The agent, called mycoplasma penetrans, a tiny organism capable of reproducing itself, can cause debilitating disease and profoundly alter immune function.

In a study by the Department of Infectious and Parasitic Disease Pathology, the Armed Forces Institute of Pathology in Washington over 400 HIV positive patients had higher antibodies to the mycoplasma than did the general population, indicating that they had been infected with it. However, antibody levels were twice as high in patients with full blown AIDS as among those with symptom free HIV.

"HIV-1 is probably a necessary but not sufficient cause of AIDS. . .Infection with M penetrans may related to the development of clinical AIDS," concluded the study, published in the Lancet (28 November 1992) .

Speaking of AIDS, the virus could be transmitted by some types of reused dental equipment, according to a US study at the University of Georgia (The Lancet, 21 November 1992).

The researchers, led by Dr David Lewis of the University of Georgia, recommend that reused, high speed, air driven handpieces, used for cleaning and drilling teeth, should be cleaned and heat treated between patients.

They found that when handpieces were brought into contact with infected blood, samples of the infection were later found inside the equipment, their connecting air/water hoses, and from water spray expelled when the equipment was reused.

The researchers call for further studies to determine ways of eliminating risk from the air/water hoses.