Herpetic Pneumonia in Indian Ringneck Parrots (Psittacula krameri): First Report of Novel Psittacid Alphaherpesvirus-5 Infection in Europe

Simple Summary Herpesviridae is a large family of double-stranded DNA viruses that infect many different animal species. Herpesvirus infections are common in avian species and, to date, three different alphaherpesvirus species have been recognized as causative agents of disease in Psittaciformes. However, there are reports of respiratory disease in parrots characterized by the presence of distinctive herpes-related histologic lesions, albeit with no identified etiology. Our study acknowledges the unprecedented presence of the novel Psittacid alphaherpesvirus-5 in Europe. Necropsy was performed on Indian ringneck parrots deceased after severe respiratory distress and diagnosis was achieved through histological examination, visualization of the virions by electron microscopy and genome sequencing. The pathogen has been reported only once in Australia and the present report raises the probability that its distribution is wider and it should be included in the list of pathogens threatening parrot populations. The first two European outbreaks of herpetic pneumonia caused by Psittacid alphaherpesvirus-5 were diagnosed based on gross pathology findings, histological examination, transmission electron microscopy visualization and genome sequencing. The outbreaks, characterized by high morbidity and high mortality rates, involved two parrot species, namely the Indian ringneck parrot (Psittacula krameri) and the Alexandrine parakeet (Psittacula eupatria). Clinical signs observed were ruffled feathers, dyspnea, tail bobbing, open wings while breathing, depression and anorexia. Necropsy was performed on Indian ringneck parrots only, and the most evident and serious gross lesion found in all the birds was a diffuse marked consolidation of the lungs associated with parenchyma congestion and oedema. Histological examination confirmed the existence of bronchopneumonia characterized by the presence of syncytial cells with intranuclear inclusion bodies. In one bird, fibrinous airsacculitis was observed as well. Lung tissue inspection through electron microscopy revealed the presence of virus particles resembling herpesviruses. Viral DNA was extracted, amplified using primers for Alloherpesviridae DNA polymerase gene detection, and then sequenced. BLAST analysis showed a 100% identity with the only previously reported sequence of PsHV-5 (MK955929.1).