Large-scale trials see decrease in dengue infections following release of Wolbachia-infected mosquitos

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With the global surge of dengue infections and fears that climate change will increase the disease’s distribution, an international team of researchers presented the first large-scale evidence that infecting mosquitoes with Wolbachia could drastically reduce infections.

Today at the Annual Meeting of the American Society of Tropical Medicine and Hygiene (ASTMH; 20–24 November 2019, MD, USA), researchers at the World Mosquito Program (WMP) reported a 76% reduction in dengue transmission in a community in Indonesia who frequently endure dengue outbreaks.

The teams work in Indonesia involved an experimental release of Wolbachia-infected mosquitoes – created in a laboratory – in an area of ~65,000 people. The large reduction in infections was calculated by comparing number of cases with a nearby control population.

“We are very encouraged by the public health impact we are seeing – it highlights the potential of this approach to fight dengue and related mosquito-borne diseases at a global scale,” commented Cameron Simmons, Director of Impact Assessment. “Evidence is rapidly accumulating that areas where Wolbachia-infected mosquitoes have been deployed have fewer reports of dengue than untreated areas.”

Dengue causes severe joint pain and can lead to fatal complications, however, currently there are no drugs available to treat the disease. Furthermore, the only licensed dengue vaccine has been associated with safety problems – the ASTMH Annual Meeting will also feature a highly anticipated update on a late-stage trial of a new vaccine.

At the ASTMH conference today, expert in the epidemiology of dengue at WMP, Katie Anders also presented findings published earlier in the year demonstrating that local transmission of dengue ceased in Far North Queensland, Australia. The release of Wolbachia-infected mosquitoes 8 years ago resulted in cases of infections being reduced by 96% in that region.

The WMP Wolbachia trials are ongoing and due to their promising findings so far, will be expanding to Colombia, Sri Lanka, India and Western Pacific island nations.

However, the team emphasized that many tools are required to control dengue. Each release was followed by intensive community outreach and education to inform the local community about the safety of Wolbachia bacteria and its potential impact on the surrounding environment.

This approach of fighting dengue has been noted to have several advantages over other methods. Wolbachia has none of the toxicity associated with conventional insecticides and does not require mosquitoes to be genetically modified. Furthermore, it is a self-sustaining method making it highly cost effective.

“This is exciting work, carried out in the midst of an explosion in dengue infections that health authorities are finding very difficult to control,” commented ASTMH President, Chandy C. John. “The combination of advanced science and committed community engagement is impressive – and essential to its success.”

Wolbachia is naturally present in many insects, however, is not found in the Aedes aegypti mosquitoes that are the main vectors of dengue, chikungunya and Zika – all of which belong to a class of viruses called arboviruses.

Near Rio de Janeiro, Brazil, a reduction of >70% was observed in an urban area for cases of both dengue and chikungunya.

Chikungunya is becoming a growing problem across Latin America and the Caribbean. “There has been an epidemic of chikungunya in these areas,” explained Lucina Moreira, WMP’s Program Lead in Brazil.

Further, Moreira commented that Brazil’s Ministry of Health is keen to expand efforts to test the capacity of Wolbachia-infected mosquitoes as a tool for controlling outbreaks of dengue, chikungunya and potentially Zika too. Plans are now being developed to target 1.5 million people with releases of Wolbachia-infected mosquitos in Brazil.

“We are very excited that this self-sustaining and cost-effective method has been embraced by communities and is delivering the public health benefits we expected it would,” commented Simmons. “Our challenge now is to work with partners and governments to bring the method to 100 million people by 2023.”

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Source: American Society of Tropical Medicine and Hygiene. Dengue infections dive where Wolbachia established in mosquitoes in parts of Asia, Australia, and Brazil. https://astmhpressroom.wordpress.com/reports-of-dengue-infections-plummet-in-areas-where-wolbachia-has-been-established-in-mosquitoes-in-indonesia-brazil-australia-vietnam/


What is Wolbachia?

Wolbachia is a genus of gram-negative bacteria that infects arthropod species, including a high proportion of insects and also some nematodes. Aedes aegypti mosquitoes – which can transmit dengue, Zika, chikungunya and yellow fever viruses – don’t normally carry Wolbachia; however, it has been discovered that when they do the bacteria competes with viruses making it harder for them to reproduce inside the mosquitoes and less likely to spread from person-to-person.

What is dengue?

Dengue is a mosquito-borne, single positive-stranded RNA virus of the family Flaviviridae. There are five serotypes that have been identified. Symptoms of a dengue infection can include a fever, severe headache, muscle and joint pain, nausea, a rash and loss of appetite.

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