Use of modified mosquitoes to combat dengue fever in Brazil

It's tropical and humid, and the laboratory in Rio de Janeiro, Brazil, is humming and shaking. Millions of mosquitoes are bred here to help combat one of the biggest health problems in the South American country today. Brazil is currently experiencing the worst outbreak of dengue fever in its history.

Since the beginning of the year, nearly three million possible dengue virus infections have been recorded in the South American country, the Ministry of Health announced on Wednesday. Brazil has long since broken the historic record of 2015, when about 1.6 million dengue cases were recorded over the course of the year.

To date, 1,117 deaths due to dengue have been confirmed – also a sad record. This means that the number of deaths since the beginning of the year is greater than in all of 2023, when there were 1,094 deaths.

A total of 1,806 additional suspected cases are still under investigation. However, the number of unreported cases is likely many times higher. Ten states and the D.C. area have now declared public health emergencies.

There are different options to combat the massive spread of dengue fever. One strategy: modified mosquitoes. The World Mosquito Program (WMP) has developed a method to neutralize viruses in mosquitoes using Wolbachia bacteria, which occur naturally in many insect species.

Researchers have found that these bacteria prevent the growth of viruses such as dengue fever in yellow fever mosquitoes (Aedes aegypti) – which transmit these viruses, among others – and reduce their incidence in the population.

“The entire environment necessary for mosquitoes is recreated in the biofactory,” says a WMP spokesperson. The temperature ranges between 28 and 30 degrees and the environment is humid.

About ten million mosquito eggs containing Wolbachia bacteria are produced each week, and the mosquitoes are then released into areas where dengue viruses are common. Through reproduction, they spread Wolbachia bacteria over several generations.

In Niteroi, Rio de Janeiro's sister city across Guanabara Bay, the spread of dengue has already been dramatically reduced using this method. Mosquitoes carrying Wolbachia bacteria have been released there since 2015. As a result, the number of dengue infections has decreased by 70 percent, the research institute Fiocruz said according to a 2021 study.

In Rio, these mosquitoes are also bred in the laboratory, but so far they have only been released in some neighborhoods — unlike Niteroi, where they are released throughout the region, according to a WMP spokesperson. According to the Ministry of Health, the infection rate, measured in cases per 100,000 inhabitants, is about seven times higher in Rio than in Niterói.

Dengue fever – sometimes called bone-crushing disease because of the pain – is widespread in tropical and subtropical regions. The course of the disease is often mild, and not everyone develops the disease.

Heavy rains and high temperatures over the past few months likely caused this sharp increase. The yellow fever mosquito can develop well under these conditions.

But according to scientists, climate is not the only reason for this increase. Brazilian cities are growing, and health infrastructure often cannot keep up, according to a recent article in the specialized journal Nature. Uncollected trash becomes a breeding ground for insects, as does stored water from people who don't have regular access to tap water.

According to the Nature report, limited natural immunity also contributes to this increase. Dengue fever is caused by four different subtypes of viruses.

After several years in which the first two subspecies dominated in Brazil, the other two have recently made a comeback. Many Brazilians are susceptible to these subtypes and therefore have a higher risk of contracting the disease.

In February, Brazil began a vaccination campaign with a new vaccine, initially for children and young people. According to the Ministry of Health, 3.2 million people are expected to be vaccinated with both doses this year.

According to critics, this is not enough in a country with a population of more than 200 million people. “To influence the rates, we will need mass vaccination,” says Ana Lucia de Oliveira, an expert in infectious diseases at the Federal University of Campo Grande in the state of Mato Grosso do Sul, according to the “Nature” report.

Even widespread vaccination cannot defeat the disease if basic hygiene issues are not addressed, researchers say.

Not only Brazil, the spread of dengue has also reached other countries on the continent: more than 3.5 million cases were reported across the American continent in the first three months, the Pan American Health Organization (PAHO) announced at the end of March. .

“This is alarming because the number of cases is three times higher than in the same period in 2023 – a record year with more than 4.5 million cases reported in the region,” said Pan American Health Organization Director Jarbas Barbosa. The Pan American Health Organization spoke of what was likely the worst dengue outbreak in the continent's history.

In addition to Brazil, Paraguay and Argentina are the most affected. With more than 215,000 confirmed cases, Argentina has recorded its worst dengue epidemic in the past 15 years.

Many hospitals in the greater Buenos Aires area are overstretched, and about 90% of patients are turning to on-call service because they suspect dengue, La Nacion reported. In Peru, a state of emergency was declared in most parts of the country.

The World Health Organization is now warning of an increase in dengue cases in Europe. Although this tropical disease is not endemic in Europe and most cases are imported due to travel, the risk of the spread of tiger mosquitoes and yellow fever increases as temperatures rise.

It is said that if the weather becomes warmer, the eggs can survive the winter and the larvae can hatch. In 2023, Italy, France and Spain reported locally transmitted dengue infections.