Plasmodium is a genus of parasitic protozoa. Infection with this genus is known as malaria. The parasite always has two hosts in its life cycle: a mosquito vector and a vertebrate host. At least ten species infect humans. Other species infect other animals, including birds, reptiles and rodents.
- A plasmodium[[1]] is also the macroscopic form of the unusual protozoa known as slime moulds.
Taxonomy and host range
The genus Plasmodium was created in 1885 by Marchiafava and Celli and there are over 175 species currently recognised in this genus. The genus is currently (2006) in need of reorganisation as it has been shown that other parasites belonging to the genera Haemocystis and Hepatocystis appear to be closely related to this genus. It is likely that other species such as Haemoproteus meleagridis will be included in this genus once it is revised.
Host range among the mammalian orders is non uniform. At least 25 species infect primates; rodents outside the tropical parts of Africa are rarely affected; a few species are known to infect bats, porcupines and squirrels; while carnivores, insectivores and marsupials are not known to act as hosts.
Discovery of the life cycle
In 1898 Ronald Ross demonstrated the existence of Plasmodium in the wall of the midgut and salivary glands of a Culex mosquito. For this discovery he won the Nobel Prize in 1902. However credit must also be given to the Italian professor Giovanni Battista Grassi, who showed that human malaria could only be transmitted by Anopheles mosquitoes.
The species of Plasmodium that parasitise humans include:
- Plasmodium falciparum (the cause of malignant tertian malaria)
- Plasmodium vivax (the most frequent cause of benign tertian malaria)
- Plasmodium ovale (the other, less frequent, cause of benign tertian malaria)
- Plasmodium malariae (the cause of benign quartan malaria)
- Plasmodium knowlesi
- Plasmodium brasilianum
- Plasmodium cynomolgi
- Plasmodium inui
- Plasmodium rhodiani
- Plasmodium schweitzi
- Plasmodium semiovale
- Plasmodium simium
The first four listed here are the most common species that infect humans. With the use of the polymerase chain reaction additional species have been and are still being identified that infect humans.
Taxonomy
Plasmodium belongs to the family Plasmodiidae (Levine, 1988), order Haemosporidia and phylum Apicomplexia. There are currently 450 recognised species in this order. Many species of this order are undergoing reexamination of thier taxonomy with DNA analysis. It seems likely that many of these species will be re assigned after these studies have been completed. [1] [2] For this reason the entire order is outlined here.
- Order Haemosporida
- Family Haemoproteidae
- Genus Haemoproteus
- Subgenus Parahaemoproteus
- Subgenus Haemoproteus
- Family Plasmodiidae
- Genus Plasmodium
- Subgenus Asiamoeba
- Subgenus Bennettinia
- Subgenus Carinamoeba
- Subgenus Giovannolaia
- Subgenus Haemamoeba
- Subgenus Huffia
- Subgenus Laverania
- Subgenus Novyella
- Subgenus Paraplasmodium
- Subgenus Sauramoeba
- Subgenus Vinckeia
- Family Garniidae
- Genus Fallisia
- Subgenus Plasmodioides
- Family Leucocytozoidae
- Genus Leucocytozoon
- Subgenus Leucocytozoon
- Subgenus Akiba
Two other subgenera have been described in Plasmodium but are no longer used: Lacertamoeba and Ophidiella
Subgenera
The full taxonomic name of a species includes the subgenus but this is often omitted. The full name indicates some features of the morphology and type of host species. The only two species in the sub genus Laverania are P. falciparum and P. reichenowi. Species infecting monkeys, and apes (the higher primates) with the exceptions of P. falciparum and P. reichenowi are classified in the subgenus Plasmodium. Parasites infecting other mammals including lower primates (lemurs and others) are classified in the subgenus Vinckeia.
The distinction between P. falciparum and P. reichenowi and the other species infecting higer primates was based on the morphological findings but have since been confirmed by DNA analysis. Vinckeia while previously considered to be something of a taxanomic 'rag bag' has been recently shown - perhaps rather suprisingly - to form a coherent grouping. The remaining groupings here are based on the morphology of the parasites. Revisions to this system are likely to occur in the future as more species are subject to analysis of thier DNA.
