Lecture 4 2/5/24 Flashcards
What is a type 1 infection?
acute generalized infection with self-limiting
What are the characteristics of a type 1 virus?
-do not cause focal persistence
-virus eliminated if host survives
What are the characteristics of parvoviruses as a type 1 virus?
-severe acute infection
-generalized and self-limiting
-animals that survive stop shedding virus
-no focal persistence in surviving animals
-no reoccurrence or reemerging symptoms
What are examples of type 1 viruses, besides parvovirus?
-rhinovirus
-rotavirus
-influenza virus
Why is parvovirus not considered a type 3 mucosal virus?
-replicates in the germinal cells of the crypt of Lieberkuhn where the stem cells live
-does not replicate in the intestinal epithelial cells
What is a type 2 infection?
acute generalized with focal persistence
What are the characteristics of a type 2 virus?
-do cause focal persistence
-can persist in specific tissues if host survives
What are the characteristics of canine distemper virus as a type 2 virus?
-can see CNS disease years after survival
-causes encephalitis
What are examples of type 2 viruses, besides canine distemper?
-measles virus (subacute sclerosing panencephalitis)
-HIV
What are the steps of canine distemper virus establishing focal persistence?
-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
How does immune status and age impact whether or not canine distemper develops focal persistence?
-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
What is a type 3 infection?
mucosal infection
What are the characteristics of a type 3 virus?
-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
What are the characteristics of respiratory type 3 infections?
-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
What are examples of respiratory type 3 viruses?
-Picornaviridae: human rhinovirus/common cold
-Herpesviridae: infectious bovine rhinotracheitis virus; feline viral rhinotracheitis
-Coronaviridae: canine respiratory coronavirus
-Paramyxoviridae: bovine PIV3
What are the characteristics of bovine shipping fever?
-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
What are the characteristics of intestinal type 3 infections?
-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
What are examples of intestinal type 3 viruses?
-Reoviridae: bovine rotavirus
-Coronaviridae: feline enteric coronavirus
-Flaviviridae: BVDV
-Caliciviridae: norovirus
What is the pathogenesis of an intestinal type 3 virus that infects the villi tips?
affects absorption and secretion
What is the pathogenesis of an intestinal type 3 virus that infects the base of crypts?
blocks villus regeneration
What clinical signs are common with intestinal type 3 infections?
-vomiting
-diarrhea
-anorexia
-depression
-dehydration (leads to death)
What are the characteristics of bovine rotavirus/scours?
-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
What is a type 4 infection?
chronic persistent infections
What are the characteristics of type 4 viruses?
-not cleared by the host’s adaptive response
-persist in immune cells or elsewhere in body
Why is it important to know which viruses classify as type 4?
-since virus is not cleared, it may be silently carried and maintained within population
-control requires identifying and culling all chronic persistent carriers
Why is it thought that acute viral infections can persist?
-large enough populations can keep an acute infection persistent within the population
-does not mean infection is persistent within the host
What are the different categories of type 4 persistent intracellular viral infections?
-chronic infections
-latent infections
-slow viral diseases
What are the characteristics of BVDV as a chronic infection?
-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
What are the characteristics of herpes as a latent infection?
-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
What is latency?
when a virus lies dormant within a host cell
What are the characteristics of slow viral diseases?
-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
What are the characteristics of VISNA-MAEDI virus as a slow viral disease?
-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
What are the potential ways to prevent and control viral disease?
-hygiene/sanitation/PPE
-vaccination
-antiviral chemotherapy
