Veterinary Virology 2025-2026 PDF

MICRO103A - VETERINARY VIROLOGY DOCTOR OF VETERINARY MEDICINE 2ND SEMESTER A.Y. 2025 – 2026 DR. KRISTINE KAITH -​ morphologic units composed of structural units embedded in the LESSON 1: Introd...

MICRO103A - VETERINARY VIROLOGY DOCTOR OF VETERINARY MEDICINE 2ND SEMESTER A.Y. 2025 – 2026 DR. KRISTINE KAITH -​ morphologic units composed of structural units embedded in the LESSON 1: Introduction to Viruses (Brief History, Classification, envelope Replication) COMPLEMENTATION DEFINITION OF TERMS -​ general term to describe situations where mixed infections result in VIRION enhanced yields of one or both -​ complete infective virus particle; viruses in the mixture may be identical to the nucleocapsid; more complex BACTERIOPHAGES virions include the nucleocapsid + -​ Viruses that infect bacterial cells envelope TRANSLATION VIROIDS -​ The mechanism by which a -​ smallest infectious agents causing particular base sequence in disease in plants messenger RNA produces a specific amino acid sequence in a CAPSID protein -​ protein shell that encloses the nucleic acid core TRANSCRIPTION NUCLEOCAPSID -​ the means by which specific -​ the capsid together with the information encoded in a nucleic enclosed nucleic acid acid chain is transferred to messenger RNA CAPSOMERES -​ morphologic units seen on the HELPER VIRUS surfaces of icosahedral virus -​ required by certain defective particles; represent clusters of closely related viruses to replicate structure units DEFECTIVE VIRUS ENVELOPE -​ functionally deficient particles in -​ outer coat some viruses acquire as some aspect of replication and may they penetrate or are budded from interfere with the replication of the nuclear or cytoplasmic normal viruses membrane; always contain altered host-cell membrane components SATELLITE VIRUSES -​ viruses that cannot reproduce from PEPLOMERS their own nucleic acid and virions are non-infectious; require a helper MICRO103A - VETERINARY VIROLOGY DOCTOR OF VETERINARY MEDICINE 2ND SEMESTER A.Y. 2025 – 2026 DR. KRISTINE KAITH virus for transmission and multiplication BRIEF HISTORY -​ Early bacteriologists believed that all contagious and infectious diseases were caused by bacteria -​ Eventually, it was learned that some infective fluids retained their ability to produce diseases even after being forced through fine-pored clay filters that retained all ordinary bacteria ​ Ivanovsky and Beijerinck (1892) -​ Transmission of tobacco mosaic virus -​ First known virus -​ Crystallized in 1935 -​ Viewed in electron microscope in 1939 ​ Loeffler and Frosch (1898) -​ Applied the filtration criteria to a disease in cattle that later would be known as foot and mouth disease ​ D’Herelle (1922) -​ Described bacteriophages that parasitized bacterial cells causing them to swell and burst MICRO103A - VETERINARY VIROLOGY DOCTOR OF VETERINARY MEDICINE 2ND SEMESTER A.Y. 2025 – 2026 DR. KRISTINE KAITH swine fever Y INVESTIGAT EVENT virus) E OR(S) A 19 Carré and Equine R 04 Vallée infectious anemia virus 18 Ivanofsky Identification of 92 tobacco 19 Spreull Insect mosaic virus 05 transmission of as filterable bluetongue agent virus 18 Loeffler and Foot-and-mout 19 Ellermann and Avian 98 Frosch h disease 08 Bang leukemia virus caused by filterable agent 19 Landsteiner Poliovirus 09 and Popper 18 Sanrello Myxoma virus 98 19 Rous Rous 11 sarcoma-virus 19 Reed Yellow fever (first tumor 00 virus virus) 19 Mcfadyean African horse 19 Twort and Bacterial 00 and Theiler sickness virus 15 d’Herelle viruses 19 Centanni, Fowl plague 19 d’Herelle Development 01 Lode, and virus (avian 17 of the plaque Gruber influenza virus) assay 19 Nicolle and Rinderpest 19 Doyle Newcastle 02 Adil-Bey virus 27 disease virus 19 Spruell and Bluetongue 19 Verge and Feline 02 Theiler virus 28 