Of some 3,500 species of mosquito, those of the genus Anopheles are widely considered to be the most dangerous because they transmit malaria. Malaria is decreasing, however, and other mosquito-borne diseases, such as dengue, chikungunya, Zika and yellow fever, are increasing (S. V. Mayer et al. Acta Tropica 166, 155–163; 2017). The mosquito Aedes aegypti, the primary carrier of these viruses, now constitutes an even greater threat (see also Nature 539, 17–18; 2016, and S. F. Dowell et al. Nature 540, 189–191; 2016).
Aedes mosquitoes have been transferring these viruses among African primates for millennia. One African primate (Homo sapiens) and one African Aedes (A. aegypti) have spread from Africa. Viruses adapted to both have spread with them. Yellow fever hit the developed world in the seventeenth century, dengue in the nineteenth, chikungunya in the twentieth, and now Zika in the twenty-first.
Scientists studying mosquito-borne viruses have catalogued hundreds more lurking in Africa. The world needs to take notice before these take hold and spread further. As Pliny the Elder (AD 23–79) wrote, “Ex Africa semper aliquid novi” ('there is always something new coming out of Africa').