Ascarids: a re-emerging threat

Ascarids (Parascaris equorum) pose a significant and growing threat, in particular to foals grazing contaminated pasture. This is often a sub-clinical infection, but can lead to poor weight gain, unthriftiness, rough hair coat, pot belly appearance, nasal discharge, coughs and mild to severe colic.
The ascarid has a complex life cycle. The foal will ingest eggs from the environment (mostly likely at pasture, but eggs can be present in stables). Larvae that hatch from these eggs will migrate into the intestinal wall and migrate through the veins into the liver, heart and lungs. Larvae will continue to develop and are coughed up and swallowed. The larvae will then develop into adult ascarids in the intestine and begin to produce many thousands of eggs per day, which are passed out in the faeces. The ascarid eggs can survive for many years under most environmental conditions. The life cycle takes around 60–70 days from ingestion of eggs to the development of egg-producing adults.
The clinical signs associated with ascarid burdens may initially be vague, and relate to the stage of migration of the larvae. Initially, there may be mild diarrhoea, or periods of dullness, with the foal being partially off suck. As the larvae migrate, there is sometimes evidence of respiratory signs, such as coughing and nasal discharge. The migrating larvae can cause a significant inflammatory response on blood samples, and is not responsive to antibiotics. At this stage, a diagnosis of ascarid infection is difficult to confirm, as there is no evidence of egg production. A serological test for ascarids may be developed in the future and may be useful in foals, although this is some way off. […]