Interruption of annual single dose DEC regimen administration: impact on Wuchereria bancrofti microfilaraemia, vector infection and infectivity rates.

The effect of single dose diethylcarbamazine regimen (6 mg/kg body wt.) in comparison to standard DEC regimen i.e; 72 mg/kg body wt (administered in 12 consecutive days) in clearing Wuchereria bancrofti microfilariae from low density micro filariae carriers (1- 8 mf per 20 microl) and its impact on vector infection rate were studied in an urban region endemic for bancroftian filariasis. The efficacy of DEC regimens were determined by assessing the rate of successful treatment, percentage cure rate and percentage decrease in microfilariae count in treated subjects. The 12 days regimen was found very effective with 100% cure rate even after 4 years of drug therapy. In subjects, who received single dose DEC regimen, the rate of successful treatment, cure rate and percent decrease in micro filariae count was significantly low when assessed 24 hour after therapy. Reexamination of subjects in this group at 6,12, 24 and 48 months after therapy showed a sharp decline in all therapeutic indices and the microfilariae count reached pretreatment levels by 4th year of drug therapy. The single dose regimen had a marginal impact on vector infection and infectivity rates in Culex quinquefasciatus. A marked increase of vector infection and infectivity rates in parallel to human microfilaraemia rate was recorded from the same households when examined after 4th yr after therapy. Thus the single dose 6 mg/kg body wt. DEC regimen (administered only once) failed to clear microfilariae even in a situation of filarial low endemicity and did not influence the transmission potential of C. quinquefasciatus.