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Characteristic tested set at

Did an epidemic occur?

Yes

Did an epidemic occur?

Yes

Maximum number sick

Maximum percentage sick

Maximum occurred on day

Summary

Write a one- to two-sentence summary that describes how the likelihood of an epidemic changes as your disease characteristic changes.

Master 4.4

Characteristics of Smallpox,

Polio, and Measles

Duration of

Rate of

Immunization Level

Disease

Virulence

Infection

Transmission

for Herd Immunity

smallpox

high (0.25)

14 days

high (2.5)

polio

low (0.01)

18 days

average (1)

measles

low (0.01)

8 days

very high (10)

Master 4.5

Cases of Smallpox in

Niger and Bangladesh

Percent of

Number of

Cases of

People

Smallpox

Smallpox per

Country

Year

Population

Vaccinated

Cases

Square Kilometer

Bangladesh

1973

72 million

33,000

0.23

Niger

1969

3.9 million

0.00002

Source: Anderson, R.M., and May, R.M. 1992. Infectious Diseases of Humans. New York: Oxford University Press, page 89.

Master 4.6

The Proposals

Characters

• Foundation Officer

• AIDS Treatment Administrator

• Public Health Physician

• Hospital Administrator

Segment 1: Introducing the Proposals

Foundation Office

FOUNDATION OFFICER: Our organization funds research projects focused on relieving

human suffering from disease. This year we have $5 million to award for a single project.

I’ve narrowed the field down to three strong proposals for work on three very different

diseases. Believe me, these are tough decisions. We’d like you to consider two major

criteria in making your recommendation. First, evaluate the magnitude of the situation.

For example, how many people are affected by the disease? How serious are the

consequences of the disease for the individual and for society?

Second, we need to know how effective the proposed plan will be for fighting or

preventing the disease. Will we be able to get the treatments to people affected by the

disease? If the plan is to develop a new treatment or prevention strategy, how likely

is it to be successful? Rate these proposals using these two criteria and then give me

a final recommendation.

Segment 2: Proposal 1

AIDS Clinic

AIDS TREATMENT ADMINISTRATOR: AIDS is a now a worldwide epidemic that affects

every sector of society. The most effective way to deal with AIDS is with powerful drugs.

We attack the disease with drugs like AZT. It stops the virus from replicating and keeps

the amount of virus in the blood low. By doing that and treating the symptoms at the

same time, the patient will survive 5, 10 years, even more. Hopefully, then, maybe the

body takes over and holds off the disease on its own. It isn’t a cure. But living with the

disease is better than dying with it. The problem is that these drugs are expensive. Our

proposal is simple. Give us the money and we will give years of life to our patients.

Master 5.1a

Segment 3: Proposal 2

Physician’s Office

PUBLIC HEALTH PHYSICIAN: Any disease like measles that affects millions of

individuals is a significant public health problem. It may not seem like a big deal to

people in the United States, where it is a somewhat uncommon childhood disease.

Most children who get it develop an itchy red rash and miss a week of school. Then,

they are immune. But measles is a major killer in developing countries where there

are not enough vaccination programs and medical care and general nutrition are poor.

We have an excellent vaccine that could eliminate the virus just as we have eliminated

smallpox. We would use the grant money to prepare and distribute measles vaccine

globally as part of a coordinated effort to wipe out the measles virus.

Segment 4: Proposal 3

Hospital Administrator’s Office

HOSPITAL ADMINISTRATOR: Patients come to our hospital for routine surgery and

then, five days later, they have a life-threatening infection of Staphylococcus aureus.

But that’s not new. Staph is everywhere, especially in hospitals where infants, surgical patients, and others in poor health provide an environment with plenty of easy prey

for the bacteria. What’s changed is that the antibiotics that once cured a Staph infection are not effective anymore. We’re lucky, because we have vancomycin, which kills the

most resistant strains of Staph aureus. But recently, we’ve discovered isolated cases of vancomycin-resistant Staph aureus (or VRSA). We must work quickly to develop new

drug therapies before these resistant strains become widespread. Our proposal is to

develop and test drug therapies that can stop Staph aureus before we have an epidemic.

