The mosquito-borne virus chikungunya may lead to severe and potentially deadly encephalitis or brain infection in some patients, particularly infants and people older than 65, according to the findings published in Neurology. The study, published online on Nov 25, reviewed chikungunya cases during an outbreak on Reunion Island off the coast of Madagascar.

The outbreak affected 300,000 people. Fifty-seven patients were diagnosed with chikungunya-associated central nervous system (CNS) disease. Twenty-four people developed encephalitis and four died from it. The infection from the chikungunya virus was most prevalent among infants below one year old, and people ages 65 and older, according to the study. Infants exhibited behavioural changes and altered thinking and memory, while healthy adults suffered epilepsy and dementia.

The death rate of people with encephalitis resulting from the virus was 17 percent. Thirty to 45 percent still suffer ongoing disabilities.

"These data are of paramount importance for public health stakeholders and policy makers, because owing to global climate warming, chikungunya threatens many countries, including those in the Western world,” said Patrick Gérardin, lead author from Central University Hospital in Saint Pierre, Reunion Island, Medscape Medical News reports. "Our findings suggest that without an appropriate strategy or mitigating the extent of the outbreak, chikungunya may become a major cause of infectious encephalitis in the US, with the potential of disease burden exceeding that of West Nile virus."

Chikungunya virus is transmitted to people by mosquitoes that mostly bite during daytime. Before, it was not considered deadly or can cause permanent disabilities. Patients infected will have fever and joint pain, according to the Australian Department of Health. Muscle pain, joint swelling, headache or rash may also be manifested. Recovery takes place within one to 12 days for most people, while in some, the disease may last for months or years.

"Before the 2005 to 2006 epidemic on La Réunion, chikungunya infection was believed to be a nonfatal benign illness, and chikungunya-associated [central nervous system] disease was thought to be a nonspecific complication of a systemic disease," Gérardin added. "But we have shown that beyond the well-described arthralgia/arthritis, this virus can be life-threatening and cause fatalities, and also long-term disabilities."

This is the first study to use the criteria to identify the encephalitic syndrome despite knowing, for many years, that the brain infection can result from the chikungunya virus.

There is currently no vaccine to prevent chikungunya,. Gérardin advises travellers to take steps to avoid mosquito bites such as wearing long-sleeves, pants and insect repellent. The Department of Health also encourages the use mosquito coils, protective and light coloured clothing and fabrics with permethrin. Screening living and sleeping areas are a must. People should also throw away stagnant water found in flowerpots or buckets.

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