Virology 1+2+3+4+5+6+7+8+9+10+11

What is immuno-staining: IHC?

-Method of identifying viruses in a cell culture

Describe mechanisms of viral persistence.

1. Latent infection 2. Chronic infection 3. Slow infection

What are the different ways a virus can enter the body?

1. skin 2. respiratory tract 3. alimentary tract 4. urogenital tract 5. conjunctiva 6. placenta 7. reproductive losses

What is a viral envelope?

A piece of the host cell's MEMBRANE that surrounds the virus -A lipid bilayer formed when a virus particle buds through cellular membrane - host derived Peplomers (spikes): Virus derived - often important in virus

What are the two main causes of disease from viruses?

Disease results from an interaction between the host and virus Is a result of: -virus induced cell injury -immunopathology

What type of pathogens does humoral immunity target?

Extracellular pathogens

Describe different patterns of viral infection

Possible entry points: 1. Skin -> enters through a break 2. Respiratory tract (most common) 3. Alimentary tract 4. Urogenital tract 5. Conjunctiva 6. Placenta

Helical capsid

Rod-shaped capsomeres that form a continuous helix around the nucleic acid

Normal Cell Cycle

Series of events a cell goes through from birth to the cell, growth to division to daughter cells

What occurs during the synthesis phase?

The synthesis of all viruses involves transcription or generation of positive messenger RNAs (mRNAs) from their genomes and the use of host ribosomes to translate the viral mRNA into viral proteins

What is the maturation phase?

The viral particles undergo structural changes in the protein coat till they become infectious

What happens during the attachment phase?

Virus attaches to the host cell

What is the Baltimore Classification?

Virus classification based on nucleic acid genomes and replication type -not used very much anymore -just note that whatever the genome is, they need a stragey to replicate mRNA

What is the uncoating phase?

Virus released genetic material i.e. nucleic acid is released inside the cell

Are viruses intracellular or extracellular?

Viruses are obligate intracellular -there are no 'free-living' viruses (versus some bacteria, fungi, nematodes, etc) -viruses lack the complex energy-generating and biosynthetic 'machinery' necssary for independent existence -in order to replicate themselves, viruses have to "highjack" the cellular machinery of the host

How can we cultivate viruses in the lab?

Viruses can only replicate in living cells, so you need a living host cell - Experimental animals - Avian embryos (in eggs) - In vitro Cell culture (most common method) - In vitro Organ culture

Specificity on viral attachment

-A virus can only infect the cells, which have the correct receptor -This specificity provides the basis for a virus's host range -Also, this binding specificity limits viruses to only infecting certain cell types within their host

Which of the following contributes to the control of the spread of West Nile Virus among a group of paddocked horses? (2 answers) -Application of insect repellent -Keeping infected and non-infected animals in different paddocks -Getting rid of old tires lying in the paddocks -Using dedicated clothing when dealing with WNV-infected horses

-Application of insect repellent -Getting rid of old tires lying in the paddocks

How are organ cultures used for virus isolation

-Difficult to maintain, hard to maintain. -Used for research purposes -Used to replace experimental animals Examples: -Tracheal rings -Embryonic intestine -Nerve tissue cultures

In which situation may you be dealing with an apparently healthy animal that is shedding a virus? (3 answers) -During an incubation period -During subclinical infection -During chronic/persistent infection -During acute infection

-During an incubation period -During subclinical infection -During chronic/persistent infection

What is haemagglutination?

-If there is no virus, RBCs will fall to the bottom of the well -If there is virus-RBC binding, the RBCs create a lattace that cannot fall to the bottom of the well

What happens during the penetration phase?

-The virus enters the cells Has mulitple strategies for doing so: 1. Receptor-mediated endocytosis (e.g. adenovirus, orthomyxoviruses) 2. Fusion with Plasma membrane (e.g. herpesvirus) 3. Direct penetration of a genome (e.g. parvovirus) -is irreversible

What is haemadsorption?

-With some viruses when they replicate, they insert viral particles into the membrane -These particles have the ability to bind to RBCs -When this happens, and you wash the cells in the culture, an uninfected cell will have all the RBCs wash off -If the RBCs are bound to a virus, they will not wash away

What does the nucleic acid part of viruses consist of?

