One dose of anti-parasite drug effective at reducing scabies

One dose of the anti-parasite drug ivermectin is just as effective as two at significantly reducing the spread of scabies — the contagious, intensely itchy skin condition — according to a new international study.

The research, led by the Murdoch Children’s Research Institute (MCRI) in collaboration with the Fiji Ministry of Health and Medical Services and the Kirby Institute at UNSW, found the mass drug administration of one dose of ivermectin was not inferior to two doses, taken a week apart, for reducing scabies prevalence in Fiji. The results were published in the journal PLOS Medicine.

Scabies is a neglected tropical disease, with high infection rates in many Pacific nations, in parts of South America and Africa, and in remote Australian Indigenous communities. The constant scratching caused by the mites leads to the skin infection impetigo, which can lead to rheumatic heart disease and chronic kidney failure if Strep A bacteria enter the wound.

MCRI Professor Andrew Steer said while a two-dose treatment of ivermectin has already proven to be successful at reducing community prevalence of scabies — an approach that has been endorsed by World Health Organization (WHO) — this has its disadvantages. The new study was thus designed to determine if community-wide treatment with one dose of ivermectin could substantially reduce both the burden and transmission of scabies.

“Ivermectin can’t kill mites’ eggs; therefore, a second dose seven to 14 days after the first (when eggs have hatched) is recommended and has been the standard for mass drug administration protocols,” Prof Steer said.

“But a second dose increases the cost, duration [and] burden on the community, and is more challenging to integrate with other neglected tropical disease mass drug administration programs, which are all one dose.”

The randomised controlled trial involved 3812 participants across 35 villages on two Fijian islands. In addition to one- and two-dose ivermectin treatments, a ‘screen and treat’ approach using a cream medication, known as permethrin, was also tested.

At 12 months, the two-dose ivermectin group had a scabies prevalence of 1.3%, down from 11.7%, while the one-dose ivermectin group was 2.7%, down from 15.2%. The screen-and-treat group was 1.1%, down from 13.6%. There was also a decrease in impetigo prevalence in all groups to 1% or less.

Kirby Institute Professor John Kaldor said despite a screen-and-treat approach being effective, the strategy was impractical to implement as a large-scale public health strategy.

“A screen-and-treat approach is labour-intensive, requiring a large workforce of highly skilled clinical examiners to screen an entire population,” he said. “Now that we have this evidence that a one-dose strategy performs well in small island settings, we need to see how well it performs in larger populations.”

The findings come as the WHO has designated MCRI’s Tropical Diseases group as its first Collaborating Centre for Scabies Control. Prof Steer will act as Head of the WHO Collaborating Centre, which will be based at MCRI for four years. MCRI and its partners are also leading a global program aiming to equip low- and middle-income countries with the tools and the resources to detect, monitor and control scabies in affected communities.

Image credit: ©stock.adobe.com/au/Dynea

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