Christofornoni parvovirus Seifried and (feline 19 Aujeszky Pseudorabies Krembs panleukopenia 02 virus virus) 19 Remlinger and Rabies virus 19 Green Fox 03 Riffat-Bay 30 encephalitis (canine 19 DeSchweinitz Hog cholera adenovirus 1) 03 and Dorset virus (classical MICRO103A - VETERINARY VIROLOGY DOCTOR OF VETERINARY MEDICINE 2ND SEMESTER A.Y. 2025 – 2026 DR. KRISTINE KAITH 19 Shope Swine 52 Vogt for first animal 31 influenza virus virus - poliovirus 19 Woodruff and Embryonated 31 Goodpasture eggs for virus 19 Madin, York, Isolation of propagation 56 and bovine McKercher herpesvirus 1 19 Dimmock and Viral etiology 33 Edwards for equine 19 Isaacs and Discovery of abortions 57 Lindemann interferon 19 Shope Swine natural 19 Horne and Development 33 host of 58 Brenner of negative pseudorabies stain electron microscopy 19 Bushnell and Avian 33 Brandly bronchitis virus 19 Becker First isolation 61 of avian 19 Stanley Tobacco influenza virus 35 mosaic virus from wild bird (TMV) reservoir crystallized; protein nature 19 Plummer and Equine of viruses 63 Waterson abortion virus confirmed = herpesvirus 19 Kausche, First electron 38 Ankuch, and microscopy 19 Temin and Discovery of Ruska pictures - TMV 70 Baltimore reverse transcriptase 19 Ellis and One-step 39 Delbruck growth curve - 19 Carmichael, Canine bacteriophage 78 Appel, and parvovirus 2 Scott 19 Olafson, Bovine viral 46 MacCallum, diarrhea virus 19 World Health WHO declares and Fox 79 Organization smallpox eradicated 19 Sanford, Cultured of 48 Earle, and isolated 19 Pedersen Feline Likely mammalian 81 coronavirus cells 19 Wensvoort Isolation of 19 Dulbecco and Plaque assay 91 and Terpstra porcine MICRO103A - VETERINARY VIROLOGY DOCTOR OF VETERINARY MEDICINE 2ND SEMESTER A.Y. 2025 – 2026 DR. KRISTINE KAITH reproductive 20 Reemergence and respiratory 14 of Ebola in syndrome West Africa virus (PRRSV) 19 Murray Hendra virus 94 isolated 19 West Nile virus 99 enters North America 20 Severe acute 02 respiratory syndrome outbreak 20 Palase, Reconstruction 05 Garcia-Sastre, of the 1918 Tumpey, and pandemic Taubenberger influenza virus 20 Development 08 of molecular tools and computer software for “next generation sequencing” and metagenomic analyses 20 World Declaration of 11 Organisation the global of Animal eradication of Health (OIE) rinderpest 20 Recognition of 12 Middle East respiratory syndrome MICRO103A - VETERINARY VIROLOGY DOCTOR OF VETERINARY MEDICINE 2ND SEMESTER A.Y. 2025 – 2026 DR. KRISTINE KAITH examples: ​ Parvoviruses (family Parvoviridae) CHARACTERISTICS OF VIRUSES -​ simples -​ viral structure proteins and DNA -​ Filterable agents that could not be cultivated on artificial media ​ Picornaviruses (family -​ All viruses are obligate intracellular Picornaviridae) parasites -​ viral proteins and DNA -​ However, all obligate intracellular parasites are not viruses ​ Herpesviridae and Paramyxoviridae -​ Members of certain bacterial -​ more complex w/ envelope genera also are unable to replicate -​ Mature by Budding Through outside a host cell (eg, Ehrlichia, different host cell membranes, Anaplasma, Legionella, and modified by the insertion of viral Rickettsia) proteins -​ Outside living cells → viruses are inert particles Glycoproteins -​ Inside the cells → viruses utilize -​ the major type of protein present on host cell processes to produce its the exterior of the membrane of proteins and nucleic acid to enveloped viruses replicate itself -​ Contain only one type of nucleic Presence of lipid envelope acid that carries the information for -​ Separates viruses into 2 distinct replicating the virus classes: -​ Some viruses contain nucleic acid 1.​ Inactivated by organic solvents molecules other than their genomic (enveloped) DNA or RNA. 2.