MERS, Middle East Respiratory Syndrome, has spread to the United States.

The patient with the first confirmed U.S. case of MERS is said to be improving in an Indiana hospital.

However, the deadly new respiratory illness is puzzling health care workers who are trying to figure out what this virus is and its threat to humans.

Doctor Jeff Duchin with the Northwest Center for Public Health Practice explained the virus on KIRO Radio’s Jason Rantz Show. He said the virus originated in animals – namely camels – and until now, human cases had been concentrated in countries on the Arabian peninsula.

“It’s possible that the camels themselves are just what we call an intermediate host and that this virus lives, in what we call, another ‘animal reservoir.’ People suspect it may be bats, which were the home to the SARS coronavirus, a distant cousin of this,” Duchin said.

Symptoms are fever and cough – and the virus presents itself much like pneumonia.

While it can be extremely deadly, Duchin believes the death rate from MERS may not be as high as it appears.

“We do know that some people get extremely ill. Among the cases that have been identified, a quarter or so of them have died. So it can cause a very severe illness,” said Duchin. “But as I suspect, and I think as many others also suspect, there are probably many, many more people who have had mild or asymptomatic infections which are probably not that significant from the personal health perspective and so therefore the death rate really is not quite as high as it looks.”

According to Duchin, much like we’ve seen with the resurgence of measles cases in America, the MERS virus is spread when people travel to areas where MERS is prevalent, like Saudia Arabia, and then come back to the U.S.

“We do know that human cases have occurred from contact with other humans and in particular in the hospital setting so patients are very sick with this infection – have pnuemonia, coughing, fever, and have very close contact with health care workers, have at times, spread as far as to health care workers.”

The MERS patient in Indiana is a health care worker who was living and working in Saudi Arabia.

The good news, according to Duchin, is that MERS appears to be a very slow-spreading virus that only spreads through very close contact with someone who has it. This includes hospital workers or family members who are taking care of someone with MERS.

“We have made special efforts in the last couple of days to educate health care providers on the front lines that when people come to them with fever and cough that they get that history. They ask them where have they been in the last 14 days,” he said. “A good doctor should always take a travel history.”

With the first confirmed case now in the U.S., the medical community is being cautious – not alarmist – about if this virus will reach outbreak status in America.

KIRO Radio’s Colleen O’Brien contributed to this report.