Diagnosis And Control Of Infection Flashcards
Definition of epidemiology
Study of when and where diseases occurs and how they are transmitted to the population
Definition of chain of infection
Concept used to explain how a patient can acquire an infection from another person
Definition of reservoirs
Places where pathogens can grow and accumulate
Definition of zoonotic diseases
Spread between animals and people
Definition of fomite
Objects/materials which are likely to carry infection (clothes, utensils, furniture)
Definition of vertical transmission
Transmission from mother to child via placenta
Definition of horizontal transmission
Person to person transmission that is not between mother and child
Definition of titre
Antibody conc in a sample, associated with the no times someone can dilute a sample and still detect the AB
Definition of serconversion
Time period during which a specific AB develops and becomes detectable in the blood
Definition of bacteriocidal
Antibacterial agent that kills bacteria
Definition of bacteriostatic
Antibacterial agents that inhibit bacterial growth
Definition of vaccination
Exposing a person to antigenic material but not pathogenic
Induces adaptive immunity and memory
Definition of herd immunity
In contagious diseases that are transmitted from person => person, chains of infection likely to be broken when large nos are immune
What 6 factors are considered in epidemiology
Aetiology, identify pathogen causing diseases
Predisposing factors, age, sex, lifestyle, susceptible populations
Incidence, rate of occurrence
Prevalence, all cases in a timeframe
Mode of transmission, how its spread
Public health policy prevention, how to reduce spread
How is the chain infection used in epidemiology
Chain of infection, how a patient can acquire an infection from 1 person to another
If chain broken, transmission stops
What are reservoirs
What are the 3 main reservoirs
Places where pathogens grow and accumulate
Human, animal, famine
What are the 3 main modes of transmission
Contact
Indirect (vehicle/vector)
Vertical
What are the 3 methods of transmission via contact
Exposed to pathogen by either touching or being close to an infected person or object
Direct
- Person to person
- No intermediate object involved
Indirect
-Via fomite
Droplet
- Spread in mucus droplets
- Travel short distances
- Sneezing, coughing, talking
What are the 3 methods of vehicle (indirect) transmission
Waterborne
-Water contaminated with sewage
Airborne
- Inhalation of small particles, pathogens
- Long distances
Food borne
-Contamination of food w pathogen
What are the 2 methods of vector (indirect) transmission
Mechanical
- Passive transport on body
- Contaminated food, water, hands, person to person
- Enteric and eye infections
Biological
- Pathogen spends part of life cycle in vector
- Bite
- Malaria, Zia, rabies
What is vertical transmission
From mother to child
What are Koch’s 4 postulates
Microbe only found in ill
Microbe must be isolated and cultured
Culture should cause disease in healthy
Microbe reisolated is identical to original
What are the 3 exceptions to Koch’s postulates
Asymptomatic infection carriers
Can’t grow in vitro/no susceptible animals
Not all exposed infected
What are the 2 main methods of laboratory diagnosis
Direct detection
- culture
- microscopy
- nucleic acid
Indirect detection (serological)
How would you culture bacteria and viruses
Bacteria
-grow in culture under controlled conditions
Viruses
-permissive cells => cytopathic effects
How would you use microscopy in direct methods
Staining, morphology
Electron microscope used for viruses
How would you use nucleic acid detection in direct detection methods
When would you use this
What are the 2 methods
PCR => amplify
Hybridisation => complemetary fluorescent probes
Detect hard/slow growing organisms
How would you use a serological test in indirect methods
Paired samples (acute, convalescent) tested for 4x increase in AB titre (seroconversion)
IgM and not IgG = indicative of current infection
What are the advantages and disadvantages of culture
Advantages
- Confirms organism presence
- Can be multiplied for further testing
Disadvantages
- Time consuming
- Must be capable of growing in vitro
What are the advantages and disadvanatges in microscopy
Advantages
-Quick, day results
Disadvanatges
-Not v specific
What are the advantages and disadvantages of nucleic acid testing
Advantages
- Results in hours
- Sensitive and specific
Disadvantages
-Knowledge of DNA sequence needed
What are the advantages and disadvantages of serological tests
Advantages
- Many body fluids can be used
- Cheap, easy
- Multiple samples can be analysed
Disadvantages
- Time consuming to obtain paired serum
- Specific AB not always available
- Not good for agents that produce disease before AB
- AB not detected due to low conc
- False positives due to cross reactivity
- Tests are retrospective
- Cannot distinguish between previous and current infection
What are the main properties of antibacterial/antiviral agents
Exploiting differences metabolism and structure of microbe and human cells
Can be natural or synthetic
What are the 4 targets of bactericidal/bacteriostatic agents
Cell wall synth
-peptidoglycan unique to bacteria
Plasma membrane
-disrupt membrane potential, target LPS
Nucleic acid
-block enzymes needed for DNA/mRNA synth
Protein synth
-disrupt prokaryotic ribosomal proteins, RNA, enzymes
What are the 3 main targets in antiviral agents
Attachment, entry
-inhibit fusion of envelope/receptor attachment
Nucleic acid synth
-target viral DNA, RNA polymerase
Assembly/budding
-Inhibit viral proteins needed for maturation/release
What are the 4 bacterial strategies for drug resistance
Prevent drug penetrating target
Modify/inactivate drug
Expulsion from cell by efflux pumps
Modify target site
What are the 2 viral strategies for drug resistance
How do we delay the appearance of drug resistance
Spontaneous mutation
Error prone polymerase in RNA virus
HAART therapy
What are the 4 types of immunity
How can they be acquired?
Natural active
-exposed to pathogen
Natural passive
-Maternal AB
Artificial active
-vaccine
Artificial passive
-given AB
Requirements of an effective vaccine
Safe, no/few side effects
Long lasting protection
Formation of memory cells
Cheap, easy admin
Stable, long shelf life
Herd immunity
