Answers to Questions About HIV and AIDS (With Journal Citations)
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Quick Reference Index of Questions and Answers
Definition
of AIDS
What is the definition of AIDS
for an adult or child 13 or older?
From NIAID "Evidence that HIV Causes AIDS:" The CDC "defines AIDS in an
adult or adolescent age 13 years or older as the presence of one of 26
conditions indicative of severe immunosuppression associated with HIV
infection, such as Pneumocystis carinii pneumonia (PCP), a condition
extraordinarily rare in people without HIV infection .... A diagnosis
of AIDS also is given to HIV-infected individuals when their CD4+
T-cell count falls below 200 cells/cubic millimeter (mm3) of blood."
(Source: http://www.niaid.nih.gov/factsheets/evidhiv.htm)
What is the definition of AIDS
for a child younger than 13?
From NIAID "Evidence that HIV Causes AIDS:" "In HIV-infected children
younger than 13 years, the CDC definition of AIDS is similar to that in
adolescents and adults, except for the addition of certain infections
commonly seen in pediatric patients with HIV."
(Source: http://www.niaid.nih.gov/factsheets/evidhiv.htm)
Are other definitions used
elsewhere? Why?
From NIAID: "In many developing countries, where diagnostic facilities
may be minimal, healthcare workers use a .... [WHO] AIDS case
definition based on the presence of clinical signs associated with
immune deficiency and the exclusion of other known causes of
immunosuppression .... An expanded WHO AIDS case definition, with a
broader spectrum of clinical manifestations ... is employed in settings
where HIV antibody tests are available (WHO. Wkly Epidemiol Rec.
1994;69:273)."
(Source: http://www.niaid.nih.gov/factsheets/evidhiv.htm)
Origin of HIV
When did HIV-1 originate?
"[A]nalysis of the molecular
divergence of SIV and HIV genes .... establishes 1931 as the date of
origin of the HIV-1 M-group viruses (the principal cause of the AIDS
pandemic)." [David Hillis, "AIDS:
Origins of HIV," Science 9 June 2000,
v288, #5472, p1757-1759. See also Korber et al, "Timing
the Ancestor of
the HIV-1 Pandemic Strains," Science 9 June 2000, v288, #5472,
p1789-1796.]
(Sources: http://www.sciencemag.org/cgi/content/summary/288/5472/1757
and http://www.sciencemag.org/cgi/content/short/288/5472/1789)
Where did HIV-1 come from?
HIV-1 jumped to humans from the related SIV in chimpanzees. [Reeves
JD, Doms
RW. "Human
immunodeficiency virus type 2." J Gen Virol. 2002
Jun;83(Pt 6):1253-65.]
Where did HIV-2 come from?
HIV-2 jumped to humans from the related SIV in the sooty mangabey
monkey. [Reeves
JD, Doms
RW. "Human
immunodeficiency virus type 2." J Gen Virol. 2002
Jun;83(Pt 6):1253-65.]
How did HIV jump from primates to humans?
The most likely explanation is that a hunter in the bush meat trade (in
which wild animals are killed for food) probably contracted SIV from a
primate he killed. For example, if the hunter had an open cut and
chimpanzee
blood with SIV got on the cut, that would be blood-to-blood contact
enabling contagion. The SIV then evolved into HIV-1.
Since SIV has existed for a long time,
why did HIV-1 only jump to humans in 1931?
You could ask the same question about why H5-N1 bird flu, SARS, or
Ebola infected humans recently. Viruses evolve in animals & humans
all the time. It's impossible to say for sure why a virus jumps to
humans at a particular moment and why it does/doesn't become
permanently established within the human population. It may have
mutated making it more capable of infecting humans, or humans may have
had increased contact with source animals due to population growth, and
travel may help it spread.
HIV Testing
How accurate are HIV tests?
Testing is specific &
accurate. "A large study
of HIV testing in 752 U.S. laboratories
reported a sensitivity of 99.7% and specificity of 98.5% .... and
studies in U.S. blood donors reported specificities of 99.8% and
greater than 99.99% (46, 47). With confirmatory Western blot, the
chance of a false-positive identification in a low-prevalence setting
is about 1 in 250 000 (95% CI, 1 in 173 000 to 1 in 379 000) (48)."
