Homosexual men, intravenous drug users and Haitianimmigrants make up the highest risk groups in the U.S for AIDSacquisition and transmission. But in sub-Saharan Africa, it'severy sexual partner, man and woman alike.

In the U.S., this heterosexual vector of HIV infection has morethan doubled in the past two or three years and is now thefastest-growing single risk component.

Infectious disease specialist David Clemetson cited a WorldHealth Organization projection that "of 10 million HIVinfections worldwide, more than 75 percent will have beentransmitted heterosexually, through penile-vaginalintercourse."

An editorial in Nature for June 3 raps "some sectors of thepress and media" for denying that "there is a major HIVepidemic in sub-Saharan Africa." Anent worldwide futuretrends, it concludes, "the greatest uncertainty has been, andstill is, among heterosexuals"

Clemetson practices medicine in St. Louis, Mo., and is on thefaculty of Washington University's School of Medicine there.For the past decade, with funding from the National Institutesof Health, he has joined colleagues from the University ofManitoba, Belgium's Institute of Tropical Medicine, Antwerp,and the University of Nairobi in studying the spread of AIDS inKenya.

On Saturday afternoon, Clemetson was on the list of speakers ata media briefing in Berlin, Germany of the International AIDSConference. His topic: "Detection of HIV DNA in Cervical andVaginal Secretions: Prevalence and Correlates Among Womenin Nairobi." The Journal of the American Medical Association(JAMA) held this press conference for coverage in JAMA'stheme issue on AIDS research, out Wednesday.

Before leaving for Berlin last Thursday, Clemetson gaveBioWorld a preview of his findings, which had not previouslybeen reported.

"AIDS is a disease of the developing world," he declared, "sub-Saharan Africa is suffering the most extensive HIV epidemicanywhere in the world."

On frequent trips to the Kenyan capital, he and his associatesexamined 97 infected women between 1988 and 1991, andshipped deep-frozen samples of their genital secretions homefor identification of the virus.

"It's very difficult to culture virus from secretions unlessthey're fresh," Clemetson explained, "and we don't always havethe technology to set up viral culture in places like Kenya." Headded that "PCR amplification allowed us to freeze specimens incryo-vials, bring them back to the U.S. en bloc, and evaluateviruses in secretions without having to culture them directly."

The most important aspect of this viral detection, he said, "isthat there are significant correlates of the presence of virus insecretions -- that's what our data shows -- and transmission ofthe disease." His 97 case studies discerned four maincomponents of viral acquisition and transmission:

-- Women on the (contraceptive) Pill;

-- pregnant women;

-- visible pus on the cervix;

-- women with cervical ectopy.

This last is a condition in which a single-cell layer of epitheliumtraverses the cervical transition zone between uterus andvagina. "These cells," Clemetson noted, "are more vascular,friable and likely to bleed, releasing T4 lymphocytes containingHIV on their surface."

Thus, cervical ectopy can lead to vertical transmission ofinfection from mother to newborn descending the birth canal.

In his cohort of 97 infected women, all either married or instable sexual partnerships, one-third shed HIV from the cervix,one-sixth from the lateral vaginal walls.

The major implication of these findings Clemetson sees "is fromthe public policy standpoint, as regards birth control --specifically, the Pill -- in countries where heterosexualtransmission is predominant. We need to confirm thatcontraception, by increasing cervical ectopy, is contributing totransmission." But, without contraception, "a pregnant womanis in a relatively immune-suppressed state, which may allowfor more viral replication and release." He concluded somberly,"So maybe the Pill is fueling transmission in both directions."

-- David N. Leff Science Editor

(c) 1997 American Health Consultants. All rights reserved.