Sarcocystis
Encyclopedia
Sarcocystis is a genus
of protozoa
. Species in this genus infect reptile
s, bird
s and mammal
s. The name is dervived from Greek
: sarx = flesh and kystis = bladder.
There are about 130 recognised species
in this genus. Revision of the taxonomy of this genus is ongoing, and it is possible that all the currently recognised species may in fact be a single species or much smaller number of species that can infect multiple hosts.
While the majority of the species in this genus infect mammals, about a dozen are known to infect snakes.
by Miescher in 1843. His findings were not recognised as a protist initially 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 meischeriana was proposed to identify them.
Initially it was unclear whether these organisms were fungi or protozoa. This uncertainty was resolved in 1967 when electron microscopic studies showed that these organism were protozoa related to Toxoplasma and Eimeria
. The life cycle remained unknown until 1970 when bradyzoites from sarcocysts in bird muscles were inoculated into cultured mammalian cells and underwent development into sexual stages and oocysts. Transmission studies with the three morphotypes found in cattle then considered a single species - Sarcoplasma fusiformis - in dogs, cats and humans revealed that these were three different species now named Sarcoplasma bovicanis, Sarcoplasma bovifelis and Sarcoplasma bovihominis.
In outline gametogony and sporogony occur in the intestine
of the definitive host while both schizogony which occurs in various tissues and the formation of sarcocysts (containing bradyzoites and metrocytes) occurs prinicpally in the muscle
s of the intermediate host. In some cases a single species may act as both the definitive and intermediate host.
Oocysts are passed in the feces
of an infected definitive host. The oocyst undergoes sporogony creating two sporocysts. Once this is complete oocyst itself undergoes lysis
releasing the sporocyst
s into the environment. Sporocysts typically contain 4 sporozoites and measure 15-19 by 8-10 micrometres.
An intermediate host such as a cow or pig then ingests a sporocyst. Sporozoites are then released in the body and migrate to vessels where they undergo the first two generation 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 mononucleate 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 that are infections for the definitive host. 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 sign or symptoms. Fusion of a macrogamont and a microgamont creates a zygote
which develops into an oocyst. The oocyst is passed through the faeces completing the life cycle.
A second life cycle has more recently been described whereby carnivore
s and omnivore
s pass the infectious stages in their faeces. Ingestion of this material may lead to successful infection of the ingesting animal.
Related genera include: Besnoitia
, Caryospora
, Cystoisospora, Frenkelia, Isospora
, Hammondia, Hyaloklossia, Lankesterella
, Neospora
and Toxoplasma.
Sarcocystis is the largest genus within the family Sarcocystidae and consists of species which infecting 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.
It appears that Besnoitia, Hammondia, Neospora and Toxoplasma form a single clade
. Within this clade Toxoplasma and Neospora appear to be sister clades. Isospora also appear 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
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.
and infect only two species of the Xenarthra
. Because of this pattern the genus may have evolved in the Northern hemisphere from a preexisting protozoan species that infected mammals.
Alternatively because a number of Australian marsupials 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 life cycles 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.
The extremes of age reported to date are a 26-day-old infant and a 75-year-old man. Infectons have been reported from Africa
, Europe
(Germany
, Spain
and Poland
), the United States
(California
), Central and South America
, China
, India
, Tibet
, Malaysia and Southeast Asia
.
Stool examinations in Thai laborers showed that sarcocystis infection had a prevalence of ~23%. Virtually all cases appeared to be asymptomatic which probably explains the lack of recognition. A study of 100 human tongues obtained at post mortum in Malaya
revealed an infection rate of 21%. There was no sex difference and the age range was 16 to 57 years (mean
37.7 years).
The invasive forms were considered to belong to a single species - S. lindemanni - and the intestinal form due to S. hominis (from undercooked beef) or S. suihominis (from undercooked pork). The description of S. lindemanni has since been considered to be unsatisfactory and has been declared a nomem nudum (a name without a recognised species). Two species currently considered to be capable of causing human infection: S. bovihominis (S. hominis) and S. suihominis.
is ingested. The incubation period is 9–39 days. Human outbreaks have occurred in Europe. Rats are a known carrier.
