Section 2. How to prevent infection.
Q2.1 How is AIDS transmitted?
Q2.2 How effective are condoms?
Q2.3 How do you minimize your odds of getting infected?
Q2.4 How risky is a blood transfusion?
Q2.5 Can mosquitoes transmit AIDS?
Q2.6 What about other insect bites?
Q2.7 Is there even a remote chance of insect transmission?
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Question 2.1. How is AIDS transmitted?
The Human Immunodeficiency Virus and Its Transmission
CDC National AIDS Clearinghouse
Research has revealed a great deal of valuable medical, scientific, and
public health information about the human immunodeficiency virus (HIV) and
acquired immmunodeficiency syndrome (AIDS). The ways in which HIV can be
transmitted have been clearly identified. Unfortunately, some widely
dispersed information does not reflect the conclusions of scientific
findings. The Centers for Disease Control and Prevention (CDC) provides
the following information to help correct a few commonly held
misperceptions about HIV.
Transmission
HIV is spread by sexual contact with an infected person, by needle-sharing
among injecting drug users, or, less commonly (and now very rarely in
countries where blood is screened for HIV antibodies), through
transfusions of infected blood or blood clotting factors. Babies born to
HIV-infected women may become infected before or during birth, or through
breast-feeding after birth.
In the health-care setting, workers have been infected with HIV after
being stuck with needles containing HIV-infected blood or, less
frequently, after infected blood gets into the worker's bloodstream
through an open cut or splashes into a mucous membrane (e.g., eyes or
inside of the nose). There has been only one demonstrated instance of
patients being infected by a health-care worker; this involved HIV
transmission from an infected dentist to five patients. Investigations
have been completed involving more than 15,000 patients of 32 HIV-infected
doctors and dentists, and no other cases of this type of transmission have
been identified.
Some people fear that HIV might be transmitted in other ways; however, no
scientific evidence to support any of these fears has been found. If HIV
were being transmitted through other routes (for example, through air or
insects), the pattern of reported AIDS cases would be much different from
what has been observed, and cases would be occurring much more frequently
in persons who report no identified risk for infection. All reported
cases suggesting new or potentially unknown routes of transmission are
promptly and thoroughly investigated by state and local health departments
with the assistance, guidance, and laboratory support from CDC; no
additional routes of transmission have been recorded, despite a national
sentinel system designed to detect just such an occurrence.
The following paragraphs specifically address some of the more common
misperceptions about HIV transmission.
HIV in the Environment
Scientists and medical authorities agree that HIV does not survive well in
the environment, making the possibility of environmental transmission
remote. HIV is found in varying concentrations or amounts in blood,
semen, vaginal fluid, breast milk, saliva, and tears. (See below, Saliva,
Tears, and Sweat.) In order to obtain data on the survival of HIV,
laboratory studies have required the use of artificially high
concentrations of laboratory-grown virus. Although these unnatural
concentrations of HIV can be kept alive under precisely controlled and
limited laboratory conditions, CDC studies have showned that drying of
even these high concentrations of HIV reduces the number of infectious
viruses by 90 to 99 percent within several hours. Since the HIV
concentrations used in laboratory studies are much higher than those
actually found in blood or other specimens, drying of HIV- infected human
blood or other body fluids reduces the theoretical risk of environmental
transmission to that which has been observed- -essentially zero.
Incorrect interpretation of conclusions drawn from laboratory studies have
alarmed people unnecessarily. Results from laboratory studies should not
be used to determine specific personal risk of infection because 1) the
amount of virus studied is not found in human specimens or anyplace else
in nature, and 2) no one has been identified with HIV due to contact with
an environmental surface; Additionally, since HIV is unable to reproduce
outside its living host (unlike many bacteria or fungi, which may do so
under suitable conditions), except under laboratory conditions, it does
not spread or maintain infectiousness outside its host.
Households, Offices, and Workplaces
Studies of thousands of households where families have lived with and
cared for AIDS patients have found no instances of nonsexual transmission,
despite the sharing of kitchen, laundry, and bathroom facilities, meals,
eating utensils, and drinking cups and glasses. If HIV is not transmitted
in these settings, where repeated and prolonged contact occurs,
transmission is even less likely in other settings, such as schools and
offices.
