The Zika virus is native to parts of Africa and Asia and the WHO believes that it might spread to the US too. The lack of natural immunity in the US is supposedly aiding the spread of the virus. The virus has already spread to more than dozen countries in South and Central America and up to Mexico and one case was confirmed in Puerto Rico in December. The virus was first found to be spreading in the US in May 2015. Read: 5 diseases caused by mosquitoes (other than dengue and malaria) What is Zika virus and how does