Experimental infection of chickens, ducks and quails with the highly pathogenic H5N1 avian influenza virus

Abstract

Highly pathogenic avian influenza viruses (HPAIV) of the H5N1 subtype have spread since 2003 in poultry and wild birds in Asia, Europe and Africa. In Korea, the highly pathogenic H5N1 avian influenza outbreaks took place in 2003/2004, 2006/2007 and 2008. As the 2006/2007 isolates differ phylogenetically from the 2003/2004 isolates, we assessed the clinical responses of chickens, ducks and quails to intranasal inoculation of the 2006/2007 index case virus, A/chicken/Korea/IS/06. All the chickens and quails died on 3 days and 3-6 days post-inoculation (DPI), respectively, whilst the ducks only showed signs of mild depression. The uninoculated chickens and quails placed soon after with the inoculated flock died on 5.3 and 7.5 DPI, respectively. Both oropharyngeal and cloacal swabs were taken for all three species during various time intervals after inoculation. It was found that oropharyngeal swabs showed higher viral titers than in cloacal swabs applicable to all three avian species. The chickens and quails shed the virus until they died (up to 3 to 6 days after inoculation, respectively) whilst the ducks shed the virus on 2-4 DPI. The postmortem tissues collected from the chickens and quails on day 3 and days 4-5 and from clinically normal ducks that were euthanized on day 4 contained the virus. However, the ducks had significantly lower viral titers than the chickens or quails. Thus, the three avian species varied significantly in their clinical signs, mortality, tissue virus titers, and duration of virus shedding. Our observations suggest that duck and quail farms should be monitored particularly closely for the presence of HPAIV so that further virus transmission to other avian or mammalian hosts can be prevented.

Fig. 1

Antibody titers in ducks inoculated intranasally with 10^6.5EID₅₀ A/Chicken/Korea/IS/06 virus. HI: hemagglutinin inhibition test, AGID: agar gel immunodiffusion test, C-ELISA: competitive enzyme-linked immunosorbent assay, Pre: Pre-inoculation, DPI: day post-inoculation.

Fig. 2

Gross and microscopic photographs in visceral organs from chickens (A) and ducks (B-F) after intranasal inoculation with A/chicken/Korea/IS/06 virus. The chickens exhibited petechial hemorrhage in the cardiac fat pad (A) while the pancreas of the ducks had mutifocal rounded grayish necrotic foci (B). The histopathological findings in ducks included inflammation of the Purkinje cell layer in the cerebellum and perivascular cuffing (C) and non-supprative necrotizing myocarditis (E). Immunohistochemical analysis for the presence of the virus revealed positive staining in the brain (D) and cardiac muscle (F) of the ducks. C, D, E and F; H&E stain. Scale bars = 100 µm.