From Asia, the Novel (and Old) Fifth Malaria Plasmodium of HumanBeings

摘要

A novel form of human malaria Plasmodium knowlesi has been identified in small epidemic foci occurredduring the last decade in Malaysia. Based on a review of the available literature data, the Authors underline the diagnosticimportance of molecular biology examinations performed with primers which are specific of Plasmodium knowlesi, sincethe standard hemoscopy may fail in distinguishing Plasmodium knowlesi from Plasmodium malariae, due to their similarappearance. P. knowlesi has been reported as a causative parasite agent of life-threatening and even lethal forms ofmalaria. In humans, its clinical picture is more severe a compared to that of P. malariae, since the disease is characterizedby a greater parasitemia, versus that is referred in the course of P. malariae disease. The most effective carrier of P.knowlesi is represented by the mosquito Anopheles leucosphyrus, which is attracted by both humans and monkeys.Among primates, the natural hosts of P. Knowlesi are known until now and have been represented by Macaca fascicularisand Macaca nemestina, while other monkeys including Saimiri scirea and Macaca mulatta, which cannot becomeinfected. These might be useful in eventual experimental models. When facing the potentially severe evolution of humandisease by P. knowlesi, we remark the key role played by a prompt disease recognition, which is expected to be more easyand obvious in patients followed in endemic countries at elevate risk, but should be carefully implemented for subjectscoming back to health care services of western countries, presenting with a number of typical signs and symptoms ofmalaria, after travelling in South-East Asia where they were engaged in staying or making excursions in the tropicalforest. In these last cases, both diagnosis and treatment should be prompt, timely, and appropriate. According to literaturedata, in non-severe human cases the old and trivial chloroquine remained very effective against P. knowlesi, achieving thedisappearance of signs and symptoms in 96% of cases within the first day of pharmacological therapy. On the ground ofthe emerging epidemiological figures, P. knowlesi was added to Plasmodium vivax, Plasmodium ovale, Plasmodiummalariae, and Plasmodium falciparum, as the fifth etiological agent of human malaria. During the next years, it willbecome mandatory to plan an adequate surveillance programme of the epidemiological evolution of this novel form ofhuman malaria, paying also maximum attention to the clinical presentation of patients affected by P. knowlesi malaria,which are expected to suffer from a more severe clinical course, according to the time elapsed from the appearance of theearly signs and symptoms. Some preliminary clinical figures suggest that a greater severity is related to an increasedparasitemia, and parallels the increased interhuman infectious passages of parasites.