Tongan study links scabies to rheumatic heart disease

A new study has found a strong link between scabies and rheumatic heart disease in Tongan schoolchildren, prompting researchers from Waipapa Taumata Rau, University of Auckland to call for further investigation.

The research was funded by the Health Research Council and conducted with the Tongan Ministry of Health and Tonga National University. See Journal of Paediatrics and Child Health.

“Tonga screens all primary school children every two years for rheumatic heart disease as part of its Mafu Sai (Good Heart) programme,” says Pacific health researcher Dr Gerhard Sundborn from the University of Auckland. “In 2023, some were also checked for scabies and skin infection.”

Researchers trained nurses in a visual method of scabies screening and supervised them for consistency. They screened 400 children from four Tongatapu schools and found:

• Scabies: 29.8 percent (around one in three children)
• Impetigo (skin infection): 20 percent (one in five)
• More severe bacterial skin infection: 15.5 percent
• Rheumatic heart disease: 4.5 percent (one in 22).

One child’s scabies diagnosis was confirmed by laboratory testing in Auckland.

Children with both scabies and a bacterial skin infection were almost five times more likely to have rheumatic heart disease compared with children with healthy skin.

The study also found that the more severe the skin problems, the higher the risk of rheumatic heart disease – a pattern that was statistically significant.

The combination of severe bacterial skin infection and scabies was strongly linked to rheumatic heart disease, while scabies or impetigo on their own were not.

Researchers estimate that around one-quarter of rheumatic heart disease cases could potentially be prevented if scabies and skin infections were eliminated. The strength of the link is considered large by international standards, similar to other well-known health risks.

Lead investigator Dr Simon Thornley from the University of Auckland says this is a very strong association, and it suggests that tackling scabies could dramatically reduce rheumatic heart disease.

“Mass drug administration using ivermectin has worked in the Pacific – studies in Fiji show scabies rates dropped by 80 to 90 percent within two years.”

The study cannot prove causation, but it offers evidence that scabies control could play a key role in prevention.

Rheumatic heart disease remains common in Tonga, affecting five in 100 children. In New Zealand, rates are one in 1,000 overall, but one in 100 Māori children and two in 100 Pacific children.

Next steps
Researchers plan a pilot project on a small island near Tongatapu with about 5,000 residents.

Working with the Ministry of Health Tonga, contingent on funding, they will carry out mass treatment to eliminate scabies and then monitor new cases of rheumatic fever and rheumatic heart disease over several years. If successful, this approach could transform prevention strategies across the Pacific.

Tongan researcher Mele Tilema Cama, Dean of Faculty of Nursing and Health Science at Tonga National University, says, “For 20 years our Mafu Sai programme has screened about 5,000 primary school children annually. It’s resource-intensive but vital for early treatment. We are excited this research may offer a way to prevent rheumatic heart disease.”