Climate crisis and urban chaos boost dengue challenges – 03/02/2024 – Reinaldo José Lopes

There are no easy answers to the public health crisis triggered in the country by dengue and, to a lesser extent, other mosquito-borne diseases Aedes aegypti. Remember, for example, that Brazil became a “territory free of Aedes” between the 1950s and the end of the 1970s seems almost like science fiction today. In this column, I try to contextualize the main factors that led to this year’s complicated situation and address the paths ahead – some promising, none miraculous.

The first thing to keep in mind is that you cannot underestimate the climate factor. Global and Brazilian temperatures have been breaking consecutive records since the beginning of this century, and 2023 and 2024 have been even further out of the curve when it comes to heat. Nothing better for an insect like Aedes aegypti.

What happens is that the heat allows the invertebrate to complete its life cycle with its foot on the accelerator. At temperatures above 30 degrees Celsius, for example, females lay three times more eggs than at 20 degrees Celsius. Furthermore, the larvae hatch from the eggs in half the time when the temperature goes from 20°C to 30°C.^°W.

This same factor also directly affects – and, from our point of view, for the worse – the mechanisms of virus transmission by the insect, and not just the animal’s success in reproduction. The time it takes between a female mosquito biting a person with dengue and being able to transmit the virus to another victim also halves in hot weather. And the female reaches the peak of her voracity to suck human blood in temperatures ranging from 30^°C to 35^°W.

Given this scenario, it is obvious that it is important to do everything to mitigate the climate crisis, but we are talking about something that does not remotely depend on Brazilian efforts alone. Mosquito control itself is still the key – and in that regard, we face other problems.

Seek the eradication of Aedes in 2024 it is very different from what it was in the 1950s. We have a population four times larger, a much more chaotic urban structure, much more intense regional, state and international connections (through which mosquitoes and their eggs can travel). The climate crisis also increases these challenges – a 2022 study, for example, showed the recent advancement of the disease to more than 60 municipalities in the South region that had never had (roughly constant) community transmission of dengue before. It’s as if the mosquito’s “house” had gained a new room overnight.

Much of the world managed to overcome another even more serious disease transmitted by A. aegypti, yellow fever, through vaccination. There are promising alternatives in this regard in the case of dengue, one of them developed in Brazil by the Butantan Institute and close to being submitted for approval by Anvisa (National Health Surveillance Agency). But the complexity of the disease virus recommends some caution.

As it has four very different subtypes, the dengue virus interacts with the body’s defense system differently depending on the subtype causing the infection. This process seems to have to do, for example, with the higher risk of severe dengue when a second infection occurs with a subtype different from the one that caused the first.

Ideally, a vaccine should produce well-balanced protection from the body to the four subtypes without producing this problem, but it is something that still needs to be monitored in detail in a population as large as ours. It makes sense, for now, not to vaccinate with the same intensity used against Covid.

In short, in addition to not neglecting the basics, eliminating as many breeding sites and mosquitoes as possible, the best way is to invest in science and innovation, with adequate financing. Brazil has plenty of qualified people in relevant areas. What is missing is a strategic vision to help them go all out against the mosquito and the virus.

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