A LITTLE-KNOWN mosquito-borne virus is spreading pain and death across the Indian Ocean, and could be headed for Europe and the Americas.
Chikungunya virus is normally little cause for concern, as it has not been fatal and large outbreaks are rare. That looks to be changing, as the virus has recently swept across the Indian Ocean, striking a third of the population of the French island of R茅union in the past three months, and killing for the first time. Meanwhile the mosquitoes that carry it are invading Europe and the Americas, and there are signs that the virus could already have reached these fresh territories.
Chikungunya causes fever, headache, nausea and a rash, but its calling card is excruciating pain in the smaller joints 鈥� hence its old name, 鈥渒nuckle fever鈥�. It usually lasts a few days, but in some cases pain and stiffness can last months or even years.
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In January 2005, travellers from east Africa, where the disease is endemic, brought the virus to the Comoros islands off the north-west coast of Madagascar. It has since spread to other previously uninfected islands including Mauritius, the Seychelles and R茅union. According to France鈥檚 health surveillance agency, as many as 230,000 people may have had the virus in R茅union so far this year, and there have been thousands of cases on the other islands. Worse, 174 deaths on R茅union have been attributed to chikungunya.
Both the size and severity of the outbreak could be because the virus is new to the islands and few people are immune, says Herv茅 Zeller, an expert on insect-borne viruses at the Pasteur Institute in Lyon, France. It is also possible that the virus has mutated. 鈥淭he chikungunya sequence from R茅union in 2006 indicates that the virus there is different from other viruses characterised until now,鈥� says R茅mi Carrel of the University of the Mediterranean in Marseille, France.
All this could be bad news for the rest of the world, because the tiger mosquito (Aedes albopictus) that carries chikungunya is also invading new territory. It is native to south-east Asia, but in the past 20 years it has invaded the southern US, Central and South America, and parts of Europe including Albania, Spain, Italy, France and Belgium. Andrew Tatem and his colleagues at the University of Oxford blame increased global trade for the spread of the mosquitoes, with the most popular air and shipping routes from infested countries closely correlating with recent migrations of tiger mosquitoes (Proceedings of the National Academy of Sciences, DOI: 10.1073/pnas.0508391103) (see Map).
While Zeller says that these new mosquito colonies might not be large or dense enough to maintain the chikungunya virus, some people in Spain and Italy have recently been found with antibodies to it, so something carrying the virus must have bitten them. In 1987 researchers found the virus, or one of its close relatives that also cause disease, in people with flu symptoms in Albania. If chikungunya really has mutated, and the new killer strain is carried into recently established colonies of mosquitoes 鈥� by an infected person travelling from R茅union, for example 鈥� then a previously obscure disease could become a lot better known.