-either DNA or RNA (never both) -single-stranded or double-stranded -RNA: positive (same as mRNA) or negative (complementary to mRNA) -monoparite (single molecule of nucleic acid) or multipartite (segmented) -haploid (one copy of the gene) exception: retroviridae -often infectious

What is attachment a determinant for?

-host range -virulence Used in: -drug development -vaccine development

What does the protein part of viruses consist of?

1 to >100 proteins. Can be divided into structural or non-structural proteins Structural -Used to construct components of the virus -Protection of viral nucleic acid -Attachment and entry -Important in host immune response Non-structural (enzymes) -Nucleic acid and protein metabolism, -Shutdown of host cell function -Subdiversion of cellular machinery

What are the steps of the virus replication process?

1. Attachment 2. Penetration 3. Uncoating 4. Synthesis 5. Assembly 6. Maturation 7. Release

What are the different ways viruses can affect cells?

1. Cell death: occurs via apoptosis (cell suicide) or necrosis (murder) -Cytopathic viruses -Removal of virus infected cells by the immune system 2. Loss of 'specialised' functions (viruses that bud rather than lyse cells) 3. Cell fusion -results in viral spread 4. Cell transformation (neoplasm) 5. No detectable adverse effects (non-pathogenic viruses)

What are the two types of acquired immunity?

1. Cell-mediated immunity 2. Humoral immunity

How to recognize virus growth in cell culture?

1. Cytopathic effects (CPE) -Viruses kill cells, causing cytopathic effects -Is recognizable in cell culture 2. Haemadsorption / haemagglutination 3. Immuno-staining (IF, IHC) -Used like PCR, tests for a specific virus 4. Polymerase chain reaction (PCR) -Can test for a specific virus

What are the outcomes of viral infections?

1. Death 2. Recovery 3. Persistent infection -latent infection -chronic infection -slow infection

Explain in detail pathogenesis of EHV-1 infection

1. EHV-1 enters through respiratory epithelium 2. Infects immune cells (dendritic cells). Moves via infected cells to lymphoid tissues and infect more cells 3. Virus travels to uterus via leukocytes, and due to damage to placenta the virus can pass through the placenta to the fetus 4. Results in reproductive losses -> fetal death/neonatal death

Describe the main steps in the course of viral infection and their relationship to disease, viral spread and persistence

1. Entry 2. Incubation and dissemination 3. Disease (not always) 4. Spread to other animals 5. Recovery or death or persistent infection Disease: results from an interaction between the host and virus Viral spread: Period during which an infected individual can infect others Persistence: Viral infection that is not cleared by immune system. Can either le latent, chronic, or slow

Examples of viral encephalitis

1. Equine eastern encephalitis: -cytocidal changes in neuron (direct damage) -50-75% mortality in humans -Survivors have permanent neurologic sequelae 2. Rabies: -"Pristine" brain: very little histopathology -100% mortality in humans -Death due to deregulation of neuronal control over basic life functions -No survivors

How does dissemination occur?

1. Local spread on epithelial surfaces (local spread) -Direct cell-to-cell -Aided by mechanical action (e.g peristaltic) 2. Via blood stream (systemic spread) -Subepithelial invasion -Travels via lymph nodes and then it can enter blood stream -Then it can enter organs and replicate there -Direct inoculation (arboviruses)

What are the different mechanisms the body uses to protect itself against viral invaders?

1. Physical barriers 2. Innate Immunity -phagocytic cells, complement, NK cells -quick, but non-specific 3. Acquired immunity (immunological memory)

What are the different types of cell cultures?

1. Primary cell cultures - Prepared directly from tissues - Often more susceptible to viral infection - Difficult to establish, type consuming, expensive - Have a finite lifespan - Benefit: most similar to what is in the body. Supports viral growth best 2. Secondary cell cultures - Primary cells passaged in vitro for a limited number of passages 3. Continuous cell lines (most common method) - Immortal cell lines - Easy to work with - Less susceptible to viral infection 4. Organ cultures - Specialised techniques, seldom used

What are the factors that affect viral resistance or susceptibility?

1. Primary defences 2. Innate immunity 3. Adaptive immune responses 3. Genetic factors -Species -Breed -Strain -Individual genetic differences 4. Physiological factors -Age -Nutritional status -Stress exposure -Body temperature -Concurrent infections/diseases

What are the phases of viral existence?

