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''Sarcocystis'' is a
genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...
of
protozoa Protozoa (singular: protozoan or protozoon; alternative plural: protozoans) are a group of single-celled eukaryotes, either free-living or parasitic, that feed on organic matter such as other microorganisms or organic tissues and debris. Histo ...
n
parasite Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson h ...
s, with many species infecting
mammal Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur ...
s,
reptile Reptiles, as most commonly defined are the animals in the class Reptilia ( ), a paraphyletic grouping comprising all sauropsids except birds. Living reptiles comprise turtles, crocodilians, squamates ( lizards and snakes) and rhynchocephalia ...
s and
bird Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweig ...
s. Its name is dervived from
Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...
''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 In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriat ...
are in this genus. Revision of the taxonomy of the genus is ongoing, and all the currently recognised species may be a much smaller number of species that can infect multiple hosts.


History

The organism was first recognised in a
mouse A mouse ( : mice) is a small rodent. Characteristically, mice are known to have a pointed snout, small rounded ears, a body-length scaly tail, and a high breeding rate. The best known mouse species is the common house mouse (''Mus musculus' ...
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 A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately fr ...
or protozoa was unclear . This uncertainty was resolved in 1967 when electron microscopic studies showed that they were protozoa, related to ''
Toxoplasma ''Toxoplasma gondii'' () is an obligate intracellular parasitic protozoan (specifically an apicomplexan) that causes toxoplasmosis. Found worldwide, ''T. gondii'' is capable of infecting virtually all warm-blooded animals, but felids, such as ...
'' and ''
Eimeria ''Eimeria'' is a genus of apicomplexan parasites that includes various species capable of causing the disease coccidiosis in animals such as cattle, poultry and smaller ruminants including sheep and goats. ''Eimeria'' species are considered to be ...
''. 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
oocyst Apicomplexans, a group of intracellular parasites, have life cycle stages that allow them to survive the wide variety of environments they are exposed to during their complex life cycle. Each stage in the life cycle of an apicomplexan organism is ...
s. 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 The Apicomplexa (also called Apicomplexia) are a large phylum of parasitic alveolates. Most of them possess a unique form of organelle that comprises a type of non-photosynthetic plastid called an apicoplast, and an apical complex structure. The ...
parasite Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson h ...
s remained obscure until 1972, when the prey-predator relationship of its definitive and intermediate hosts was recognised. The lifecycles of about 60 of these species are now known. In outline,
gametogony Apicomplexans, a group of intracellular parasites, have life cycle stages that allow them to survive the wide variety of environments they are exposed to during their complex life cycle. Each stage in the life cycle of an apicomplexan organism is ...
and
sporogony Apicomplexans, a group of intracellular parasites, have life cycle stages that allow them to survive the wide variety of environments they are exposed to during their complex life cycle. Each stage in the life cycle of an apicomplexan organism is ...
occur in the
intestine The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the digestive system that leads from the mouth to the anus. The GI tract contains all the major organs of the digestive system, in humans an ...
of the definitive host, while both
schizogony Fission, in biology, is the division of a single entity into two or more parts and the regeneration of those parts to separate entities resembling the original. The object experiencing fission is usually a cell, but the term may also refer to how ...
