In the group of viruses that includes dengue and chikungunya, a newcomer now has people talking about it. Also originating in Africa, zika was isolated in humans in the 1970s. Several years earlier, only a few human cases had been reported. It took until 2007 for the virus to show its epidemic capacity, with 5,000 cases in Micronesia in the Pacific, and then especially, at the end of 2013 in Polynesia, where 55,000 people were affected. In light of these recent events, researchers from IRD and the CIRMF in Gabon restarted work on the concomitant dengue and chikungunya epidemic that occurred in 2007 in the capital, Libreville, and which affected 20,000 people. Showing almost the same symptoms as its two dreaded cousins, did zika pass unnoticed by the researchers?
As many cases of zika fever as of dengue and chikungunya
To remove any doubt, the researchers conducted a second analysis of the blood samples taken seven years earlier from the patients. The result: many cases were due to the zika virus. The latter infected the inhabitants of Libreville with the same frequency as by the dengue or chikungunya viruses. Therefore, the capital actually experienced a concomitant epidemic of dengue, chikungunya, and zika in 2007. Additionally, analysis of the phylogenetic tree of the zika viruses detected in Libreville confirms that it was a strain belonging to the old African line. In other words, the latter was found to be more virulent than thought.
An emerging threat to human health
The researchers also re-analysed the mosquitoes captured in 2007. These studies attested to the first known presence of zika in Aedes albopictus, better known as the tiger mosquito. Thus, this insect, known to be the vector of dengue and chikungunya, also carries the zika virus. It is the predominant species in Libreville, where it represents more than 55% of the mosquitoes collected. The tiger mosquito prospers in small bodies of standing water such as in broken bottles, tins, flowerpots, abandoned used tires, etc.
Originally from Asia, the tiger mosquito was introduced to Africa in 1991 and detected in Gabon in 2007, where its arrival undoubtedly contributed to the emergence of dengue, chikungunya, and as shown by this new study, zika. The rapid geographic expansion of this invasive species in Africa, Europe, and America allows for a risk of propagation of zika fever around the world, including in the south of France.
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