Common Only in Farm Animals : S.D. Doctors Find Pathogen in 2 AIDS Patients

Researchers in San Diego have isolated from the blood of two AIDS patients a pathogen found commonly in farm animals, identifying what one researcher said is a new complication of the deadly disease and one that is difficult to treat.

The pathogen, known as rhodococcus equi , had been found previously in rare cases of individuals with severely suppressed immune systems. Most appeared to have inhaled the organism, though it lives in soil and can be ingested in contaminated plants.

“It’s a troublesome infection,” said Dr. Paul Wolf, co-author of a report on the findings in the May issue of the British Journal of Clinical Pathology. “ . . . It’s a more important complication (of acquired immune deficiency syndrome) in that it’s a difficult organism to treat with antibiotics.”

35-Year-Old Patient

The first case reported involved a 35-year-old AIDS patient admitted last year to the Veterans Administration Medical Center in La Jolla. Dr. Joshua Fierer, a specialist in infectious disease at UC San Diego, identified the organism in the patient’s blood and stool.

The second case was a 55-year-old AIDS patient with evidence of the organism in tissue. In both cases, the pathogen proved resistant to penicillin. Only one of the patients recovered from the infection and both have since died of complications of AIDS.

The researchers reported that the cases are the first instances of the infection in humans outside the lungs. Whereas all previously reported cases involved pneumonia, neither of the San Diego patients had pneumonia while he had the infection.

Wolf, a clinical professor of pathology at UCSD and director of autopsy at the VA hospital, said Thursday that all of the previously reported cases of the infection involved cancer patients with immunosuppression caused by their treatment or their tumors.

However, in recent months, cases of other AIDS patients with the infection have begun appearing in the medical literature, Wolf said. The AIDS virus destroys its victims’ immune systems, leaving them open to a variety of opportunistic infections.

Identified in 1923

Rhodococcus equi first was identified in 1923 when it was shown to be the cause of pneumonia in foals, the researchers reported. It is believed to enter the body through the respiratory or alimentary tract.

“The natural habitat of the organism seems to be the soil, which accounts for the prevalence of infection in grazing and rooting animals,” the researchers wrote. “About half the reported cases in man (seven of 15) had had contact with domestic animals.”

However, Wolf said neither of the AIDS patients had had contact with animals. He noted the earlier case of a person who appeared to have contracted the infection through eating contaminated vegetables.

The researchers observed that the best treatment for the infection is not known. The infection in one of the AIDS patients responded to the antibacterial drug vancomycin, but relapses of the infection are common.