The risk of sustained sexual transmission of Zika is underestimated

Antoine Allard, Benjamin M. Althouse, Laurent Hébert-Dufresne, Samuel V. Scarpino
PLoS Pathogens
13(9): e1006633
September 21, 2017


Pathogens often  follow more than one transmission route during outbreaks-from needle sharing  plus sexual transmission of HIV to small droplet aerosol plus fomite  transmission of influenza. Thus, controlling an infectious disease outbreak  often requires characterizing the risk associated with multiple mechanisms of  transmission. For example, during the Ebola virus outbreak in West Africa,  weighing the relative importance of funeral versus health care worker  transmission was essential to stopping disease spread. As a result, strategic  policy decisions regarding interventions must rely on accurately  characterizing risks associated with multiple transmission routes. The  ongoing Zika virus (ZIKV) outbreak challenges our conventional methodologies  for translating case-counts into route-specific transmission risk.  Critically, most approaches will fail to accurately estimate the risk of  sustained sexual transmission of a pathogen that is primarily vectored by a  mosquito-such as the risk of sustained sexual transmission of ZIKV. By  computationally investigating a novel mathematical approach for multi-route  pathogens, our results suggest that previous epidemic threshold estimates  could under-estimate the risk of sustained sexual transmission by at least an  order of magnitude. This result, coupled with emerging clinical,  epidemiological, and experimental evidence for an increased risk of sexual  transmission, would strongly support recent calls to classify ZIKV as a  sexually transmitted infection.

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