The mosquito that helped spread the Zika virus across Brazil during the Olympics is on the move, expanding into new territories after cross-breeding with a close but less harmful relative. The carrier mosquito is also beginning to breed 12 months of the year in places that had previously been free of the insect, including southern California, Washington DC, the holiday island Madeira and along the Black Sea.
This rapid movement into new territories potentially leaves the world's population more at risk of a severe epidemic, according Prof Jeffrey Powell in a Perspective article published yesterday in the journal Science. Prof Powell is the professor of ecology and evolutionary biology in the Yale School of Public Health.
Ireland has had 15 reported cases of Zika since 2015. Zika virus infection is a notifiable disease under the infectious disease regulations, so must be reported by clinicians if confirmed.
Cross-breeding has helped the mosquito, Aedes aegypti, move into and acclimatise from a rural to an urban environment. The spread and interbreeding of A aegypti mosquitoes increase the risk of Zika, dengue and other viral epidemics in places where these diseases have yet to emerge. "These expansions are putting at risk large human populations that never experienced aegypti-borne viruses and therefore have no immune defences against them," he writes. "This greatly increases the likelihood of severe epidemics. "
There are two main subspecies of the mosquito, referred to as Aaa and Aaf. The Aaa mosquito is found throughout the tropics and subtropics outside Africa, and prefers to consume human blood. It is already spreading diseases such as Zika, which is implicated in causing major birth defects in newborns. The Aaf mosquito until recently lived in forests in sub-Saharan Africa and typically feeds on non-human animals.
Prof Powell points to worrying emerging trends, however. The rural dwelling Aaf insect is now spreading and breeding in urban environments such as Dakar, Yaounde, Luanda and Libreville. Females of this group have changed their egg-laying behaviour, for example in discarded tyres instead of trees. The insects readily rely on human blood to complete their egg-laying biology.
The result has been outbreaks of dengue and yellow fever in African cities. Diseases such as chikungunya fever outbreaks have occurred in the New World, and Aaf has been introduced into Argentina where it is breeding with Aaa, Prof Powell said. The Aaa mosquito expanded into southern California in 2013.
As of November 10th, 71 countries and territories have reported mosquito-borne transmission of the virus, says the European Centre for Disease Prevention and Control. The World Health Organisation says that 26 countries or territories have reported microcephaly and other central nervous system malformations in newborns potentially linked with Zika infection.
