Estimation of Zika Virus Prevalence by Appearance of Microcephaly

Due to international travel, the current Zika virus (ZIKV) epidemic in Brazil and other South American countries poses a severe public health risk of ZIKV importation to other countries. Saad-Roy, et al. (2016) estimate the prevalence of ZIKV in an import region by the time a microcephaly case is detected, since microcephaly is presently the most significant indication of ZIKV presence.

The researchers established a mathematical model to describe ZIKV spread from a source region to an import region. This model incorporates both vector transmission (between humans and mosquitoes) and sexual transmission (from males to females). They took account of population structure through a contact network for sexually active individuals. Parameter values of the model were either taken from the literature or estimated from travel data.

Saad-Roy, et al. (2016) explain, "This model gives us the probability distribution of time until detection of the first microcephaly case. Based on current field observations, our results also indicate that the percentage of infected pregnant women that results in fetal abnormalities is more likely to be on the smaller end of the 1% to 30% spectrum that is currently hypothesized. Our model predicts that for import regions with at least 250,000 people, on average 1,000 to 12,000 will have been infected by the time of the first detection of microcephaly, and on average 200 to 1,500 will be infectious at this time. Larger population sizes do not significantly change our predictions."

The researchers conclude that by the first detection of a microcephaly case, a sizable fraction of the population will have been infected by ZIKV. It is thus clear that adequate surveillance, isolation, and quarantine are needed in susceptible import regions to stop the dissemination of a Zika epidemic.

Reference: Saad-Roy CM, et al. Estimation of Zika virus prevalence by appearance of microcephaly. BMC Infectious Diseases. 2016;16:754

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