Plasmodium ovale
Plasmodium ovale | |
---|---|
Plasmodium ovale Giemsa stain.
| |
Scientific classification | |
Domain: | Eukaryota |
Clade: | Diaphoretickes |
Clade: | SAR |
Clade: | Alveolata |
Phylum: | Apicomplexa |
Class: | Aconoidasida |
Order: | Haemospororida |
Family: | Plasmodiidae |
Genus: | Plasmodium |
Species: | P. ovale
|
Binomial name | |
Plasmodium ovale Stephens, 1922
|
Plasmodium ovale is a species of
P. ovale has recently been shown by genetic methods to consist of what is considered to be two species (despite having been given subspecies names), namely P. ovale curtisi and P. ovale wallikeri.[1] The procedure necessary to rectify the nomenclature has been outlined.[2]
History
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).[3]
Epidemiology
P. ovale is primarily concentrated in sub-Saharan Africa and islands in the western Pacific.[5][6] However P. ovale has also been reported in the Philippines, eastern Indonesia, and Papua New Guinea,[7] as well as in Bangladesh,[8] Cambodia,[9] India,[10] Myanmar,[11] Thailand[12] and Vietnam.[13]
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%.[5]
It has been estimated that there are about 15 million cases of infection each year with this parasite.[1]
While similar to P. vivax, P. ovale is able to infect individuals who are negative for the
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.[5]
In some cases, relapse may occur up to 4 years after infection.[5]
Diagnosis
The microscopic appearance of P. ovale is very similar to that of P. vivax and if there are only a small number of parasites seen, it may be impossible to distinguish the two species on morphological grounds alone. There is no difference between the medical treatment of P. ovale and P. vivax, and therefore some laboratory diagnoses report "P. vivax/ovale", which is perfectly acceptable as treatment for the two is very similar. Schüffner's dots are seen on the surface of the parasitised red blood cell, but these are larger and darker than in P. vivax and are sometimes called James' dots or James' stippling. About twenty percent of the parasitised cells are oval in shape (hence the species name) and some of the oval cells also have fimbriated edges (the so-called "comet cell"). The mature schizonts of P. ovale never have more than twelve nuclei within them and this is the only reliable way of distinguishing between the two species.
Molecular tests (tests that detect DNA in blood) must take into account the fact that there are two P. ovale sensu lato taxa. Tests designed for one will not necessarily detect the other.[16]
Treatment
Standard treatment is concurrent treatment with
Phylogenetics
Among the species infecting the great apes, Plasmodium schwetzi morphologically appears to be the closest relation to P. ovale. As of 2013[update] this had not been confirmed by DNA studies.
The original species has been shown to be two morphologically identical forms – Plasmodium ovale curtisi and Plasmodium ovale wallikeri – which can be differentiated only by genetic means.[1] Both species have been identified in Ghana, Myanmar, Nigeria, São Tomé, Sierra Leone and Uganda. The separation of the lineages is estimated to have occurred between 1.0 and 3.5 million years ago in hominid hosts. A second analysis suggests that these species separated 4.5 million years ago (95% confidence interval 0.5 – 7.7 Mya).[18] A third worked sequenced the whole genome of both species, confirmed the differences and dated the split at around million years.[19] 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.[18]
The two species appear to differ biologically, with P. ovale wallikeri having a shorter latency period than P. ovale curtisi.[20]
Life cycle
P. ovale is introduced into the human host by the bite of an infected mosquito, in a motile form called a
When gametocytes are ingested by a mosquito, the gametocytes enter the mosquito gut where
There are situations where some of the sporozoites hypothetically do not immediately start to grow and divide after entering the hepatocyte, but remain in a dormant,
Hosts
While humans appear to be the natural mammalian host of P. ovale, chimpanzees and
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[5]
Genomes
The full genomes of the two P. ovale species can be seen on geneDB.org – P. ovali curtisi P. ovale wallikeri and plasmoDB.org, published 2017.[19]
See also
- List of parasites (human)
References
- ^ PMID 20380562.
- .
- S2CID 86121600.
- PMID 27777030.)
{{cite journal}}
: CS1 maint: multiple names: authors list (link - ^ PMID 16020691.
- PMID 9861368.
- ^
Baird JK, Hoffman SL (November 2004). "Primaquine therapy for malaria". Clinical Infectious Diseases. 39 (9): 1336–45. PMID 15494911.
- PMID 20595481.
- PMID 15964956.
- ^
Snounou G, Viriyakosol S, Jarra W, Thaithong S, Brown KN (April 1993). "Identification of the four human malaria parasite species in field samples by the polymerase chain reaction and detection of a high prevalence of mixed infections". Molecular and Biochemical Parasitology. 58 (2): 283–92. PMID 8479452.
- PMID 24112638.
- ^
Cadigan FC, Desowitz RS (1969). "Two cases of Plasmodium ovale malaria from central Thailand". Transactions of the Royal Society of Tropical Medicine and Hygiene. 63 (5): 681–2. PMID 5824291.
- ^
Gleason NN, Fisher GU, Blumhardt R, Roth AE, Gaffney GW (1970). "Plasmodium ovale malaria acquired in Viet-Nam". Bulletin of the World Health Organization. 42 (3): 399–403. PMID 4392940.
- ^ "Biology: Malaria (CDC malaria)". Archived from the original on 2008-10-13.
- PMID 35399558.
- PMID 24478466.
- PMID 9015517.
- ^ PMID 23536840.
- ^ PMID 28117441.
- PMID 23793668.
- PMID 26577930.)
{{cite journal}}
: CS1 maint: multiple names: authors list (link - S2CID 1727294.
- PMID 34526770.
- ^ "Malaria eModule – Exo-Erythrocytic Stages".
External links
- Malaria – TDR: For research on diseases of poverty