Biology:Sarcocystis

Sarcocystis is a genus of protozoan parasites, with many species infecting mammals, reptiles and birds. Its name is derived from Greek sarx = flesh and kystis = bladder.

The lifecycle of a typical member of this genus involves two host species, a definitive host and an intermediate host. Often, the definitive host is a predator and the intermediate host is its prey. The parasite reproduces sexually in the gut of the definitive host, is passed with the feces, and ingested by the intermediate host. There, it eventually enters muscle tissue. When the intermediate host is eaten by the definitive host, the cycle is completed. The definitive host usually does not show any symptoms of infection, but the intermediate host does.

About 130 recognized species are in this genus. Revision of the taxonomy of the genus is ongoing, and all the currently recognized species may be a much smaller number of species that can infect multiple hosts.

History

The organism was first recognized in a mouse by Miescher in 1843. His findings were not initially interpreted as involving a protist, and the literature referred to the structures he described as "Miescher's tubules". Incidentally, Miescher's son, Johann Friedrich Miescher, discovered DNA. Similar structures were found in pig muscle in 1865, but these remained unnamed until 1899, when the name Sarcocystis miescheriana was proposed for them. Initially, whether these organisms were fungi or protozoa was unclear . This uncertainty was resolved in 1967 when electron microscopic studies showed that they were protozoa, related to Toxoplasma and Eimeria. The lifecycle remained unknown until 1970, when bradyzoites from sarcocysts in bird muscles were inoculated into cultured mammalian cells and seen to undergo development into sexual stages and oocysts. Transmission studies with Sarcocystis of cattle (then considered a single species, Sarcocystis fusiformis) in dogs, cats, and humans revealed three morphologically distinct species, which were named S. bovicanis, S. bovifelis, and S. bovihominis. This and post-1972 research on Sarcocystis was reviewed during the same decade; and that account is still a very useful source of information today.

Lifecycle

The heteroxenous (more than one obligatory host) lifecycle of these apicomplexan parasites remained obscure until 1972, when the prey-predator relationship of its definitive and intermediate hosts was recognized. The lifecycles of about 60 of these species are now known.

Merozoites entering muscle cells round up to form metrocytes and initiate sarcocyst formation. Sarcocysts begin as unicellular bodies containing a single metrocyte and through asexual multiplication numerous metrocytes accumulate and the sarcocyst increases in size. As the sarcocyst matures, the small, rounded, noninfectious metrocytes give rise to crescent-shaped bodies called bradyzoites (also known as "bradyzoic merozoites") that are infectious for the definitive host. The time required for maturation varies with the species and may take 2 months or more.

Birds

Although sarcocysts were first reported in the muscles of birds by Kuhn in 1865, the first lifecycle involving a bird (Gallus gallus) and a carnivore (Canis familiaris) was not described until 1977 by Munday et al. In 1986 the first life cycle involving birds as both the definitive (northern goshawk – Accipiter gentilis) and intermediate (Atlantic canary – Serinus canaria) hosts was described by Cerná and Kvasnovská.

Taxonomy

Within the genus, a number of clades have been identified. These include one that contains S. dispersa, S. lacertae, S. mucosa, S. muris, S. neurona, and S. rodentifelis. Frenkelia also groups with this clade.

