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  운영자 2006-09-18 14:19:13 | Hit : 8295 | Vote : 2539
Subject   [소식] Avian Influenza (Influenzareport, 2006)
Avian Influenza

Timm C. Harder and Ortrud Werner


(Green links: Free full-text articles)

Highly pathogenic avian influenza, or, as it was termed originally, 'fowl plague', was initially recognised as an infectious disease of birds in chickens in Italy, 1878 (Perroncito 1878). Due to a former hot spot in the Italian upper Po valley it was also referred to as 'Lombardian disease'. Although Centanni and Savonuzzi, in 1901, identified a filtrable agent responsible for causing the disease, it was not before 1955 that Schäfer characterised these agents as influenza A viruses (Schäfer 1955). In the natural reservoir hosts of avian influenza viruses, wild water birds, the infection generally runs an entirely asymptomatic course as influenza A virus biotypes of low pathogenicity co-exist in almost perfect balance with these hosts (Webster 1992, Alexander 2000).

When low pathogenic avian influenza virus (LPAIV) strains are transmitted from avian reservoir hosts to highly susceptible poultry species such as chickens and turkeys (i.e., a transspecies transmission step!), only mild symptoms are induced in general. However, in cases where the poultry species supports several cycles of infection, these strains may undergo a series of mutation events resulting in adaptation to their new hosts. Influenza A viruses of the subtypes H5 and H7 not only run through a host adaptation phase but may have the capability to saltatorily switch by insertional mutations into a highly pathogenic form (highly pathogenic avian influenza viruses, HPAIV) inducing overwhelming systemic and rapidly fatal disease. Such HPAI viruses may arise unpredictably de novo in poultry infected with LPAI progenitors of H5 and H7 subtypes.

HPAI in poultry is characterised by a sudden onset, severe illness of a short duration, and a mortality approaching virtually 100 % in vulnerable species. Due to excessive economical losses to the poultry industry, HPAI receives immense attention in the veterinary world and is globally treated as a disease immediately notifiable on suspicion to the authorities. Because of their potential to give rise to HPAIV, LPAI caused by subtypes H5 and H7 is also considered notifiable (OIE 2005). Before 1997, HPAI was fortunately a rare disease, with only 24 recorded primary outbreaks globally since the 1950s (Table 1).

Recently, however, avian influenza acquired world-wide attention when a highly pathogenic strain of the subtype H5N1, which probably arose before 1997 in Southern China, gained enzootic status in poultry throughout South East Asia and unexpectedly 'traversed interclass barriers' (Perkins and Swayne 2003) when transmitted from birds to mammals (cats, swine, humans). Although not an entirely unprecedented event (Koopmans 2004, Hayden and Croisier 2005), the substantial number of documented cases in humans, associated with severe disease and several fatalities raised serious concerns about a pandemic potential of the H5N1 strain (Klempner and Shapiro 2004; Webster 2006). There are several further lines of evidence - which will be discussed below - suggesting that the H5N1 virus has acquired increased pathogenic potency for several mammal species. Justifiably, this has caused world-wide public concern (Kaye and Pringle 2005).

 Prev   [소식] Avian Influenza (The New York Times, 2006. 09. 18)
 Next   [자료] Control and prevention of rabies in animals: paradigm shifts.

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