Is Zika virus a cause of neurological disorders?

ISPM, the World Health Organization (WHO) and Pan American Health Organization (PAHO) have published their perspective in the New England Journal of Medicine about the evidence for causal links between Zika virus and outbreaks of microcephaly and Guillain-Barré syndrome. Nicola Low, Fabienne Krauer and Maurane Riesen in the Sexual and Reproductive Health research group are leading this project.

Zika virus is currently spreading in Brazil and other parts of Latin America and the Caribbean, carried by mosquitoes like Aedes aegypti. Previously thought to be a mild viral illness, Zika virus infection is being linked to increases in microcephaly and a range of other congenital anomalies, and the post-infectious paralytic Guillain-Barré syndrome. On February 1 2016, Margaret Chan, Director General of WHO declared the clusters of microcephaly and Guillain-Barré syndrome a Public Health Emergency of International Concern.

The research team developed a causality framework, based on the “Bradford-Hill criteria.” The framework defines questions about each of ten dimensions of causality: temporality; biological plausibility; consistency; exclusion of alternative explanations; dose-response relationship; strength of association; reversibility; experiment; analogy; and specificity.

The research team from ISPM, together with colleagues at WHO, PAHO and other international institutions are using systematic review methods to appraise the evidence. This ‘living review’ will generate methods to allow real time updates about the evidence for causality in the fast moving world of emerging infectious diseases.

Picture credit: Ekins S et al.