Master 5.1b

Reference Database—AIDS

For up-to-date statistics on HIV/AIDS, visit the Web sites for the Centers for Disease Control and Prevention and the World Health Organization: http://www.cdc.gov and http://www.who.int.

AIDS—Cause

AIDS is caused by the human immunodeficiency virus (HIV). HIV attacks particular cells of the victim’s immune system. As a result, the person’s immune defenses are weakened tremendously, and the victim is unable to fight off infections. Even worse, the victim is left vulnerable to many serious diseases, such as tuberculosis, pneumonia, fungal infections, and cancer. Death usually occurs as a result of one of these diseases.

AIDS—Cost

The economic cost of the AIDS epidemic is staggering. First, there is the cost of caring for one patient with AIDS. The most common treatment in the United States is a “cocktail,” or mixture, of drugs that can cost up to $23,000 per patient per year. These drugs slow the progress of the disease but do not eliminate HIV from the patient’s body. Research also shows that these drugs must be taken regularly from the time of diagnosis for the rest of the patient’s life: As soon as the drugs are stopped, the virus bounces back, as dangerous and life threatening as ever. A further drawback is that the virus in a patient may become resistant to these drugs.

In the United States alone, the cost of providing these drugs to AIDS patients is in the millions of dollars and is rising each year. Unfortunately, developing nations cannot afford to treat their HIV-infected citizens with these drugs. African nations have an average of $10 per year per person for medical care, yet Africa is the part of the world that is hardest hit with the disease.

The epidemic has other costs, too. In some countries, such as Uganda, Zambia, and Zimbabwe, three-fourths of the hospital beds are filled with children who are HIV-positive. Millions of adults have died, and many of them have left orphaned children. Many others have left surviving spouses who also are ill, need treatment, and cannot work. Families cannot find money to pay for funerals, and employers must find and train new employees. This problem is eating away at these countries’ economies.

As one scholar described the problem, “The epidemic’s direct and indirect consequences are wiping out the gains that many of these countries have made in the past 30 years.”

AIDS—Death Rate

The total number of worldwide deaths from AIDS in 1998 was about 2.5 million (2 million adults and 510,000 children under the age of 15). In 2011, it was 1.7 million (1.5 million adults and 230,000 children under the age of 15).

In 1998, the total number of worldwide deaths since the beginning of the epidemic was about 13.9

million (10.7 million adults and 3.2 million children under the age of 15). By 2010, that number had reached 30 million, and there are roughly 7,000 new HIV infections in the world every day.

AIDS—Definition

AIDS, acquired immune deficiency syndrome, is a disease in which the immune system no longer functions effectively. It is caused by the human immunodeficiency virus (HIV). People with AIDS are vulnerable to a variety of other diseases (opportunistic infections) that only rarely occur in people with healthy immune systems.

Master 5.2a

AIDS—Diagnosis

If a person is infected with HIV, his or her body will make antibodies, special proteins produced by the immune system that recognize and can attach to HIV. To test for HIV infection, doctors look for these antibodies in the person’s blood. If antibodies against HIV are present, they are evidence that the person is infected with HIV. If antibodies against HIV are not present, the person either is not infected or was infected recently enough that his or her body has not yet made these antibodies in detectable quantities.

Only another test at a later date can distinguish between these possibilities.

Infection with HIV is not the same as having AIDS. When a physician suspects that a person may have AIDS, he or she may order another laboratory test of the person’s blood. The diagnosis of AIDS is confirmed if the person’s CD4 T-cell concentration is lower than 200 cells per cubic millimeter of blood (normal levels are at least 800 cells per cubic millimeter of blood) or if the person develops one or more of the opportunistic infections associated with AIDS.

