The CDC has confirmed that a patient who had recently returned to the US from China is infected with the newly discovered Wuhan coronavirus. The patient returned to the US without symptoms, and prior to the time that screening of passengers from the area was implemented. The patient has a mild case of pneumonia and is in stable condition.
Coronaviruses are part of a large family of viruses and also include the viruses that spread from animals to people in the outbreaks of MERS and SARS in recent years. While the original source of the infection is uncertain, it is believed to have started at a seafood and poultry market, so an animal origin is suspected in the current outbreak.
Chinese officials have also confirmed that person-to-person spread of the virus is occurring. China has reported over 800 cases of the disease, with 26 deaths. In addition to China, cases have been confirmed in several other Asian countries, including Taiwan, Thailand, Japan, and South Korea.
More information on emergence of zoonotic diseases is available in the Merck Veterinary Manual.