In response to the growing reports of neurologic disorders related to the Zika virus, the World Health Organization (WHO) has declared a Public Health Emergency of International Concern, and launched an effort to accelerate research on the links between the Zika virus and neurologic disorders, namely, microcephaly and the Guillain-Barré syndrome (Broutet N, et al. N Engl J Med. 2016 March 9. Epub ahead of print).
“How can currently available evidence about causality guide the choice and implementation of interventions?” asked Nathalie Broutet, MD, PhD, of the WHO, and colleagues. “For this purpose, the WHO is developing a framework for systematic appraisal of evidence about these causal relationships.”
The researchers reviewed currently available population- and individual-level studies on the potential associations between the Zika virus and the Guillain-Barré syndrome or microcephaly.
At the population level, 3 published studies reported Guillain-Barré syndrome after a Zika virus infection outbreak in several South American countries, in El Salvador, Martinique, Panama, and Puerto Rico. Microcephaly has been linked to the Zika virus from Paraíba and Bahia in Brazil, but not in neighboring countries, possibly because it is still too soon after the introduction of the virus for the neurologic sequelae to develop.
At the individual level, 3 studies have been published on the association between the Zika virus and Guillain-Barré syndrome, and 14 studies have been published on the association between the Zika virus and microcephaly. The only published case-control study showed that 41 of 42 patients with Guillain-Barré syndrome that was diagnosed during the 2013-2014 Zika virus outbreak in French Polynesia were carrying Zika virus antibodies compared with 35 of 98 hospitalized control patients. Of note, no association was found between Guillain-Barré syndrome and exposure to dengue, which has the same mosquito vector and was circulating at the same time as the Zika virus.
“The available data are mainly observations regarding temporal associations between infection and disease from routine population surveillance and clinical and pathological studies of single cases or groups of cases,” Dr Broutet and colleagues wrote. That being said, “the severe potential [neurologic] risks demand decisive, immediate action to protect public health.”
Populations in areas at risk for outbreaks of the Zika virus should be informed of the risk for neurologic disorders, and public health measures should be adjusted accordingly.