1. Transmission phase -outside of cell; do not behave like a living organism -very fragile. Will not live long unless they can get into a cell. 2. Replication phase -enters host cell, begins to act like living organism

What are the different mechanisms of virus shedding?

1. Via respiratory tract -through coughing, sneezing, eating, drinking 2. From the oropharynx and intestinal tract -through feces (diarrhea): rotavirus -through saliva (licking, grooming, biting): rabies, FeLV, FIV 3. From the skin -through direct contact and small abrasions: papillomaviruses -large quantities of virus in vesicles: FMD virus 4. From the urinary tract -Hantaviruses 5. From the genital tract -EAV 6. In milk -CAE 7. Via blood and tissues -Arboviruses -Iatrogenic transmission 8. Infection without shedding -Via germplasm: retroviruses -Via consumption of contaminated tissues: hog cholera, ASF

What are the steps of viral pathogenesis?

1. Viral entry 2. Incubation and dissemination 3. Disease (not always) 4. Spread to other animals 5. Recovery/death/persistant infection

icosahedral capsid

3 dimensional, 20 sided figure with 12 evenly spaced corners

What is an antigen?

A molecule that can generate an immune response when introduced to the animal (e.g. a part of a virus, bacteria, etc)

What is the structure of a virus?

A typical virus is composed of a core of DNA or RNA surrounded by a protein coat -has nucleocapsid -some have lipid envelope (host derived) -some have matrix protein between nucleocapsid and envelope ('packing material') -capsomers: morphologic "building blocks"

What are some examples of host cell receptors?

ACE - SARS-CoV-2 CD4 on macrophages and T cells - HIV Sialic acid - orthomyxoviruses (influenza virus) paramyxoviruses (New castle disease virus)

What type of pathogens does cell mediated immunity target?

Abnormal cells and intracellular pathogens

Adsorption vs Attachment

Adsorption: non-specific binding of viral particle to the cell membrane - random initial virus-cell contact -occurs before attachment Attachment: specific binding of viral glycoproteins to cell surface receptors - Reversible - Followed immediately by penetration - irreversible -Lock and key: ligand and receptor have to fit eachother very well -Viruses utilizes receptors that cells have for normal function

What is the release phase?

All the infectious virions are released from the host cell via bursting of the host cell or budding of the host cell

What are B cells?

B-lymphocytes; they release antibodies into blood. -Small, long-lived resting cells survive without continuous Ag exposure -Large, slowly dividing cells in germinal centers: need continuous exposure to Ag on dendritic cells -Long-lived plasma cells: accumulate in bone marrow

Describe virus-induced changes at the level of the cell.

Could be any one of these things: 1. Cell death via apoptosis or necrosis 2. Loss of specialized functions 3. Cell fusion 4. Cell transformation (neoplasm) 5. No detectable adverse effects

What is the synthesis phase?

DNA replication occurs -large amount of viral proteins and viral nucleic acid is produced inside the host cell

How do viruses enter via urogenitcal tract?

Enter via small tears or abrasions during sexual activity or via latrogenic route (AI, reproductive exam) ex: herpesviruses, equine arteritis virus, papillomaviruses

How do viruses enter via the placenta?

Enter when there is damage to the placenta -Viruses pass through the placenta to the fetus Results in reproductive losses: -fetal death/abortion -neonatal death -persistently infected animals

How does a virus enter through the skin?

Enters through a breach in integrity (cannot enter through intact skin) 1. Minor abrasions: -Papillomaviruses -Herpesviruses -Pox viruses 2. Arthropod bite: -Bluetongue virus -Equine encephalitidies viruses -West Nile virus 3. Bite of vertebrate: -FIV -Rabies 4. Iatrogenic

True or false: All animals are infectious during an incubation period

False

True or false: Each virus can use only one specific way to enter its host

False

True or false: The words "infection" and "disease" can be used interchangeable as they describe the same state

False

virus taxonomy

Family names end in -viridae Genus names end in -virus In formal virus taxonomy, the names of orders, families, subfamilies, genera and species are always printed in italics and the first letters of the names are capitalized

Besides nucleic acid and proteins, what are some other components of viruses?

