http://www.sfgate.com/cgi-bin/article.cgi?file=/chronicle/archive/2000/05/30/ED9
6076.DTL

San Francisco Chronicle
Proven Connection -- HIV Causes AIDS
Differences between U.S. and African epidemics don't disprove cause of
both

Jay Levy, Nancy Padian, Jeff Sheehy

Tuesday, May 30, 2000

--THE VIEW PUBLISHED in Open Forum last week during South African
President Thado Mbeki's visit to San Francisco gives the impression
that the association between HIV and AIDS is still questionable. The
contrary is true.--

The overwhelming evidence indicates that HIV causes AIDS.

The HIV deniers have pointed to President Mbeki's recognition that HIV
in Africa has been transmitted predominately by heterosexual contact,
as opposed to the United States and other developed countries where
HIV has been transmitted predominately by homosexual contact. The
belief has been stated that this discrepancy somehow proves that HIV
does not cause AIDS.

It is important not to confuse the epidemiology of HIV transmission in
the United States with what is occurring in Africa. In this county,
the studies used to determine the odds of transmitting HIV in a single
act of unprotected vaginal sex between an infected man and an
uninfected woman, which stand at about 1,000 to 1, excluded risk
factors known to increase HIV transmission. These low odds do not hold
in the presence of other well-established risk factors, prominent in
Africa, such as other sexually transmitted diseases, which can
increase the risk. Thus warnings, based on science about heterosexual
transmission that lead people to change their behaviors to save their
own lives and the lives of others, have been a critical component of
our prevention strategies.

Indeed, successful HIV prevention programs have actually been
responsible for maintaining low infection rates among heterosexuals in
this country. Notwithstanding this country's success in limiting
heterosexual transmission of HIV, there are many factors that could
account for the widespread heterosexual epidemic in Africa that differ
from what we have observed here. As is the case with virtually all
illnesses and infections, patterns of disease distribution and
transmission differ depending on location.

Some of these factors are biological, and some are behavioral and
social. Biological factors include the high prevalence of other
sexually transmitted diseases, which facilitate transmission, and the
high rates of bacterial vaginosis among women, known to increase
susceptibility. Also, in Africa a predominant virus (clade C) may be
more easily transmitted through mucosal contact. Further, the presence
of many tropical diseases, as well as nutritional and other factors
among people in developing countries, may compromise their general
immune competence and thus increase susceptibility to HIV infection.

Behavioral and social factors that could facilitate the heterosexual
spread of HIV in Africa include a greater power imbalance between
genders that makes it much more difficult for women to avoid sexual
contact with an infected husband or to negotiate condom use.
Importantly, there is less access to health care, which greatly
contributes to high rates of sexually transmitted diseases and other
health problems that might increase susceptibility to HIV.

Finally, far fewer resources have been available for successful
prevention programs when such resources are urgently needed in Africa
and the developing world to fight this disease. There is an abundance
of evidence proving that HIV causes AIDS. A fact sheet (found at
hivinsite.ucsf.edu/) prepared by the Office of Communications and
Public Liaison at the National Institute of Allergy and Infectious
Diseases clearly shows the link:

Koch's postulates, developed in the late 19th century, are the most
cited criteria used over the years to prove the connection between
disease-causing agents and disease. These tenets have served as the
litmus test for determining the cause of any epidemic disease.

To restate:

1. Epidemiological association: The suspected cause must be strongly
associated with the disease.

2. Isolation: The suspected pathogen can be isolated -- and propagated
-- outside the host.

3. Transmission pathogenesis: Transfer of the suspected pathogen to an
uninfected host, man or animal, produces the disease in that host.
With regard to postulate 1, numerous studies from around the world
show that virtually all AIDS patients carry antibodies that indicate
HIV infection.

With regard to postulate 2, modern laboratory techniques have allowed
the isolation of HIV in virtually all AIDS patients, as well as in
almost all HIV-positive individuals with both early- and late-stage
disease. In addition, the polymerase chain reaction procedure and
other sophisticated molecular techniques have enabled researchers to
document the presence of HIV genes in virtually all patients with
AIDS, as well as in individuals in earlier stages of HIV disease.

HIV infection always precedes AIDS. Postulate 3 has been fulfilled in
tragic incidents such as those involving three laboratory workers with
no other risk factors who have developed AIDS or severe immune
deficiency after accidental exposure to concentrated, pure HIV in the
laboratory. In all three cases, HIV was isolated from the infected
individual, sequenced and shown to be identical to the infectious
virus from the laboratory.

In addition, through June 1999, the Centers for Disease Control
received reports of 55 health care workers in the United States with
documented, occupationally acquired HIV infection, of whom 25 have
developed AIDS in the absence of other risk factors. The development
of AIDS following infection with HIV also has been repeatedly observed
in pediatric and adult blood-transfusion cases, in mother-to-child
transmission, and in studies of hemophilia, injection-drug use and
sexual transmission in which antibodies to HIV can be documented using
serial blood samples. Indeed, young children free of any risk factors
that might be associated with immune disorders (e.g., illicit drug
use, malnutrition, therapy for other diseases) have developed AIDS.
HIV was the only infectious agent associated with their disease. We
know that HIV causes AIDS. We know how HIV is transmitted. We know
that advising people to avoid contact with HIV is the best way to
avoid infection. We can only hope that the public is aware that
encouraging even one person to stop practicing safe sex, to believe
that HIV is no longer something to be feared, can have tragic
consequences.

The reality underlying this divisive controversy is that so much
remains to be done. In several communities here in the United States,
HIV is spreading. In Africa and in much of the developing world, the
spread of the disease is catastrophic. If left unchallenged, HIV will
continue to infect and sicken the populations of the world. Instead of
continuing to question the overwhelming evidence that HIV causes AIDS,
let us join together to fight this infectious agent before it can
create even more devastating damage in the world.

Dr. Jay Levy is professor of medicine at UCSF, and director of the
Laboratory for Tumor and AIDS Virus Research. Dr. Nancy Padian is
professor of obstetrics, gynecology, and reproductive science at UCSF,
and director of international research at UCSF's AIDS Research
Institute. Jeff Sheehy is the communications deputy director for
UCSF's AIDS Research Institute.

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