Internal parasites such as roundworms (nematodes) regularly infect ruminants. High infection burdens can have a detrimental effect on the health and production of the animal. The most prevalent species of helminths that infect cattle in South Africa are Haemonchus contortus/ Haemonchus placei (more commonly known as wireworm or “haarwurm” in Afrikaans), Ostertagia ostertagi (brown stomach worm), Cooperia spp. (cattle bankrupt worm). It is well known to farmers that their animals are more likely to be infected and with higher burdens of these parasites during the rainy season. A better understanding of the life cycle of these internal parasites, the diagnosis of high worm burdens and using integrated treatment strategies could lower the economic impact on the farmer.
Common life cycle of roundworms
The eggs from adult roundworms are passed in the faeces and deposited into the soil. The eggs will develop into first stage larvae (L1), then second stage larvae (L2) and finally to the infective third stage larvae (L3). Under ideal conditions (temperatures of ~ 30°C and 100% humidity), larvae will develop to L3 as quickly as 3 – 4 days. The infective L3 larvae will migrate to the top of herbage, until it is ingested by grazing cattle. Further development to fourth stage larvae (L4) will take place within the abomasum of the ruminant, where development of the buccal cavity will arise (making it possible for the worm to feed on the blood of the host). The adult worm will develop 14 – 16 days after infection with a single female being able to produce between 1300 and 7000 eggs per day and can survive up to 50 days.
L3 larvae are more resistant to environmental conditions, in contrast to the vulnerable L1 – L2 larvae. It is therefore possible for L3 larvae to survive moderate fluctuations in temperatures and humidity. Given the sub-tropical and temperate climate in South Africa, it is possible for L3 larvae to survive in most parts of the country throughout the year. L4 larvae can either immediately develop into adult worms (typically during warmer climates) or their development will undergo arrest (hypobiosis) during cold winters. During hypobiosis, L4 larvae will be able to survive for long periods of time or until conditions are favourable and the development to mature worms can continue. The break of hypobiosis will typically arise shortly after winter periods, where a surge of adult worms will be released in the abomasum. This occurrence can have a detrimental effect on the health of the animal, especially if the animal did not receive sufficient nutrient stimulation during the winter months and their immunity are compromised.
Diagnosis and clinical signs of high worm burdens
Anaemia (blood deficiency) and other clinical signs such as pallor, bottle jaw (submandibular oedema), lethargy, weight loss and poor coat quality is commonly present in animals with high roundworm burdens. This is caused by the significant rate at which these parasites feed on the blood of their hosts. An adult roundworm can consume as much as 0.05 mL blood on average per day. A significant loss of blood may also continue after the worm detaches, as the worm releases calreticulin which prevents blood from clotting and inhibits the hosts immune response to react against the parasite.
Infection can be confirmed by a variety of diagnostic tools such as faecal egg counts (FEC), FAMACHA© scoring and packed cell volume (PCV). FEC and PCV tests are not practical diagnostic tools to use on a farm as it requires laboratory techniques, which is not always feasible and accessible to farmers. The FAMACHA© scoring system is therefore a good indicator technique to use when screening animals for intestinal worm infections. This technique combines the ability to detect anaemia (assessing the mucous membranes around the eyes of the animal against the FAMACHA© score card) with the need to treat the animal.
Treatment strategies
An integrated (medicated and non-medicated) treatment strategy is more likely to be successful in managing roundworm infections in animals. Implementing non-medicated techniques such as increasing the correct supplementation given to animals can increase their immunity against roundworm infections, especially after the harsh winter season. Although other techniques such as rotational grazing has been proven as an effective method of preventing worm infections, it is highly dependent on the temperature variation to make any eggs or larvae that could possibly be present in those grazing camps or pastures non-viable. Furthermore, it is highly likely for L3 larvae to translocate between camps during high rainfall seasons. This technique may not be feasible as not all farmers follow the same management strategy.
For medicated treatment against roundworms, it is important to select anthelminthic products that is effective against mature and immature worms. The following chemical classes of anthelmintics will be effective against hypobiotic larval stages: Benzimidazoles, macrocyclic lactones and monepantel. However, wrong treatment strategies have led to the resistance of worms against many of these products. It is therefore important to follow dosing instructions carefully and not to dose animals too frequently, as this will influence their natural immunity against roundworms. It is advisable to consult with your vet or animal health technician in this regard.
Conclusion
The high fecundity of individual roundworms can result in the development of clinical disease that was not previously observed on the farm. It is therefore important to control round worm infections. Together with good nutrition and taking the life cycle of roundworms into consideration, it is important to dose cattle shortly after the winter season and before the rainfall season, in order to prevent high worm burdens that could possibly have a detrimental effect on the production of cattle.
Written by: Ms A Grobler
Contact details: amegrobler17@gmail.com