Veterinary virology

Question 1

Foot and mouth disease

Answer 1

• Loeffler and Frosch (1898) reported transmission in cattle of filterable and contagious agent

Question 2

From 1900-1905 the filterable nature of some virulent infections demonstration with

Answer 2

• African horse sickness
• fowl plague (HP avian influenza)
• canine distemper
• equine infectious anemia
• rinderpest
• classical swine fever

Question 3

Dr. Peyton Rous

Answer 3

• 1911 discovered first virus capable of inducing neoplasia
  
  • Rous sarcoma virus
  • nobel prize in medicine

Question 4

embryonated eggs

Answer 4

• used started 1931
• viruses could now be grown

Question 5

Dr. Shope 1933

Answer 5

• isolates flu virus H1N1 from swin isolated from humans in 1933
  
  • first emerging disease in animals that cross species barrier

Question 6

Chorioallantoic membrane inoculation

Answer 6

• Herpes simplex virus
• Pox virus
• Rous sarcoma virus

Question 7

Amniotic inoculation

Answer 7

• Influenza virus
• Mumps virus

Question 8

Yolk sac inoculation

Answer 8

• Herpes simplex virus

Question 9

Allantoic inoculation

Answer 9

• Influenza virus
• Mumps virus
• Newcastle disease virus
• Avian adenovirus

Question 10

Price of virus outbreaks in domestic animals

Feline parvovirus

Answer 10

• variant crosses species barrier
• produced worldwide epizootic in dogs in late 70s
• vaccine was eventually developed to control dz

Question 11

Price of virus outbreaks in domestic animals

HPAI virus epornitic

Answer 11

• April-June 2015 in upper Midwest US
• affected 211 commercial farms
• causes destruction of 7.5 million turkeys and 38.5 million hens
• more than US $1.5 billion in industry losses
• Probably inc in price for consumers > US $2 billion

Question 12

Molecular era of Virology

Answer 12

• 1981 DNA cloning led to development of infectious viral clones
• 1983 PCR developed
• Viruses that we couldn’t culture now characterized molecularly
  
  • papillomavirus
  • norovirus
  • rotavirus
• Molecular reconstruction of 1918 flu virus from RNA frags

Question 13

Head of a dress-makers pin

Answer 13

• Large enough for five hundred million rhinoviruses (common cold)

Question 14

Virus characteristics

(5 characteristics)

Answer 14

• All are obligate intracellular parasites
• lack metabolic machinery to reproduce
• inert particles outside living cells
• Do not reproduce by binary fission
• replication like an assembly line with parts from a host cell

Question 15

Eclipse period

Answer 15

• Time elapsed between virus penetration into host cell and production of new virus

Question 16

Enveloped virus

Answer 16

• Examples
  
  • herpes
  • pox
  • retro
  • paramyxo
  • orthomyxoviruses
• inactivated by organic solvents

Question 17

Naked viruses

Answer 17

• Examples
  
  • Adeno
  • Pappilloma
  • parvo
  • circo
  • calici
  • picornavirus
• Resistant to inactivation

Question 18

Genetic info storage

Answer 18

• RNA viruses store genes in RNA
• DNA viruses store genes in DNA

Question 19

Virus symmetry

Icosahedral

Answer 19

• isometric viruses invariably icosahedrons
• 12 corners, 30 edges, 20 faces (eachface an equilateral triange)
• subunit repeats optimizes maximum volume
• e.g. Herpes virus

Question 20

Virus symmetry

Helical

Answer 20

• Nucleocapsid of some RNA viruses self-assembles into cylindrical structure
  
  • the helix
• helical nucleocapsid of RNA viruses wound into coil enclosed in an envelope
• e.g. Rabies virus

Question 21

Herpes virus immunogenicity

Answer 21

• In the virus membrane
• many vaccines based on glycoproteins on the virus envelope/membrane

Question 22

Rabies virus immunogenicity

Answer 22

• glycoprotein G
  
  • one of the most immunogenic proteins

Question 23

Viral proteins (can code from 1-100)