AIDS—Incidence (Predictions)

Globally, great strides have been made in terms of scientifically proven HIV-prevention modalities, such as medically supervised, voluntary adult male circumcision; preventing mother-to-child HIV transmission and using HIV drugs as prevention; and increasing access to HIV treatment for those who need it. As a result, the scientific community is much more hopeful that an end to the HIV/AIDS pandemic is possible.

To achieve this, however, will require significant scale-up of these proven HIV-prevention measures as well as a commitment by countries, governments, and communities to strengthen their healthcare systems and build the capacity to provide HIV treatment and prevention. Further, continued basic and clinical research is needed to find additional HIV treatment and prevention interventions as well as a preventive vaccine and, ultimately, a cure.

AIDS—Incidence (United States)

In the United States, roughly 1.1 million people were living with HIV infection as of 2009. Each year, about 50,000 more people are infected. In 1998, AIDS was the leading cause of death for men between the ages of 25 and 44 and the fourth-highest cause of death for women in this age category. By 2008, AIDS ranked sixth as a cause of death for men and women in this age group.

The largest number of new HIV infections in the United States currently occurs among men who have sex with men of all races and ethnicities, followed by African-American heterosexual women.

Injection-drug users and transgender people also represent populations at highest risk for HIV infection.

AIDS—Incidence (Worldwide)

Since the early 1980s, more than 60 million people worldwide have contracted the human immunodeficiency virus (HIV), and more than 25 million have died of HIV-related causes. In 2011, more than 34 million people were living with HIV, and there were 2.5 million new infections and 1.7 million deaths.

Worldwide, the highest incidence of HIV infection is in sub-Saharan Africa. Two-thirds of all HIV-positive people and 90 percent of all infected children live in this area. In some African countries, one in four adults is HIV-positive.

The second highest incidence of HIV infection is in Southeast Asia. Here, the epidemic is worst in India and Thailand.

Master 5.2b

AIDS—Modes of Infection

You can get HIV (the virus that causes AIDS) from anyone who is infected with the virus, even if they do not look sick, do not know they’re sick, and do not yet test positive for the virus (that is, are not yet HIV-positive).

Most people get HIV by

• having unprotected sex with a person who is infected,

• sharing a needle (shooting drugs) with a person who is infected, or

• being born from or drinking the breast milk of a woman who is infected.

There are no known cases of someone getting HIV through contact with an infected person’s tears or saliva, but it is possible to catch HIV through oral sex, especially if you have open sores in your mouth or bleeding gums.

In the past, some people were infected with HIV from getting a blood transfusion from an infected person. Today, the blood supply is carefully tested, and the risk of infection from a blood transfusion in the United States is very low.

AIDS—Name

The name “AIDS” means “acquired immune deficiency syndrome.”

The word “acquired” means that a person can catch AIDS; it is an infectious disease.

The words “immune deficiency” mean that the disease causes a weakness in a person’s immune system.

The immune system is the part of the body that fights disease.

The word “syndrome” is a medical term for a group of health problems that all are associated with a particular disease. People with AIDS display many health problems, such as weight loss, problems with infections, brain tumors, and other health problems.

AIDS—Treatment (General Information)

There is still no cure for AIDS. Drugs are available that can slow down the damage to a person’s immune system and the multiplication of the virus. Some scientists think that the new, strong, anti-HIV drugs that are currently available might eliminate all the HIV from a person’s body if the drugs are taken for several years. Research is under way to determine whether this is the case.

Drugs are available that can prevent some of the opportunistic infections that people with AIDS are susceptible to. There is little that a person can do to prevent some of the other infections.

AIDS—Treatment (Drug Therapies, General Information)

The best and most widely used treatment for AIDS today is designed to slow down a person’s progression from being HIV-positive to having AIDS. This treatment involves taking a “cocktail,” or mixture, of several drugs that suppress the multiplication of the human immunodeficiency virus (HIV), which slows down the damage to a person’s immune system.

The use of these drugs has led to a 44 percent decline in AIDS deaths in the United States, as well as to a significant drop in the number of cases of opportunistic infections among AIDS patients. These drugs do not, however, cure AIDS, because they do not completely eliminate HIV from a person’s body.

