Zika Virus

Abstract

Zika virus is closely related to the viruses causing yellow fever, West Nile or Dengue fever and, similar to them, is an arbovirus, actively transmitted by mosquito vectors. Sexual transmission between humans also occurs. Zika virus was not associated with serious human disease until after its arrival in the Americas. Since 2015 it has been associated with a range of pathologies. The most significant is congenital Zika syndrome, marked by foetal microcephaly. The number of Zika infections has fallen since 2016. Confirmed infections in the Americas total over 200 000 cases, with more than 50% of these in Brazil. Deaths are rare, and congenital effects have been the major concern, particularly in Brazil, where more than 80% of such cases have occurred. The reasons for this high rate are unclear, although poverty is often cited as a likely contributor. Eighty‐four countries or territories worldwide have had evidence of mosquito‐borne Zika virus transmission. Relatively small numbers of infections have been reported in the United States, with transmission restricted to the far south of Texas and Florida. There is no vaccine or antiviral drug effective against Zika. The best preventive measures as of 2017 involve controlling or avoiding the vector mosquitoes. Key Concepts Zika virus is a Flavivirus with an RNA genome, related to other viruses such as yellow fever, West Nile and Dengue fever. The virus was identified in Africa in 1947 and exists as two broad lineages, African and Asian. The virus is an arbovirus (arthropod‐borne virus), spread by bites from vector mosquitoes of the genus Aedes , although direct person to person transmission also occurs. Historically, most people infected with Zika did not develop symptoms, and even when they did these were relatively mild. Until 2007, Zika virus infection was restricted to an equatorial belt in Africa and Asia, but in 2015, the Asian form of Zika was identified in Brazil, the first time it was seen in the Americas. By the end of 2016, more than 100 000 confirmed cases had occurred in Brazil. Later in 2015, Zika infection was associated with severe forms of microcephaly in newborns, predominantly in the northeast of Brazil. Zika infection has also been associated with the autoimmune‐mediated Guillain–Barré syndrome. In 2017, numbers of infections in the Americas have dropped sharply, but the virus continues to spread, with mosquito‐borne infections seen in 84 countries and territories around the world. There is no vaccine or therapeutic drug for Zika virus, although clinical trials are proceeding. The best strategy at present is to control mosquitoes and avoid mosquito bites. Future control approaches need to be informed by effective public health surveillance to support both analysis and response.