Scientists say the Zika virus, which is known for causing birth defects, also poses a threat of dangerous brain inflammation to adults.

A team of French researchers found that an 81-year-old man who was infected with Zika during a cruise in the South Pacific developed the condition after returning to France.

Clinicians ruled out the presence of any other virus in the man, and are warning other doctors there may be a link with Zika.

The man showed no symptoms during the four-week cruise, and was admitted to the hospital in semi-comatose condition within 10 days of returning to Paris.