Brazil and Colombia to scale up bacterial fight against Zika and dengue

Health authorities in Colombia and Brazil will launch large-scale mosquito-control campaigns using a using naturally occurring bacteria known as Wolbachia to fight the spread of dengue and Zika viruses among people.

Small-scale trials of the technique, which involves infecting mosquitoes with Wolbachia to prevent them from spreading the viruses, have shown a significant reduction in their ability to transmit Zika and dengue, prompting donors to back scale-up plans.

"The use of Wolbachia is a potential ground-breaking sustainable solution to reduce the impact of these outbreaks around the globe and particularly on the world's poorest people," said Britain's international development secretary Priti Patel as the larger project was announced in London.

The control campaigns, scheduled to begin early next year in Colombia's Antioquia and Brazil's Rio de Janeiro, will be funded with $18 million from the British and United States governments, the Wellcome Trust global health charity and the Bill & Melinda Gates Foundation.

Zika has been linked to the birth defect microcephaly, characterized by an abnormally small head, that has been sweeping through South and Central America and the Caribbean and making its way north to the United States.

In February, the World Health Organization declared Zika a global health emergency. The connection between Zika and microcephaly came to light last year in Brazil.

Brazil has now confirmed more than 1,800 cases of babies with microcephaly that it considers are linked to Zika infections in the mothers.

The Wolbachia bacteria is occurs naturally in many insect species worldwide, and research has shown that it can significantly reduce the capacity of mosquitoes to transmit viruses to humans.

But it doesn't occur naturally in Aedes aegypti, the mosquito species largely responsible for transmitting a range of diseases including Zika, dengue, chikungunya and yellow fever.

Over the past decade, international researchers working with the Australian-led non-profit Eliminate Dengue Program (EDP) have found a way to transfer Wolbachia into Aedes aegypti mosquitoes and get them to pass it on to their offspring.

When mosquitoes with Wolbachia are released into an area, they breed with local mosquitoes and pass the bacteria on to future generations. Within a few months, the majority of mosquitoes carry Wolbachia and the effect is then self-sustaining.

Since 2011, field trials using this method have been carried out in five countries and show that when a high proportion of mosquitoes in an area carry Wolbachia, local transmission of viruses is halted.

Trevor Mundel, head of the Gates Foundation's global health division, said he hoped the large-scale campaigns had the potential to show Wolbachia as a "revolutionary form of protection against mosquito-borne disease".

"It's affordable, sustainable, and appears to provide protection against Zika, dengue, and a host of other viruses," he said in a statement. "We're eager to study its impact and how it can help countries."