Lecture 26

Question 1

1. What are the three things the virulence of a pathogen depends on?
2. What does Adherence involve?

Answer 1

1. Depends on its abilities.
   
   1. To adhere to the appropriate host tissue.
   2. To invade and grow in that tissue.
   3. To produce virulence factors.
2. Involves production, for example, of a capsule or slime layer, specific adherence proteins, fimbriae, or other bacterial cell surface components, which interact directly with specific host tissues or specific host cell types.

Question 2

1. What does adherence, invasion, and growth of a pathogen depend on?
2. To cause disease, what must a pathogen do?
3. What does each kind of pathogen have?
4. How does Clostridium tetani tissue specificity work?

Answer 2

1. Depends on tissue specificity.
2. A pathogen must colonize the body at a site where it can survive, obtain nutrients, and grow.
3. Has specific needs and abilities for survival and growth; these needs and abilities determine if it can infect a host.
4. Clostridium tetnai causes tetanus, it does not survive well in the gastrointestinal tracts. Stomach acidity kills it and it does not compete well against intestinal microbes.

Question 3

1. What are virulence factors?
2. What do virulence factors function to do?
3. What are many virulence factors?

Answer 3

1. Toxins and enzymes produced by a pathogen that promote its growth and invasiveness and thereby enhance its pathogenicity.
2. Virulence factors fuction to break down tissues and destroy cells, allowing the pathogen to invade deeper into the tissue and to obtain nutrients for growth.
3. Most are cytolytic toxins. Others are enzymes, examples of which include proteases, nucleases, coagulases (break down fibrin clots), and many others.

Question 4

1. Why do we have multiple defense layers?
2. What is non-specific defense?
3. What is innate immunity?
4. What is adaptive immunity?

Answer 4

1. To protect us from invasion. To limit the places in and on the body where microbes can persist, and to attack and remove pathogens that invade the body.
2. The primary defense against invasion by pathogenic bacteria, viruses, fungi, and protist; non-specific barriers to invasion are found in all animals and plants; in humans: skin, saliva, low stomach pH, proteases, mucous, cilia, and commensal microbes.
3. Second level of defense, immediate response to attach and remove pathogens that get through the primary defense a general non-specific response to invasion. This system also functions to activate the third level of defense.
4. Third level of defense, highly specific response to invasion by a pathogen.

Question 5

1. What is epidemiology?
2. What do we learn by using population based, geographic, seasonal, demographic, and behavioral data?

Answer 5

1. The study of factors and mechanisms involved in the occurrence, distribution and control of disease.
2. We can learn where a disease occurs and how it spreads, what age groups are susceptiable to the disease and when during the year susceptibility is greatest, what behaviors are conductive to getting the disease, and what treatment programs are effective in preventing and stopping the spread of the disease.

Question 6

1. Why have we not become immune to colds, or have a vaccine for them?

Answer 6

1. Difficult due to the number of different viruses that cause colds. Rhizovirus causes 75% of colds (115 different species); Coronaviruses cause 15% of colds; all others cause 10%.

Question 7

1. Why have infectious diseases declined throughout most of the 20th century?
2. Some terms:
   
   1. Chronic?
   2. Acute?
   3. Mortality?
   4. Morbidity?
   5. Zoonosis?

Answer 7

1. Overall, we are more knowledgeable about how to stop the spread of infectious disease. Proper handwashing, people are more spread out, and the development of antibiotics have all played a role.
2. Terms
   
   1. a long-term, persistant illness
   2. a rapid and dramatic onset of illness
   3. incidence of deaths due to a disease
   4. incidence of a disease, including fatal and non-fatal cases.
   5. a disease primarily of other animals but sometimes is transferred to humans.

Question 8

1. What is an endemic?
2. What is an epidemic?
3. What is a pandemic?

Answer 8

1. Infectious disease agent is present continually in a population in a particular geographic area, but the number and severity of reported disease is too low to be a public health concern. Example: mumps, a viral disease of the oral cavity caused by paramyxovirus.
2. A higher-than-normal incidence of a disease in a population; morbidity and mortality rates become a public health. Often first called an “outbreak” if cases of the disease occur in a short period of time.
3. An epidemic that has spread to many widely separated geographic locations. Example: Asian Flu of 1957.

Question 9

1. What is a common-source epidemic? What limits the time-course of this kind of epidemic? Give an example
2. What is a propagated epidemic? Why do the numbers rise more slowly than a common-source epidemic? Why do the numbers fall slowly? Give an example

Answer 9

1. an epidemic arising from contact with contaminated substances. The cause of the epidemic is isolated so it doesn’t keep infecting people. Typhoid fever, salmonella typhi via human fecal contamination of food and water.
2. A host-to-host epidemic. An epidemic arising from person-to-person contact, with the disease moving from infected person to suseptible unifected people. The number of cases rises more slowly and falls more slowly than with a common-source epidemic, generating a longer lasting epidemic. Example: pneumococcal pneumonia, Streptococcus pneumonia.

Question 10

1. What is the simple SIR model?
2. What is R₀?
3. What does it mean when R₀ < 1?
4. What does it mean when R₀ > 1?
5. What is herd immunity?

Answer 10

1. Susceptible ⇔ Infected ⇒ Resistant
2. Basic reproductive rate. The number of cases one case of the disease can generate. The value of R₀ indicates whether a disease will spread and how quickly.
3. Infection will not spread, will die out in time.
4. Infection will be able to spread in a population
5. Immunization (or naturally acquired immunity) of a high proportion of a population blocks the spread of a disease. With herd immunity, there are not enough susceptible host for the disease to keep spreading.

Question 11

1. Where are nosocomial infections (HAIs) aquired?
2. How many patients overall have HAIs?
3. How many patients in the ICU have HAIs?
4. How manuy HAIs are there per year? How many deaths?
5. Why are they so common?

Answer 11

1. Hospital aquired
2. 5%
3. 10%
4. 1.7 million HIAs per year, 100,000 deaths per year.
5. Reasons
   
   1. Pathogens are present and selected for.
   2. Weakened population
   3. carriers (patients who are ill, staff who are carriers).
   4. Invasive procedures.

Question 12

1. What does the rise in deaths due to infectious disease and the U.S. health care system suggest?
2. What do you think accounts for the diffence in the picture between Africa and Americas?
3. Does what happens in Africa influnce health in the rest of the world?

Answer 12

1. Health care research is under funded, We need everyone to practice better prevention.
2. The difference in availability of antibiotics.
3. Yes

Question 13

1. Why are there so many emerging and re-emerging infectious diseases?

Answer 13

1. Reasons:
   
   1. Increasing human population size and global interactions. Increased numbers of susceptible people; easier and faster spread of pathogens and disease.
   2. Encroachment of human population on natural, pristine habitats where people previously had not lived or were present in lower or very low numbers. Breaks down normal ecological interactions, brings people into contact with potential pathogens new to people. Increases contamination of the environment and upsets natural ecological balances, allowing certain kinds of rare organisms to flourish.
   3. Spread of antibiotic resistant strains due to use and overuse of antibiotics. Decrease our ability to cure disease and stop its spread.
   4. Decline in public health funding and social awareness of disease. Hand washing and routine sanitation ignored or taken for granted.