Evaluation of specific pathogen-free ducks infected with the highly pathogenic avian influenza virus H5N1 subtype derived from wild birds

Wild birds of the anseriformes and gharadriiformes are the natural hosts and reservoirs of avian influenza virus (aiv). these birds play a key role in the transmission of the highly pathogenic avian influenza virus (hpaiv) of the h5n1 subtype. the pathogenicity of h5n1 hpaiv in waterfowl appears to have increased. in this study,specific pathogen-free (spf) ducks (shaoxing sheldrake) of different ages were used as a model to imitate the natural infection with the h5n1 hpaiv. the results showed that 1-2 weeks old spf ducks are not sensitive to the virus. however,the virus can replicate in the digestive and respiratory tracts of 3-6-weeks old spf ducks. there was an inverse ratio between mortality and age (3 and 6 weeks old) of ducks. although the amount of virus shed by 6-week-old spf ducks was highest,the mortality rate was the lowest. the disease in ducks shows a range of degree of severity from mild clinical signs to mortality. but the virus can replicate to a high level in some vital organs (brain,pancreas and kidneys) which causes death directly. the high virus titer in the pancreas may be related to the carriage,distribution and spread of the virus within ducks. this study has confirmed that there is a correlation between the pathogenicity of the h5n1 hpaiv and age of waterfowl. the data suggested that the degree of pathogenicity of the virus may be closely related to the development status of the duck's immune system. copyright © 2014 zoological society of pakistan.