Infectious Disease Transmission/ Host Defenses

Question 1

Prions-Agents of Infectious Disease

Answer 1

Protein particles without a genome
Infectious and capable of producing disease
Examples: Creutzfeldt-Jakob disease, Kuru and “mad cow” disease

Question 2

Viruses

Answer 2

Intracellular pathogen**…incapable of replication outside a living cell
Consist of a protein coat (capsid), surrounding either RNA or DNA
Some viruses have a lipoprotein envelope derived from the parasitized host cell
Viruses MUST penetrate a susceptible living cell & use the biosynthetic machinery of the cell to produce viral progeny (Latency)

Question 3

ONCOGENIC

Answer 3

Some viruses have the ability to transform normal host cells into malignant cells during the replication cycle (HPV)

Question 4

Gram-positive

Answer 4

Purple

Question 5

Gram-negative

Answer 5

Red

Question 6

Bacteria

Answer 6

Autonomously replicating unicellular organisms—prokaryotes*
contain no organized intracellular organelles
Genome consists of a single chromosome of DNA and RNA
Does have reproductive and metabolic machinery in the cytoplasm of the cell (unlike viruses)
Most produce asexually be cellular division

Question 7

Fungi

Answer 7

Free-living, eukaryotic saprophytes
Few fungi are capable of causing serious disease in humans & serious fungal infections are rare**
Reproduction is sexual or asexual (Involves production of spores)

Question 8

Yeasts (Fungi)

Answer 8

Single-celled organisms
Reproduce by a budding process
Colonies are smooth with a waxy or creamy texture

Question 9

Molds- Fungi

Answer 9

Produce long, hollow, branching filaments—hyphae
Some produce cross walls which segregate the hyphae others do not
Produce cottony or powdery colonies of mats of hyphae–mycelium

Question 10

Arthropods (Parasites)

Answer 10

vectors such as ticks, mosquitoes, biting flies
Actual infectious agent is carried by the arthropod
Usually a virus

Question 11

Ectoparasites (Parasites)

Answer 11

Infest external body surfaces and cause localized tissue damage or inflammation secondary to the bit or burrowing action
Some of the most prominent:
Mites (scabies)
Chiggers
Lice
Fleas

Question 12

Protozoa (Parasites)

Answer 12

Unicellular animals with complete eukaryotic machinery**
Reproduction may be sexual or asexual
Most are saprophytes, but some can cause disease in the human
Examples: amebic dysentery, malaria, and giardiasis

Question 13

Helminths (Parasites)

Answer 13

Collection of wormlike parasites
Include nematodes (roundworms),  cestodes (tapeworms),  & trematodes (flukes)
Often an intermediate host is required for development & maturation of the offspring and then humans are infected and sexual reproduction occurs in the human host
Helminth infections often involve multiple organ systems

Question 14

Incidence

Answer 14

number of new cases

Question 15

Prevalence

Answer 15

number of active cases at any given time

Question 16

Exotoxins

Answer 16

Proteins released from the bacterial cell DURING growth
Enzymatically inactivate or modify key cellular constituents, leading to cell death or dysfunction (diptheria, botulism, toxic shock syndrome)
Bacterial exotoxins produce vomiting/diarrhea—enterotoxins (E. coli 0157:H7)

Question 17

Endotoxins

Answer 17

Complex molecules composed of lipid & polysaccharides found in the cell wall of gram-negative bacteria
NOT actively released during growth of the bacteria & have no enzymatic activity
They are potent activators of regulatory systems (induce clotting, hypotension, fever)
Can induce endotoxic shock

Question 18

Penicillins/Cephalosporins Microbial Resistance

Answer 18

Inactivation of the drug by beta-lactamases (enzymes):
DNA by plasmid insertion
Direct chromosomal DNA mutations
Overcoming resistance—add a beta-lactam inhibitor (clavulanic acid)
Decreased penetration to the target site (gram-negative bacteria)
Alterations of the binding site (penicillin-binding-proteins—PBPs)

Question 19

Sulfonamides Microbial Resistance

Answer 19

Overproduction of PABA
Surplus of folic acid
Structural changes in enzymes so there is less affinity for the sulfonamide substrate
To overcome resistance used in combination w/ other agents (trimethoprim)

Question 20

Fluoroquinolones Microbial Resistance

Answer 20

Chromosomal mutations—such as active efflux of the drug or protection of DNA gyrase
Sometimes plasmids carry the DNA for resistance
Alterations in their ability to permeate the bacterial cell wall
Longer duration of use leads to greater likelihood of resistance

Question 21

Macrolides Microbial Resistance

Answer 21

Alterations in the macrolide binding site on the ribosomal subunit
Altered transport of the macrolide