Pathogenesis and patterns of Viral infections

Question 1

Which of the following can impact the ability of a barrier to prevent infection of an individual host?
i) Time or year and humility;
ii) genetics of the host;
iii) concentration of the viral
inoculum;
iv) the health status of the host

Answer 1

all of them

Question 2

Not all viral encounters with receptor-bearing cells lead to a productive infection. List four
obstacles that could prevent a productive infection.

Answer 2

1. Anatomical and chemical barriers
2. intrinsic barriers (apoptosis etc)
3. innate imminity (phagocytosis, NK cells, neutrophils etc)
4. acquired immunity (T cells, B cells, antibodies, and memory lymphocytes)

Question 3

What host and viral parameters govern if a virus will remain localized or can disseminate into other tissues?

Answer 3

Host:
-immune system
-receptor distrabution
-host tissue barriers
-host health

virus:
-tropism
-mechanisms
-ability to go to viremia
-ability to esape viral detection

Question 4

Describe the various portals of infection in human. Which type of infections are most common
and why?

Answer 4

1. respiratory track: air-borne pathogenes
2. GI tract: oral fecal route of transmission, food-borne, water-borne
3. Uro-genitial tract: STDs
4. skin abrasions: arthropod sting, scratch, injury, rabid bites, piercing, tattoos, needles
5. surgical: blood transfusions, organ transplates
6. vertical transmission: cross placenta

Question 5

What are the differences between acute infections and chronic infections? Describe the several
forms of persistent infections and how they differ from one another.

Answer 5

Acute: an infection that results in rapid production of virions, followed by complete elimination of the virus by the host immune system (none left). caused by many strains, use innate and adaptive immune (establishes memory) response, life-long immunity

chronic: infections that are not resolved by the host immune system; virions or viral genomes continue to be produced but at very low levels over prolonged periods.

-persistent (antigen always present)
-latency (do not until immune system is weak)
-reactivating infection (periodic episodes of infection)
-slow infection (slow replication cycle)

Question 6

Describe the different ways certain viruses establish persistent infections after the initial acute phase of infection. What are the tissues/organs commonly used by viruses to establish chronic or latent infections?

Answer 6

1. persistent infections: viruses replicate slowly but steadily. progeny virion continues to be produced at low levels. Long incubation period.
2. latent/re-activating infections: virus goes ‘dormant’, no or few viral protiens are produced, reactivated late upon stimulation
3. slow infections: usually brain and lymphocytes, leading to death years later
4. transforming infections: lead to cell transformation and oncogenesis

CNS, PSN, mononuclear cells, lymhocytes, liver, eyes, testes, heart

Question 7

pathogen

Answer 7

a microbe that is able to cause a disease in a host organism

Question 8

pathogenesis

Answer 8

the process and mechanisms by which a virus causes disease upon infection of its host

Question 9

pathogenicity

Answer 9

a qualitative descriptor for the capacity of a virus to cause disease

Question 10

pathology

Answer 10

study of diseasees nature cause and effects.

Question 11

Ro

Answer 11

of people that can be infected by a person initially infected with a virus

Question 12

Name several viruses with different genome types that are known to induce human cancer and
their mechanisms of oncogenesis.

Answer 12

1. retrovirusis:
   -insertional activation of cellular oncogenes
   -insertional inactivation of tumor suppressor genes
   -Transformation by acute transforming retroviruses (viral oncogene added)
2. DNA hep c and b
   -oncogenes target tumor suppressor protiens
   -no cellular homologues

Question 13

what is localized infections?

Answer 13

infections is restricted to only one part of the body: do not disseminate to other locations

Question 14

what is systemic infections?

Answer 14

infections that spread to tissues/organs beyond the initial infection site. Occurs via blood stream or the nervous system

Question 15

what is an abortive infection?

Answer 15

viruses infect a cell or tissue, bnut replication cannot reach completion, no disease.

Question 16

what is transforming infections?

Answer 16

oncolytic viruses (simple retrociruses: some DNA viruses, HCV and HBV)

Question 17

how does RNA viruses counter host defenses

Answer 17

Antigenic drift: point mutations due to lack of proof-reading of RdRp. this causes the body to not recognize the slightly mutated virus
Antigenic shift: re-assortment of genomic segments or recombination of mixed infections. This results in the creation of a new subtype of the virus, with surface proteins that are radically different from those seen before. ex spanish flu and swine flu

Question 18

A viral infection will result in a persistent infection when…

Answer 18

the replication and cytopathic effects of the virus and host defense are both reduced, reaching an equilibrium.

Question 19

what are the hallmarks of persistent infections?

Answer 19

-blockage of apoptosis
-modulation and inhibition of the interferon response and ISGs
-modulation of monocytes and DCs involved in innate immunity
-evasion and inhibition of the adaptive immune system

Question 20

what is primary viremia

Answer 20

This occurs shortly after the virus enters the bloodstream, often after initial infection at the site of entry (e.g., skin, mucosal surfaces). During primary viremia, the virus begins to spread to various organs and tissues, often before it reaches the target organs in higher concentrations.

Question 21

what is seconary viremia?

Answer 21

This occurs when the virus, after initially spreading through the bloodstream, reaches other organs, replicates, and then re-enters the bloodstream in larger amounts. Secondary viremia is typically associated with the peak of viral replication and symptom onset.

Question 22

Explain Transmission of VZV

Answer 22

-aerosol, respiratory droplets, mocosal surface
-replicates on epithelium and lymph nodes and moves to blood circulation via tonsillar T cells (primary viremia)
-cutaneous exanthema in 10-21 days
-latency in sensory neurons
Reactivation later: dermatomal or facial shingles

Question 23

explain transmition of Measles

Answer 23

-respiratory infection
-incubation period:10-14 days
-infection of epithelial surface
-procues giant cells due to membrane fusion
-1st virus to shown induce immune suppression
-tuberculosis reactiviation

Question 24

messles neurologic complications

Answer 24

APME: acute post-infectious measles encephalitis
MIBE: measles inclusion-body enchalistis (100% fatality)
SSPE: subacute sclerosing pan-encephalitis

Question 25

what are viral factors that affect virulence?

Answer 25

-speed of viral replication: size, polymerase, kinetics, regulatory RNA sequences -factors that modify, suppress, subvert or block host defense mechanism: immune modulators etc. -ability to spread within the body -direct toxicity of viral protiens