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Several years before the AIDS epidemic, many gay men became infected by intestinal parasites which previously had occurred mostly in the tropics. These diseases -- mainly amebiasis and giardiasis -- started to spread through sexual transmission, to infect as many as 60 percent of gay men. Once infected, persons can carry the parasites for years unless they are treated. Many gay men show only slight symptoms or none at all, yet they may have a loss of energy, and can spread the infection to others.

Now scientists are studying the relationship of intestinal parasites to AIDS. Many of them suspect that the AIDS virus usually cannot cause the disease by itself, but that other factors usually help it to infect. These "cofactors" do not cause AIDS, but may make it more likely that exposure to the virus will develop into the disease. Some experts believe that the continuing epidemic of parasites among gay men has been a cofactor for AIDS and a major contributor to its spread.


This theory has important practical value, because it suggests ways to reduce the risk of AIDS, both in those not yet exposed and in those have a positive antibody test and may already have the virus. Doctors and scientists still differ in their interpretation of the available information about parasites and AIDS, but there is little argument about what people need to do to protect themselves. Gay men should get tested regularly for parasites, and have them eradicated if they are found, and take steps to avoid transmission.


But since scientists don't know for sure that parasites contribute to AIDS, national public policy has largely ignored this approach, as it has ignored so many promising leads toward AIDS prevention and treatment. Individuals must take the initiative and learn on their own how to get the best possible protection for themselves and others. Fortunately, the San Francisco Health Department does have an active program for parasite eradication; and many private physicians here have experience in handling this problem. Still, each individual must make the decision to take advantage of the services which are available.


Evidence That Parasites May Help Cause AIDS



The scientific case against parasites is complex, and scattered in many different publications. Here we will outline some of it, and the best possible mechanisms involved, then we will suggest other sources for detailed information.


* Laboratory studies have shown that the AIDS virus is much more infective against helper T-cells which are "activated" -- meaning that they are doing their job in fighting disease. Ordinary minor diseases and infections increase activation of the T-cells for a few days or so, but the parasites (like other chronic infections) can cause a permanent increase.


* Parasites also can suppress other components of the immune system, perhaps as part of the mechanism by which they protect themselves against it.


* Suppressed immunity can open the door to the AIDS virus. For example, in one incident in Scotland, 300 hemophiliacs were given a blood product later found to contain the AIDS virus. Only about half of them became antibody positive. Scientists then studied frozen blood samples taken before these people were exposed, and found that the main difference between the groups was that those who became positive had had a suppressed immune system to start with. In those with good immunity, the virus did not get far enough to cause the antibodies to be produced.

* Parasites may damage the intestinal wall, which may make it easier for the AIDS virus to get into the bloodstream. Also, intestinal wall damage allows undigested proteins in food to get into the blood, causing further activation of the T-cells because they try to fight this protein.

* Parasites and intestinal damage cause malabsorption and resulting malnutrition, further weakening the body and the immune system.

* All the populations which have developed AIDS have had cofactors, either parasites or other conditions which could have the same effect on the immune system. For example, central Africa, Haiti, and Belle Glade, Florida, where AIDS is epidemic through heterosexual transmission, all have warm climates and poor sanitation, conditions which lead to prevalence of parasitic diseases; and those with the parasites are much more likely to test positive for the AIDS virus than those without. Hemophiliacs and transfusion recipients seldom have parasites, but they regularly receive foreign substances in the blood, which may cause similar immunological effects. The same applies to intravenous drug users.

* One group which should have the highest risk for AIDS in fact has practically none. Of about two hundred "needlestick" cases -- medical or laboratory workers who cut themselves with contaminated needles or other instruments -- almost nobody has developed even a positive antibody response, let alone ARC or AIDS. It is possible that lack of parasites or other cofactors contributed to the very low rate of infection.

