San Francisco Chronicle - The Voice of the West, 901 Mission Street, San Francisco, CA 94119, 22 March 1996, p.A1
Sabin Russell, Chronicle Staff Writer

Dr. Max Essex, chairman of the Harvard AIDS Institute, told an audience at the eighth annual National AIDS Update conference in San Francisco that there is virtually no early warning system to determine whether different subtypes of the AIDS virus responsible for heterosexual epidemics in Africa and Asia are taking root in the American population.

Essex later told reporters that there is "more than a 50-50 chance" of a similar outbreak in the United States within five to 10 years.

"It's fair to say I'm quite concerned," he said. "We are not screening for it. We are not on top of it enough to know when a new epidemic takes hold."

On a global scale, said Essex, there are really two simultaneous epidemics of human immunodeficiency virus. The American strain, known as subtype B, has infected an estimated 1.5 million people worldwide. Other subtypes, known as A, C, D and E, are responsible for at least 20 million infections, mostly in developing countries outside the United States and Europe.

Scientists have long been puzzled by the fact that the AIDS virus in the United States has been concentrated primarily among homosexual men and injection drug users. In Africa, Southeast Asia and South America, 90 percent of AIDS cases can be traced to heterosexual contact.

This month, Essex and a team of researchers reported in the journal Science that subtype E, the strain of HIV found most commonly in Thailand, readily infects the Langerhans' cells, which line the cervix, vagina and foreskin, whereas the subtype that has devastated the American gay community does not.

In fact, lab tests on cultures of human cells show that subtype E grew five times as well on Langerhans' cells than did subtype B, indicating a heightened susceptibility to infection from unprotected heterosexual intercourse.

Although standard AIDS diagnostic tests detect the presence of any of a dozen strains of HIV, they do not tell clinicians which one has infected a patient. That requires an additional and more costly test, called PCR, which traces the genetic fingerprints of each viral strain.

Yesterday, Essex suggested that U.S. cities should conduct the additional tests on select populations -- such as young men and women tested for HIV at sexually transmitted disease clinics -- to track the emergence of the foreign strains.

Dr. Mitch Katz, director of the San Francisco Office of AIDS, said that the city Health Department is looking at the feasibility of conducting additional tests to determine the subtype of virus among injection drug users, but that it has not yet committed to such a study.

Stanford AIDS researcher Dr. Thomas Merigan said testing for the various subtypes of the AIDS virus is not a bad idea, but he does not believe the problem is as serious as Essex has portrayed it. "The overseas strains are not moving very rapidly; otherwise, we would have seen it," he said.

Merigan stressed that safer-sex practices, which can keep the common American strain in check, are also effective with the subtypes of the virus that appear to be readily spread by heterosexual contact.

"We've had almost 20 years of experience with this virus," he said. "It's got to change fundamentally to cause new kinds of problems."

Despite a dearth of sophisticated testing, researchers have already picked up isolated cases of foreign strains in the United States.

In November, researchers from the Naval Health Research Center in San Diego reported in the journal Lancet that five servicemen returning from overseas posts in Thailand and Africa had contracted strains A, E and D.

Canadian researchers have also identified the E strain among prostitutes in Toronto.

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