LONDON (AP) — Doctors searching for the source of the mysterious flu-like illness spreading from Asia say 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 yesterday that 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, Spain and Slovenia. Unconfirmed cases were being investigated in many other places, including Canada and 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.