Randy Gaugler & Ary Faraji
Center for Vector Biology – Rutgers University / NJAES
Zika virus is not a new disease. Zika virus has been largely confined to equatorial Africa in the tropics where it circulated predominately between forest dwelling mosquitoes and wild primates. The virus was actually discovered from a sentinel monkey that had been placed in a cage in the Zika forest of Uganda in 1947. But the virus rarely spilled over into human populations even in highly endemic areas of Africa. The explosive reemergence we are current witnessing is truly extraordinary. Human activities are the greatest factor attributing to this spread because of rapid changes in land use and globalization leading to rapid increases in the movement of goods and people.
Zika is a pandemic because the virus is no longer confined to Africa but has spread to Asia, the Pacific Islands, and now the Americas where the World Health Organization is predicting several million infections and classifying Zika a ‘global health emergency’. The virus is not continent-hopping via the spread of mosquitoes, but because of the frequency and rapidity of air travel by humans. An individual can be bitten by an infected mosquito where the virus is circulating, and then fly long distances within a short span of time. Since the incubation period in humans usually lasts several days, if that infected individual is bitten by a local mosquito that can replicate and transmit the virus (i.e. vector competency in the host mosquito), then local infections in a new area may occur. However, only a handful of Aedes mosquitoes are vector competent for Zika virus. The primary vector is the yellow fever mosquito, Aedes aegypti; a highly invasive urban species. Their eggs may remain dormant for months in small containers, which contribute to a wide geographical distribution. Not coincidentally, these mosquitoes are abundant in the areas where Zika virus is currently circulating in the Americas. In short, humans are responsible for the transportation of Zika virus, whereas mosquitoes are responsible for transmission of the virus to humans.