Glycoproteins: most often as peplomers (spikes) extending outwards from the envelope Lipids: viral envelope (derived from cell membranes)

Ex: HFN1 virus

H5N1 Binding to cells in respiratory tract of human and avian species. Influenza receptor: sialic acid: Avian strains: SA-α-2,3-GAL Human strains: SA-α-2,6-GAL -Virus cannot be spread from birds to humans due to it being deeply inbedded in the alveoli -Strains are slightly different between species

How does a virus enter via alimentary tract?

Has to bypass the protective mechanisms: -mucus + IgA -Acid and bile -proteolytic enzymes Viruses who enter this route thrive in this type of environment. These include: 1. Acid-stable non-enveloped viruses -rotaviruses -caliciviruses -enteroviruses 2. Acid-labile enveloped viruses: -coronaviruses -pestiviruses -avian influenza virus

What is the significance of host cell receptors?

Host receptors - cell surface proteins crucial for fundamental cellular functions - highly conserved -Many different cellular molecules are used as receptors by different viruses, they are mainly cell surface glycoproteins or carbohydrate residues present on glycoproteins or glycolipids, components of the extra cellular matrix and receptors involved in cell signaling and activation

Define incubation period and period of infectivity

Incubation period: the time of viral infection to time of clinical signs Period of infectivity:

Localized vs systemic viral infection of respiratory tract

Localized: virus enters and replicates in respiratory tract -ex: rhinoviruses, mammalian influenza viruses, adenoviruses Systemic: virus enters through respiratory tract and then spreads to rest of body (can replicate in other organs) -ex: canine distemper virus, newcastle disease virus, foot-and-mouth disease virus

What actually causes virus disease?

Many infections are subclinical Disease results when: 1. A sufficient number of essential, non-replaceable cells are killed: -motor neurons in Taflan disease, hepatocytes in CAdV-1 infection 2. Rate of cell destruction exceeds max cell regeneration rate, resulting in organ failure -Feline panleucopenia - loss of PBL and all dividing cells 3. Circulatory disturbances due to infection of endothelium (or DIC) occur → thrombosis, haemorrhage, effusions, ischaemia -Classical swine fever, AHS 4. Epithelial damage &/or immunosuppression allow secondary invasions by other pathogens -Parainfluenza 3, BVD, FIV 5. Widespread inflammation -Canine distemper 6. Interference with normal morphogenesis in the foetus: -Pestiviruses 7. Excessive formation of immune complexes that are not removed by the immune system (immunopathology) -FIP

How are cell cultures used for virus isolation?

Most common way to grow viruses Cell culture medium needs: -Nutrients -Growth factors +/- antibiotics

What is the period of infectivity?

Period during which an infected individual can infect others -May begin before the end of the incubation period (e.g., FMD) -Short (days) or long (weeks to months) -Chronically infected animals ('carriers') may shed the virus in the absence of clinical signs -Continuous or intermittent shedding is possible

What is a virus?

Small, obligate intracellular parasites -In their simplest form, viruses consist of nucleic acid and protein

Explain how viruses cause disease

Some causes for disease: 1. Non-replaceable cells are killed 2. Rate of destruction > cell regeneration 3. Circulatory disturbances 4. Epithelial damage/immunosuppresion -> secondary invasion 5. Widespread inflammation 6. Interference with noraml marphogenesis in fetus 7. Formation of immune complexes that are not removed by immune system

What is dissemination?

Spread of viral infection from the site of the initial infection.

What is a virion?

The complete, infective form of a virus outside a host cell, with a core of RNA or DNA and a capsid. Metabolically inactive

What is virulence?

The extent to which a virus causes disease in a specified host -Some highly pathogenic influenza viruses cause deadly disease in chickens, but no disease at all in ducks. -For many viruses, virulence varies by strain, not just by species e.g., velogenic, mesogenic and lentogenic strains (pathotypes) of Newcastle disease virus

What is the incubation period of a virus?

The time from virus entry (infection) to onset of observable clinical signs Can be: SHORT when clinical signs are due to viral replication at the site of entry (1-5 days) LONGER when virus must spread before causing disease (1-2 weeks) -There are many other virus- and host-associated reasons for variation

Characteristics of enveloped virions

They are pleomorphic, as the envelope is not rigid

How do viruses enter via the conjunctiva?