Master 5.2c

Following this treatment plan correctly is a challenge for patients. The cost of these drugs is about $15,000 per year per patient. Side effects include nausea, diarrhea, rashes, headaches, and elevated triglyceride and cholesterol levels in the blood. Patients must take several pills every day, some of which must be taken on an empty stomach, some with food, and some with or without other pills. If patients miss doses, they risk not completely suppressing the multiplication of the virus and also risk the appearance of strains of HIV that are resistant to the drugs.

AIDS—Treatment (Drug Therapies, Viral Resistance)

When drugs against HIV do not work, it is often because the virus has become resistant to one of the drugs being used. This resistance is the result of mutations that occur in the viral genes.

Unfortunately, use of anti-HIV drugs can actually promote the reproduction of resistant virus particles.

Untreated, HIV makes approximately 10 billion new virus particles every day in an infected person. But HIV does not copy its genetic material very accurately. Because of its sloppy replication, each one of these new virus particles may be different from the parent virus in one or more genes. And because so many virus particles are produced each day, it is very likely that at least one virus is produced each day that is resistant or partially resistant to one of the antiviral drugs the person is taking. This virus particle now has an advantage over other virus particles that are not resistant to the drug, and it may reproduce faster than nonresistant strains. Thus, taking anti-HIV drugs can actually promote the reproduction and accumulation of viruses that are not inhibited by the drugs the patient is taking.

Because resistance can occur so easily and because no single drug on the market can inhibit HIV

reproduction completely on its own, physicians now treat patients with mixtures (cocktails) of drugs.

Physicians must also stay on the lookout for signs of viral resistance emerging in a patient, and if resistance appears to be emerging, must consider new combinations of drugs that will be effective for that patient.

HIV—Course of Infection

Many people do not know when they are first infected by HIV because they have no symptoms. Other people don’t know because although they get a fever, a headache, and sore muscles and joints for one or two weeks, they think it is just the flu.

The virus multiplies inside the victim’s body for a few weeks (or even a few months) before his or her immune system responds. During this period of time, the person is infected with HIV and can infect others, but he or she won’t test positive for HIV.

When a person’s immune system begins to respond to the virus by making antibodies, the person will test positive for HIV.

Some people with HIV stay healthy for many years after infection. During this time, however, the virus is damaging the person’s immune system. Healthcare professionals can measure this damage by counting the number of CD4 T-cells a person has. These cells, also called T-helper cells, are part of a person’s immune system. Healthy people have between 500 and 1,500 CD4 T-cells in each cubic millimeter of blood, but people with HIV disease have many fewer. As a person’s CD4 T cell count goes down, he or she may start having signs of HIV disease (for example, fevers, night sweats, diarrhea, weight loss, or swollen lymph nodes).

HIV disease is diagnosed as AIDS when the person’s CD4 T-cell count drops below 200 CD4 T-cells per cubic millimeter of blood or when the person gets one of the opportunistic infections identified by the Centers for Disease Control and Prevention as characteristic of AIDS.

Master 5.2d

AIDS progresses at different rates in different people. Some people die within five years of being infected with HIV, whereas other people live for many years, even after they develop AIDS. In the early years of the epidemic 30 years ago in the United States, people with HIV could expect to die from AIDS

within about 10 years after becoming infected. With the treatment nowadays, though, people who are HIV-positive can expect to live for decades and to die from other causes.

HIV—Definition

HIV stands for “human immunodeficiency virus.” HIV is the virus that causes AIDS.

HIV—Definition of HIV-Positive (or HIV Disease)

When a person is infected with HIV, his or her body responds by making antibodies against the virus.

(Antibodies are special proteins that fight disease.) Blood tests for AIDS look for antibodies in the blood against HIV. People who have antibodies against HIV in their blood are said to be “HIV-positive.” They also might be said to have “HIV disease.”