Similarly, there is no known risk of HIV transmission to co- workers,
clients, or consumers from contact in industries such as food service
establishments (see information on survival of HIV in the environment).
Food service workers known to be infected with HIV need not be restricted
from work unless they have other infections or illinesses (such as
diarrhea or hepatitis A) for which any food service worker, regardless of
HIV infection status, should be restricted; The Public Health Service
recommends that all food service workers follow recommended standards and
practices of good personal hygiene and food sanitation.
Kissing
Casual contact through closed-mouth or "social" kissing is not a risk for
transmission of HIV. Because of the theoretical potential for contact
with blood during "French" or open-mouthed kissing, CDC recommends against
engaging in this activity with an infected person. However, no case of
AIDS reported to CDC can be attributed to transmission through any kind of
kissing.
Saliva, Tears, and Sweat
HIV has been found in saliva and tears in only minute quantities from some
AIDS patients. It is important to understand that finding a small amount
of HIV in a body fluid does not necessarily mean that HIV can be
transmitted by that body fluid. HIV has not been recovered from the sweat
of HIV-infected persons. Contact with saliva, tears, or sweat has never
been shown to result in transmission of HIV.
Insects
>From the onset of the HIV epidemic, there has been concern about
transmission of the virus by biting and blood-sucking insects. However,
studies conducted by researchers at CDC and elsewhere have shown no
evidence of HIV transmission through insects--even in areas where there
are many cases of AIDS and large populations of insects such as
mosquitoes. Lack of such outbreaks, despite intense efforts to detect
them, supports the conclusion that HIV is not transmitted by insects.
The results of experiments and observations of insect biting behavior
indiciate that when an insect bites a person, it does not inject its own
or a previous victim's blood into the new victim. Rather, it injects
saliva. Such diseases as yellow fever and malaria are transmitted through
the saliva of specific species of mosquitoes. However, HIV lives for only
a short time inside an insect and, unlike organisms that are transmitted
via insect bites, HIV does not reproduce (and, therefore, cannot survive)
in insects. Thus, even if the virus enters a mosquito or another sucking
or biting insect, the insect does not become infected and cannot transmit
HIV to the next human it feeds on or bites.
There is also no reason to fear that a biting or blood-sucking insect,
such as a mosquito, could transmit HIV from one person to another through
HIV-infected blood left on its mouth parts. Two factors combine to make
infection by this route extremely unlikely-- first, infected people do not
have constant, high levels of HIV in their bloodstreams and, second,
insect mouth parts do not retain large amounts of blood on their surfaces.
Further, scientists who study insects have determined that biting insects
normally do not travel from one person to the next immediately after
ingesting blood.
Effectiveness of Condoms
The proper and consistent use of latex condoms when engaging in sexual
intercourse--vaginal, anal, or oral--can greatly reduce a person's risk of
acquiring or transmitting sexually transmitted diseases, including HIV
infection.
Under laboratory conditions, viruses occasionally have been shown to pass
through natural membrane ("skin" or lambskin) condoms, which contain
natural pores and are therefore not recommended for disease prevention.
On the other hand, laboratory studies have consistently demonstrated that
latex condoms provide a highly effective mechanical barrier to HIV.
In order for condoms to provide maximum protection, they must be used
consistently (every time) and correctly. Incorrect use contributes to the
possibility that the condom could leak or break. Proper use should
include the following:
* Put on the condom as soon as erection occurs and before any sexual
contact (vaginal, anal, or oral).
* Leave space at the tip of the condom.
* Use only water-based lubricants. (Oil-based lubricants can weaken the
condom.)
* Hold the condom firmly to keep it from slipping off and withdraw from
the partner immediately after ejaculation.
When condoms are used reliably, they have been shown to prevent pregnancy
up to 98 percent of the time among couples using them as their only method
of contraception. Similarly, numerous studies among sexually active
people have demonstrated that a properly used latex condom provides a high
degree of protection against a variety of sexually transmitted diseases,
including HIV infection.
