Serological evidence of schistosomiasis among Orang Asli from three areas of Peninsular Malaysia

Using ELISA and COPT diagnostic tests, serological evidence of Malaysian schistosomiasis was discovered among Orang Asli populations from three areas in Peninsular Malaysia. Serum samples collected in 1975 indicated an ELISA-positive prevalence of 25% and a COPT prevalence of 11% from Pos Iskandar, Pahang and an ELISA prevalence of 13% and a COPT of 4% from Bukit Lanjan, Selangor. Resurveys at these site in 1982-1984 showed a continued presence of serological positive individuals but prevalence rates were markedly lower: 7% and 1% for ELISA and 4% and 2% for COPT at Pos Iskandar and Bukit Lanjan respectively. Snail hosts were not found at either site. The source of infection for persons living in these lowland areas remains unknown. In a third area, Kuala Tahan, Pahang, located in the foothills of the central mountain range, foci of transmission have been found near to Orang Asli settlements. The serological prevalence rate among Negrito Orang Asli in that study area was 9% for ELISA and 4% for COPT. Thirty-three of 36 COPT-positive sera produced vacuolated bleb precipates and in 31 these were the only reactions seen. The high percentage of positives producing only these precipates suggests that among Orang Asli schistosomiasis patients such reactions are not an indication of recently acquired infection as has been reported for schistosomiasis patients in the Philippines.