Plasmodium coatneyi
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''Plasmodium coatneyi'' is a
parasitic 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 ha ...
species that is an agent of
malaria Malaria is a mosquito-borne infectious disease that affects humans and other animals. Malaria causes symptoms that typically include fever, tiredness, vomiting, and headaches. In severe cases, it can cause jaundice, seizures, coma, or death. S ...
in nonhuman primates. ''P. coatneyi'' occurs in Southeast Asia. The natural host of this species is the
rhesus macaque The rhesus macaque (''Macaca mulatta''), colloquially rhesus monkey, is a species of Old World monkey. There are between six and nine recognised subspecies that are split between two groups, the Chinese-derived and the Indian-derived. Generally ...
(''Macaca mulatta'') and crab-eating macaque (''Macaca fascicularis fascicularis''), but there has been no evidence that
zoonosis A zoonosis (; plural zoonoses) or zoonotic disease is an infectious disease of humans caused by a pathogen (an infectious agent, such as a bacterium, virus, parasite or prion) that has jumped from a non-human (usually a vertebrate) to a human. ...
of ''P. coatneyi'' can occur through its vector, the female ''
Anopheles ''Anopheles'' () is a genus of mosquito first described and named by J. W. Meigen in 1818. About 460 species are recognised; while over 100 can transmit human malaria, only 30–40 commonly transmit parasites of the genus ''Plasmodium'', which ...
'' mosquito. While ''P. coatneyi'' cannot be transmitted to humans, it is similar enough to '' Plasmodium falciparum'' to warrant laboratory study as a model species.


History

''Plasmodium coatneyi'' was first discovered in 1961 by Dr. Don Eyles in the Malaysian state of
Selangor Selangor (; ), also known by its Arabic language, Arabic honorific Darul Ehsan, or "Abode of Sincerity", is one of the 13 Malaysian states. It is on the west coast of Peninsular Malaysia and is bordered by Perak to the north, Pahang to the east ...
. ''Plasmodium coatneyi'' was isolated from an ''Anopheles hackeri'' before being found in its primate host species. This was the first occurrence of acquiring a new form of malaria through its vector instead of an infected host specimen. The sample was first thought to be ''
Plasmodium knowlesi ''Plasmodium knowlesi'' is a parasite that causes malaria in humans and other primates. It is found throughout Southeast Asia, and is the most common cause of human malaria in Malaysia. Like other ''Plasmodium'' species, ''P. knowlesi'' has a li ...
'' due to the morphological similarities of the two species, but was later identified as separate due to having a tertiary periodicity compared to ''P. knowlesi''’s quartan periodicity. The presence of ''P. coatneyi'' in a host was confirmed in 1963 by Dr. Eyles and his team when the protozoan was discovered in a crab-eating monkey found in the same area Selangor and again in a separate crab-eating monkey in the Philippines. The newly discovered species was then named in honor of Dr. G. Robert Coatney, an American malariologist.


Life Cycle

The life cycle of ''P. coatneyi'' takes the complex form representative of the genus ''Plasmodium''. When a female ''Anopheles'' mosquito bites a human, a haploid form of the protozoan called a sporozoite is transferred from the salivary glands into the
circulatory system The blood circulatory system is a system of organs that includes the heart, blood vessels, and blood which is circulated throughout the entire body of a human or other vertebrate. It includes the cardiovascular system, or vascular system, tha ...
of the human. These motile sporozoites are then taken by the circulatory system to the liver, where they invade the liver cells (
hepatocyte A hepatocyte is a cell of the main parenchymal tissue of the liver. Hepatocytes make up 80% of the liver's mass. These cells are involved in: * Protein synthesis * Protein storage * Transformation of carbohydrates * Synthesis of cholesterol, ...
s). During the next 5–16 days, these sporozoites mature and divide by asexual reproduction into schizonts. Schizonts are structures that contain thousands of haploid merozoites, and rupture to release merozoites into the circulatory system. These merozoites then infect the red blood cells (
erythrocyte Red blood cells (RBCs), also referred to as red cells, red blood corpuscles (in humans or other animals not having nucleus in red blood cells), haematids, erythroid cells or erythrocytes (from Greek ''erythros'' for "red" and ''kytos'' for "holl ...
s) where they consume the hemoglobin of the red blood cells for energy and become immature, ring stage trophozoites. The trophozoites act as an intermediate stage, from which two forms can be formed. The trophozoites can mature into schizonts and release more merozoites into the circulatory system, or they can differentiate into still haploid
gametocyte A gametocyte is a eukaryotic germ cell that divides by mitosis into other gametocytes or by meiosis into gametids during gametogenesis. Male gametocytes are called ''spermatocytes'', and female gametocytes are called ''oocytes''. Development ...
s. The gametocyte is the sexual stage of the life cycle, with female macrogametocytes and male microgametocytes.
Sexual reproduction Sexual reproduction is a type of reproduction that involves a complex life cycle in which a gamete ( haploid reproductive cells, such as a sperm or egg cell) with a single set of chromosomes combines with another gamete to produce a zygote th ...
does not occur in the human host. Instead, the gametocytes only fuse to form a diploid
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 ...
when ingested by the female ''Anopheles''. The fertilization takes place in the stomach, where the zygotes can move into the midgut after they differentiate into motile version of the zygote, an ookinetes. Ookinetes then mature into oocytes inside the epithelial tissue of the midgut. Once grown, the oocyte ruptures and releases sporozoites into the salivary glands of the mosquito. The process then repeats itself through the human host if the mosquito lives long enough to infect a human.


