Infectious Disease Transmission/ Host Defenses Flashcards
Prions-Agents of Infectious Disease
Protein particles without a genome
Infectious and capable of producing disease
Examples: Creutzfeldt-Jakob disease, Kuru and “mad cow” disease
Viruses
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)
ONCOGENIC
Some viruses have the ability to transform normal host cells into malignant cells during the replication cycle (HPV)
Gram-positive
Purple
Gram-negative
Red
Bacteria
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
Fungi
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)
Yeasts (Fungi)
Single-celled organisms
Reproduce by a budding process
Colonies are smooth with a waxy or creamy texture
Molds- Fungi
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
Arthropods (Parasites)
vectors such as ticks, mosquitoes, biting flies
Actual infectious agent is carried by the arthropod
Usually a virus
Ectoparasites (Parasites)
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
Protozoa (Parasites)
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
Helminths (Parasites)
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
Incidence
number of new cases
Prevalence
number of active cases at any given time
Exotoxins
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)
Endotoxins
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
Penicillins/Cephalosporins Microbial Resistance
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)
Sulfonamides Microbial Resistance
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)
Fluoroquinolones Microbial Resistance
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
Macrolides Microbial Resistance
Alterations in the macrolide binding site on the ribosomal subunit
Altered transport of the macrolide
