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. One possible experimental infection has been reported with Plasmodium eylesi. Fever and low grade parasitemia were apparent at 15 days. The volunteer (Dr Bennett) had previously been infected by Plasmodium cynomolgi and the infection was not transferable to a gibbon (P. eylesi 's natural host) so this cannot be regarded as definitive evidence of its ability to infect humans. A second case has been reported that may have been a case of P. eylesi but the author was not certain of the infecting species. A possible infection with Plasmodium tenue has been reported. This report described a case of malaria in a three year old black girl from Georgia, USA who had never been outside the US. She suffered from both P. falciparum and P. vivax malaria and while forms similar to those described for P. tenue were found in her blood even the author was skeptical about the validity of the diagnosis.
Confusingly Plasmodium tenue was proposed in the same year (1914) for a species found in birds. The human species is now considered to be likely to have been a misdiagnosis and the bird species is described on the Plasmodium tenue page.
The only known host of P. falciparum are humans; neither is any other host currently known for P. malariae. There has been a single report of P. falciparum in a brown howler monkey and in black howler monkeys (Alouatta caraya) but until this is confirmed its validity should be considered dubious. This paper also reported several cases of P. malariae in both species of monkey. Again this needs confirmation.
P. vivax will infect chimpanzees. Infection tends to be low grade but may be persistent and remain as source of parasites for humans for some time.
P. vivax is also known to infect orangutans and the brown howler monkey (Alouatta guariba clamitans)
Like P. vivax, P. ovale has been shown to be transmittable to chimpanzees. P. ovale has a unusual distribution pattern being found in Africa, the Philippines and New Guinea. In spite of its admittedly poor transmission to chimpanzees given its discontigous spread, it is suspected that P. ovale may in fact be a zooenosis with an as yet unidentified host. If this is actually the case, the host seems likely to be a primate. The remaining species capable of infecting humans all have other primate hosts. Plasmodium shortii and Plasmodium osmaniae are now considered to be junior synonyms of Plasmodium inui
P. laverani var. tertium
P. laverani var. quartum
P. malariae var. immaculatum
P. malariae var. incolor
P. malariae var. irregularis
P. malariae var. parva
P. malariae var. quartanae
P. malariae var. quotidianae
P. pleurodyniae P. praecox
Interrelatedness - The evolution of these species is still being worked out and the relationships given here should be regarded as tentative. This grouping, while originally made on morphological grounds, now has considerable support at the DNA level.