The mosquitoes of a “domestic” subspecies accustomed to living in cities transmit the Zika virus more easily, and not only for reasons of physical proximity. According to a study published in Science,
Aedes aegypti aegypti, which proliferates in urban environments between the two tropics, is genetically predisposed to acquire the Zika virus and to transmit it in turn. The finding could explain why, when the Zika epidemic broke out in 2015, the disease spread mainly to cities in Central and South America and did not take hold in Africa, where this invasive mosquito subspecies is absent.
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Two different ways. The Aedes aegypti mosquito, one of the insects most responsible for zoonotic infections, is a native species of Africa. The original version of this mosquito is found in the current subspecies Aedes aegypti formosus, widespread in the forest areas of sub-Saharan Africa. The insect nests in the hollows of trees and is greedy for animal blood, characteristics that do not make it particularly formidable for humans.
Between 10,000 and 5,000 years ago, however, the Aedes aegypti gave rise to another subspecies more passionate than human blood, the Aedes aegypti aegypti. In recent centuries this mosquito has spread to all tropical and subtropical regions outside the African continent, and in particular to cities: it nests in stale puddles and among urban waste, and then feeds on human blood.
A destiny written in the genes. Precisely because of his predilection for our species, the A.
aegypti aegypti is considered the main vector of diseases such as yellow fever and dengue. Now, however, thanks to the comparison between 14 different populations of Aedes aegypti mosquitoes present in various parts of the world, it has been discovered that the subspecies that proliferates in urban environments is unfortunately also very efficient in transmitting Zika,
an infection that if contracted during pregnancy can cause serious harm to the unborn child. This ability of the mosquito does not depend, as one might think, only on proximity to humans, but also on a greater susceptibility to the virus linked to genetic reasons.
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A crucial difference. African A. aegypti, on the other hand, acquire the Zika virus more difficultly during their meals and therefore have fewer amounts of the virus to transmit. The greater susceptibility to the virus of the subspecies spread outside Africa in urban areas could depend on some genetic differences identified on chromosome 2: this would explain the high diffusion of Zika outside Africa (for example in Brazil and Cuba) and the low diffusion , in some ways unexpected, on the African continent.