Examples of the use of full names include:
Plasmodium (Asiamoeba) draconis
Plasmodium (Asiamoeba) vastator
Plasmodium (Carinamoeba) basilisci
Plasmodium (Carinamoeba) minasense
Plasmodium (Carinamoeba) rhadinurum
Plasmodium (Carinamoeba) volans
Plasmodium (Giovannolaia) circumflexum
Plasmodium (Giovannolaia) dissanaikei
Plasmodium (Giovannolaia) durae
Plasmodium (Giovannolaia) fallax
Plasmodium (Giovannolaia) garnhami
Plasmodium (Giovannolaia) gundersi
Plasmodium (Giovannolaia) lophurae
Plasmodium (Giovannolaia) pedioecetii
Plasmodium (Giovannolaia) polare
Plasmodium (Haemamoeba) cathemerium
Plasmodium (Haemamoeba) coggeshalli
Plasmodium (Haemamoeba)elongatum
Plasmodium (Haemamoeba) gallinacium
Plasmodium (Haemamoeba) giovannolai
Plasmodium (Haemamoeba) matutinum
Plasmodium (Haemamoeba) parvulum
Plasmodium (Haemamoeba) relictum
Plasmodium (Haemamoeba) subpraecox
Plasmodium (Haemamoeba) tejera
Plasmodium (Huffia) elongatum
Plasmodium (Huffia) hermani
Plasmodium (Laverania) falciparum
Plasmodium (Laverania) reichenowi
Plasmodium (Novyella) bambusicolai
Plasmodium (Novyella) corradettii
Plasmodium (Novyella) hexamerium
Plasmodium (Novyella) juxtanucleare
Plasmodium (Novyella) kempi
Plasmodium (Novyella) nucleophilum
Plasmodium (Novyella) papernai
Plasmodium (Novyella) rouxi
Plasmodium (Novyella) vaughani
Plasmodium (Paraplasmodium) mexicanum
Plasmodium (Paraplasmodium) chiricahuae
Plasmodium (Plasmodium) brasilianum
Plasmodium (Plasmodium) cynomolgi
Plasmodium (Plasmodium) eylesi
Plasmodium (Plasmodium) fieldi
Plasmodium (Plasmodium) fragile
Plasmodium (Plasmodium) georgesi
Plasmodium (Plasmodium) girardi
Plasmodium (Plasmodium) gonderi
Plasmodium (Plasmodium) inui
Plasmodium (Plasmodium) jefferyi
Plasmodium (Plasmodium) knowlei
Plasmodium (Plasmodium) hyobati
Plasmodium (Plasmodium) malariae
Plasmodium (Plasmodium) ovale
Plasmodium (Plasmodium) petersi
Plasmodium (Plasmodium) pitheci
Plasmodium (Plasmodium) rhodiani
Plasmodium (Plasmodium) schweitzi
Plasmodium (Plasmodium) semiovale
Plasmodium (Plasmodium) shortii
Plasmodium (Plasmodium) silvaticum
Plasmodium (Plasmodium) simium
Plasmodium (Plasmodium) vivax
Plasmodium (Plasmodium) youngi
Plasmodium (Sauramoeba) achiotense
Plasmodium (Sauramoeba) aeuminatum
Plasmodium (Sauramoeba) agamae
Plasmodium (Sauramoeba) giganteum
Plasmodium (Sauramoeba) heischi
Plasmodium (Sauramoeba) josephinae
Plasmodium (Sauramoeba) pelaezi
Plasmodium (Sauramoeba) tropiduri
Plasmodium (Vinckeia) aegyptensis
Plasmodium (Vinckeia) anomaluri
Plasmodium (Vinckeia) atheruri
Plasmodium (Vinckeia) berghei
Plasmodium (Vinckeia) booliati
Plasmodium (Vinckeia) bubalis
Plasmodium (Vinckeia) bucki
Plasmodium (Vinckeia) cephalophi
Plasmodium (Vinckeia) chabaudi
Plasmodium (Vinckeia) coulangesi
Plasmodium (Vinckeia) cyclopsi
Plasmodium (Vinckeia) foleyi
Plasmodium (Vinckeia) girardi
Plasmodium (Vinckeia) inopinatum
Plasmodium (Vinckeia) lemuris
Plasmodium (Vinckeia) odocoilei
Plasmodium (Vinckeia) percygarnhami
Plasmodium (Vinckeia) sandoshami
Plasmodium (Vinckeia) traguli
Plasmodium (Vinckeia) uilenbergi
Plasmodium (Vinckeia) vinckei
Plasmodium (Vinckeia) watteni
Plasmodium (Vinckeia) yoelli
- Notes
Species of Novyella are characterized by very small schizonts. Sexual stages in this subgenus resemble those of Haemoproteus.
