A new virus in the group that includes dengue and chikungunya is the subject of an article in the journal PLOS Neglected Tropical Diseases. 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, and 55,000 cases in Polynesia in 2013.
In light of these recent events, researchers in Gabon restarted work on a concomitant dengue and chikungunya epidemic that occurred in 2007 in the capital, Libreville, which affected 20,000 people. Showing almost the same symptoms as its two dreaded cousins, did zika pass unnoticed by the researchers?
To remove any doubt, the researchers conducted a second analysis of the blood samples taken seven years earlier from the patients. The results showed that many of them actually were infected by the zika virus. 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 confirmed that it was a strain belonging to the old African line. In other words, the latter was found to be more virulent than thought.
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 Asian tiger mosquito. 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 represented more than 55% of the mosquitoes collected. The tiger mosquito prospers in small bodies of standing water, like that found in broken bottles, tins, flowerpots, abandoned 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.
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