Species

• Sarcocystis accipitris
• Sarcocystis alces
• Sarcocystis alceslatrans
• Sarcocystis ameivamastigodryasi
• Sarcocystis americana
• Sarcocystis arieticanis
• Sarcocystis asinus
• Sarcocystis atheridis
• Sarcocystis aucheniae
• Sarcocystis bertrami
• Sarcocystis bigemina
• Sarcocystis booliati
• Sarcocystis bovicanis
• Sarcocystis bovifelis
• Sarcocystis bovihominis
• Sarcocystis buffalonis
• Sarcocystis calchasi
• Sarcocystis cameli
• Sarcocystis camelopardalis
• Sarcocystis campestris
• Sarcocystis chamaleonis
• Sarcocystis cernae
• Sarcocystis cervi
• Sarcocystis cervicanis
• Sarcocystis canis
• Sarcocystis capracanis
• Sarcocystis cornixi
• Sarcocystis crotali
• Sarcocystis cruzi
• Sarcocystis cuniculi
• Sarcocystis cymruensis
• Sarcocystis danzani
• Sarcocystis dasypi
• Sarcocystis debonei
• Sarcocystis diminuta
• Sarcocystis dirumpens
• Sarcocystis dispersa
• Sarcocystis dubeyella
• Sarcocystis dubeyi
• Sarcocystis equicanis
• Sarcocystis falcatula
• Sarcocystis fayeri
• Sarcocystis felis
• Sarcocystis fulicae
• Sarcocystis fusiformis
• Sarcocystis gallotiae
• Sarcocystis garnhami
• Sarcocystis gracilis
• Sarcocystis grueneri
• Sarcocystis halieti
• Sarcocystis hoarensis
• Sarcocystis fusiformis
• Sarcocystis gallotiae
• Sarcocystis gerbilliechis
• Sarcocystis gigantea
• Sarcocystis giraffae
• Sarcocystis gongyli
• Sarcocystis gracilis
• Sarcocystis greineri
• Sarcocystis grueneri
• Sarcocystis hardangeri
• Sarcocystis hemioni
• Sarcocystis hemionilatrantis
• Sarcocystis hericanis
• Sarcocystis hircicanis
• Sarcocystis hirsuta
• Sarcocystis hjorti
• Sarcocystis hofmanni
• Sarcocystis hominis
• Sarcocystis horvathi
• Sarcocystis iberica
• Sarcocystis idahoensis
• Sarcocystis inghami
• Sarcocystis jamaicensis
• Sarcocystis jorrini
• Sarcocystis kinosterni
• Sarcocystis kirkpatricki
• Sarcocystis kirmsei
• Sarcocystis klaseriensis
• Sarcocystis kortei
• Sarcocystis lacertae
• Sarcocystis lamacanis
• Sarcocystis leporum
• Sarcocystis levinei
• Sarcocystis lindemanni
• Sarcocystis lindsayi
• Sarcocystis linearis
• Sarcocystis markusi
• Sarcocystis medusiformis
• Sarcocystis melis
• Sarcocystis mephitisi
• Sarcocystis miescheriana
• Sarcocystis mihoensis
• Sarcocystis mitrani
• Sarcocystis mongolica
• Sarcocystis montanaensis
• Sarcocystis morae
• Sarcocystis mucosa
• Sarcocystis moulei
• Sarcocystis murinotechis
• Sarcocystis muris
• Sarcocystis muriviperae
• Sarcocystis neotomafelis
• Sarcocystis nesbitti
• Sarcocystis neurona
• Sarcocystis odoi
• Sarcocystis odocoileocanis
• Sarcocystis ovicanis
• Sarcocystis ovifelis
• Sarcocystis oviformis
• Sarcocystis ovalis
• Sarcocystis phacochoeri
• Sarcocystis phoeniconaii
• Sarcocystis pilosa
• Sarcocystis podarcicolubris
• Sarcocystis poephagi
• Sarcocystis poephagicanis
• Sarcocystis porcifelis
• Sarcocystis porcihominis
• Sarcocystis rangi
• Sarcocystis rangiferi
• Sarcocystis rauschorum
• Sarcocystis rileyi
• Sarcocystis rodentifelis
• Sarcocystis roudabushi
• Sarcocystis scandinavica
• Sarcocystis sebeki
• Sarcocystis sibirica
• Sarcocystis sigmodontis
• Sarcocystis silva
• Sarcocystis singaporensis
• Sarcocystis speeri
• Sarcocystis stehlinii
• Sarcocystis stenodactylicolubris
• Sarcocystis strixi
• Sarcocystis suicanis
• Sarcocystis suihominis
• Sarcocystis sulawesiensis
• Sarcocystis sybillensis
• Sarcocystis tarandi
• Sarcocystis tarandivulpes
• Sarcocystis tenella
• Sarcocystis tilopodi
• Sarcocystis turcicii
• Sarcocystis turdi
• Sarcocystis ursusi
• Sarcocystis venatoria
• Sarcocystis villivilliso
• Sarcocystis wapiti
• Sarcocystis zamani

Evolution

These protozoa are being increasingly well studied in mammals, birds and reptiles. They do not appear to infect mammals of the superorder Afrotheria and infect only two species of the Xenarthra. Because of this pattern, the genus may have evolved in the Northern Hemisphere from a pre-existing protozoan species that infected mammals.

Clinical: Human

Epidemiology

Although human intestinal infection is common, extraintestinal human sarcocystosis is considered to be rare.

