Infections and Isolation of Viruses

Acute Infection

• symptoms worsen over short period followed by the elimination of the virus and recovery

Persistent Infection

• virus stays in certain tissues or organs of infected person

Persistent Latent Infection

• virus stays hidden or dormant inside the cells 

Examples of Persistent Latent Infection

• chicken pox

• shingles

• herpes virus 

Examples of Chronic Persistent Virus

• HIV

How are viruses isolated?

• viruses require a living host to grow

• these infected living hosts can be cultured and grown 

• filtration is used to separate virions that are released in the liquid medium from host cells

How can you see viruses and plates?

• clear plaques are visible were host bacterial cells have been lysed

• bacteriophage lyse the bacteria leading to the formation of plaques 

Why do we cultivate animal viruses?

• identification and diagnosis of viruses in clinical specimens

• production of vaccines

• basic research studies 

Why do we cultivate viruses in eggs

• viruses can be replicated in various locations within the egg

• the cells within the chicken eggs can be used to culture different types of viruses 

Continuous Cell Growth Cultures

• not affected by contact inhibition 

• they continually grow regardless of cell density 

Primary Cell Cultures

• grow attached to the surface of the culture container

• contact inhibition slows growth of the cell once they become to dense and begin touching each other 

• at this point growth can only be sustained by makinh a second culture

Cultivation of Viruses in Tissue Cells

• can be prepared to be used for viral infection 

Cytopathic Effects (CPE’s)

• distinct observable cell abnormalities caused by viral infection 

What are examples of CPEs

• loss of adherence to surface 

• change in cell shape

• shrinkage of nucleus

• vacuoles in the cytoplasm 

• fusion of the cytoplasmic membranes

• formation of multinucleated syncytia 

• inclusion bodies in the nucleus or cytoplasm 

• complete cell lysis 

Hemagglutinin

• present in spikes protruding from some viruses 

How can you detect a virus?

• observing cells under the microscope

• detection by hemagglutination assay

• enzyme immunoassay

• looking for cytopathic effects (CPEs)

Hemmagglutination 

• agglutination (clumping) together of erythrocytes 

Hemagglutination

RBC + Virus

Virus neutralized and hemagglutination inhibited

RBC + Virus + antiviral antibody from serum

Enzyme Immunoassay

• rely on antibodies that detect and attach specific biomolecules (antigens)

• antibody is linked to enzyme that can interact with substrate and produces a colored end product 

What is the Enzyme Immunoassay used for?

• preliminary screen for the presence of viral antigens 

Steps in detection by enzyme immunoassay

1. apply patient sample to membrane filter

2. add antibody with enzyme conjugate, antibodies will attach to antigen if present 

3. wash to remove unattached conjugate

4. add substrate to see color change for detection 

What does it mean when there is no color reaction in an enzyme immunoassay?

• there is a lack of enzyme

Prions

• proteinaceous infectious particles

• creates misfolded rogue form

• can be infectious, and stimulate other normal proteins to become misfolded

What causes prions to form?

• genetic mutation 

• can be spontaneous

What causes transmissible spongiform encephalopathy in humans and animals?

pirons

Persistant Chronic Infection

• disease with symptoms can be recurrent over a time