Basis of Infectious Disease Flashcards
What are the major groups of human pathogens?
- protozoa: single celled animals (eukaryotes)
- fungi: higher plant like organisms (eukaryotes)
- bacteria: generally small, single celled (prokaryotes)
- viruses: small, obligate parasites (non-living)
History of infectious disease:
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- Infection control: Semmelweis 1840s
- Germ Theory: Pasteur 1860s
- Antiseptics: Lister 1870s
- Germ theory of disease: Kochs 1880s
What is Kochs postulates?
Germ theory of disease:
- microorganism present in every case of disease, but absent from health organisms
- suspected organism must be isolated and grown in a pure culture
- same disease must result when the isolated microorganism is inoculated into a healthy host
- same microorganism must be isolated again from diseased host
Define:
a) Pathogen:
b) Commensal/symbiont:
c) Opportunistic pathogen:
a) Pathogen: a harmful organism that produces a pathology
b) Commensal/symbiont: an organism that is part of the normal flora, often mutualistic relationship, endogenous
c) Opportunistic pathogen: an organism that causes infection when opportunity/change in natural immunity arises (e.g. in an immunocompromised individual) e.g. cut, bacteria getting into blood
Define:
- Virulence:
What is the lethal dose 50?
What is infectious dose?
- Virulence: the capacity of a microbe to cause damage to the host
Lethal Dose: 50% of organisms to die
Infectious Dose: how many of a particular infectious agent you need before any pathology is produced
Which is more virulent and why?
Strain A as a smaller number cause a damaging pathology
Define:
- Exogenous:
- Endogenous:
- Microbiome:
- Exogenous: infective material derived from outside patients body
- Endogenous: bacteria/fungi part of natural microbiome (commensal)
- misplaced, transfer from non-sterile to normally sterile site
- change in natural flora e.g. antibiotic therapy
- Microbiome: community, or its associated genetic material, associated with host during health or disease
Supra-gingivally, what bacteria dominates?
Streptococci
Define:
- Commensal:
- Mutualistic:
- Parasitic:
- Commensal: organism gains advantage but host does not gain from association
- Mutualistic: (symbiotic) when host and organism gain mutual value
- Parasitic: live on or in living creatures causing harm/damage to the host
How can a mutualistic relationship be disturbed?
Can be disturbed by illness or treatment e.g. antibiotics
- organism can produce nutrients or vitamins
- can degrade harmful chemicals
- can exclude access/colonisation by exogenous pathogens (colonisation resistance)
Examples of endogenous microbe to pathogen:
- damage to epithelium
- presence of foreign body
- transfer of bacteria to incorrect site
- suppression of immune system
- infection by exogenous pathogen
- disruption of microflora by antibiotics
List some key ways on spreading to new host:
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- direct contact - vertical/horizontal
- indirect spread - dental instruments not cleaned properly
- air-borne spread - droplets
- vector borne spread - insects
What is epidemiology?
Things to consider:
- the study of the occurence, spread and control of disease
Must consider: infective dose, virulence of organism, host status
Define:
Sporadic:
Endemic:
Epidemic:
Pandemic:
List problems of infectious disease today:
Sporadic: low level, comes and goes, variety of population
Endemic: always present in a population, usually low/acceptable level
Epidemic: sudden large amount of disease over short period of time
Pandemic: 2 or more continents with disease
Infectious disease today: anti-microbial resistance, anti-vaxers, global travel
Describe molecular Koch’s postulates:
- a virulence trait should be strongly associated with pathogenic strains of the species
- inactivation of genes associated with the virulence trait should decrease pathogenicity
- restoration of inactivated gene with the wild type retores pathogenicity
- gene is expressed at some point during infection
- antibodies directed against the gene product protect the host
