Host Pathogen Interactions

Question 1

Describe pathogenicity VS pathogenesis VS pathogen.

Answer 1

1. Pathogenicity
   -ability of virus to cause disease in host
2. Pathogenesis
   -mech of development of disease
3. Pathogen
   -virus that causes disease

Question 2

Describe virulence VS avirulent.

Answer 2

1. Virulence
   -quantitative/relative measure of degree of pathogenicity of infecting virus
   -not an absolute property of a virus (depends on variables)
2. Avirulent
   -not virulent

Question 3

Describe lethal dose VS infectious dose.

Answer 3

1. Lethal dose (LD50)
   -dose of virus needed to cause death of 50% of animals
2. Infectious dose (ID50)
   -dose of virus that will infect 50% of animals
   LOWER THE ID50 OR LD50 = MORE VIRULENT

Question 4

Describe the routes of entry of viruses into host.

Answer 4

1. Skin [outer layer of keratin, low pH, FA, bacterial flora, dryness, innate & adaptive immunity]
   -bite (arthropod/animals), contaminated objects (needle)
2. Mucous membrane
3. GIT [mucous membrane, acidity/alkalinity, lipolytic/proteolytic, defensins, IgA, scavenging macrophages]
4. Respiratory tract [mucociliary, alveolar macrophages, NALT, BALT, temp]

Question 5

Describe the subepithelial invasaion & lymphatic spread.

Answer 5

1. Disseminated infection
   -inf that spreads beyond primary site of inf
2. Systemic infection
   -# of organs/tissues infected

Question 6

Describe directional shedding of viruses from infected epithelium.

Answer 6

critical to subepithelial spread
1. Apical release
-virus dispersal
2. Basolateral release
-access to underlying tissue = systemic spread

Question 7

Describe primary viremia VS secondary viremia.

Answer 7

1. Primary
   -initial entry of virus into blood after inf
2. Secondary
   -virus replicated in major organs & enter circ

Question 8

Describe active viremia VS passive viremia.

Answer 8

1. Active
   -release of virions from initial site of replication -> blood stream
2. Passive
   -direct inoculation of virus in host (contaminated obj or arthropod bite) -> no initial replication elsewhere in host before

Question 9

Describe how viruses spread via nerves in the host.

Answer 9

1. Neurotropic virus
   -virus infect neural cells
   -inf occur via neural or hematogenous spread
2. Neuroinvasive virus
   -virus enter CNS after inf of peripheral site
3. Neurovirulent virus
   -virus cause disease of nervous tissue
   -neurological symptoms & death

Question 10

Describe examples of virus spread via nerves in host.

Answer 10

1. Virus w low neuroinvasiveness of CNS but high neurovirulence
   -enters PNS but rarely CNS
   -severe consequences severe/fatal when it does
2. Virus w neuroinvasiveness but low neurovirulence
   -inf lead to invasion of CNS but neuro disease is mild
3. Virus w high neuroinvasiveness & high neurovirulence
   -infects PNS & spreads to CNS w 100% lethality unless antiviral therapy is given after infection

Question 11

Describe retrograde VS anterograde spread.

Answer 11

1. Retrograde
   -travel in opp direction of nerve impulse flow
   -invades axon terminals & spread to dendrite or cell body & cross synapse to reach next axon terminal
2. Anterograde
   -travel in direction of nerve impulse flow
   -virus invade dendrite or cell body & spread to axon terminals & cross synaptic contact to invade dendrite of next neuron

Question 12

Describe other ways viruses can spread thru the CNS.

Answer 12

-olfactory
-BBB

Question 13

Describe localized & systemic acute viral infections.

Question 14

Describe acute VS persistent infections in virus shedding.

Answer 14

1. Acute
   -intensive shedding over short time period
2. Persistent
   -shed at lower titers for months to yrs

Question 15

Describe tropism VS pantropic viruses.

Answer 15

1. Tropism
   -specificity/affinity of virus for a particular host tissue
2. Pantropic virus
   -replicate in more than one host organ/tissue

Question 16

Describe virus injury to organs/tissues in the skin.

Answer 16

1. Vesicles = fluid filled elevations
2. Ulcer = opening in skin by sloughing of necrotic tissue past the epi
3. Nodule/tumor = solid elevated mass w borders & deep into dermis
4. Warts = benign skin growth appear when viruses infect top layer of skin
5. Papule = solid elevation without sharp borders
6. Erythema = red skin due to systemic viral inf

Question 17

Describe virus injury to organs/tissues in the GIT.

