Zika virus (ZIKV) – Incidence and Trends
Overall, reporting of Zika virus cases in the Region of the Americas is still showing a downward trend which is also observed with the other arbovirus circulating in the Region as shown in Colombia, El Salvador, and Honduras (Figure 1). This trend could change due to delays in reporting when retrospective data is received.
According to available data provided from Member States in the Region[2], the majority of cases of Zika virus (98%) are suspected cases. In comparison, the laboratory-confirmed cases of Zika virus are only 2% of the total reported cases. There are various factors that could explain the difference, including the different surveillance systems in countries, challenges in detecting Zika virus RNA in serum samples during the short phase of viremia, and the lack of serological tests available for the diagnosis during the convalescent phase, among others.
Since the last Epidemiological Update on 17 March, no new countries or territories reported autochthonous (vector-borne) cases of Zika virus infection (Figure 2). There are currently 33 countries or territories reporting local, vector-borne transmission of Zika virus in the Region of the Americas.
Reported increase off congenittal microcephaly and other central nervous system disorders
First report of microcephaly and other congenital malformation in Panama
On 19 March, the Ministry of Health of Panama confirmed Zika virus in a newborn at 31 weeks gestation that was diagnosed with microcephaly and occipital encephalocele. The newborn died on 17 March within a few hours after birth. Samples from the umbilical cord tested positive for Zika virus by RT-PCR. Samples from the mother tested negative for Zika virus. Furthermore, the mother had no history of Zika virus related illnesses during her pregnancy.
Ultrasonography performed at 19 weeks gestation had indicated deficits in the development of neural tube and microcephaly. These findings indicate the ability of the virus to cross the transplacental barrier, and reinforce the hypothesis of vertical transmission.
Congenital microcephaly in Brazil
According to the Ministry of Health of Brazil, as of EW 11 of 2016, 6,671 suspected cases of microcephaly or other nervous system malformation among newborns have been reported since 22 October 2015. Of these, 2,378 cases (36%) had been investigated, revealing 907 confirmed cases of microcephaly and/or other central nervous system (CNS) malformations with evidence suggestive of congenital infection. Out of the total reported cases, 1,471 cases were discarded as being due to non-infectious causes or not fitting the case definition, and 4,293 remain under investigation.
The confirmed cases of microcephaly are distributed in 19 out of 27 Federal Units, but 97% of confirmed cases and 79% of total cases are reported from the Northeast region (Figure 3).