(Chou et al, Annals of Internal Medicine, 5 July 05, vol 143, #1, p
55-73)
HIV's Connection to AIDS
How do we know that HIV is the cause
of AIDS?
Because HIV infection is a serious condition that is incurable and
usually develops into clinical AIDS which is frequently fatal, it would
not be ethical to perform an experiment where a person was
deliberately, knowingly infected with HIV to demonstrate the
progression to clinical AIDS. However, there are multiple independent
lines of evidence proving that HIV is the cause of AIDS by other means.
For full details with references, see "The Evidence
That HIV Causes AIDS" and "The Evidence
That HIV Causes AIDS" among many other sources. Here are a few
quick summaries:
- NIAID: By 12/31/94, "CDC had
received reports of 42 health care workers in the United States with
documented, occupationally acquired HIV infection, of whom 17 have
developed AIDS in the absence of other risk factors .... These
individuals all had evidence of HIV seroconversion following a discrete
percutaneous or mucocutaneous exposure to blood, body fluids or other
clinical laboratory specimens containing HIV." [CDC, "HIV/AIDS
surveillance report, 1994 year-end edition," 1995a;6(no.2).] (Source: http://www.niaid.nih.gov/publications/hivaids/all.htm)
- NIAID "Evidence That HIV
Causes
AIDS:" "through December 1999, the CDC had received reports of 56
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." (Source: http://www.niaid.nih.gov/factsheets/evidhiv.htm)
- NIAID "Relationship Between
HIV and AIDS": Known HIV seroconversion
followed by development of AIDS "has been repeatedly observed in
pediatric and adult blood transfusion," in mother-to-child
transmission, "and in studies of hemophilia, injection drug use, and
sexual transmission in which the time of seroconversion can be
documented using serial blood samples." [Ward 89, Ashton 94, ECS
91&92, Turner 93, Blanche 94,Goedert 89, Rezza 89, Biggar 90,
Alcabes 93, Gisecke 90, Buchbinder 94, Sabin 93] (Source: http://www.niaid.nih.gov/publications/hivaids/all.htm)
- NIAID "Evidence That HIV
Causes
AIDS:" "in a 10-year study in the Netherlands, researchers followed 11
children who had become infected with HIV as neonates by small aliquots
of plasma from a single HIV-infected donor. During the 10-year period,
eight of the children died of AIDS. Of the remaining three children,
all showed a progressive decline in cellular immunity, and two of the
three had symptoms probably related to HIV infection (van den Berg et
al. Acta Paediatr 1994;83:17)" (Source: http://www.niaid.nih.gov/factsheets/evidhiv.htm)
- NIAID "Evidence:"
"transmission of
HIV from a Florida dentist to six patients has been documented by
genetic analyses of virus isolated from both .... The dentist and three
of the patients developed AIDS and died, and at least one of the other
patients has developed AIDS. Five of the patients had no HIV risk
factors other than multiple visits to the dentist for invasive
procedures (O'Brien, Goedert. Curr Opin Immunol 1996;8:613; O'Brien,
1997; Ciesielski et al. Ann Intern Med 1994;121:886)." (Source: http://www.niaid.nih.gov/factsheets/evidhiv.htm)
- NIAID: "Among HIV-infected
patients who receive anti-HIV therapy, those whose viral loads are
driven to low levels are much less likely to develop AIDS or die than
patients who do not respond to therapy. Such an effect would not be
seen if HIV did not have a central role in causing AIDS." [Montaner AIDS 1998;12:F23; Palumbo JAMA 1998;279:756; O'Brien NEJM 1996;334:426; Katzenstein NEJM 1996;335:1091; Marschner
J Infect Dis 1998;177:40; Hammer NEJM 1997;337:725; Cameron Lancet 1998;351:543] (Source: http://www.niaid.nih.gov/factsheets/evidhiv.htm)
- NIAID: Cases have been
documented
where HIV+ mothers gave birth to twins where one was HIV-infected and
the other wasn't. "The HIV-infected children developed AIDS, while the
other children remained clinically and immunologically normal." [Park. J Clin Microbiol 1987;25:1119; Menez-Bautista. Am J Dis Child 1986;140:678; Thomas. Pediatrics 1990;86:774; Young. Pediatr Infect Dis J 1990;9:454; Barlow
and Mok. Arch Dis Child 1993;68:507; Guerrero
Vazquez. An Esp Pediatr 1993;39:445] (Source: http://www.niaid.nih.gov/factsheets/evidhiv.htm)
- NIAID: Animal models also
show
that HIV causes AIDS. "Chimpanzees experimentally infected with HIV
have developed severe immunosuppression and AIDS. In severe combined
immunodeficiency (SCID) mice given a human immune system, HIV produces
similar patterns of cell killing and pathogenesis as seen in people.
