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Bird Flu Disease Categories • Sporadic occurrences: Limited in scope. Affect a few individuals in a small area. • Epidemics: More widespread. Affect large areas. • Pandemics: Occurs worldwide. The 1918 super flu killed 40 million people. • Endemic: Caused by an infectious agent that is always present in a population. – Hantavirus –endemic in rats in western US. Viruses • Viruses require a host • Viruses are essentially packets of genetic information; RNA or DNA. • Viruses can be latent. • Viruses are specific for different cell types. – Polio virus infects nerve cells – HIV infects immune T cells – Hepatitis B infects liver cells • Essentially, Viruses are composed of: – Envelope – Caspid (capsule that holds genetic material) – Genetic Material, RNA or DNA • RNA=Retrovirus • 1. Binding--this requires specialized envelope proteins. These proteins make viruses specific for different cells. • 2. Penetration--viral particles enter the cell, the caspid is removed and genetic material enters the nucleus. • 3. Replication--the virus uses the host replication machinery to make many copies of itself. • • 4. Viral protein production--the virus uses the host’s translation machinery -copies of the viral proteins - capsid and new envelope proteins. Envelope proteins move to the plasma membrane thanks to protein secretion performed by the host. • 5. Assembly--genetic material is packaged into the new caspids. • 6 Budding--the caspids move to the cell membrane, get wrapped in their envelope proteins and move on to infect a neighboring cell. How a virus changes • Antigenic drift: Mutations cause a gradual change in caspid spikes – Antibody gradually becomes less effective • Antigenic shift: An abrupt , major change occurs in the antigen of the spike. – Because the virus acquires one or more new genome segments. – This is how pandemic strains of flu occur What is Avian Influenza • Is an infection caused • Bird flu is very by avian (bird) contagious among influenza viruses. birds. • These flu viruses • Can make occur naturally among domesticated birds birds. like chickens, ducks, and turkeys very sick • Birds carry the and kill them. viruses in their intestines, but usually do not get sick. How is it Transmitted ? • • • • From Bird to Bird Domesticated birds may become infected with avian influenza virus through direct contact with infected waterfowl or other infected poultry, or through contact with surfaces (dirt, or cages) or materials (water, or feed) that have been contaminated with virus. Infected birds shed virus in their saliva, nasal secretions, and feces People, vehicles and other inanimate objects can spread the virus from one farm to another. • From Bird to Human • • • Two main ways Directly from birds or from avian virus-contaminated environments to people Through an intermediate host, such as a pig Structure of the H5N1 Avian Virus • Influenza viruses have eight separate RNA gene segments. PB2, PB1, PA, HA, NP, NA, M, and NS • HA, NA, and M specify the structure of proteins that are most medically relevant as targets for antiviral drugs and antibodies. • HA and NA make the spikes in the protein coat surface which helps the virus attach to a host cell Structure of the H5N1 Avian Virus • The influenza virus RNA polymerase is a multifunctional complex composed of the three viral proteins PB1, PB2 and PA, • Together with the viral nucleoprotein NP, these form the minimum complement required for viral mRNA synthesis and replication. Structure of the H5N1 Avian Virus • HA codes for hemagglutinin which is an antigenic glycoprotein found on the surface of the influenza viruses and is responsible for binding the virus to the cell that is being infected. • forms spikes at the surface of flu viruses that function to attach viruses to cells Structure of the H5N1 Avian Virus • NA codes for neuraminidase which is an antigenic glycoprotein enzyme found on the surface of the influenza viruses. • It helps the release of progeny viruses from infected cells. Structure of the H5N1 Avian Virus • The segmented genome allows viruses from different species to mix and create new influenza A virus if viruses from two different species infect the same person or animal. • Resulting new virus might then be able to infect humans and spread from person to person, but it would have surface proteins not previously seen in influenza viruses that infect humans. The Influenza Pandemic of 1918 • Killed more people than world war one – Within 6 months 1/5 of the world was infected – Most deadly to those aged 20 to 40. • "Spanish Flu" • In the USA: infected 28% of the population – An estimated 675,000 Americans died of influenza during the pandemic (10 times the number KIA) – An estimated further 43,000 U.S. servicemen mobilized for WWI died of influenza The Influenza Pandemic of 1918 The 1918 flu overwhelmed the body's natural defenses, that the usual cause of death in influenza patients---a secondary infection of lethal pneumonia---oftentimes never had a chance to establish itself. Instead, the virus caused an uncontrollable hemorrhaging that filled the lungs, and patients would drown in their own body fluids Trends in Infectious Disease Mortality in the United States During the 20th Century Armstrong, GL. JAMA. 1999 Jan 6;281(1):61-6. What About today? Pandemic Influenza Outbreak of Avian Influenza A (H5N1) in Asia What about today? • W.H.O. • More advanced medical practices • Better isolation techniques • Better Medical and genetic knowledge • Global communications What is the risk? • The risk is generally low. • However, during an outbreak of bird flu among poultry (domesticated chicken, ducks, and turkeys), there is a possible risk to people who have contact with infected birds or surfaces that have been contaminated with excretions from infected birds. • The current outbreak of avian influenza among poultry in Asia is an example of a bird flu outbreak that has caused human infections and death. What is being done to prevent an Avian Flu Pandemic? • CDC is working with the Association of Public Health Laboratories on training workshops for state laboratories on the use of special laboratory (molecular) techniques to identify H5 viruses. • Starting a $5.5 million initiative to improve influenza surveillance in Asia. • Performing laboratory testing of H5N1 viruses. • Working with other agencies such as the Department of Defense and the Veterans Administration on antiviral stockpile issues. What you need to Take Home from This? • The current risk to Americans from the H5N1 bird flu outbreak in Asia is very low. • The CDC is working on ways to prevent and cure the U.S in the event a pandemic occurs. • Don’t play with domesticated birds in the wild