, which occurs in various tissues, and the formation of sarcocysts (containing bradyzoites and metrocytes) occurs principally in the
muscle Skeletal muscles (commonly referred to as muscles) are organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other types of mus ...
s of the intermediate host. In some cases, a single species may act as both the definitive and intermediate host.
Oocysts Apicomplexans, a group of intracellular parasites, have life cycle stages that allow them to survive the wide variety of environments they are exposed to during their complex life cycle. Each stage in the life cycle of an apicomplexan organism is ...
are passed in the
feces Feces ( or faeces), known colloquially and in slang as poo and poop, are the solid or semi-solid remains of food that was not digested in the small intestine, and has been broken down by bacteria in the large intestine. Feces contain a rela ...
of an infected definitive host. The oocyst undergoes sporogony, creating two sporocysts. These sporocysts of ''Sarcocystis'' characteristically contain four sporozoites and measure approximately 15–19 by 8–10 μm. Oocysts of ''Sarcocystis'' are thin-walled and easily break open. The result is that sporocysts recovered from feces outnumber intact oocysts. Intermediate hosts such as
cattle Cattle (''Bos taurus'') are large, domesticated, cloven-hooved, herbivores. They are a prominent modern member of the subfamily Bovinae and the most widespread species of the genus '' Bos''. Adult females are referred to as cows and adult ...
or pigs then ingest sporocysts. Sporozoites are released in the body and migrate to vessels, where they undergo the first two generations of asexual reproduction. These rounds result in the development of meronts. This stage lasts about 15 to 16 days after ingestion of sporocysts. Merozoites emerge from the second-generation meronts and enter the mononucleated cells, where they develop by endodyogeny. Subsequent generations of merozoites develop downstream in the direction of blood flow to arterioles, capillaries, venules, and veins throughout the body, subsequently developing into the final asexual generation in muscles. 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. In species in which symptoms develop, these typically occur 20–40 days after ingestion of sporocysts and during the subsequent migration of sporozoites through the body vessels. Acute lesions (oedema, hemorrhages, and necrosis) develop in the affected tissues. The parasite has a predilection for skeletal muscle (myositis), cardiac muscle (petechial hemorrhages of cardiac muscle and serosae), and lymph nodes (oedema, necrosis, and hemorrhage). These lesions are associated with maturation of second generation of meronts within the endothelial and subendothelials cells. Occasionally mononuclear infiltration or hyperemia has been observed in the lamina propria of the small intestine. After the acute phase, cysts may be found in various muscular tissues, generally without pathology. Once the intermediate host is eaten by the definitive host, such as a dog or human, the parasite undergoes sexual reproduction within the gut to create macrogamonts and microgamonts. Most definitive hosts do not show any clinical signs or symptoms. Fusion of a macrogamont and a microgamont creates a
zygote A zygote (, ) is a eukaryotic cell formed by a fertilization event between two gametes. The zygote's genome is a combination of the DNA in each gamete, and contains all of the genetic information of a new individual organism. In multicell ...
, which develops into an oocyst. The oocyst is passed through the faeces, completing the lifecycle. A second lifecycle has more recently been described whereby
carnivore A carnivore , or meat-eater (Latin, ''caro'', genitive ''carnis'', meaning meat or "flesh" and ''vorare'' meaning "to devour"), is an animal or plant whose food and energy requirements derive from animal tissues (mainly muscle, fat and other s ...
s and
omnivore An omnivore () is an animal that has the ability to eat and survive on both plant and animal matter. Obtaining energy and nutrients from plant and animal matter, omnivores digest carbohydrates, protein, fat, and fiber, and metabolize the nu ...
s pass the infectious stages in their faeces. Ingestion of this material may lead to successful infection of the ingesting animal.


