One dose of ivermectin reduces scabies transmission as well as two doses

A single dose of ivermectin was as effective as two doses one week apart at reducing the spread of scabies in Fiji.

This finding comes from a study conducted by the Murdoch Children’s Research Institute (MCRI) in collaboration with the Fiji Ministry of Health and Medical Services and the Kirby Institute at the University of New South Wales.

The research group also found that a ‘screen-and-treat’ approach using permethrin cream was also effective in reducing scabies among participants and their households.

“Scabies and impetigo are common in Fiji, affecting 20 per cent of the population at any one time, and up to half of our children. Research into how to tackle scabies is important for Fiji and many Pacific countries,” said lead Fijian researcher Dr. Josaia Samuela in a press release on Feb. 11, 2022.

The study, a randomized controlled trial, involved 3,812 participants across 35 villages on two Fijian islands. At 12 months, the two-dose ivermectin group had a scabies prevalence decrease to 1.3% from 11.7%In the one-dose ivermectin group, prevalence decreased to 2.7% from 15.2%. Patients in the permethrin screen-and-treat group had a decrease to 1.1% from 13.6%. There was also a decrease in impetigo prevalence in all groups to 1% or less.

In the release, MCRI Professor Andrew Steer said while two doses of ivermectin had already proven to be successful at reducing community prevalence of scabies, a one-dose strategy would have substantial advantages.

“Ivermectin cannot 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,” he said.

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

Kirby Institute Professor John Kaldor said in the release that despite the screen-and-treat approach also 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 study findings were published in PLOS Medicine (Nov. 10, 2021; 18(11):e1003849).