Research Article: Impact of an Ivermectin Mass Drug Administration on Scabies Prevalence in a Remote Australian Aboriginal Community

Date Published: October 30, 2015

Publisher: Public Library of Science

Author(s): Thérèse M. Kearns, Richard Speare, Allen C. Cheng, James McCarthy, Jonathan R. Carapetis, Deborah C. Holt, Bart J. Currie, Wendy Page, Jennifer Shield, Roslyn Gundjirryirr, Leanne Bundhala, Eddie Mulholland, Mark Chatfield, Ross M. Andrews, Joseph M. Vinetz.

Abstract: BackgroundScabies is endemic in many Aboriginal and Torres Strait Islander communities, with 69% of infants infected in the first year of life. We report the outcomes against scabies of two oral ivermectin mass drug administrations (MDAs) delivered 12 months apart in a remote Australian Aboriginal community.MethodsUtilizing a before and after study design, we measured scabies prevalence through population census with sequential MDAs at baseline and month 12. Surveys at months 6 and 18 determined disease acquisition and treatment failures. Scabies infestations were diagnosed clinically with additional laboratory investigations for crusted scabies. Non-pregnant participants weighing ≥15 kg were administered a single 200 μg/kg ivermectin dose, repeated after 2–3 weeks if scabies was diagnosed, others followed a standard alternative algorithm.Principal FindingsWe saw >1000 participants at each population census. Scabies prevalence fell from 4% at baseline to 1% at month 6. Prevalence rose to 9% at month 12 amongst the baseline cohort in association with an identified exposure to a presumptive crusted scabies case with a higher prevalence of 14% amongst new entries to the cohort. At month 18, scabies prevalence fell to 2%. Scabies acquisitions six months after each MDA were 1% and 2% whilst treatment failures were 6% and 5% respectively.ConclusionScabies prevalence reduced in the six months after each MDA with a low risk of acquisition (1–2%). However, in a setting where living conditions are conducive to high scabies transmissibility, exposure to presumptive crusted scabies and population mobility, a sustained reduction in prevalence was not achieved.Clinical Trial RegistrationAustralian New Zealand Clinical Trial Register (ACTRN—12609000654257).

Partial Text: Scabies mites infect up to 300 million people worldwide, most of whom are children living in poverty and overcrowded conditions.[1–3] In remote Australian Aboriginal communities, scabies has been near universal during the first year of life (69%).[4] Secondary infections with highly pathogenic bacterial pathogens Streptococcus pyogenes and Staphylococcus aureus contribute to high rates of pyoderma in these communities.[5–8] Acute post-streptococcal glomerulonephritis (APSGN) and streptococcal and staphylococcal sepsis,[9],[10] are recognised complications of pyoderma, whereas rheumatic fever, rheumatic heart disease and chronic renal failure are postulated sequelae that all occur in Australian Aboriginal people at the highest rates in the world.[11,12] In contrast, scabies is infrequently seen in non-Indigenous Australians.[2,8,13]

The setting was a remote island community, 550km from Darwin, Australia with an estimated population of 2121.[22] Most residents lived in the main community; 200–400 lived in one of 10 associated homelands outside the community (five of which were accessible only by air/water).

At baseline, there were 1256 residents on the household occupancy lists in the population census (March-September 2010), of which 1013 (81%) consented to participate. Most participants (n = 960, 95%) were seen over a four month period (April-July). The median number of participants per house was nine (IQR 4–13) from 127 (80%) houses visited. Non-participating households were mostly those occupied by non-Aboriginal residents working in the community. Seven of the 10 homelands consented to participate; one refused whilst residents from the other two homelands were seen in houses in the main community. A total of 1002 participants had data recorded on scabies at baseline, with scabies data missing for the remaining 11 participants (1%).

In our study, MDA incorporating ivermectin had a demonstrable but relatively short-term impact on scabies prevalence. In the six-months following each MDA, both the low overall prevalence (1–3%) and the low acquisition rates (1–2%) suggest that transmission was substantially reduced. However, the rapid rise in prevalence at month 12 highlights that an MDA program, where utilised, needs to be incorporated with a multi-faceted control program and ongoing surveillance in the community.



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