Haemonchus contortus | |
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These 11 Haemonchus contortus adult females were taken from one sheep infected with a single strain of this worm species. | |
Haemonchus contortus egg | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Nematoda |
Class: | Chromadorea |
Order: | Rhabditida |
Family: | Trichostrongylidae |
Genus: | Haemonchus |
Species: | H. contortus |
Binomial name | |
Haemonchus contortus (Rudolphi, 1803) Cobb, 1898 | |
Synonyms | |
Haemonchus placeiPlace, 1893 [1] (closely related species) Contents |
Haemonchus contortus, also known as the barber's pole worm, is a 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 in warm, humid climates. [2]
Females may lay over 10,000 eggs a day, [3] 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. [4]
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 and N'Dama cattle, are more resistant than other breeds to H. contortus (haemonchotolerance). [5]
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 18–30 millimetres (3⁄4–1+1⁄8 in) 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 millimetres (3⁄8–13⁄16 in) 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 and 10,000 eggs, which are passed out in the faeces. [6] 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 24–29 °C (75–84 °F). 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.
The H. contortus draft genome was published in 2013. [7] Further work to complete the reference genome is underway at the Wellcome Trust Sanger Institute [8] 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.[ citation needed ]
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.
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. [9]
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.[ citation needed ]
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 nonsusceptible species (e.g. swine or poultry). [10]
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. [11]
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 organic 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. [12]
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. [13]
Trichuriasis, also known as whipworm infection, is an infection by the parasitic worm Trichuris trichiura (whipworm). If infection is only with a few worms, there are often no symptoms. In those who are infected with many worms, there may be abdominal pain, fatigue and diarrhea. The diarrhea sometimes contains blood. Infections in children may cause poor intellectual and physical development. Low red blood cell levels may occur due to loss of blood.
Onobrychis viciifolia, also known as O. sativa or common sainfoin was an important forage legume in temperate regions until the 1950s. During the Green Revolution it was replaced by high yielding alfalfa and clover species. Due to its anthelmintic properties, common sainfoin is a natural alternative to drugs to control nematode parasitism in the guts of small ruminants. This is the main reason why O. viciifolia returned to the scientific agenda in recent years.
Hookworm infection is an infection by a type of intestinal parasite known as a hookworm. Initially, itching and a rash may occur at the site of infection. Those only affected by a few worms may show no symptoms. Those infected by many worms may experience abdominal pain, diarrhea, weight loss, and tiredness. The mental and physical development of children may be affected. Anemia may result.
Brugia malayi is a filarial (arthropod-borne) nematode (roundworm), one of the three causative agents of lymphatic filariasis in humans. Lymphatic filariasis, also known as elephantiasis, is a condition characterized by swelling of the lower limbs. The two other filarial causes of lymphatic filariasis are Wuchereria bancrofti and Brugia timori, which both differ from B. malayi morphologically, symptomatically, and in geographical extent.
Moxidectin is an anthelmintic drug used in animals to prevent or control parasitic worms (helminths), such as heartworm and intestinal worms, in dogs, cats, horses, cattle, sheep and wombats. Moxidectin kills some of the most common internal and external parasites by selectively binding to a parasite's glutamate-gated chloride ion channels. These channels are vital to the function of invertebrate nerve and muscle cells; when moxidectin binds to the channels, it disrupts neurotransmission, resulting in paralysis and death of the parasite.
Dictyocaulus is a genus of nematode parasites of the bronchial tree of horses, sheep, goats, deer, and cattle. Dictyocaulus arnfieldi is the lungworm of horses, and Dictyocaulus viviparus is the lungworm affecting ruminants.
Uncinaria stenocephala is a nematode that parasitizes dogs, cats, and foxes as well as humans. It is rare to find in cats in the United States. Uncinaria stenocephala is the most common canine hookworm in cooler regions, such as Canada and the northern regions of the US, where it can be found primarily in foxes (40%). U. stenocephala is also one of the most common hookworms in the UK, called the northern hookworm, however it has a rather low prevalence. U. stenocephala is also considered to be zoonotic hookworms because they live in animals but can be transmitted to humans.
Toxocara canis is a worldwide-distributed helminth parasite that primarily infects dogs and other canids, but can also infect other animals including humans. The name is derived from the Greek word "toxon," meaning bow or quiver, and the Latin word "caro," meaning flesh. T. canis live in the small intestine of the definitive host. This parasite is very common in puppies and somewhat less common in adult dogs. In adult dogs, infection is usually asymptomatic but may be characterized by diarrhea. By contrast, untreated infection with Toxocara canis can be fatal in puppies, causing diarrhea, vomiting, pneumonia, enlarged abdomen, flatulence, poor growth rate, and other complications.
Angiostrongyliasis is an infection by a roundworm of the Angiostrongylus type. Symptoms may vary from none, to mild, to meningitis.