Being HIV-positive (or having HIV disease) is not the same as having AIDS. Many people are HIV-positive, meaning that they have been infected with HIV, but they are not yet sick. As HIV remains in the body, it slowly wears down the immune system.

HIV—Rate of Mutational Change

Untreated, HIV reproduces very rapidly inside a person’s body, making approximately 10 billion new virus particles every day. But HIV does not copy its genetic material very accurately. In fact, because of its sloppy replication, each one of these new virus particles may be different from the parent virus in one or more genes. Thus, HIV shows a very rapid rate of mutational change.

The result of this high rate of mutational change is that there are many different HIV strains, not only in the world, but even within one person’s body. This presents a problem for developers of new drugs to combat HIV (some of these different strains may be resistant to the drug) and for developers of vaccines against HIV (the vaccine may be effective against one strain of HIV but not another).

Sources for the data include the UNAIDS and the CDC Wonder Web sites (http://www.unaids.org/en/ and http://wonder.cdc.gov/).

Master 5.2e

Reference Database—Measles

For up-to-date statistics on measles, visit the Web sites for the Centers for Disease Control and Prevention and the World Health Organization: http://www.cdc.gov and http://www.who.int.

Measles—Definition

Measles (also called rubeola) is a severe and highly contagious viral infection of the respiratory tract, although its most prominent symptom is a skin rash.

The measles virus spreads by direct contact with an infected person. Usually, the virus spreads via droplets of fluid from the person’s respiratory tract. These droplets contain millions of virus particles that can infect another person, entering through the respiratory tract. Here, the virus incubates for one to two weeks before symptoms appear: fever, discomfort, sore throat, coughing, and finally a painful and itchy rash. After a few more weeks, the infection usually subsides. In a few cases, infection leads to pneumonia, brain damage, ear and sinus infections, convulsions, and sometimes death.

In developed countries, measles is usually not a fatal disease. In many developing countries, however, measles has a much higher mortality rate, accounting for 10 percent of all deaths in children under five years old.

Measles—Diagnosis

People who have measles show a variety of symptoms, ranging from mild fever to severe skin rashes, to life-threatening seizures and infections. Doctors diagnose measles by the presence of Koplik’s spots—tiny, white specks, surrounded by a red halo, that appear on the inside of the cheek, near the molars. Doctors can also use blood tests to check for antibodies against the measles virus.

Measles—Epidemics

Measles epidemics occur when the measles virus spreads rapidly through a susceptible population.

Epidemics pose the greatest threat to unvaccinated people or people who have had only one dose of the vaccine and failed to develop antibodies against the virus.

Populations with high vaccination rates are less susceptible to epidemics. However, such populations can experience measles outbreaks in which three or more linked cases of the disease occur. Outbreaks are shorter in duration and more limited in transmission than epidemics.

The higher the percentage of unvaccinated people, the more susceptible a population is to an epidemic.

The “epidemic threshold” is the point at which the percentage of unvaccinated people is high enough to risk an epidemic.

Measles—Immunity

There are three kinds of immunity to measles: passive immunity, natural immunity, and immunity derived from vaccination. Infants born to mothers who have either had measles or been vaccinated are protected by maternal antibodies; that is, they have passive immunity. This protection lasts six months, on average, and then the child becomes susceptible to measles. A person is naturally immune if he or she has had contact with the measles virus and has developed antibodies against it. People born before 1957

are considered naturally immune because of the high probability that they were exposed to the virus during childhood. People born after 1957 are considered immune if they have been fully vaccinated, have had a confirmed case of measles, or have had blood tests that confirm previous exposure to the virus.

Master 5.3a

Full vaccination requires two doses of vaccine: one between the ages of 12 and 18 months, and the other between the ages of 4 and 6 years or 11 and 12 years. (The second dose helps catch the small number of people who do not become immunized by the first dose.)

Measles—Incidence (Historic)

During this century, there has been a dramatic decrease in measles epidemics. Before the development of the measles vaccine, 5.7 million people died each year

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