It has been suggested that contaminated water may be able to cause infection but this presently remains a theoretical possibility.
and myositis
and an intestinal form that presents with nausea
, abdominal pain, and diarrhea
. 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
.
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.
of an infected muscle. Sarcocysts are identifiable with hematoxylin and eosin
. 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.
, metronidazole
and cotrimoxazole for myositis. Corticosteroid
s have also been used for symptomatic relief.
Amprolium
and salinomycin
was effective in preventing severe illness and death in experimentally infected calves and lambs. These agents have not been tried in humans to date.
s, 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 (42C or more), anemia
, cachexia
, enlarged palpable lymph node
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 non-pathogenic. 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 extra intestinal 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 micrometres) 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 utilize 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.
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 hameorrhage, necrosis and degeration. Infection by S. tilopodi of muscle tissue in the Guanaco has been reported.
S. hemionilatrantis infects mule deer. Death from experimental inoculation have 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".
, 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.
The diagnosis is usually made post mortum by examination of the skeletal muscle. In some species the cysts may be visible to the naked eye (ducks, mice, rabbits and sheep) but in most microscopic examination is required. Ante mortum diagnosis may be made with the use of dermal sensitivity testing or complement fixation tests. Muscle biopsy is also diagnostic but this is much less commonly used.
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 micrometres and those of S. suihominis average 10.5 by 13.5 micrometres. 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. PCR amplification of the rRNA may also be used.
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 micrometres thick and appears radially striated from villar protrusions up to 7 micrometres long. Its bradyzoites are 7 to 9 micrometres long. The wall of S. suihominis is 4 to 9 micrometres thick, with villar protrusions up to 13 micrometres long. Its bradyzoites are 15 micrometres long.
In horses treatment has been confined to dihydrofolate reductase inhibitors such as the sulfonamide
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
and Toltrazuril
and other coccidiostats are being evaluated to treat EPM.
A listing of the known host-parasite relations can be found on the page Sarcocystis: Host-parasite relations
.
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.
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
of protozoa
Protozoa
Protozoa are a diverse group of single-cells eukaryotic organisms, many of which are motile. Throughout history, protozoa have been defined as single-cell protists with animal-like behavior, e.g., movement...
. Species in this genus infect reptile
Reptile
Reptiles are members of a class of air-breathing, ectothermic vertebrates which are characterized by laying shelled eggs , and having skin covered in scales and/or scutes. They are tetrapods, either having four limbs or being descended from four-limbed ancestors...
s, bird
Bird
Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...
s and mammal
Mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...
s. The name is dervived from Greek
Greek language
Greek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...
: sarx = flesh and kystis = bladder.
There are about 130 recognised species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
in this genus. Revision of the taxonomy of this genus is ongoing, and it is possible that all the currently recognised species may in fact be a single species or much smaller number of species that can infect multiple hosts.
While the majority of the species in this genus infect mammals, about a dozen are known to infect snakes.
History
The organism was first recognised in a mouseMouse
A mouse is a small mammal belonging to the order of rodents. The best known mouse species is the common house mouse . It is also a popular pet. In some places, certain kinds of field mice are also common. This rodent is eaten by large birds such as hawks and eagles...
by Miescher in 1843. His findings were not recognised as a protist initially and the literature referred to the structures he described as "Miescher's Tubules". Incidentally Miescher's son — Johann Friedrich Miescher — discovered DNA
DNA
Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...
. Similar structures were found in pig
Pig
A pig is any of the animals in the genus Sus, within the Suidae family of even-toed ungulates. Pigs include the domestic pig, its ancestor the wild boar, and several other wild relatives...
muscle in 1865 but these remained unnamed until 1899 when the name Sarcocystis meischeriana was proposed to identify them.