Infections in primates
The species that infect primates other than humans include: P. brasilianum, P. bucki, P. coulangesi, P. cynomolgi, P. coatneyi, P. eylesi, P. fieldi, P. foleyi, P. fragile, P. girardi, P. georgesi, P. gonderi, P. hylobati, P. inui, P. knowlesi, P. lemuris, P. percygarnhami, P. petersi, P. reichenowi, P. rodhaini, P. sandoshami, P shortii, P. silvaticum, P. simiovale, P. simium and P. uilenbergi.
- Host record
Most if not all Plasmodium species infect more than one host: the host records shown here should be regarded as being incomplete.
P. bucki - Lemur macaco macaco
P. coatneyi - several macaque species: Macaca fascicularis and Macaca irus.
P. coulangesi - Lemur macaco macaco
P. cynomolgi - Macaca cyclopis, Macaca fascicularis, Macaca nemestrina, Macaca radiata, Macaca sinica, Presbytis cristatus and Presbytis entellus
P. eylesi - several gibbon (Hylobates) species
P. fieldi - Macaca fascicularis and Macaca nemestrina
P. foleyi - Lemur fulvus rufus
P. fragile - several macaque species - Macaca fascicularis, Macaca mulatta, Macaca radiata, and Macaca sinica
P. georgesi - Cercocebus albigena
P. girardi - Lemur fulvus rufus
P. gonderi - Mangabeys (Cercocebus albigena) and drills (Mandrillus)
P. hylobati - several gibbon (Hylobates) species
P. inui - the Celebes black ape (Cynopithecus niger), Macaca fascicularis, Macaca nemestrina, and several Presbytis species
P. jefferyi - several gibbon (Hylobates) species
P. knowlesi - Macaca fascicularis, Macaca nemestrina, and Presbytis malalophus
P. knowlesi edesoni - the Javanese long-tailed macaque (Macaca irus)
P. lemuris - the lemur Lemur collaris
P. percygarnhami - Lemur macaco macaco
P. petersi - Cercocebus albigena
P. pitheci - orangutans (Pongo pygmaeus)
P. reichenowi - chimpanzees (Pan) species and gorillas (Gorilla) species
P. rodhaini - chimpanzees (Pan) species and gorillas (Gorilla) species
P. sandoshami - the Malayan flying lemur (Cynocephalus variegatus)
P. schwetzi - chimpanzees (Pan) species and gorillas (Gorilla) species
P. semiovale - Macaca sinica
P. silvaticum - orangutans (Pongo pygmaeus)
P. simium - the woolly spider monkey (Brachyteles arachnoides) and several howler monkeys (Alouatta) species
P. shortii - Macaca radiata, and Macaca sinica
P. uilenbergi - Lemur fulvus fulvus
P. youngei - white handed gibbon (Hylobates lar)
- Mosquito vectors
Anopheles dirus - P. inui
Anopheles farauti - P. coatneyi and P. vivax [3]
Anopheles maculatus - P. youngei
Anopheles stephensi - P. cynomogli and P. inui
Anopheles sundaicus - P. youngei
- Subspecies
P. cynomolgi - P. cynomolgi bastianelli and P. cynomolgi ceylonensis.
P. inui - P. inui inui and P. inui shortii
P. knowlesi - P. knowlesi edesoni and P. knowlesi knowlesi.
P. vivax - P. vivax hibernans, P. vivax chesson and P. vivax multinucleatum.
- Interrelatedness
The evolution of these species is still being worked out and the relationships given here should be regarded as tentative.
