Recently, the Chikungunya (pronounced chi-kən-guun-yə) virus – a mosquito-transmitted infection largely indigenous to Africa and Asia – made headlines when the Centers for Disease Control and Prevention reported two cases of Chikungunya Fever (CKFV) in Florida that occurred in non-travelers, suggesting that the infection was acquired locally. This means a mosquito bit someone with the virus and then bit someone else.
Why did a transmission locally make the news? Over the past 10 years, the virus has begun to “travel” from its eastern hemisphere home to parts of the Caribbean and northern South America. Between 2006 and 2013, the CDC reported a handful of cases in the United States annually; these cases occurred in individuals with recent travel to areas endemic for the virus.
For the year through August 5, 2014, the CDC also reported two locally acquired cases in the U.S. Virgin Islands and 201 local cases in Puerto Rico. During this same period, Pennsylvania reported 12 cases of CKFV, all of which were acquired by travelers to endemic regions.
In Africa, the natural host for this virus is non-human primates; in other areas, mammals, such as bats, appear to serve as reservoirs for the virus. The virus gains access to humans via mosquitoes. The species implicated in transmission are indigenous to parts of Africa and Asia, but also the Caribbean, South America, and the southeastern U.S. In highly endemic regions, infected mothers can pass the infection to their unborn children.
The incubation period for the disease is up to two weeks (an average of two to four days) following inoculation by an infected mosquito. Infections classically begin with the explosive onset of fever, muscle pain (myalgia), headache, rash and increased visual sensitivity to light (photophobia). The clinical characteristic that separates CKFV from other mosquito-borne viral illnesses is intense joint pain (arthralgia). The pain affects many joints on both sides of the body. The joints of the hands as well as elbows and knees are typically swollen but not red or hot to touch. In children, swelling of the ankles and/or wrists is common.
The majority of cases resolve spontaneously within two weeks. Persistent joint pain is the major complication of this infection and occurs most often in those over 45 years of age or those with coexisting chronic diseases. Pain can continue for as long as three years after the infection. Neurological problems are not typical of CKFV, but are the leading reason infected patients are hospitalized. Changes in awareness (encephalopathy), seizures, and paralysis have been described in both adults and children with CKFV. Infants who acquire the infection from their mothers before they are born are at risk for intellectual impairment. The reported mortality rate is 1:1000; most victims are at the extremes of age.
While a variety of diagnostic tests are available to confirm the diagnosis of CKFV, the initial symptoms are relatively non-specific. It is critical that individuals seeking medical care for an acute illness with fever alert the treating physicians as to any recent travel to endemic areas, particularly Florida and the Caribbean. There is no vaccine or treatment for CKFV. The use of insect repellents containing DEET and mosquito netting at bedtime is recommend for travel to endemic areas. Non-steroidal anti-inflammatory agents such as ibuprofen are recommended for relief of joint pain and fever control.
The risk of acquiring CKFV in the Philadelphia region is unlikely given that the mosquito that transmits this disease is not endemic to this region. That being said, migration of the Aedes species has been northerly and is now found in Florida. Individuals who travel to endemic regions, notably the Caribbean and South America who develop fever and joint pains should be evaluated by their health care provider.