BOSTON -- A herpes virus, cousin of the culprits behind cold sores and genital herpes, has been found to cause a rare and deadly lung condition that can make patients gasp for breath and overload their hearts, researchers say.

The findings, published today in The New England Journal of Medicine, focus on a long-mysterious disease known as primary pulmonary hypertension -- high blood pressure in the blood vessels of the lungs. It can be fatal and sometimes prompts a lung transplant.

The AIDS virus has been implicated as one possible cause, but the condition's origins have been largely obscure.

This study, led by the University of Colorado and backed by the National Institutes of Health, pinpoints a member of the herpes family, human herpesvirus 8, as a seemingly important cause. In the past, this virus has been blamed for Kaposi's sarcoma, a cancer seen in AIDS patients.

The researchers checked lung tissue from 16 patients with primary pulmonary hypertension and 14 with a so-called secondary form caused by other heart and lung conditions.

In an antibody test, evidence of herpesvirus 8 turned up in 10 of the primary group -- or 62 percent -- but none of the secondary group. A separate DNA test confirmed the presence of the virus in the first group.

In an accompanying editorial, Cornell University's Dr. Ethel Cesarman, who also studies herpesvirus 8, suggested ways that the virus might enter the lungs.

She said it can be present in saliva and, from there, breathed into the lungs.

However, she said its role in primary pulmonary hypertension should be confirmed in future studies.