Prevalent Parasites: Common Types of Equine Internal Parasites

different species of small strongyles found in the horse. Small strongyles Cyathostomes have a similar life cycle to large strongyles in that they are found on pasture grasses ingested by the horse as larvae and then move through the digestive system. However once the small strongyle larvae reach the large intestines they do not migrate into other organs or tissues. Small strongyles are unique in that they often burrow into the walls of the large colon and cecum becoming what we call encysted. This makes management of small strongyles difficult because while encysted these parasites can remain in the body for up to two years and are not affected by most dewormer treatments. They will wait until conditions within the intestines are ideal for maturation and then emerge from the intestinal wall to mature and produce eggs.
Small strongyles are prolific and have become resistant to most dewormers currently available. Small strongyle resistance to deworming is one of the primary reasons recommended deworming protocols have changed within the past decade. It is assumed that all grazing adult horses are infected with small strongyles but clinical symptoms are rare.
Ascarids
Ascarids Parascaris equorum or roundworms typically affect younger foals and weanlings as most horses develop immunity to them by the time they are yearlings. Foals ingest ascarids as eggs consuming them from many different places in their environments. Unlike many other equine parasites ascarids are not just found on pasture grass they can be found on many surfaces such as buckets troughs and even the udder of the mare. Once ingested ascarid eggs develop into larvae in the small intestine. Hatched larvae then migrate through a series of tissues they move from the small intestine to the liver and then to the lungs. Once in the lungs the parasites are coughed up swallowed and

then migrate back to the small intestine for maturation. Similar to small strongyles they are developing resistance to certain types of dewormers which could lead to problems with dewormers remaining effective against ascarids in the future.
Tapeworms
There are three species of tapeworms found in horses but the most common one is Anoplocephala perfoliata. Tapeworms are unique in that they have two hosts in their life cycle the first is the oribatid mite and the second is the horse. Mites consume tapeworm eggs which then develop into larvae inside of the mite. Horses then ingest the mites while grazing and the mite