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15 March 2023

Across the Pacific, outbreaks of arboviruses (mosquito-borne diseases) such as dengue, chikungunya, and Zika viruses are increasing in frequency, scale and impact. These outbreaks have the potential to overwhelm the health systems of small island nations. There is no treatment for these diseases, so prevention is crucial.

A ground-breaking AITHM-led study has mapped the distribution of arboviruses (mosquito-borne viruses) in the Solomon Islands to help the Pacific nation determine the best use of limited resources to safeguard residents from these escalating health threats.

“Understanding the prevalence of dengue, Zika, chikungunya and Ross River viruses across the country is essential baseline information to effectively plan and prioritise precious resources to implement the best possible mosquito control programs,” said the study’s lead scientist, AITHM Senior Research Fellow and medical entomologist, Dr Tanya Russell.

The ambitious research project, undertaken in close collaboration with the Solomon Islands Ministry of Health and National Vector Borne Diseases Control Program, visited 23 urban and rural villages across four provinces, where a total of 2,393 residents volunteered to provide blood samples to determine whether they had previously been infected with any of the viruses.

Prior to the study fieldwork in 2019, the Solomon Islands had weathered two unexpected major outbreaks of dengue, with at least 5,000 cases in 2013 and 12,000 in 2016/17. (The country’s total population at that time was 670,000.)

The first outbreak appears to have coincided with the arrival of the mosquito species Aedes aegypti, a much more efficient dengue vector (transmitter) than long-term Solomon Islands resident Aedes albopictus.

Dengue symptoms range from headaches and prolonged fever through to encephalitis and haemorrhagic fever (which both attack the brain). Even mild cases are debilitating and jeopardise ability to work (in a country with no social welfare safety net for the sick).

Subsequent analysis of the 2019 study blood samples, undertaken in Cairns by AITHM virologist, Associate Professor Paul Horwood, found 56 per cent of the study participants tested positive for exposure to either dengue or Zika viruses.

The results for Ross River virus provided the biggest surprise. Never previously recorded in the Solomon Islands, the study found the disease was not only present, but had gained a substantial foothold in the country, with 31 per cent of study participants testing positive for the virus.

Dr Russell said the study, which also collected a range of demographic data, would assist the Solomon Islands to tailor proactive vector control measures (such as insecticidal residual spraying) for villages most at risk, as well as respond rapidly to outbreaks.

AITHM will continue to support the country’s surveillance efforts via collaborative initiatives such the Pacific Mosquito Surveillance Strengthening for Impact project (PacMOSSI project). Dr Russell and AITHM vector biologist, Professor Tom Burkot lead the project, which has partnered with all Pacific Island Countries in the region.

“Australia doesn’t operate in isolation from other countries that are neighbouring us. We have seen this strongly through COVID. These diseases are transmitted around the world, between countries, very fast and very efficiently,” said Dr Russell.

“Our regional support to the Pacific and neighbouring countries to help improve capacity and understand the diseases that are in transmission in our region is hugely important for Australia.”

The Solomon Islands study was funded by the Australian Department of Foreign Affairs and Trade, and United States-based Intellectual Ventures Laboratory.

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