CDC: Chikungunya reported in W. Hemisphere among non-travelers

Lyle Petersen, MD, MPH

On Dec. 7, 2013, WHO reported the first local (autochthonous) transmission of chikungunya virus in the Western Hemisphere. Cases were originally identified on the French side of St. Martin; however, since that time the outbreak has spread to the Dutch side of the island (St. Maarten), St. Barthelemy, Martinique, and Guadeloupe. Case numbers have steadily increased. As of Jan. 10, 201 confirmed or probable cases have been reported from St. Martin, 2 from St. Maarten, 25 from St. Barthelemy, 48 from Martinique, and 10 from Guadeloupe. Analysis of the epidemiological situation is complicated by an ongoing dengue outbreak throughout the Caribbean. Thus it is possible that the extent of the outbreak is not fully recognized.

Chikungunya virus is a mosquito-borne alphavirus transmitted primarily by Aedes aegypti and Aedes albopictus mosquitoes. Humans are the primary reservoir during epidemics. Outbreaks have been documented in Africa, Southern Europe, Southeast Asia, the Indian subcontinent and islands in the Indian Ocean and Western Pacific. Prior to the cases on St. Martin, the only chikungunya cases identified in the Americas were in travelers returning from endemic areas. Genetic sequencing of the outbreak strain indicate that it is of the Asian subtype, which does not carry a mutation that increases the vector potential for Aedes albopictus that is found in some strains of African genotype.

Further spread of the virus throughout the Caribbean and Latin America is likely. In the United States, Puerto Rico and the US Virgin Islands are at high risk for outbreaks given their high endemnicity for Aedes aegypti. The potential for outbreaks in the contiguous United States is unknown; however, local transmission is possible given that Aedes aegypti and Aedes albopictus are endemic in southern and eastern parts of the country.

Most people infected with chikungunya virus become symptomatic. The incubation period is typically 3–7 days (range, 2–12 days). The most common clinical findings are acute onset of fever and polyarthralgia. Joint pains are often severe and debilitating and can persist for months or years. In fact, chikungunya means “that which bends over” in the Makonde language, a name resultant from the crippling arthralgias. Other symptoms may include headache, myalgia, arthritis, or rash. People at risk for more severe disease include neonates (aged <1 month) exposed intrapartum, adults older than 65 years and people with underlying medical conditions (eg, hypertension, diabetes, or cardiovascular disease). Fatalities are uncommon.

Chikungunya virus infection should be considered in patients with acute onset of fever and polyarthralgia, especially those who have recently traveled to the Caribbean. CDC encourages health care providers to report suspected chikungunya cases to their state or local health department to facilitate diagnosis and to mitigate the risk of local transmission. Laboratory diagnosis is generally accomplished by testing serum to detect virus, viral nucleic acid, or virus-specific immunoglobulin M (IgM) and neutralizing antibodies. During the first week of illness, chikungunya virus infection can often be diagnosed by using viral culture or nucleic acid amplification on serum. Virus-specific IgM and neutralizing antibodies normally develop toward the end of the first week of illness. To definitively rule out the diagnosis, convalescent-phase samples should be obtained from patients whose acute-phase samples test negative.

Chikungunya virus diagnostic testing is performed at CDC, two state health departments (California and New York), and one commercial laboratory (Focus Diagnostics). Health care providers should contact their state or local health department to facilitate testing. Up-to-date information about chikungunya virus as well as the “Guidelines for Preparedness and Response for Chikungunya Virus Introduction in the Americas” prepared by the CDC and the Pan American Health Organization can be obtained from CDC at http://www.cdc.gov/chikungunya/.