Initially it was unclear whether these organisms were fungi or protozoa. This uncertainty was resolved in 1967 when electron microscopic studies showed that these organism were protozoa related to Toxoplasma and Eimeria
Eimeria
Eimeria is a genus of Apicomplexan parasites that includes various species responsible for the poultry disease coccidiosis. The genus is named for the German zoologist Theodor Eimer...
. The life cycle remained unknown until 1970 when bradyzoites from sarcocysts in bird muscles were inoculated into cultured mammalian cells and underwent development into sexual stages and oocysts. Transmission studies with the three morphotypes found in cattle then considered a single species - Sarcoplasma fusiformis - in dogs, cats and humans revealed that these were three different species now named Sarcoplasma bovicanis, Sarcoplasma bovifelis and Sarcoplasma bovihominis.
Life cycle
The heteroxenous (more than one obligatory host in its life cycle) life cycle of these apicomplexan parasites remained obscure until 1972 when the prey-predator relationship of its definitive and intermediate hosts was recognised. The life cycles of about 60 of these species is now known.In outline gametogony and sporogony occur in the intestine
Intestine
In human anatomy, the intestine is the segment of the alimentary canal extending from the pyloric sphincter of the stomach to the anus and, in humans and other mammals, consists of two segments, the small intestine and the large intestine...
of the definitive host while both schizogony which occurs in various tissues and the formation of sarcocysts (containing bradyzoites and metrocytes) occurs prinicpally in the muscle
Muscle
Muscle is a contractile tissue of animals and is derived from the mesodermal layer of embryonic germ cells. Muscle cells contain contractile filaments that move past each other and change the size of the cell. They are classified as skeletal, cardiac, or smooth muscles. Their function is to...
s of the intermediate host. In some cases a single species may act as both the definitive and intermediate host.
Oocysts are passed in the feces
Feces
Feces, faeces, or fæces is a waste product from an animal's digestive tract expelled through the anus or cloaca during defecation.-Etymology:...
of an infected definitive host. The oocyst undergoes sporogony creating two sporocysts. Once this is complete oocyst itself undergoes lysis
Lysis
Lysis refers to the breaking down of a cell, often by viral, enzymic, or osmotic mechanisms that compromise its integrity. A fluid containing the contents of lysed cells is called a "lysate"....
releasing the sporocyst
Sporocyst
Sporocyst is a common name of a lifecycle stage in two unrelated groups of species:*Apicomplexa parasites: see Apicomplexa lifecycle stages*Trematode flatworms: see Trematode lifecycle stages...
s into the environment. Sporocysts typically contain 4 sporozoites and measure 15-19 by 8-10 micrometres.
An intermediate host such as a cow or pig then ingests a sporocyst. Sporozoites are then released in the body and migrate to vessels where they undergo the first two generation 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 mononucleate 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 that are infections for the definitive host. 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 sign or symptoms. Fusion of a macrogamont and a microgamont creates a zygote
Zygote
A zygote , or zygocyte, is the initial cell formed when two gamete cells are joined by means of sexual reproduction. In multicellular organisms, it is the earliest developmental stage of the embryo...
which develops into an oocyst. The oocyst is passed through the faeces completing the life cycle.
A second life cycle has more recently been described whereby carnivore
Carnivore
A carnivore meaning 'meat eater' is an organism that derives its energy and nutrient requirements from a diet consisting mainly or exclusively of animal tissue, whether through predation or scavenging...
s and omnivore
Omnivore
Omnivores are species that eat both plants and animals as their primary food source...
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 not until 1977 was the first life cycle involving a bird (Gallus gallus) and a carnivore (Canis familiaris) described by Munday et al. In 1986 the first life cycle involving birds as both the definitive (Northern Goshawk) and intermediate (Serinus canaria) hosts was described by Cern and Kvasnovsk.Taxonomy
The taxonomy of this genus and its relationship to other protozoal genera is currently under investigation.Related genera include: Besnoitia
Besnoitia
Besnoitia is a genus of Apicomplexan parasite.- Life cycle :The life cycle of many of the species in this genus are not known but it's probably complex with various intermediate hosts and many vectors...
