Infectious Diseases Flashcards
Global burden of disease - how important are infection
Top - Circulatory, cancer, infectious.
Infectious disease
Viruses, Bacteria, Fungi, Protozoa, Helminths, Prions.
Classification and comparison of diseases
Organism or particle size Genome size organismsation Replication/Reproduce/Spreas Immunity Extracellular/Intracellular
Viruses
Nucleic acid wrapped in protein coat Most widespread of all pathogens Receptors Classification based on : envelope nucleic acid
Virus immunity
Intracellular phase:
Interferon
NK cells via loss of MHC
Cytotoxic T cells via MHC peptide recognition
Extracellular phase
Antibodies block entry to cells
Bacteria
Unicellular organism
Fully independent existence
Prokaryotes
Extracellular or intracellular
Bacteria classification (cell wall): Gram +ve - a lot of peptidoglycan Gram -ve - not a lot of peptidoglycan Acid fast - contain layer of fat
Immunity to bacteria
Extracellular and unicellular
- Phagocytes
- Antibody
- Complement
Intracellular
- Cytotoxic T cells kill host infected cells and activate macrophages
- Helper T cells activate macrophages to kill bacteria by MHC recogniction
Fungi
Eukaryotic Unicellular Single cells/filaments or Dimorphic Extracellular/Unicellular Independant
Similar to bacteria, but main difference is the cell wall, Chitin is exclusive to fungi only.
Fungal diseases
Yeast (Candida albicans), commensal but can overgrow in mouth, vagina following prolonged antibiotic treatment
Mold (Aspergillus fumigatus), lung infection in the immunocomproised.
Fungal immunity
Similar to bacteria
Protozoa
Unicellular organism
Eukaryotic
Many alternate between vegetative form and resting form
They are much more complicated.
They can constantly changing from a diverse life cycle, hence harder to develop immunity.
i.e a confusing number of signals for the host to deal with.
They have 2 sexes which reproduce to get diversification.
Immunity to protozoa
Diseases are extremely chronic Only partial immunity Resistance in some genetic diseases -Sickle cell anemia, resistance to malaria -Absence of the Duffy antigen
Helminths (worms)
Multi-cellular
Hard exoskeleton
Eukaryotic
Well developed organs
Do not replicate in their human host, they get bigger.
Complex life cycle with intermediate hosts.
Examples: Nematodes
Immunity to Helminths
Any immunity is directed at larval stage Well developed evasion mechanism Chronic term disease Bias towards TH2 response IL-3,4,5,9,13 Increases mast cells and eosinophils High IGE Strong immunopathology Immunsuppression
Prions
Composed solely of proteins
Different from viruses
Main difference between prion and viruses is prion does not contain nucleic acid
All humans express prion proteins
They are heat resistant
Examplies: CJD,Kuru
Prion protein:
Host encoded
253 amino acid
N terminal 22aa are removed after transport to the ER
Exists in two forms, conformers
Normal cellular protein, Prp and a pathogenic misfolded protein,PrPsc
Both encoded by PNRP gene
Primary structu
Immunity to Prions
They is NO immunity
Antibodies can be raised exponentially
No good evidence for protective immunity
When the abnormal form of the protein comes into contact with normal form, the normal form is mutated into the abnormal.