Answer 17

Question 18

Describe virus injury to organs/tissues in the respiratory tract.

Answer 18

-loss of ciliary activity
-loss of integrity of lining of mucus layer
-multi focal destruction of epi
-inflammation
-exudation
-influx of inflam cells
-obstruction of air passages
-hypoxia & respiratory distress
-2ndary bacterial inf

Question 19

Describe virus injury to organs/tissues in the CNS.

Answer 19

-encephalitis or encephalomyelitis characterized by neuronal necrosis
-phagocytosis of neurons (neuronophagia)
-perivascular infiltrations of inflam cells (perivascular cuffing)
-neuronal vacuolation
-progressive demyelination (k9 distemper)

Question 20

Describe virus injury to organs/tissues in the hemopoietic system.

Answer 20

-petechial (pinpoint) & ecchymotic (larger areas w ill defined margins) hemorrhages
-disseminated IV coagulation (DIC)
>clots form in small blood vessels thru out body -> organs dont get blood -> organ failure
>late stage: raw material for clot exhausted bc over use -> no clot forms = hemorrhage thru out body
-edema
-infarction
>ischemic necrosis

Question 21

Describe teratogenesis VS arthrogryposis.

Answer 21

1. Teratogenesis
   -abnormal development or arrest in development of embryo or fetus
   >may result in death or malformations fur antenatal period
2. Arthrogryposis
   -joint malformations

Question 22

Describe virus injury to organs/tissues in the fetus.

Answer 22

1. Porencephaly
   -BVDV
2. Congenital hydraencephaly
   -calf showing recumbence, depression, dome shaped skull
   -BVDV

Question 23

Describe virus injury to organs/tissues - virus induced immunopathology.

Answer 23

-tissue injury mediated by host immune response to virus inf (price paid by host to clear viral inf)
-depends on balance between protective & destructive effects of the host immune response to viruses
-immunopathology = cause of damage w viruses that are non cytolytic & persistent (ex. Infected cells not immediately destroyed & immune response becomes chronic)
>if immune response clears inf by destroying small # of virus inf cells = host survives w min symptoms & no permanent damage
>if lg # of cells inf before immune induction = same immune mediated destruction can cause severe or fatal path consequences

Question 24

Describe immunopathology.

Answer 24

-tissue damage mediated by hypersensitivity reactions
-autoimmune disease (ex. Moon blindness in horses)
-inflam mediated tissue damage (ex. Fibrosis)
-immunodeficiency disorders

Question 25

Describe virus injury to organs/tissues - the role of T cells.

Answer 25

-cytotoxic cell mediated lysis/killing of infected host cells -release of cytokines from T cells (CD4+ & CD8+) & other cells that cause inflam & tissue damage that becomes chronic against persistent virus inf

Question 26

Describe virus injury to organs/tissues - the role of the innate immunity.

Answer 26

-toll like receptors (TLR) >persistent activation of receptors of innate host cells by viruses causes production of pro inflam cytokines & interferons + signals that recruit & activate cells involved in inflam >injury mediated by free radicals like NO, & superoxide

Question 27

Describe virus injury to organs/tissues - toxicity from antibody responses.

Answer 27

-antibody responses to viruses contribute to tissue damage -when antibody binds to infected cell = activates complement & causes inflam reaction -antibody mediated inflam reactions involving toxicity following: >engagement of IgG w Fc receptors on inflam cells which causes inflam mediator release >deposition of viral Ag-Ab complex in capillary beds, leading to activation of the complement cascade

Question 28

Describe immunosuppresion.

Answer 28

*a type of virus induced immunopathology* -infectious bursal disease: >virus replication causes atrophy of bursa & deficiency of B lymphocytes >infected birds become sus to other pathogens

Question 29

Describe the different types of viral infections.

Answer 29

1. In apparent -CS & symptoms not evident -too few cells may be infected -stim host immune response -poss source of virus spread 2. Acute (short term) -short clinical course -rapid clearance from host immune response 3. Latent (persistent) -infectious virus not demonstrable except when reactivation occurs >stim by immunosuppression or action of cytokine or hormone 4. Chronic (persistent) -acute inf followed by chronic inf where the virus is continuously shed from or is present in infected tissue 5. Slow (persistent) -prolonged incubation period (months, yrs) -slow progressive lethal disease