Pathogens and the host Flashcards
What is the difference between a pathogen and a commensal?
Pathogens will cause disease whereas commensals are organisms that exist as part of the normal flora and do not cause harm
Define pathogenicity.
The capacity of a micro-organism to cause an infection
What 2 factors are essential in determining a virus’s pathogenicity?
Virulence
Infectivity
What does infectivity mean?
The ability of a pathogen to become established on or within a host
What structural feature of a bacterium increases it’s infectivity, and why?
Fimbriae
Allows attachment to cell
Helicobacter pylori infects in the stomach. What feature of it increases it’s infectivity?
It has acid resistance
Allows it to survive
What is virulence?
The capacity of a pathogen to cause harmful effects once established on or within a cell
Virulence factors determine how harmful a pathogen is.
List the virulence factors.
Invasiveness
Toxin production
Evasion of immune system
Virulence factors are specific to strains, not species.
Give an example of a type of bacteria, who’s strains vary greatly in their virulence.
E. Coli
Some strains are completely harmless and live in gut normally
Some are not so good
What is the difference between infection and colonisation?
Infection will cause symptoms to show
Colonisation will not cause symptoms to show
Define colonisation.
When a pathogen grows at a site of infection, without causing symptoms to show
Using fancy words, a patient who’s body was the host to colonisation of bacteria would be what?
Asymptomatic
What is the difference between an acute infection, and a chronic infection?
Acute = short term Chronic = long term
What is a sub-clinical infection?
Asymptomatic
Occult
No apparent symptoms
In general, what are the differences between the symptoms of a viral infection, and those of a bacterial infection?
Viral infections are systemic, and often affect more than one system at once. Affected systems/areas tend to be itchy and/or burning, and few are painful.
Bacterial infections often involve localised pain, swelling, redness and burning in a specific area, not a system.
Describe the 3 types of toxins.
Exotoxins - released by the pathogen
Enterotoxins - type of exotoxin - act in GI tract
Endotoxins - structurally part of gram negative cell wall
Describe the structure of an endotoxin.
Lipopolysaccharide
Composed of lipid A, an oligosaccharide core and a specific polysaccharide chain
Although bacterium can cause harmful effects using toxins, how else can infection of bacteria cause harm?
The host’s response
hypersensitivity and all that stuff
What is the difference between a primary and a secondary infection?
Primary - Root cause of infection
Secondary - caused/allowed due to another infection
When a latent virus goes into dormancy, how does it exist?
The virus is latent in the nucleus
What is opsonisation?
Covering of pathogen in antibodies or compliment proteins
Phagocytic cells have receptors for both
Efficiency for phagocytosis is greatly improved
What effect do compliment proteins have on the immune system?
Opsonise
Breakdown of Gram negative organisms
Compliment cascade signals polymorphs (neutrophils, eosinophils, basophils) to come to site of infection
Humoral (extra-cellular) immunity MOSTLY deals with what type of infection; viral or bacterial? Acute or chronic?
Bacterial
Acute
Cell mediated immunity MAINLY combats what type of infection?
Viral infection
some bacterial and some fungi
What are the 3 types of vaccine?
Live attenuated
Killed (inactivated)
Toxoid
What is a toxoid vaccine?
Toxin treated with formalin
Antigens remain but no toxic activity
Bacterium X produces toxin Q
You are given a toxoid vaccination and all is good
You are exposed to bacterium X again. Describe what will happen.
Bacterium X is still able to colonise
However it can not infect you
Sub-clinical infection as no symptoms
Toxoid vaccinations are against the toxin, not the organism
Why are live attenuated vaccinations difficult to administer in developing nations?
Must be refrigerated until they are given
There is a risk with live-attenuating vaccinations that killed vaccinations do not have. What is this?
Risk of pathogen reverting back to ‘wild-type’
What are the main sites of viral entry?
Conjuctiva Respiratory tract Alimentary tract Urinogenital tract Skin Capillaries (via a vector)
