Asymptomatic malaria infections among foreign migrant workers in Thailand.

OBJECTIVE To determine the prevalence of malaria infections among foreign migrant workers in Thailand. METHODS Giemsa-stained thin and thick blood films were prepared from blood samples of 294 foreign migrant workers recruited in the study. Microscopic examination of these blood films was performed for malaria detection. RESULTS Blood film examination revealed 1.36% malaria infections in these 294 subjects. All positive cases were male Myanmar workers in which their blood films only ring stage of Plasmodium spp. was found at low parasite density (mean= 144 parasites/μ L of blood). The prevalence of malaria infections was not significantly different among foreign migrant workers classified by age, gender, and resident province (P>0.05). Thin blood films of these workers also showed 78.91% hypochromic erythrocytes and 61.9% relative Eosinophilia. CONCLUSIONS These findings indicate a high risk of malaria transmission. Therefore active malaria surveillance by using molecular methods with more sensitive and specific than microscopy should be considered for malaria control in foreign migrant workers.