Two billion-plus at risk of Zika virus spread

An estimated 2.17 billion people are living in parts of the world susceptible to the spread of the Zika virus, according to a joint UK-US research study.

Mosquito with Zika virus
Scientists at the University of Oxford and the Institute for Health Metrics and Evaluation in Seattle have produced a new map that details tropical and subtropical regions of the Americas, Africa and Asia where there are favourable conditions for the mosquitoes that carry the virus.The Zika virus, which has already led to 1,000 cases being confirmed in Brazil and almost another 5,000 suspected cases, results in babies being born with the microcephaly birth defect characterised by a smaller than normal head, and brain damage.According to the research, areas of the US with the potential to be affected by the virus include much of Texas and all of Florida. In South America, at-risk areas include long stretches of coastline as well as cities along the Amazon river and its tributaries.The report said it was surprising that no large outbreaks stemming from the virus, first discovered in Uganda in 1947, had been reported in Africa or Asia despite large regions being highly suitable for breeding mosquitoes and transmission of the virus. The authors say this could be due to under-reporting, misdiagnosis or even a high level of immunity in the indigenous population where the virus has been present for a many years.Epidemiologist Dr Janey Messina, the lead author from Oxford University, said, "We have comprehensively assembled all the data for Zika occurrence in humans, displayed it as a map, and combined it with detailed predictions of where the virus could spread next."Our global risk map reveals priority regions where authorities could intervene to control the vector population and where surveillance of the virus should be concentrated in order to improve rapid outbreak response and clinical diagnosis."Another of the Oxford team, Dr Oliver Brady, told the BBC, "These are the first maps to come out that really use the data we have for Zika – earlier maps were based on Zika being like dengue or chikungunya. We are the first to add the very precise geographic and environmental conditions data we have on Zika.""Mosquitoes are just one condition needed for Zika to spread but there's a whole range of other ones. It needs to be warm enough for Zika to replicate inside the mosquito and for there to be a large enough (human) population to transmit it."Recent analysis has revealed the Zika virus was first introduced to Brazil in 2013, where it circulated undetected until it was eventually reported for the first time last year."Our findings that a global area inhabited by over 2.17 billion people is highly suitable for transmission of Zika virus, combined with the rapid cross-continent spread we have already seen, emphasise why the World Health Organisation has declared the current outbreak as a Public Health Emergency of International Concern," said David Pigott from the Institute for Health Metrics and Evaluation."With our maps and with the wealth of other information emerging from the global science and public health community, policy-makers can decide where to prioritise vector control and other preventative measures as well as where to be most vigilant about correctly diagnosing Zika as opposed to the many other prevalence arboviruses."

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