Birds

Although sarcocysts were first reported in the muscles of birds by Kuhn in 1865, the first lifecycle involving a bird (''
Gallus gallus The red junglefowl (''Gallus gallus'') is a tropical bird in the family Phasianidae. It ranges across much of Southeast Asia and parts of South Asia. It was formerly known as the Bankiva or Bankiva Fowl. It is the species that gave rise to the ...
'') and a carnivore (''
Canis familiaris The dog (''Canis familiaris'' or ''Canis lupus familiaris'') is a domesticated descendant of the wolf. Also called the domestic dog, it is derived from the extinct Pleistocene wolf, and the modern wolf is the dog's nearest living relative. Do ...
'') 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

The taxonomy of this genus and its relationship to other protozoal genera are currently under investigation. Related genera include: ''
Besnoitia ''Besnoitia'' is a genus of apicomplexan parasites. Life cycle The life cycle of many of the species in this genus are not known. The life cycle may be complex with various intermediate hosts and vectors including ''Stomoxys'' and ''Tabanidae ...
'', '' Caryospora'', ''
Cystoisospora ''Cystoisospora'' is a genus of parasitic alveolates belonging to the phylum Apicomplexa. Taxonomy This genus was originally created by J. K. Frenkel in 1977. Its use was discontinued but was resurrected in 2005. This genus currently includes sp ...
'', ''
Frenkelia ''Frenkelia'' is a genus of parasites in the phylum Apicomplexa. The species in this genus infect the gastrointestinal tracts of birds of prey (definitive hosts) and the tissues of small rodents (intermediate hosts). Taxonomy Species of this ...
'', ''
Isospora ''Isospora'' is a genus of internal parasites in the subclass Coccidia. It is responsible for the condition isosporiasis, which causes acute, non-bloody diarrhoea in immunocompromised individuals. Taxonomy At least 248 species were originall ...
'', ''
Hammondia ''Hammondia'' is a genus of parasitic alveolates in the phylum Apicomplexa. History This genus was created in 1975. Before this date the species of this genus were confused with '' Toxoplasma gondii'' to which they are closely related. The ca ...
'', ''
Hyaloklossia ''Hyaloklossia'' is a genus of parasitic alveolates in the phylum Apicomplexa. Only one species in this genus is currently recognised - ''Hyaloklossia lieberkuehni''. History This parasites of this genus was first observed by Lieberkuhn in 185 ...
'', '' Lankesterella'', ''
Neospora ''Neospora'' is a single celled parasite of livestock and companion animals. It was not discovered until 1984 in Norway, where it was found in dogs. Neosporosis, the disease that affects cattle and companion animals, has a worldwide distributio ...
'', and ''
Toxoplasma ''Toxoplasma gondii'' () is an obligate intracellular parasitic protozoan (specifically an apicomplexan) that causes toxoplasmosis. Found worldwide, ''T. gondii'' is capable of infecting virtually all warm-blooded animals, but felids, such as ...
''. ''Sarcocystis'' is the largest genus within the family Sarcocystidae and consists of species that infect a range of animals, including mammals, birds, and reptiles. ''Frenkelia'', another genus within this family, consists of parasites that use rodents as intermediate hosts and birds of prey as definitive hosts. ''Besnoitia'', ''Hammondia'', ''Neospora'', and ''Toxoplasma'' apparently form a single
clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English ter ...
. Within this clade, ''Toxoplasma'' and ''Neospora'' appear to be sister clades. ''Isospora'' also appears to belong to this clade and this clade is a sister to ''Sarcocystis''. ''Frenkelia'' appears to be very closely related to ''Sarcocystis''. Several molecular studies have suggested that ''Frenkelia'' is actually a species of ''Sarcocystis''. This genus was distinguished from ''Sarcocystis'' on the basis of its tendency to encyst within the
brain A brain is an organ (biology), organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It is located in the head, usually close to the sensory organs for senses such as Visual perception, vision. I ...
rather than within muscle. This distinction may not be taxonomically valid. 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 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 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 Afrotheria ( from Latin ''Afro-'' "of Africa" + ''theria'' "wild beast") is a clade of mammals, the living members of which belong to groups that are either currently living in Africa or of African origin: golden moles, elephant shrews (also k ...
and infect only two species of the
Xenarthra Xenarthra (; from Ancient Greek ξένος, xénos, "foreign, alien" + ἄρθρον, árthron, "joint") is a major clade of placental mammals native to the Americas. There are 31 living species: the anteaters, tree sloths, and armadillos. ...
. Because of this pattern, the genus may have evolved in the Northern Hemisphere from a pre-existing protozoan species that infected mammals. Alternatively, because a number of Australian
marsupials Marsupials are any members of the mammalian infraclass Marsupialia. All extant marsupials are endemic to Australasia, Wallacea and the Americas. A distinctive characteristic common to most of these species is that the young are carried in a po ...
are also infected by this genus, marsupials may have been the original hosts of this genus and the parasites were spread to the Northern Hemisphere by birds. A third possibility is that the genus originally infected birds and was spread world wide by these hosts. A final possibility because of the existence of lifecycles where both the intermediate and final hosts are reptiles, the genus may have originated in reptiles and spread from there to other genera. The resolution of this question awaits the outcome of further molecular studies.