Muelleries capillaris, also known as the hair or goat lungworm, is one of the most economically important nematodes of small ruminants. Although normally non-pathogenic in sheep, the parasite causes a disease condition called muelleriosis in goats. Sheep and goats commonly become infected after accidentally ingesting M. capillaris infected snails or slugs, and the parasite produces eggs in the lungs of its host, causing life-threatening bronchopneumonia in serious cases.
Trichostrongylus species are nematodes, which are ubiquitous among herbivores worldwide, including cattle, sheep, donkeys, goats, deer, and rabbits. At least 10 Trichostrongylus species have been associated with human infections. Infections occur via ingestion of infective larvae from contaminated vegetables or water. Epidemiological studies indicate a worldwide distribution of Trichostrongylus infections in humans, with the highest prevalence rates observed in individuals from regions with poor sanitary conditions, in rural areas, or who are farmers / herders. Human infections are most prevalent in the Middle East and Asia, with a worldwide estimated prevalence of 5.5 million people.
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 also be called vermifuges or vermicides. Anthelmintics are used to treat people who are infected by helminths, a condition called helminthiasis. These drugs are also used to treat infected animals, particularly small ruminants such as goats and sheep.
Oxfendazole is a broad spectrum benzimidazole anthelmintic. Its main use is for protecting livestock against roundworm, strongyles and pinworms. Oxfendazole is the sulfoxide metabolite of fenbendazole.
Ticks of domestic animals directly cause poor health and loss of production to their hosts. Ticks also transmit numerous kinds of viruses, bacteria, and protozoa between domestic animals. These microbes cause diseases which can be severely debilitating or fatal to domestic animals, and may also affect humans. Ticks are especially important to domestic animals in tropical and subtropical countries, where the warm climate enables many species to flourish. Also, the large populations of wild animals in warm countries provide a reservoir of ticks and infective microbes that spread to domestic animals. Farmers of livestock animals use many methods to control ticks, and related treatments are used to reduce infestation of companion animals.
Teladorsagia circumcincta is a nematode that is one of the most important parasites of sheep and goats. It was previously known as Ostertagia circumcincta and is colloquially known as the brown stomach worm. It is common in cool, temperate areas, such as south-eastern and south-western Australia and the United Kingdom. There is considerable variation among lambs and kids in susceptibility to infection. Much of the variation is genetic and influences the immune response. The parasite induces a type I hypersensitivity response which is responsible for the relative protein deficiency which is characteristic of severely infected animals. There are mechanistic mathematical models which can predict the course of infection. There are a variety of ways to control the infection and a combination of control measures is likely to provide the most effective and sustainable control.
FAMACHA is a selective treatment method for controlling the level of parasitic barber's pole worm among domesticated small ruminant populations. In contrast with earlier, more aggressive approaches, under FAMACHA only certain sheep or goats in a flock are selected for treatment. Selection for treatment is based on the degree of anaemia the animals are displaying in their mucous membranes, which is assessed through a colour guided chart.
Taenia hydatigena is one of the adult forms of the canine and feline tapeworm. This infection has a worldwide geographic distribution. Humans with taeniasis can infect other humans or animal intermediate hosts by eggs and gravid proglottids passed in the feces.
Cooperia oncophora is one of the most common intestinal parasitic nematodes in cattle in temperate regions. Infections with C. oncophora may result in mild clinical symptoms, but can lead to weight loss and damage of the small intestine, especially when co-infections with other nematodes such as O. ostertagi occur. Infections are usually treated with broad-spectrum anthelmintics such as benzimidazole, but resistance to these drugs has developed in the last decades and is now very common. C. oncophora has a direct life cycle. Infective larvae are ingested by the host. The larvae grow to adults, which reproduce in the small intestines. Eggs are shed onto the pasture with the faeces, which leads to new infections. Co-infections with other gastro-intestinal nematodes such as O. ostertagi and H. contortus are common.
Ostertagia ostertagi, commonly known as the medium stomach worm or brown stomach worm, is a parasitic nematode of cattle. O. ostertagi can also be found to a lesser extent in sheep, goats, wild ruminants, and horses. It causes ostertagiosis, which is potentially fatal in cattle. It is found worldwide and is economically important to cattle industries, particularly those found in temperate climates.
Gastropod-borne parasitic diseases (GPDs) are a group of infectious diseases that require a gastropod species to serve as an intermediate host for a parasitic organism that can infect humans upon ingesting the parasite or coming into contact with contaminated water sources. These diseases can cause a range of symptoms, from mild discomfort to severe, life-threatening conditions, with them being prevalent in many parts of the world, particularly in developing regions. Preventive measures such as proper sanitation and hygiene practices, avoiding contact with infected gastropods and cooking or boiling food properly can help to reduce the risk of these diseases.