Mass Treatment With Ivermectin Decreases Scabies Prevalence

Jennifer Garcia

December 22, 2015

Administration of oral ivermectin to whole communities can significantly decrease the prevalence of scabies and impetigo, according to results of a new study published in the December 10 issue of the New England Journal of Medicine.

"In many resource-poor settings and especially in tropical regions, scabies is a major underlying cause of high rates of bacterial skin infections and their consequences," Lucia Romani, MSocDev, from the Kirby Institute, University of New South Wales, Sydney, Australia, and colleagues write. "Mass drug administration shows promise as an important control strategy in countries in which scabies is endemic."

As part of the comparative Skin Health Intervention Fiji Trial (SHIFT), the researchers randomly assigned three Fijian island communities to receive three different scabies treatment protocols between September 2012 and September 2013.

Participants were grouped as follows: administration of topical permethrin to affected persons and their contacts (standard care group, n = 803), mass administration of topical permethrin (permethrin group, n = 532) regardless of the presence of scabies, or mass administration of oral ivermectin (200 μg/kg body weight), regardless of the presence of scabies (ivermectin group, n = 716). Depending on group allocation, a second application of permethrin or second dose of ivermectin was given 7 to 14 days later for participants with scabies at baseline. Children weighing less than 15 kg, pregnant women, participants with neurologic disease, or those with impaired function of the cytochrome P-450 pathway who were assigned to the ivermectin group were instead treated with topical permethrin. All participants with impetigo at baseline were also referred to clinics for antibiotic therapy.

The researchers found that the prevalence of scabies from baseline to 12 months went from 36.6% to 18.8% in the standard care group and from 41.7% to 15.8% in the permethrin group. The greatest reduction was noted in the ivermectin group, which went from 32.1% to 1.9% (relative reduction, 94%; 95% confidence interval [CI], 83% - 100%). The severity of scabies at baseline was similar across all three groups.

Similar results were seen in the decrease in impetigo, with the greatest decrease seen in the ivermectin group. The prevalence declined from 21.4% to 14.6% in the standard care group, 24.6% to 11.4% in the permethrin group, and 24.6% to 8.0% in the ivermectin group (relative reduction, 67%; 95% CI, 52% - 83%).

Itching and headache were the most common adverse events and were reported more frequently in the ivermectin group (5.3% and 3.8%, respectively) compared with those treated with permethrin (3.8% vs 0.9%, respectively).

The authors acknowledge that differences in community movement to the main island may have contributed to reinfestation, and therefore a perceived decline in treatment efficacy. They also note that the trial introduced a "higher level of care," which may have skewed results in the standard care group.

In an accompanying editorial, Bart J. Currie, MBBS, DTM&H, FRACP, from the Charles Darwin University and the Royal Darwin Hospital in Darwin, Australia, writes: "This study is timely, because scabies was added to the World Health Organization (WHO) list of neglected tropical diseases in 2013 and is estimated to affect more than 130 million people globally at any time."

Dr Currie goes on to write that "[m]ass drug administration is central to global control of some neglected tropical diseases," and that "SHIFT shows that, although the administration of topical permethrin and oral ivermectin may have similar efficacy in individual persons with scabies, the practical aspects of oral therapy translate to superior effectiveness on a large scale."

"SHIFT fills an important gap in evidence for scabies control, but effectiveness must now be evaluated beyond island settings and in larger populations," the study authors conclude.

Funding for this study was provided through a grant from the Australian National Health and Medical Research Council. The authors report receiving nonfinancial support from Merck Sharp & Dohme, Australia, who donated the ivermectin used in this study.

New Engl J Med. 2015;373:2305-2313, 2371-2372. Article full text, Editorial full text

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