Doctors Discover New Worm, One That's Lethal to Humans

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June 28, 1996

Doctors Discover New Worm, One That's Lethal to Humans By LAWRENCE K. ALTMAN

Scientists in California said today that they had discovered what they

believe is a previously unknown parasitic worm that can be fatal to humans.

Fragments of the worm were found in an AIDS patient who died from the

infestation, but they were not identified until a year later. The worm had

molecular biology resembling that of a tapeworm but acted more aggressively in

the body than most tapeworms.

Doctors initially thought the patient was suffering from a rapidly growing

cancer in his abdomen. But a biopsy and the use of new genetic laboratory

techniques found that the large mass of tissue was from the worm's fast growth,

which caused scar tissue.

In reporting the discovery in the international journal The Lancet, Stanford

University scientists said they wanted to alert doctors to the worm's existence

so they might treat anyone suspected of having it with drugs known to be

effective against similar parasites.

The scientists who solved the puzzle are from both Stanford and the

Kaiser-Permanente Medical Center in Santa Clara, Calif. The authors said they

did not find the entire worm, which has not been named, but identified it from

fragments by using the genetic techniques.

The scientists do not know how often the new worm causes disease in humans and

where the microbe exists in nature, Dr. David Relman, a co-author, said in an

interview.

In recent years, scientists have identified a number of new microbes,

including one called cyclospora, which is causing intestinal illness in at least

11 states. Health officials have tentatively linked many such cases to eating

fresh fruits like raspberries and strawberries.

The man who died from the worm infection was a 44-year-old accountant from the

San Francisco Bay area who had been infected with the AIDS virus for five years.

He often went camping in California and had two dogs but had never traveled

outside the United States.

In early 1994 he began suffering pain in his abdomen and back, weight loss,

sweating at night and fever. After the man was admitted to the hospital in Santa

Clara in March, his abdomen swelled as the worm invaded and destroyed parts of

his intestine and liver. Doctors initially thought he had developed one of the

many types of cancer that often complicate the course of someone with AIDS.

Shortly before his deaths nine weeks later, doctors performed a surgical

procedure to remove tissue from his abdomen.

Pathologists headed by Dr. Luis Fajardo examined slides containing thin slices

of the man's tissue under a microscope. Some were stained with chemicals to help

identify a known microbe. But the experts could not determine precisely what it

was in the tissue that caused the man's death, although the damage seemed to be

caused by a parasitic infection. It then took about a year to solve the mystery.

Slides were sent to pathologists and experts in cancer and infectious disease

around the country. Some infectious disease specialists thought it was a cancer.

But some cancer experts thought it was an infection.

The cells were too small to be of human origin. But they were unlike those of

any known parasite.

Eventually a chemist at Stanford found unusually large amounts of silicon in

the tissue, a finding inconsistent with human tissue.

About 10 months after the man's death, Dr. Fajardo asked a Stanford colleague,

Dr. David Relman, to help solve the mystery by using a strategy he had developed

and used to identify a new microbe as the cause of a rare illness called

Whipple's disease a few years ago.

Dr. Relman used a molecular technique, polymerase chain reaction (P.C.R.), to

create millions of copies of some particularly useful sequences of DNA from the

suspected microbe. Since such DNA blueprints vary in various species they are

used to help classify microbes.

But the sequences from the man's tissue did not match any stored in genetic

data bases. The sequences were distinct from human DNA and placed the microbe in

the tapeworm class, Dr. Relman said. Sequences have been determined for far

fewer disease-causing tapeworms than for disease-causing bacteria.

" We don't know whether this is an organism that has been recognized previously

and may be quite well known but has not had its sequence determined, or is truly

novel, " Dr. Relman said. " But we think it is a truly novel organism because the

pathology is unusual and has not been published before. "

It is not known whether the AIDS-weakened immune system had any effect on the

infestation's course.

 

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