Veterinary Epidemiology and Zoonosis

SARCOCYSTOSIS

Type of zoonosis

• Cyclozoonosis

Definition

• Sarcocystosis is a type of cyclozoonotic disease in man, clinically characterized by nausea, stomach ache, diarrhoea and dyspnoea in man. In cattle, can cause fever, anorexia, anaemia, loss of weight, hair loss, weakness, muscle twitching, prostration, abortion, reduced milk-yield, hypersalivation, neurologic signs and death.
• Sarcocysts (in Greek, Sarkos – flesh, Kystis – bladder) are the terminal asexual stages found encysted, primarily in striated muscles of mammals, birds, poikilothermic animals and intermediate hosts). Sarcocysts also have been found in central nervous system and in Purkinje fibres of the heart and muscle bundles.

Etiology

• Different species of Sarcocystis belongs to the phylum: Apicomplexa and family: Sarcocystidae.
• Sarcocystis spp. lack flagella and cilia, but they infect the host cells by way of an organelle, called the apicoplast.
• Species-specific prey (intermediate host) – predator (final host) life cycles have been demonstrated. Examples are:
  • Sarcocystis cruzi - Cattle-dog
  • S.hirsuta - Cattle-cat
  • S.hominis - Cattle-human
  • S.capracanis and S.hircicanis - Sheep-dog
  • S.gigantea and S.medusiformis - Sheep-cat
  • S.capracanis and S.hircicanis - Goat-dog
  • S.moulei - Goat-cat
  • S.meischeriana - Pig-dog
  • S.suihominis - Pig-human
  • S.porcifelis - Pig-cat

Reservoir and incidence

• Sarcocystis spp. normally develops in two-host cycles consisting of species-specific prey (intermediate host) – predator (final host) life cycles.
• Apart from domestic animals, wild animals may also serve as intermediate hosts (such as raccoons) or final hosts (coyotes) for some species of Sarcocystis.
• After ingestion of sarcocystis infested meat and meat products by the intermediate hosts such as humans, horses, cattle, sheep, goats, pigs, birds, rodents, camelids, wildlife and reptiles, they invade in to the endothelium, muscles and other soft tissues, and then cysts (vary in size from a few micrometers to several centimeters) are formed.

Transmission and life cycle

• Fatal dose of sporocysts is 5x10⁶ or more.
• Transmission only through ingestion of sarcocystis infested meat and meat products.
• Birds and other invertebrates consume the parasite in egg or oocyst form from the faeces of infected vertebrates.
• The oocysts then develop into the sporozoite form in the intestines of the invertebrate.
• The sporozoites migrate to the animal's bloodstream and invade certain cells, which are then multiplied and give rise to the merozoite form.
• These merozoites are carried by the blood to the animal's muscles, where whitish macrocysts are produced.
• When carnivores eat the invertebrate's muscle tissue, the parasites reach maturity and reproduce sexually in the host's intestine, releasing oocysts.

Disease in animals

• In cattle (S.cruzi, the most pathogenic species), the disease manifests fever, anorexia, anaemia, loss of weight, loss of body hair (particularly at the tip of the tail), weakness, muscle twitching, prostration, abortion, reduced milk-yield, hypersalivation, neurologic signs and death.
• Pregnant cows may abort and milking cows may have reduced milk yield.
• Haemorrhages are most evident on the serous surface of viscera, in cardiac and skeletal muscles, and in the sclera of the eyes.
• In acute sarcocystosis, skeletal muscles are seen mottled or striped with pale areas, interspersed with dark haemorrhagic areas.

Disease in humans

• Nausea, stomach ache, diarrhoea and dyspnoea.

Diagnosis

• Presumptive diagnosis based on clinical signs and history.
• Periodic Acid Schiff (PAS) staining can be used to stain bradyzoites, which contain amylopectin granules that stain bright red.
• Serology by ELISA.
• Animal inoculation method: Intraperitioneal inoculation of mice with the infected blood containing sarcocystis results in the appearance of merozoites in the peritoneal fluid and cysts in the muscles.

Treatment

• Therapeutic treatment of animals has been ineffective, but
  • In cattle, prophylactic dose of amprolium (100 mg/kg body weight, SID for 30 days) may reduce illness.
  • In sheep, prophylactic administration of amprolium or salinomycin can be given.

Prevention and control

• The main objective in controlling sarcocstosis is to interrupt the life cycle, which will minimize the spread of sporocysts the definitive hosts.
• Uncooked meat or offal should never be left to feed carnivores.
• Dead livestock should be buried or incinerated to avoid access of carnivores.
• Cooking of the meat above 55^oC for 20 minutes or at 70^oC for 15 minutes destroys the cysts.
• Freezing of the meat at 4^oC for 2 days or -20^oC for 1 day can kill sarcocysts in meat.