by Andrew Roszak, JDA, MPA, Senior Director, and Lisa Brown, MPH, Program Analyst, Environmental Health, Pandemic Preparedness, and Catastrophic Response

The end of the year is fast approaching and people across the country are focused on shopping, cold weather, and holiday celebrations. As Christmas trees are going up and snowstorms are already battering much of the United States, warm-weather threats such as mosquitoes and the diseases they spread are likely not on the minds of most.

But such diseases pose a significant health threat to the United States. One in particular, chikungunya, has sickened more than 900,000 in 40 countries and territories in the Western Hemisphere. Chikungunya produces fever, joint and muscle pain, headache, lethargy, and rash. Though it is rarely fatal, some cases can lead to chronic pain and arthritis.

The first noted case of Chikungunya in the Western Hemisphere occurred in late 2013 in the Caribbean Islands. Its spread since has been so persistent that Jamaican officials have had to declare a state of emergency as the country grapples with the disease. Some estimate as much as 60% of the Jamaican population has fallen ill with the virus.

In July 2014, only seven months after chikungunya’s recognition in the Western Hemisphere, the first locally acquired case of the disease surfaced in the continental United States, in Florida. Since then, 11 locally transmitted cases have been identified in Florida. As of Dec. 2, a total of 1,911 chikungunya cases have been reported from the United States. Before this outbreak, an average of 28 travelers with chikungunya virus returned to the country each year.

CDC estimates that about nine million people travel between the United States and Caribbean each year. A recently conducted study found that the United States alone accounted for 52% of the final destinations for all international travelers departing from chikungunya-affected areas of the Caribbean, and that New York City, Miami, and San Juan, Puerto Rico are the leading destination cities. Travel-associated chikungunya cases continue to be seen weekly in Florida. People traveling to the Caribbean or Central or South America should be aware of the risk of chikungunya and remember their insect repellent and other tips for staying safe.

Additionally, mosquito-borne diseases such as chikungunya are among those most sensitive to climate. As the climate continues to change, there is the potential for increased transmission and geographic expansion of mosquitoes and mosquito-borne diseases. Currently, the geographic ranges of Aedes aeqypti and Aedes albopictus – the mosquito species primarily responsible for spreading the chikungunya virus – have been expanding, a potential consequence of climate change and globalization. Both mosquito species are found in the southeastern United States and limited parts of the Southwest; Aedes albopictus is also found further north along the East Coast, through the Mid-Atlantic States, and the lower Midwest. Currently, the type of chikungunya virus circulating in North America is associated with the less common mosquito, Aedes aegypti. However, if the virus were to mutate to prefer the more common mosquito Aedes albopictus, which has a wider geographic range, this could present a larger threat for the United States. This situation has already been seen in Brazil, where a more problematic strain of chikungunya spread easily by Aedes albopictus has been detected.

The combination of international travel and increasing geographic expansion of disease-carrying mosquitoes has set the stage for the introduction and spread of chikungunya to new areas. Since the disease is new to the Americas, most people are not immune, which means they can be infected and spread the virus to others. Currently, chikungunya is not a nationally notifiable disease, but cases can be reported to ArboNET, a national surveillance system. There is no vaccine or antiviral treatment for chikungunya. The only way to prevent chikungunya is to prevent mosquito bites.

As highlighted in a May 27 blog post, local health departments are on the front lines of protecting the public from the spread of this virus. Local health departments are encouraged to review mosquito surveillance capacities, implement mosquito control plans as appropriate, and ensure communication strategies exist to educate the public and health care professionals about symptoms and preventative measures for reducing mosquito bites.