Lecture 4 2/5/24

Question 1

What is a type 1 infection?

Answer 1

acute generalized infection with self-limiting

Question 2

What are the characteristics of a type 1 virus?

Answer 2

-do not cause focal persistence
-virus eliminated if host survives

Question 3

What are the characteristics of parvoviruses as a type 1 virus?

Answer 3

-severe acute infection
-generalized and self-limiting
-animals that survive stop shedding virus
-no focal persistence in surviving animals
-no reoccurrence or reemerging symptoms

Question 4

What are examples of type 1 viruses, besides parvovirus?

Answer 4

-rhinovirus
-rotavirus
-influenza virus

Question 5

Why is parvovirus not considered a type 3 mucosal virus?

Answer 5

-replicates in the germinal cells of the crypt of Lieberkuhn where the stem cells live
-does not replicate in the intestinal epithelial cells

Question 6

What is a type 2 infection?

Answer 6

acute generalized with focal persistence

Question 7

What are the characteristics of a type 2 virus?

Answer 7

-do cause focal persistence
-can persist in specific tissues if host survives

Question 8

What are the characteristics of canine distemper virus as a type 2 virus?

Answer 8

-can see CNS disease years after survival
-causes encephalitis

Question 9

What are examples of type 2 viruses, besides canine distemper?

Answer 9

-measles virus (subacute sclerosing panencephalitis)
-HIV

Question 10

What are the steps of canine distemper virus establishing focal persistence?

Answer 10

-infect lymphoid cells in resp. tract
-infected cells drain to local LNs
-infected cells disseminate to all lymphoid tissues
-cell-associated viremia develops
-can infiltrate CNS to induce focal persistence

Question 11

How does immune status and age impact whether or not canine distemper develops focal persistence?

Answer 11

-neonate puppies with no immunological protection or passive immunity (colostrum) are most at risk for CNS involvement and death
-older puppies with inadequate immunity are more likely to recover, but are likely to have focal persistence and eventually develop CNS disease
-older dogs with proper immunity are likely to stop the infection before viremia occurs, preventing focal persistence

Question 12

What is a type 3 infection?

Answer 12

mucosal infection

Question 13

What are the characteristics of a type 3 virus?

Answer 13

-do not cause focal persistence
-virus eliminated if host survives
-potential to also be a type 1 virus
-restricted to mucosal epithelium
-no disseminate
-produce clinical disease by causing cytopathic effects and inflammation of mucosa and epithelium

Question 14

What are the characteristics of respiratory type 3 infections?

Answer 14

-usually transmitted via aerosol
-primarily enveloped viruses
-damage to resp. mucosa and mucociliary escalator leads to coughing/sneezing that increases aerosol transmission
-young, stressed animals most susceptible

Question 15

What are examples of respiratory type 3 viruses?

Answer 15

-Picornaviridae: human rhinovirus/common cold
-Herpesviridae: infectious bovine rhinotracheitis virus; feline viral rhinotracheitis
-Coronaviridae: canine respiratory coronavirus
-Paramyxoviridae: bovine PIV3

Question 16

What are the characteristics of bovine shipping fever?

Answer 16

-polymicrobial disease in which viral type 3 infection precedes bacterial infection
-resp. virus damages mucociliary escalator and impairs phagocytosis
-damage allows M. haemolytica to enter deep into lung

Question 17

What are the characteristics of intestinal type 3 infections?

Answer 17

-young animals most susceptible
-often fecal-oral transmission
-often naked viruses that can survive low pH
-brief incubation periods
-replicate to high levels
-shed in diarrhea

Question 18

What are examples of intestinal type 3 viruses?

Answer 18

-Reoviridae: bovine rotavirus
-Coronaviridae: feline enteric coronavirus
-Flaviviridae: BVDV
-Caliciviridae: norovirus

Question 19

What is the pathogenesis of an intestinal type 3 virus that infects the villi tips?

Answer 19

affects absorption and secretion

Question 20

What is the pathogenesis of an intestinal type 3 virus that infects the base of crypts?

Answer 20

blocks villus regeneration

Question 21

What clinical signs are common with intestinal type 3 infections?

Answer 21

-vomiting
-diarrhea
-anorexia
-depression
-dehydration (leads to death)

Question 22

What are the characteristics of bovine rotavirus/scours?

Answer 22

-common in calves less than a week old
-very short incubation period
-diarrhea from infected calves is highly contaminated with virus
-immature crypt cells migrate to damaged tip in place of lost absorptive cells, leading to diarrhea
-high morbidity with low mortality
-calves older than 3 months are resistant

Question 23

What is a type 4 infection?

Answer 23

chronic persistent infections

Question 24

What are the characteristics of type 4 viruses?

Answer 24

-not cleared by the host’s adaptive response
-persist in immune cells or elsewhere in body

Question 25

Why is it important to know which viruses classify as type 4?

Answer 25

-since virus is not cleared, it may be silently carried and maintained within population -control requires identifying and culling all chronic persistent carriers

Question 26

Why is it thought that acute viral infections can persist?

Answer 26

-large enough populations can keep an acute infection persistent within the population -does not mean infection is persistent within the host

Question 27

What are the different categories of type 4 persistent intracellular viral infections?

Answer 27

-chronic infections -latent infections -slow viral diseases

Question 28

What are the characteristics of BVDV as a chronic infection?

Answer 28

-PI cattle shed non-cytopathic BVDV without showing clinical disease -eventually, non-cytopathic BVDV recombines with host RNA to produce a cytopathic BVDV resulting in severe mucosal disease

Question 29

What are the characteristics of herpes as a latent infection?

Answer 29

-virus dsDNA maintained as episome within cell nuclei -viral RNA accumulates in host cells and keeps most of viral DNA inactive -viral latency can be broken by host stimuli, leading to an active infection and clinical disease

Question 30

What is latency?

Answer 30

when a virus lies dormant within a host cell

Question 31

What are the characteristics of slow viral diseases?

Answer 31

-long incubation period between exposure and clinical disease development -disease becomes increasingly severe until resulting in death -pathology usually localized to one or two organ systems

Question 32

What are the characteristics of VISNA-MAEDI virus as a slow viral disease?

Answer 32

-lentivirus that persists in lymphocytes, monocytes, and macrophages -primary replication in lung macrophages that can lead to dissemination in brain and deeper lung tissue -severe dyspnea and secondary bacterial pneumonia occur -eventually get inflammation of CNS, demyelination and meningitis, causing posterior paralysis

Question 33

What are the potential ways to prevent and control viral disease?

Answer 33

-hygiene/sanitation/PPE -vaccination -antiviral chemotherapy