(CNN) -- A new virus in the same family as SARS -- found for the first time in humans in recent months -- has infected 40 people, most of them in the Middle East.
Half of those infected have died, according to the World Health Organization. Earlier this week, the WHO reported two health care workers in Saudi Arabia had been sickened while treating patients.
Cases of the virus, called the novel coronavirus or nCoV, have also been reported in European countries, most recently France but also Germany and the United Kingdom.
NCoV is part of a family called coronaviruses, which cause illnesses ranging from the common cold to SARS, or Severe Acute Respiratory Syndrome, as well as a variety of animal diseases. However, the new virus is not SARS.
NCov acts like a cold and attacks the respiratory system, the Centers for Disease Control and Prevention has said. But symptoms, which include fever and a cough, are severe and can lead to pneumonia and kidney failure. Gastrointestinal symptoms such as diarrhea have also been seen, according to the WHO.
Here are five things you need to know about nCoV:
Widespread transmission hasn't been seen
All the clusters of cases seen so far have been transmitted between family members or in a health care setting, the WHO said in an update Friday. "Human-to-human transmission occurred in at least some of these clusters, however, the exact mode of transmission is unknown."
That means it's not yet known how humans contract the virus. But, experts say, there has been no evidence of cases beyond the clusters into communities.
Dr. William Schaffner, an infectious disease specialist at Vanderbilt University Medical Center in Nashville, previously has said the infection is "very serious" but appears "very difficult to acquire."
"The recent increase in cases may in part be related to increased awareness among the medical community, however the demonstrated ability of this virus to transmit between humans and to cause large outbreaks has increased concerns about the possibility of sustained transmission," according to the WHO.
Cases are connected to the Middle East
"All of the European cases have had a direct or indirect connection to the Middle East," the WHO said in a statement Friday. "However, in France and the United Kingdom, there has been limited local transmission among close contacts who had not been to the Middle East but had been in contact with a traveler recently returned from the Middle East."
Most of the cases so far are seen in older men with other medical conditions, experts have said. Precise numbers are difficult to ascertain, as officials don't know how many people might contract a mild form of nCoV.
Saudi Arabia leads the number of laboratory-confirmed cases with 30.
No cases have been reported in the United States as of Friday, but infectious disease experts have said they would not be surprised if it happens.
Underlying health conditions may make you more susceptible
A large number of nCoV patients have another condition, the WHO said, suggesting "increased susceptibility from underlying medical conditions may play a role in transmission." In addition, the infection has shown up "atypically" and without respiratory symptoms in people whose immune systems are compromised.
No travel warnings have been issued
The WHO and CDC have not issued travel health warnings for any country related to the novel coronavirus.
Travelers planning to visit the Middle East, however, should see their health care provider if they develop a fever and respiratory symptoms like a cough or shortness of breath within 10 days of returning from the Arabian Peninsula or surrounding nations, according to the CDC.
There are no treatments and no vaccine
So far, those with nCoV have received supportive treatments to relieve their symptoms.