Vectors

*''
Anopheles balabacensis ''Anopheles balabacensis'' is a species of mosquito in the Culicidae Mosquitoes (or mosquitos) are members of a group of almost 3,600 species of small flies within the family Culicidae (from the Latin ''culex'' meaning "gnat"). The word "mosq ...
'' *''
Anopheles freeborni ''Anopheles freeborni'', commonly known as the western malaria mosquito, is a species of mosquito in the family Culicidae. It is typically found in the western United States and Canada. Adults are brown to black, with yellow-brown hairs and gr ...
'' *''
Anopheles hackeri ''Anopheles'' () is a genus of mosquito first described and named by J. W. Meigen in 1818. About 460 species are recognised; while over 100 can transmit human malaria, only 30–40 commonly transmit parasites of the genus ''Plasmodium'', which c ...
'' *''
Anopheles maculatus ''Anopheles'' () is a genus of mosquito first described and named by J. W. Meigen in 1818. About 460 species are recognised; while over 100 can transmit human malaria, only 30–40 commonly transmit parasites of the genus ''Plasmodium'', which c ...
''


Clinical Features

When infected with ''P. coatneyi'', the host shows the general symptoms of malaria are fever, headache, chills, vomiting, diarrhea, jaundice, joint pain and
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 ...
. These symptoms occur in the form of
paroxysmal attack Paroxysmal attacks or paroxysms (from Greek παροξυσμός) are a sudden recurrence or intensification of symptoms, such as a spasm or seizure. These short, frequent symptoms can be observed in various clinical conditions. They are usually ...
s, which is a sudden increase of these symptoms after a period of remission. This is due to the release of merozoites from schizonts inside the red blood cells. This cycle occurs every other day when infected with ''P. coatneyi'', a tertiary periodicity. This is compared to the quartan periodicity shown in some other ''Plasmodium'' species, such as ''P. knowlesi'' which occurs every three days. Infection causes metabolic disturbances. Davis et al 1993 experimented with
rhesus macaque The rhesus macaque (''Macaca mulatta''), colloquially rhesus monkey, is a species of Old World monkey. There are between six and nine recognised subspecies that are split between two groups, the Chinese-derived and the Indian-derived. Generally ...
s and produced increased glucose and lactate correlated with increased
parasitemia Parasitemia is the quantitative content of parasites in the blood. It is used as a measurement of parasite load in the organism and an indication of the degree of an active parasitic infection. Systematic measurement of parasitemia is important in ...
. They believed this also correlated with increased insulin resistance and lactate acidosis. ''P. coatneyi'', unlike many other species in the genus ''Plasmodium'', is a cause of
cerebral malaria Malaria is a Mosquito-borne disease, mosquito-borne infectious disease that affects humans and other animals. Malaria causes Signs and symptoms, symptoms that typically include fever, fatigue (medical), tiredness, vomiting, and headaches. In se ...
. The symptoms of this severe form of malaria include impaired consciousness such as a coma,
seizure An epileptic seizure, informally known as a seizure, is a period of symptoms due to abnormally excessive or synchronous neuronal activity in the brain. Outward effects vary from uncontrolled shaking movements involving much of the body with l ...
s, brain swelling,
intracranial hypertension Intracranial pressure (ICP) is the pressure exerted by fluids such as cerebrospinal fluid (CSF) inside the skull and on the brain tissue. ICP is measured in millimeters of mercury (mmHg) and at rest, is normally 7–15 mmHg for a supine adult. Th ...
, and other neurological abnormalities. While the exact mechanism for cerebral malaria is not known, the most commonly used explanation is the sequestration of the protozoan infected erythrocytes in the microvasculature of the brain. Due to the fact that it is a species of ''Plasmodium'' which only causes malaria in nonhuman primates, no treatment for this form of malaria has been specifically adapted. However, treatment with subcurative levels of
artemether Artemether is a medication used for the treatment of malaria. The injectable form is specifically used for severe malaria rather than quinine. In adults, it may not be as effective as artesunate. It is given by injection in a muscle. It is also ...
has been shown to reduce symptoms. This used to treat ''P. falciparum'', and is grouped into artemisinin-based combination therapies used most for ''P. falciparum'' treatment.


Use as a Model Organism

While more closely related to ''
Plasmodium vivax ''Plasmodium vivax'' is a protozoal parasite and a human pathogen. This parasite is the most frequent and widely distributed cause of recurring malaria. Although it is less virulent than ''Plasmodium falciparum'', the deadliest of the five huma ...
'' than to ''P. falciparum'', ''P. coatneyi'' has been used as a model organism for ''P. falciparum'' in a model organism for humans, rhesus macaques. This is due to the several similarities that ''P. coatneyi'' and ''P. falciparum'' have in common. These similarities includes having a tertiary periodicity, causing cerebral malaria, causing knob protrusion on the surface of infected red blood cells, and adhering the red blood cells to the same sites of the
endothelium The endothelium is a single layer of squamous endothelial cells that line the interior surface of blood vessels and lymphatic vessels. The endothelium forms an interface between circulating blood or lymph in the lumen and the rest of the vesse ...
. Because of these similarities, experiments have been run to further research the mechanism(s) for cerebral malaria. On a broader scale, ''P. coatneyi'' can cause metabolic dysfunction, coagulopathy, and anemia very close to that found in humans. Therefore, ''P.coatneyi'' was predicted to be able to test pathophysiological interactions between the parasite and its host. This can be used to mimic the conditions of a human with malaria, allowing for testing without any sort of human exposure taking place.


References

{{Taxonbar, from=Q16988200 coatneyi Parasites of primates