Introduction to Virology

Virus Review Structure of a virus: How viruses cause disease: 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 Acquisition: entry into the body Initiation of infection at a primary site (tropism) 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)

Viral diseases that are carried in an animal are called zoonoses 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 katherine.harris@fortbendisd.com 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