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Sarcocystosis - An Overview

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Sarcocystosis, also known as sarcosporidiosis, is caused by the Sarcocystis species with a definitive-intermediate host life cycle. Read the article below to know more.

Medically reviewed by

Dr. Shubadeep Debabrata Sinha

Published At September 12, 2022
Reviewed AtMay 30, 2024


Sarcocystosis is a disease or infection caused by the parasite Sarcocystis. It occurs in both humans and animals, while two types of disease occur in humans. One of its types, known as intestinal type, causes mild fever, diarrhea, and vomiting. The other type, known as the muscular type, causes fever, muscle pain, and transitory edema. However, most people with sarcocystis do not experience any symptoms, and it is seen mostly in tropical or subtropical countries. The muscular form of sarcocystosis has mostly been reported in Southeast Asian countries.

What Is the Causative Agent for Sarcocystosis?

Sarcocystosis is a protozoan disease of almost all species of domestic animals caused by Sarcocystis species. Cattle and pigs act as the main sources of human disease. Three species of Sarcocystis have been recognized in cattle, and of these,

  • Sarcocystis cruzi has the dog as its definitive host.

  • Sarcocystis hirsuta, in the cat.

  • Sarcocystis hominis, in men.

Pig harbors three species of Sarcocystis, namely,

  • Sarcocystis miescheriana, with their definitive host as the dog.

  • Sarcocystis porcifelis, in the cat.

  • Sarcocystis suihominis, in man, respectively.

Sarcocystis have been commonly found in retailed foods and can remain viable for several days under refrigerated conditions.

How Does Sarcocystosis Occur?

Human beings act as a definitive host for Sarcocystis hominis and Sarcocystis suihominis, and they get infected by eating raw or undercooked beef and pork. Meat with visible sarcocysts is unacceptable to the consumer, and the condemnation of carcasses leads to considerable losses to the meat industry. In intermediate hosts, signs are evident at the time when schizonts parasitize vascular endothelium. Later, the schizonts disappear within about a month and lead to the formation of cysts in the muscles. The detailed life cycle of sarcocystosis is as follows:

  1. Sporocysts contain a refractile residual body and four sporozoites. When the intermediate hosts (cattle and pigs) ingest these sporocysts, it becomes ruptured and produces "sporozoites."

  2. These sporozoites enter into the endothelial cells in the intermediate host's blood vessel and produce "first-generation schizonts" by undergoing schizogony.

  3. "Second-generation schizonts" result when the small capillaries and blood vessels become invaded by "merozoites" derived from the first generation.

  4. The invasion of muscle cells happens through the "second-generation merozoites'' and results in the formation of sarcocysts that contain bradyzoites. This becomes the stage that can cause infection for the definitive hosts (humans).

  5. When undercooked meat containing these sarcocysts is eaten by humans, they enter the body and cause infection. Cysts begin to form in the small intestine, and they rupture to release the "bradyzoites."

  6. At this stage, the bradyzoites differentiate into macro and microgametocytes. Male and female gametes become fused, resulting in the formation of "oocysts."

  7. Oocysts sporulate in the intestinal epithelium and are shed from the definitive host in feces. However, due to the fragile nature of the oocyst wall, it is possible for individual sporocysts to be detected in feces.

What Is the Incidence Rate of Sarcocystosis?

Previous studies indicate a high incidence of sarcocystosis all over the world. Studies using conventional techniques have reported the presence of Sarcocystis suihominis in India. Sarcocystis species have been reported from many countries. In India, Sarcocystis cruzi has been reported from Uttranchal, Madhya Pradesh, Bihar, and Assam, whereas Sarcocystis hominis has been reported from Uttar Pradesh and Madhya Pradesh states only. Sarcocystis species mainly infect skeletal and cardiac muscles and have been found in the muscles of:

  • Esophagus.

  • Thigh.

  • Cardiac.

  • Diaphragm.

