Sarcocystosis Infection in Dogs

Sarcocystis is an infection caused by a protozoan parasite species called Sarcocystis. Most Sarcocystis infections are asymptomatic. This means that the dog shows no recognizable symptoms related to the infection. Complications can arise when the parasite migrates from the gut to other tissues in the body.

In sarcocystosis, the muscles and other soft tissues are invaded by single-celled organisms, called protozoans, of the genus Sarcocystis. Although their final hosts are predators such as dogs and cats, these organisms form cysts in various intermediate hosts, including cattle, pigs, people, horses, sheep, goats, birds, camels, wildlife, rodents, and reptiles. Some cysts are visible to the naked eye, but others are too small to see.

How Dogs Become Infected

In its juvenile form, Sarcocystis is eaten by prey animals such as horses, cattle, sheep and birds. The infection then forms into cysts in the muscle tissue. When a predator species, such as dogs, eat the infected muscle tissue, the parasitic protist is passed on. The Sarcocystis then grow in the capillaries, muscle fibers and lymph nods. The juveniles are shed in the feces of the predator and picked up by prey species to continue the cycle.

Symptoms of Sarcocystis Infections in Dogs

Symptoms in dogs are rarely seen but may include:

• Lack of appetite
• Weight loss
• Diarrhea, potentially bloody diarrhea
• Dehydration
• Depression
• Paralysis
• Muscle pain
• Myositis (inflammation with the muscle)
• Muscle atrophy (muscle wasting

Diagnosis

The diagnosis is usually made post mortem by examination of the skeletal muscle. In some species, the cysts may be visible to the naked eye (ducks, mice, rabbits and sheep), but in most, microscopic examination is required.

Ante mortem diagnosis may be made with the use of dermal sensitivity testing or complement fixation tests. Muscle biopsy is also diagnostic, but this is much less commonly used.

Treatment of Sarcocystis Infection in Dogs

A Sarcocystis infection does not commonly cause much distress for canines, and generally clears up on its own. As such symptomatic Sarcocystis may not require any treatment at all. Therapeutic treatments have been mostly ineffective on tissue cysts once they develop, but depending on your specific circumstances your veterinarian may choose to consider anti-parasitic agents or antimicrobial drugs in an attempt to reduce the length and severity of the infection.