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Mosquitoes transmit chikungunya in continental US

Posted on behalf of Mark Zastrow.

Two people have acquired the mosquito-borne chikungunya virus in the continental United States, the state of Florida’s Department of Health announced today. The cases, one in Miami-Dade County and another in Palm Beach County, confirm that the virus has infected US mosquitoes.

Chikungunya is an illness marked mainly by discomfort: a high fever, rashes, and severe joint, back and muscle pain. It is rarely fatal, and most recover within days or weeks. However, joint pain can sometimes persist for months. Chikungunya cannot be transmitted from person to person; it can be contracted only from a mosquito.

The United States is only the latest destination for the globetrotting virus. First described in the 1950s in East Africa, it has spread throughout central and southern Africa, India and Southeast Asia, generally through the mosquito Aedes aegypti. But a mutation that is suspected to have occurred in a 2005–06 outbreak on Réunion Island appears to have allowed it to infect Aedes albopictus, also known as the Asian tiger mosquito. This enabled the virus to spread as far north as Italy in 2007.

Previously, the only reported chikungunya cases in the United States had been in people returning from abroad — mostly from the 23 countries in the Caribbean, South America and Central America, where the virus has established itself since reaching the Western Hemisphere in December. The number of cases imported to the United States so far this year has spiked to 243 from an average of 28 annually since 2006.

The US Centers for Disease Control and Prevention (CDC) said in a statement that it expects chikungunya to continue to crop up, with only sporadic cases of local transmission initiated by travellers returning to the United States from abroad. But the CDC said as imported cases rise, so does the likelihood of local outbreaks. They could appear anywhere the Asian tiger mosquito does — as far west as Texas, and, in the north, from Minnesota to New Jersey.

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