Although mosquitos of the Anopheles umbrosus group have long been recognized as important vectors of human malaria in Malaya, there have been doubts about the origin of some of the malaria infections found, especially in A. umbrosus and A. letifer. Investigations have accordingly been carried out in the Malayan swamp-forest, in conjunction with laboratory studies, into the nature of malaria infections in wild-caught mosquitos, the biting behaviour of anophelines and the presence of malaria infection in man and animals. The authors conclude from the results reported in this paper that A. umbrosus is a vector of mouse deer malaria and rarely, if ever, transmits primate malaria; that A. letifer transmits both human and mouse deer malaria; and that A. baezai and A. roperi are probably vectors of mouse deer malaria.
An immature Glossy Tree-Starling (Aplonis panayensis strigatus), also known as ‘burong perling’ in Malay, was captured in the vicinity of the Institute for Medical Research, Kuala Lumpur. It was found to harbour a small malaria parasite which showed the characteristics of the sub-genus Novyella (Corradetti et al, 1963) viz:
1. Trophozoites small with little cytoplasm, relatively large nuclear elements, the parasite usually applied to the host-cell nucleus.
2. Schizonts with usually less than eight merozoites. 3. Pigment small and difficult to see except in the schizonts and in the gametocytes where the pigment granules are large and usually clustered at one end.
4. The parasite rarely distorts the host erythrocyte. Unfortunately the bird died a few days later before detailed work on duration of the schizogonic cycle and experimental transmission could be done. The parasite has the following morphological features and most of the larger forms, asexual and sexual, assume the characteristic position proximal to the nucleus of the avian erythrocyte. Trophozoites: The earliest forms are ‘rings’ with a fairly marked vacuole. As the organism grows older, it produces a grain or two of pigment. The parasite at this stage tends to occupy a polar position in the host erythrocyte. Schizonts: The segmenting forms are usually attached to the pole end of the host-cell nucleus. The number of chromatin segments varies from 3 to 8, with a prevalent range of 4 to 6. The cytoplasm is scanty and pale with a prominent little mass of blackish-brown pigment or a close collection of granules. A rare mature schizont with 8 merozoites was seen in which the nucleus of the parasitised erythrocyte was displaced somewhat similar to figure 20 of Plate I portrayed in the original paper by Manwell (1935). Gametocytes: The sexual forms are often narrow and elongate, and are closely applied to the nucleus of the host erythrocyte. The outline of the parasite is frequently irregular. The cytoplasm is pale and vacuolated with coarse conspicuous granules of blackish-brown pigment usually collected at one end; sometimes either one or both ends curved around the host-cell nucleus. Although this parasite has some affinites to both P. nucleophiltim and P. hexamerium the lack of adequate study of the avian malarias of South-East Asia precludes even provisional identification of this parasite. On two occasions numerous gametocytes were seen in the peripheral blood of the bird and four species of laboratory-reared culicines (three indigenous to Malaya) were allowed to feed on it. Ten Andes togoi, 19 Culex sitiens and seven Culex fatigans were completely refractory to development of the parasite. Two of 17 Aedes aegypti had a single small oocyst each; both oocysts appeared to be degenerating. A Giemsa-stained thin blood film together with drawings made from the microscope showing the different forms of the parasite were demonstrated. REFERENCES
Corradetti, A., Garnham, P. C. & Laird, M. (i963). Parassitologia, 5, 1-4.
Manwell, R. D. (l935). Amer. J. Trop. Med 15, 265-283.
...(1938). Ibid., 18, 565-575
Chloroquine resistance is a well established entity in South East Asia, and presents a problem of increasing importance. Strains of P. falciparum resistant to chloroquine have also been found to be resistant to amodiaquine and a combination of pyrimethamine and sulphadoxine. Knowledge of the drug sensitivity of the strains of malaria parasite in a given locality is important so that the right choice of drugs can be made in treatment of the disease. The treatment of chloroquine resistant malaria in West Malaysia is a subject of another paper but suffice it to say that increased doses of chloroquine have still been found to be effective in treating many cases of falciparum malaria from areas of chloroquine resistance.