Clinical: Human

Infection with ''Sarcocystis'' is known as sarcosporidiosis or sarcocystosis. Because of initial confusion over the nature of this parasite, the organism in the intestine was originally referred to as ''Isospora hominis'' (as seen in older literature).


Epidemiology

Although human intestinal infection is common, extraintestinal human sarcocystosis is considered to be rare. The extremes of age reported to date are a 26-day-old infant and a 75-year-old man. Infections have been reported from
Africa Africa is the world's second-largest and second-most populous continent, after Asia in both cases. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 6% of Earth's total surface area ...
,
Europe Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a Continent#Subcontinents, subcontinent of Eurasia ...
(
Germany Germany,, officially the Federal Republic of Germany, is a country in Central Europe. It is the second most populous country in Europe after Russia, and the most populous member state of the European Union. Germany is situated betwee ...
,
Spain , image_flag = Bandera de España.svg , image_coat = Escudo de España (mazonado).svg , national_motto = '' Plus ultra'' (Latin)(English: "Further Beyond") , national_anthem = (English: "Royal March") , ...
and
Poland Poland, officially the Republic of Poland, is a country in Central Europe. It is divided into 16 administrative provinces called voivodeships, covering an area of . Poland has a population of over 38 million and is the fifth-most populou ...
), the
United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country Continental United States, primarily located in North America. It consists of 50 U.S. state, states, a Washington, D.C., ...
(
California California is a state in the Western United States, located along the Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the most populous U.S. state and the 3rd largest by area. It is also the m ...
), Central and
South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the sou ...
,
China China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's List of countries and dependencies by population, most populous country, with a Population of China, population exceeding 1.4 billion, slig ...
,
India India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the List of countries and dependencies by area, seventh-largest country by area, the List of countries and dependencies by population, second-most populous ...
,
Tibet Tibet (; ''Böd''; ) is a region in East Asia, covering much of the Tibetan Plateau and spanning about . It is the traditional homeland of the Tibetan people. Also resident on the plateau are some other ethnic groups such as Monpa people, ...
,
Malaysia Malaysia ( ; ) is a country in Southeast Asia. The federal constitutional monarchy consists of thirteen states and three federal territories, separated by the South China Sea into two regions: Peninsular Malaysia and Borneo's East Mal ...
, and
Southeast Asia Southeast Asia, also spelled South East Asia and South-East Asia, and also known as Southeastern Asia, South-eastern Asia or SEA, is the geographical south-eastern region of Asia, consisting of the regions that are situated south of mainland ...
. 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 There are several kinds of mean in mathematics, especially in statistics. Each mean serves to summarize a given group of data, often to better understand the overall value ( magnitude and sign) of a given data set. For a data set, the '' ar ...
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.


History

The first report of human infection was made in 1868. Although several additional reports were subsequently published, these early descriptions were not considered definitive. The first generally agreed definitive description of this disease was published in 1894 by Baraban and Saint-Remy.Baraban M. Le and Saint-Remy M. G.(1894) Sur un cas de tubes psorospermiques observés chez l'homme. Compt. Rend. Soc. Biol. 46: 231–203 This species was named by Rivolta after Lindemannl in 1898. The cysts in human muscle were considered to belong to a single species, ''S. lindemanni'', and the intestinal form to be ''S. hominis'' (from undercooked beef) or ''S. suihominis'' (from undercooked pork). The
description Description is the pattern of narrative development that aims to make vivid a place, object, character, or group. Description is one of four rhetorical modes (also known as ''modes of discourse''), along with exposition, argumentation, and narra ...
of ''S. lindemanni'' has since been considered to be unsatisfactory and has been declared a ''
nomen nudum In taxonomy, a ''nomen nudum'' ('naked name'; plural ''nomina nuda'') is a designation which looks exactly like a scientific name of an organism, and may have originally been intended to be one, but it has not been published with an adequate desc ...
'' (a name lacking a description). Two species are currently considered to be capable of causing human intestinal infection: ''S. bovihominis'' (''S. hominis'') and ''S. suihominis''. Other species including ''S. nesbitti'' have occasionally been reported as infecting humans extraintestinally.