Diagnosis and Treatment Issues

Symptoms of parasites can include loose stools, flatulence (gas), or diarrhea (usually mild), and especially malaise -- feeling ill, depressed, or tired. Often these problems come and go, so people don't recognize them as symptoms. They think they are tired because they work hard, or because that's just the way they are. In one study, for example, about

half the gay men in San Francisco who had amebiasis did not recognize any symptoms at all.

Diagnosis is by no examination of stool samples. Unfortunately, the parasites are easy to miss in the lab. Taking three stool samples gives about an 80 percent chance of finding them if they are there.

The available treatments have drawbacks. Flagyl, the oldest antibiotic for treating amebiasis and giardiasis, causes unpleasant side effects, and very large doses have caused cancer in laboratory animals. But flagyl is very effective, and it kills a wide variety of disease-causing organisms. It is often used for infections acquired in the tropics, and it has a long history of being used widely.

The sexually transmitted amebiasis is less virulent than the strains found in the tropics, so physicians can usually use milder drugs, such as humatin (also called paromomycin). Humatin does not leave the digestive system, so it does not have side effects elsewhere in the body. It is about 95 percent effective for amebiasis. One disadvantage of humatin is the expense; it costs about sixty dollars for the treatment. All of these drugs can cause serious side effects in rare cases, so they must be used carefully by doctors. It is best to consult a physician who has experience in treating these parasites; you could get referrals through the San Francisco Health Department, or through various organizations concerned with AIDS or other sexually transmitted diseases.

Persons who live or work in San Francisco can use the screening program run by the San Francisco Health Department. There is a small clinic fee which can be waived if you do not have the money. If you test positive, you can be treated by your own physician, or at a Health Department clinic. This program is strictly confidential to protect your privacy. For more information about San Francisco's program of screening for parasites, call the San Francisco City Clinic.

Other Treatment and Prevention Issues

* Any kind of drug may be more dangerous to persons with ARC or AIDS. Only an experienced physician can recommend the treatment appropriate for each individual.

* It's very important that sexual partners be diagnosed for parasites and treated together, to prevent re-infection.

* The safe-sex guidelines for preventing AIDS will not always stop transmission of parasites. In addition to safe sex, persons must also avoid transmission of feces, for example through toys or by careless handling of condoms after use. Tiny amounts of feces, too small to see or smell, can contaminate hands, other parts of the body, or other objects, and later get into the mouth during eating, smoking, or other activities, causing an infection.

* Some intestinal protozoa (single-celled animals) are called "non-pathogenic", meaning that they do not cause obvious disease. They might be cofactors for AIDS; no one knows at this time. Also, they may be "markers" for the more serious organisms that were missed in the test. Physicians differ on whether treatment should be given if only non-pathogens are found.

* Some people use Chinese medicine or other herbs as an alternative to antibiogics like flagyl or humatin. These may be effective in some cases, but you should be tested afterwards to see if the treatment worked.


Most people exposed to the AIDS virus do not get AIDS. That's why it is so important to look for "cofactors," to find out what factors can reduce or increase the risk of AIDS in those who are exposed to it. By eliminating suspected cofactors, we can help to protect ourselves against AIDS.

At this time there is no conclusive proof that parasites are a cofactor, but there is considerable evidence. In any case, the parasites are a serious helath problem which is epidemic in our community. All gay men should get tested periodically, have these diseases eradicated if they are found, and take care to avoid transmission. This is one measure that all of us (and
especially those with a positive antibody test) can take to protect ourselves and others against AIDS.


Archer, Douglas L. and Walter H. Glinsmann, "Enteric Infection and Other Cofactors in AIDS," Immunology Today (October 1985).

Pearce, Richard B., "Intestinal Protozoal Infections and AIDS," The Lancet (July 2, 1983).

-------, "Parasites and AIDS: Evidence of a Link," DAIR Update, Number 1, published by the Documentation of AIDS Issues and Research Foundation.

Zagury, D., et al., "Long-term Cultures of HTLV-III-infected T- cells: A Model of Cytopathology of T-cell Depletion in AIDS," Science (February 21, 1986).


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