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Chikungunya nears half a million cases in the Americas

The Pan American Health Organization (PAHO) announced July 19 that the total of confirmed and suspected chikungunya cases it has received reports upon now total 442,359. The report is through July 18. Over 30 nations and territories have seen cases of this mosquito borne illness, including the United States, Puerto Rico and the U.S. Virgin Islands.

Maps showing the countries and terriroties reporting locally acquired or imported cases of chikungunya in the Western Hemisphere through week 29 of 2014.
Pan American Health Organization

On the island of Guadeloupe, in the French Antilles, 16 percent of the population has contracted chikungunya since Jan. 1. A neighboring island, Martinique, has seen 13 percent of its population suffer the same illness in that time. The Dominican Republic, with its outbreak beginning in April, has reported chikungunya affecting 2.4 percent of its population.

A number of countries in Central and South America have reported imported cases of chikungunya and / or locally acquired cases. The most serious outbreak at this time is in El Salvador. The PAHO reports 1,775 suspected chikungunya illnesses in that tiny nation.

The continental United States saw the first two cases of locally acquired chikungunya this past week. Florida announced a confirmed case in Miami-Dade County and another in Palm Beach County. The PAHO and the Centers for Disease Control report that Puerto Rico and the Virgin Islands have also reported locally acquired cases.

Through June 25, the Puerto Rican Health Department reports 182 confirmed chikungunya cases. On July 17, the government of the Commonwealth declared that chikungunya was epidemic on the island.

The New England Journal of Medicine published a feature titled "Chikungunya at the Door — Déjà Vu All Over Again?" on July 16. David M. Morens, M.D., and Anthony S. Fauci, M.D. authored the piece, and they note:

According to historians, chikungunya fever arrived in Asia and the Americas two or more centuries ago to cause, among other outbreaks, a notable epidemic in Batavia (now Jakarta) in 17794 and a pandemic involving parts of the Western Hemisphere in the 1820s. These outbreaks were at the time called dengue, since chikungunya was not fully distinguished from dengue until the 1950s.4 Chikungunya may thereafter have left Asia and the Americas, only to return to Asia in the mid-1900s ...

The authors note that the strain of chikungunya now in circulation in the Americas appears to be only transmitted by one mosquito species, the Aedes aegypti or Yellow Fever mosquito. They cite a 2012 study which suggests that this strain has mutated enough to restrict its potential transmission by another mosquito believed to transmit the virus, Aedes albopictus, the Asian Tiger mosquito. The Yellow Fever mosquito has a limited habitat in the continental U.S. and that limits the potential for the spread of locally acquired chikungunya.