Condoms are classified as medical devices and are regulated by the Food
and Drug Administration. Each latex condom manufactured in the United
States is tested for defects, including holes, before it is packaged, and
several studies clearly show that condom breakage rates in this country
are less than 2 percent. Even when condoms do break, one study showed
that more than half of such breaks occurred prior to ejaculation.
Latex condoms can provide up to 98-99 percent protection against pregnancy
and most sexually transmitted diseases, including HIV infection, but only
if they are used consistently and correctly.
For more detailed information about condoms, see CDC's fact sheet, "The
Role of Condoms in Preventing HIV Infection and Other Sexually Transmitted
Diseases."
The Public Health Service Response
The U.S. Public Health Service is committed to providing the scientific
community and the public with accurate and objective information about HIV
infection and AIDS. It is vital that clear information on HIV infection
and AIDS be readily available to help prevent further transmission of the
virus and to allay fears and prejudices caused by misinformation. In
addition to research on the virus and its transmission, the PHS program to
prevent the spread of HIV/AIDS includes counseling, testing, and
education. Through these programs, individuals who have engaged in
high-risk behaviors can receive voluntary HIV-antibody testing for
themselves and their partners, and those found to be infected can be
counseled regarding preventive services and treatment options, as well as
how to prevent transmission to others.
For more information:
CDC National AIDS Hotline: 1-800-342-AIDS
Spanish: 1-800-344-7432
Deaf: 1-800-243-7889
CDC National AIDS Clearinghouse
P.O. Box 6003
Rockville, MD 20849-6003
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Question 2.2. How effective are condoms?
Update: Barrier Protection against Sexual Diseases
CDC National AIDS Clearinghouse
Although refraining from intercourse with infected partners remains the
most effective strategy for preventing human immunodeficiency virus (HIV)
infection and other sexually transmitted diseases (STDs), the Public
Health Service also has recommended condom use as part of its strategy.
Since CDC summarized the effectiveness of condom use in preventing HIV
infection and other STDs in 1988 (1), additional information has become
available, and the Food and Drug Administration has approved a
polyurethane "female condom." This report updates laboratory and
epidemiologic information regarding the effectiveness of condoms in
preventing HIV infection and other STDs and the role of spermicides used
adjunctively with condoms. *
Two reviews summarizing the use of latex condoms among serodiscordant
heterosexual couples (i.e., in which one partner is HIV positive and the
other HIV negative) indicated that using latex condoms substantially
reduces the risk for HIV transmission (2,3). In addition, two subsequent
studies of serodiscordant couples confirmed this finding and emphasized
the importance of consistent (i.e., use of a condom with each act of
intercourse) and correct condom use (4,5). In one study of serodiscordant
couples, none of 123 partners who used condoms consistently seroconverted;
in comparison, 12 (10%) of 122 seronegative partners who used condoms
inconsistently became infected (4). In another study of serodiscordant
couples (with seronegative female partners of HIV-infected men), three
(2%) of 171 consistent condom users seroconverted, compared with eight
(15%) of 55 inconsistent condom users. When person-years at risk were
considered, the rate for HIV transmission among couples reporting
consistent condom use was 1.1 per 100 person-years of observation,
compared with 9.7 among inconsistent users (5). Condom use reduces the
risk for gonorrhea, herpes simplex virus (HSV) infection, genital ulcers,
and pelvic inflammatory disease (2). In addition, intact latex condoms
provide a continuous mechanical barrier to HIV, HSV, hepatitis B virus
(HBV), Chlamydia trachomatis, and Neisseria gonorrhoeae (2). A recent
laboratory study (6) indicated that latex condoms are an effective
mechanical barrier to fluid containing HIV-sized particles. Three
prospective studies in developed countries indicated that condoms are
unlikely to break or slip during proper use. Reported breakage rates in
the studies were 2% or less for vaginal or anal intercourse (2). One
study reported complete slippage off the penis during intercourse for one
(0.4%) of 237 condoms and complete slippage off the penis during
withdrawal for one (0.4%) of 237 condoms (7). Laboratory studies indicate
that the female condom (Reality (trademark) **) -- a lubricated
polyurethane sheath with a ring on each end that is inserted into the
vagina -- is an effective mechanical barrier to viruses, including HIV. No
clinical studies have been completed to define protection from HIV
infection or other STDs. However, an evaluation of the female condom's
effectiveness in pregnancy prevention was conducted during a 6-moperiod for 147 women in the United States. The estimated 12-month failure
rate for pregnancy prevention among the 147 women was 26%. Of the 86 women
who used this condom consistently and correctly, the estimated 12-month
failure rate was 11%. Laboratory studies indicate that nonoxynol-9, a
nonionic surfactant used as a spermicide, inactivates HIV and other
sexually transmitted pathogens. In a cohort study among women, vaginal use
of nonoxynol-9 without condoms reduced risk for gonorrhea by 89%; in
another cohort study among women, vaginal use of nonoxynol-9 without
condoms reduced risk for gonorrhea by 24% and chlamydial infection by 22%
(2). No reports indicate that nonoxynol-9 used alone without condoms is
effective for preventing sexual transmission of HIV. Furthermore, one
randomized controlled trial among prostitutes in Kenya found no protection
against HIV infection with use of a vaginal sponge containing a high dose
of nonoxynol-9 (2). No studies have shown that nonoxynol-9 used with a
condom increases the protection provided by condom use alone against HIV
infection.
