Immunomonitoring of filarial patients during DEC therapy in an endemic area: a seven-year follow-up.

A group of 27 Wuchereria bancrofti infected persons from an endemic area, who had undergone treatment with diethylcarbamazine (DEC), were followed for 7 years to understand its effect on microfilaraemia, immune status and on the recurrence of infection. Treatment with DEC was for 14 days (day 1, 1 mg kg-1 body weight, day 2, 2 mg kg-1 body weight and from day 3 onwards 6 mg kg-1 body weight) followed by one dose (6 mg kg-1 body weight) on days 360, 540 and at the end of years 2, 3, 4, 6 and 7. After a 2-year follow-up the patients were divided into two groups. Group A consisted of cases that showed no reappearance of microfilariae (mf) and Group B of those cases that showed reappearance of mf. Further follow-up in the next 5 years showed that none of the cases in Group A were positive for mf at any time. In contrast, mf were detected in Group B in 14, 15, 27 and 33% of the cases followed at the end of years 3, 4, 6 and 7 respectively. Both groups showed a decrease in filarial IgG antibody and mf excretory-secretory antigen levels in the initial 4 years followed by increased levels at the end of years 6 and 7. The reappearance of filarial antibody and antigen in 50-70% of Group A and 68-100% of Group B at the end of year 7 suggests the existence of active infection in these cases. No cases followed in this study developed clinical symptoms. This study shows that long-term DEC therapy and immunomonitoring of mf patients is essential in an endemic area for arresting transmission and prevention of pathology associated with clinical manifestations.