An overview to virology! U luv ‘em U hate ‘em They make you sick They make you scared They make you work U fight ‘em

Objectives To describe the classification of viruses. To understand the spectrum of disease caused by viruses. To understand the public health implications of viral infections. To describe the pathogenesis of viral infections. To discuss the transmission of viral infections.

What is a virus? Genetic material inside a protein coat. Very small nm. E.coli 1000nm Pox virus 300nm Parvovirus 20nm

What else makes up a virus? A virus is an obligate intracellular parasite. It is completely dependent on living cells for replication and survival. Unlike other larger organisms, it contains either RNA or DNA. Never both forms of nucleic acid.

Viral structure. There are two basic shapes found in viruses: Icosahedral structure:

Helical structure:

Viruses consist of the following components: The genome. RNA or DNA. The capsid The matrix protein The envelope Glycoprotein spikes Various non-structural proteins

Viral classification. Type of nucleic acid: –RNA or DNA Number of strands of nucleic acid. Polarity of the genome. –Positive sense or Negative sense Shape of the capsid / nucleocapsid –Icosahedral or Helical Presence of an envelope

Virus DNA RNA DS SS DS SS Non Enveloped Enveloped Non Enveloped Enveloped Non Enveloped Adeno Papova Herpes Pox Hepadna Parvo Retro Arena Reo Para, Ortho etc Picorna Calici

Nomenclature conventions: Family:---viridaee.g. Herpesviridae Subfamily:---virinae e.g. alphaherpesvirinae Genus: ---virus e.g. Herpesvirus Species: ---e.g. Herpes Simplex virus Type: --- e.g. Herpes simplex virus type 1

Pathogenesis of viral infections: Localized: –Portal of entry is where the virus replicates and causes disease. –There is seldom spread of the virus beyond the localized area of infection –Short incubation period of 1-5 days. –Symptoms may be caused by the viral replication or by the immune response to the virus.

Generalized infections Portal of entry Migration to local lymph nodes Primary viraemia RES Secondary viraemia Target organs Incubation period days Prodrome 2-3 days Sick

How transmission happens: Inhalation Ingestion Direct contact with skin or mucous membranes Indirect contact - fomites Transplacental Organ transplant or blood transfusion.

Conclusion Small BUT: –Virulent –Dangerous –Major public health threats –Major public health disasters.