A disabling mosquito-borne disease called chikungunya has killed six people in the French Indian Ocean island of La Réunion, though authorities say the outbreak appears to be easing.

The island, located east of Madagascar, has been battling the epidemic since last August, with local authorities estimating that one in nine people has been affected.

France's public health agency said six people have died since the start of the year, adding that all the victims were people aged "over 70 with comorbidities" or underlying health conditions.

Sante Publique France also reported that the outbreak is showing signs of decline, with approximately 4,900 cases recorded in the first week of April.

More than 33,000 cases have been confirmed since January, although the actual number is believed to be much higher, as many patients do not get tested.

Over 220 people have been hospitalized for more than 24 hours. A quarter of the patients were infants under six months old, and 46 percent were over 65, the health agency said.

La Réunion has a population of nearly 900,000 residents.

The island's top health official, Gérard Cottelon, said over 100,000 residents have likely been affected by the virus during the current outbreak.

While there is no specific treatment for chikungunya, a vaccination campaign was launched this spring to curb its spread.

The name "chikungunya" originates from a word in the Kimakonde language of southern Tanzania, meaning "to become contorted," describing the bent posture of sufferers due to joint pain, according to the World Health Organization.

Before the current outbreak, La Réunion had not reported any cases of chikungunya since 2010.

In 2005 and 2006, a chikungunya outbreak in La Reunion affected nearly 40 percent of the island's population, killing 225 people.