Plasmodium ovale

This species was first described in 1914 by Stephens in a blood sample taken in the autumn of 1913 from a patient in the sanitarium of Pachmari in central India and sent by Major W. H. Kenrick to Stephens (who was working in Liverpool). ==Epidemiology==

P. ovale is primarily concentrated in sub-Saharan Africa and islands in the western Pacific. However P. ovale has also been reported in the Philippines, eastern Indonesia, and Papua New Guinea, as well as in Bangladesh, Cambodia, India, Myanmar, Thailand and Vietnam. In several studies, the reported prevalence of P. ovale was low relative to other malaria parasites, with fewer than 5% of malaria cases being associated with P. ovale infection. Higher prevalences of P. ovale are possible under certain conditions, as at least one study in Cameroon found the prevalence of P. ovale infection to be greater than 10%. However, low-parasitaemia or subpatent P. vivax cases might be more prevalent in Africa than has been thought. ==Clinical features==

In humans, symptoms generally appear 12 to 20 days after the parasite has entered the blood. In the blood, the parasite's replication cycle lasts approximately 49 hours, causing tertian fever which spikes approximately every 49 hours as newly replicated parasites erupt out of red blood cells. Mean maximum parasite levels have been found to be 6,944/microl for sporozoite-induced infections and 7,310/microl for trophozoite-induced infections. In some cases, relapse may occur up to 4 years after infection. Treatment Standard treatment is concurrent treatment with chloroquine and primaquine. The combination atovaquone-proguanil may be used in those patients who are unable to take chloroquine for whatever reason. An overdose on Chloroquine can be very dangerous and can result in death. ==Phylogenetics==

Among the species infecting the great apes, Plasmodium schwetzi morphologically appears to be the closest relation to P. ovale. this had not been confirmed by DNA studies. The original species has been shown to be two morphologically identical forms – Plasmodium ovalecurtisi and Plasmodium ovalewallikeri – which can be differentiated only by genetic means. A third worked sequenced the whole genome of both species, confirmed the differences and dated the split at around million years. Although dating is always difficult, the authors date that split to be 5 times older than the P. falciparum and P. reichenowi split. These species appear to be more closely related to Plasmodium malariae than to Plasmodium vivax. ==Life cycle==

P. ovale is introduced into the human host by the bite of an infected mosquito, in a motile form called a sporozoite. The sporozoites are carried by the blood to the liver, where they replicate asexually by merogony into non-motile merozoites. Several hundred merozoites are produced and released into the bloodstream where they infect erythrocytes. Inside the erythrocyte, the parasite's replication cycle takes approximately 49 hours, after which the erythrocyte ruptures and between 8 and 20 merozoites are released to infect other erythrocytes. Some of these merozoites will instead form gametocytes which remain in the blood and are ingested by a mosquito. for weeks or months. However, unlike the P. vivax situation, hypnozoites have yet to actually be seen in the life cycle of P. ovale. The duration of latency is variable from one (assumed in the case of P. ovale) hypnozoite to another and the factors that will eventually trigger growth are not known; this could explain how a single infection can be responsible for a series of waves of parasitaemia or "relapses". ==Hosts==

While humans appear to be the natural mammalian host of P. ovale, chimpanzees and Saimiri monkeys have also been experimentally infected. Anopheles gambiae and Anopheles funestus are likely the natural mosquito hosts of P. ovale. Experimentally, several other mosquito species have been shown to be capable of transmitting P. ovale to humans, including: • Anopheles albimanus • Anopheles atroparvus • Anopheles dirus • Anopheles farauti • Anopheles freeborni • Anopheles maculatus • Anopheles quadrimaculatus • Anopheles stephensi* • Anopheles subpictus == Genomes ==

The full genomes of the two P. ovale species can be seen on geneDB.org – P. ovalecurtisi [ftp://ftp.sanger.ac.uk/pub/project/pathogens/Plasmodium/ovale/PovaleWallikeri/CR01/ P. ovalewallikeri] and plasmoDB.org, published 2017. == See also ==