Avian influenza News / Technical Articles Posted by JimEdwards on Oct 17, 2005 - 12:34 PM Source: Prof. Zdenek Posp??il, University of Veterinary and Pharmaceutical Sciences, Brno, Czech Republic Avian influenza (AI) is one of the diseases caused by influenza viruses that affect certain bird and mammalian species including humans. Included in the Orthomyxoviridae family, three types of influenza viruses, A, B and C, are recognized. Influenza A virus has been recovered from the whole range of species mentioned above, and influenza B and C are almost exclusively pathogenic to humans. Influenza viruses contain eight specific segments of ribonucleic acid (RNA) and their identification is based on two glycoproteins, haemagglutinin (HA) and neuraminidase (NA), present on the surface of the virus. Until now 15 HA subtypes and nine NA subtypes have been known; most recently the 16th HA subtype has been added. The fact that the influenza RNA genome is segmented may allow for rearrangement of the segments, known as genetic reassortment, if one cell is simultaneously infected by two different influenza viruses. This is the “hottest” problem of the whole influenza issue, because this mechanism gives rise to completely new viruses against which the human populations have no protection; consequently, world-wide epidemics – pandemics – may develop. For inter-species transmission of influenza viruses it is important that humans generally have no receptors for avian influenza viruses on the surface of cells lining their respiratory tract; but only receptors for porcine and, of course, human influenza viruses. This “safeguard”, however, does not work if pig populations, due to concurrent infection with both avian and swine influenza viruses, produce recombinants that have acquired ability to bind to the human receptors. It appears that the pig has a role of a “mixing vessel” in this process. Until recently it was believed that humans cannot directly acquire avian influenza disease. The most recent information, however, indicates the contrary. The first reports came from Hong Kong in 1997 where 18 persons became infected by avian influenza virus and six died. In recent years avian influenza has affected ten countries in southeast Asia; exactly, from December 26, 2003 to October 5, 2005, 116 people got ill and 61 died, accounting for 40 death in Vietnam, 12 in Thailand, 4 in Cambodia and 5 in Indonesia. Fortunately, direct transmission from one human being to another has not been recorded yet. Avian influenza viruses are classified according to the severity of disease as follows: • Highly Pathogenic Avian Influenza (HPAI) viruses that cause a highly contagious disease affecting most of the body organs, with serious outcome and high mortality, sometimes up to 100 %. • Low Pathogenic Avian Influenza (LPAI) viruses that produce only mild diseases in poultry; this usually affects the gastrointestinal organs. Then the virus excreted with feces is spread by contaminated water. The vectors for influenza A viruses are mainly water birds, particularly migrating ones, that act as reservoirs of LPAI viruses. However, these may mutate to produce HPAI viruses, especially in strains containing H5 or H7 haemagglutinins. In view of high contagiousness of HPAI viruses it is more probable that flocks become infected by direct contact with diseased poultry or indirectly by contaminated feed, water or infected attendants. In July 2005 it was reported that H5N1 avian influenza virus had been brought by infected wild migrating birds as far as the Ural region and, at the beginning of October 2005, infected birds were identified in the Danube delta, in Romania. Subtype identification is in progress. The first news on poultry vaccination has appeared. The Hong Kong authorities began to require vaccination with an attenuated vaccine containing H5 antigen for all imported poultry. Italy has been involved in the development of a vaccine since 2002 as well as several major research centres. The Fort Dodge Company has prepared a bivalent inactivated vaccine based on avian influenza serotypes containing H5 and H7 antigens, and has named it Poulvac i AI H5N9 H7N1. For the case that HPAI virus infection should appear in the European Union, the 92/40/EEC Directive has been drawn up. It requires that any flock with confirmed infection should be eradicated by the “stamping-out” method. All birds in the infected area must be killed and safely removed; this applies also to eggs and meat products. This article is from World Veterinary Association   http://www.worldvet.org/ The URL for this story is:   http://www.worldvet.org/modules.php?op=modload&name=News&file=article&sid=2415