The West Nile virus was considered a tropical disease confined to East Africa, at least until the first North American case was identified in 1999. Fast forward 15 years, and now EPs from New Jersey to Southern California routinely consider West Nile infection in patients presenting with meningoencephalitis from mid-summer to early fall.
This expansion of arboviruses has been termed the globalization of vector-borne diseases, which describes the spread of West Nile virus, dengue, and now chikungunya from localized tropical areas to more temperate regions of the globe. (New Engl J Med 2007;356:8.) The way in which the viruses spread is not a mystery. The Aedes mosquito species, which transmits dengue and chikungunya viruses, are increasingly able to thrive outside tropical regions. (PLoS Negl Trop Dis 2014;8:e2921.) Climate change, migration, international travel, and the globalization of trade are all considered factors in the emergence of these viruses. Anthony S. Fauci, MD, the director of the National Institute of Allergy and Infectious Diseases, co-wrote an article this year entitled, “Chikungunya at the door-Déjà vu all over again?” (New Engl J Med 2014;371:885.)
This article describes an unexpected outbreak of chikungunya in Italy in 2007, and the subsequent spread from Africa to the Caribbean in 2013. More than 350,000 cases had spread to more than 20 countries in the Americas by last July. This past summer, the Centers for Disease Control had reported more than 232 imported cases of chikungunya in the United States. What is significant is that these travelers returned with chikungunya to more than 14 states with the mosquito vector Aedes aegypti, which is found in most southeastern states such as Mississippi and Florida, and is particularly adapted to living in an urban environment.
Chikungunya in the Kimakonde language of southeast Tanzania and northern Mozambique means “that which bends up.” This refers to the characteristic feature of the infection in causing diffuse joint pain and immobility. Similar to the dengue virus, chikungunya has a very short incubation period, presenting as a high fever within seven days of infection. (Lancet 2012;379:662.)
Other etiologies, such as malaria, should be considered when a traveler with febrile illness returns from an endemic area within 10 days of presentation. The characteristic feature of chikungunya is polyarthralgias that begins a few days after the fever starts. Arthralgias are usually symmetric and can involve up to 10 joints, with the hands, wrists, and ankles most commonly affected. (Clin Infect Dis 2008;46:1436.) Up to a week after the onset of illness, a diffuse maculopapular rash is common. Lymphopenia and a transaminitis are the most frequently encountered laboratory abnormalities in patients with arboviruses.
Most patients with chikungunya recover spontaneously after a febrile illness and debilitating polyarthralgias. Persistent stiffness and joint pain may accompany up to 75 percent of infections. (Clin Infect Dis 2007;44:1401.) Severe disease including meningoencephalitis, multi-organ failure, myocarditis, and renal failure has been described more commonly in recent outbreaks than in the classic literature. Treatment is supportive care and analgesia with no evidence for corticosteroids. Differentiating dengue virus from chikungunya can be clinically difficult. Both present with short incubation periods, fever, rash, and myalgias. Chikungunya is less commonly associated with thrombocytopenia, and dengue is less likely to cause diffuse polyarthralgias.
Notes from the Field: Chikungunya Virus Spreads in the Americas - Caribbean and South America, 2013-2014
MMWR Morb Mortal Wkly Rep
The authors of this important report from the Centers for Disease Control and Prevention provide epidemiologic data tracking the emergence of local transmission of the chikungunya virus through the Caribbean and South America. More than 103,000 suspected and 4,406 laboratory-confirmed cases have been identified since the first case in December 2013 in the Caribbean. More than 95 percent of these locally transmitted cases have been localized to the Dominican Republic, Haiti, and St. Martin.
Chikungunya is not currently a nationally reportable disease but tracked by passive surveillance through the CDC's ArboNET. Most cases have been reported from Puerto Rico and the U.S. Virgin Islands, though others have been imported by travelers from South America, the Pacific Islands, and Asia. If this outbreak has lost your interest because you work in an ED in Nebraska, consider this: Florida has reported 11 locally transmitted cases. (http://1.usa.gov/1yPGDJz.)
The lesson from the West Nile emergence in North America in the late 1990s is that it takes just one. We in the ED are at the forefront of emerging infectious diseases. The awesomeness of our specialty is that the possibility of recognizing the next locally acquired case of Chikungunya is all in a day's work.
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Read Dr. James Roberts' article, “Dengue: Another Disease for the Differential,” on p. 12.