The new Middle East Respiratory Syndrome strain was diagnosed in Saudi Arabia last year.
It is a coronavirus, the same viral family that triggered the outbreak of SARS, Severe Acute Respiratory Syndrome, that killed 775 people in 2003.
At first, the symptoms can seem like a severe stomach virus accompanied by breathing problems.
The illness can lead to pneumonia and kidney failure.
Dr. Anthony S. Fauci, Director of the U.S. National Institute of Allergy and Infectious Diseases said they do not yet know how the virus is transmitted to people.
"We are assuming that they are being exposed inadvertently to an infected animal.
The characteristics are that it doesn't spread well at all from person to person,
so it doesn't have what's called sustained transmissibility from you to me, from me to my family, etcetera,'' said Fauci.
While the number of cases is relatively low so far,
Fauci said there is growing concern the deadly virus could mutate and be spread by direct human contact.
If that happens, it could spark a global outbreak, something experts fear.
"When you look at a typical influenza virus, for example seasonal flu,
where you have millions and millions of people infected, the mortality is less than one percent, a fraction of a percent.
The mortality for this if you do the math is 50 cases and you have 30 deaths,
so you are talking about a 60 percent mortality already," said Fauci.
The virus has been found in Middle East countries and isolated cases have been exported to Europe by visitors.
But the largest cluster of infections is in Saudi Arabia,
home to the Muslim holy cities of Mecca and Medina, which draw millions of pilgrims a year.
The World Health Organization says it is closely monitoring the situation but is not currently recommending any travel or trade restrictions.
relating to breathing
The lungs are respiratory organs.
caused by a virus
A viral illness left her barely able to walk.
At present, if too many turtles are inadvertently caught in Hawaiian waters, the entire fishery is closed down.
to develop new physical characteristics because of a permanent change in the genes. These changes can happen naturally or can be produced by the use of chemicals or radiation
In the Darwinian run, the body code would mutate over time.
the way that people do not live for ever
Infant mortality is still very high in some developing countries.