, Caryospora
Caryospora
Caryospora is a genus of fungi in the family Zopfiaceae....
, Cystoisospora, Frenkelia, Isospora
Isospora
Isospora is a genus of internal parasites classified under Coccidia.It is responsible for the condition isosporiasis.At least 248 species have been described in this genus, but most of them are little studied and it is doubtful whether all should be recognized as distinct species...
, Hammondia, Hyaloklossia, Lankesterella
Lankesterella
Lankesterella is a genus of flowering plants from the orchid family, Orchidaceae.- References :*Pridgeon, A.M., Cribb, P.J., Chase, M.A. & Rasmussen, F. eds. . Genera Orchidacearum 1. Oxford Univ. Press....
, Neospora
Neospora
Neospora is an important pathogen in cattle and dogs. It was not discovered until 1984 in Norway, where it was found in dogs. It is highly transmissible and some herds can have up to a 90% prevalence. Neospora causes abortions in cattle and up to 33% of pregnancies can result in aborted fetuses on...
and Toxoplasma.
Sarcocystis is the largest genus within the family Sarcocystidae and consists of species which infecting 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.
It appears that Besnoitia, Hammondia, Neospora and Toxoplasma form a single clade
Clade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...
. Within this clade Toxoplasma and Neospora appear to be sister clades. Isospora also appear 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
Brain
The brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...
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.
Evolution
These protozoa are mostly found in mammals. They do not appear to infect mammals of the superorder AfrotheriaAfrotheria
Afrotheria is a clade of mammals, the living members of which belong to groups from Africa or of African origin: golden moles, sengis , tenrecs, aardvarks, hyraxes, elephants and sea cows. The common ancestry of these animals was not recognized until the late 1990s...
and infect only two species of the Xenarthra
Xenarthra
The superorder Xenarthra is a group of placental mammals , existent today only in the Americas and represented by anteaters, tree sloths, and armadillos. The origins of the order can be traced back as far as the Paleogene in South America...
. Because of this pattern the genus may have evolved in the Northern hemisphere from a preexisting protozoan species that infected mammals.
Alternatively because a number of Australian marsupials 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 life cycles 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 notes: Human
Infection with this parasite is known as sarcosporidiosis. Because of initial confusion over the taxonomy of this parasite it was originally referred to as Isospora hominis. The older literature may refer to this organism.Epidemiology
Human infection is considered rare with less than one hundred published cases of invasive disease (approximately 46 cases reported by 1990). These figure represent a gross underestimate of the human burden of disease.The extremes of age reported to date are a 26-day-old infant and a 75-year-old man. Infectons have been reported from Africa
Africa
Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...
, Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
(Germany
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...
, Spain
Spain
Spain , officially the Kingdom of Spain languages]] under the European Charter for Regional or Minority Languages. In each of these, Spain's official name is as follows:;;;;;;), is a country and member state of the European Union located in southwestern Europe on the Iberian Peninsula...
and Poland
Poland
Poland , officially the Republic of Poland , is a country in Central Europe bordered by Germany to the west; the Czech Republic and Slovakia to the south; Ukraine, Belarus and Lithuania to the east; and the Baltic Sea and Kaliningrad Oblast, a Russian exclave, to the north...
), the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
(California
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...
), Central and South America
South America
South America is a continent situated in the Western Hemisphere, mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere. The continent is also considered a subcontinent of the Americas. It is bordered on the west by the Pacific Ocean and on the north and east...
, China
China
Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...
, India
India
India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...
, Tibet
Tibet
Tibet is a plateau region in Asia, north-east of the Himalayas. It is the traditional homeland of the Tibetan people as well as some other ethnic groups such as Monpas, Qiang, and Lhobas, and is now also inhabited by considerable numbers of Han and Hui people...
