Dengue outbreak worst in decade in DF and five states

Aedes aegypti mosquitoes infected with Wolbachia bacteria, at the Fundação Oswaldo Cruz, in Rio de Janeiro, in 2014 (Photo: Reproduction / Christophe Simon)

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

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

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

To fight the outbreak, health officials at all levels are stepping up a familiar routine. Application of larvicide, sensitization of the population to avoid creating breeding grounds for mosquitoes and training of health workers, among other activities.

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

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

In Santa Catarina, 56,000 cases were reported in the first four months.

This is the third consecutive year of growth. Before 2019, the record was 4,800 cases between January and April 2016.

In Rio Grande do Sul, there have been 41,400 cases. The explosion is similar to that seen in the neighboring state, with a gradual growth since 2019, reaching figures well above those recorded in previous years.

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

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

The Ministry of Health of Tocantins, another state with a record number, has identified “late diagnosis by professionals who were focused on Covid-19” and the “decrease in vector control actions due to the targeting of professionals on the covid-19”.

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

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

According to Luciano Moreira, head of the WMP (World Mosquito Programme, which coordinates the project at the global level) and researcher at Fiocruz, the first step of the method, for the moment complementary, consists in introducing the bacterium into the eggs of Aedes aegypti.

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

In nature, the mosquito reproduces and transmits the bacteria to its offspring. Over time, it tends to become dominant in the area, making it difficult to transmit the virus.

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

The first place that received mosquitoes carrying the bacteria was Niterói and certain neighborhoods of Rio de Janeiro, also 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 have any. received the method.

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

To solve the mosquito’s bacteria supply problem, 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”, specifies Moreira .

A study by researchers from the universities of São Paulo (USP) and Cambridge (UK) showed that flies of the species Drosophila melanogaster – common in all kitchens – are infected with fewer viral species and contain lower viral load when colonized. by bacteria of the genus Wolbachia.

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

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