Viral Pathogenesis

Question 0

Mechanisms of viral transmission

Answer 0

Respiratory: aerosols
Fecal-oral: food, water, dirty hands
Contact: lesions, saliva, fomites
Zoonoses: animals, insects 
Blood: direct contact, blood products, organ transplants 
Sexual: mucous membranes, blood
Maternal-neonatal: birth, breast milk
Genetic: prions, retroviruses

Question 1

Where do we encounter viruses?

Answer 1

People, animals, insects, food and water

Question 2

Susceptibility and severity of viral disease depend on:

Answer 2

The nature of exposure (route)
The viral dose (increase risk if more virus)
The status of person (age, general health, immune status)
Virus-host interactions

Question 3

Routes of entry

Answer 3

Eyes, skin, mouth, genital
GI tract via M cells (sample gut contents and present to underlying immune cells), viruses infect M cells and easily reach blood stream

Question 4

Reoviruses

Answer 4

Attach to M cells and in intracellular vesicles

Cause diarrhea

Question 5

Rotavirus

Answer 5

Fecal-oral transmission
Diarrhea
Immunity depends on IgA in gut lumen

Question 6

Virus dissemination

Answer 6

Viruses may spread from surface of body to lymph nodes and then blood stream
Primary viremia (virus in blood for the first time) leads to replication I’m internal organs, may occur without symptoms (incubation stage)
Secondary viremia disseminates the virus to organs where it is shed, transmission may be by direct contact or through environment (exposure to infected blood is common)

Question 7

Chicken pox and shingles

Answer 7

Transmitted by respiratory route but spreads by viremia to skin causing lesions, latent infection in neurons

Question 8

Virus-host interactions

Answer 8

Virus infection may be unnoticed, cause illness, induce immunity, be persistent or be lethal
Successful virus will avoid destruction by immune system and avoid destroying host before replication is finished

Question 9

General patterns of infection

Answer 9

Acute: not long lasting
Persistent: remains at detectable level, shedding
Latent: no detectable infectious virus, no shedding symptoms
Slow: build up over time

Question 10

Direct effects (injury induced by viruses)

Answer 10

Cell lysis
Cell inactivation (infection may halt essential cell functions, susceptible to apoptosis, can lead to organ damage or failure)
Ex) respiratory syncytial virus cause syncytium (fusion of cells to make multinucleated cell)

Question 11

Indirect injuring effects

Answer 11

Host immune response to virus may be sole cause of disease

Usually caused by T cells and antibody complexes