Proposal to reduce Zika-associated pregnancy complications by seasonal timing of conception

In response to the threat posed by Zika virus (ZIKV), several governments in Latin America have advised women to delay pregnancy, potentially for years. In a Perspective publishing on July 28, 2016 in the Open Access journal PLOS Biology, Micaela Elvira Martinez, Ph.D., from Princeton University, USA, proposes a less dramatic alternative: Timing conception such that the most sensitive period during pregnancy coincides with the seasonal period of lower risk of infection. While Dr. Martinez's work suggests this could substantially reduce ZIKV disease burden on developing fetuses, further research on ZIKV is needed before such a public health practice could be put in place.

Data on transmission of Zika and related viruses carried by the same mosquitoes suggest seasonal changes in the risk of infection over the course of the calendar year. Mosquito breeding cycles are affected by temperatures and rainfall, among other factors. Seasonal conditions also affect the behavior of human hosts that put them at risk of mosquito bites - think light clothing, open windows, time spent outdoors, etc.

Knowledge on ZIKV is still limited. To understand and calculate the actual health risks - and predict the benefits of any interventions - Martinez lists three specific areas that research should focus on: (1) seasonality of ZIKV transmission from mosquitoes to humans; (2) ZIKV transmission from mother to child and how the virus harms the fetus; and (3) how humans develop immunity against ZIKV (important for prediction how the ZIKV epidemic will develop over time).

Without additional data in these areas, it is not possible to calculate the absolute reduction in risk if women adjust the timing of conception. Based on available data from Puerto Rico and Brazil on the number of births, estimates of seasonal variations in mosquito-borne illnesses, and assuming that fetuses are vulnerable in the first two trimesters, however, Martinez estimates that even a small change in the timing of conception, such that fewer births experienced a susceptible trimester during the high transmission season, would translate into a significant risk reduction in pregnancies annually.

As soon as a key unknown, namely the susceptible period of gestation, is determined, Martinez proposes that seasonally-planning pregnancy be integrated into the portfolio of ZIKV interventions. "Planned seasonal conception", she argues, "would be an effective low-cost means of empowering women to protect themselves and their children [...] as they wait for a ZIKV vaccine and/or clinical interventions". To implement it, she suggests that countries need to determine region-specific high and low ZIKV transmission seasons, educate women and health care providers, and ensure access to contraception.

MEM is supported by a US National Science Foundation Postdoctoral Fellowship in Biology Award Number 1523757. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

The author has declared that no competing interests exist.

Article: Preventing Zika Virus Infection during Pregnancy Using a Seasonal Window of Opportunity for Conception, Martinez ME, PLoS Biology, doi:10.1371/journal.pbio.1002520, published 28 July 2016.