Mass Drug Administration Yields Sustained Reductions in Scabies Infections

A study in PLOS Neglected Tropical Diseases suggests that mass treatment with ivermectin followed by active case finding can result in a significant and sustained reduction of the presence of both scabies and bacterial skin infections.

The finding is potentially important in tropical areas where scabies (a parasitic infection caused by the mite Sarcoptes scabiei) is an ongoing risk factor and can lead to kidney disease and possibly rheumatic heart disease. Traditional management of scabies involves treating individuals and close contacts with topical medicines, which may cure the patient but, according to the researchers, “does not have any impact on the overall amount of scabies in a community.”

Mass drug administration (MDA) against scabies using ivermectin has been shown to be effective, but the current study is among the first to look at how long the beneficial effect of the MDA lasts. It provides a 15-year follow-up on one of the first communities in the world to ever receive ivermectin MDA for the control of scabies--the Lau Lagoon region in the Solomon Islands.

During the initial MDA, a step-wedge design was used. There was an initial round of community mass treatment that was highly successful, taking the prevalence of scabies in children from 25% at the start of the study to 0.7% at the final visit. There was an accompanying decline in the prevalence of impetigo from 40% to 22%. The prevalence of scabies in adults fell from approximately 20% at the start of the study to 0.8% at the final visit. Since the cessation of the study in 2000 no further active control measures have been undertaken in these communities.

All residents underwent a standardized examination for the detection of scabies and impetigo. Three hundred and thirty eight residents were examined, representing 69% of the total population of the five communities. Only 1 case of scabies was found, in an adult who had recently returned from the mainland. The prevalence of active impetigo was 8.8% overall and 12.4% in children aged 12 years or less. This represents an “extremely low” prevalence, according to the study authors.

“The prevalence of scabies found in this follow-up study is similar to that at the end of the original control programme in 2000 and suggests that the intervention undertaken has resulted in a sustained reduction in the prevalence of scabies on these islands,” the researchers noted. “Of interest, the original study used only a single dose of ivermectin, rather than the two dose regime that is now recommended. It is likely that the frequent follow-up and retreatment undertaken in the control program mitigated the effect of a reduced initial dose and contributed to the sustained reduction in scabies prevalence observed.”

The researchers would like to see larger-scale studies and integration with other neglected tropical disease programs to further the effort. “The extremely low prevalence of scabies found in this study, despite the cessation of the scabies control program for more than 15 years, suggests that long-term disease control is a realistic possibility,” the authors concluded.