The high prevalence of Wuchereria bancrofti infections in indigenous tribes in northern Mindanao, Philippines.

Human filariasis was detected in an anthropological and medical survey among the indigenous Mamanwa people of the northernmost region of Mindanao, Philippines in specimens of thin blood smears and cultures of leucocytes from blood samples taken in the day time in September, 1978. Microfilaria positives were 23.2% (22/95) at Bo. Pangaylan, Santiago, 26.7% (28/105) at Kitcharao, Agusan del Norte, 19.3% (16/83) at Urbistondo, Surigao del Norte, Mindanao and none (0/50) at Abucay, Bataan, Luzon. Morphological characteristics of microfilaria were those of Wuchereria bancrofti. The periodicity of microfilaria observed in 3 Mamanwa people was nocturnally periodic with the peak hours at 12 o'clock midnight and the periodicity index at 124.4 following the method of Aikat & Das, or 92.35 following the method of Sasa & Tanaka. Microfilaria positives in the culture of leucocytes were as high as 41.2% (28/68). Since blood samples were taken in the day time and the filaria in these areas was nocturnally periodic, the prevalence of infection among these people is assumed to be much higher than the observed prevalence.