National Institutes of Health Emerging and Re-emerging Infectious Diseases Part 4

Part 4 Read Master 4.1Master 4.1 Measles Outbreak at Western High

The story is based on an outbreak of measles that occurred in Washington State in Speculate about what might have happened to cause a sudden outbreak of a disease such as measles that normally, today, is relatively rare in the United States.

Master 4.2Master 4.2, A Little Sleuthing, Despite the success of the measles vaccine, there continue to be small outbreaks of measles in the United States. The key to understanding why this is true and to answering the question that ends the story about Western High lies in understanding how disease spreads in a population.

In class students participated in a simulation of the spread of a fictitious disease we called the “two-day disease.” That means that a person was sick one day, and the next day (s)he was recovering but still contagious and the third day the person was immune. When 25% of the students were infected, there was an epidemic. Look up the word epidemic

The disease transmission simulation simulated the spread of two-day disease in a population. You can do a similar activity on the internet. Go to ts/nih1/diseases/activities/activity4.htm ts/nih1/diseases/activities/activity4.htm

Click on launch simulation Use the following numbers in the boxes This is the same as we did in class. It was a 2 day disease and no one was immune to begin with. Run the simulation and fill in Master 4.3 Come in during Seminar if you don’t understand

Master 4.3 Master 4.3 Simulation 1 0% immune, 100% susceptible Write 0% immune, 100% susceptible on the top of master 4.3 where it says title

Plot the data from the table onto the graph and draw the curve on the graph. Make three or four observations about the table and graph the class has created.

Do a second simulation. 50% immune; 50% susceptible Pull out your other master: 4.3 and write Simulation 2: 50% immune, 50% susceptible across the top. This means that 50% of the population is immune. Lets say that 50% were vaccinated and the other 50% were not vaccinated.

Run the simulation The difference on the simulator will be 50 on the first box. The other boxes remain the same.

Plot the data from the table onto the graph and draw the curve on the graph. Make three or four observations about the table and graph the class has created.

What is an epidemic? An “epidemic” is typically defined as “more cases of a disease than is expected for that disease.” Epidemics are generally considered to be larger in scale and longer lasting than outbreaks Today, five cases of measles within a population could be considered an epidemic because no cases are expected.

For this simulation, assume that an epidemic is in progress if 10 percent or more of the population is sick at one time. Observations that you might make about the table and graph that result from the first simulation include:

an epidemic occurred because a large portion of the class was sick at the same time; at the beginning of the epidemic, only a few people were sick in the same day; in the middle of the epidemic, a lot of people were sick at the same time; and at the end, only a few people were sick; by the end of the simulation, everyone was immune; and once it started, the disease spread rapidly.

Observations that you might make about the table and graph that result from the second simulation include: only a few people were sick on any one day; no epidemic occurred; at the end of the simulation, some people were still susceptible; and some people in the population never got sick.

Why did an epidemic occur in the first population, but not in the second?”

Why didn’t all of the susceptible people in the second population get sick? The answer is….

Herd immunity A phenomenon that occurs when most of the people in a population are immune to an infectious disease.

Based on your experience in the disease transmission simulation, what would happen here if measles vaccinations dropped to a low level in a population.

Measles would re-emerge in the population. There would be many susceptible people in the population, So the disease would be transmitted from one to another without dying out. A measles outbreak or epidemic would occur.

HW: Write a final paragraph to the story. Use the term herd immunity to anser the following questions Why didn’t the unvaccinated or inadequately vaccinated students and teacher at Western High get measles when they were children rather than as teenagers or adults? Why is vaccination not only a personal health issue, but also a public health issue?

Major Concepts: The re-emergence of some diseases can be explained by the failure to immunize enough individuals, which results in a greater proportion of susceptible individuals in a population and an increased reservoir of the infectious agent. Increases in the number of individuals with compromised immune systems (due to the stress of famine, war, crowding, or disease) also explain increases in the incidence of emerging and re- emerging infectious diseases.

Objectives: After completing activity #4, students will be able to explain how immunizing a significant proportion of a population against a disease prevents epidemics of that disease (herd immunity), be able to list factors that affect the proportion of a population that must be immunized to prevent epidemics, and understand how large-scale vaccination programs help control infectious diseases.

Why are new diseases emerging and old ones re-emerging environmental changes, indiscriminate use of antibiotics, and failure to vaccinate populations.

What steps can we take to avoid disease emergence and re-emergence? carefully considering the impact of development in wilderness areas being alert to the possibility of pathogens having access to a new and/or larger host population, avoiding unnecessary uses of antibiotics, Increasing efforts to enforce vaccination.

How Can Research Contribute to Better Ways to Control Infectious Diseases? (5) Research can help us develop better ways to recognize and understand new pathogens, create new or improved antimicrobial drugs to prevent or treat infection, develop new vaccines to protect individuals and the population, and discover new ways to prevent transmission of infection

Fighting infectious diseases requires money as well as knowledge There is a limit to the money that is available for this purpose. How do people decide where to invest money in fighting infectious diseases? Who gets to decide?

Go to you tube and watch the movies entitled “vaccine wars” Fill in the worksheet of vaccine wars. If you can’t get it at home, come in and do it in seminar or after school.

More homework: Play this computer simulation. Pandemic mic-2.html#game mic-2.html#game