Sarcocysts

Sarcocystis is a genus of coccidian parasites with 130 recognised species that mainly infect animals but can also infect humans. They form tissue cysts (called sarcocysts) in intermediate hosts such as herbivores and omnivores and complete their life cycle in carnivorous definitive hosts like dogs, cats and humans

The parasite reproduces sexually in the definitive host's gut, is excreted in faeces, and then ingested by the intermediate host, where it enters muscle tissue. When the definitive host consumes the intermediate host, the cycle repeats. Typically, only the intermediate host shows symptoms of infection.

Four Sarcocystis species infect cattle: S. bovifelis, S. hominis, S. cruzi, and S. hirsute which are microscopic and cannot be seen with the naked eye during meat inspection examination. Of these, S. cruzi is the primary cause of infection and the only species known to be pathogenic in cattle.

Sheep can be infected by four identified species: S. arieticanis and S. ovicanis, which are pathogenic, and S. gigantea and S. medusiformis, which are considered nonpathogenic.

S. gigantea and S. medusiformis produce macroscopic cysts that are visible to the naked eye.

Photo 1 Sarocysts in sheep; Sgi - S. gigantea and Sme - S. medusiformis

Note: S. gigantea sarcocysts occur in several different forms, yellowish or orange in colour, whereas those of S. medusiformis are elongated thin white, spindle shaped.

Photo 2:  S. gigantea in Ovine oesophaguses

S. capracanis, S. hircicanis, and S. moulei are the species that frequently infect goats.

Four species infect pigs: S. medusiformis, S. meischeriana, S. porcifelis, and S. suihominis, with S. meischeriana and S. suihominis as the main causes of Sarcocysts.

Only the cysts of S. miescheriana can typically be seen with the naked eye.

Photo 3: S. Miescheriana in pork

Note: S. Miescheriana appear as white, spindle-shaped, rice grain–like cysts.

Seven species infect deer: S. hjorti, S. venatoria, S. Iberica, S linearis, S. taeniata, S. Pilosa and S.ovalis with S. hjorti, S.vaeniata and S, Iberica as the main causes of Sarcocysts. All of cysts of these species are microscopic and cannot be seen with the naked eye.

Five species infect horses: S. asinus, S. bertrami, S. equicanis, S. fayeri, and S. neurona. Sarcocystis in horses usually involves S. bertrami.

Only two Sarcocystis species, S. hominis (from cattle) and S. suihominis (from pigs), both microscopic, use humans as definitive hosts.

Infections from the common cattle species like S. cruzi or sheep species S. gigantea and S. medusiformis are not a concern for human consumption. Proper cooking of meat destroys all forms of the parasite.

Key Sites for Inspection

The following muscles are frequently affected by Sarcocystis cysts

• Oesophagus
• Diaphragm
• Heart
• Tongue
• Masseter

While these are the primary locations, sarcocysts can potentially be found in virtually any striated or skeletal muscle throughout the body. 

Disposition

Australian Standards AS4696-2023

The Schedule states:

DAFF Post-mortem decision notes

Parasites not transmissible to humans

Carcases and their carcase parts that have macroscopic lesions due to infestation with parasites not transmissible to humans via meat or offal are dealt with in accordance with the following general rules:

• If the lesions are slight in nature, are localised and are such that they can be completely removed, the parasitic lesions are removed and condemned. The affected carcase or carcase part, if it is otherwise healthy, may be passed for human consumption.
• If the infestation is moderate, the carcase is retained, boned, thoroughly searched for observable lesions and the lesions removed. The remainder of the carcase, if it is otherwise healthy, may be passed for human consumption.
• If a carcase part shows numerous lesions caused by the parasites, or if the infestation is such that the complete removal of the lesions is impractical or their removal would render the carcase part of little commercial value, the carcase part is condemned.
• If the parasites are distributed throughout the carcase in such a way that the complete removal of all parasites and any lesions resulting from their presence is impracticable, the carcase is condemned.
• Where all parasitic lesions are removed by an establishment operative, viscera that would otherwise be condemned due to the presence of parasites not transmissible to humans may be saved as animal food.

Note:

Notwithstanding the provisions of the above general rules, the disposition of carcases and carcase parts affected by the parasitic diseases detailed below are in accordance with the following specific criteria:

Disposition guidance

The amount of time and effort put into removing / trimming sarcocysts needs to be considered when making a disposition. If all that will remain after a lot of time and effort is damaged primals or trimmings, then it’s probably not worth the time and effort.

Its really just good sensible judgement by the inspector, but if the company wants to bone and trim the product under supervision they should be given the option.

In the case of moderate to heavy infestation they would not want to take the option of trimming.

Note chilling of meat does not kill the cysts, but they do break down during freezing

Sarcocystis tenella