Spread and Replication

Question 1

Describe a surface infection

Answer 1

• 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)

Question 2

What are some examples of surface infections and why

Answer 2

Common cold - restricted to your respiratory sx

- influenza stays in the respiratory tract (surface), while measles spreads into your blood (systemic)

Question 3

Describe a systemic infection

Answer 3

• shed via the blood/ lymph
• migration from surface to deeper tissue
• eq. meningococci from nasal mucosa to meninges

Question 4

What are the factors affecting the location of infection?

Answer 4

1. temperature
   - rhinovirus - URT (33 degrees) LRT (37 degrees)
   - mycobacterium leprae (nasal mucosa, skin and superficial nerves
2. budding
   - influenza, parainfluenza viruses - released from he lung epithelial cells not basal layers
3. 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

Question 5

Is a lung infection always a surface infection?

Answer 5

• NO! A lung infection can be systemic first before it ever gets to the lung -can be in the blood first

Question 6

How is bacteria spread from blood?

Answer 6

• 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

Question 7

How are viruses spread in the nerves

Answer 7

-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)

Question 8

What kind of antibiotics would be good for treating bacteria that cross the blood brain barrier?

Answer 8

hydrophobic drugs because they can diffuse through the layer

Question 9

How do microbes spread in the pleural and peritoneal cavities?

Answer 9

• 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

Question 10

What virus spreads to only humans or closely related primates?

Answer 10

measles!

Question 11

What virus has a wide range of hosts?

Answer 11

rabies!

Question 12

What determines a narrow range of spread or a broad range?

Answer 12

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)

Question 13

How does malaria affect people with sickle cell anemia?

Answer 13

• 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

Question 14

What is sickle cell anemia?

Answer 14

• 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

Question 15

What bacterial species causes malaria?

Answer 15

plasmodium

Question 16

What is the most important feature of pathogens?

Answer 16

virulence

Question 17

What is the difference between pathogenicity and virulence

Answer 17

ability to cause disease is pathogenicity, and the measure of pathogenicity is virulence

Question 18

What is ID50?

Answer 18

the dose of the pathogen needed to infect 50% of the test host
- this measure is used to measure the virulence of the pathogen

Question 19

What ate the factors that must be taken into consideration when thinking about virulence?

Answer 19

• adhesion
• penetration
• toxin production
• interaction with immune system
• attenuation- serial passaging on artificial media

Question 20

The fate of microorganisms in the blood depends on whether or not they are free or associated with circulating blood. How so?

Answer 20

• 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

Question 21

In transcient bacteremia, the bacteria is typically filtered out and destroyed by macrophages in the liver and spleen. When does this not occur?

Answer 21

• when the bacteria can localize at less well defended sites- congenital heart valves - viridins streptococci

Question 22

What happens when bacteria is free in blood?

Answer 22

Gets filtered out and destroyed by lymphocytes

Question 23

What are some examples of pathogens that associate with circulating cells in the bloodstream?

Answer 23

Ebseteine Barr Virus, rubella, listeria

Question 24

If microorganisms are not fought off by the IS in a certain period of time, what happens?

Answer 24

they becomes localized elsewhere in the vasculature

- for a specific organ, for example

Question 25

Why does a microorganism localize at a particular organ in the body?

Answer 25

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

Question 26

How do microorganisms evade the innate immune system by producing iron binding molecules?

Answer 26

- 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

Question 27

How do some viruses evade the host immune system by blocking interferons?

Answer 27

some viruses are poor inducers of interferons(hepatitis B) or produce molecules that block the action of INF in the cell (HIV)