Stool examinations in Thai laborers showed that Sarcocystis infection had a high prevalence of around 23%, reflecting ingestion of raw or undercooked meat. Virtually all cases appeared to be asymptomatic. A study of 100 human tongues obtained post mortem in Malaya revealed an infection rate of 21%. No sex difference was found and the age range was 16 to 57 years (mean 37.7 years).

A non-enteric outbreak affecting 93 people was reported in 2012 in Malaysia. Sarcocystis nesbitti was confirmed to be the cause in several cases.

Events occurring within animals

Between the years 1992 and 1996, an investigation was conducted where 605 sheep, 826 goats, 1080 cattle, 580 water buffaloes and 36 camels had been slaughtered. The event happened in the Baghdad area in Iraq, the research used naked eye examination for macroscopic Sarcocysts, and peptic digestion, muscle squash, squeezing methods and indirect fluorescent antibody tests for microscopic types. Dogs had also been used in the trials as well when they had consumed cysts containing the infectious parasite or any other microscopic lifeform.

The prevalence of these parasitic lifeforms including Sarcocysts(Sarcocystis) was as follows from the results, the macroscopic cysts were 4.1, 33.6, 0.2, 15.6 and 0, and of the microscopic type, 97.0, 97.4, 97.8, 82.9 and 91.6 for the above-mentioned hosts. The most effective method was peptic digestion, giving a 93.3% rate, fluorescent antibody test (IFAT) (88.6%), squeezing (81.3%), and muscle squash (81.2%). And as for the dogs, each one had shed about a total of 150-120 million sporocysts.

Route of infection

Intestinal infection occurs when raw or undercooked meat is ingested. Contaminated water might be a source of very rare human extraintestinal infection (it is not possible for water to be the origin of a gut infection), but this remains a theoretical possibility. Fecal matter is also another way of transportation from one host to another for the parasitic lifeform.

Prevention

Infection can be prevented by cooking the meat before eating. Alternatively, freezing the meat at −5 °C for several days before ingestion kills the sporocysts.

Clinical: Nonhuman

Sarcocysts within pig skeletal muscle: Note the readily visible striated border.

Four recognised species infect cattle: S. bovifelis, S. bovihominis (S. hominis), S. cruzi (S. bovicanis), and S. hirsuta. S. cruzi is the only species known to be pathogenic in cattle. Several clinical syndromes have been reported in connection with this parasite: eosinophilic myositis; abortions, stillbirths, and deaths in pregnant cows; two cases of necrotic encephalitis in heifers have also been reported. Typical clinical signs of acute bovine sarcocystosis are: anorexia, pyrexia (42 °C or more), anemia, cachexia, enlarged palpable lymph nodes, excessive salivation, and loss of hair at the tip of the tail.

Sheep may be infected by four recognized species of Sarcocystis: S. arieticanis and S. tenella (S. ovicanis) are pathogenic; S. gigantea (S. ovifelis) and S. medusiformis are nonpathogenic. Infection with these parasites is common in the US with over 80% of sheep examined showing evidence of infection. S. arieticanis and S. tenella both produce extraintestinal disease. Anemia, anorexia, ataxia, and abortions are the chief clinical signs. Myositis with flaccid paralysis has been reported as a consequence of infection. Ovine protozoan myeloencephalitis is a recognised syndrome that may occur in outbreaks. The usual pathological findings in such cases are multifocal spinal cord white matter oedema and necrosis, glial nodules and mild to moderate nonsuppurative encephalomyelitis. The diagnosis may be established finding protozoan bodies (12.7–23.0 μm) that stain immunocytochemically for Sarcocystis epitopes.

Five species infect horses: S. asinus, S. bertrami, S. equicanis, S. fayeri, and S. neurona (S. falcatula). All use canids as definitive hosts; transplacental infection has also been reported. S. neurona causes equine protozoal myeloencephalitis. Exposure to this parasite appears to be common in the United States, with serological surveys indicating that 50–60% percent of all horses in the Midwest United States have been exposed to it. Clinical signs include gait abnormalities including ataxia, knuckling, and crossing over. Muscle atrophy, usually unilateral, may occur. The lesions are typically focal. Brain stem involvement is common. Depression, weakness, head tilt, and dysphagia also occur.

