Spread and Replication Flashcards
Describe a surface infection
- multiply in epithelial cells at the site of entry (don’t penetrate deeper down)
- and spread to other areas (fluid flow- coughing, sneezing, flow of mucous over GI and respiratory tract)
- large areas of the body may be covered
- innate immunity is involved - not enough time for adaptive (no contact with blood vessels)
What are some examples of surface infections and why
Common cold - restricted to your respiratory sx
- influenza stays in the respiratory tract (surface), while measles spreads into your blood (systemic)
Describe a systemic infection
- shed via the blood/ lymph
- migration from surface to deeper tissue
- eq. meningococci from nasal mucosa to meninges
What are the factors affecting the location of infection?
- temperature
- rhinovirus - URT (33 degrees) LRT (37 degrees)
- mycobacterium leprae (nasal mucosa, skin and superficial nerves - budding
- influenza, parainfluenza viruses - released from he lung epithelial cells not basal layers - systemic spread
- failure to spread and multiply at the site of primary infection
- measles: No replication
- typhoid: GI
- HAV: alimentary canal-liver
- mumps: respiratory canal-salivary glands
- —- sometimes organizations cause systemic infections because they cannot replicate at the primary site of infection
Is a lung infection always a surface infection?
- NO! A lung infection can be systemic first before it ever gets to the lung -can be in the blood first
How is bacteria spread from blood?
- transcient bacteremia
- filtered out and destroyed by macrophages (liver and spleen)
- localization at less well-defended sites (viridians streptococci - hide in heart valves and are not accessible to the immune system)
- if free in blood, encounter Abs and phagocytes (unless associated with circulating cells in bloodstream - EBV, rubella, listeria)
- characteristic target organs and tissue for circulating microoganisms
How are viruses spread in the nerves
-CNS from peripheral nerves (rabies, HSV, VZV)
- travel in axons to CNS and back to peripheral nerves during recurrent outbreaks
- host defences unable to control viral spread in nerves
(for an organism to be good at causing an infection in the CNS, it has to be able to cross the BBB)
What kind of antibiotics would be good for treating bacteria that cross the blood brain barrier?
hydrophobic drugs because they can diffuse through the layer
How do microbes spread in the pleural and peritoneal cavities?
- microbes can spread from one visceral organ to another through the peritoneal or pleural cavity
- injury or disease in abdominal organs may lead to infections -peritonitis
What virus spreads to only humans or closely related primates?
measles!
What virus has a wide range of hosts?
rabies!
What determines a narrow range of spread or a broad range?
receptors
- if we share receptors with other hosts, this organism that identifies with this receptors are considered broad host range (prairie dogs and humans share the same receptor)
How does malaria affect people with sickle cell anemia?
- malaria works in the favour of people with sickle cell anemia - the people that carry the mutation of sickle cell anemia will not die from malaria
What is sickle cell anemia?
- defect in a gene that encodes fro hemoglobin causes sickle cell anemia(hemoglobin s is the defective gene)
- hemoglobin s impacts our ability to carry O2- lethal mutation. RBC’s take the shape of the sickle- mutation is lethal to the homozygous mutation
What bacterial species causes malaria?
plasmodium
What is the most important feature of pathogens?
virulence
What is the difference between pathogenicity and virulence
ability to cause disease is pathogenicity, and the measure of pathogenicity is virulence
What is ID50?
the dose of the pathogen needed to infect 50% of the test host
- this measure is used to measure the virulence of the pathogen
What ate the factors that must be taken into consideration when thinking about virulence?
- adhesion
- penetration
- toxin production
- interaction with immune system
- attenuation- serial passaging on artificial media
The fate of microorganisms in the blood depends on whether or not they are free or associated with circulating blood. How so?
- if microorganisms are free in the blood, they are exposed to body defences such as antibodies and phagocytes
- if microorganisms are associated with circulating cells, they are protected from host defences and can be carried around the body this way
In transcient bacteremia, the bacteria is typically filtered out and destroyed by macrophages in the liver and spleen. When does this not occur?
- when the bacteria can localize at less well defended sites- congenital heart valves - viridins streptococci
What happens when bacteria is free in blood?
Gets filtered out and destroyed by lymphocytes
What are some examples of pathogens that associate with circulating cells in the bloodstream?
Ebseteine Barr Virus, rubella, listeria
If microorganisms are not fought off by the IS in a certain period of time, what happens?
they becomes localized elsewhere in the vasculature
- for a specific organ, for example
Why does a microorganism localize at a particular organ in the body?
Not entirely known
Could be due to:
- specific tissue receptors for certain microbes
-only some organs suitable for replication
-areas with local inflammation become sticky; slower flow due to inflamed vessels may trap microbes
How do microorganisms evade the innate immune system by producing iron binding molecules?
- nearly all bacteria need iron, but the host’s iron binding proteins (transferrin) limit the availability of this element to the bacteria. Certain bacteria (Neisseria) produce their own iron binding proteins to circumvent the shortage - has a higher affinity for iron than transferrin
How do some viruses evade the host immune system by blocking interferons?
some viruses are poor inducers of interferons(hepatitis B) or produce molecules that block the action of INF in the cell (HIV)
