Dengue outbreak is the worst of the decade in DF and in five states

In addition to having already exceeded the number of cases recorded throughout last year in just four months, the current outbreak of dengue in Brazil shows the arrival of the mosquito Aedes aegypti to new locations and is the worst of the decade in the Federal District and in Goiás, Piauí, Rio Grande do Sul, Santa Catarina and Tocantins.

The most affected state governors and the federal government point to the Covid-19 pandemic as one of the causes that made it difficult to combat the spread of the disease.

In addition to the well-known prevention routine, Fiocruz (Fundação Oswaldo Cruz, linked to the Ministry of Health) says it has obtained promising results in the use of the Wolbachia bacteria, whose effectiveness has been tested since 2014, but the method is applied in few cities.

To combat the outbreak, health managers at all levels intensify a familiar routine. Application of larvicide, awareness of the population to avoid creating places conducive to mosquito breeding and training of health agents, among other activities.

Despite this, the mosquito has reached regions that previously did not have this problem.

These are the cases of Santa Catarina and Rio Grande do Sul. Both have a record outbreak of dengue.

In Santa Catarina, 56,000 cases were reported in the first four months. It is the third year in a row of growth. Before 2019, the record was 4,800 cases between January and April 2016.

In Rio Grande do Sul, there were 41,400 cases. The explosion is similar to that observed in the neighboring state, with a gradual growth since 2019, reaching numbers much higher than those recorded in previous years.

Among the causes, the Santa Catarina Health Department pointed out “changes in climatic conditions, which allow the mosquito to reproduce throughout the year”. The cold prevents mosquito breeding. As temperatures rise, the climate becomes more favorable for the Aedes aegypti.

Another problem was the pandemic. The Ministry of Health said that there had been a reduction in visits by health agents to homes “due to the difficulty encountered during the Covid-19 health emergency to control the proliferation of the mosquito”.

The Health Department of Tocantins, another state with a record number, listed “the late diagnosis by professionals who were focused on Covid-19” and the “reduction of vector control actions due to the targeting of professionals to Covid-19”.

In Niterói, Rio de Janeiro, Belo Horizonte, Campo Grande and Petrolina, Fiocruz has been testing the use of Wolbachia for some years, in parallel with research being carried out on the method in 11 countries.

This bacterium is naturally present inside the cell of several insects, but not in the mosquito that transmits dengue, zika and chikungunya.

According to Luciano Moreira, leader of the WMP (World Mosquito Programme, which coordinates the project worldwide) and researcher at Fiocruz, the first step of the method, which for now is complementary, consists of introducing the bacteria into the eggs from Aedes aegypti.

This happens in a Fiocruz factory in Rio de Janeiro and another in Belo Horizonte, a city that has also had mosquito releases. After that, there are two options: release the eggs or the adult mosquito.

In nature, the mosquito reproduces and passes the bacteria on to its offspring. Over time, the tendency is for it to become dominant in the area, thus making the transmission of the virus difficult.

In Belo Horizonte, mosquitoes were released between October 2020 and January 2021. Results should only be measured four years from now.

The first place that received mosquitoes with the bacterium was Niterói and some neighborhoods of Rio de Janeiro, still in 2014. When analyzing the data collected after the experiment, Fiocruz found a 70% reduction in the number of cases compared to neighborhoods that did not had received the method.

Campo Grande (MS) and Petrolina (PE) are also already participating in the program. In addition to them, more than 20 municipalities asked for membership, but Fiocruz does not have the capacity to meet new requests.

To solve the problem of supply of the mosquito with the bacteria, the plan is to build a new factory with the capacity to produce 50 million eggs per week. Today, the capacity is 8 million. If there is an expansion, negotiated between the Ministry of Health, Fiocruz and WMP, the “very conservative calculation is to cover 67 million inhabitants in Brazil (32% of the population) in ten years”, says Moreira.

A study conducted by researchers from the universities of São Paulo (USP) and Cambridge (United Kingdom) showed that flies of the species Drosophila melanogaster —common in any kitchen— are infected by fewer virus species and contain a lower viral load when colonized by bacteria of the Wolbachia genus.

The work, supported by Fapesp and the Royal Society, was published in the journal Communications Biology.