Zika virus and congenital microcephaly

Zika virus was first identified in 1947, in a rhesus macaque in Uganda, and human cases were documented in Africa in the 1950s. It is spread mainly by Aedes mosquitoes. From 2007 outbreaks were recorded across Africa, the Americas, Asia and the Pacific, and in 2015 a large epidemic swept Brazil.

Brazil then reported a cluster of microcephaly cases and other neurological disorders, following a similar cluster in French Polynesia in 2014. On 1 February 2016 the WHO Director-General, advised by an Emergency Committee, declared these clusters a Public Health Emergency of International Concern and issued temporary recommendations under the International Health Regulations. Brazil, France, the United States and El Salvador had given the committee information on a possible link with Zika.

The question of cause was settled within weeks. On 13 April 2016 Sonja Rasmussen, Denise Jamieson, Margaret Honein and Lyle Petersen of CDC published a review of the evidence in the New England Journal of Medicine, and CDC announced its conclusion that Zika virus is a cause of microcephaly and other severe fetal brain defects. The agency's director, Tom Frieden, said it was now clear that the virus causes microcephaly.

The virus also passes from mother to fetus during pregnancy and can spread through sexual contact, laboratory exposure and transfusion of blood products. WHO ended the emergency on 18 November 2016, when its committee judged that Zika remained a significant and enduring public health challenge that needed a longer-term response. WHO now counts 92 countries and territories that have reported mosquito-borne Zika infection.