Infectious Diseases part 2

Question 1

By which ways microbes can spread within the body?

Answer 1

• Lysis & Invasion:
  initially follow tissue planes of least resistance and drain into regional lymphatics.
• Through blood and lymph:
  transport occurs in various ways: in the plasma, in RBCs/WBCs etc.
• Cell-to-Cell Transmission: most viruses spread locally by this way.

Question 2

What is the most common and efficient mode of microbial dissemination?

Answer 2

Through the blood stream.

Question 3

Give 3 examples of viruses that spread through the nervous system:

Answer 3

• Rabies, Poliovirus, Varicella

Question 4

The consequences of blood borne pathogen spreading depend on what?

Answer 4

• The virulence of the organism.
• The magnitude of the infection.
• The pattern of seeding.
• Host factors such as immune status.

Question 5

The outcome of infection depends on what?

Answer 5

• The virulence of the microbe and the status of the host immune response.
• Sometimes the host immune system can be the cause of post-infection diseases.

Question 6

With which post infection complications can occur because of s.pyogens?

Answer 6

• Rheumatic Fever (joints, kidneys and heart valves)

- Glomerulonephritis.

Question 7

By which ways infectious agents establish infection and damage tissues?

Answer 7

• By direct contact/entering the host cell and directly cause death of infected cell.
• By releasing enzymes/toxins that can damage tissues like blood vessels or kill cells. damage to blood vessels by bacterial enzymes can lead to hemorrhage.
• By inducing host immune response.

Question 8

Tropism refers to the tendency of specific virus to attack specific cell types. Thus, the manifestations of viral infection are largely determined by the tropism of the virus for specific tissues an cell types.
What features influence the tropism?

Answer 8

• Host receptor for the viruses:
  A lot of viruses need to bind a specific cell surface protein in order to enter to it and establish infection.
  Host proteases may be needed to the process too.
• Specificity of transcription factors:
  The presence of specific transcription abilities like recognizing the viral enhancer and promoter.
• Physical characteristics of tissues:
  The environment and temperatures are differ from tissues to tissues.

Question 9

HIV express a glycoprotein which binds to molecules on T cells and Macrophages. What glycoprotein and molecules am I talking about?

Answer 9

gp 120 of HIV,

CD4, CXCR4 and CCR5 on T-cells and Macrophages.

Question 10

Which virus replicates ONLY in the oligodendroglia of the CNS and what disease is associated with its infection?

Answer 10

• JC virus, causes Leukoencephalopathy (severe multi-located white matter infection).
  The promoter and enhancer regulating viral gene expression are active in glial cells but not in endothelial cells or neurons.

Question 11

Once viruses penetrated the cell they can damage or kill the cell by number of mechanisms. What are they?

Answer 11

• Direct cytopathic effects like preventing synthesis of critical molecules, producing harm enzymes and toxins or by inducing apoptosis.
• Anti-Viral Immune responses (making CTLs to kill infected cell)
• Transformation of infected cells - interfere the cell cycle machinery, anti-apoptotic strategies etc.

Question 12

Which virus blocks the cap protein?

Answer 12

Poliovirus.

Question 13

HSV (Herpes simplex virus) produces proteins that inhibits the synthesis of which cellular molecules?

Answer 13

DNA, mRNA and it produces other proteins that degrade host DNA.

Question 14

Why Rhinoviruses attack cells only within the upper respiratory tract?

Answer 14

Because they can only replicate at the lower temperatures there.

Question 15

Give examples of 2 viruses that can stimulate cell growth and survival.

Answer 15

HPV (Human Papilloma Virus)

EBV (Epstein-Barr Virus)