Plasmodium Knowlesi - History of Discovery

History of Discovery

The first person to see P. knowlesi was probably the Italian Giuseppe Franchiti in 1927 when he was examining the blood of Macaca fascicularis and he noted that it differed from Plasmodium cynomogli and Plasmodium inui. It was later seen by Campbell in 1931 in a long-tailed macaque imported from Singapore to the Calcutta School of Tropical Medicine and Hygiene in India. Campbell was interested in kala azar and was working under Napier. Napier inoculated the strain into three monkeys, one of which was a rhesus macaque (Macaca mulatta), which developed a fulminating infection. Knowing that the Protozoological Department were looking for a monkey malaria strain, they handed the original infected monkey to Biraj Mohan Das Gupta, who was the assistant of Robert Knowles. Dr Das Gupta maintained the species by serial passage in monkeys until Dr Knowles returned from leave. In 1932, Knowles and Das Gupta described the species in detail for the first time and showed that it could be transmitted to man by blood passage, but failed to name it. It was named by Sinton and Mulligan in 1932 after Dr Knowles. From early in the 1930s to 1955, P. knowlesi was used as a pyretic agent for the treatment of patients with neurosyphillis.

In 1957, it was suggested by Garnham et al. that P. knowlesi could be the fifth species capable of causing endemic malaria in humans.

In 1965, the first case of a naturally occurring infection of knowlesi malaria in humans was reported in an American man who had returned after working in the jungle in peninsular Malaysia. Although the infecting parasite was initially identified as P. falciparum, one day later it was then identified as P. malariae and it was only confirmed to be P. knowlesi after infected blood was used to inoculate Rhesus monkeys. A second report emerged in 1971 about the natural infection of a man in Malaysia with Plasmodium knowlesi followed by the description of a large focus of human infections in the Kapit Division of Sarawak, Malaysian Borneo. This was made possible due to the development of molecular detection assays which could differentiate between Plasmodium knowlesi and the morphologicall similar Plasmodium malariae. Since 2004, there has been an increasing number of reports of the incidence of P. knowlesi among humans in various countries in South East Asia, including Malaysia, Thailand, Singapore, the Philippines, Vietnam, Myanmar and Indonesia.

Work with archival samples has shown that infection with this parasite has occurred in Malaysia at least since the 1990s and it is now known to cause 70% of the malaria cases in certain areas of Sarawak.