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Fighting Disease:
Health At The End Of The Millennium
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Q&A with Dr. Stephen Corber

Questions sent in via e-mail and posted on the "Fighting Diseases" discussion board by students were answered by Dr. Stephen Corber, Director, Division of Disease Prevention and Control, Pan American Health Organization (PAHO).

Question 1
We have invented vaccines for many viral infections. How close are we to an AIDS vaccine? Why is AIDS so much harder to vaccinate against?

Seventh Grade
New Athens Jr. High
New Athens, Illinois

There are basically 2 reasons why there have been no successful vaccines developed against AIDS so far.

a) It normally takes several years to develop a vaccine against a disease. When a person is infected by a virus, he/she generally learns to develop antibodies to the virus. The next time he/she is infected by that virus, he/she has antibodies prepared. They attack the virus and neutralize it before it can multiply and cause illness.

In vaccinating people against the disease we try to expose them to something that is very similar to the real virus. When people are injected with this vaccine they will produce antibodies. We hope that the vaccine is so close to the real virus that these antibodies that have been produced will also work on the virus. In the future when they are exposed to the "real" virus these antibodies will react to it and neutralize it before it can cause illness.

AIDS is a new disease and we have had to learn about the virus which causes it, HIV, before we could produce the vaccine. This virus has proven to be very complicated in the way it attacks the body -- it stimulates antibody production but these antibodies are not effective in destroying the virus. It also changes itself in ways that we have not seen before. This has made the development of a vaccine extremely difficult.

b) Companies who develop vaccines must put these proposed vaccines through several experiments. They have to be sure first that the vaccine is safe and then that it will prevent the disease. For this we often use animal experiments before trying a vaccine on humans. You can appreciate that each of these experiments takes months and the results must reviewed with care. So in fact it usually takes years to develop a vaccine.

There has been a tremendous effort by researchers around the world to develop a vaccine against AIDS. At present there are some vaccines being proposed for experiments in human beings and I think some countries have agreed to participate. I think it will still be a few years at least before a vaccine will be available for AIDS.

Question 2
How has the incidence of HIV/AIDS in the U.S. grown in the 1990's and what is the projected percentage of infected people by 2006 (the year I graduate from college)?

Todd Archer
7th grade

We do not have good figures for the incidence of HIV in the USA because in most States it is not a reportable condition. AIDS itself must be reported to public health authorities, so that whenever a doctor sees a new patient with AIDS it is reported. Laboratories that test people to see if they are infected must also report AIDS cases.

In the USA the incidence rates of AIDS for every million people were:
1990: 192.4
1991: 234.8
1992: 303.5
1993: 297.3
1994: 256.6
1995: 212.9

You can see that the rates of AIDS continued to increase until 1992-3 and then they began to decrease. We do not know whether this is because there were fewer people infected or whether many people infected with HIV were taking medication which made it take longer for the HIV infection to turn into AIDS.

For more detailed information about what is being predicted for the future, you can contact the CDC National AIDS Clearinghouse. Telephone: 1-800-458-5231. Their e:mail is You could also browse their web page at

Question 3
Lately there has been a lot of talk about the drug cocktail that is being given to people with HIV and AIDS. In certain people the drugs have no effect. If this is true than don't they run the risk of mutating the virus? What happens if just one dosage of the medicine is missed, but the user then continues on the regular dossage? Does it build up the resistance of the virus?

High school student in the California Bay Area

When people take one drug against an infection, the bacteria may develop resistance to the drug. This tends to occur more frequently when the "patient" must take the drug for a long time. (As the bacteria multiplies during this period, it may have some changes in genes that protect it against the drug and, of course, these bacteria, unaffected by the drug, multiply in the "patient" and can be transmitted to other people.)

To prevent the development of this resistance, doctors often prescribe several drugs at the same time. This is very effective. However, it can be more uncomfortable for the patient to take more pills.

In the case of the cocktail for HIV, it does seem to be successful in delaying the onset of AIDS in many people. It may even be effective in preventing the development of AIDS completely. (We do not have enough experience with them to know yet.) Of course, we do not yet know the effect of missing 1 or more doses of the cocktail. I would suspect that this would depend of the severity of the infection in each person and many other factors. But I do not think that missing 1 dose would cause resistance to develop.

As you know the cocktail is new. We have not had enough time to see how well it acts over a long time. At this time we do not know how long this cocktail will be effective or whether resistance will develop. The fact that the drugs are given together reduces significantly the chance of resistance developing.

Question 4
My name is Robin Chauvin, I am 15 and a Sophmore at De Anza High School in El Sobrante, California. I have a few questions. Why do some people get Chicken Pox worse than others? Ex. When I had Chicken Pox, I had it only on the external surfaces of my skin (i.e. arms, legs, etc.), but when my sister had it, she had it on her internal and external surfaces of her body including the insides of her mouth and throat to name a few. And why is it better to have Chicken Pox when you are a child rather than when you are an older person such as a person in their 70's or 80's? Is your immune system weaker, or what?

