Estimation of Zika virus prevalence by appearance of microcephaly
C M Saad-Roy1, P van den Driessche1, Junling Ma2
1Department of Mathematics and Statistics, University of Victoria, Victoria, BC, V8W 2Y2, Canada.
Background:
There currently is a severe Zika Virus (ZIKV) epidemic in Brazil and other South American countries. Due to international travel, this poses severe public health risk of ZIKV importation to other countries. We 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.
Methods:
We establish 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). We take account of population structure through a contact network for sexually active individuals. Parameter values of our model are either taken from the literature or estimated from travel data.
Results:
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%-30% spectrum that is currently hypothesized. Our model predicts that for import regions with at least 250,000 people, on average 1,000-12,000 will have been infected by the time of the first detection of microcephaly, and on average 200-1,500 will be infectious at this time. Larger population sizes do not significantly change our predictions.
Conclusions:
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.
Insights
By the time a microcephaly case is detected, many people may be infected with Zika Virus (ZIKV). This highlights the need for swift public health interventions like surveillance and quarantine to prevent widespread epidemics.
Area of Science:
- Epidemiology
- Mathematical Modeling
- Public Health
Background:
- A severe Zika Virus (ZIKV) epidemic is ongoing in South America.
- International travel poses a significant risk for ZIKV importation.
- Microcephaly is a key indicator for detecting ZIKV presence.
Purpose of the Study:
- To estimate ZIKV prevalence in import regions by the time of microcephaly detection.
- To model ZIKV transmission dynamics, including vector and sexual routes.
- To assess the impact of population structure on ZIKV spread.
Main Methods:
- Developed a mathematical model for ZIKV spread from source to import regions.
- Incorporated vector-borne and sexual transmission pathways.
- Utilized a contact network for sexually active individuals.
- Estimated model parameters from literature and travel data.
Main Results:
- Predicted the probability distribution for the first microcephaly case detection.
- Indicated that the rate of fetal abnormalities from ZIKV infection is likely at the lower end of the 1%-30% range.
- Estimated 1,000-12,000 infections and 200-1,500 infectious individuals in populations over 250,000 by the first microcephaly detection.
Conclusions:
- A significant portion of the population can be infected by ZIKV before the first microcephaly case is identified.
- Urgent need for surveillance, isolation, and quarantine in susceptible regions.
- Interventions are crucial to contain ZIKV epidemic dissemination.
