Parasite Spotlight: Haemonchus contortus, the Barber’s Pole Worm
From endoparasites like liver fluke and Toxoplasma, to ectoparasites, like ticks and mites, controlling parasites is a routine part of livestock farming. While the vast majority of animals carry some parasites, some species are much more dangerous than others. Whilst a low level of infection might be asymptomatic, when there are lots of parasites in an animal’s system, it can cause problems. One of these worms is the Barber’s Pole Worm, Haemonchus contortus.
What is Haemonchus contortus?
Haemonchus contortus, or the barber’s pole worm, is a parasitic roundworm that infects sheep, goats, and occasionally other ruminants. It is a blood-sucking worm which lives in the abomasum (fourth stomach) of its host. It’s known as the barber’s pole worm for the distinctive red striping of the female worm where the red intestine is wrapped around the white uterus. Infection with this parasite is very common across the world, particularly in warm climates and causes significant economic losses. While symptoms may start out relatively mild, if can be fatal.
What is the lifecycle of Haemonchus contortus?
Adult worms in the abomasum lay thousands of eggs and release them into the faeces of the host. In the faeces, these eggs then develop into juvenile larval forms. If the temperature is too low, below around 9°C, the eggs can’t develop. As such, infections tend to occur more frequently in hot countries, or during the warmer months in seasonal areas.
The larvae continue to develop outside of the hosts and become infective. Ruminants grazing on the same pasture, or in the same area, ingest the parasite. Once inside the host, the larvae travel through the digestive system until they reach the abomasum. Here, they burrow into the wall and begin feeding. They then eventually mature into adult worms and begin producing eggs.
What are the signs of infection?
Most of the signs of Haemonchus infection, or haemonchosis, are the result of blood loss. As the worms feed on the host’s blood and multiply, blood loss increases. Severity of the disease increases similarly, and can result in the animal’s death.
The signs to look out for in sheep and goats are:
- Slow growth rates
- Weight loss
- Bottle jaw
This swelling, or oedema, occurs when fluid builds up underneath the chin and is characteristic of severe protein loss.
Very pale under eyelid or gums can be an indicator of anaemia.
- Sudden death
In severe cases, animals might die suddenly. Investigation after death might reveal signs of Haemonchus contortus. If one animal in a flock has the parasite, it is extremely likely that other animals will. Immediate action is necessary to prevent further losses.
How are infections detected and treated?
Aside from the clinical signs of infection, an important diagnostic tool is faecal egg counts (FECs). As Haemonchus infection can cause sudden death, regular FECs provide a monitoring tool for parasite burden. It can be difficult to differentiate between Haemonchus contortus eggs and those of other worm species. Combining this with observation, however, can provide strong evidence for diagnosis. Specialist laboratories can perform larval differentiation tests to determine species. An unexpectedly high FEC can be an indicator of an infection. Vets can also perform post mortems of dead livestock to find out whether the animal had Haemonchus worms.
The FAMACHA test quantifies the degree of anaemia present in a flock based on the colour of their eyelids. It is a popular tool in areas where Haemonchus is typical. This allows specific treatment with anthelmintic drugs and so helps to reduce the risk of resistance developing.
If infection is identified, treatment is usually either broad spectrum wormers, or narrow spectrum wormers. As with all anthelmintic drugs, these should be used carefully and selectively. Targeted treatment is especially important with this parasite, as anthelmintic resistance is a particular issue with Haemonchus worldwide.
What control methods are there?
Preventing initial infections of animals is an important step in reducing Haemonchus infection. In a naïve population, on a clean farm for example, quarantining any incoming animals is extremely valuable. If an infected animal joins a flock, the parasite can spread quickly with devastating effects. As such, new animals should be monitored and treated if they have an infection before introducing them.
If a pasture becomes infected with the parasite, moving a flock away from it can reduce the level of infection. In colder and drier countries, weather conditions will wipe out parasite populations in the environment, although the worms can overwinter in sheep in the form of hypobiotic larvae. Thus, if Haemonchus is endemic, it is very difficult to completely remove the parasite. Management, therefore, is usually the goal. Whilst this was a parasite traditionally associated with the southern part of the UK, there is some evidence that it is now becoming more widespread.