We really do not know why some people get more severe cases of chickenpox. We believe that it perhaps has something to do with the immune system. If someone has a weaker immune system, it may be more likely that the virus can multiply more and cause more damage than it does in people who have a fully functioning immune system.

You are correct. Generally chickenpox is a milder disease in children than it is in the elderly. Again, we believe that this is due to a weakening of the immune system of the elderly. Perhaps the elderly are suffering form other stresses or infections and their immune system is not able to concentrate on the chickenpox virus.

Question 5
By studying these diseases - watching them mutate and get worse as we're trying to find cures - are we not still putting the entire human race at more risk? Nature, as we know through history, does noy like to be messed with. How much more doe we need to know and are there safer ways of aquiring the information?

Please respond I 'm a tenth grade student from De Anza High School,
Richmond, California
David Sloane

You raise a very important point. We cannot stop our desire to learn more or to improve our condition through research and science. However, we must be careful not to do more harm than good. In fact, the first rule of doctors is "Do no harm".

There is a danger that research that we do might affect the future of other living organisms and with the environment. In these cases we must make an assessment as to whether the possible benefits of the research is worth more than the possible harm which may occur.

For this reason most countries have established laws and procedures on what type of research is permissible and how it must be carried out. These laws must be changed from time to time to take into account new knowledge. For example, now that cloning has become a possibility, and an active area of research, we must make sure that what we do is in line with our ethics and values.

Of course, not everyone always agrees on what should be in the laws and procedures, but this is certainly the best way we have found to date to resolve this question. We value our freedom to pursue our interests as long as they don't affect others in our society and I do believe that rules which are too restrictive or prohibitive would not be appropriate.

Question 6
How many airborne diseases are known? And how many can be lethal?

Mike McMillan

There are numerous airborne diseases -- too many for me to count. Bacteria, viruses, fungi, and other organisms can all be transmitted through the air and their are thousands of each of these. I think your second question really gets to the point: "How many are lethal?"

The severity of any infection depends on several factors:

a) How virulent (strong) is the bacteria or virus that is causing the illness and how big a dose did the person get?

b) How good are the defenses of the person? For example, people may ave been vaccinated against certain very serious infections, such as polio. Also, people who are weakened by other conditions or by age may be more likely to die from a given infection. This is true for influenza, for example. This disease usually causes a few days or a week of fever and discomfort in young people. But each year it causes thousands deaths in the elderly, particularly if they are suffering from other illnesses at the same time.

c) Do we have good medicines? As you know we have antibiotics that are extremely effective against many infectious diseases. Even in cases where there are no antibiotics that are effective, doctors can often keep people alive through life-support measures until the person's own defenses can become strong enough to recover.

Question 7
Our teacher said that scientists were going to dig up bodies that contained the 1918 influenza virus to study it. Is that true? Should they be allowed to?

Jackie de los Reyes

The bodies have already been looked at. This is done to help us to learn more about the disease that killed millions of people at that time. By studying the virus, we can learn more about how to protect ourselves against it in the future. When such procedures are carried out special precautions are taken to ensure that the virus does not affect the people working with the body.

Question 8
What is the hanta virus? Where is it located in the world?

Jackie de los Reyes

Hantaviruses infect rodents worldwide. They can be transmitted to human beings when people are in close contact with these rodents and they can cause various types of disease.

In 1993 there as on outbreak of disease in the USA caused by a new hantavirus. This is a very severe disease characterized by a fever, chills and muscle aches, followed by a sudden difficulty in breathing which can be severe and even fatal. This form of disease called "hantavirus pulmonary syndrome" has now been seen in many countries, including Argentina, Chile, Paraguay, the Balkan countries and Asia.

Since 1993 there have been 155 cases reported in the USA. The age range of the patient has ben from 11 years to 69 years. 60% of the patients have been male and 74 (or 47.7%) have died.

Question 9
Why have some epidemics started in Peru?

This is a very difficult question. I am aware that cholera started in Peru again in 1991 and that there have been outbreaks of yellow fever and plague in that country that have not spread in major ways to other countries to date.

Several factors can contribute to an outbreak of infectious disease:

- poor water supply (which contains bacteria or viruses)
- poor waste disposal (garbage is lying about and rats and insects which carry disease are attracted to it and come into contact with people)
- unhealthy cooking practices (especially if the food is being prepared for may people)
- poverty which does not allow people to take the proper precautions when cooking or eating)
- development of new rural areas which exposes people to insects or viruses which are new to them and for which they are not prepared.

Several of these factors occur at times in Peru -- and in many other counties too, many of which also have outbreaks of infectious diseases. In addition Peru has a very interesting geography, with an arid coast, a very crowded major city with surrounding slums, a poorly accessible mountain region with relatively poor communications by North American standards, and an even more remote jungle area. This variety in its geography creates the possibility of a wider variety of infectious diseases occurring. And luck plays a role too -- whether infected people are visiting, etc.

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