​ Resistant to organic solvents ​ e.g. Retroviruses- cellular (non-enveloped) transfer (t)RNAs are essential for the reverse CLASSIFICATION OF VIRUS transcriptase reaction Reverse Transcriptase -​ The process of naming viruses and -​ enzyme that converts RNA into -​ placing them into a taxonomic DNA system -​ Two main classification systems: CHEMICAL COMPOSITION OF THE ​ ICTV (International VIRION Committee on Taxonomy of Viruses) established in -​ various markedly between those of 1966 individual virus families ​ Baltimore classification system MICRO103A - VETERINARY VIROLOGY DOCTOR OF VETERINARY MEDICINE 2ND SEMESTER A.Y. 2025 – 2026 DR. KRISTINE KAITH ​ Negative sense or polarity ICTV CLASSIFICATION SYSTEM -​ the genomic nucleotide sequence is -​ Hierarchy of recognized viral tax complementary to the of -​ e.g. human respiratory syncytial mRNA virus A2 -​ requires transcription of the genome to generate mRNA equivalents -​ Within negative-strand group: ​ Single-strand whole-genome viruses (e.g. Paramyxoviridae) ​ Segmented genome viruses (e.g. Orthomyxoviridae – 6,7or 8 Viral Nucleic Acids in the Virion segments; Bunyaviridae – 3 -​ The type and structural segments; Arenaviridae – 2 characteristics of the viral genomic segments) nucleic acids are used to classify -​ Retroviridae viruses ​ Considered diploid (2 copies of -​ Viruses can simply be divided into their genome); contains two RNA viruses and DNA viruses whole-genomic positive-sense RNAs BALTIMORE CLASSIFICATION SYSTEM ​ Use reverse transcriptase to create (7 CLASSES) a DNA copy of their RNA genome -​ Developed by David Baltimore DNA VIRUSES -​ Classes based on genome type and mode of replication and -​ Overall structure of genome is less transcription complex -​ Either single molecule of RNA VIRUSES single-stranded (ss)DNA or single molecule of double- stranded -​ Size of animal RNA viral genomes (ds)DNA. ranges 30kb (Coronaviridae) REPLICATIONS -​ Major distinction is whether the virion RNA is: -​ Process of reproduction resembles ​ Positive sense or polarity an assembly line -​ it is of the same sense as -​ Various parts of the virus come mRNA together from different parts of the -​ directly capable of host cell to form new virus particles translation to protein MICRO103A - VETERINARY VIROLOGY DOCTOR OF VETERINARY MEDICINE 2ND SEMESTER A.Y. 2025 – 2026 DR. KRISTINE KAITH thousands of progeny virus 1.​ The virus attaches to a host cell particles 2.​ Enters the cell 3.​ Intact virus particle ceases to exist (uncoating) 4.​ Viral genome directs the production of new viral macromolecules 5.​ Assembly and appearance of new progeny virus particles LESSON 2: Pathogenesis of Viral Infections and Diseases -​ Viral infection is not synonymous with disease ​ There are some subclinical viral infections (syn. Asymptomatic, inapparent) Virulence -​ used as a quantitative or relative measure of the pathogenicity of the infecting virus (pathogenic or non-pathogenic); stated in relative terms (‘more virulent than/in...than) ECLIPSE PERIOD For viruses to cause disease, they must: -​ Period of time between the -​ Infect their host penetration of the virus particle into -​ Spread within the host the host cell and the production of -​ Damage target tissues the first new virus particle -​ Disrupting cells during this period Virus Propagation will interrupt the release of (must be transmitted to another susceptible significant numbers of infectious host) virus particles -​ They must be shed within -​ If uninterrupted, single infectious secretions or excretions into the particle can replicate to produce environment MICRO103A - VETERINARY VIROLOGY DOCTOR OF VETERINARY MEDICINE 2ND SEMESTER A.Y. 2025 – 2026 DR. KRISTINE KAITH -​ Taken up by another host or a -​ Comparison requires that the vector following factors be equal: -​ Passed congenitally from mother