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? ------------------------------------------------------------------------------- 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 ------------------------------------------------------------------------------- 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. ------------------------------------------------------------------------------- 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: email@example.com 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. ------------------------------------------------------------------------------- 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. ------------------------------------------------------------------------------- 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. ------------------------------------------------------------------------------- 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. ------------------------------------------------------------------------------- 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.