Zika virus – Incidence and trends
To date, 35 countries and territories have confirmed local, vector-borne transmission of Zika virus in the Region of the Americas since 2015 (Figure 1). Belize is investigating a potential case of autochthonous transmission reported by another country.
Zika virus cases and other mosquito-borne diseases, like dengue and chikungunya have been showing a downward trend in many countries in the Americas consistent with what was observed in the same period in the previous year. However, trends of suspected Zika virus cases by sub-national levels show variations in different geographic areas. This is illustrated by data from Colombia showing an increasing trend in reported Zika cases in the regions of Orinoquía and Pacifico, while in the rest of the regions, the number of cases is decreasing (Figure 2).
Congenital syndrome associated with Zika virus infection
Summary
Since the detection of Zika virus in Brazil in 2015 to date, six countries have reported cases of congenital syndrome associated with Zika virus (Table 1). In addition, two cases were reported, one in the United States of America and the other in Slovenia, both linked to a stay in Brazil. Approximately 98% (1,113 cases) of confirmed cases of congenital syndrome associated with Zika virus have been reported from Brazil, which was also the first country to report increased cases of microcephaly since 22 October 2015.
As reported in a previous Zika Epidemiological Update (31 March), the New England Journal of Medicine published a report on a 33-year-old pregnant woman who tested positive for Zika virus (IgG and IgM) at 4 weeks and 10 weeks after the onset of symptoms. The patient developed Zika virus symptoms after travel to Mexico, Guatemala, and Belize in the 11th gestational week (late November 2015). None of these countries have reported cases of congenital syndrome associated with Zika virus to date. The report indicated, fetal ultrasonography that was performed at 13, 16, and 17 weeks of gestation (1, 4, and 5 weeks after the resolution of symptoms) showed no evidence of microcephaly or intracranial calcifications. However, there was a decrease in the fetal head circumference from the 47th percentile at 16 weeks to the 24th percentile at 20 weeks. Abnormal intracranial anatomy showed at 19 weeks of gestation, and diffuse atrophy of the cerebral mantle showed at 20 weeks of gestation, which was most severe in the frontal and parietal lobes. The patient elected termination of pregnancy at 21 weeks of gestation.
A decreased head circumference were found in the fetal brain, with substantial viral loads in the placenta, fetal membranes, umbilical cord and fetal brain, as detected on quantitative RT-PCR. See full report.