BOSTON (CBS) – Four Boston residents have tested positive for the Chikungunya virus, city health officials confirmed on Saturday.

The illness, which only first turned up in the Americas last year, is transmitted by mosquitoes.

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Mosquitoes carrying Chikungunya are common in parts of Africa and Asia. They have recently been found on several Caribbean islands and a handful of central and South American countries, but have not turned up in the continental U.S.

Health officials say all four patients had traveled to Caribbean islands recently. They said the cases were not connected.

There is no vaccine to prevent or medicine to treat Chikungunya virus infection. But it is typically not fatal. All four Boston residents who tested positive have since recovered.

“The most common symptoms of Chikungunya virus infection are fever and joint pain. Other symptoms may include headache, muscle pain, joint swelling, or rash,” the CDC’s website reports.

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The Boston Public Health Commission sent out an alert advisory to healthcare providers because the illness is not typically seen in Boston.

They want healthcare providers to be conscious of the symptoms.

The illness, which is carried by mosquitoes, is not contagious between humans, and officials say there is no threat to other people in Boston.