Monash University-led dengue fever study offers hope in disease battle

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Dengue fever infections dropped dramatically in an Indonesian study where a bacteria was introduced into disease-carrying mosquitoes, offering hope in the battle against an illness that sickens millions annually around the world.

Few people had heard of dengue 50 years ago, but it has been a relentless slow-burning pandemic and cases have increased dramatically. In 1970, only nine countries had faced severe dengue outbreaks, while now it is endemic to over 100 countries with up to 400 million infections a year. In 2021 dengue is the most rapidly spreading mosquito-borne disease in the world, including about eight million cases annually in Indonesia.

Dengue is commonly known as "breakbone fever" because it causes severe pain in muscles and bones, along with fever and nausea. Dengue can also leave long-term ill effects including joint and muscle pain, alopecia, anxiety and depression. Explosive outbreaks can overwhelm hospitals.

Results of a three-year study, was conducted by the World Mosquito Program at Monash University and Indonesia's Gadjah Mada University, was published in the New England Journal of Medicine

The trial involved releasing a harmless bacteria, called Wolbachia, into the dengue-carrying mosquito population in areas of Yogyakarta, a city on Java island where the experiment was conducted. The research team measured how it impacted the incidence of infections among three- to 45-year-olds.

Over the course of the trial, 318 dengue cases were detected in the untreated areas of the trial site and only 67 in the Wolbachia treated areas, which translates to a 77% reduction in dengue incidence in the treated areas of Yogyakarta. Efficacy against hospitalised dengue was even higher at 86%, with only 13 hospitalisations for dengue in the Wolbachia-treated area compared to 102 in the untreated area. It has now been expanded to other parts of the city.

All four dengue virus serotypes were detected among trial participants and efficacy was similar across them all.

"The 77% figure is honestly quite fantastic for a transmittable disease and we're very grateful with the result," said Adi Utarini, a public-health researcher from Gadjah Mada university who was a co-lead on the study.

Wolbachia suppresses the ability of the virus to replicate in dengue-carrying Aedes aegypti mosquitoes and cause infections when they bite humans. Previous trials involving Wolbachia, commonly found in fruit flies and other insects, also showed positive results in reducing dengue cases, researchers said.

Dr Katie Anders, director of impact assessment at the World Mosquito Programme, describes the bacteria as "naturally miraculous."

"This result is ground-breaking. We think it can have an even greater impact when it is deployed at scale in large cities around the world, where dengue is a huge public health problem," she said.

Cameron Simmons, who heads the World Mosquito Program at Monash University, said "in public health, 77% is a really, really big impact." 

"If this was a vaccine for COVID-19 we'd be delighted with a 77% impact. We're thrilled."

The Wolbachia bacteria has persisted at a very high level in the wild population. This is in sharp contrast to other control methods,  such as insecticides or releasing large numbers of sterile male mosquitoes,  that need to be kept up in order to suppress the mosquitos.

"The beauty of this approach is it's a 'once and done' method. After the upfront effort to establish Wolbachia in the mosquito population, it then sustains itself for years without needing more work,” Professor Simmons said.

Scientists hope the method could be a game-changer in a global battle against the sometimes fatal disease.

"This is the result we've been waiting for," said World Mosquito Program director Scott O'Neill.

"We have evidence our Wolbachia method is safe, sustainable and dramatically reduces incidence of dengue. It gives us great confidence in the positive impact this method will have worldwide when provided to communities at risk of these mosquito-transmitted diseases," he added.

While not endemic to Australia, in the past 30 years there have been almost 7,500 cases in Queensland and over 21,000 nationally, historically driven by imported cases from South-East Asia. Since 2011 the World Mosquito Program has been working in dengue-prone areas across northern and far northern Queensland, including large parts of the Cairns and Townsville regions. After a decade working in northern Queensland communities, long-term monitoring shows that Wolbachia has become self-sustaining at high levels. In areas where high levels of Wolbachia are present, there has been no evidence of local dengue transmission. 

Dr Richard Gair, Director Tropical Public Health Services in Cairns said that “Far North Queensland is now essentially a dengue-free area for the first time in well over 100 years.”

For information about disgnosing a suspected dengue patient please visit Queensland Health's dengue advice for health practitioners.