Mass drug administration reduces scabies cases

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Mass drug administration (MDA) of two antibiotics can be highly effective at reducing cases of scabies and the bacterial infection impetigo, according to research. The study was conducted by the London School of Hygiene & Tropical Medicine (LSHTM), Murdoch Children’s Research Institute (MCRI), the Kirby Institute at University of New South Wales Sydney and the Solomon Islands Ministry of Health and Medical Services.

It saw the entire population of Choiseul Province of the Solomon Islands (26,000 people), in the Pacific, given one round of the antibiotics ivermectin and azithromycin together. The prevalence of scabies and impetigo in residents of 10 randomly selected villages before and after MDA by the Solomon Islands Ministry of Health and Medical Services was then compared.

The strategy reduced scabies cases from 19% to 2% (90% reduction), and impetigo cases from about 25% to about 6% (75% reduction), in one year.

The study is the largest evaluation of ivermectin-based mass drug administration for the control of scabies, and supports large-scale implementation of this strategy for control of scabies in locations where the condition is identified as a public health priority.

Dr Michael Marks from LSHTM and co-author of the study, said: “We know that treating individual cases of scabies is not effective, however treatment of entire communities has been shown in small community-based trials to substantially reduce cases. Our study demonstrates this can be an effective approach when delivered at a larger scale.”

Scabies is a parasitic skin disease that affects an estimated 200m people worldwide. The disease causes skin inflammation with itch that is frequently severe, and often associated with bacterial skin infection caused by Staphylococcus aureus and Streptococcus pyogenes (impetigo). This can in turn lead to severe complications including septicaemia and post-streptococcal glomerulonephritis. In 2017, growing awareness of the burden of disease due to scabies led the World Health Organisation to recognise it as a neglected tropical disease.

Dr Lucia Romani from the Kirby Institute and lead author on the paper, said: “Scabies is too common in many tropical developing countries, especially in rural and remote communities where people share small living and sleeping spaces access to treatment is limited.”

This new study was conducted in Choiseul Province of the Solomon Islands where a very high number of scabies cases have been reported. 1,399 people had their skin examined at the start of the MDA in 2015, with 261 (one in five) having scabies and 347 having impetigo. Twelve months on, 1,261 people were examined with only 29 people with scabies and 81 with impetigo. Additionally, there was also almost 6,000 less people presenting to outpatient clinics, a drop of 36.1% cent, in the three-months after MDA. Presentations for skin sores, boils and abscesses also fell by 50.9%.

MCRI professor and study PI Andrew Steer said: “Treatment is highly effective at reducing both scabies and impetigo and we saw significant reductions in outpatient presentations, especially those needing treatment for skin sores, boils and skin abscesses.”

Oliver Sokana, from the Solomon Islands Ministry of Health, said: “Both diseases were most common in children aged between five and nine years old.”

Marks said: “Scabies is extremely common, and is a major risk factor for dangerous bacterial skin infection. Our study provides crucial evidence for the global strategy of scabies control being developed.”

The authors acknowledge limitations of their study including that is was non-randomised so they are unable to say with certainty that factors other than the intervention did not influence the outcome. Further research is needed to assess durability and scalability of mass drug administration in larger, non-island populations, and to assess its effect on the severe bacterial complications of scabies.

The study was funded by the International Trachoma Initiative; the Murdoch Children’s Research Institute, Australia; the Scobie and Claire Mackinnon Trust, Australia; and the Wellcome Trust.

Background: In small community-based trials, mass drug administration of ivermectin has been shown to substantially decrease the prevalence of both scabies and secondary impetigo; however, their effect at large scale is untested. Additionally, combined mass administration of drugs for two or more neglected diseases has potential practical advantages, but efficacy of potential combinations should be confirmed.
Methods: The azithromycin ivermectin mass drug administration (AIM) trial was a prospective, single-arm, before-and-after, community intervention study to assess the efficacy of mass drug administration of ivermectin for scabies and impetigo, with coadministration of azithromycin for trachoma. Mass drug administration was offered to the entire population of Choiseul Province, Solomon Islands, and of this population we randomly selected two sets of ten sentinel villages for monitoring, one at baseline and the other at 12 months. Participants were offered a single dose of 20 mg/kg azithromycin, using weight-based bands. Children weighing less than 12·5 kg received azithromycin oral suspension (20 mg/kg), and infants younger than 6 months received topical 1% tetracycline ointment. For ivermectin, participants were offered two doses of oral ivermectin 200 μg/kg 7–14 days apart using weight-based bands, or 5% permethrin cream 7–14 days apart if ivermectin was contraindicated. Our study had the primary outcomes of safety and feasibility of large-scale mass coadministration of oral ivermectin and azithromycin, which have been previously reported. We report here the prevalence of scabies and impetigo in residents of the ten baseline villages compared with those in the ten 12-month villages, as measured by examination of the skin, which was a secondary outcome of the trial. Further outcomes were comparison of the number of all-cause outpatient attendances at government clinics in Choiseul Province at various timepoints before and after mass drug administration. The trial was registered with the Australian and New Zealand Trials Registry (ACTRN12615001199505).
Findings: During September, 2015, over 4 weeks, 26 188 people (99·3% of the estimated population of Choiseul [n=26 372] as determined at the 2009 census) were treated. At baseline, 1399 (84·2%) of 1662 people living in the first ten villages had their skin examined, of whom 261 (18·7%) had scabies and 347 (24·8%) had impetigo. At 12 months after mass drug administration, 1261 (77·6%) of 1625 people in the second set of ten villages had their skin examined, of whom 29 (2·3%) had scabies (relative reduction 88%, 95% CI 76·5–99·3) and 81 (6·4%) had impetigo (relative reduction 74%, 63·4–84·7). In the 3 months after mass drug administration, 10 614 attended outpatient clinics for any reason compared with 16 602 in the 3 months before administration (decrease of 36·1%, 95% CI 34·7–37·6), and during this period attendance for skin sores, boils, and abscesses decreased by 50·9% (95% CI 48·6–53·1).
Interpretation: Ivermectin-based mass drug administration can be scaled to a population of over 25 000 with high efficacy and this level of efficacy can be achieved when mass drug administration for scabies is integrated with mass drug administration of azithromycin for trachoma. These findings will contribute to development of population-level control strategies. Further research is needed to assess durability and scalability of mass drug administration in larger, non-island populations, and to assess its effect on the severe bacterial complications of scabies.

Lucia Romani, Michael Marks, Oliver Sokana, Titus Nasi, Bakaai KamorikiBillie Cordell, Handan Wand, Margot J Whitfeld, Daniel Engelman, Anthony W Solomon, John M Kaldor, Andrew C Steer

London School of Hygiene & Tropical Medicine material
The Lancet Infectious Diseases abstract

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