Also known as small redworm or small strongyles, these parasites are of particular significance due to their prevalence and ability to ‘encyst’ into the gut wall where they can lay dormant for several years. Emergence of these parasites has the potential to cause severe consequences such as weight loss, colic, and anaemia. Adult redworms lay eggs which are detected in a faecal worm egg count. Encysted red worm burdens can be diagnosed via a simple blood test to check antibody levels. Importantly, horses can have high levels of encysted red worm but have a negative faecal worm egg count. This is due to the lack of active adult redworms laying eggs.
Tapeworm eggs are intermittently shed from horses, meaning they can be missed on routine faecal worm egg counts. Tapeworms attach to the gut wall and live off food that horses ingest which can lead to weight loss, diarrhoea, and colic. Saliva testing has proven to be a simple and accurate test for diagnosing infections by measuring the antibody levels horses produce against tapeworm.
Also known as ‘roundworms’, these large white worms tend to be more prevalent in foals and youngstock under four years old. Resistance often develops as horses age, making them less of a problem in adult horses, however they can become an issue in older, immunocompromised horses such as horses with PPID (Cushing’s disease). Foals can quickly accumulate large burdens of these worms which can lead to a noticeable inability to hold weight, severe debilitation, and unfortunately can be fatal. Due to the worm’s size, they can cause intestinal obstruction leading to colic, constipation, or diarrhoea, and larvae can also migrate into the airways causing coughing. Some other clinical signs of infection can include lethargy, a rough coat, and a pot belly appearance. Adult worms can be easily seen in faeces and eggs can be detected via a faecal worm egg count.
Unlike the other parasites, pinworm isn’t a major threat to horse health, however infection can cause severe irritation around the rear end causing horses to rub themselves raw, leading to painful skin infections, and lethargy or depression. Yellow proteinaceous deposits can sometimes be seen around the anus or tail head region. Pinworms are diagnosed by an adhesive tape test performed around the anus and microscopic examination.