In the next of our 6 part OvaCyte Blog Series, we delve deeper into our Speciation offering, focusing on Haemonchus, and how OvaCyte can support your parasite control programmes!
Haemonchus contortus is a blood sucking roundworm of significance in small ruminants, especially sheep. In fact scientists at the Moredun Research foundation have referred to Haemonchus as the most important roundworm in sheep and goats in the world.
Infection with Haemonchus contortus causes serious economic losses in sheep and goat farming, due to its impact on production and treatment costs. These losses are substantial, with reports estimating annual costs in different regions to be millions.
Haemonchosis:
These abomasal parasites differ from other gastrointestinal nematodes in that the adults and mature larvae feed on blood. The clinical signs of this disease, known as haemonchosis, are associated with resultant blood loss, which is distinct from the diarrhoea we see in other forms of parasitic gastroenteritis.
Haemonchus contortus larval development occurs from eggs deposited on pasture from infected animals. Development occurs at temperatures above 9˚C with optimum development at 25-37˚C and development from egg to larvae can occur in just 3.5 days at temperatures of 30˚C which can result in massive numbers being present on grazed pasture. The larvae need a water film to travel , moving from the faecal pat onto the grass in order to be ingested, and so rainfall following a warm spell creates the potential for the perfect storm of massive larvae development and ingestion on grazed pasture.
After ingestion the larvae can carry on to develop into adult worms or undergo hypobiosis until conditions favour further development. When moderate numbers of larvae are ingested and develop into adults the female worm’s high fecundity coupled with a short larval development period allows rapid population expansion in a herd and on pasture, which can result in sudden subacute and acute clinical disease on farms.
Hypobiosis – a hidden threat hiding in the coffin:
Larvae that undergo hypobiosis after ingestion also have implications for farms. This hypobiotic state allows the larvae to persist in the host’s gut and evade the immune system, particularly when environmental conditions are unfavourable, like during winter or dry periods.
Hypobiosis might also be initiated by a threshold of infection that is regulated by the adult worm population already established in the gastrointestinal tract.
These hypobiotic larvae serve as a reservoir for future infections. Farmers who are not adequately quarantining new stock, performing faecal egg counts and treating bought in stock risk introducing animals that could potentially be harbouring these hypobiotic larvae. This larvae can re-emerge at a later date causing clinical disease in previously unaffected farms.
Clinical signs:
The disease itself presents in three forms, each causing significant and often fatal disease. Which form the disease takes is influenced by worm burden and exposure levels on pasture.
The clinical signs of haemonchosis are caused by the late stage larvae and adult worms. These parasitic stages consume 0.5-1 ml blood /day while attached to the mucosa and this blood loss continues from the damaged muscoa after they detach. The feeding worms also release calreticulin which impairs blood clotting and dampens the immune response to the worms. The larvae also contribute to clinical signs as their development within the gastric glands causes further intestinal wall damage.
Hyperacute haemonchosis can lead to sudden death due to severe frank blood loss and anaemia and haemorrhagic abomasitis caused by an overwhelming infection following exposure to large numbers of larvae on pasture and subsequent simultaneous development of large number of adults within the host.
Acute haemonchosis involves severe anaemia, lethargy, weakness, increased respiratory and heart rate, dark mushy faeces, loss of wool, pale to white conjunctiva, ascites, and sub-mandibular and cervical oedema.
Chronic disease is characterized by anorexia, loss of weight, agalactia, pallor of the conjunctiva and the mucosa, and bottle jaw . In some cases it can be mistaken for liver fluke infestation as clinical signs are similar .
The role of faecal egg counts in control of Haemonchus contortus?
Haemonchus worms, especially H. contortus, are highly prolific, producing a large number of eggs (5,000-15,000 per day) compared to other trichostrongyles, such as Teladorsagia which produce around 400 eggs per day.
The use of faecal egg counts in the detection of Haemonchus has a greater value when compared to that of the other trichostrongyles. This is because of the strong relationship between the number of adult worms and the worm egg output.
This high egg output means that a relatively high faecal egg count (FEC) is often a good indicator of a significant worm burden in Haemonchus infections. Light burdens are indicated by values less than 3000epg ,moderate relate to 2000-20,000 epg and severe burdens are indicated by values >30,000 epg.
However this linear relationship is not always the case when there are mixed strongyle populations contributing to an egg count. The ability to detect and estimate Haemonchus eggs from other strongyle eggs within samples to assess individual worm burdens is crucial.
