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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 • • 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 • • • • 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