Chikungunya, a virus spread through mosquito bites, has now sickened thousands of people in Haiti, according to the Haitian government.

Historically, chikungunya has affected people in Africa, Asia, and Europe. In late 2013, the first cases of the virus appeared in the Caribbean, and this spring, health officials confirmed the virus in Haiti for the first time. The virus is rarely fatal but causes fever and severe joint pain; the symptoms can be treated with analgesics but there is no drug to stop the virus itself.

Since first detected in Haiti, the virus has spread rapidly. The Haitian Ministry of Health has reported more than 27,000 suspected cases at the end of May, and there are likely many more people who have been sick but haven’t gone to a health facility where the case could be recorded. Only lab testing can confirm a case of the virus.

People living in Port-au-Prince have been most affected, but Partners In Health clinicians have seen cases in the Central and the Artibonite departments of Haiti as well. At University Hospital in Mirebalais, for example, clinicians recorded more than 200 suspected cases, including about 20 children, during the month of May. Cate Oswald, senior program officer for PIH in Haiti, said that even as the staff cares for sick patients, they’re also falling ill.

“So many of our staff have gotten sick over the past weeks—all with the same symptoms,” Oswald said. “People are unable to come to work because of fever and severe joint pain.”

Dr. Gregory Jerome, director of Monitoring, Evaluation, and Quality Improvement for Zanmi Lasante, PIH’s sister organization in Haiti, said that most patients don’t seek care in a health facility, since there is no specific treatment. Many opt instead to take medicine such as acetaminophen and stay at home to wait out the virus.

The illness caused by the virus is most often a painful but self-limited disease with symptoms usually beginning three to seven days after being bitten by an infected mosquito, and lasting up to one week. Symptoms most often include joint and muscle pain, headache, and fever, with the occasional presence of a rash.  Occasionally, joint pain and arthritis can last for weeks to months.

“The vast majority of people sick with chikungunya don't actually seek for care at any institution, which means their cases go unrecorded,” Jerome said. “By now, there are probably thousands of cases in Mirebalais, because the attack rate of this infection is very high all over the country.”

Chikungunya affects 95 percent of those who are infected with the virus. Although it is not clear what percentage of people infected with chikungunya develop severe disease, there are severe and even life-threatening complications including respiratory, cardiac, and kidney failure as well as meningitis and hepatitis.

To avoid the virus, people must protect themselves from mosquitoes that bite during the day. This is nearly impossible for most Haitians, who don't have access to mosquito repellent. The Haitian government has begun mass fumigation efforts to kill mosquitoes and advised people to eliminate standing water where mosquitoes breed.

Read more from the Centers for Disease Control and Prevention.