The ECDC has published a 20 page, data-rich, overview and analysis on the Zika virus called Rapid Risk Assessment: Zika virus disease epidemic: potential association with microcephaly and Guillain-Barré syndrome (first update).
As we've come to expect from the ECDC, it is comprehensive, well documented, and makes an invaluable reference.
You'll want to download to read and keep this PDF file handy, as it is simply too large to excerpt the full gist here.
You'll find sections devoted to genetic lineage and possible changes to the Zika virus (see AFD Blog Paper: Zika Adaptations To Humans Helped Spark Global Spread), the risks from blood transfusion, advice to international travelers and their doctors, and of course the two big (and as yet, unanswered) $64 questions:
Risk of microcephaly and other congenital central nervous system malformations
To date, health authorities have reported eight adverse pregnancy outcomes and/or other congenital CNS malformations with laboratory confirmation of Zika virus in amniotic fluid, placenta or foetal tissues. In addition, information on six cases of Zika virus detection in newborns from the Paraíba State with partly severe congenital malformations has been recently published. All fourteen reported cases have history of exposure in Brazil.
After performing a retrospective analysis following the alert from Brazil, the health authorities of French Polynesia reported an increase from an average of one case annually to 17 cases of CNS malformations in foetuses and infants during 2014–2015, following a Zika virus outbreak in 2013–2014.
No cases of microcephaly or other CNS malformations potentially related to Zika virus have been reported from other countries of Americas and Caribbean affected by Zika virus outbreaks. However, autochthonous transmission of Zika virus did presumably not start before the last trimester of 2015 in most of these countries, and the prospective monitoring of congenital malformations will support the evaluation of the association with Zika virus infections.
In summary, the evidence regarding a causal link between Zika virus infections during pregnancy and congenital CNS malformations is growing, although the available information is not yet sufficient to confirm it. The definitions of suspected cases applied in the epidemiological surveillance protocol for Brazil are broad and will capture many healthy children who are within the normal variation as well as children with medical conditions that are unrelated to Zika virus infections. The cases identified with the surveillance protocol will need to be further investigated and assessed, and many will have to be followed over time. It is expected that many of the suspected cases will be reclassified and discarded. So far, no results have been made public from the epidemiological studies that reportedly are ongoing and may substantiate or disprove the association between intra-uterine Zika virus infections and congenital lesions in CNS.
Risk of Guillain–Barré syndrome
No new scientific evidence about the association of GBS and Zika virus infection has been published since the ECDC RRA published on 10 December 2015. Two new countries, El Salvador and Venezuela (according to media), have reported an unusual increase above the baseline, concomitant with the development of Zika outbreaks in the country. This observation supports a temporal and spatial association as that seen in French Polynesia.
The bottom line is, despite a growing body of evidence, there is not yet conclusive proof that microcephalic births or the rise in GBS are due to Zika virus infection. For now, however, it remains the most likely culprit.
With no vaccine, no specific treatment, and far too many unanswered questions - the immediate focus is on prevention.Better mosquito control, limiting personal exposure to mosquitoes, and taking steps (using repellents, wearing long sleeved shirts, etc.) to prevent mosquito bites will be the best way to limit the spread of Zika, along with Dengue and Chikungunya.