Plasmodium knowlesi: the fifth human malaria parasite.

In 1932, when Knowles and Das Gupta [ 1 ] succeeded in transmitting to humans the monkey malaria they had discovered, it appeared that a new agent for malaria therapy had been discovered. Since the Nobel Prize-winning research of Julius WagnerJauregg, malaria therapy had become widely used for the treatment of general paralysis of the insane (neurosyphilis), one of the main reasons for admission to psychiatric institutions. But it soon became apparent that this infection could rapidly become uncontrollable, and after several fatalities, its use was largely discontinued in favor of the less virulent human parasite Plasmodium vivax. Malaria parasites are generally rather choosy, both about their mammalian, avian, or reptilian hosts and their respective mosquito vectors. Transmission of Plasmodium knowlesiy for malaria therapy, from human to human was by blood passage. So initially, it was uncertain whether natural infection could take place and, thus, whether this could be a zoonosis. In 1960, Eyles et al. [2] demonstrated the first experimental mosquito transmission of a