A new coronavirus, a cousin of the SARS virus, has infected more than 10,000 people since the outbreak began in Wuhan, China, in December. Scientist Leo Poon, who first decoded the virus, thinks it likely started in an animal and spread to humans. Here are things you should know about a coronavirus. Coronaviruses are a large group of viruses that are common among animals. In rare cases, they are what scientists call zoonotic (人畜共患病) , meaning they can be transmitted from animals to humans, according to the US Centers for Disease Control and Prevention. The viruses can make people sick, usually with a mild to moderate upper respiratory tract illness ( 上 呼 吸 道 疾 病 ) , similar to a common cold. Coronavirus symptoms include a runny nose, cough, sore throat, possibly a headache and maybe a fever, which can last for a couple of days. For those with a weakened immune system, the elderly and the very young, there's a chance the virus could cause a lower, and much more serious, respiratory tract illness like a pneumonia or bronchitis (支气管炎) . There are a handful of human coronaviruses that are known to be deadly. Middle East Respiratory Syndrome (中东呼吸综合征) , also known as the MERS virus, was first reported in the Middle East in 2012 and also causes respiratory problems, but those symptoms are much more severe. Three to four out of every 10 patients infected with MERS died, according to the CDC. Severe Acute Respiratory Syndrome (严重急性呼吸综合征) , also known as SARS, is the other coronavirus that can cause more severe symptoms. First identified in the Guangdong province in southern China, according to the WHO, it causes respiratory problems but can also cause diarrhea (腹泻) , fatigue (疲劳) , shortness of breath, respiratory distress (呼吸窘迫) and kidney failure (肾衰) . Depending on the patient's age, the death rate with SARS ranged from 0-50% of the cases, with older people being the most vulnerable (易受 伤害的) . Viruses can spread from human contact with animals. Scientists think MERS started in camels, according to the WHO. With SARS, scientists suspected civet cats (狸猫) were to blame. When it comes to human-to-human transmission of the viruses, often it happens when someone comes into contact with the infected person's secretions (分泌物) such as droplets ( 小水滴, 飞沫 ) in a cough. Depending on how virulent (有毒的) the virus is, a cough, sneeze or handshake could Cause exposure. The virus can also be transmitted by touching something an infected person has touched and then touching your mouth, nose or eyes. Caregivers ( 护理人员) can sometimes be exposed by handling a patient's waste, according to the CDC.