The chikungunya virus has officially arrived in the United States. On July 17, public health authorities confirmed the first 2 cases of local transmission of the virus in the United States in Florida.
An abrupt onset of a fever higher than 102°F and severe pain or swelling in multiple joints are hallmarks of chikungunya infection, said Anna M. Likos, MD, MPH, state epidemiologist and director of the division of disease control and health protection at the Florida Department of Health. Patients may also develop a rash, muscle pain, or headache, according to the US Centers for Disease Control and Prevention (CDC). On average, symptoms appear 3 to 5 days after exposure but can occur 1 to 12 days after exposure.
The spread of chikungunya virus within the continental United States was not unexpected, said health authorities. On December 2013, the World Health Organization reported the first local transmission of chikungunya virus in the Western Hemisphere, in the Caribbean. Within months, the disease spread through much of the Caribbean and Central and South America.
Reflecting this spread, the number of US travelers who became infected with the virus during travel to affected regions also has rapidly climbed, with 234 as of July 15, according to the CDC.
The species of mosquitoes that spread the virus, Aedes aegypti and Aedes albopictus, live in the southeastern United States and parts of the Southwest, and A albopictus can also be found in the Mid-Atlantic states and lower Midwest. Amy Vittor, MD, PhD, an infectious disease physician at the University of Florida, noted that the currently circulating strain of chikungunya in the Americas is spread more easily by A aegypti, which is less common in the United States than A albopictus.
However, chikungunya is unlikely to spread as extensively in the continental United States as it has in the Caribbean and other parts of the Americas. J. Erin Staples, MD, PhD, medical epidemiologist with the CDC’s division of vector-borne diseases in Fort Collins, Colorado, noted that US individuals spend far less time outside and typically have air conditioning and door and window screens.
The spread of chikungunya infection in the United States will likely be similar to the spread of dengue virus, which is transmitted by the same mosquitoes. Staples noted that during 2013 there were about 2.4 million cases of dengue reported in the Caribbean and Central and South America, 773 travel-related cases in the United States, and 48 cases of local transmission in the continental United States. However, in contrast to dengue, for which many infections are mild or asymptomatic, an estimated 80% of people infected with chikungunya will likely develop symptomatic disease. Most recover, but some have lasting joint pain.
During the last large-scale chikungunya outbreak in 2006 in Africa and Southeast Asia, a single mutation caused a change in the virus that allowed A albopictus to spread it more efficiently. Vittor explained that if a similar mutation occurs in the currently circulating strain, the United States will be at greater risk of local transmission.
“It will be a game changer,” she said.
Public health officials in Florida are working to quickly curb spread of the virus. The department has reached out to public health directors and physicians throughout the state and is trying to identify every travel-associated and locally transmitted chikungunya case. Once a case has been identified, the department works with local mosquito control agencies to prevent local transmission by stepping up mosquito abatement efforts.
“We are taking steps to ensure we are finding every case,” said Likos.
The Florida Department of Health recommends that individuals living in or visiting areas where chikungunya infection is spreading take steps to prevent mosquito bites throughout the day (because the mosquitoes that carry the virus are active and bite during the day), by using insect repellent, wearing long sleeves, and making sure window and door screens are intact and closed. The department also recommends that Floridians be careful to remove standing water from boat covers, pots, and other places water collects to eliminate potential breeding sites for chikungunya’s mosquito vectors.
Updated information about chikungunya is available on the CDC’s website.