1. Observations on filariasis made during medical travels in the Malay Peninsula are described. 2. The tentative diagnosis of endemic filariasis was made when cases typical of filarial elephantiasis were found in members of the indigenous population who have never resided in a previously known filariasis area, and was confirmed by finding microfilariae of Wuchereria malayi in bloods from that population. 3. Endemic filariasis has previously been reported associated with jungle swamp along the lower reaches of some of the larger rivers, and in certain coastal ricefield areas. It is reported in this paper in undeveloped inland areas of Perak, Pahang and Selangor, far distant from the previously described foci. This data has been summarized in maps and an Appendix. 4. In most inland areas where a search has been made, it has been possible to find evidence of endemic filariasis and sometimes the parasite rate has been over 50%. 5. The geographical distribution of the disease has not yet been defined, but is certainly more extensive than that described in this paper. 6. Infection probably takes place at an altitude of 1,500 feet in mountain valleys in Malaya.
The author reviews the distribution, epidemiology, and treatment of filarial infection due to Brugia malayi, with special reference to Malaya. B. malayi infection in man is confined to the Far East between longitudes 75 degrees E and 140 degrees E and is essentially rural. The chief vectors are Mansonia spp., Anopheles hyrcanus group, A. barbirostris group, and Aëdes togoi. The epidemiological picture is complicated by the fact that B. malayi and other closely related species have now been found in several species of animals. The existence of an animal reservoir of infection might have important implications for filariasis control. As to the treatment of B. malayi infection, diethylcarbamazine has been found to reduce the microfilaria count and to kill the adult worms; the severe febrile reactions of microfilaria carriers to the initial doses of this drug may be reduced by administration of the steroid prednisolone.
The periodicity of the microfilariae of Brugia malayi was studied in 9 human carriers from Shin-san Ri, Seong-san Myon, Cheju Island. The periodicity pattern was markedly nocturnal and the peaks were observed between 21:30 p.m. and 5:30 a.m. The average peak count was 1:30 a.m. and the percentage of peak count at this time was 95.3. The ratio of minimum of the average peak count percentage to the maximum was 8.3. The periodicity pattern of B.malayi in Cheju Island was compared with that in Inland and no differences were found between two forms. From the above observations, it was concluded that the periodicity of B. malayi in Korea is markedly nocturnal and closely resembles that in the strain of Penang, Malaya.
R. sabanus and R. muelleri are very common in the lowland forests of Malaysia. In nature they are infected with Breinlia sp. and D. ramachandrani. In an attempt to determine whether they are also susceptible to subperiodic B. malayi and thereby being potential reservoirs of infection of the disease, 24 R. muelleri and 17 R. sabanus were experimentally infected with the parasite. Results show that although they can support the full development of the parasite, they are poor hosts. This confirms the observation that in Malaysia natural infection of Rattus spp. with the parasite has not been seen. These rats therefore are probably not important in the zoonotic transmission of subperiodic B. malayi in Malaysia.