chapter 10

How does a population of pathogens become resistant to a drug?

Natural selection: some are resistant to start, and those survive and reproduce

A highly-virulent pathogen is reproducing in the host most quickly, so it should "win," and therefore most pathogens should evolve to be highly virulent. Why don't they?

A highly virulent pathogen may be less likely to infect more humans if it disables the first host too quickly.

If an insecticide like DDT were found that killed mosquitoes but was otherwise perfectly safe, would the problem of malaria infection be solved for good?

No. There would be some resistant mosquitoes, and those would live to create an increasingly resistant population until the insecticide no longer worked on them.

About how long has malaria been around?

At least as long as humans have been around

What was the source for the drug penicillin, and what type of drug is that?

Mold; antibiotic

Most vaccines cause the formation of antibodies against a particular pathogen, but if the pathogen mutates quickly, the vaccines don't stay effective. How does the vaccine against diphtheria work that avoids this problem?

Because the vaccine works against the toxin produced, not the bacteria cell itself, mutations to the cell don't alter the vaccine's effectiveness.

Why do hospitals tend to harbor particularly resistant strains of bacteria?

Because there are antibiotics in use continuously so there is time for mutations for resistance to be shared among the bacteria populations

The study of the interactions among species and their physical environments is called what?

Ecology

What does Dr. Ewald study?

Evolutionary medicine

What are the four stages of a new infectious disease?

Exposure, infection, transmission, epidemic

Which of the following interactions is an example of commensalism?

Eyebrow mites and humans

Many bacteria do not interact with humans, but those that do can always be classified as either harmful or not harmful to humans. True or False?

False. Some are fine in small numbers, but in big numbers they can overwhelm the immune system and cause problems.

In addition to outcompeting other bacteria in the host, what else do pathogens have to do to survive over the long term?

Get to the next host

Dr. Ewald got interested in host-pathogen interactions as a result of considering what question under what circumstance?

He had a severe case of diarrhea and wondered whether that was his body's way of getting rid of an organism, or the organism's way of infecting the next host.

Which of the following is an example of a mutualistic relationship?

Healthy bacteria creating too acidic an environment for unhealthy bacteria to live in

Over time, how does a pathogen normally get better suited to infect and transmit?

Mutations

In general, how does the malaria-causing bacteria Plasmodium, increasingly resistant to our drugs?

Natural selection and evolution

What do antibodies do?

Identify specific "foreign" particles in your body so other immune system cells can ingest and destroy them

It makes sense that you should take antibiotics long enough to kill off most of the pathogens affecting you, but why shouldn't you take them for too long?

If you expose the pathogens to antibiotics for too long, those with resistance will have time to outcompete the non-resistant variations and the whole population will be resistant.

Why is the HIV that causes AIDS particularly dangerous? What does it do to people?

It weakens the very immune system that could fight it.

If human behavior were to change, making HIV much less easily transmittable, what might happen to the virus according to the trade-off hypothesis?

It would become less deadly.

If resistance is possible, why aren't all bacteria resistant to antibiotics by now?

Maintaining resistance leaves less energy for reproduction, so non-resistant bacteria do better in general.

We get very few infections resulting from the many pathogens to which we are exposed. Why is this?

Our immune system

What causes malaria?

Particular species of protozoan

Why do humans continue to get sick due to infection by pathogens, even with modern sanitation and medical care?

Pathogens continue to evolve to overcome our defenses.

Where do new diseases most commonly originate?

Pathogens from other species that jump to humans

Why can't antibiotics be considered an effective long-term strategy for controlling disease?

Pathogens will keep evolving resistance.

In the trade-off hypothesis, what is being "traded off?"

Reproduction in the host versus ease of transmission

In pathogens, what does natural selection select for?

Reproductive success

How is competition between the various microscopic organisms that live on us a good thing for us?

The "good" species make it difficult for any "bad" ones to move in and cause disease.

How is it that scientists didn't know until fairly recently that humans carry around whole ecosystems of bacteria?

The bacteria don't grow well in the lab, and only lately have we had the technology to identify bacterial species by RNA.

How do these changes in the pathogens happen so they become resistant?

These changes are the result of genetic mutations.

Most of the bacteria and molds that grow on and in humans don't grow well in a lab. Why is this?

These organisms tend to be very specifically adapted to their habitat on a person and that habitat is difficult to duplicate in a lab.

According to the trade-off hypothesis, why are diseases like mumps, measles, or chickenpox rather mild?

They require direct human-to-human contact to spread so the human hosts can't be too sick to get around.

Why don't "live" vaccines make you sick?

They've been allowed to adapt to non-human conditions such that they no longer affect humans.

A resistant bacterium can share its resistance with its neighbors through what processes?

Transformation, transduction, conjugation

For what does the trade-off hypothesis offer an explanation?

Why some pathogens are more virulent than others

The disease cholera is highly virulent and is spread by contact with infected water. Does this support the trade-off hypothesis of disease virulence?

Yes because it's easy to come into contact with water directly. There is no need to keep the host up and about for transmission.

A malaria infection almost immediately puts a sick person in bed. If the pathogen has to infect other people, wouldn't it be better if it weren't quite so bad initially, so the victim could get around?

Yes, but malaria is transmitted by mosquitoes, not humans, so it doesn't matter if the infected human is confined to bed right away.

The virus myxoma was introduced into Australia to try to limit a population explosion of rabbits introduced from Europe. Did it work?

Yes. At first it worked, but then only resistant rabbits were left, so the virus changed to become less virulent. That allows the virus to be more easily spread though, so the rabbit populations are still somewhat controlled.

Is malaria treatable?

Yes. But there are different drugs to treat malaria and none is effective against every strain of protozoa which can cause the disease.

Is it reasonable to consider a human body to be an ecosystem?

Yes. Many organisms living in and on "our" environment compete, reproduce, and evolve, so combined, we are a working ecosystem.

Does the typical pattern of symptoms for a sexually- transmitted disease make sense in light of the trade-off hypothesis?

Yes. Symptoms are often so mild that people are unaware they have the disease; therefore, the disease is more likely to get transmitted to the next host.