Epidemic Traced to Sole Mutation in Mosquito Virus

Scientists from the University of Texas Medical Branch at Galveston (UTMB) have reported their discovery of the reason behind a mysterious epidemic on the island of La Reunion in the Indian Ocean. An outbreak in 2005 and 2006 resulted in the first deaths from a virus called Chikungunya, a mosquito born virus that mutated and became lethal.

In all, 266,000 people were infected and at least 260 deaths resulted. Researchers proved the epidemic was caused by a single mutation and the virus was carried by a mosquito not previously known to be a carrier. The species, Aedes albopictus, also called the Asian tiger mosquito, has been established in the U.S. for around 20 years and has recently started spreading to Europe.

In its non-lethal form the Chikungunya causes extreme arthritis like pain sometimes lasting for months or years. Many tourists became infected at La Reunion and carried that strain home with them. Although no epidemics broke out in Europe the possibility was there. Another strain of the virus causing an ongoing epidemic in India has spread to humans in Italy through the Asian tiger mosquito.

"Chikungunya virus had been known to be primarily carried by a different mosquito, Aedes aegypti, which is not found on La Reunion," said UTMB professor Stephen Higgs, of the outbreak on La Reunion. "Adaptation to Aedes albopictus and introduction to a human population that had never been exposed to the virus before set everything up for this outbreak."

The researchers say the mutation gives the new strain of virus an evolutionary edge over its predecessor, and was predominantly transmitted versus the original strain. The new strain evolved when a single amino acid chain changed, leading to the ability for the virus to infect the new mosquito. One of the authors created the same changed in a strain collected in Africa in 1983, which then also showed a greater ability to infect Aedes albopictus.

The virus is transmitted through the saliva of the mosquito just as other deadly diseases like Malaria and West Nile Virus.

"This is such a simple genetic change - the equivalent of a missing comma in a six-page short story - and yet it facilitated a huge epidemic," Higgs said. "With Aedes albopictus already present in so many countries and likely to spread to others, perhaps helped by global warming, this shows us that we need to be ready for the possibility that Chikungunya will soon be spreading to other locations as well."

University of Texas Medical Branch at Galveston, UTMB Scientists Discover Key To Chikungunya Virus, UTMB Newsroom