to ​ Infecting dose of virus, age, offspring sex, condition of host animal and immune status Interplay of viral virulence and host -​ assays in inbred animals (e.g. resistance, or susceptibility factor mice) but only feasible for viruses that grow in mice -​ Viruses differ greatly in their ​ Care must always be virulence exercised in extrapolating -​ Differences in the outcome of data from lab mice to host infection between individual species of interest animals -​ May be assessed by determining -​ Variation amongst viruses of the the ability to cause disease, death, same species and the determinants specific clinical signs or lesions of viral virulence ​ LD50 or lethal dose 50 ​ often multigenic (several -​ the dose of the genes contribute to the virus required to virulence of individual cause death in viruses) 50% of animals -​ Determinants of host ​ ID50 or infectious dose 50 resistance/susceptibility are -​ ratio of the dose of multifactorial a virus that causes ​ e.g. host factors and infection in 50% of environmental factors individuals -​ Application of molecular technologies has allowed the Example: mapping of virulence determinants -​ For virulent strain of ectromelia in the genome of many viruses (e.g. virus whole-genomic sequencing) and ​ BALB/c mice → ID50: 2 virions ; resistance/susceptibility LD50 : 5 virions determinants in the genome of ​ Resistant C57BL/6 mice → ID50: 2 experimental animals virions ; LD50 : 1 million virions -​ Can also be estimated through the assessment of: ​ severity of an infection ​ Location ​ Distribution of gross, histological and ASSESSMENT OF VIRAL VIRULENCE ultrastructural lesions in affected animals MICRO103A - VETERINARY VIROLOGY DOCTOR OF VETERINARY MEDICINE 2ND SEMESTER A.Y. 2025 – 2026 DR. KRISTINE KAITH host cell types such as DETERMINANTS OF VIRAL VIRULENCE myocytes, neurons and salivary gland epithelium -​ Molecular biology has facilitated the -​ Changes in viral attachment determination of the genetic basis ​ emergence of variant of virulence of many viruses viruses with different -​ Genetic sequence comparison tropism and disease ​ identified the role of potential potential determinants of -​ E.g. porcine respiratory virulence coronaviruses which arose from transmissible gastroenteritis virus DETERMINANTS OF HOST (strictly enteric pathogen) RESISTANCE/SUSCEPTIBILITY -​ Due to Substantial deletion in the gene encoding the -​ Viral infections tend to be less viral spike protein which pathogenic in their natural host mediated virus attachment species than in exotic or introduced -​ This change affected the species tropism and transmissibility ​ E.g. myxoma virus → small benign fibroma in natural MECHANISMS OF VIRAL INFECTIONS host wild rabbits of AND VIRUS DISSEMINATION Americas but causes fatal generalized infection in European rabbit ROUTES OF VIRUS ENTRY ​ Some zoonotic infections are severe in humans but VIA THE RESPIRATORY TRACT mild or subclinical in their reservoir animal hosts -​ Mucociliary blanket -​ Expression of critical receptors on ​ protects the respiratory target cells tract; consists of a layer of ​ The fundamental mucus produced by goblet determinant of host cells resistance/susceptibility to -​ Inhaled virions → trapped in the particular virus viscous mucus layer → carried by -​ More conserved or ubiquitous ciliary action from nasal cavity → receptors = wider host range airways → pharynx → swallowed or -​ E.g. Rabies virus coughed out ​ uses sialylated -​ Larger particles (>10 um) → gangliosides and trapped on the mucociliary blanket acetylcholine receptor = lining nasal cavity and airways very wide host range; but infection is restricted to MICRO103A - VETERINARY VIROLOGY DOCTOR OF VETERINARY MEDICINE 2ND SEMESTER A.Y. 2025 – 2026 DR. KRISTINE KAITH -​ Smaller particles (