Mosquito-borne virus may cause brain swelling, death

Catching the mosquito-borne virus chikungunya usually leads to fever and severe pain, but a new study shows it may also lead to inflammation in the brain, and even death in some people.

In the study, researchers looked at an epidemic of the virus on Reunion Island, in the Indian Ocean near Madagascar, that lasted from 2005 to 2006 and sickened 300,000 people. As a result of their infections, 24 people developed encephalitis, which is inflammation of the brain, and four of those people died from their infection.

Encephalitis from the chikungunya virus was most common among babies younger than one and people aged 65 and older, according to the study.

The researchers noted that the encephalitis rates in these groups were "much higher than the rates of encephalitis in the United States in these age categories, even when you add together all the causes of encephalitis," study author Dr. Patrick Gérardin, of Central University Hospital in Saint Pierre, Reunion Island, said in a statement.

Chikungunya virus is transmitted to people by mosquitoes. The most common symptoms of an infection are fever and joint pain as well as muscle pain, joint swelling and rash, according to the Centers for Disease Control and Prevention (CDC). Most people recover within a week of becoming infected, but for some people, the pain and other symptoms may continue for months or even years, the researchers said. [The 9 Deadliest Viruses on Earth]

There is currently no vaccine to prevent chikungunya or medicine to treat the virus, according to the CDC. People who catch the virus are typically treated with fever-reducing medications and painkillers, Gérardin told Live Science. If people develop arthritis as a result of infection with the virus, they are given anti-inflammatory drugs, he said.

Outbreaks of chikungunya have occurred in many regions of the world, including Africa, Asia, and the Caribbean islands, the researchers said. And in recent years, the disease has been spreading to new areas. As of September 2015, more than 7,000 cases had been reported in Mexico, according to the CDC.

"Since there is no vaccine to prevent chikungunya and no medicine to treat it, people who are traveling to these areas should be aware of this infection and take steps to avoid mosquito bites, such as wearing repellent and long-sleeves and pants if possible," Gérardin said.

In 2014, a Florida man became the first person to become infected with the virus in the U.S. (previously, other people had been diagnosed with chikungunya in the U.S., but they had contracted the virus while traveling elsewhere).

This year, 571 cases of chikungunya virus disease have been reported so far in 42 U.S. states, including cases contracted both here and elsewhere. And 196 cases have so far been reported in Puerto Rico and the U.S. Virgin Islands in 2015, according to the CDC.

When the researchers followed up with the people in the new study three years after the outbreak, they found that an estimated 30 to 45 percent of the 24 people who had developed encephalitis went on to develop persisting disabilities. (The researchers were not able to calculate the exact percentage as some people were unable to be located.)

Among the children who had been infected as infants and developed encephalitis, these disabilities included behavioral changes and problems with thinking and memory skills, the researchers said.

"The consequences of this encephalitis seem to be particularly harmful in newborns," Gérardin said.

Among the adults who were infected with the virus and developed encephalitis as a result of the infection, the disabilities included dementia and epilepsy, according to the study, published Friday in the journal Neurology.