HIV-2 .... also causes an AIDS-like syndrome in baboons." [O'Neil et al. J Infect Dis 2000;182:1051; Aldrovandi et al. Nature 1993;363:732; Locher et al. Arch Pathol Lab Med 1998;22:523]
Course of the Disease in an
Individual
Does everyone who contracts HIV develop
clinical AIDS?
No. Some will die of other unrelated causes (e.g. a car accident) or
natural causes before HIV progresses to clinical AIDS. Some have
natural resistance to HIV that may greatly slow or totally prevent the
progression from HIV to clinical AIDS. Some go on antiretroviral
medication before their HIV disease meets the criteria for clinical
AIDS and as a result never get the opportunistic infection or CD4 cell
count that would lead to a diagnosis of clinical AIDS. However, all but
a few HIV positive individuals
progress to AIDS within 20 years. ["Course of HIV Infection",
NIH, 1995]
How long does it take for HIV to progress to
clinical AIDS?
From NIAID "Evidence:" "The median
period of time between infection
with HIV and the onset of clinically apparent disease is approximately
10 years in industrialized countries, according to prospective studies
of homosexual men .... Similar
estimates ... have been made for HIV-infected
blood-transfusion recipients, injection-drug users and adult
hemophiliacs." [Alcabes
et al. Epidemiol Rev 1993;15:303] All but a few
progress to AIDS within 20 years. ["Course of HIV Infection",
NIH, 1995]
Why don't people infected with HIV
immediately develop clinical AIDS?
HIV is only one of many viruses that produce an acute symptomatic
infection, then may have a long period where the infected person
experiences few no symptoms, then later in life develops symptoms
again. Examples include: chicken pox, which causes an acute infection
and then after decades without symptoms leads to shingles in about 1/7
of infected people; recurring oral herpex simplex ("cold sores') which
may go a long time with no symptoms and then recur; etc. The reasons
for these asymptomatic periods can be completely different. The chicken
pox virus (varicella-zoster virus) and herpes simplex virus type 1
remain dormant in the nerves and can reactivate causing localized
shingles or cold sores respectively. HIV usually appears asymptomatic
because the body's immune system is holding it at bay, generating new
CD4 cells as fast as HIV kills them. When the body falls behind in this
running battle, HIV can progress to clinical AIDS.
Course of the Pandemic
Why didn't an epidemic occur
immediately after the first known HIV infections?
"HIV did not become epidemic until 20 to 30 years later [after known
infection in 1959], perhaps because of the migration of poor and young
sexually active individuals from rural areas to urban centers in
developing countries, with subsequent return migration and,
internationally, due to civil wars, tourism, business travel and the
drug trade" (NIAID citing Quinn, "Population migration and the spread
of types 1 and 2 human immunodeficiency viruses," Proc Natl Acad Sci
USA 1994;91(7):2407-14.)
(Sources: http://www.niaid.nih.gov/publications/hivaids/all.htm,
citing Quinn TC. Population migration and the spread of types 1 and 2
human immunodeficiency viruses. Proc Natl Acad Sci USA
1994;91(7):2407-14.)
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