Lecture 5: Infectious Diseases Flashcards
Host-microorganism interactions
-commensalism
-mutualism
-infectious diseases
-infectious agents
commensalism
-bacteria get nutrition
-host is neither benefit nor harmed
-flora
mutualism
-both benefit
Viruses
-obligate intracellular pathogens
-capsid with genome
-cause lysis and death of cell during replication
-some latent (chicken pox)
-some cancerous (HPV cervical cancer)
Bacteria
-prokaryotic
-spherical (cocci)
-elongated (bacilli)
-helical (spirilla)
Types of bacteria
-spirochetes
-mycoplasmas
-rickettsiaceae
-chlamydiaceae
Spirochetes
-anaerobic
-lyme disease and syphilis
Mycoplasmas
-small
-no cell wall
-resistant to cell-wall antibiotics (penicillins)
-mycoplasma pneumoniae
Rickettsiaceae
-obligate intracellular pathogen
-transmitted via arthropod vectors (mites, fleas, ticks, lice)
-rocky mountain spotted fever
Chlamydiaceae
-obligate intracellular pathogen
-transmitted person-to-person contact
-chlamydia
-conjunctivitis in newborns
Fungi
-superficial vs systemic mycoses
-bacterial flora and immune system keep them in check
-opportunistic
superficial mycoses (dermatophytosis)
-ringworm, athlete’s foot, jock itch
-caused by dermatophytes whose infection is limited to cooler cutaneous surfaces
Systemic mycoses
-infections of deep tissue (rare)
-candidiasis (yeast infection)
-aspergillosis (lethal form of pneumonia)
Parasite types
-protozoa
-helminths
-parasitic arthropods
Protozoa
-unicellular
-plasmodium (malaria)
-Entamoeba histolytica and giardia (amebic dysentery)
Helminths
-wormlike parasites
-roundworms, tapeworms, flukes
-transmission primarily through ingestion of fertilized eggs or penetration of infections larval stages through skin
Parasitic arthropods
-ectoparasites: mites, lice, fleas
-may serve as vectors of other disease (fleas with plague)
Epidemiology
-study of patterns and determinants of health with goal of controlling health problems
incidence
-number of new cases of diseases within defined population over defined period of time
disease prevalence
number of active cases in a population
endemic
-relatively stable incidence and prevalence in region
epidemic
-abrupt increase in incidence of disease over endemic rates
pandemic
-spread of disease beyond continental boundaries
Modes of transmission
-penetration
-direct contact
-ingestion
-inhalation
Direct contact transmission
-STI
-congenital infection (vertical transmission) (toxoplasmosis, rubella, herpes)
Ingestion transmission
-cholera, typhoid, dysentery
-bacteria resistant to low pH of GI
-shigella and giardia
-differences in infectious dose
-bowel flora compete with pathogens
Inhalation
-bacterial pneumonia, meningitis, TB
-Viruses: measels, mumps, pox, flu, cold, covid
-respiratory tract has good defense systems
-smoking and CF impair defenses
Fomites
-inanimate object contaminated
-shared toys
-shared syringes
Zoonoses
-disease passed from animal to humans
-HIV, rabies, plague, flu
-70% of emerging viral infections
vector
-biting arthropod
-lyme disease, west nile
nosocomial infection
-healthcare-associated infection
Disease Course
- incubation period
- Prodromal stage
- Acute stage
- Convalescent Stage
- Resolution stage
Incubation period
-active replication
-no symptoms
Prodromal stage
-initial symptomes
-nonspecific symptoms
Acute stage
-max impact of infection
-inflammation and tissue damage
Convalescent stage
-progressive elimination of pathogen
Resolution stage
-total elimination of pathogen
Virulence factors
-substances or products generated by infectious agents that enhance ability to infect
-exo vs endo toxins
-adhesion factors
-evasive and invasive factors
Exotoxins
-proteins released by pathogenic bacteria
-inactivate key cellular constituents
-superantigens inducing excessive and nonspecific inflammatory responses
superantigens
-bind to MHC of APC and T cell receptors
-T cells activated regardless of antigen on MHC
Endotoxins
-lipids and polysaccharides
-can induce clotting, bleeding, inflammation, hypotension, and fever
-endotoxic shock
Adhesion factors (adhesins)
-bind to molecules on surface of host cell
-some pathogens form mucous layer
Evasive factors
-inactivate host immune system
-leukocidins form pores in cell membrane of neutrophils and macrophages
-some pathogens survive and reproduce within phogocytes after phagocytosis by neutralizing lysosome with evasive factors
Invasive factors
-facilitate penetration of barriers
-pseudomonas aeruginosa collagenase breaks skin