, Malaysia and Southeast Asia
Southeast Asia
Southeast Asia, South-East Asia, South East Asia or Southeastern Asia is a subregion of Asia, consisting of the countries that are geographically south of China, east of India, west of New Guinea and north of Australia. The region lies on the intersection of geological plates, with heavy seismic...
.
Stool examinations in Thai laborers showed that sarcocystis infection had a prevalence of ~23%. Virtually all cases appeared to be asymptomatic which probably explains the lack of recognition. A study of 100 human tongues obtained at post mortum in Malaya
Malay Peninsula
The Malay Peninsula or Thai-Malay Peninsula is a peninsula in Southeast Asia. The land mass runs approximately north-south and, at its terminus, is the southern-most point of the Asian mainland...
revealed an infection rate of 21%. There was no sex difference and the age range was 16 to 57 years (mean
Mean
In statistics, mean has two related meanings:* the arithmetic mean .* the expected value of a random variable, which is also called the population mean....
37.7 years).
Historical details
The first report of human infection was by Lindemannl 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. This species was named by Rivolta after Lindemannl in 1898.The invasive forms were considered to belong to a single species - S. lindemanni - and the intestinal form due to S. hominis (from undercooked beef) or S. suihominis (from undercooked pork). The description of S. lindemanni has since been considered to be unsatisfactory and has been declared a nomem nudum (a name without a recognised species). Two species currently considered to be capable of causing human infection: S. bovihominis (S. hominis) and S. suihominis.
Route of infection
Infection occurs when undercooked meatMeat
Meat is animal flesh that is used as food. Most often, this means the skeletal muscle and associated fat and other tissues, but it may also describe other edible tissues such as organs and offal...
is ingested. The incubation period is 9–39 days. Human outbreaks have occurred in Europe. Rats are a known carrier.
It has been suggested that contaminated water may be able to cause infection but this presently remains a theoretical possibility.
Pathology
The pathology is of two types: a rare invasive form with vasculitisVasculitis
Vasculitis refers to a heterogeneous group of disorders that are characterized by inflammatory destruction of blood vessels. Both arteries and veins are affected. Lymphangitis is sometimes considered a type of vasculitis...
and myositis
Myositis
Myositis is a general term for inflammation of the muscles. Many such conditions are considered likely to be caused by autoimmune conditions, rather than directly due to infection It is also a documented side effect of the lipid-lowering drugs statins and fibrates.Elevation of creatine kinase in...
and an intestinal form that presents with nausea
Nausea
Nausea , is a sensation of unease and discomfort in the upper stomach with an involuntary urge to vomit. It often, but not always, precedes vomiting...
, abdominal pain, and diarrhea
Diarrhea
Diarrhea , also spelled diarrhoea, is the condition of having three or more loose or liquid bowel movements per day. It is a common cause of death in developing countries and the second most common cause of infant deaths worldwide. The loss of fluids through diarrhea can cause dehydration and...
. 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
Larynx
The larynx , commonly called the voice box, is an organ in the neck of amphibians, reptiles and mammals involved in breathing, sound production, and protecting the trachea against food aspiration. It manipulates pitch and volume...
.
Clinical features
In volunteer studies with infected beef symptoms appeared 3–6 hours after eating. These included anorexia, nausea, abdominal pain, distension, diarrhea, vomiting, dyspnoea 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 biopsyBiopsy
A biopsy is a medical test involving sampling of cells or tissues for examination. It is the medical removal of tissue from a living subject to determine the presence or extent of a disease. The tissue is generally examined under a microscope by a pathologist, and can also be analyzed chemically...
of an infected muscle. Sarcocysts are identifiable with hematoxylin and eosin
Eosin
Eosin is a fluorescent red dye resulting from the action of bromine on fluorescein. It can be used to stain cytoplasm, collagen and muscle fibers for examination under the microscope. Structures that stain readily with eosin are termed eosinophilic....
