Zika Virus: More Questions Than Answers

The recent Zika virus (ZIKV) outbreak has been declared a Public Health Emergency of International Concern (PHEIC) by the World Health Organization in February 2016. It started in Brazil in 2015, rapidly spread through South and Central America, and is expected to reach the continental US in the summer of 2016. The appearance of ZIKV has been connected with an increase in cases of microcephaly in newborns of the affected areas and Guillain–Barré Syndrome (GBS) (WHO, 2016). Since the virus' first isolation in Uganda in 1947, the two major outbreaks happened in Micronesia (2007) and in French Polynesia (2013). The 2013 outbreak is the only precedent where ZIKV was associated with serious complications (GBS) and a causal link between ZIKV infection and GBS was suggested based on a large study (Cao-Lormeau et al., 2016). The mechanism of ZIKV-induced GBS is not clear, but one possibility is cross-reactivity between a viral antigen and the selfpeptide myelin. The evidence for ZIKV causing fetal microcephaly has been under debate due to the small number of studies reported, but as new reports appear every week the evidence seems clearer, although it has not been scientifically proven yet. A recent cohort study of 88 pregnant women in Brazil showed that 29% of infected mothers delivered babies with fetal abnormalities (Brasil et al., 2016). Furthermore, from nine current reported cases of ZIKV-positive pregnant women in the US that traveled to ZIKV endemic areas, five pregnancies resulted in fetal abnormalities or death, two in healthy babies while two women are still pregnant (MeaneyDelman et al., 2016). ZIKV has also been found both in the amniotic fluid and in fetal brain after pregnant mothers were infected, supporting the causal link between ZIKV-infected mothers and fetal microcephaly (Marrs et al., 2016). There are precedents of closely related neutrotropic flaviviruses that cause neurological diseases. West Nile Virus (WNV) can cause encephalitis and meningitis, and chikungunya virus (CHIKV) can cause neonatal encephalopathy and microcephaly (Gerardin et al., 2014). Additionally, other viruses causing congenitally acquired infections (TORCH) like rubella virus,