Download Welcome to Ms. Looney`s Biology Class

Introduction to Virology
Virus Review
• Structure of a virus:
– DNA or RNA surrounded by a protein coat, called a
capsid
• Capsid allows for attachment to a host cell
– A host cell is necessary for the virus to reproduce
• How viruses cause disease:
– Attach to a host cell, inject their genetic material, use
the cell to reproduce, lysing the cell
Viral Specificity
• Capsid’s surface markers determine what
type of cells (what organisms) the virus
can infect and what tissue(s) it can infect.
– This is called the virus’ tropism.
• May infect only one specific type of tissue or many
different ones, but shape of the surface markers
determine which cells is can attach to.
Virus Virulence
• Viruses have genetic material that can
encode for virulence factors to help them
replicate and transmit more efficiently.
• Loss of these virulence factors can result
in viral attenuation
– Attenuated viruses are “weakened” forms of
the virus, usually unable to cause disease.
• Lots of vaccines are attenuated
Steps in viral disease
1) Acquisition: entry into the body
2) Initiation of infection at a primary site
(tropism)
3) Incubation: Virus is attached but not
necessarily enough to make you feel sick
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May be asymptomatic (no symptoms)
May be symptomatic (generalized symptoms at
onset called prodromal)
– Symptoms caused by cells beginning to lyse in the area
Steps in Viral Disease cont.
4) Replication at target tissue
5) Convalescence: Immune response limits
and contributes to disease
6) Resolution or persistent infection
• Viruses are carried in the blood and
lymphatics
– If carried in the blood, its called viremia
Viral Infection
• Manifestations of the viral disease are
determined by the hypersensitivity and
inflammatory reactions.
• The relative susceptibility and severity of
disease is determined by
– Immune status, age, general health of the
person
– The viral dose
– Genetics of the virus and the host.
Viral Transmission
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Direct contact
Injection with contaminated blood/fluids
Organ transplant
Airborne droplets
Depends on the type of tissue it infects
Viral Transmission
• The presence or absence of a viral envelope is
the major determinant of the mode of
transmission
– Non-enveloped viruses can withstand drying,
detergents, extreme pH and temps.
– Enveloped viruses cannot survive these
– Non-enveloped= sturdy
– Enveloped= fragile because they rely on the envelope
to be intact in order to infect
• Usually must remain wet (resp. droplets, blood, mucus)
• Animals can act as vectors that spread
viral disease and can be reservoirs for the
virus
• Viral diseases that are carried in an animal
are called zoonoses
– Specifically, many viruses are carried by
insect vector…these are called arboviruses
Antiviral agents
• Get into your numbered groups.
• You will be assigned a classification of antiviral agents
• Design, on paper 1-3 powerpoint slides to explain your
drugs/agents
• Take turns on the computers, once approved, to create
the slides. Email them to
[email protected] and be ready to
present.
Laboratory Diagnosis
• Patients symptoms and history provide the
first clues to diagnosis
– Usually you have to rule out bacterial and
fungal infections first
• There are laboratory methods that can
confirm diagnosis
Cytology
• Look for changes in cell morphology (any
change in the normal cells is called a
CPE, cytopathologic effect).
• Common CPEs:
– Syncytia= multinucleated giant cells caused
by viral fusion of cells (HIV does this)
– Inclusion bodies- cell structure changes
Electron Microscopy
• Not a standard clinical lab technique