Out of every 100,000 people who get Zika virus, 24 could develop Guillain-Barré syndrome, suggests research published in The Lancet.
Guillain-Barré syndrome (GBS) is a severe neurological disorder that affects the immune and nervous systems. Apart from trauma, it is the most common cause of paralysis.
Symptoms develop rapidly and include pain and weakness in the muscles and limbs. About 5% of cases are fatal, and 20-30% of patients face respiratory failure. It is usually triggered by an infection such as herpes, influenza or dengue virus, and it affects about 1-2 people per 100,000 annually in Europe and North America.
The current outbreak in Central and South America, which the World Health Organization (WHO) have declared as a global emergency, has been accompanied by unusually high rates of microcephaly and GBS.
Now, analyses of blood samples from 42 patients diagnosed with the syndrome in French Polynesia during the Zika virus outbreak have suggested there could be a link.
French Polynesia experienced a major Zika outbreak between October 2013 to April 2014, the largest outbreak globally at that time.
There are normally 3,000-6,000 cases of GBS per year in the US
It appears randomly rather than in clusters
Most people recover within weeks or months, but 1 in 20 cases are fatal
Approximately 32,000 patients consulted a doctor about a suspected Zika virus infection, and from November 2013 to February 2014, 42 patients were diagnosed with GBS.
Lead author Prof. Arnaud Fontanet, from the Institut Pasteur in Paris, France, and colleagues set out to examine the link between Zika virus infection and GBS.
They also looked at dengue virus as a potential risk factor for GBS, because French Polynesia is also prone to outbreaks of dengue.
At the Centre Hospitalier de Polynésie Française in Papeete, Tahiti, 42 patients were diagnosed with GBS, all of whom were included in the study.
Two control groups were matched for age, gender and island of residence. In Control Group 1, there were 98 patients who attended the same hospital but did not have a fever.
Control Group 2 consisted of 70 patients who were diagnosed with Zika virus infection, but the patients did not show any of the neurological symptoms associated with GBS.
Blood samples were collected from all patients.
Of the patients with GBS, 88% experienced symptoms of Zika virus infection approximately 6 days before the neurological symptoms appeared. While the patients did not test positive for Zika after hospitalization, blood tests showed they all had neutralizing antibodies against the Zika virus.
All 42 patients were diagnosed with a specific type of GBS, called acute-motor axonal neuropathy (AMAN), but they mostly did not have the biological markers normally associated with AMAN, indicating a previously unknown disease mechanism.
The patients with GBS spent an average of 11 days in the hospital, and 29% of them needed breathing assistance; 38% spent time in intensive care, and these patients remained for 51 days on average.
Recovery was generally faster than usual for GBS. Three months after discharge, 57% of the patients could walk without assistance. There were no fatalities.
There were signs of dengue fever in 95.2% of the group with GBS. Between 8-9 out of 10 patients in the two control groups also had signs of dengue virus, suggesting that dengue is not a risk factor for GBS among patients with Zika virus.
In French Polynesia, 66% of people are estimated to have been affected by Zika virus. Based on this figure, the team calculates the risk of GBS at 0.24 per 1,000 Zika virus infections.
“Most of the patients with GBS reported they had experienced symptoms of Zika virus infection on average 6 days before any neurological symptoms, and all carried Zika virus antibodies,” says Prof. Fontanet.
Prof. Fontanet cautions that high rates of Zika in Central and South America in the coming months could mean a higher prevalence of GBS.
“The results of our study support that Zika virus should be added to the list of infectious pathogens susceptible to cause Guillain-Barré syndrome.”
In a linked comment, Prof. David W. Smith, of the University of Western Australia, points out that it is not yet certain that the current strain of Zika virus in South America is the same as in previous outbreaks, and that any similarities or differences, as well as the specific genetic features of the affected population, could affect its behavior.
However, he concludes that Zika virus can be added to the list of viruses that can cause GBS, and testing for Zika is, therefore, appropriate if there is a possibility that a patient with GBS has been exposed to it.
How serious a risk factor Zika is for GBS, however, is not yet known.
Medical News Today recently reported on a study exploring the link between Zika virus and stillbirth.