Zika’s first wave could infect 1.65 million childbearing women

Woman in Cúcuta, Columbia, interviewed about Zika exposure. (Credit: Pan American Health Organization-PAHO Pan American Health Organization-PAHO/Flickr)

As many as 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.

Further, research shows that across Latin America and the Caribbean more than 90 million infections could result from the initial stages of the spread of Zika. The projections also show that Brazil is expected to have the largest total number of infections (by more than three-fold), due to the country’s size and suitability for transmission.

Brazil is expected to have the largest total number of infections, by more than three-fold.

The estimates reflect the sum of thousands of localized projections of how many people could become infected within every 5 by 5 km grid cell across Central and South America. Because the virus may not reach each corner of this region, or may do so slowly, the total figure of 1.65 million represents an upper limit estimate for the first wave of the epidemic.

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“It is difficult to accurately predict how many childbearing women may be at risk from Zika because a large proportion of cases show no symptoms,” says Andrew Tatem, professor of environmental sciences at the University of Southampton. “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.”

In fact, an estimated 80 percent of Zika infections don’t show symptoms and of those that do, some may be due to other viruses. Coupled with inconsistent case reporting and variable access to health care for different populations, these factors make case based data unreliable.

The latest research, published in the journal Nature Microbiology, constructs a picture of the projected spread of the disease by examining its likely impact at very local levels—at a scale of five kilometers squared.

Scientists build a placenta to study infections like Zika

Researchers used the local data together to model infection rates across the region. They 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 behavior 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 socioeconomic conditions for the region, the team has been able to model the possible scale of the projected spread of Zika and offer a detailed understanding of the places most likely to be affected—and so most in need of support to fight the disease and treat sufferers.

“These projections are an important early contribution to global efforts to understand the scale of the Zika epidemic,” Tatem says, “and provide information about its possible magnitude to help allow for better planning for surveillance and outbreak response, both internationally and locally.”

Source: University of Southampton