Most of the media coverage of the Zika virus epidemic currently underway in the Americas focuses on its suspected ties to microcephaly – a devastating neurological disorder that causes newborns to develop abnormally small skulls and brains - but the infection is also thought to be linked to Guillain-Barré syndrome (GBS), a rare but severe neurological disease that leads to temporary paralysis and sometimes death (in about 5 percent of cases).
Now a new study is the first to provide scientific evidence that Zika virus might cause GBS, with an analysis of blood samples taken from patients during the 2013–2014 Zika outbreak in French Polynesia suggesting that GBS could develop in 24 out of every 100,000 Zika cases.
"This is the first study to look at a large number of patients who developed Guillain-Barré syndrome following Zika virus infection and provide evidence that Zika virus can cause GBS," said epidemiologist Arnaud Fontanet from the Institut Pasteur in France. "Most of the patients with GBS reported they had experienced symptoms of Zika virus infection on average six days before any neurological symptoms, and all carried Zika virus antibodies."
The researchers examined 42 patients diagnosed with GBS during the previous Zika outbreak and found that 41 of them (98 percent) were carrying Zika virus antibodies, while all had neutralising antibodies against Zika virus. In contrast, only 54 percent of patients in a control group that didn't show any symptoms of Zika virus fever carried Zika-neutralising antibodies.
With an attack rate – the speed of spread of the infection in an 'at risk' population – for Zika virus of 66 percent in French Polynesia, the researchers estimated that the risk of GBS in the French Polynesian community during the outbreak was around 24 people per 100,000 infections.
There's no way of telling if the prevalence of GBS in the current Zika outbreak would occur at similar rates, but the researchers say it's a possibility.
"Although it is unknown whether attack rates of Zika virus epidemics will be as high in affected regions in Latin America [as] in the Pacific Islands, high numbers of cases of Guillain-Barré syndrome might be expected in the coming months as the result of this association," said Fontanet. "The results of our study support that Zika virus should be added to the list of infectious pathogens susceptible to cause Guillain-Barré syndrome."
Still, we shouldn't necessarily take the findings – which are published in The Lancet – as predictive of other Zika outbreaks until more is known about the virus.
"A little caution should be taken because the data are still scarce and we do not know whether the current Zika virus is identical to that in previous outbreaks, whether it will behave exactly the same in a different population with a different genetic and immunity background, or whether a cofactor or co-infection is responsible," write researchers David W Smith and John Mackenzie from the University of Western Australia and Curtin University, who were not involved with the research, in a commentary on the study.
While Zika virus at present appears to be contained in a defined set of countries in the Americas, Oceania, and Africa, there are numerous reported instances of travellers to some of these areas being diagnosed with the infection upon their return home to the US and other countries.
Although the link between Zika and microcephaly is not yet proven, the sad recent cases of some pregnant women in the US infected with the virus may strengthen the case that the two are related. Of the nine women (infected during travel overseas), one baby born had severe microcephaly, and at least one terminated foetus showed early signs of abnormality.
Here's hoping global efforts to fight and contain Zika virus start making some significant headway before this terrible outbreak gets worse.