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Describe this figure
- Model of viral infection w/ varicella-zoster (chicken pox)
- The infection is initiated either in the conjunctiva of the eye or in the mucosa of the upper respiratory tract
- moves quickly to regional lymph nodes, where it can infect T cells
- 4 to 6 days later, infected T cells move into the blood causing a primary viremia.
- It moves to the liver, spleen and other organs, causing a second round of infection and then back into the blood causing secondary viremia (skin lesions appear)
- moves into sensory ganglia in the peripheral nervous system, where it becomes latent
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What is an acute infection?
- Best understood infections and involve the rapid production of viron's followed by rapid resolution and elimination of the infection by host defenses
- Some are asymptomatic
- main problem is the incubation period; by the time they show symptoms the virus has already been transmitted. two examples: common cold and influenza.
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What is a latent infection?
- Is known as a persistent infection (chronic infection is also persistent)
- caused when host defenses are either modulated or completely bypassed
- virions are produced for months or even years
- Cytotoxic T cells (CD8+) are key in getting rid of these infections (adaptive immune response).
- no large scale production of virions
- reduced or absent immune response
- persistence of an intact viral genome so infections can reoccur
- can be re-actived years after entry into host
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Explain slow infections
- Lethal- associated usually w/ brain infections
- Signs may not be seen until years after the primary infection
- Once S/S appears (difficulties w/ brain function and motor skills), death usually follows very quickly
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What is antigenic drift?
- Minor
- Involves small changes in viron structure Results from mutations
- Occurs after infection has began
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What is antigenic shift?
- Major changes in viron structure
- due to acquisition of new genes
- this through co-infection or recombination
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Define virulent
viruses cause significant disease
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Define non-virulent, attenuated
At one point it was virulent, but now its not. They cause little or no disease.
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What are the three types of vaccines?
- Live attenuated vaccine: made of intact virions rendered non-infectious
- Inactivated or killed vaccine: composed of killed or dead virions
- Subunit vaccine: composed of immunogenic parts of virions
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What are passive and active immunization?
- Passive immunization: a performed antiviral product, such as antibody, is administered
- Active immunization: antigen is administered & causes the onset of the immune response
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What are some methods to measure virulence?
- LD50= how much virus is required to kill 50% of a subject population
- ID50= how much virus is required to infect 50% of a subject population
- PD50= how much virus is required to paralyze 50% of a subject population
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Cytopathic viruses
produce virions and kill host cells rapidly (cytopathology)
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Non-cytopathic viruses
produce virions but do not cause cytopathology
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Viral dissemination
Spread of viruses in an infected body
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