. 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. There have been no published trials so treatment remains empirical. Agents that have been used include albendazoleAlbendazole
Albendazole, marketed as Albenza, Eskazole, Zentel and Andazol, is a member of the benzimidazole compounds used as a drug indicated for the treatment of a variety of worm infestations. Although this use is widespread in the United States, the U.S. Food and Drug Administration has not approved...
, metronidazole
Metronidazole
Metronidazole is a nitroimidazole antibiotic medication used particularly for anaerobic bacteria and protozoa. Metronidazole is an antibiotic, amebicide, and antiprotozoal....
and cotrimoxazole for myositis. Corticosteroid
Corticosteroid
Corticosteroids are a class of steroid hormones that are produced in the adrenal cortex. Corticosteroids are involved in a wide range of physiologic systems such as stress response, immune response and regulation of inflammation, carbohydrate metabolism, protein catabolism, blood electrolyte...
s have also been used for symptomatic relief.
Amprolium
Amprolium
Amprolium is a coccidiostat used in poultry.-Synthesis:The drug is a thiamine analogue and blocks the thiamine transporter of Eimeria species...
and salinomycin
Salinomycin
Salinomycin is an antibacterial and coccidiostat ionophore therapeutic drug.- Use in cancer :Salinomycin has been shown by Piyush Gupta et al. of the Massachusetts Institute of Technology and the Broad Institute to kill breast cancer stem cells at least 100 times more effectively than another...
was 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 -5C for several days before ingestion will kill the sporocysts.Clinical notes: Other
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. A number of clinical syndromes have been reported in connection with this parasite: eosinophilic myositis; abortionAbortion
Abortion is defined as the termination of pregnancy by the removal or expulsion from the uterus of a fetus or embryo prior to viability. An abortion can occur spontaneously, in which case it is usually called a miscarriage, or it can be purposely induced...
s, stillbirths and deaths in pregnant cows; two cases of necrotic encephalitis
Encephalitis
Encephalitis is an acute inflammation of the brain. Encephalitis with meningitis is known as meningoencephalitis. Symptoms include headache, fever, confusion, drowsiness, and fatigue...
in heifers have also been reported. Typical clinical signs of acute bovine sarcocystosis are: anorexia
Anorexia (symptom)
Anorexia is the decreased sensation of appetite...
, pyrexia (42C or more), anemia
Anemia
Anemia is a decrease in number of red blood cells or less than the normal quantity of hemoglobin in the blood. However, it can include decreased oxygen-binding ability of each hemoglobin molecule due to deformity or lack in numerical development as in some other types of hemoglobin...
, cachexia
Cachexia
Cachexia or wasting syndrome is loss of weight, muscle atrophy, fatigue, weakness, and significant loss of appetite in someone who is not actively trying to lose weight...
, enlarged palpable lymph node
Lymph node
A lymph node is a small ball or an oval-shaped organ of the immune system, distributed widely throughout the body including the armpit and stomach/gut and linked by lymphatic vessels. Lymph nodes are garrisons of B, T, and other immune cells. Lymph nodes are found all through the body, and act as...
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 non-pathogenic. 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 extra intestinal disease. Anemia, anorexia, ataxia, and abortions are the chief clinical signs. Myositis with flaccid paralysis
Paralysis
Paralysis is loss of muscle function for one or more muscles. Paralysis can be accompanied by a loss of feeling in the affected area if there is sensory damage as well as motor. A study conducted by the Christopher & Dana Reeve Foundation, suggests that about 1 in 50 people have been diagnosed...
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
Spinal cord
The spinal cord is a long, thin, tubular bundle of nervous tissue and support cells that extends from the brain . The brain and spinal cord together make up the central nervous system...
white matter oedema and necrosis, glial nodules and mild to moderate nonsuppurative encephalomyelitis
Encephalomyelitis
Encephalomyelitis is a general term for inflammation of the brain and spinal cord, describing a number of disorders:* Acute disseminated encephalomyelitis or postinfectious encephalomyelitis, a demyelinating disease of the brain and spinal cord, possibly triggered by vaccination or viral...
