Up to 1.65 million childbearing women in Central and South America could become infected by the Zika virus by the end of the first wave of the epidemic, scientists have estimated. The team’s projections, detailed in the journal Nature Microbiology, also showed that Brazil is expected to have the largest total number of infections (by more than three-fold), due to its size and suitability for transmission. “It is difficult to accurately predict how many child-bearing women may be at risk from Zika because a large proportion of cases show no symptoms,” said Professor Andrew Tatem from the University of Southampton in Britain. “This largely invalidates methods based on case data and presents a formidable challenge for scientists trying to understand the likely impact of the disease on populations,” Tatem noted. However, this latest research has built a picture of the projected spread of the disease by examining its likely impact at very local levels — at a scale of five kilometres squared. The researchers brought this local data together to model infection rates across the region. The team took into account disease patterns displayed in similar epidemics, along with other factors such as how the virus is transmitted (in this instance by mosquito), climate conditions and virus incubation periods.
They also examined transmission behaviour in dengue and chikungunya viruses. Their projections for Zika are largely consistent with annual, region-wide estimates of 53 million infections by the dengue virus (2010), which has many similarities to Zika. Coupled with existing data on population, fertility, pregnancies, births and socio-economic conditions for the region, the team modelled the possible scale of the projected spread of the Zika virus and provided a detailed understanding of the places likely to be most affected – helping to inform which areas will need the most support in combating the disease and helping sufferers. “These projections are an important early contribution to global efforts to understand the scale of the Zika epidemic, and provide information about its possible magnitude to help allow for better planning for surveillance and outbreak response, both internationally and locally,” Tatem noted.