Tens of thousands of pregnant women across South America have been infected with the Zika virus as the outbreak continues to sweep across the Americas. For only the fourth time since 2007 the epidemic has prompted WHO to declare a public health emergency of international concern. Dr Zsuzsanna Jakab, WHO Regional Director for Europe, has defined the recent cluster of microcephaly and neurological disorders in Latin America and the Caribbean as an “extraordinary event” and a public health threat to other parts of the world which requires a united response. Zika is transmitted to people primarily through the bite of an infected Aedes species mosquito. These are the same mosquitoes that spread dengue and chikungunya viruses. The combination of broad geographical distribution of mosquito species that can transmit the virus, the absence of immunity against the virus throughout the world and lack of both a vaccine and rapid, reliable diagnostic tests raises concerns that Zika virus disease will spread globally. Moreover, conditions associated with this year’s El Nino weather pattern, which causes droughts in parts of the world and floods in others, are expected to increase mosquito populations greatly in many areas. There have been also reported cases of sexual transmission with the virus spreading to people who have not visited affected countries. About 1 in 5 people infected with Zika virus become ill. The illness is usually mild with symptoms lasting for several days to a week. The most common symptoms are fever, rash, joint pain and conjunctivitis (red eyes), but people usually do not get sick enough to go to hospital. Although Guillain- Barre syndrome, a rare nervous system disorder that can cause temporary paralysis has been linked to the infection, the biggest concern is the impact it could have on babies developing in the womb and the surge in microcephaly. Microcephaly is a congenital disease which causes below average head size and stunts the growth of the brain. It can be deadly if the brain is so underdeveloped that it cannot regulate the functions vital to life. Children that do survive face intellectual disability and development delays. The prognosis for Zika-linked cases of microcephaly appears ominous, but it’s still too early to know the full picture. There will be a generation of babies with disabilities, which poses a huge social, economic and public health problem. The stage of pregnancy in which the mother is infected can affect how severe the impact is on the child. Exposure to infection in the first trimester of pregnancy may lead to more severe problems, while exposure to the Zika virus later in pregnancy when major brain structures have been formed, may result in different outcomes. Zika outbreaks have been reported in many countries and the virus continues to spread. Public Health England has confirmed four cases of Zika virus in the UK. In total, seven people have been diagnosed with Zika in Britain in the last three years but more than half of those have been reported since January. Brazil had fewer than 150 cases of microcephaly in the whole of 2014. But more than 4,700 cases have been reported since 22 October 2015. The link with Zika has not been confirmed, but WHO says it is “strongly suspected”. So far more than 1.5 million Brazilians have caught Zika. Both Brazil’s Zika outbreak and the spike in microcephaly have been concentrated in the poor and underdeveloped northeast of the country – the prosperous south-east, where Sao Paulo and Rio de Janeiro are located, is the second hardesthit region. Colombia’s national health institute has reported 31,555 cases of the mosquito-borne virus in the country, including 5,013 pregnant women. Disease continues its rapid spread across the Americas. Rio de Janeiro will host the Olympic Games between 5 and 21 August 2016. If Brazil and the International Olympic Committee aren’t up to the challenge, as they think they are, their decision to proceed with the games could detrimentally impact much of the globe. The United States Olympic Committee told U.S. sports federations that athletes and staff concerned about the Zika virus should consider not going to the Rio 2016 Olympic Games in August. European countries also have the same concerns. Jessica Ennis-Hill’s coach said British athletes competing in the Olympics in Brazil should not be based in the city because of the risks of contracting the illness. The possibility of virus transmission through sex is considered an important factor in spreading the disease in the countries with no native Aedes mosquito. Men returning home from affected countries are advised to use condoms if their partner is pregnant or might become pregnant. This should be done for 28 days after coming home if there are no symptoms and for six months if Zika symptoms do develop. Zika virus has also been found in other bodily fluids including saliva and urine, but it is not known whether the virus can spread through these routes. There is no evidence that women can transmit the disease by sex. Two recent independent studies now believe pyriproxyfen – a pesticide used to kill mosquitos – may be the real cause of microcephaly. The researchers from Brazil and Argentina – point out that in 2014 the government started adding pyriproxyfen to the drinking water supply in the area of Brazil where the majority of microcephaly cases have been reported. The researchers point out that Zika has spread across Africa, Asia, Micronesia since it was discovered in 1947 and epidemics have been reported across the globe without any associated outbreak of microcephaly. However this hypothesis is not supported by another report published in the New England Journal of Medicine which said that traces of Zika virus was found in the brain of an aborted foetus with severe microcephaly in Slovenia. The infant’s mother, from Europe, had probably been infected with Zika in Brazil.