Disease: Haemonchosis (verminosis)

This page provides general information about this condition; reveal the text by clicking on the green headers. Press releases, results from DWHC investigations as well as other useful documents and relevant literature can be found at the bottom of the page.


Haemonchosis refers to both the acute and chronic form of the disease of ruminants caused by infection with the parasitic worm Haemonchus contortus. This member of the nematode phylum of parasites has a direct life cycle meaning that it requires only one host animal in which adult worms live in the abomasum (4th stomach of ruminants or the 3rd stomach, C3, of camelids) and produce eggs which are shed in the feces and undergo development to infectious larval stages on the ground when conditions are suitable (i.e. warm and wet).

Adult worms are around 1-3 cm in length (males are shorted than females) and their fine thread-like bodies can be seen intermixed with the stomach contents with the naked eye. The blood-sucking female worms are distinctive looking as the white ovaries and uterus are wrapped around the red, blood-filled intestines creating a twisted red and white striped appearance (this is the origin of the alternative name, the barber’s pole worm).

Susceptible species

All ruminant and camelid species, both wild and domesticated are susceptible to infection with H. contortus. Young animals, with no resistance may develop severe disease when the worm burden is heavy for example in densely grazed areas. In domestic species, infection is typically controlled by regular worming treatments, however, when weather conditions permit and in the case of resistance to the drugs, disease in farmed sheep, deer, cattle can be seen.

In Europe, haemonchosis is an occasional cause of disease in a range of wildlife species including Ibex, roe deer, European bison.


Lavin S et al. Haemonchosis in Spanish Ibex. Journal of wildlife diseases 33(3):656-9.
Ferté H., Cléva D., Depaquit J., Gobert S., Léger N. Status and origin of Haemonchinae (Nematoda: Trichostrongylidae) in deer: a survey conducted in France from 1985 to 1998. Parasitol. Res.2000;86:582–587.
Karbowiak G, Demiaszkiewicz AW, Pyziel AM, Wita I, Moskwa B, Werszko J, Bień J, Goździk K, Lachowicz J, Cabaj W. The parasitic fauna of the European bison (Bison bonasus) (Linnaeus, 1758) and their impact on the conservation. Acta Parasitol. 2014 Sep;59(3):363-71.

Signs in animals

The clinical signs are largely due to the blood-sucking nature of these worms with heavy infections resulting in anemia and oedema (fluid build-up in tissues due to loss of protein in the blood). In addition, the damage to the wall of the stomach caused by hundreds or thousands of adult worms can lead to weight loss and in some cases diarrhoea. The duration of disease depends largely on the health status of the host and the infection pressure (number of infectious larvae); animals that ingest large numbers may die suddenly or become acutely ill; ingestion of fewer infectious larvae may result in chronic disease characterized by gradual loss of condition.

Depending on the time of year at which infectious larvae are ingested, the classic signs of acute haemonchosis can be seen in heavily infected animals in the late summer-autumn or in spring. The timing of the clinical signs reflects the life cycle of the worm which is optimally timed to ensure that adults lay eggs during the spring-summer when outside conditions are suitable for hatching and development. Infectious larvae ingested in early summer develop into adult worms causing disease in their host within a few weeks; infectious larvae ingested at the end of summer can undergo a period of latency (waiting) in the stomach wall during the winter months, re-emerging in the spring time to cause disaese.

Infection of animals

Animals become infected by ingestion of infectious larval stages from grassland. Infection is most likely in areas of high stocking density i.e. where sheep or deer are intensively farmed, and at certain times of year i.e. spring-summer when animals are grazing outside and conditions (temperature and humidity) are favorable to egg hatching and larval development.

Geographical distribution

The distribution of this parasite is determined by the requirement for wet and warm conditions for the development of infectious larvae in the environment. Haemonchus contortus is found in tropical, sub-tropical and temperate regions such as Europe. However, with increasing temperatures and rainfall associated with global warming, changes in the spatio-temporal occurrence of this worm are predicted.

Rosa H et al. Exploiting parallels between livestock and wildlife: Predicting the impact of climate change on gastrointestinal nematodes in ruminants. (2014) 3: 2; 209–219

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