Reported by: Food and Drug Administration. Center for Population Research,
National Institute of Child Health and Human Development, National
Institutes of Health. Office of the Associate Director for HIV/AIDS; Div
of Reproductive Health, National Center for Chronic Disease Prevention and
Health Promotion; Div of Sexually Transmitted Diseases and HIV Prevention,
National Center for Prevention Svcs; Div of HIV/AIDS, National Center for
Infectious Diseases, CDC.
Editorial Note: This report indicates that latex condoms are highly
effective for preventing HIV infection and other STDs when used
consistently and correctly. Condom availability is essential in assuring
consistent use. Men and women relying on condoms for prevention of HIV
infection or other STDs should carry condoms or have them readily
available.
Correct use of a latex condom requires 1) using a new condom with each act
of intercourse; 2) caref handling the condom to avoid damaging it with
fingernails, teeth, or other sharp objects; 3) putting on the condom after
the penis is erect and before any genital contact with the partner; 4)
ensuring no air is trapped in the tip of the condom; 5) ensuring adequate
lubrication during intercourse, possibly requiring use of exogenous
lubricants; 6) using only water-based lubricants (e.g., K-Y jelly
(trademark) or glycerine) with latex condoms (oil-based lubricants (e.g.,
petroleum jelly, shortening, mineral oil, massage oils, body lotions, or
cooking oil) that can weaken latex should never be used); and 7) holding
the condom firmly against the base of the penis during withdrawal and
withdrawing while the penis is still erect to prevent slippage.
Condoms should be stored in a cool, dry place out of direct sunlight and
should not be used after the expiration date. Condoms in damaged packages
or condoms that show obvious signs of deterioration (e.g., brittleness,
stickiness, or discoloration) should not be used regardless of their
expiration date.
Natural-membrane condoms may not offer the same level of protection
against sexually transmitted viruses as latex condoms. Unlike latex,
natural- membrane condoms have naturally occurring pores that are small
enough to prevent passage of sperm but large enough to allow passage of
viruses in laboratory studies (2).
The effectiveness of spermicides in preventing HIV transmission is
unknown. Spermicides used in the vagina may offer some protection against
cervical gonorrhea and chlamydia. No data exist to indicate that condoms
lubricated with spermicides are more effective than other lubricated
condoms in protecting against the transmission of HIV infection and other
STDs. Therefore, latex condoms with or without spermicides are
recommended.
The most effective way to prevent sexual transmission of HIV infection and
other STDs is to avoid sexual intercourse with an infected partner. If a
person chooses to have sexual intercourse with a partner whose infection
status is unknown or who is infected with HIV or other STDs, men should
use a new latex condom with each act of intercourse. When a male condom
cannot be used, couples should consider using a female condom.
Data from the 1988 National Survey of Family Growth underscore the
importance of consistent and correct use of contraceptive methods in
pregnancy prevention (8). For example, the typical failure rate during the
first year of use was 8% for oral contraceptives, 15% for male condoms,
and 26% for periodic abstinence. In comparison, persons who always abstain
will have a zero failure rate, women who always use oral contraceptives
will have a near-zero (0.1%) failure rate, and consistent male condom
users will have a 2% failure rate (9). For prevention of HIV infection and
STDs, as with pregnancy prevention, consistent and correct use is crucial.
