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Over 500 chikungunya cases in the United States

The number of imported and locally acquired chikungunya illnesses in the United States has now reached 537. The weekly report from the Centers for Disease Control (CDC) lists a total of 497 reported cases from 35 states, Puerto Rico and the U.S. Virgin Islands. Additional reports from state and local public health agencies raise that total to 537.

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Locally transmitted chikungunya illnesses have been reported from three locations. The CDC shows that Puerto Rico is reporting 193 locally acquired chikungunya illnesses. Florida and the Virgin Islands have each reported two.

Florida has reported the largest number of travel-associated, or imported, chikungunya cases. The CDC lists 77 while the latest reports from the state of Florida show 89 imported chikungunya cases. New York State ranks second with 30 reported cases, followed by Tennessee with 18.

The CDC has yet to list five imported illnesses in Alabama and three in South Carolina. Other states reporting chikungunya that have not been included in the CDC figures include Indiana with four, Texas with three, Massachusetts with two, and California and North Carolina with one each. The Virgin Islands have also report three illnesses not reflected in CDC data.

Chikungunya is a viral illness that can only be transmitted to humans through the bite of an infected mosquito. It is rarely fatal but patients may experience joint pain and swelling, and debilitating fatigue, for months or years after the infection is over. There is no cure and no vaccine. Treatment consists of relieving the severe pain and intense itching.

The current strain of chikungunya which began circulating in the Americas in Dec. 2013 can only be transmitted by one species of mosquito, Aedes aegypti, or the Yellow Fever mosquito. There is another chikungunya strain, not yet found in the Western Hemisphere, that can be transmitted by Aedes albopictus, the Asian Tiger mosquito.

The Yellow Fever mosquito was nearly driven from the continental United States through mosquito control programs and the use of pesticides in the 1950s and 1960s. It has been reclaiming former habitat for the last 30 to 40 years and has established itself in Florida, along the Gulf Coast and into east Texas. It makes its year-round habitat in tropical and sub-tropical climates but can temporarily appear much farther north if the weather is hot and wet enough. Boston has suffered Yellow Fever outbreaks during the summer in the historical past.

Aedes aegypti is highly adapted to living around humans. We are almost exclusively its source for blood. It reproduces in fresh water, such as in discarded tires, cans, gutters or unused bird baths that hold rainwater. It feeds in the day time and will enter buildings to shelter in closets or under tables where there is some shade.