Viral Pathogenesis

Question 1

where do we encounter viruses?

Answer 1

• people
• animals
• insects
• food and water

Question 2

mechanisms of viral transmission

Answer 2

• resp-aerosols
• fecal oral-food, water, dirty hands
• contact-lesions,saliva,fomites
• zoonoses-animals and insects
• blood-direct, products, organ transplants
• sexual-mucous membranes and blood
• maternal-neonatal-birth, breastmilk
• genetic-prions, retroviruses

Question 3

susceptibility and severity depend on

Answer 3

• nature of exposure
• viral dose-more virions increase risk
• status of person-age, general health, immune status
• virus-host interactions

Question 4

routes of entry

Answer 4

• conjunctive
• resp tract
• alimentary tract
• urogenital tract
• anus
• skin
• scratch/injury
• capillary
• athropod

Question 5

entry into GI tract

Answer 5

• m cells sample the gut contents and present it to underlying immune cells
• viruses can infect M cells and easily reach the blood stream
• rotavirus-fecal oral

Question 6

virus dissemination

Answer 6

• spread from the surface of the body to lymph nodes to blood stream
• then to target organs then back to blood

Question 7

primary viremia

Answer 7

• leads to
• replication in internal organs
• may occur without symptoms

Question 8

secondary viremia

Answer 8

• disseminates the virus to organs where it is shed
• transmission may be by direct contact or through the environment
• exposure to infected blood is now a common route of transmission
• chicken pox-in mouth, to liver spleen and resp then sheds on skin
• HIV1-mostly in CSF, some in semen and ear secretions

Question 9

virus-host interactions

Answer 9

• may be unnoticed, cause illness, induce AI, be persistent, or be lethal
• a successful virus will avoid destruction by the immune system and avoid destroying the host before replication is finished
• 4 graphs, differing survivals- see slide

Question 10

general patterns of infection

Answer 10

• acute-can lead to late complication
• persistent-hep B or causes second disease
• latent-2 humps
• slow-takes a long time
• transforming
• SEE SLIDE

Question 11

injury induced by viruses

Answer 11

• symptoms of viral disease- fever, tissue damage, rash, aches, pains, nausea- caused by host response
• viral replication-cell injury is direct
• host response-cell injury is indirect
• cell injury is caused directly by viruses and indirectly by the host

Question 12

cell lysis-direct

Answer 12

• norwalk
• infect intestinal brush border and prevent proper absorption of water and nutrients
• fecal oral
• diarrhea, vomiting, abd cramps, nausea, headache, malaise, fever

Question 13

direct effect-cell inactivation

Answer 13

• virus may halt essential cell functions
• infected cells are susceptible to apoptosis
• loss of cell functions can lead to organ damage or failure
• RSV

Question 14

indirect-immunopathology

Answer 14

• host immune response to a virus may be the sole cause of a disease
• immune pathology usually caused by T cells and antibody complexes
• vaccination can make some viral infections worse!
• corneal scarring by chronic response to HSV reactivation

Question 15

factors that contribute to a viral infection (host-virus)

Answer 15

• immune status-antigenic diversity
• route of exposure-infectious dose
• age-cell killing or inactivation
• habits-pattern of infection
• barriers to dissemination-ability to disseminate
• contagiousness-shedding