The determinants of proper condom use are complex and incompletely
understood. Better understanding of both individual and societal factors
will contribute to prevention efforts that support persons in reducing
their risks for infection. Prevention messages must highlight the
importance of consistent and correct condom use (10).
References
1. CDC. Condoms for prevention of sexually transmitted diseases. MMWR
1988;37:133-7.
2. Cates W, Stone KM. Family planning, sexually transmitted diseases, and
contraceptive choice: a literature update. Fam Plann Perspect
1992;24:75-84.
3. Weller SC. A meta-analysis of condom effectiveness in reducing sexually
transmitted HIV. Soc Sci Med 1993;1635-44.
4. DeVincenzi I, European Study Group on Heterosexual Transmission of HIV.
Heterosexual transmission of HIV in a European cohort of couples (Abstract
no. WS-CO2-1). Vol 1. IXth International Conference on AIDS/IVth STD
World Congress. Berlin, June 9, 1993:83.
5. Saracco A, Musicco M, Nicolosi A, et al. Man-to-woman sexual
transmission of HIV: longitudinal study of 343 steady partners of infected
men. J Acquir Immune Defic Syndr 1993;6:497-502.
6. Carey RF, Herman WA, Retta SM, Rinaldi JE, Herman BA, Athey TW.
Effectiveness of latex condoms as a barrier to human immunodeficiency
virus- sized particles under conditions of simulated use. Sex Transm Dis
1992;19:230- 4.
7. Trussell JE, Warner DL, Hatcher R. Condom performance during vaginal
intercourse: comparison of Trojan-Enz (trademark) and Tactylon (trademark)
condoms. Contraception 1992;45:11-9.
8. Jones EF, Forrest JD. Contraceptive failure rates based on the 1988
NSFG. Fam Plann Perspect 1992;24:12-9.
9. Trussell J, Hatcher RA, Cates W, Stewart FH, Kost K. Contraceptive
failure in the United States: an update. Stud Fam Plann 1990;21:51-4.
10. Roper WL, Peterson HB, Curran JW. Commentary: condoms and HIV/STD
prevention -- clarifying the message. Am J Public Health 1993;83:501-3.
* Single copies of this report will be available free until August 6,
1994, from the CDC National AIDS Clearinghouse, P.O. Box 6003, Rockville,
MD 20849- 6003; telephone (800) 458-5231.
** Use of trade names is for identification only and does not imply
endorsement by the Public Health Service or the U.S. Department of Health
and Human Services.
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Question 2.3. How do you minimize your odds of getting infected?
"Playing the AIDS Odds" (21 Oct 93)
Robert S. Walker, Ph.D. Phone: (210)224-9172
Emeritus professor Internet: rwalker@trinity.edu
Trinity University, Pol.Sci.
715 Stadium Drive office: 128 Main Plaza, No.310
San Antonio, TX 78212 San Antonio, TX, 78205
Everyone worries about the degree of transmission-risk involved in various
activities. Can you get infected from mutual masturbation? From fisting?
>From using poppers? From this and from that? The real question is, "Is it
possible to provide answers with sufficient precision to allow an
individual confidently to assess risk and modify behavior in specific
situations?" The answer is "No." No one knows enough about either sexual
or drug behaviors, and their relation to HIV sero- conversion, to speak
with assurance. But this doesn't mean that meaningful recommendations are
out of the question.
