Development and Validation of a Histologic Respiratory Index (HRI) in Poultry

Viral respiratory diseases infecting poultry lead to variable lesions in the respiratory or-gans, including nasal sinuses, eyelids, trachea, lungs, and air sacs. The distribution and the intensity of lesions depend on multiple factors, including virulence, the host’s im-munity, and secondary or concurrent infections. It may be challenging to detect remarka-ble lesions during experimental infections conducted in a controlled environment. This creates a challenge in developing a reliable model to study pathogenicity or vaccine effi-cacy experimentally. The development of the proposed histologic respiratory index (HRI) aims to help monitor the least microscopic changes that can be scored, thereby creating an objective and accurate grading of lesions in experimentally infected birds. HRI scores the changes in respiratory mucosa, including hyperplasia, metaplasia, inflammatory cellular infiltration in the submucosa, including lymphocytes and heterophils, and vascular changes (vasculitis) in nasal sinuses, eyelids, trachea, and lungs. The score was validated in birds infected experimentally with avian metapneumovirus (aMPV) and low patho-genic avian influenza (LPAI-H4N6). The HRI was reliable in grading lesions in the respir-atory organs of experimentally infected birds compared with non-infected control birds. The HRI was initially proven to be a reliably recruited in pathogenicity and vaccine trials of certain poultry respiratory viral diseases.