Sarcosporidiosis

Abstract

Sarcosporidiosis is a disease that occurs worldwide in many animals and human beings as a result of oral infections with developmental stages of several Sarcocystis species, the life cycle of which includes two types of hosts: a prey and a predator. Humans may be involved in both groups. The prey hosts are herbi‐ or omnivores, which are infected by oral uptake of oocysts and sporocysts from the feces of the predator hosts, which are carnivorous beings including man. The specimens of the latter group are infected by eating raw or undercooked meat of the prey animals containing so‐called cyst merozoites (cystozoites) inside tissue cyst in muscle cells or in brain cells. The final hosts (=carnivores with the sexual development inside their intestinal cells) may suffer from diarrhoea in case of severe infections. The intermediate hosts (=prey hosts) may severely suffer from bleeding of inner blood vessels (where the schizonts and merozoites develop within the first month after infection) and by destruction of brain and muscle cells, where the cysts are formed. After about 3 months the cyst merozoites inside the tissue cysts are infectious for the final host.

Key Concepts:

  • Human intestinal infections with Sarcocystis species are completely prohibited by noneating raw or undercooked meat.

  • Strict separation of human, dog and cat feces from food of farm animals prohibits their infections with Sarcocystis species.

  • Sarcosporidiosis is completey avoidable on farms by strict hygienic measurements.

  • Deep freezing or cooking of meat will kill sarcosporidians.

Keywords: Sarcocystis; Sporozoa; coccidiosis; domestic animal disease; economic losses; human infections

Figure 1.

Diagrammatic representation of the life cycle of Sarcocystis suihominis: (1) sporozoite (set free in the pig's intestine); (2) schizont in endothelial cells of the blood vessels, for example, in the ommentum (two generations); (3) merozoite (set free from schizonts); (4) tissue cyst in muscle fibre or also in brain cells; (5) cyst‐merozoite (set free in intestine of human); (6, 7) gamonts; (8) macrogamont; (9) male gamete (produced by microgamont); (10) young fertilised zygote (oocyst); (11–13) formation of two sporocysts (each with four sporozoites inside an oocyst). N, nucleus.

Figure 2.

Light micrograph of an oocyst of Sarcocystis suihominis containing two sporocysts (each with four sporozoites). The oocyst wall is invisible and smooth and is often ruptured already in the intestine of the pig, so that many single sporocysts are found ( = as a species characteristic) in the faeces. (Magnification ×2000.) R, residual body; S, sporozoite.

Figure 3.

Light micrograph of two schizonts of Sarcocystis suicanis in a blood vessel of the ommentum of a pig. In the stage on the right, merozoites (ME) are still present, while the schizont on the left is still in the phase of nuclear division. BL, basal lamina; DS, developing schizont; E, erythrocyte; LU, lumen of the blood vessel; NH, nucleus of the host cell. (Magnification ×500.)

Figure 4.

Light micrograph of two cross‐sectioned cysts of Sarcocystis ovicanis in muscle fibres of the pig. Note the long protrusions of the primary cyst wall (arrows). The cyst on the right (containing metrocytes=precursors of the cyst merozoites) is younger than that on the left, in which cyst‐merozoites are mature. (Original magnification ×1000.)

Figure 5.

Transmission electron micrograph of the periphery of a young tissue cyst of Sarcocystis suicanis showing metrocytes (m) and cyst‐merozoites (cy) situated in chamber‐like hollows (ch) of the ground substance (G), which is rather thick below the primary cyst wall (pw). S, sarcomeres of muscle fibre. (Original magnification ×3000.)

Figure 6.

Transmission electron micrograph of a section of the anterior pole of a cyst‐merozoite of Sarcocystis suihominis from a pig, showing the typical organelles (C, conoid; D, dense bodies; MN, micronemes; R, rhoptries) involved in the cell penetration process. (Magnification ×20 000.) Inset: Light micrograph of such stages (magnification ×1000).

Figure 7.

Photograph of macroscopically visible tissue cysts (white globules) of Sarcocystis ovifelis (formerly called Sarcocystis tenella) within the muscle of sheep (magnification ×2).

Figure 8.

Two pigs of the same age (born at the same day) – one was experimentally infected with oocysts and sporocysts of Sarcocystis suicanis. Guess which one? You are right: the smaller one.

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Aryeetey ME and Piekarski G (1976) Serological studies on Sarcocystis in humans and animals. Parasitology Research 50: 109–124.

Mehlhorn H, Düwel D and Raether W (1993) Diagnosis and therapy of parasitosis of house, farm and pet animals, 2nd edn. Stuttgart: G. Fischer.

Mehlhorn H, Eichenlaub D, Löscher T and Peters W (1995) Diagnosis and therapy of human parasitic diseases, 2nd edn. Stuttgart: G. Fischer.

Piekarski G, Heydorn AO and Kimmig P (1978) Clinical parasitological studies of the sarcosporidiosis in humans. Infection and Immunity 6: 153–159.

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Mehlhorn, Heinz(Aug 2011) Sarcosporidiosis. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0001933.pub2]