This is the Health Report from VOA Learning English.
Experts are watching the outbreak of a virus in the Middle East for signs that it could spread around the world.
David Swerdlow is with the U.S. Centers for Disease Control and Prevention. He studies the spread of diseases through large populations. He leads the CDC's response to the Middle East Respiratory Syndrome, or MERS.
First, here is the bad news.
"Thirty to 40 percent of people who get it have died. It's caused illness in multiple countries. The virus clearly spreads from person to person and it's severe and there's no treatment or vaccine."
MERS is a member of the viral family of germs that cause the common cold, as well as severe acute respiratory syndrome, or SARS. That disease appeared in southern China in 2003. It infected about 8,000 people in 29 countries and killed about 800 before it was contained.
The MERS virus first appeared in September of 2012. Most reported cases have been in Saudi Arabia.
Now, for the good news. MERS does not spread as easily as SARS, says Amesh Adalja with the Infectious Diseases Society of America.
"With SARS we saw much more human transmissibility. And we also saw individuals who we called 'super-spreaders,' people who disproportionately spread the virus more than anybody else and were really responsible for how the virus made its way all around the world."
Mr. Adalja says there are no MERS super-spreaders -- at least, not yet.
The World Health Organization reports 261 MERS infections, including 93 deaths. Other organizations put those numbers higher.
In April, there was a sharp rise in cases in Saudi Arabia. Some health experts fear that means the MERS virus has changed, or mutated. That would be a danger sign.
But the CDC's David Swerdlow says German researchers have examined DNA from some of the new Saudi cases.
"The information they have shown suggests that there has not been any significant change in the virus."
That is, again, good news. But Mr. Swerdlow says researchers need more information to be sure. Scientists still do not know a lot about MERS. They do not even know where it came from, although camels are the prime suspect.
But, Amesh Adalja says scientists have learned from the SARS virus.
"The world is a small place ... that borders don't mean anything. And that the total health security of the globe is really tied up in identifying these threats as quickly as possible and then trying to stop them in their tracks."
That's why health officials around the world are keeping a close eye on MERS.
On Friday, the CDC reported the first case of MERS within the United States.
CDC officials said an American health care worker infected with the virus is being treated at a hospital in the northern state of Indiana. They said the patient traveled from Saudi Arabia to London on April 24th, and then on to the United States.
The CDC is working to identify people who may have been in contact with that patient.
When health officials find that a virus such as MERS is traveling from country to country, they often issue "travel advisories." Travel advisories warn people of certain events taking place in a country such as civil war, crime and public health threats like a virus. Currently, the CDC is not advising people to change their travel plans because of the MERS virus.
And that's the Health Report.
Has MERS been reported where you live? Do you remember the SARS virus? Share your thoughts in the comment section. It's a great place to practice your written English.
I'm Anna Matteo.