Route of infection

Intestinal infection occurs when raw or undercooked
meat Meat is animal flesh that is eaten as food. Humans have hunted, farmed, and scavenged animals for meat since prehistoric times. The establishment of settlements in the Neolithic Revolution allowed the domestication of animals such as chic ...
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.


Pathology

The pathology is of two types: a rare invasive form with
vasculitis Vasculitis is a group of disorders that destroy blood vessels by inflammation. Both arteries and veins are affected. Lymphangitis (inflammation of lymphatic vessels) is sometimes considered a type of vasculitis. Vasculitis is primarily caused ...
and
myositis Myositis is a rare disease that involves inflammation of the muscles. This can present with a variety of symptoms such as skin involvement (i.e., rashes), muscle weakness, and other organ involvement. Systemic symptoms such as weight loss, fatigue ...
and an intestinal form that presents with
nausea Nausea is a diffuse sensation of unease and discomfort, sometimes perceived as an urge to vomit. While not painful, it can be a debilitating symptom if prolonged and has been described as placing discomfort on the chest, abdomen, or back of th ...
, abdominal pain, and
diarrhea Diarrhea, also spelled diarrhoea, is the condition of having at least three loose, liquid, or watery bowel movements each day. It often lasts for a few days and can result in dehydration due to fluid loss. Signs of dehydration often begin w ...
. While normally mild and lasting under 48 hours, the intestinal form may occasionally be severe or even life-threatening. The invasive form may involve a wide variety of tissues including lymph nodes, muscles, and the
larynx The larynx (), commonly called the voice box, is an organ in the top of the neck involved in breathing, producing sound and protecting the trachea against food aspiration. The opening of larynx into pharynx known as the laryngeal inlet is about ...
.


Clinical features

In volunteer studies with infected beef, symptoms appeared 3–6 hours after eating. These included anorexia, nausea, abdominal pain, distension, diarrhea, vomiting, dyspnea, and tachycardia. All symptoms were transient and lasted about 36 hours. In a second series, symptoms—abdominal pain, distension, watery diarrhea, and eosinophilia—appeared at 1 week and resolved after 3 weeks. Clinical cases have been associated with acute fever, myalgias, bronchospasm, pruritic rashes, lymphadenopathy, subcutaneous nodules associated with eosinophilia, elevated erythrocyte sedimentation rate, and elevated creatinine kinase levels. Symptoms may last as long as five years. Segmental necrotizing enteritis has been reported on one occasion.


Diagnosis

Definitive diagnosis by
biopsy A biopsy is a medical test commonly performed by a surgeon, interventional radiologist, or an interventional cardiologist. The process involves extraction of sample cells or tissues for examination to determine the presence or extent of a dise ...
of an infected muscle. Sarcocysts are identifiable with
hematoxylin Haematoxylin or hematoxylin (), also called natural black 1 or C.I. 75290, is a compound extracted from heartwood of the logwood tree ('' Haematoxylum campechianum'') with a chemical formula of . This naturally derived dye has been used as ...
and
eosin Eosin is the name of several fluorescent acidic compounds which bind to and form salts with basic, or eosinophilic, compounds like proteins containing amino acid residues such as arginine and lysine, and stains them dark red or pink as a resul ...
. The PAS stain may be helpful, but variable uptake of stain is common. Along with the sarcocysts, inflammatory cells may be found. Other findings include myositis, myonecrosis, perivascular and interstitial inflammation, vasculitis, and eosinophilic myositis.


Treatment

Because infection is rarely symptomatic, treatment is rarely required. No trials have been published, so treatment remains empirical. Agents that have been used include
albendazole Albendazole (also known as albendazolum) is a broad-spectrum anthelmintic and antiprotozoal agent of the benzimidazole type. It is used for the treatment of a variety of intestinal parasite infections, including ascariasis, pinworm infection, ho ...
,
metronidazole Metronidazole, sold under the brand name Flagyl among others, is an antibiotic and antiprotozoal medication. It is used either alone or with other antibiotics to treat pelvic inflammatory disease, endocarditis, and bacterial vaginosis. It is ...
, and cotrimoxazole for myositis.
Corticosteroid Corticosteroids are a class of steroid hormones that are produced in the adrenal cortex of vertebrates, as well as the synthetic analogues of these hormones. Two main classes of corticosteroids, glucocorticoids and mineralocorticoids, are inv ...
s have also been used for symptomatic relief. 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.


