Chapter 14
Define etiology and pathogenesis.
Etiology is the study of the cause of a disease; pathogenesis is the manner in which the disease develops.
Define sporadic, endemic, epidemic, and pandemic diseases.
Sporadic = occasional; endemic = constant in population; epidemic = many cases in short time; pandemic = worldwide epidemic.
What is a reservoir of infection?
Source where pathogen lives and multiplies (human, animal, nonliving).
Define pathogenicity and virulence.
Pathogenicity = ability to cause disease; virulence = degree of pathogenicity.
Name two cell wall components that resist phagocytosis.
M protein (Streptococcus pyogenes), mycolic acid (Mycobacterium).
What is the difference between communicable and noncommunicable diseases?
Communicable diseases spread from host to host; noncommunicable diseases do not.
What are symptoms vs. signs?
Symptoms = subjective changes felt by patient; signs = measurable changes observed by physician.
Define systemic infection.
Microorganisms spread via blood or lymph from local infection to entire body.
What is the parenteral route?
Entry through breaks in skin or mucous membranes (e.g., bites, injections).
What is the role of coagulase?
Clots fibrinogen to protect bacteria from host defenses.
Give an example of microbial cooperation in disease.
One microbe makes it possible for another to cause disease or worsen symptoms (e.g., HIV and opportunistic infections).
Define nosocomial infection and give two common causes.
Healthcare-associated infection; caused by invasive procedures and antibiotic-resistant microbes.
What is herd immunity?
Protection of nonimmune individuals because most of the population is immune.
What are adhesins and their role?
Surface molecules (glycoproteins/lipoproteins) that bind to host receptors; often on fimbriae.
What do bacterial kinases do?
Break down fibrin clots, allowing spread of bacteria.
State Koch’s postulates.
1) Same pathogen present in every case; 2) Pathogen isolated and grown; 3) Pathogen causes disease in healthy host; 4) Pathogen re-isolated from host.
What is congenital transmission?
Pathogen transmitted from mother to fetus during pregnancy.
What is an opportunistic pathogen?
A microorganism that does not cause disease under normal conditions but can under special conditions (e.g., immunosuppression).
Define ID₅₀ and LD₅₀.
ID₅₀ = infectious dose for 50% of hosts; LD₅₀ = lethal dose for 50% of hosts.
Function of hyaluronidase?
Hydrolyzes hyaluronic acid, helping bacteria spread through tissues.
Name two exceptions to Koch’s postulates.
Some pathogens cannot be cultured; some cause multiple diseases or require cofactors.
What is a vector? Give examples.
Animal that transmits disease (e.g., mosquitoes for malaria).
List the stages of disease development.
Incubation → Prodromal → Illness → Decline → Convalescence.
How do capsules contribute to virulence? Provide an example bacteria.
Prevent phagocytosis (e.g., Streptococcus pneumoniae).
What do siderophores do?
Bind iron from host proteins for bacterial growth.