The deadly and mysterious coronavirus that first appeared in Saudi Arabia last year has claimed two more victims, bringing the official death toll to 11.
The World Health Organization said a 73-year-old man from the United Arab Emirates who was taken to Germany for medical treatment died at a Munich hospital on Tuesday (local time).
The United Nations health authority also announced that a man from Britain who became sick in January has died. That man had traveled to Saudi Arabia and Pakistan and presumably became infected there.
This new strain of coronavirus has puzzled doctors since September when it was identified as the cause of death for a 60-year-old man in Saudi Arabia in June. The virus aggressively attacks its victim's lower respiratory system, leading to trouble breathing, fever, pneumonia and even death.
It is part of a family of viruses that includes the common cold and is a distant cousin of severe acute respiratory syndrome, or SARS, which killed almost 800 people during a global outbreak in 2002 and 2003.
So far, 17 cases of coronavirus infection have been confirmed by the World Health Organization. Patients with the virus are overcome with severe lower respiratory infections, sometimes leading to multi-organ failure. Though the virus hasn't sickened many people, the fact that it has killed 65 percent of its known hosts has scientists and health officials concerned.
Coronaviruses earned their name because of their physical appearance. The virus has a globular center ringed by a spiny halo - or corona - of proteins.
The virus tricks a body's immune system into turning against it, said Pinghui Feng, a professor of microbiology at the University of Southern California.
The bug attacks the lower respiratory system and triggers a dangerous immune system reaction known as a cytokine storm. Even after the immune system has cleared the virus, the body continues to attack cells.
The fast-spreading virus - its peak production is 48 hours after infection - and the out-of-control immune response simultaneously attack the cell lining of the lungs, Feng said. The virus also aims for the kidneys, which may shut down.
The virus appears to have originated in bats, a team of European experts wrote in the journal mBio, which is published by the American Society for Microbiology.
"It is currently not clear how the virus is spreading or where it comes from," said Volker Thiel of Switzerland's Institute of Immunobiology and a co-author of that study. "It is related to coronaviruses detected in bats, but still we don't know how it jumped to humans."
Another study published in Nature revealed that the receptor that allows the virus to latch onto and infect cells is very similar in humans and several types of animals, including bats. The particular strain isolated from people is genetically very similar to three of the 60 known strains of bat coronaviruses, although it's possible that bats gave it to another animal, which then gave it to humans.
Coronaviruses like this new one are "somewhat unpredictable," said Dr. Peter Katona, a clinical professor of medicine and infectious diseases at the University of California, Los Angeles.
"I think these kinds of situations are a warning to us that these agents can mutate - and mutate quickly - and they can potentially cause great harm," Katona said. "We may have a false sense of complacency."
The 17 patients identified so far are just the "tip of the iceberg," he said. There are probably countless other cases of infection in which people didn't die, or they died from something as common as pneumonia, so no one bothers to identify the virus, he added.
The virus' ability to infect and replicate means there will probably be many more cases, but nothing of pandemic proportions because it's not as contagious as the flu, Feng said. Usually, when a virus mutates and is able to spread more easily from person to person, it becomes less dangerous in the process, he said.
"This is a cause for concern, but not alarm," said Susan Gerber, an epidemiologist with the Centers for Disease Control and Prevention's Division of Viral Diseases. "There are no cases in the United States to date."
