Chapter 9: Infection

Question 1

Microorganisms and Humans: a Dynamic Relationship

Answer 1

1. Infectious disease is a significant cause of morbidity and mortality in the United States and worldwide.
2. Pathogens have unique characteristics that influence their ability to overcome body defense mechanisms and cause disease.
3. The process of infection includes encounter and transmission, colonization, invasion, dissemination, and cellular or tissue damage by
   the pathogenic microorganisms.
4. There are four distinct stages of infection: incubation period, prodromal stage, invasion or acute illness stage, and convalescence.

Question 2

Infectious Disease

Answer 2

1. Bacteria have virulence factors that promote their ability to cause infection and cell injury, including pili, flagella, capsules, enzymes, competition for iron, and toxins.
2. Bacteria produce exotoxins or endotoxins. Exotoxins are enzymes that can damage the plasma membranes of host cells or can inactivate enzymes critical to protein synthesis, and endotoxins activate the inflammatory response and produce fever.
3. Septicemia results from the proliferation of bacteria in blood. Toxin released by blood borne bacteria cause the release of vasoactive enzymes that increase the permeability of blood vessels. Leakage from vessels causes hypotension that can result in septic shock.
4. Viruses are intracellular parasites. They enter host cells and use their metabolic processes to proliferate and cause disease.
5. Viruses that have invaded host cells may decrease protein synthesis; disrupt lysosomal membranes; form inclusion bodies, where synthesis of viral nucleic acids is occurring; fuse with host cells to produce giant cells; alter antigenic properties of the host cell; transform host cells into cancerous cells; and promote bacterial infection.
6. Viruses can elude the immune system by making small changes to the genes that produce viral surface antigens, a process known as antigenic variation.
7. Diseases caused by fungi are called mycoses, and fungi occur in two forms: yeasts (spheres) and molds (filaments or hyphae).
8. Dermatophytes are fungi that infect skin, hair, and nails with diseases, such as ringworm and athlete’s foot.
9. Candida albicans is the most common cause of fungal infections in humans.
10. Parasitic microorganisms range from unicellular protozoa to large worms. Although less common in the United States, parasites and protozoa are common causes of infection worldwide.
11. Parasitic and protozoal infections are rarely transmitted from human to human. Infection mainly spreads through vectors (e.g., through mosquito bites) or through contaminated water or food (i.e., malaria, Chagas disease, sleeping sickness, and leishmaniasis).

Question 3

Antibiotic/Antimicrobial Resistance

Answer 3

1. Pathogens can use various mechanisms to resist the effects of antibiotics, including transmission of resistance genes to new generations of bacteria, enzyme degradation of the antibiotic, ejection of the antibiotic from the pathogen, modification of the cell wall to prevent binding or uptake of the antibiotic, or modification of the target of the antibiotic.

Question 4

Vaccines and Protection Against Infection

Answer 4

1. Vaccines are biologic preparations of antigens that, when administered, stimulate production of protective antibodies or cellular immunity against a specific pathogen.
2. Passive immunotherapy is the administration of preformed antibodies for protection against a specific pathogen, such as hepatitis A and B or rabies.