LAS VEGAS – Southern Nevada health officials are monitoring an undisclosed number of Clark County residents quarantined at home after trips to mainland China to determine whether they are infected with coronavirus.

“These are individuals who were found not to have symptoms after receiving a medical screening and were allowed to return home and be monitored under a 14-day self-quarantine,” said Jennifer L. Sizemore, communications manager with the Southern Nevada Health District.

The self-quarantines follow guidelines from the Centers for Disease Control and Prevention, according to Sizemore.

The number of people being monitored changes daily, she told the USA TODAY Network.

A Southern Nevada patient isolated in January with a possible case of coronavirus tested negative. After returning from more than a month in China and experiencing respiratory issues, the patient was isolated at a local hospital, according to health officials.

But while health officials awaited test results from the CDC, the patient recovered from those symptoms.

What is coronavirus? What are the symptoms?

The total number of cases in mainland China is now 44,653 and the death toll has increased to 1,113. Two people have died elsewhere, one in Hong Kong and one in the Philippines. There have been 13 recorded cases in the U.S.

Many of the initial cases were linked to a seafood market in Wuhan, a city of 11 million in the central China province of Hubei. Although Chinese health officials show the number of daily coronavirus cases stabilizing, international and U.S. health officials said Wednesday that it is too early to predict a foreseeable end to the crisis.

Coronaviruses are a large family of viruses that cause illness ranging from the common cold to more severe diseases such as pneumonia to Middle East respiratory syndrome, known as MERS, and severe acute respiratory syndrome, or SARS. Common signs of infection include fever, cough, shortness of breath and breathing difficulties. In more severe cases, infection can cause pneumonia, severe acute respiratory syndrome, kidney failure and death.

How is coronavirus similar to Ebola, MERS and SARS?

Coronaviruses, Ebola and SARS are zoonotic, meaning they are transmitted between animals and people. Ebola was carried by fruit bats, which spread it to other animals. SARS was transmitted from civet cats to humans and MERS from camels to humans.

The virus can be spread from animals to people. But it also can be spread by coughing, sneezing and through close contact with an infected person or an object carrying the virus.

The coronavirus from China is believed to have originated in bats and transferred to humans through some other animal, health officials say. The pangolin – the world's only scaly mammal – may be that key link, according to researchers at South China Agricultural University.

"This latest discovery will be of great significance for the prevention and control of the origin of the new coronavirus," South China Agricultural University said in a translated statement to USA TODAY.

The research team tested more than 1,000 samples from wild animals and found a 99% match between the genome sequences of viruses found in pangolins and those in human patients, the AFP reported, citing Chinese state media.

Pangolins have long been valued for their meat, viewed as a delicacy in some Asian countries, and scales, used for traditional medicine, according to the World Wildlife Fund.

Is there a coronavirus vaccine?

There is no vaccine yet. Nine studies are examining coronavirus vaccine development.

"Development of vaccine is a complex process, and it's not going to be available tomorrow," Nancy Messonnier, director of the National Center for Immunization and Respiratory Diseases, told USA TODAY.

While there is no particular treatment for the coronavirus, recommended measures are similar to those for cold, such as rest and drinking a lot of fluid.

Contributing: USA TODAY.