Chikungunya Virus Can Cause Fatal Encephalitis

November 25, 2015

The mosquito-borne virus chikungunya can lead to severe encephalitis and even death, especially in young babies and older adults, a new study has found.

The study, published online November 25 in Neurology, reviewed cases of chikungunya that occurred during an outbreak on Reunion Island off the coast of Madagascar in 2005 to 2006, but the authors say the findings have implications for many other counties, including those in Europe and North America.

"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, with possibilities of epidemics in Southern Europe, Southern Central, and even North America," lead author Patrick Gérardin, MD, from Central University Hospital in Saint Pierre, Reunion Island, told Medscape Medical News.

He added, "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."

The authors report that outbreaks of chikungunya have occurred in numerous areas, including Africa, Asia, and the Caribbean islands, and as of September 2015, more than 7000 cases have been reported in Mexico. Many cases of chikungunya also have occurred in the United States in people who acquired the virus while traveling, but the first locally transmitted US case was reported in Florida in 2014.

The most common symptoms of the infection are fever and joint pain. Although most people recover within a week, for some people, the joint pain can continue for months and even years.

The researchers note that the 2005 to 2006 epidemic on La Réunion Island affected 300,000 people and enabled information to be gained on severe forms of the disease. These included rare severe or fatal cases with central nervous system involvement in both adults and neonates.

"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," Dr Gérardin commented. "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 (lifelong in infants) such as cerebral palsy, neurocognitive delays and learning difficulties, and postinfective dementia in older adults."

He elaborated: "The possibility of encephalitis resulting from chikungunya infection has been known about for many years, but this is the first study to have used consensual criteria (International Encephalitis Consortium), in a sufficiently developed country with modern diagnostic facilities, for defining the encephalitic syndrome and counting cases to assess the real disease burden."

For the study, the researchers focused on those patients who had neurological symptoms at disease onset and were still affected 3 years later. They report 24 cases of encephalitis associated with chikungunya virus, giving a cumulative incidence rate of 8.6 per 100,000 people.

Encephalitis was more likely to occur in young infants and adults older than 65 years. The incidence rate in infants was 187 per 100,000 people; it was 37 per 100,000 people in people older than 65 years.

"These numbers are both 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," Dr Gérardin said.

The death rate for those with chikungunya virus–associated encephalitis was 16.6%, and 30% to 45% of those with the disease had persisting disabilities, which included behavioral changes and problems with thinking and memory skills in infants and postinfectious dementia in adults. "The consequences of this encephalitis seem to be particularly harmful in newborns," Dr Gérardin added.

"The possibility of encephalitis may be around one to five per 1000 chikungunya infections. Thousands of human cases are required to observe recurrent cases of viral-associated encephalitis," he commented to Medscape Medical News. "The magnitude of the epidemic depends on many things: population background immunity, mosquito densities, fitness of the virus to the mosquito to increase the viral load, responsiveness of vector control teams, adequate mitigation strategies, mass media communication, etc. I fear, like for dengue virus, chikungunya could become endemic in the Caribbean and in the Americas and may threaten international travels to these areas.

"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," he advised.

The study was supported by the Pasteur Institute, Institut national de la santé et de la recherche médicale, Integrated Chikungunya Research, LabEx Integrative Biology of Emerging Infectious Diseases, Ville de Paris, and BNP Paribas Foundation.

Neurology. Published online November 25, 2015. Abstract

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