Sarcocystosis is a disease caused by protozoa, which is distinguished by generate alterations in the striated muscles of the birds and other animal species.

In the case of birds, the causative agent is Sarcocystis horvathi. Se presenta como una infección lenta y sigilosa que afecta predominantemente a las aves adultas. Sarcocystis, término que proviene de las palabras griegas sarx (carne) y kystis (vejiga), se clasifica como protozoos del grupo Apicomplexa, que se desplazan y penetran las células, provocando sarcosporidiasis o sarcocistiosis.

Infections are marked by the production of multiple sarcoquistes, which are sacs that contain parasites, ranging in size from micrometers (µm) to several inches, and are located in the muscles or in the nervous tissue of several animal species.

The genus includes more than 100 species show differences in their level of pathogenicity, which depend on the host specificity, as well as the structure and the place of the sarcoquistes. Have a typical life cycle of coccidios, which develops in three stages: merogonia (asexual multiplication-division multiple), gametogonia (sexual phase) and sporogonic (which is to infect new hosts).

In general, the disease is asymptomatic, given that its development is chronic and, in its initial phase, the changes do not impact directly on the muscle fibers, but the intercellular space. The occurrence of lameness and stiffness is observed only in severe cases.

Sarcocystis horvathi acts as a protozoan parasite-type intracellular. The definitive hosts of this parasite are carnivores or predators, such as dogs, cats, foxes, coyotes, and even humans. Birds, specifically chickens and ducks, working as a host intermediates to become infected by eating oocysts of S. horvathi or esporoquistes excreted through the feces of carnivores or predators.

The sarcosporidios are more frequently found in certain species duckssuch as:

• Mallard (Anas platyrhynchos).
• Crescent (Spatula discors).
• Garganey (Spatula querquedula).
• Or in flatfish (Pleuronectiformes).

In contrast, we observe a different behavior in ducks that feed on aquatic vegetationfor example:

• Duck copetudo (Aythya fuligula).
• Duck, black-headed (Heteronetta atricapilla).
• Duck stickleback (Oxyura jamaicensis).

This phenomenon is related to the differences in the manner of feeding of these birds. In addition, it has been shown that the pathological changes, which involve the analysis of the characteristics of a tissue sample, they are more frequent in adult birds (over a year), suggesting a prolonged incubation period of the disease.

The ducks, in their role as hosts intermediates, are infected through the digestive system, by means of the intake of plant foods, water, or any drink that is contaminated. It is likely that transmission occurs through drinking water, ponds, or areas contaminated shallow inhabited by predators that contain oocysts ooculados. Consequently, their main hosts intermediates are, in their majority, wild ducks.

In the digestive tract of ducks, the membrane of the ooquiste features a wrap-extremely fragile at the moment of the separation of the host cell, or during the passage through the intestine, breaking it with ease. This process allows it to be digested and that the sporozoites are released, entering the epithelial cells of the intestine.

From this point, after multiple divisions, are transformed and penetrate the epithelial layers in search of capillary blood vessels that facilitate their spread throughout the circulatory system. The merozoites become metrocitos in the muscles, which are then converted into cistozoitos, which in turn evolve to sarcoquistes.