Epidemiology of Zika virus, 1947-2007

Abstract

Introduction: Since 1947, Zika virus has been identified sporadically in humans in Africa and Asia; however, clinically consequential Zika virus disease had not been documented prior to the current outbreak in the Americas. Considering 6 decades have passed since the first identification of the virus, it is perhaps unexpected that Zika virus was recognised only recently as capable of causing disease epidemics. Substantial work on understanding the epidemiology of Zika virus has been conducted since the virus' first outbreak in 2007 in Micronesia; however, there has been little study of the earlier data on Zika virus.

Methods: A systematic literature search was conducted to identify evidence of Zika virus infection in humans from 1947 to 2007. Data extracted included seroprevalence of Zika virus infection, age distributions of positive test results and serologic test modalities used. Country-level and age-specific seroprevalence was calculated. Estimates of seroprevalence by different serologic test modalities were compared.

Results: 12 026 citations were retrieved by the literature search, and 76 articles were included in this review. Evidence of Zika virus infection in humans was found in 29 countries in Africa, 8 countries in Asia and 1 country in Europe. Country-level seroprevalence of Zika virus infection ranged from 0.4% to 53.3%. Seroprevalence of Zika virus infection was found to increase across the lifespan; 15-40% of reproductive-age individuals may have been previously infected. No significant difference was found between estimates of seroprevalence by different serologic test modalities.

Discussion: Zika virus has likely been endemic for decades in certain regions of the world; however, the majority of reproductive-age individuals have likely not been infected. Historical evidence of Zika virus infection exists regardless of the serologic test modality used.

Figure 1

Map of Zika virus seroprevalence in countries with evidence of Zika virus infection in humans prior to 1 April 2007.

Figure 2

Years of first identification of Zika virus seropositivity by country.

Figure 3

Age distribution of seroprevalence of Zika virus infection. The shaded area represents the interquartile range for maternal age in Brazil, the origin of the current outbreak of Zika virus. Age intervals: narrower intervals report on individuals aged 0–4, 5–9, 10–14, 15–19, 20–29, 30–39 and ≥40 years; wider intervals report on individuals aged 0–9, 10–19, 20–29, 30–39 and ≥40 years; and dual age intervals with a cut-point at 13 or 15 years, compare children to adults. Data were reported in the narrower intervals for 16 223 individuals tested in Cameroon, Central African Republic, Côte d'Ivoire, Kenya, Nigeria, Philippines, Senegal and Uganda, in the wider intervals for 874 individuals in Central African Republic, and in dual intervals for 13 892 individuals in all 20 countries where seroprevalence by age was reported. Methods: Bézier spline smoothed scatterplot with point data for age intervals placed at the upper bound of each interval. Point data from studies comparing children to adults were placed at 15 and 39 years, and the line was then projected under an assumption of constant slope. The IQR for maternal age in Brazil was estimated by indirect standardisation using 2010 age-specific fertility rates and female population by age in Brazil.