Tapeworms in Horses
The tapeworm is an increasingly common parasite of horses in many parts of the world, including Australia.
In the past tapeworms were not considered to cause disease or gut damage, however research has shown that these worms are involved in serious bowel disorders including colic, intestinal blockages and even death. It is therefore very important for tapeworm control to be included in worming programs.
The Tapeworm
There are several species of tapeworms that infect horses with Anoplocephala perfoliata being the most common in Australia. This worm is a yellow-green colour and has a riangular 'fluke-shaped' body. They grow to between 3-8 cm in length. A horse may be infected with 1 tapeworm or hundreds. A survey in Victoria found that the average infection intensity was 99 tapeworms per horse.
Tapeworms commonly live in clusters in an area of the gut known as the ileo-caecal junction. This junction is the site where the small intestine enters the large intestine. The worms anchor themselves to the bowel lining using 4 suckers and then absorb nutrients from the bowel through their cuticle, as they do not have a mouth or a digestive tract.
How Do Tapeworms Cause Disease?
Tapeworms cause bowel disease due to their habit of clustering around the ileo-caecal junction. The attachment of the worms to this area of the bowel lining causes thickening, inflammation and ulceration of the intestinal wall. The greater the number of worms, the greater the degree of gut damage. Clusters of the worms at the junction of the small and large intestine may also cause physical blockage of the small bowel. Additionally tapeworms secrete chemicals that may increase the motility or movement of the bowel, leading to intestinal twists and intussusceptions where part of the bowel telescopes inside itself, resulting in blockage.
Bowel disorders caused by heavy tapeworm infections can lead to signs such as ill-thrift, recurring bouts of spasmodic colic and acute colic due to potentially fatal bowel blockages or ruptures.
How Do Horses Get Tapeworms?
Horses become infected with tapeworms by eating small pasture mites during grazing. These free-living 'oribatid' mites are an essential stage in the tapeworm’s lifecycle. The mites eat tapeworm eggs passed in the manure of infected horses. The eggs develop into larval tapeworms within the mites over 12-15 weeks.
Horses then accidentally eat the mites and become infected with tapeworms. Pasture mites occur in very large numbers on pastures, particularly in low lying or wet areas, with up to 20,000 mites per square metre of pasture reported.
Mites may also be present in hay and straw. The mites are long lived and can survive for over 12 months in the pasture.
Which Horses are at Risk from Tapeworms?
Horses of any age can become infected with tapeworms, with prevalence rates of up to 62% reported in some parts of Australia. Horses less than two years of age and aged horses usually have the heaviest tapeworm infections. Foals can become infected as young as 4-5 months of age. Pastured horses are at greater risk than stabled horses as they are more likely to ingest infected mites while grazing, however it is thought that the mites that carry tapeworms may also be able to survive in hay and straw.
How do you Treat Tapeworms?
Regular worming for tapeworms should be an important part of all horse parasite control programs. Many common horse-worming products do not control tapeworms. Choose a broad-spectrum worming product such as EQUIMAX®, EQUIMAX® ELEVATION or STRATEGY-T®, which are effective against all horse worms including tapeworms. Equimax and Equimax Elevation contain the active ingredient praziquantel, which is the only compound that is 100% effective against tapeworms.
To control tapeworms you should administer an effective worming paste or drench at least twice a year, ideally in May and September. However it is very safe to use a worming product which treats tapeworms, such as Equimax, every 6-8 weeks when you are worming for other common internal parasites.
Summary
There has been an increasing awareness of the significance of tapeworms in causing disease in horses over the past 10 years. Highly effective tape-worming pastes and liquid drenches are now available and should be routinely given to horses of all ages. Effective tapeworm control will avoid the risk of bowel disorders and even death that can result from tapeworm infection.
By Virbac Animal Health - Last updated 2 August 2016