Structureal proteins

Answer 23

• Present in mature virions
• Protect genomic nucleic acid enzymes
• Provide receptor-binding sites to initiate infection
• Facilitate penetration of genome into correct cell location

Question 24

Viral proteins

Non-structural proteins

Answer 24

• Involved in
  
  • assembly
  • genome replication
  • modifying host innate immune response
  • polymerases must be part of mature virion

Question 25

International Committee on taxonomy of Viruses (ICTV)

Answer 25

• established in 1966
• in 2011
  
  • 94 families
  • 394 genera
  • 2480 virus species

Question 26

Hieracrchy of recognized viral taxa

Answer 26

• Order
  
  • Mononegavirales
• Family
  
  • Paramyxoviridae
• Subfamily
  
  • Pneumovirinae
• Genus
  
  • Pneumovirus
• Species
  
  • Bovine respiratory syncytial virus (BRSV)

Question 27

Quantitative assays in clinical samples:

Physical assays

Answer 27

• EM viral particles count
• Hemagglutination
• Antigen-capture ELISAs
• Quantitative PCRs

Question 28

Quantitative assays in clinical samples:

Biological assays

Answer 28

• Based on replicating virus particles that successfully initiate infection
  
  • viral plaque assays
  • end-point titration of infectivity

Question 29

Physical virus particles

vs

Infectious virus particles

(5 reasons)

Answer 29

• Ratio varies between 100:1 and 10,000:1
  
  • assembly process inefficient
  • replication of RNA is error prone
  • poor stocking of virusis leading to inactivation
  • Inefectivity assays done in suboptimal in vivo systems
  • Host-cell defenses prevent infectious virus particles from completing replication process

*DNA viruses more effective, lower ratio of noninfectious to infectious

Question 30

Direct particle counts by electron microscopy

Answer 30

• Counting of virus particles using electron microscope
• Expensive, not routinely used
• numbers must be compared to known conc latex beads for accuracy
  
  • dilution and volume are keys to calculate conc
• mainly for firuses with unique geometic shape
  
  • adenoviruses
  • herpesviruses
  • picornaviruses

Question 31

Hemagglutination assays

Answer 31

• Binding of some viruses to erythrocytes
  
  • produces lattice of cross-linked erythrocytes
• Visually detected with Flu virus particles at and above 10⁶/ml for 0.5% turkey or chicken RBCs
• Sample diluted serially and RBCs are added
• Hemagglutination (HA) titer
  
  • highest dilution inducing complete agglutination of RBCs
• HA does not require intact/infectious virus

Question 32

Antigen-capture assay for Rotaviruses

Answer 32

• 1) well coated with anti-rotavirus antibody
• 2) rotavirus antigens captured by antibody
• 3) specific anti-rotavirus enzyme conjugate binds to captured rotavirus antigens
• 4) color develops

*not all viruses hemagglutinate: most pox viruses

*Physical technique

• won’t tell us if infectious

Question 33

Quantitative PCR assays

Answer 33

• Detect conc of target nucleic acid in viral sample
  
  • must previously treat sample with nucleases to degrade non-viral nucleic acids
  • Virus nucleic acid protected by capsid
• Doesn’t detect empty capsids
• Titers don’t strictly related to infectivity of virus sample
• Real-time PCR
  
  • results observed in minutes

Question 34

Biological assay: Plaque assay

Answer 34

• For viruses that produce discrete holes in cell monolayers
  
  • visually observed after staining with vital dyes
• Immunohistochemical techniques used for non-cytopathic viruses
  
  • immunoperoxidase
• Based on the fact that a single infectious virus particle is enough to establish and infection
  
  • plaque numbers follow one-hit kinetic curve

Question 35

Biological assay: Endpoint titration of virus stocks

Answer 35

• Virus dilution that infects 50% of infected
  
  • embryonated eggs
  • tissue culture cells (inc tracheal rings)
  • experimental animals
• Two methods
  
  • Reed-Muench
  • Spearman-Karber
  • LD50, EID50, TCID50, TRLD50
• Not as accurate as plaque assay but easier to implement and automate