Fatal infection of an alpaca (Lama pacos) with an unnamed species has been reported. Findings included disseminated eosinophilic myositis, abortion, and haemoabdomen. The myositis was associated with haemorrhage, necrosis, and degeneration. Infection by S. tilopodi of muscle tissue in the guanaco has been reported.

S. hemionilatrantis infects mule deer. Death from experimental inoculation has been reported.

These parasites can also infect birds, producing three different clinical forms: an acute pulmonary disease, muscular disease, and neurological disease. Symptoms include lethargy, shortness of breath, tail bobbing, yellow-tinted droppings, and sudden death. The presence of the cysts in the muscle of wild birds is known as "rice breast".

Incidence in animals

H&E micrograph showing Sarcocystis in a 3-year-old sheep cardiac muscle tissue (40X)

Infection with Sarcocystis is common. Rates in pigs vary: 18% in Iowa, 27% in the Philippines, 43% in Spain, 57% in Uruguay, and 68% in India The infection rate in sheep is commonly above 90%. Camels have a similarly high incidence of infection. Rates above 80% are known in cattle and goats. The incidence in water buffaloes, yak and hainag exceeds 80% while the incidence in horses, donkeys, and chickens is lower.

Diagnosis

Microscopy

Oocysts with two sporocysts or individual sporocysts in human feces are diagnostic of intestinal infection. These first appear 14 to 18 days after ingesting beef (S. hominis), and 11 to 13 days after ingesting pork (S. suihominis). Flotation based on high-density solutions incorporating sodium chloride, cesium chloride, zinc sulfate, sucrose, Percoll, Ficoll-Hypaque, or other such density gradient media is preferred to formalin-ethyl acetate or other sedimentation methods. Sporocysts of S. hominis average 9.3 by 14.7 μm and those of S. suihominis average 10.5 by 13.5 μm. Because of the overlap in size, size alone is not reliable as a diagnostic criterion of the species. Confirmatory staining with the periodic acid-Schiff (PAS) can be performed, as the walls stain positively. Heated safranin + methylene blue has been used for staining, as well. PCR amplification of the rRNA may also be used.

Differential diagnosis

Several other genera of heteroxenous and cyst-forming coccidia are known, including Besnoitia, Cystoisospora, Frenkelia, Hammondia, Neospora and Toxoplasma. Related but monoxenous spore-forming genera include Isospora. Differentiating these genera from Sarcocystis in diagnostic material may be difficult without immunochemical stains.

Treatment

Current treatments are not entirely satisfactory. Amprolium (100 mg/kg, daily for 30 days), fed prophylactically, reduced illness in cattle inoculated with S. cruzi. Prophylactic administration of amprolium or salinomycin also protected experimentally infected sheep.

In horses, treatment has been confined to dihydrofolate reductase inhibitors such as the sulfonamides and pyrimethamine. Sulfadiazine (20 mg/kg orally) once or twice a day is a commonly used. Infected horses should also be placed on pyrimethamine at the dose of 1.0 mg/kg given once a day orally for 120 days or longer. Diclazuril and toltrazuril and other coccidiostats are being evaluated to treat EPM.

Since infection is rarely symptomatic, treatment is rarely required. No trials have been published, so treatment remains empirical. Amprolium and salinomycin were effective in preventing severe illness and death in experimentally infected calves and lambs. These agents have not been tried in humans to date.

Used to treat neurocysticercosis, an infection of the nervous system caused by pork tapeworms.

Muscle Sarcocystis is a parasitic infection causing muscle inflammation, pain, and weakness. Diagnosis is difficult and may require a biopsy. Albendazole has been effective in some cases. Albendazole is a medication used to treat parasitic infections by disrupting the parasites' ability to absorb nutrients, leading to their elimination. It is effective against infections caused by worms and some protozoa, including conditions like tapeworms, roundworms, and muscle Sarcocystis.

While Albendazole has been used to deter Sarcocystis, it is not a definitive cure, often used with combinations of other medicines such as prednisone, cotrimoxazole, and methotrexate.

See also

• Equine protozoal myeloencephalitis

External links

Classification	D ICD-11: 1A34

• Sarcocystis at the US National Library of Medicine Medical Subject Headings (MeSH)
• Sarcocystis genome project
• Review: "Sarcocystis spp. in human infections". Clin. Microbiol. Rev. 17 (4): 894–902, table of contents. 2004. doi:10.1128/CMR.17.4.894-902.2004. PMID 15489353. 

Wikidata ☰ Q2658061 entry