Amicrofilaraemic carriers of adult Wuchereria bancrofti

To determine the extent to which Wuchereria bancrofti infections can be detected in asymptomatic amicrofilaraemic men in Greater Recife, Brazil, we studied 100 asymptomatic men who were long-term residents (> or = 15 years) of this filariasis-endemic area and who were amicrofilaraemic in 60 microL of capillary blood collected at night. Increasing amounts (1, 5, and 10 mL) of venous blood were collected in consecutive weeks, filtered, and examined for microfilariae; 27 men were eventually found to be microfilariaemic and 10 remained amicrofilaraemic but were found to be carriers of living adult W. bancrofti by ultrasound examination of the scrotal area. Thus, 37% of 'amicrofilaraemic' men (in 60 microL of blood) were found to be infected by more thorough investigation. Ultrasound is a valuable tool to identify adult worm infections in amicrofilaraemic persons, particularly for evaluation of serological assays and immunological studies in which the distinction between 'amicrofilaraemic adult worm carriers' and 'endemic normal subjects' is critical.