Movement of Chikungunya Virus into the Western Hemisphere

C hikungunya virus (CHIKV) is an alphavirus transmitted in an urban epidemic cycle by the mosquitoes Aedes aegypti and Ae. albopictus. CHIKV outbreaks are characterized by rapid spread and infection rates as high as 75%; 72%–93% of infected persons become symptomatic. The disease manifests as acute fever and potentially de-bilitating polyarthralgia. In a variable proportion of cases, polyarthritis and fatigue can persist for 2 years or longer (1). During outbreaks, the large percentage of symptomatic infections places a considerable strain on resources of local health care providers and hospitals. Fortunately, death from chikungunya is rare. CHIKV was first identified in Tanganyika (now Tan-zania) in 1952 (2). The virus was later found to be widely distributed and to cause sporadic, mostly small outbreaks in Africa and Asia through the 1960s and 1970s. Little activity was reported from the mid-1980s until June 2004, when an epidemic occurred on Lamu Island, Kenya, then spread during 2005 to Comoros, La Reunion, and to other Indian Ocean islands, causing ≈500,000 cases (3). This was followed in 2006–2009 by an epidemic in India that produced >1.5 million cases in 17 of the country's 28 states and subsequently spread through Southeast Asia to the islands of the Pacific Ocean (4). The public health community has come to recognize CHIKV as a major emerging, epidemic-prone pathogen. The global expansion of CHIKV has been broadened by the movement of infected persons to areas with competent mosquito vectors and a susceptible human population (5). CHIKV-infected travelers have been documented in >22 countries throughout Asia, Europe, and North America (1,6,7); their travel led to outbreaks in northern Italy (8) and southern France (9). Until a few months ago, only travel-related cases had been detected in the Western Hemisphere (7,10,11) with no evidence of local transmission. The first known autochthonous chikungunya cases in the Western Hemisphere occurred in October 2013 on the island of Saint Martin and were reported in December 2013 (12). During the next 4 months, >31,000 confirmed and probable autochthonous cases were reported from numerous other Caribbean islands and Saint Vincent and the Grenadines). Infected travelers originating from the island countries have carried the virus around the region, leading to authochthonous chikungunya cases occurring in mid-February 2014 in French Guiana on the mainland of South America. Virus spread to other island countries and expansion into mainland areas of South, Central, and North America are inevitable. Three CHIKV genotypes (East-Central-South …