Those interested in risk assessment might read two articles representing
different approaches. First: Michael Shernoff, "Integrat- ing Safer Sex
Counseling into Social Work Practice, Social Casework: The Journal of
Contemporary Social Work, vol. 69 (1988), pp. 334-339. The author offers
a scaled list of 30 sexual behaviors from abstinence through fisting to
condomless, receptive anal intercourse. The list is graded from "least
likely" to transmit virus to "most likely." Some of the relative rankings
are arguable, but the biggest problem is that the intervals of the "risk"
scale are not equal. For example, #29 is "vaginal intercourse to orgasm
without condoms," #30 is "anal inter- course to orgasm without condoms;"
these two are separated by the same scaler distance as abstinence (no.1)
and solitary masturbation (no.2). But everyone agrees that, anal
intercourse is many times more dangerous than vaginal for the receptive
partner, not just "one interval" more dangerous. Such lists are not too
useful; I doubt that any subscriber to this list needs to be told that
solitary masturbation is safer than receptive anal intercourse. Further,
until a lot more is known about the relationships between specific
behaviors and sero-conversion, the intervals cannot be meaningfully
quantified.
The second article is Norman Hearst and Stephen B. Hulley, "Heterosexual
AIDS," Journal of the American Medical Association, April 22, 1988. The
authors calculate probabilities for HIV transmission for different
parameters (such as: the area's seroprevalence rate, the infectiousness of
a partner, the condom/spermicide failure rate, and the number of sexual
encounters). The "odds" of transmission with different parameters (such
as: 500 encounters, .01 condoms failure rate, area seroprevalence of
.0001, and so forth) are then projected. The resulting odds range from a
"low" of 1 chance in 5 billion to a "high" of 1 transmission in 500
encounters. In the lowest risk example, there is 1 in 5 billion chance
that HIV will be transmitted when: (1) your partner tests negative; (2)
he/she has no history of high-risk behavior; (3) condoms are used in
intercourse, and the condom failure rate is .01; (4) the area
seroprevalence rate is 0.000001, (5) the infectivity value is 0.002; and
(6) there is only one sexual encounter.
As behavioral guides, neither approach is very helpful. When the possible
sex or drug scenarios become as disparate as they are in real-life
situations, and when the odds resemble your chances of winning a major
lottery, then stating intervals or odds does not provide much more than a
illusion of knowledge and resulting security.
I suggest a different approach to thinking about risk. First, do not
worry about practices for which there is no documentation of transmission
(as distinct from speculation about it). If there is any risk in kissing,
masturbation, skinny-dipping or whatever, it is probably much less than
the chance of being hit by lightning - and few people worry about that.
Focus on those activities, like intercourse and/or injecting drugs, which
common sense tells you are risky, if for no other reason than that they
have a long history of transmitting other diseases (like syphilis or
hepatitis). Such behaviors would clearly include injecting drug use
within a group, condomless anal and/or vaginal intercourse, and less
clearly oral sex, fisting, or any S&M practice that involved a possible
blood exchange.
Second, take into account the overall setting within sexual or drug
activity is taking place. While it seems that we are all biologically at
equal risk, we do not face equal environmental risks. While HIV
theoretically can spread uniformly from the North to the South pole, it
has not in fact done so. It is one thing to pick up someone at a bar in
Brahma, Oklahoma and another in San Francisco, California. The risk
involved in employing a prostitute in Des Moines is much less than in
Newark, NJ or Washington D.C. where the seroprevalence rate among
prostitutes is very high. Similarly, patronizing a Newark shooting gallery
or crack house is like asking for AIDS, but the risk of transmission
within the West Coast drug scene is much less. For area comparisons see
the Centers for Disease Control's quarterly HIV/AIDS Surveillance Report,
and/or Jonathan Mann et al, AIDS in the World, Harvard U. Press, 1993.
What I am suggesting is that some information plus common sense is a
better guide than current statistical or quasi-statistical statements
about relative risk. This will remain the case until a great deal more
empiric data is amassed about some of our most private behaviors. If you
are a person who does not feel comfortable without precise, reliable,
quantified guidelines, then your only course is to abstain from activities
wherein there is a possibility of transmission. There are many
mood-altering substances that do not require injection, and a lot of
sexual behavior that does not involve penetration and fluid exchange.
