Karposi’s sarcoma (KS) is a cancer marked by purple tumors on the skin. Although extremely rare in the population, it is found in approximately 25% of gay men infected with HIV, the virus that causes AIDS. It has been suggested that KS itself is caused by a virus, the human herpesvirus 8 (HHV8). To help confirm this hypothesis, the following observations were made:
At regular intervals over a two-year period, samples of blood were taken from gay men who tested positive for HIV at the beginning of the study. In 38 of the subjects, no KS developed, although 18% had antibodies against HHV8 in their blood samples. However, in 40 subjects who developed KS, 80% had HHV8 antibodies. In 11 of these men, HHV8 antibodies were detected from the beginning of the study, but 21 of the men developed HHV8 antibodies during the study. In these subjects, the antibodies appeared several months before the onset of KS.
Individuals not known to have been infected with HIV were tested for antibodies against HHV8. In 141 blood donors, only 1% were found to test positive for the antibodies. In addition, 300 hemophiliacs who had regular blood transfusions were also examined. Three percent had HHV8 antibodies.
In 176 patients who had syphilis, a sexually transmitted disease, 36 (or 20%) had antibodies to HHV8.
What conclusion can be drawn from these observations?