Lecture 5: Infectious Diseases Flashcards by Brooke Thornburg

Host-microorganism interactions

-commensalism
-mutualism
-infectious diseases
-infectious agents

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commensalism

-bacteria get nutrition
-host is neither benefit nor harmed
-flora

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mutualism

-both benefit

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Viruses

-obligate intracellular pathogens
-capsid with genome
-cause lysis and death of cell during replication
-some latent (chicken pox)
-some cancerous (HPV cervical cancer)

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Bacteria

-prokaryotic
-spherical (cocci)
-elongated (bacilli)
-helical (spirilla)

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Types of bacteria

-spirochetes
-mycoplasmas
-rickettsiaceae
-chlamydiaceae

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Spirochetes

-anaerobic
-lyme disease and syphilis

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Mycoplasmas

-small
-no cell wall
-resistant to cell-wall antibiotics (penicillins)
-mycoplasma pneumoniae

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Rickettsiaceae

-obligate intracellular pathogen
-transmitted via arthropod vectors (mites, fleas, ticks, lice)
-rocky mountain spotted fever

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Chlamydiaceae

-obligate intracellular pathogen
-transmitted person-to-person contact
-chlamydia
-conjunctivitis in newborns

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Fungi

-superficial vs systemic mycoses
-bacterial flora and immune system keep them in check
-opportunistic

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superficial mycoses (dermatophytosis)

-ringworm, athlete’s foot, jock itch
-caused by dermatophytes whose infection is limited to cooler cutaneous surfaces

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Systemic mycoses

-infections of deep tissue (rare)
-candidiasis (yeast infection)
-aspergillosis (lethal form of pneumonia)

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Parasite types

-protozoa
-helminths
-parasitic arthropods

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Protozoa

-unicellular
-plasmodium (malaria)
-Entamoeba histolytica and giardia (amebic dysentery)

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Helminths

-wormlike parasites
-roundworms, tapeworms, flukes
-transmission primarily through ingestion of fertilized eggs or penetration of infections larval stages through skin

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Parasitic arthropods

-ectoparasites: mites, lice, fleas
-may serve as vectors of other disease (fleas with plague)

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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

1. incubation period 2. Prodromal stage 3. Acute stage 4. Convalescent Stage 5. 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