China is fighting an outbreak of the chikungunya virus. What is it

Chinese health officials are responding to an outbreak of a mosquito-borne virus that can cause severe pain.
More than 7,000 cases of chikungunya have been reported in the Chinese province of Guangdong in recent weeks, with most in the southern city of Foshan. 
Reports from the region say those who are infected are being quarantined in hospital until they test negative for the virus, and workers are going to homes in Foshan to check for risk factors like standing water where mosquitoes can breed.