Where the Zika Virus Came From

Epidemiology in the News: Incidence and Prevalence of the Zika Virus Healy (2016) reports in the L.A. Times that scientists are currently pursuing five strategies of dealing with the Zika virus. Before reporting on these strategies, Healy provide an epidemiology of the virus, beginning with its first reported incidence in 1947 in Uganda. From Africa, Healy shows that the virus spread to Asia and the Americas.

Connected to the spread of the disease is the concern of "whether cases of microcephaly followed in its wake but were undetected at the time" (Healy, 2016). To determine the connection of microcephaly to Zika, the island of Yap was studied by epidemiologists, who noted that in 2007 "between 68% and 88% of residents over the age of 2 were infected with the virus" (Healy, 2016).

Yap provides a useful means of studying the disease because island nations such as Yap, which are small and isolated, allow researchers an opportunity to see how a virus like Zika interacts with persons over time. Thus, the effects of the virus can be studied with an almost control-like view. However, just because there is no indication of incidence of microcephaly doesn't mean that there is no connection -- it could just indicate that there have not been good records kept.

At the same time, Healy notes that there are other questions that epidemiologists must pose -- such as, "Have birth defects been absent before because Africans and Asians have lived with Zika for so long that almost all pregnant women have developed immunity to the virus?" The article concludes with the assertion that more study is required and that scientists are examining the history of the virus as well as possible vaccinations that could help immunize.

When considered alongside the work by Gordis (2014), possible problems with the measurements involved in this case could be that the number of cases in Yap, for instance, are too small -- or the population sample is too small. Point prevalence and period prevalence are also issues that might be problematic in this case as the spread of the disease or how it migrated is unstated and the points at which it entered the communities is not quite determined.

Today's manifestations and the correlations between them and microcephaly are noted in the popular media but epidemiologists are uncertain whether there is a correlation or not because the data that is available on Zika is not enough to go on and small population sizes like the community in the Yap island is not sufficient for saying anything for certain regarding a relationship between the disease and the birth defect.

So while new cases will add to the information available on prevalence, the incidence rate of Zika and the point prevalence are areas that need to be studied more so that total correlation can be understood. At the same time, death will decrease prevalence, so this needs to be taken into consideration when doing measurements of the spread.