With respect to non-sex or drug modes of transmission, all one can say is
that there have been no documented cases of transmission through insect
bites, shared utensils, shared occupational space or equipment, food
handling, and so on. Theoretical risks for an infinite number of imagined
scenarios can be computed, but in the actual world there are no data
supporting transmission in these scenarios. An excellent survey of 14
principal articles searching for data on other routes of transmission can
be found in: Robyn R.N Gershon et al, "The Risk of Transmission of HIV-1
Through Non-Percutaneous, Non-Sexual Modes: A Review," Department of
Environmental Health Sciences and Department of Epidemiology, The Johns
Hopkins University School of Hygiene and Public Health, distribut- ed by
New York City's Gay Men's Health Crisis, AIDS Clinical Update, October 1,
1990. There have been cases of transmission through transfusions
/transplants of contaminated whole blood, blood products, donor organs,
and dental work. The only thing one can do is to be aware of the
possibility, and make sure that those who treat you take all precautions.
Currently, the only way to load the dice in your favor is to use common
sense in any situation wherein someone else's body fluids might be
introduced into yours through sexual or drug behaviors. If one can
foresee that there would be opportunity for fluid exchange - blood, semen,
vaginal secretions - then a large measure of safety can be had from the
use of condoms (see: Condom Faq) and/or your own works for injecting
drugs. The only safer course - and it is an honorable and intelligent one
- would be to abstain from such activities altogether.
What must be kept in mind is that the risk of HIV transmission is totally
unlike the risk of losing at the races. Because you cannot recoup the
loss represented by infection, you ought not think of the "odds" in the
same way. In fact, it is better not to focus on the so- called "odds" at
all. Given that (1) infection almost always leads to AIDS (estimates=95%),
and (2) that AIDS almost always leads to death (estimates=99%), people
must now think of sex or injecting drug use as an all-or-nothing game, .
Each time you play, there are only two possible outcomes. If you win you
have, perhaps, enjoyed a pleasant encounter; if you lose, you die. And
each time you play without regard to common sense evaluation and personal
protection, you enhance the possibility that you will lose. Its as simple
as that.
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Question 2.4. How risky is a blood transfusion?
The following October 15, 1993 United Press International article, was
summarized in the CDC AIDS Daily News Summary.
"CDC Study Finds Five Transfusion-Related AIDS Cases Per Year" United
Press International (10/25/93)
Miami Beach, Fla.--Since screening for HIV began in 1985, very few people
have become infected with the virus via blood transfusions, according to
experts at the Centers for Disease Control and Prevention. The rate of
transfusion-related AIDS cases rose steadily from 1978 to 1984, then fell
dramatically when testing began in 1985, said the CDC. Officials report
that between 1986 and 1991, the number of such cases may have been as low
as five per year. "While the risk of getting AIDS from a transfusion is
not zero, this study corroborates other CDC research and published data
indicating that the risk is extremely low," said Dr. Arthur J.
Silvergleid, president of the American Association of Blood Banks. A
total of 4,619 individuals are believed to have been infected through the
blood supply. Each year in the United States, about 4 million people
receive blood transfusions.
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Question 2.5. Can mosquitoes transmit AIDS?
Please see Q2.1 `How is AIDS transmitted?' for general information about
insects and AIDS transmission.
Malaria is transmitted to humans through mosquito bites. Why can't AIDS
be transmitted this way?
Plasmodium, the protozoan that causes malaria, is highly specialized to
infect through a mosquito vector. The gametocytes ingested by the mosquito
from an infected host undergo a further stage of development and give rise
to sporozoites. These migrate through the insects body until they reach
the salivary glands . They are then injected into a new host by the
mosquito along with its saliva which is an anti-coagulant and needed to
stop clotting.
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Question 2.6. What about other insect bites?
From: "Natural History", July 1991, p. 54:
Acquired Immune Deficiency Syndrome (AIDS), the deadly epidemic caused by
the HIV virus, is most often transmitted by contaminated hypodermic
needles or sexual contact. Since mosquitos feed on human blood and may
attack a series of individuals, the question arises: can you get AIDS from
a mosquito bite?
According to Jonathan F. Day, of the University of Florida's Medical
Entomology Laboratory, insects can transmit viruses in two ways,
mechanically and biologically. With mechanical transmission, infected
blood on the insect's mouthparts might be carried to another host while
the blood is still fresh and the virus still alive. Infection by this
means is possible but highly unlikely, because mosquitos seldom have fresh
blood on the outside of their mouthparts. Mechanical transmission does
occur in horses, however, with equine infectious anemia, a virus closely
related to AIDS and transmitted by horseflies. These flies are "pool
feeders"; their bite causes a small puddle of blood to form, and they
immerse their mouthparts, head, and front legs while lapping it up. If
disturbed, however, they quickly move on to another horse, where the fresh
blood of the two hosts may mingle. Blood-feeding mosquitos are much neater
and more surgical; they insert a tube for drawing blood, and by the time
they are ready for their next meal, even on a second host following an
interrupted meal, any viruses from their first meal are safely stored away
in their midgut.
