A field study on malaria prevalence in southeastern Laos by polymerase chain reaction assay.

A detection survey for malaria infection by routine microscopy and polymerase chain reaction (PCR) assay was conducted on 336 inhabitants of two villages in Khammouane Province, Lao People's Democratic Republic (Lao PDR), in July 1997. Malaria infection was demonstrated in 58 (17.3%) subjects by microscopy and in 117 (34.8%) by PCR assay. Specimens positive by both methods were frequent in young villagers, suggesting the presence of many subclinical infections in older persons. The most common species of malaria parasite was Plasmodium falciparum (82.9%). Polymerase chain reaction assay detected mixed infections with 2-4 species in 27 specimens (23.1%). The results demonstrate that there are many subclinical malaria infections with low parasite level and infection with all four human malaria species in Lao PDR. The total estimated population in Phavang Village was 230 and in Sisomsouen Village, 430. Blood samples were collected from 143 and 193 of residents of each village, re- spectively. Samples were collected after informed consent was obtained for the survey of malaria infection. The ages of the subjects ranged from 2-68 years old (mean 22.9 19.3) in Phavang and 0-75 years old (mean 21.8 19.1) in Sisomsouen. Children 15 years old constituted 50% of the residents examined. The population of male : female par- ticipants in Phavang and Sisomsouen was 1.03 and 1.38, respectively.