Doctors searching for the source of the mysterious flu-like illness spreading from Asia said Tuesday that some victims appear to be infected with a virus group that causes measles and some diseases in animals.
Specialists at the Institute for Medical Virology at Frankfurt University in Germany said samples from two people there resemble a paramyxovirus, the family of microbes that causes measles, mumps and canine distemper. There is no treatment for that virus group.
The finding is the first potential clue to emerge in the three weeks since the illness, called "severe acute respiratory syndrome," or SARS, came to the attention of health experts.
The disease, first described as a new form of pneumonia, has sickened 219 people worldwide in the past few weeks. A total of nine people have died — five of those in China from an outbreak months ago.
Most of the illnesses have been health workers in Singapore, Hong Kong and Vietnam. A few probable cases have turned up in England, Taiwan and Slovenia. Unconfirmed cases were being investigated in many other places, including the United States.
The World Health Organization, which is coordinating the disease investigation, is taking the paramyxovirus theory seriously, but officials say it's too early to draw conclusions.
"It's in two specimens and it's not been confirmed anywhere else," said Dr. David Heymann, WHO's communicable diseases chief. "It's really premature to put out something like this because it will automatically make everybody who's dealing with patients try to alter their therapies, and it may be altering them in the wrong way if this is not confirmed."
Heymann said other labs around the world are now looking to see if they can find the same thing in their samples.
Dr. Wolfgang Preiser, a consultant virologist at Frankfurt University Hospital, also urged caution over his group's findings, which are based on results from an electron microscope. Other more rigorous work, such as genetic testing, has not been done.
"It could possibly, potentially be the agent responsible for SARS, but we don't know at this stage," Preiser said. "The size fits a paramyxovirus. The structure, as far as we can make out, fits."
Samples were being sent Wednesday to a specialist lab in Rotterdam, Netherlands, which has previously identified new paramyxoviruses.
The paramyxovirus family includes hundreds of different viruses of varying degrees of danger to people. Besides measles and mumps, there is respiratory syncytial virus — a common cause of croup in children — and parainfluenza viruses, which are not influenza but cause flu-like symptoms.
The samples were taken from a Singapore physician and his mother-in-law, who were quarantined at the Frankfurt hospital Saturday after getting off a Singapore Airlines flight from New York. The Singapore doctor had treated two patients suffering from SARS.
Preiser said he is quite sure influenza is not to blame for his cases. "We ad other labs have screened the samples against all known types of influenza. We can be pretty confident it's not that," he said.
Investigators say it could take weeks to determine the cause of the outbreak. So far, the infection doesn't seem to spread by casual contact.
The incubation period for SARS appears to be three to seven days. It often begins with a fever of over 100 degrees and other flu-like symptoms, such as headache and sore throat. Victims typically develop coughs, pneumonia, shortness of breath and other breathing difficulties. Death results from respiratory failure.
Heymann said WHO continues to get reports that some patients seem to be getting better.
"Thirteen of the 57 patients in Vietnam show some clinical improvement," Heymann said. "Some are using antibiotic cocktails, others are using antivirals and it doesn't seem to matter."