P. brasilianum, P. inui and P. rodhaini are similar to P. malariae
P. cynomolgi, P. fragile, P. knowlesi, P. simium and P. schwetzi are similar to P. vivax
P. fieldi and P. simiovale are similar to P. ovale
P. falciparum is closely related to P. reichenowi.
This last grouping while originally made on morphological grounds now has considerable support at the DNA level.
- Notes
P. kochi has been described as a parasite of monkeys. This species is currently classified as Hepatocystis kochi. This may be subject to revision.
P. brasilianum and P. rodhaini seem likely to be the same species as P. malariae.
Infections in non primate mammals
The subgenus Vinckeia was created by Garnham to accommodate the mammalian parasites other than those infecting primates. Species infecting lemurs have also been included in this subgenus.
P. aegyptensis, P. bergei, P. chabaudi, P. inopinatum, P. yoelli and P. vinckei infect rodents. P. bergei, P. chabaudi, P. yoelli and P. vinckei have been used to study malarial infections in the laboratory. Other members of this subgenus infect other mammalian hosts.
- Host records
P. aegyptensis - Egyptian grass rat (Arvicanthis noloticus)[4]
P. atheruri - African porcupine (Atherurus africanus), large vesper mouse (Calomys callosus) and Meriones unguiculatus
P. booliati - Malayan giant flying squirrel [5]
P. bubalis - water buffaloes (Bubalus bubalis)
P. cephalophi - grey duiker (Sylvicapra grimmia) [6]
P. cyclopsi - the bat (Hipposideros cyclops) [7]
P. odocoilei - white tailed deer (Odocoileus virginianus)
P. traguli - the mouse deer
P. watteni - Formosan giant flying squirrel (Petaurista petaurista grandis)[8]
- Vectors
Anopheles stephensi - P. atheruri
- Subspecies
P. yoellii - P. yoelli nigeriensis and P. yoelli yoelli.
P. vinkei - P. vinckei brucechwatti, P. vinckei petteri and P. vinckei vinckei.
P. chabaudi - P. chabaudi adami and P. chabaudi chabaudi
- Notes
Calomys callosus seems unlikely to be a natural host for P. atheruri as P. atheruri is found in Africa and Calomys callosus in South America.
Infections in birds
Species in five of these subgenera infect birds - Bennettinia, Giovannolaia, Haemamoeba, Huffia and Novyella. [9] Giovannolaia appears to be a polyphytic group and may be sudivided in the future. [10]
Species infecting birds include: P. anasum, P. bambusicolai, P. bigueti, P. cathemerium, P. circumflexum, P. coggeshalli, P. corradettii, P. coturnix, P. dissanaikei, P. durae, P. elongatum, P. fallax, P forresteri, P. gallinacium, P. garnhami, P. giovannolai, P. griffithsi, P. gabaldoni, P. gundersi, P. hegneri, P. hermani, P. hexamerium, P. huffi, P. juxtanucleare, P. kempi, P. lophurae, P. matutinum, P. nucleophilum, P. papernai, P. paranucleophilum, P. parvulum, P. pediocetti, P. pitmani, P. pinotti, P. polare, P. praecox, P. relictum, P. rouxi, P. tenue, P. tejerai and P. vaughani.
- Host records
- Vectors
- Subspecies
P. relictum has been divded into two subspecies: P. relictum relictum and P. relictum capistranoae.
- Notes
Plasmodium relictum is probably responsible for more bird extinctions than any other protist.
P. praecox has been re classiified as P. relictum. Both names have been recorded here as a guide to the literature.
P. dominicana is species known only from fossil amber. [11] It is thought to have been a species infecting birds.
Infections in reptiles
Species in the subgenera Carinamoeba, Paraplasmodium and Sauramoeba infect reptiles. [12]
Species infecting reptiles include: P. achiotense, P. aeuminatum, P. agamae, P. azurophilum, P. balli, P. basilisci, P. brygooi, P. chiricahuae, P. circularis, P. cnemidophori, P. colombiense, P. diminutivum, P. diploglossi, P. egerniae, P. fairchildi, P. floridense, P. giganteum, P. gracilis, P. guyannense, P. heischi, P. holaspi, P. icipeensis, P. josephinae, P. kentropyxi, P. lepidoptiformis, P. lygosomae, P. mabuiae, P. mackerrasae, P. maculilabre, P. mexicanum, P. minasense, P. pelaezi, P. pifanoi, P. pitmani, P. rhadinurum, P. robinsoni, P. sasai, P. tomodoni, P. torrealbai, P. tribolonoti, P. tropiduri, P. vacuolatum, P. volans and P. wenyoni.
