French scientists studying a 2013 and 2014 Zika outbreak in French Polynesia found an increase in cases of Guillain-Barre (GBS), a syndrome in which the body`s immune system attacks the nervous system.
The research, published in the medical journal "The Lancet," found GBS in 2.4 of every 10,000 people infected by Zika - a 20-fold increase in what would otherwise be expected.
The scientists analyzed 42 patients who developed GBS at the time of the epidemic in French Polynesia. Each patient was found to have been previously infected with Zika and 93 percent of them had been infected within three months of developing GBS.
"The links are as strong as they would be for saying that tobacco causes lung cancer," Arnaud Fontanet of France`s Institut Pasteur, who co-led the study, told AFP news agency.
With the best of care, about five percent of GBS cases result in death, although others are left severely debilitated for weeks or months. In Tahiti, of the 42 cases, all were non-fatal, and 40 percent of patients could walk after three months in the hospital.
"In areas that will be hit by the Zika epidemic, we need to think about reinforcing intensive care capacity," Fontanet said. "We know that a certain number of those patients are going to develop GBS, and 30 percent of them are going to need intensive care, especially for assisted breathing," he added.
Scientists already suspect the Zika virus to be linked to babies with microcephaly, a condition leading to deformities in skull development and cognitive problems. Since October 2015, Brazil has reported nearly 600 cases of babies with microcephaly, which is four times the annual average.
The suspicion of links between Zika and other conditions has already prompted the World Health Organization (WHO) to declare an international emergency as the virus spreads after a major outbreak in Brazil.
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