. The diagnosis may be established finding protozoan bodies (12.7-23.0 micrometres) 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 utilize canids as definitive hosts: transplacental infection has also been reported. S. neurona causes equine protozoal myeloencephalitis
Equine Protozoal Myeloencephalitis
Equine protozoal myeloencephalitis, or EPM, is a disease cause by a protozoal infection of the central nervous system of horses.-History:...
. 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.
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 hameorrhage, necrosis and degeration. Infection by S. tilopodi of muscle tissue in the Guanaco has been reported.
S. hemionilatrantis infects mule deer. Death from experimental inoculation have 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 IowaIowa
Iowa is a state located in the Midwestern United States, an area often referred to as the "American Heartland". It derives its name from the Ioway people, one of the many American Indian tribes that occupied the state at the time of European exploration. Iowa was a part of the French colony of New...
, 27% in the Philippines
Philippines
The Philippines , officially known as the Republic of the Philippines , is a country in Southeast Asia in the western Pacific Ocean. To its north across the Luzon Strait lies Taiwan. West across the South China Sea sits Vietnam...
, 43% in Spain, 57% in Uruguay
Uruguay
Uruguay ,officially the Oriental Republic of Uruguay,sometimes the Eastern Republic of Uruguay; ) is a country in the southeastern part of South America. It is home to some 3.5 million people, of whom 1.8 million live in the capital Montevideo and its metropolitan area...
, 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
There are several other genera of heteroxenous and cyst-forming coccidia 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.The diagnosis is usually made post mortum by examination of the skeletal muscle. In some species the cysts may be visible to the naked eye (ducks, mice, rabbits and sheep) but in most microscopic examination is required. Ante mortum diagnosis may be made with the use of dermal sensitivity testing or complement fixation tests. Muscle biopsy is also diagnostic but this is much less commonly used.
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 micrometres and those of S. suihominis average 10.5 by 13.5 micrometres. 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. PCR amplification of the rRNA may also be used.
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 micrometres thick and appears radially striated from villar protrusions up to 7 micrometres long. Its bradyzoites are 7 to 9 micrometres long. The wall of S. suihominis is 4 to 9 micrometres thick, with villar protrusions up to 13 micrometres long. Its bradyzoites are 15 micrometres long.
Treatment
Current treatments are not entirely satisfactory. Amprolium (100 mg/kg, sid 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
Sulfonamide (medicine)
Sulfonamide or sulphonamide is the basis of several groups of drugs. The original antibacterial sulfonamides are synthetic antimicrobial agents that contain the sulfonamide group. Some sulfonamides are also devoid of antibacterial activity, e.g., the anticonvulsant sultiame...
s and pyrimethamine
Pyrimethamine
Pyrimethamine is a medication used for protozoal infections. It is commonly used as an antimalarial drug , and is also used in the treatment of Toxoplasma gondii infections in immunocompromised patients, such as HIV-positive individuals.-Mechanism of action:Pyrimethamine interferes with...
. 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
Diclazuril is a coccidiostat....
and Toltrazuril
Toltrazuril
Toltrazuril is a coccidiostat....
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 life cycle 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
Sarcocystis: Host-parasite relations
Sarcocystis is a genus of parasitic protozoa. Species in this genus infect reptiles, birds and mammals. The name is derived from Greek: sarkos = flesh and kystis = bladder.There are about 130 recognised species in this genus...
.
Genome
S. neurona is the subject of an on-going (as of September 2011) genome project.Synonoms
S. bertrami is a synonym of S. equicanis.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 MyeloencephalitisEquine Protozoal MyeloencephalitisEquine protozoal myeloencephalitis, or EPM, is a disease cause by a protozoal infection of the central nervous system of horses.-History:...
- Sarcocystis genome project http://www.reeis.usda.gov/web/crisprojectpages/219487.html