- Host records
P. heischi - skinks (Mabuya striata) [13]
P. giganteum - Agama cyanogaster. [14]
P. siamense - lizards. [15]
P. tribolonoti - skinks
P. gracilis - skinks
P. lygosomae - skink (Lygosoma moco)
P. tomodoni - snakes
P. wenyoni - snakes
- Vectors
P. agamae - Lutzomyia or Culicoides species
- Subspecies
P. minasense - P. minasense minasense, P. minasense carinii, P. minasense anolisi, P. minasense capitoi, P. minasense plicae, P. minasense tegui and P. minasense diminutivum. [16] An additional subspecies P. minasense calcaratae has also been decribed. [17]
P. traguli - P. traguli traguli and P. traguli memmina.
P. tropiduri - P. tropiduri tropiduri, P. tropiduri panamense and P. tropiduri aquaticum. [16]
P. lygosomae - P. lygosomae nucleoversans.
Life cycle
The life cycle of Plasmodium is very complex. Sporozoites from the saliva of a biting female mosquito are transmitted to either the blood or the lymphatic system[18] of the recipient. Mosquitoes of the genera Culex, Anopheles, Culiceta, Mansonia and Aedes may act as vectors. The currently known vectors for human malaria (> 100 species) all belong to the genus Anopheles. The life cycle of Plasmodium was discovered by Ross who worked with species from the genus Culex.
The sporozoites migrate to the liver and invade hepatocytes. The so-called latent or dormant stage of the Plasmodium sporozoite in the liver is called the hypnozoite. From the hepatocytes, the parasite replicates into thousands of merozoites, which then invade red blood cells. Here the parasite grows from a ring-shaped form to a larger trophozoite form. In the schizont stage, the parasite divides several times to produce new merozoites, which leave the red blood cells and travel within the bloodstream to invade new red blood cells. Most merozoites continue this replicative cycle, but some merozoites differentiate into male or female sexual forms (gametocytes) (also in the blood), which are taken up by the female Anopheles mosquito. In the mosquito's midgut, the gametocytes develop into gametes and fertilize each other, forming motile zygotes called ookinetes. The ookinetes penetrate and escape the midgut, then embed themselves onto the exterior of the gut membrane. Here they divide many times to produce large numbers of tiny elongated sporozoites. These sporozoites migrate to the salivary glands of the mosquito where they are injected into the blood of the next host the mosquito bites. The sporozoites move to the liver where they repeat the cycle.
This life cycle is best understood in terms of its evolution. It is thought that Plasmodium evolved from a parasite spread by the orofaecal route which infected the intestinal wall. At some point this parasite evolved the ability to infect the liver. This pattern is seen in the genus Cryptosporidium to which Plasmodium is distantly related. At some later point this ancestor developed the ability to infect blood cells and to survive and infect mosquitoes. Once mosquito transmission was firmly established the previous orofecal route of transmission was lost.
Molecular biology
On a molecular level, the parasite damages red blood cells using plasmepsin enzymes. Plasmepsins are aspartic acid proteases which degrade hemoglobin.
Notes
- ^ Perkins SL, Schall JJ (2002) A molecular phylogeny of malarial parasites recovered from cytochrome b gene sequences. J. Parasitology 88 (5): 972-978
- ^ Yotoko, K. S. C. and Elisei C. (2006) Malaria parasites (Apicomplexa, Haematozoea) and their relationships with their hosts: is there an evolutionary cost for the specialization? J. Zoo. Syst. Evol. Res. 44 (4) 265
- ^ Collins WE,Sullivan JS,Nace D, Williams T,Sullivan JJ, Galland GG,Grady KK and Bounngaseng A. 2002. Experimental infection of Anopheles farauti with different species of Plasmodium. J. Parasitol. 88(2):295-298.
