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2. Vial Pathogenesis - Viral Properties Viral Pathogenesis...

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1 Viral Pathogenesis and Viral Pathogenesis and Host Response Host Response Viral Properties Viral Properties Viruses are intracellular parasites which need living cells to survive and reproduce. They bind to specific cell receptors – they display cell tropism They require host cell machinery for viral protein synthesis (to make new viruses) Viral Reservoirs Some viruses are host specific – Small pox, HIV are specific to humans – A subset of Influenza infect humans Some viruses can infect multiple hosts – Rabies, SARS (?) Routes of Transmission Routes of Transmission a) Contact with a sick person Direct - genital herpes, colds Fomite (kleenex) - adenovirus (eye infections) Droplet - influenza, chickenpox b) Vehicle (things viruses can travel in) Food - hepatitis A – infected food handler Water – Norwalk virus (causes diarrhoea) c) Vector (insects that spread viruses) Arthropods - mosquito – Dengue, West Nile Encephalitis tick - Rocky Mountain Spotted Fever Portals of Entry Portals of Entry a) Non-intact skin (cuts, eczema) examples: hepatitis B and C, HIV b) Mucous membranes inhaled (respiratory tract) examples: influenza, cold viruses direct contact (splash to the eye or mouth, sexual contact) examples: hepatitis B, herpes, HIV contaminated food, water (GI tract) example: hepatitis A, Norwalk virus c) Parenteral (through the blood) transfusion (West Nile) IV drug use (HIV, hepatitis C) needle stick injury (hepatitis B and C, HIV) Factors determining if Infection Occurs Occurs Viral: – Viral load (number of copies present) – Viral fitness to avoid host immunity – Site of entry – Degree of adaptation to host
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2 Factors determining if Infection Factors determining if Infection Occurs Occurs Host: – Pre-existing immunity due to vaccination or previous exposure – Age (very young and old at greatest risk) – Immune status (HIV and transplants at greatest risk) – Nutritional status (protein needed for immune response) – Genetic factors (HLA and Immunodeficiency) – Pregnancy How do we defend ourselves?
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