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

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;
abortion Abortion is the termination of a pregnancy by removal or expulsion of an embryo or fetus. An abortion that occurs without intervention is known as a miscarriage or "spontaneous abortion"; these occur in approximately 30% to 40% of pre ...
s, stillbirths, and deaths in pregnant cows; two cases of necrotic
encephalitis Encephalitis is inflammation of the brain. The severity can be variable with symptoms including reduction or alteration in consciousness, headache, fever, confusion, a stiff neck, and vomiting. Complications may include seizures, hallucinations ...
in heifers have also been reported. Typical clinical signs of acute bovine sarcocystosis are:
anorexia Anorexia nervosa, often referred to simply as anorexia, is an eating disorder characterized by low weight, food restriction, body image disturbance, fear of gaining weight, and an overpowering desire to be thin. ''Anorexia'' is a term of Gre ...
,
pyrexia Fever, also referred to as pyrexia, is defined as having a temperature above the normal range due to an increase in the body's temperature set point. There is not a single agreed-upon upper limit for normal temperature with sources using va ...
(42 °C or more),
anemia Anemia or anaemia (British English) is a blood disorder in which the blood has a reduced ability to carry oxygen due to a lower than normal number of red blood cells, or a reduction in the amount of hemoglobin. When anemia comes on slowly, t ...
,
cachexia Cachexia () is a complex syndrome associated with an underlying illness, causing ongoing muscle loss that is not entirely reversed with nutritional supplementation. A range of diseases can cause cachexia, most commonly cancer, congestive heart fa ...
, enlarged palpable
lymph node A lymph node, or lymph gland, is a kidney-shaped organ of the lymphatic system and the adaptive immune system. A large number of lymph nodes are linked throughout the body by the lymphatic vessels. They are major sites of lymphocytes that includ ...
s, 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 Paralysis (also known as plegia) is a loss of motor function in one or more muscles. Paralysis can also be accompanied by a loss of feeling (sensory loss) in the affected area if there is sensory damage. In the United States, roughly 1 in 5 ...
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 The spinal cord is a long, thin, tubular structure made up of nervous tissue, which extends from the medulla oblongata in the brainstem to the lumbar region of the vertebral column (backbone). The backbone encloses the central canal of the sp ...
white matter oedema and necrosis, glial nodules and mild to moderate nonsuppurative
encephalomyelitis Encephalomyelitis is inflammation of the brain and spinal cord. Various types of encephalomyelitis include: * '' Acute disseminated encephalomyelitis'' or ''postinfectious encephalomyelitis'', a demyelinating disease of the brain and spinal cord, ...
. The diagnosis may be established finding protozoan bodies (12.7–23.0 μm) that stain immunocytochemically for ''Sarcocystis'' epitopes. Four recognised species infect pigs: ''S. medusiformis'', ''S. meischeriana'' (''S. suicanis''), ''S. porcifelis'', and ''S. suihominis''. ''S. porcifelis'' is pathogenic for pigs causing diarrhea, myositis and lameness. 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 Equine protozoal myeloencephalitis (EPM), is a disease caused by the apicomplexan parasite '' Sarcocystis neurona'' that affects the central nervous system of horses. History EPM was first discovered in the 1960s by the American biologist Dr. Ji ...
. Exposure to this parasite appears to be common in the United States, with
serological survey Serology is the scientific study of serum and other body fluids. In practice, the term usually refers to the diagnostic identification of antibodies in the serum. Such antibodies are typically formed in response to an infection (against a given mi ...
s 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. ''S. fayeri'' may cause myositis in horses. 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 The guanaco (; ''Lama guanicoe'') is a camelid native to South America, closely related to the llama. Guanacos are one of two wild South American camelids, the other being the vicuña, which lives at higher elevations. Etymology 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

