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More chikungunya seen in United States

The July 1 release of the latest data on chikungunya in the United States revealed 32 percent more cases than last week. The Centers for Disease Control (CDC) reported 129 chikungunya cases in the United States, Puerto Rico and the Virgin Islands. Five additional cases were noted in non-residents.

Map showing the 29 states reporting imported cases of chikungunya through July 1, 2014.
Map showing the 29 states reporting imported cases of chikungunya through July 1, 2014.
Charles Simmins, based upon publicly available data

Locally transmitted chikungunya illnesses have been reported in just two locales, Puerto Rico with 14 and the Virgin Islands with 1. All of the remaining illnesses are imported, caught outside the country but diagnosed in the U.S. Despite the growing number of imported cases in the continental United States, no locally acquired illnesses have been found through July 1.

The Florida Arbovirus Surveillance Report for June 28 reports 52 imported cases of chikungunya, 18 more than the CDC has at this point. Haiti is the source of the infection for 38 of these cases and the Dominican Republic another 11.

The CDC data does not include five chikungunya cases in Alabama or one in West Virginia. WBRC reported the five confirmed Alabama chikungunya illnesses on July 1. The West Virginia Department of Health also confirmed its first case of imported chikungunya on July 1.

Imported cases of chikungunya have now been diagnosed in 29 states of the contiguous 48. Florida has reported the most cases. New York and Tennessee have each reported eight illnesses. California is fourth with seven, followed by Connecticut and Virginia with six each.

Chikungunya is a viral illness spread by the bite of infected female mosquitoes of two species, Aedes aegypti and Aedes albopictus. Both have established habitat in the United States. The chikungunya strain in the Western Hemisphere is presently carried only by Aedes aegypti. It is a tropical mosquito, and common in Puerto Rico and the Virgin Islands but has a limited range in the sub-tropical areas of the continental U.S.

Chikungunya is not able to spread from person to person. It can only be caught through the bite of an infected mosquito. If a vector species of mosquito does not exist in the region, chikungunya cannot be spread. If a vector species is found locally, the potential for a cluster of illnesses exists if a patient with an imported case is bitten by the right species of mosquito.