Topic 2: Orthomyxovirus case study After completing the Orthomyxovirus case study of Topic 2 in the Virology segment, students should be able to: · explain the disease caused by Influenza virus. . describe the structure of the Influenza virus and its genome, and the function of its two viral envelope proteins: hemagglutinin (HA) and neuraminidase (NA). · describe the host range of Influenza A viruses. • explain the replication cycle of Influenza virus including the host cell receptor, the two modifications of HA needed for genome entry, stealing of the 5'- methylated cap from the cellular mRNA during the synthesis of its own mRNA, replication of the genome, assembly of the progeny, and release from the cell. . how anti-viral medications may interfere with virus progeny production. • explain the process of antigenic drift and antigenic shift, and why pigs are an important vessel in the formation of new Influenza strains with pandemic potential. • describe the types of vaccines available for the prevention of Influenza virus, and explain why people need to be repeatedly immunized against this virus. 1
Orthomyxoviruses Enveloped viruses, RNA genome Influenza A has a broad host range (humans, other mammals, birds). ortho (Greek) - standard myxo (Greek) - mucus Pleomorphic (many shapes) At least 3 types of Influenza: A, B, C. What is the risk factor for contracting Influenza? Image courtesy of Centers for Disease Control and Prevention, Atlanta, GA (image #11214) 3 This image is in the public domain and thus free of any copyright restrictions.
Seasonal vs. Pandemic Influenza A Seasonal flu: In Canada, typically between Usually the same strains as previous year; there may be minor variations due to antigenic drift. People may have from previous infections or vaccinations. Pandemic flu: . Can occur at any time of the year, usually 2 or 3 'waves' several months apart, each wave lasts about 2 - 3 months. With pandemic flu, most people have New strains are often the result of a shift, but could result when an avian Influenza is directly transmiced to humans. Vaccines are prepared in advance of flu season based on what is circulating elsewhere. No vaccines are available early in the pandemic - it can take at least 6 months to produce the vaccine. 4