Dengue crisis: Brazil relies on bacteria-infected laboratory mosquitoes
In Brazil, the number of dengue cases is rising and the country is facing a massive public health crisis. The mosquito-borne viral disease has sickened more than a million Brazilians this year alone and overwhelmed hospitals.
Advertisement
The current dengue crisis is the result of the convergence of two key factors. On the one hand, the often humid and warm weather this year favors the reproduction of the transmitting mosquito species Temples of the Egyptians. Second, all four types of dengue virus are circulating this year, but few people have built up immunity to all types.
Anti-Dengue-Strategie
But Brazil is fighting back. One of the country’s anti-dengue strategies aims to hamper the spread of the disease-carrying mosquitoes by infecting them with a bacterium in the genus Wolbachia that is common in insects. The bacterium appears to enhance the mosquitoes’ immune response and make it harder for dengue and other viruses to grow in the insects. The bacterium also competes directly with the viruses for important molecules that they need for replication. Wolbachia does not affect humans.
The World Mosquito Program breeds Wolbachia-infected mosquitoes in insectariums and releases them into communities. There they mate with wild mosquitoes. Wild females that mate with Wolbachia-infected males produce eggs, but these do not hatch. Wolbachia-infected females, in turn, produce offspring that are also infected.
Over time, the bacteria spread throughout the population. The program’s largest insectarium is in Medellín, Colombia, where thousands of mosquitoes buzz around in mesh cages. “We’re basically vaccinating the mosquitoes against disease transmission to humans,” says Bryan Callahan, the public relations director.
Bacterial infiltration in a few years
The World Mosquito Program began releasing Wolbachia mosquitoes in Brazil in 2014. The insects now cover an area with more than three million inhabitants in five municipalities: Rio de Janeiro, Niterói, Belo Horizonte, Campo Grande and Petrolina.
In Niterói, a municipality of around 500,000 residents located on the coast directly across a large bay from Rio de Janeiro, the first small pilot tests were launched in 2015, and in 2017 the World Mosquito Program began larger operations. By 2020, Wolbachia had infiltrated much of Niterói’s mosquito population: the bacteria’s prevalence ranged from 40 percent in some parts of the city to 80 percent in others.
When the researchers compared the incidence of viral diseases in the areas where mosquitoes had been released with that in a small control zone that had not received mosquitoes, they found a 69 percent decrease in dengue cases. In areas with Wolbachia mosquitoes, the number of other mosquito-borne infections also decreased: Chikungunya cases decreased by 56 percent and Zika cases decreased by 37 percent.
Low incidence in the study area
How is Niterói faring during the current wave? It is still too early to make a final judgment. However, initial data is encouraging. The number of new dengue cases (incidence) is one of the lowest in the state at 69 confirmed cases per 100,000 population. In Rio de Janeiro, a city of nearly seven million people, there have been more than 42,000 cases, an incidence of 700 per 100,000.
“Niterói is the first Brazilian city that we have fully protected with our Wolbachia method,” says Alex Jackson, global editorial and media relations manager for the World Mosquito Program. “The entire city is covered by Wolbachia mosquitoes, which is why dengue cases are decreasing significantly.”
The program hopes to release Wolbachia mosquitoes in six additional cities this summer. However, Brazil has more than 5,000 communities. To reduce the total number of dengue cases across Brazil, the program would need to release millions more mosquitoes. That’s exactly the plan.
The “World Mosquito Program” is about to begin construction of the world‘s largest mass breeding facility in Curitiba. “We believe this will allow us to cover most of urban Brazil within the next decade,” says Callahan.
New ideas for mosquito control
In addition to the “World Mosquito Program,” a whole range of other mosquito-based approaches are in the works. The British company Oxitec has been supplying genetically modified “friendly” mosquito eggs to Indaiatuba in Brazil since 2018. The insects that hatch from them – all males – do not sting people themselves. Once they mate, their female offspring do not survive, reducing populations.
Another company called Forrest Brasil Tecnologia has released sterile male mosquitoes in parts of Ortigueira. When these males mate with wild females, they produce eggs that do not hatch. From November 2020 to July 2022, the Ortigueira company experienced a decrease in the Temples of the Egyptianspopulation by 98.7 percent.
In addition, Brazil is also working to equip its citizens with better immunity by offering a new vaccine from Japan to those most at risk, while also working on its own dengue vaccine.
None of these solutions are quick fixes. But they all offer hope that the world can find ways to fight back, even as climate change pushes dengue and other infections to new highs and into new areas. “Cases of dengue fever are increasing at an alarming rate,” Gabriela Paz-Bailey, a dengue specialist at the US Centers for Disease Control and Prevention (CDC), told the Washington Post. “It is becoming a public health crisis and is coming to places where it has never occurred before.”
(vs.)
To home page