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References1. Teutsch SM. Considerations in Planning a SurveillanceSystem. In: Teutsch SM, editor. Principles andPractice of Public Health Surveillance. New York:Oxford University Press; 1994.2. Miller M, et al. Australia’s notifiable disease status,2003 Annual report of the National NotifiableDiseases Surveillance System. CommunicableDisease Intelligence. 2005;29(1):1-61.3. Hall G and Kirk M. Foodborne illness in Australia.National Centre for Epidemiology and PopulationHealth. Canberra: OzFoodNet Working Group; 2005.4. Combs BG, Raupach JCA, Kirk M. Surveillanceof Shiga toxigenic Escherichia coli in Australia.Communicable Disease Intelligence. 2005;29(4):366-369.5. Cameron AS, et al. Community Outbreak of HemolyticUremic Syndrome Attributable to Escherichia coliO111:NM - South Australia, 1995. Morbidity andMortality Weekly Report. 1995;44(29): 550-558.6. Department of Health and Ageing (DOHA).Surveillance systems reported in CDI, 2006.Communicable Disease Intelligence. 2006;30(1):156-160.7. Dicker RC. A brief review of the basic principles ofepidemiology. In: Gregg M, editor. Field Epidemiology.London: Oxford University Press; 2002.8. Hutwager LC, et al. Using Laboratory-BasedSurveillance Data for Prevention: An Algorithm forDetecting Salmonella Outbreaks. Emerging InfectiousDiseases. 1997;3(3):395-400.Emerging communicablediseases: Pandemic andAvian InfluenzaDr Ann KoehlerBSc, MBBS, FRCPA, MPHConsultant MicrobiologistCommunicable Disease Control BranchDepartment of HealthA pandemic (from Greek pan all + demos people) isan epidemic (an outbreak of an infectious disease) thatspreads across a large region or worldwide.There are three types of influenza virus, A, B, and C.Influenza A causes much of the seasonal influenzaoutbreaks that occur annually, as well as less frequentpandemics. Influenza B and C are ‘human’ viruses thatare not found in avian hosts, though C viruses havebeen isolated from pigs and dogs. Neither types B norC cause pandemics and both typically cause milderrespiratory illness than influenza A.Influenza A is a zoonotic infection in humans. Its naturalhosts are wild aquatic birds, principally ducks, gulls,and waders, in whom it causes asymptomatic infectionof the gastrointestinal tract 1 . All of the subtypes ofinfluenza A (16 different neuraminidase types [N] and9 different haemagglutinin types [H]) can be isolatedfrom these birds. (Neuraminidase and haemagglutininare molecules on the surface of the virus involvedin attachment and release from host cells, and areimportant inducers of antibody response 2 .) They caninfect a wide range of birds and mammals, includingaquatic mammals such as whales. When a subtypechanges and is able to infect humans readily it maybecome established as a human influenza strain.The origins of recently circulating strains of influenzaA in humans can be traced back to pandemics of the20 th century – H1N1 from the 1918-19 ‘Spanish’ flupandemic, H2N2 from the 1957-58 Asian flu, and H3N2from the 1968-69 Hong Kong flu pandemic. Of the threeinfluenza pandemics last century, the 1918 pandemicwas the worst human disease outbreak ever recorded,causing acute illness in 30% of the world’s population,and killing up to 40 million people, more than thosekilled by the “Black Death”. The first recorded pandemicoccurred in 1580, though no doubt they occurred beforethis, and 31 have been documented since, most recentlyin 1968-69 3 . It is inevitable that another one will occur,and by historical measures it is overdue.Influenza pandemics occur when the influenza virusmutates to produce a virulent strain for humans to whichthe existing population has not been exposed. Influenza
viruses are RNA viruses, and like all RNA viruses lack‘proofreading’ when they are replicating, making themgenetically unstable and variable. While each roundof RNA virus replication results in a mixed populationwith many variants, most of which are not viable, somehave potentially advantageous mutations that canbecome dominant under the right selective conditions.Reassortment of the viral genome occurs rapidly amonginfluenza viruses in nature, and is important in theappearance of pandemics in human populations.To date just over 100 people have died worldwidefrom the current H5N1 ‘bird flu’ infections which havegeographically encompassed countries housing morethan half the world’s population. Concern remainsin the medical and scientific community that H5N1may develop into the next pandemic influenza strain.Although most attention is focussed on the H5N1 virus,it is entirely possible that the next pandemic might becaused by a different influenza virus.Current human influenza viruses are believed to havearisen by genetic reassortment between previoushuman influenza viruses and nonhuman viruses, whenthere has been simultaneous infection of a host animalwith both avian and human influenza viruses. Thoughthere is no scientific proof to support it, the pig hasbeen the leading contender for the role of ‘mixingvessel’. The pig is the only mammalian species whichis domesticated, reared in abundance, and a commonhost for human influenza viruses, though mixing mayoccur in humans who are co-infected with two strains 4 .One remarkable exception to this mode of selectionof new strains was the 1918 pandemic strain, whichwas revealed by molecular sequencing in 2005 to beof purely avian origin 5 . The 1918 strain jumped species,from birds to humans, and there is concern that theH5N1 strain might do the same, or might recombinewith a human strain, either way producing a newpandemic strain. In recent years, purely avian influenzaviruses of subtypes H5, H7 and H9 have crossed thespecies barrier to directly cause disease, sometimesfatal, in humans in many Asian countries, as well asTurkey, Holland and Canada 6 .The majority of pandemic strains of human influenzafrom the 20 th century appear to have originated in China,with its large population of humans, pigs, and domesticand wild ducks. In temperate countries, influenza in pigsand humans tends to occur in winter, when free-flyingaquatic birds are absent. In tropical and subtropicalcountries such as Southern China, influenza occurs yearround in humans, pigs, and birds. There is interminglingof these species, and the opportunity for interspeciestransmission and genetic exchange among influenzaviruses 4 .Even though pandemic strains emerge only rarely,available information indicates that interspeciestransmission of influenza viruses may not be so rare,for up to 10% of persons with occupational exposureto pigs develop antibodies to swine influenza virus 7 .It remains unclear what viral and human geneticcharacteristics allow the transmission of avian influenzaviruses to humans. So far the H5N1 strain isolates fromhumans have not acquired gene segments from humaninfluenza virus strains.(Source: http://europa.eu.int/comm/health/ph_threats/com/Influenza/influenza_en.htm)
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