  • Eye.

  • Tongue.

  • Anus.

What Are the Signs and Symptoms of Sarcocystosis?

A) Clinical Signs in Animals:

1. The disease is of economic importance, as it causes both direct and indirect financial problems.

  • A direct loss occurs through losses experienced in holding or condemning carcasses.

  • Indirect losses arise from delayed growth and production losses on the farm.

  • In heavy infections of the intermediate host (cattle), the important symptoms experienced are,

  • Anorexia.

  • Pyrexia (42 degrees Celsius or more).

  • Anemia.

  • Cachexia.

  • Enlarged palpable lymph nodes.

  • Excessive salivation.

  • Nervousness.

  • Lameness.

  • Hair loss on the extremities. Hair loss is noticed, especially at the end of the tail and complete hair loss gives the animals a rat tail appearance.

  • Abortions may occur in breeding stocks.

2. The cystic stage of sarcocystosis is basically non-pathogenic. Pathological changes that are observed at necropsy are,

  • Eosinophilic myositis.

  • Generalized lymphadenopathy.

  • Erosions and ulcerations in the oral cavity and esophagus.

3. Histologically, the evidence includes,

  • Lymphadenitis.

  • Myositis.

  • Myocarditis.

  • Glomerulonephritis.

  • Schizonts of Sarcocystis species may be found in the endothelial cells of blood vessels in many organs.

B) Clinical Signs in Man:

Human sarcocystosis is reviewed under two sections, namely,

  • Intestinal Sarcocystosis - In this type, a man acts as a definitive host, and it is mainly characterized by abdominal pain and diarrhea.

  • Muscular Sarcocystosis - A man acts as an intermediate host for various Sarcocystis species in muscular form. Muscular Sarcocystosis is characterized by pain, swelling, stiffness, and displacement of myofibrils in the affected muscles.

How Is Sarcocystosis Diagnosed?

Samples of the animal’s muscle tissues like heart, jaw, tail, thigh, neck, esophagus, diaphragm, eye muscles, and brain should be collected in polythene bags containing ice at 4 degrees Celsius. First, they should be examined grossly and then subjected to the pepsin digestion method after removing fat and connective tissue. The diagnosis from muscles can be made using the following methods:

  • Isolation of intact microsarcocysts from muscles.

  • Pepsin digestion technique.

  • Histopathological examination.

  • Serological tests like ELISA (enzyme-linked immunosorbent assay), etc.

  • Electron microscopic studies - In transmission electron microscopy, Sarcocystis cruzi appears thin-walled, showing zoites in the granulomata and hair-like projections on the cyst wall.

How Is Sarcocystosis Treated?

In Humans - intestinal sarcocystosis may not be treated, as infections are usually self-limiting. Some patients with symptomatic myositis (inflammation of the muscle) have been given antiparasitic drugs such as:

  • Metronidazole.

  • Trimethoprim.

  • Sulfonamide.

  • Pyrimethamine.

  • Sulfonamide.

  • Albendazole.

Supportive care may include anti-inflammatory agents.

In Animals - Equine protozoal myeloencephalitis can be treated with:

  • Toltrazuril.

  • Ponazuril.

  • Diclazuril.

  • Sulfonamide combined with either Pyrimethamine or Trimethoprim.

Pyrimethamine is more effective against protozoa than trimethoprim. Supportive care, including anti-inflammatory drugs, may also be necessary.


Sarcocystosis is usually affected by animals, and it can also affect humans. This happens when humans consume undercooked meat of animals affected by the parasite Sarcocystis. It cannot be transmitted from one person to another, it is better to begin practicing safe food and water in general and while traveling, as it may help prevent the condition. In addition, following basic self-hygiene practices such as using clean toilets, washing hands frequently, and keeping the house clean can assist in disease prevention.

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Dr. Shubadeep Debabrata Sinha
Dr. Shubadeep Debabrata Sinha

Infectious Diseases


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