Through small tears ex: Herpesviruses (e.g. IBR, EHV-1) , Canine adenovirus 1 and 2

True or false: intact skin is an effective barrier against entry of viruses

True

How can we use experimental animals for virus isolation?

Used infrequently - when cell culture methods have not been developed (e.g., "wobbly possum disease"). Also used in virus research - Animal models for viral pathogenesis and host immune responses - Vaccine testing - Production of reagents

What occurs after dissemination?

Viral disease -Is not always presence (infection without observable disease)

What is the assembly phase?

Viral nucleic acid is packed into viral protein coat to form large number of viral particles

Define the term virulence

Virulence describes the potency of a pathogen measured in the numbers required to kill the host.

Can viral dissemination occur via nerves?

Yes, but it is uncommon. -Is fatal -slow spread -occurs through axonal or schwann cells -may use olfactory nerve endings -ex: Rabies, Aujeszky's disease, herpes B, Borna disease viruses

Are there any infectious agents simpler than viruses?

Yes: -Viroids: infectious RNA -Prions: infectious protein

What are T cells?

a lymphocyte of a type produced or processed by the thymus gland and actively participating in the immune response. -Persist in the absence of Ag -Divide slowly -Remain in secondary lymphoid tissues (e.g. lymph nodes)

What is an epitope?

a part of the antigen that is recognised by the immune system. Not all epitopes are equal: when the complex molecule (e.g. a virus) is introduced to the body, the immune response is predominantly raised to selected epitopes: these are referred to as immunodominant

How does a virus enter via the respiratory tract?

is the most common route of entry The normal respiratory tract has protective mechanisms: ▪ Mucus blanket produced by goblet cells ▪ Ciliated epithelium ▪ Alveolar macrophages If the respiratory epithelium is damaged, it is susceptible to viral infection

What is remdesavir?

it blocks RNA dependent RNA polymerase that is necessary for replication of coronaviruses -is an antiviral drug

What are antigen presenting cells?

macrophages, dendritic cells, B cells -Antigen is fragmented and presented in conjunction with either MHC I or MHC II molecules

What is an emerging disease?

one that appears in a population for the first time or is a disease that has mutated into something new -60-70% of emerging infectious diseases are zoonotic

What is viraemia?

presence of virus in the blood Can be 1. Cell-associated -canine distemper -herpes viruses 2. Free in plasma -bovine viral diarrhea -west nile virus -equine encephalitis viruses

What is the major histocompatibility complex?

proteins on the surface of each cell that help the body present the antigens. -allows the immune system to distinguish between "self" and "non self" -antigens are presented bound to MHC molecules -T cells learn to recognize "self" antigens when they mature in the thymus. All T-cells that recognize selef-antigens are destroyed MHC I & II: involved in antigen presentation MHC III: comprise other secreted proteins with immune functions e.g. components of the complement system, cyotkines, or heat shock proteins

What is a nucleocapsid?

the capsid together with the nucleic acid capsid = protein coat viral nucleic acid

What is clonal selection?

the process through which immature B and T Cells go through so that only certain types are permitted to mature

What is a cross-reactive epitope?

the same or similar epitopes that are present on unrelated molecules. If similar epitopes are present on two different viruses, the immune response to the first virus is cross-reactive against the second virus (e.g. CAdV-1 and 2).

What is capsid symmetry?

two types: Icosahedral (cubic) -maximizes space Helical

How are viruses classified?

type of nucleic acid, presense of an envelope, shape, size

How are avian embryos used for virus isolation?

• Bacteriologically sterile - makes them a good vessels • Immunologically incompetent -Some viruses grow really well in eggs Still used for isolation of certain viruses: - Influenza virus - ILT - Poxviruses

Specificity in Attachment

• Determines cell type specificity • Redundancy in ligand-receptor combinations ex: polio can only affect humans

What occurs during the uncoating phase?

• Viral DNA or RNA has to be released from the surrounding capsid • Complete or incomplete • Various mechanisms and various sites used by different viruses - At the cell surface - Within a cytoplasm - At a nuclear pore - Within a nucleus • Uncoating may be targeted by drugs e.g., amantadine for influenza viruses