It is important to refer to your own herd, combined with individual vet advice and local guidelines in interrupting results as SCOPs has reported that the presence of Haemonchus eggs in a sample does not mean that there will be clinical disease.
Previously, identification of Haemonchus eggs and larvae in faeces in the lab required considerable operator skill and sample preparation which made it impractical for routine diagnosis. The use of peanut agglutination (PNA) to fluorescently label Haemonchus eggs in a sample is also available but this requires samples be sent to reference labs and there is considerable delay in results.
The development of a rapid inhouse egg detection test using AI which requires no operator skill for specific Haemonchus detection is important for a number of reasons.
- Rapid identification of Haemonchus eggs in the faeces allows farmers and vets to react quickly to infections in the flock. Hyperacute and acute infection can cause significant clinical signs and mortality in days in sheep and goats. Waiting for results from a reference laboratory may cause a delay in treatment which could have catastrophic consequences.
- Specific species identification allow targeted treatment with monodrug anthelmintic therapy when Haemonchus levels are high and avoids the use of multidrug combinations which contributes to on-farm anthelminthic resistance. Resistance to benzimidazoles, levamisole and the macrocyclic lactones is reported worldwide. Resistance develops rapidly in Haemonchus quickly due to the high genetic diversity and the high biotic potential of the individual worms.
- Unlike other gastrointestinal nematodes where adult sheep mount an effective immune response to gastrointestinal nematode infection adult ewes are often the first to succumb to haemonchosis within the flock. This is presumably due to worm control strategies being aimed at the lambs and the presumed protective role of age against parasitic disease in sheep. Therefore one of the first parts of Haemonchus control on farm is ensuring that there is some form of flock monitoring. The ability to detect Haemonchus eggs in faecal samples on farm or in clinic without the need for referral to reference laboratories is a significant development in effective parasite control and future proofing against losses.
- The ability to detect Haemonchus eggs in new arrivals minimises the introduction of Haemonchus contortus onto uninfected holdings and allows effective quarantine measures to be implemented which is paramount to flock health plans.
Given the trends of climate change and spread of resistance over recent years Haemonchus contortus is an important pathogen in small ruminants and will continue to be. The differences in its epidemiology and pathophysiology compared to other gastrointestinal nematodes means a separate approach is required in implementing sustainable parasite control programmes.
New developments in AI-led on farm Haemonchus contortus faecal egg detection and estimation, requiring no specialised training or sample preparation, allows further scope for implementation of sustainable , targeted and effective parasite control programs.
OvaCyte Speciation, including testing for Haemonchus, is now available in the UK on our EQ & LA Plus Cassettes, and will be available in Ireland in November 2025 on our EQ & LA Dual Cassettes. Contact us for more information.
Arsenopoulos, K et al (2021) ‘Hemonchosis: A Challenging Parasitic Infection of Sheep” Animals
Besier, R.B(2016) ‘ The Pathophysiology, Ecology and Epidemiology of Haemonchus contortus Infection in Small Ruminants’ Advances in Parasitology, Vol 93
Besier, R.B (2016) ‘Diagnosis, Treatment and Management of Haemonchus contortus in Small Ruminants’ Advances in Parasitology
Charliee, J et al (2020) “Initial assessment of the economic burden of major parasitic helminth infections to the ruminant livestock industry in Europe’ Preventative Veterinary Medicine, vol 182
Carvalho, N et al (2023) ‘Hypobiosis and Development of Haemonchus contortus and Trichostrongylus colubriformis Infection in Lambs under Different Levels of Nutrition’ Ruminants, 3, 401-412 https://doi.org/10.3390/ruminants3040033
Jawad, H et al (2024) “PSX-27 Growth performance and immune response dynamics in weaned lambs with subclinical Haemonchus contortus parasite infection” Journal of Animal Science
Rose H, Caminade C, Bolajoko MB et al.. Climate-driven changes to spatiotemporal distribution of the parasitic nematode, Haemonchus contortus, in sheep in Europe. Glob Change Biol. 2016;22(3):1271–1285.
Rose H, Rinaldi L, Bosco A et al. Widespread anthelmintic resistance in European farmed ruminants: a systematic review. Veterinary Record . 2015;176(21):546. doi:10.1136/vr.102982
https://www.scops.org.uk/internal-parasites/worms/haemonchus-contortus/
https://www.scops.org.uk/workspace/pdfs/3-1-4-haemonchus-contortus-updated-aug-2024.pdf
