Pathogenesis of Highly Pathogenic Avian Influenza A Virus (H7N1) infection in chickens inoculated with three different doses

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Chaves Hernández, Aida Jeannette | Majó I Masferrer, Natàlia | Darji, Ayub | Busquets, Nuria | Campos, Naiana | Ramis, Antonio | Rivas, Raquel | Valle, Rosa

Edité par CCSD ; Taylor & Francis -

International audience. To study the pathogenesis of a H7N1 highly pathogenic avian influenza virus (HPAIV) strain, specific pathogen free (SPF) chickens were inoculated with decreasing concentrations of virus: 105.5 ELD50 (G1), 103.5 ELD50 (G2) and 101.5 ELD50 (G3). Disease progression was monitored over a period of 16 days and sequential necropsies and tissue samples were collected for histological and immunohistochemical examination.Viral RNA loads were also quantified in different tissues, blood, oropharyngeal, and cloacal swabs using quantitative real time RT-PCR (RT-qPCR). Clinical signs of depression, apathy, listlessness, huddling and ruffled feathers were recorded in G1 and few G2 birds, whilst neurological symptoms were only observed in chickens inoculated with the highest dose. Gross lesions of haemorrhages were observed in the unfeathered skin of the comb and legs, skeletal muscle, lung, pancreas and kidney of birds inoculated with 105.5 ELD50 and 103.5 ELD50 doses. Microscopic lesions and viral antigen was demonstrated in cells of the nasal cavity, lung, heart, skeletal muscle, brain, spinal cord, gastrointestinal tract, pancreas, liver, bone marrow, thymus, bursa of Fabricius, spleen, kidney, adrenal gland, and skin. Besides, viral RNA was detected by RT-qPCR in kidney, lung, intestine, and brain samples of G1 and G2 birds. However in birds infected with the lowest dose, viral RNA was detected only in brain and lung in low amounts at 5 and 7 dpi. Interestingly, viral shedding was observed in oropharyngeal and cloacal swabs with proportionate decrease with the inoculation dose. We conclude that although an adequate infectious dose is critical in reproducing the clinical infection, chickens exposed to lower doses can be infected and shed virus representing a risk for the dissemination of the viral agent.

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