Mechanisms of Disease (Exam 2)

host

supporting organism, thing providing pathogen with the environment it needs to live, grow, and reproduce

infection

invasion and multiplication of harmful microorganisms, which can lead to damage to tissues and disease 

pathogen

microorganisms capable of producing a disease

opportunistic infection 

cause disease in immunocompromised host 

prions - what are they 

• protein particles that lack a genome 

• resistant to enzymes which normally break down proteins 

  • normal cells tricked into producing abnormal proteins which deposit s amyloid plaques 

prions - pathophysiology

• slowly progressive degeneration of nerves (don’t see symptoms right away)

• amyloid plaques in brain, spread throughout nervous system 

• prion proteins are mutant forms of normal host protein which cause disease

prions - examples 

• chronic wasting disease - seen in deer and elk

• bovine spongiform encephalopathy (mad cow disease) - affects cattle but humans can get from eating infected meat 

• creutzfeld-jacob disease - humans 

• S/S: ataxia, dementia, wasting

*no treatment, rare 

virus - thrive, replication, structure

• thrive and reproduce only in a host cell (intracellular)

• simple organisms w/ no organelles 

• basic structure contains nucleic acid protected by capsid 

  • some enclosed within a lipoprotein envelope 

virus - classification

7 classes based on presence of dna OR rna and single or double strands (viral genome), type of replication, and disease produced 

virus - life

1. attachment to cell surface proteins, receptors

2. penetration

3. uncoating - release of nucleic acid 

4. replication

5. assembly & release of new virions 

virus - how body gets rid

• antibodies (tagging of virus for phagocyte to eat, clumping, etc.) 

• cytotoxic T cells - search for infected cells presenting on MHC1

• interferons - proteins inside cell that are turned on by a virus coming in, tells other cells to not let the virus in 

virus - damage to cells

• disrupt protein synthesis

• promote apoptosis

• cause infected cells to become malignant 

virus - evade hosts immunity

mutate, hide, shut down immune signaling, sabotage MHC presentation, or attack immune cells directly

bacteria - basics

• prokaryotic, unicellular

  • 1 chromosome

  • plasmids w/ circular DNA

  • typically both RNA and DNA

bacteria - categorization

• based on morphology, staining

  • cocci, bacilli - shape 

  • gram negative or positive 

  • attachement - pili 

bacteria - staining

• cell walls contain peptidoglycan

  • gram negative stain red - thin layer peptidoglycan, outer layer of lipopolysaccharide 

  • gram positive stain purple - thick layer of peptidoglycan 

• tells us susceptibility to antibiotics 

bacteria - harder to kill

gram negative bacteria are harder to kill because outer layer of lipopolysaccharide is an extra barrier thus making them harder to penetrate

bacteria - toxins (how they cause damage to cells) 

• when we ingest bacteria they produce toxins that cause inflammation and damage 

  • exotoxins: both + and -, secreted proteins and enzymes that are very specific and potent

    • neurotoxins (nerves), enterotoxins (gut), cytotoxins (kill/damage cells) 

  • endotoxins: gram - only specifically their lipopolysaccharide walls, released when bacteria die, cause excessive inflammation symptoms 

fungi - overview

• eukaryotic (have nucleus w/ rna and dna) organisms, different wall than bacteria

• types: mold, yeast, dimorphic

• mycosis = infection with fungus

fungi - where they grow

skin and mucous membranes because require cooler temperature than body temp so most on surface

fungi - who is most susceptible

immunocompromised or infants are most susceptible, opportunistic infection (healthy people typically not affected, but immunocompromised people are likely to be)

*need antifungal agents, antibiotics do not penetrate wall 

parasites - what are they 

• members of the animal kingdom that infect us

• helminths (parasitic worms) spread by the ingestion of eggs, or through the skin (roundworms, tapeworms, flukes)

• arthropods that carry parasites = ticks, mites, lice, fleas, mosquitos 

parasites - protozoa infection 

• eukaryotic, unicellular

• spread directly by host to host (sexually) or indireclty from arthropod or food/water ingestion

• example: plasmodium, the malarial parasite, transmitted by anopheles mosquito → invades liver cells → liver cells rupture → released in blood → RBCs infected → plasmodium multiply in RBCs → S/S: intermittent fever, chills, anemia, neurological damage, death

how do infections overcome the immune system

• microbial adherence - attach to mucous membranes

• encapsulation (thick carb/protein coat) - protects against phagocytosis

• rapid replication - overwhelms immune system

• mutation - constant genetic changes can alter surface proteins, leading to antibiotic resistance

• enzyme/toxin production - dissolve EC matrix, prevent antibiotics from reaching

• biofilm formation - form slimy protective layer on surfaces to shield from antibiotics and immune cells

• intracellular survival - hide inside cells

• antigenic variation - change surface antigens so antibodies don’t recognize them

• coating with host antigens - disguise themselves to avoid detection

S/S of infection

• related to site of infection

• general: fever, malaise, increased WBC count

clinical stages of infectious disease

• incubation - exposure

• prodromal - in b/n stage, start to develop generalized symptoms

• acute - increase in severity of symptoms + become specific

• convalescence - treatment has started to kick in

atypical courses

• fulminant - no prodrome

• insidious - prolonged prodromal phase

• subclinical/subacute - no clinical S/S

diagnosing infection

• culture and sensitivity

  • growth of microorganisms outside body

  • determination of antibiotic effectiveness

  • gram stain

• serology

  • measuring specific antibodies in the serum

• detection of antigens

  • DNA and RNA sequencing of organisms