The Centers for Disease Control and Prevention said Thursday that the mosquito-borne illness chikungunya has spread to more than 10,000 in Puerto Rico since first reported in May.
USA Today reported that the real number of cases is likely to be larger as household tests of people who didn’t go to the doctor found that 28 percent also tested positive for chikungunya.
The CDC said about 13 percent of patients in Puerto Rico were hospitalized and 3 percent suffered major bleeding. Four patients have died, although they had other serious health issues that complicated their cases, they added.
The tropical virus that causes painful symptoms and has no known treatment or vaccine spread to the mainland United States over the summer, when the first locally-acquired case was diagnosed in Florida, the CDC said.
Since then, at least 11 people in Florida who had not traveled outside of the country have been diagnosed with the disease.
Chikungunya is a mosquito-borne illness whose African name roughly translates to “bent in to” because of the severe joint and muscle pain it causes. Other symptoms include fever, headache, nausea and a rash.
Like the West Nile virus, the disease comes from mosquito bites and cannot spread from person to person.
According to the CDC, more than 1,100 cases of chikungunya were “imported” into the U.S. – by travelers, not local mosquitoes – between January and mid-October.
According to the World Health Organization, the illness has sickened more than 776,000 people in the Caribbean, Central America and South America.
William Schaffner, a professor of infectious diseases at Vanderbilt University, told USA Today that he does not expect chikungunya to become as common in the continental United States as it is in more tropical regions.
He said the mosquitoes that carry the disease are more common in the Caribbean and Latin America and they can spread more easily there because fewer people have air conditioning or window screens.
Schaffner added that the cold winters in North America also tend to kill off any mosquitoes.