With biological transmission, the pathogen must complete a portion of its
life cycle within the carrier, or vector species. Protozoans that cause
malaria, for instance, go through an extremely complex cycle within the
mosquito, eventually congregating in the salivary glands, from which they
may infect avian, primate, rodent, or reptilian hosts, depending on the
malaria species. The HIV virus, however, does not replicate or develop in
the mosquito; once in the insect's gut, the virus quickly dies. Repeated
studies since 1986 show that AIDS-infected blood fed to mosquitos and
other arthopods does not live to be passed on and that, fortunately, there
is no biological-transmission cycle of AIDS in blood-feeding arthopods,
which frequently ingest the virus as part of their blood meal.
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Question 2.7. Is there even a remote chance of insect transmission?
An interesting paper is:
Do Insects Transmit Aids?
by Lawrence Miike
Health Program; Office of Technology Assessment
United States Congress; Washington D.C. 20510-8025
September 1987 -- A Staff Paper in OTA's Series on
AIDS-Related Issues
For sale by the Superintendent of Documents
U.S. Government Printing Office
Washington, D.C. 20402
This paper indicates that "The conditions necessary for successful
transmission of HIV through insect bites, and the probabilities of their
occurring, rule out the possiblility of insect transmission of HIV
infection as a significant factor in the way AIDS is spread. If insect
transmission is occurring at all, each case would be a rare and unusual
event."
Miike suggests that there are two theoretical mechanisms by which biting
insects might transmit HIV infections: 1). biological (insect's saliva
to person's blood) and 2). mechanical (HIV-infected person's fresh blood
to another's blood). Based on experimental results, they were able to
rule out biological transmission. This leaves mechanical transmission
during interrupted feeding as a viable mechanism. So it COULD happen;
HOWEVER...
"The probability of HIV transmission from an insect bite would be
calculated by multiplying (not adding, because each event's probability is
independent of each other) the following factors: 1) how frequently
interrupted feeding occurs, 2) the probability the the insect had bitten
an HIV-infected person prior to biting an uninfected person, and 3) the
probability that the insect bite contained enough HIV to transmit
infection."
"The frequency of interrupted feeding depends on the type of insect; in
general, the larger the insect and the more painful the bite -- such as
horse flies -- the greater the probability that interrupted feeding will
occur. Other bites, such as from mosquitoes and bedbugs, are usually
unnoticed and therefore usually uninterrupted. With others, such as
ticks, if their feeding is interrupted, the probability of quickly
transferring to another person is extremely low."
"In mechanical transmission, the maximum amount of HIV that insects would
be able to transfer would be the amount of virus in the blood they had
ingested prior to biting an uninfected person. Experience with viruses
actually transferred in this manner has shown that the amount of blood
that might be transferred is limited to the amount of blood on the
insect's mouthparts (on the order of 1/100,000 of a milliliter of blood).
An uninfected person would also have to be bitten within an hour of the
insect's biting an infected person; and both infected and uninfected
persons would have to be in close proximity to each other (a few hundred
feet for mosquitoes and biting flies, in the same household for bedbugs),
or else the insect will not have an opportunity to transfer to another
person if its feeding was interrupted."
"Most HIV-infected persons (70-80 percent) do not have detectable levels
of infectious virus in their blood. Those that do have measurable HIV
have very low levels, much below the levels that are needed for insect
transmission of other viral diseases. Only rarely does an HIV-infected
person have a blood virus level that might contain enough infectious HIV
for insect transmission."
There you go... it seems that you CAN become HIV-infected via a mosquito
bite. Then again, you CAN also win the multi-million dollar lotto game
five times consecutively! 8-) I wouldn't lose any sleep worrying about
either of those.