Aedes

I recall learning about chikungunya¹ virus when I was a Ph.D. student in the late 1970s – only because its exotic name made an impression on me. The virus, first identified in Tanzania in 1953, causes severe rashes and joint pains, but is rarely fatal, and the infection was considered benign. The outbreaks were massive, but largely confined to developing countries in Africa and Asia. I was surprised to discover several years ago that the virus had moved into Europe and was threatening the United States. What changed to bring this third-world viral disease into the forefront of public concern?

Since its discovery over 50 years ago, infection by chikungunya virus was known to be spread by mosquitoes, primarily Aedes aegypti, which feeds almost exclusively on humans. In 2004, an outbreak of chikungunya disease started in Kenya and spread to islands in the Indian Ocean and finally India, where it had not been reported for 32 years. On Réunion, one of the Indian Ocean Islands, nearly 40% of the population of 785,000 fell ill. An outbreak in Italy three years later, the first ever in Europe, was started by an infected traveler from India. Cases of chikungunya have been reported in travelers returning to the US, although transmission within the country has not been reported.

The rapid global movement of chikungunya virus appears to be a consequence of a change in its mosquito vector. Some time during 2005 a virus was selected with a single amino acid change in the envelope glycoprotein which allows efficient replication in Aedes albopictus, the predominant mosquito in Réunion. This mosquito was never a good host for chikungunya virus, partly because it bites so many different animal species. The amino acid change enhances viral replication in the mosquito, leading to much higher levels of virus in the salivary gland. Consequently the virus is more likely to be transmitted upon biting a new host.

To further complicate matters, not only is Aedes albopictus now a good host for chikungunya virus, but the mosquito is spreading across the globe from eastern Asia to Europe and the United States. The mosquito was first found in the New World in 1985 when it was isolated in Houston, Texas. It probably traveled there from northern Asia in ships carrying scrap tires. But there are at least five other reasons to worry about Aedes albopictus: the mosquito has also been found to carry eastern equine encephalitis, Keystone, Tensaw, Cache Valley, and Potosi viruses.

¹Chikungunya is believed to be derived from an East African dialect describing the contorted posture of patients with the severe joint pain characteristic of this disease.

Enserink, M. (2007). INFECTIOUS DISEASES: Chikungunya: No Longer a Third World Disease Science, 318 (5858), 1860-1861 DOI: 10.1126/science.318.5858.1860

Vazeille, M., Moutailler, S., Coudrier, D., Rousseaux, C., Khun, H., Huerre, M., Thiria, J., Dehecq, J., Fontenille, D., Schuffenecker, I., Despres, P., & Failloux, A. (2007). Two Chikungunya Isolates from the Outbreak of La Reunion (Indian Ocean) Exhibit Different Patterns of Infection in the Mosquito, Aedes albopictus PLoS ONE, 2 (11) DOI: 10.1371/journal.pone.0001168

Tsetsarkin, K., Vanlandingham, D., McGee, C., & Higgs, S. (2007). A Single Mutation in Chikungunya Virus Affects Vector Specificity and Epidemic Potential PLoS Pathogens, 3 (12) DOI: 10.1371/journal.ppat.0030201