Studies were accomplished in residents of South Vietnam to determine the geographic extent, prevalence, and periodicity of filariasis. Examination of concentrated, peripheral-blood samples revealed endemic foci of infection with Wuchereria bancrofti in Montagnard tribespeople residing in areas north and west of Saigon. No infections were demonstrated in residents of Saigon, in a central highland village, or in a Mekong River delta district. Prevalences in endemic areas ranged from 5 to 22%. In 12 persons with microfilaremia, quantitative studies on blood specimens collected at regular intervals over a 24-hour span demonstrated a nocturnal periodicity. Some specimens were obtained from native residents and U.S. servicemen for determination of filarial antibodies with the soluble-antigen fluorescent-antibody (SAFA) test. In native residents of endemic areas, the rates of seropositivity were 84% in those with microfilaremia, and 51% in those without demonstrable microfilaremia (total equals 55% seropositive). Rates of seropositivity in U. S. servicemen were 11% in endemic areas compared with 3% in apparently non-endemic areas. Moreover, when U. S. servicemen in an endemic area were characterized according to type of duty, the rate of positive reactions in field troops was three times higher than that of base-camp personnel. One U. S. field soldier, who was first seen with inguinal adenopathy and peripheral hypereosinophilia, was found to have circulating microfilariae of W. bancrofti and a positive SAFA test. The high rates of seropositivity in native residents and U. S. servicemen in endemic areas probably reflect immunologic responses to the Filarioidea that infect man or other animals, or to both.
U. S. Army Hospital, Fort Ord, California 93941.
Los Angeles County General Hospital, Los Angeles, California 90033.