Infection with ''Sarcocystis'' is common. Rates in pigs vary: 18% in
Iowa Iowa () is a U.S. state, state in the Midwestern United States, Midwestern region of the United States, bordered by the Mississippi River to the east and the Missouri River and Big Sioux River to the west. It is bordered by six states: Wiscon ...
, 27% in the
Philippines The Philippines (; fil, Pilipinas, links=no), officially the Republic of the Philippines ( fil, Republika ng Pilipinas, links=no), * bik, Republika kan Filipinas * ceb, Republika sa Pilipinas * cbk, República de Filipinas * hil, Republ ...
, 43% in Spain, 57% in
Uruguay Uruguay (; ), officially the Oriental Republic of Uruguay ( es, República Oriental del Uruguay), is a country in South America. It shares borders with Argentina to its west and southwest and Brazil to its north and northeast; while bordering ...
, 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

The diagnosis is usually made ''post mortem'' by examination of the skeletal muscle. In some species, the cysts may be visible to the naked eye (
duck Duck is the common name for numerous species of waterfowl in the family Anatidae. Ducks are generally smaller and shorter-necked than swans and geese, which are members of the same family. Divided among several subfamilies, they are a form ...
s,
mice A mouse ( : mice) is a small rodent. Characteristically, mice are known to have a pointed snout, small rounded ears, a body-length scaly tail, and a high breeding rate. The best known mouse species is the common house mouse (''Mus musculus'' ...
,
rabbit Rabbits, also known as bunnies or bunny rabbits, are small mammals in the family Leporidae (which also contains the hares) of the order Lagomorpha (which also contains the pikas). ''Oryctolagus cuniculus'' includes the European rabbit sp ...
s and
sheep Sheep or domestic sheep (''Ovis aries'') are domesticated, ruminant mammals typically kept as livestock. Although the term ''sheep'' can apply to other species in the genus '' Ovis'', in everyday usage it almost always refers to domesticate ...
), but in most, microscopic examination is required. ''Ante mortem'' diagnosis may be made with the use of dermal sensitivity testing or
complement fixation test The complement fixation test is an immunological medical test that can be used to detect the presence of either specific antibody or specific antigen in a patient's serum, based on whether complement fixation occurs. It was widely used to diagnose ...
s. Muscle biopsy is also diagnostic, but this is much less commonly used.


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 Ribosomal ribonucleic acid (rRNA) is a type of non-coding RNA which is the primary component of ribosomes, essential to all cells. rRNA is a ribozyme which carries out protein synthesis in ribosomes. Ribosomal RNA is transcribed from ribos ...
may also be used.


Cell walls

The walls of the sarcocyst may be helpful in species diagnosis with 24 wall types identified in 62 species. ''S. hominis'' and ''S. suihominis'' both have walls of type 10. The wall of ''S. hominis'' is up to 6 μm thick and appears radially striated from villar protrusions up to 7 μm long. Its bradyzoites are 7 to 9 μm long. The wall of ''S. suihominis'' is 4 to 9μm thick, with villar protrusions up to 13 μm long. Its bradyzoites are 15 μm long.


