produces antibodies against the protein which circulate in the blood. When the Barber's pole worm drinks the blood the antibodies attach to its stomach lining, preventing digestion and starving the animal. Following this, the worm produces fewer eggs and eventually dies off. Targeted selective treatment methods such as the FAMACHA method may be valuable in reducing the number of dosing intervals, thus reducing the percentage of surviving parasites that are resistant to anthelmintics. Faecal 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 In agriculture, rotational grazing, as opposed to Grazing#Continuous, continuous grazing, describes many systems of pasturing, whereby livestock are moved to portions of the pasture, called Paddock (field), paddocks, while the other portions rest. ...

, especially during peak parasite season; and "cleaning" infested pastures by haying, tilling, or grazing with a nonsusceptible species (e.g. swine or poultry). Recent research has also shown that the use of hair sheep breeds, such as Katahdins, Dorpers, and St. Croix, can be chosen for resistance to internal parasites for economical standards; additionally, the hair breeds provide resistance without showing any significant effect growth performance of their progeny. One of the riskiest methods that can be used for treatments is the use of copper oxide wire particles (COWP) to aid in the destruction of the parasites inside the gut without the use of chemicals. However, in sheep, the dosing would need to be monitored extremely closely because if they are administered too high of a dose, then they will slip into copper toxicity. For the COWP, the lowest recommended dose would need to be administered to remain safe for sheep. The study conducted found that treatment with the COWP reduced faecal egg counts by >85%. Treatment with the copper oxide wire particles could lead to less reliance on anthelmintics because the COWP allows for the reduction in establishment of parasitic infections, especially if the producer is trying to reduce the larval population on their pastures. Recent research shows fugal lectins are able to inhibit larval development. These fungal lectins are Corprinopsis cinerea lectins - CCL2, CGL2; Aleuria aurantia lectin - AAL; and Marasmius oreades agglutinin - MOA. These four toxic lectins bind to specific glycan structures found in ''H. controtus''. Some of these glycan structures might represent antigens which are not exposed to host immune system, and thus have potential for vaccine or drug development.

Morphology

Life cycle

Genetics

Pathogenicity

Prevention and treatment

References

Further reading