- ^ Abd-el-Aziz GA, Landau I, and Miltgen F. (1975) Description of Plasmodium aegyptensis n. sp., presumed parasite of the Muridae Arvicanthis noloticus in Upper Egypt Ann Parasitol Hum Comp. 50(4):419-424.
- ^ Sandosham AA, Yap LF, Omar I. (1965) A malaria parasite, plasmodium (Vinckeia) booliati sp.nov., from a Malayan giant flying squirrel. Med J Malaya. 20(1):3-7
- ^ Keymer IF. (1966) Studies on Plasmodium (Vinckeia) cephalophi of the grey duiker (Sylvicapra grimmia). Ann Trop Med Parasitol. 60(2):129-138
- ^ Landau I, and Chabaud AG. (1978) Description of P. cyclopsi n. sp. a parasite of the microchiropteran bat Hipposideros cyclops in Gabon. Ann. Parasitol. Hum. Comp. 53(3):247-253.
- ^ Lien JC, Cross JH. (1968) Plasmodium (Vinckeia) watteni sp. n. from the Formosan giant flying squirrel, Petaurista petaurista grandis. J Parasitol. 54(6):1171-1174
- ^ Wiersch SC, Maier WA, Kampen H. Plasmodium (Haemamoeba) cathemerium gene sequences for phylogenetic analysis of malaria parasites. Parasitol Res. 96(2): 90-94
- ^ Martinsen ES,Waite JL,Schall JJ Morphologically defined subgenera of Plasmodium from avian hosts: test of monophyly by phylogenetic analysis of two mitochondrial genes (2006) Parasitology 1 - 8
- ^ Poinar, G. (2005) Plasmodium dominicana n. sp. (Plasmodiidae: Haemospororida) from Tertiary Dominican amber. Systematic Parasitology 61 (1) 47-52
- ^ Schall JJ (2000) Transmission success of the malaria parasite Plasmodium mexicanum into its vector: role of gametocyte density and sex ratio. Parasitology. 121 (6):575-580
- ^ Garnham PC, Telford SR Jr. (1984) A new malaria parasite Plasmodium (Sauramoeba) heischi in skinks (Mabuya striata) from Nairobi, with a brief discussion of the distribution of malaria parasites in the family Scincidae. J Protozool. 31(4):518-521.
- ^ Southgate BA. (1970) Plasmodium (Sauramoeba) giganteum in Agama cyanogaster: a new host record. Trans R Soc Trop Med Hyg. 64(1):12-13
- ^ Telford SR (1986) Fallisia parasites (Haemosporidia: Plasmodiidae) from the flying lizard, Draco maculatus (Agamidae) in Thailand. J Parasitol. 72(5):766-769
- ^ a b Telford SR Jr. (1979) A taxonomic revision of small neotropical saurian Malarias allied to Plasmodium minasense. Ann Parasitol Hum Comp. 54(4):409-422 Cite error: The named reference "Telford1979" was defined multiple times with different content (see the help page).
- ^ Telford SR Jr and Telford SR 3rd. Rediscovery and redescription of Plasmodium pifanoi and description of two additional Plasmodium parasites of Venezuelan lizards. Journal of Parasitology (2003) 89(2):362-368
- ^ [http://www.hhmi.org/news/menard20060122.html HHMI Staff (22 January 2006) "Malaria Parasites Develop in Lymph Nodes" HHMI News Howard Hughes Medical Institute
References
- Short, H. E. (1951) Life-cycle of the mammalian malaria parasite" British Medical Bulletin 8(1): pp. 7-9, (PMID 14944807);
- Baldacci, Patricia and Ménard, Robert (Oct. 2004) "The elusive malaria sporozoite in the mammalian host" Molecular Microbiology 54(2): pp. 298-306, (AN 14621725);
- Bledsoe, G. H. (December 2005) "Malaria primer for clinicians in the United States" Southern Medical Journal 98(12): pp. 1197-204 (PMID 16440920);
External links
- Life cycle of plasmodium (Flash animations)