LEC 8 - Virus Structure + Function II Flashcards by Raegan Chambers

What are the two basic survival strategies for viruses?

Acute

– and –

Persistent infections

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Describe: Acute viral survival

Lytic infections

Successive propagation in a series of hosts

Destroys host cells

Multiply rapidly until host immune system catches up

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Describe: Persistant infections

Long term infection in single host

Transmission to new host occur but not as rapid

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What is the fate of the host with non-lytic viruses?

Establigh a quiescent interaction with host cell

Host has an increase rate of survival since virus isn’t as damaging

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What is the quiescent virus called?

Provirus

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What can terminate the quiescent phase of a viral infection?

Environmental conditions

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What are the three basic viral infection patterns?

Acute

Chronic

Latent

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What are the three types of persistent infections?

Latent

Chronic

Transforming

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Describe: Latent infections

Intermittent acute episodes

Between there is apparent absence of virus particles + very little synthesis

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What are examples of latent infections?

Herpes

Feline viral rhinotracheitis

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Describe: Chronic infections

Constant production of virus

Periods of time where symptoms are not present

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What are examples of chronic infections?

Canine distemper virus

Old dog encephalitis

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Describe: Transforming

Cells are immortalized

Properties are altered to those of cancer cells

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What are five basic ways that persisting viruses are able to evade the host’s immune system?

Blockade APC mechanisms - change MHC expression

INterrupt cytokine synthesis or receptor function

Inhibit apoptosis induction

Evade antibody/complement killing

Avoidance

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How are persistant viruses able to AVOID the immune system?

Infect non-permissive/quiescent cells

Store genome with no lysis

Invade immunological priviledged sites = lack MHC markers

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What are the three methods viruses can move throughout the body?

Blood

Lymphatics

Neurons

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What occurs with viremia in regards to replication?

Virus enters blood = Viremia

Another round of replication

Amplifies infection

Secondary viremia

= MORE DISSEMINATION

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Describe: Iceberg concept

Infection does not always mean disease

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What are the three things a virus must do?

Infect host

Persist + Spread to damage tissues

Be transmitted

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What are the three parts to clinical disease?

Death

Severe disease

Mild illness

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What is sub clinical disease?

Infection without clinical illness

What are the six susceptibility factors?

Age

Nutritional status

Immune function

Pregnancy

Stress

Presence of receptors

Why are embryos susceptible to viral infection?

Rapidly dividing

What is a virion? What must happen with a virion?

They are inert

Must be implanted on suitable part of host body

Enter the body

What types of tropism are there?

Cellular Tissue Host

How does tropism occur?

Virus is highly selective for certain kinds of receptors

What symptoms generally occur with non-specific host responses?

Vague clinical symptoms Fever + Malaise Due to production of cytokines

What can cause hemorrhage due to a virus?

Vascular bed damage

What disease process can occur when a virus causes endothelial damage?

DIC

What are examples of CPE (visable cytipathic effects)?

Inclusion body formation Syncytia formation Nuclear/morphological modifications

Describe: Syncytia formation

Multinucleated giant cells

What viruses cause multinucleated giant cell formation?

Herpes Paramyxo

What causes inclusion body formation?

Site of viral replication Or Product accumulation

What special inclusion body goes with the rabies virus?

Negri bodies

How can a diagnosis be made with direct examination of clinical samples?

Electron microscopy Viral cytopathic effects Antigen detection with fluorescent antibody Hemabsorption Hemaggultination

Describe: Hemadsorption

RBC's adhere to surface of infected cells expressing viral hemagglutinin

Describe: Hemagglutination

RBCs are cross-linked by viron hemagglutinin protein and form a network

How can you detect viral genetic material?

PCR | (Polymerase chain reaction)

What is the down side to using PCR as a diagnosis?

Will reveal latent infections + specimens harboring inactivated virus So dont know if thats whats causing the problem or not

What kind of virus can be detected with PCR?

DNA RNA

What type of PCR is used for RNA virus?

rt-PCR

How are cultures used to make a diagnosis?

CPE Plaque formation (cell killing) to assay virus Pock formation Death or pathology in whole animal assay

What titer are you looking for in serology?

Greater than 4x's

Describe: ELISA

Immobilized viral antigens or antibodies capture specific reactive antibodies to host

What are three major ways viruses are controled?

Quarantine Vaccination Antiviral agents

What is the problem with anti-viral agents?

Halt viral replication Toxic to host because viruses are so intermigled with our cells

What is another name for vaccination (process by which it works)?

Artifical acquired active immunity

What can be given to induce passive immunization?

Immunoprophylaxis by provision of immune serum globulin

What is the goal of biosecurity?

Prevent disease -- and-- Prevent outbreaks

What is involved in biosecruity?

Controlling the pathogen transmission by understanding the relationships between host + disease + environment