Differential diagnosis

Several other genera of heteroxenous and cyst-forming coccidia are known, including ''
Besnoitia ''Besnoitia'' is a genus of apicomplexan parasites. Life cycle The life cycle of many of the species in this genus are not known. The life cycle may be complex with various intermediate hosts and vectors including ''Stomoxys'' and ''Tabanidae ...
'', ''
Cystoisospora ''Cystoisospora'' is a genus of parasitic alveolates belonging to the phylum Apicomplexa. Taxonomy This genus was originally created by J. K. Frenkel in 1977. Its use was discontinued but was resurrected in 2005. This genus currently includes sp ...
'', ''
Frenkelia ''Frenkelia'' is a genus of parasites in the phylum Apicomplexa. The species in this genus infect the gastrointestinal tracts of birds of prey (definitive hosts) and the tissues of small rodents (intermediate hosts). Taxonomy Species of this ...
'', ''
Hammondia ''Hammondia'' is a genus of parasitic alveolates in the phylum Apicomplexa. History This genus was created in 1975. Before this date the species of this genus were confused with '' Toxoplasma gondii'' to which they are closely related. The ca ...
'', ''
Neospora ''Neospora'' is a single celled parasite of livestock and companion animals. It was not discovered until 1984 in Norway, where it was found in dogs. Neosporosis, the disease that affects cattle and companion animals, has a worldwide distributio ...
'' and ''
Toxoplasma ''Toxoplasma gondii'' () is an obligate intracellular parasitic protozoan (specifically an apicomplexan) that causes toxoplasmosis. Found worldwide, ''T. gondii'' is capable of infecting virtually all warm-blooded animals, but felids, such as ...
''. Related but
monoxenous Monoxenous development, or monoxeny, characterizes a parasite whose development is restricted to a single host species. The etymology of the terms monoxeny / monoxenous derives from the two ancient Greek words (), meaning "unique", and (), m ...
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
sulfonamide In organic chemistry, the sulfonamide functional group (also spelled sulphonamide) is an organosulfur group with the structure . It consists of a sulfonyl group () connected to an amine group (). Relatively speaking this group is unreactive. ...
s 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 Diclazuril (trade name Vecoxan) is a coccidiostat. See also * Clazuril * Ponazuril * Toltrazuril Toltrazuril is a coccidiostat. See also * Clazuril * Diclazuril Diclazuril (trade name Vecoxan) is a coccidiostat. See also * Clazu ...
and
toltrazuril Toltrazuril is a coccidiostat. See also * Clazuril * Diclazuril Diclazuril (trade name Vecoxan) is a coccidiostat. See also * Clazuril * Ponazuril * Toltrazuril References Antiparasitic agents Nitriles Chlorobenzenes Triaz ...
and other coccidiostats are being evaluated to treat EPM.


Vaccination

No vaccines are currently known. Experimentally inoculated pigs appear to develop a persistent immunity, so a vaccine may be possible.


Host-parasite relations

The parasite's lifecycle typically involves a predator and a prey animal. A single species may infect multiple prey or predator animals. In at least 56 species, definitive and intermediate hosts are known. Many species are named after their recognised hosts. A listing of the known host-parasite relations can be found on the page Sarcocystis: Host-parasite relations.


Notes

''Hoareosporidium'' is now considered a synonym of ''Sarcocystis''. The original type species was ''Sarcocystis miescheriana''. Its description has since been considered less than satisfactory and ''S. muris'' has been proposed as the type species. ''S. turdi'' may not be a valid species. ''Isospora bigemina'' has been reclassified as ''Sarcocystis bigemina''. ''Isospora hominis'' has been reclassified as ''Sarcocystis hominis''. ''S. bovihominis'' is a synonym of ''S. hominis''. ''S. cruzi'' is a synonym of ''S. bovicanis''. ''S. gigantea'' is a synonym of ''S. ovifelis''. ''S. hirsuta'' is a synonym of ''S. bovifelis''. ''S. idahoensis'' and ''S. roudabushi'' may be the same species. ''S. miescheriana'' is a synonym of ''S. suicanis''. ''S. neurona'' is a junior synonym of ''S. falcatula''. ''S. neuroma'' is the more commonly used name for this species. ''S. poephagi'' may be the same species as ''S. hirsuta''. ''S. poephagicanis'' may be the same species as ''S. cruzi''. ''S. tenella'' is a synonym of ''S. ovicanis''.


See also

*
Equine protozoal myeloencephalitis Equine protozoal myeloencephalitis (EPM), is a disease caused by the apicomplexan parasite '' Sarcocystis neurona'' that affects the central nervous system of horses. History EPM was first discovered in the 1960s by the American biologist Dr. Ji ...


References


External links

*
''Sarcocystis'' genome project
* Review: {{Taxonbar, from=Q2658061 Apicomplexa genera Conoidasida Rodent-carried diseases Parasitic diseases Parasites of equines Parasites of mammals Parasitic diseases associated with beef and pork consumption