State and federal health officials reported Thursday the first locally acquired cases of a mosquito-borne virus known as chikungunya that causes intense joint pain and high fever, and has been spreading throughout the Caribbean and Central and South America.
Florida officials reported two cases, one in Miami Dade County and the other in Palm Beach County. The Centers for Disease Control and Prevention has confirmed one of the cases, a man who had not recently traveled outside the United States. Preliminary testing for the second case also suggests infection with the virus, CDC officials said.
Until now, people in the United States who have become sick with the virus have acquired the infection abroad. The confirmed Florida case represents the first time that mosquitoes in the continental United States are thought to have spread the virus to a non-traveler.
“The arrival of chikungunya virus, first in the tropical Americas and now in the United States, underscores the risks posed by this and other exotic pathogens,” said Roger Nasci, chief of CDC’s Arboviral Disease Branch, which investigates mosquito-borne illnesses like West Nile and St. Louis encephalitis.
The CDC and Florida health officials are assessing whether there are additional locally acquired cases.
Chikungunya is spread by bites from two kinds of mosquitoes found in the United States. It is not transmitted from person to person. If a person is infected and bitten by a mosquito, that mosquito may later spread the infection by biting another person.
Similar in some ways to dengue fever, the virus, pronounced chik-en-gun-ye, causes high fever and severe pain and swelling in joints, as well as muscle pain and headaches. It is transmitted by two kinds of mosquitoes found in parts of the United States. The disease is rarely fatal, but there is no treatment other than pain relief. And while the virus tends to run its course in a week or so, it can cause debilitating arthritis that can linger for months and, in some cases, years. Infection is thought to provide lifelong immunity, according to the CDC.
Unlike dengue, the percentage of people who show symptoms and become sick with chikungunya is much higher, officials said.
Since 2006, the United States has averaged 28 imported cases of chikungunya a year in travelers returning from countries where the virus is common. To date this year, 234 travel-related cases have been reported. More chikungunya-infected travelers coming into the United States increases the likelihood that local virus transmission will occur. That’s because the local mosquitoes can bite infected people and spread the virus.
“We’ve been anticipating this for some time,” Nasci said. “We don’t expect widespread sweeping outbreaks, but we do expect some local limited outbreaks to occur. What we don’t know is how many cases there will be.”
He suggested the infections may follow the patterns of transmission of dengue. The United States has about 800 travel-related dengue cases reported each year. There have been about 48 locally transmitted cases, primarily in South Florida and south Texas.
