The 28-year-old actress picked up the incurable bug during a festive vacation to Bora Bora, reported Independent.
She is currently in King Edward VII's Hospital and is reportedly being kept in because she has a high fever and the joint pain is 'unbearable'.
The star addressed the illness herself while still on her holiday in December via social media.
"Being sick is no fun. But happy new year everyone. Be safe. Love all.
"In good faith with good people. I refuse to let a virus affect my peaceful vacation be safe and happy on the new year all wildfox and a positive, healthy new year (sic)," she wrote on Twitter.