Zika Virus From a Risk Assessment Point of View
Zika virus appears to have a transmission cycle of infected human host –> mosquito (via blood meal) –> susceptible host (in course of a second blood meal). To understand transmission via the route, the following need to be known:
- What are the levels in blood of an infected individual?
- What is the volume of blood ingested in feeding by a mosquito?
- What is the volume of disgorgement of blood by a mosquito upon a second blood meal?
- What is the die-off of Zika virus within a mosquito between blood meals?
- What is the dose-response in the human host for infection by Zika virus.
Questions (2) and (3) should be identifiable by a literature review and would not be expected to be a function of the pathogen (Zika). Question (1) may be obtainable from a review of case reports and deliberate trials in the literature, as well as on the ongoing primate trials at the University of WIsconsin, which are being done in an open science manner (http://www.nature.com/news/zika-researchers-release-real-time-data-on-viral-infection-study-in-monkeys-1.19438).
It is not anticipated that data on question (4) is available per se, however inferences may be drawn from persistence of other Flaviviridae in conditions analogous to carriage in the mosquito. A preliminary scan of the literature suggests prior data that could be useful in developing a dose-response relationship per question (5) for Zika. We have developed dose response relationships for many other organisms including several vector borne pathogens:
- Rickettsia typhi (Tamrakar, S. B., Y. Huang, S. S. Teske, and C. N. Haas. 2012. “Dose-response model of murine typhus (Rickettsia typhi): time post inoculation and host age dependency analysis.” BMC Infectious Diseases 12 (1):77. doi: 10.1186/1471–2334–12–77.)
- Yersinia pestis (Huang, Yin, and Charles N. Haas. 2009. “Time-Dose-Response Models for Microbial Risk Assessment.” Risk Analysis 29 (5):648–661.)
The assembly of this information can be useful, when embedded in a population transmission model, for projecting consequence and estimating the effectiveness of public health interventions. To my knowledge, such risk assessment approach has not been underway.
Unfortunately, serious risk analysis seems to be minimized as a tool to respond, right now. Decision makers and funders need to be educated.