Ovine gammaherpesvirus-2 infection associated with chronic interstitial pneumonia in a sheep

Authors: HEADLEY, SELWYN - University Of Londrina; DALL AGNOL, ALAIS - University Of Londrina; NAVOLAR, FELIPE - University Of Londrina; FRUCCHI, ANA - University Of Londrina; DE MATOS, ANDRESSA - University Of Londrina; PEREIRA, PRISCILLA - University Of Londrina; XAVIER, ANA - University Of Londrina; SANTOS, VITOR - University Of Londrina; SILVA, LUARA - University Of Londrina; DEPES, VICTORIA - University Of Londrina; ALFIERI, ALICE - University Of Londrina; Cunha, Cristina; ALFIERI, AMAURI - University Of Londrina

Submitted to: Microbial Pathogenesis
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/28/2021
Publication Date: 10/1/2021
Citation: Headley, S.A., Dall Agnol, A.M., Navolar, F.M., Frucchi, A.P., de Matos, A.M., Pereira, P.F., Xavier, A.A., Santos, V.H., Silva, L.E., Depes, V.C., Alfieri, A.F., Cunha, C.W., Alfieri, A.A. 2021. Ovine gammaherpesvirus-2 infection associated with chronic interstitial pneumonia in a sheep. Microbial Pathogenesis. 161. Article 105220. https://doi.org/10.1016/j.micpath.2021.105220.
DOI: https://doi.org/10.1016/j.micpath.2021.105220

Interpretive Summary: Malignant catarrhal fever (MCF) is a severe and often fatal disease primarily of ruminants. The disease is caused by herpesviruses belonging to the MCF virus group. Ovine herpesvirus 2, one of the most common MCF virus associated with disease worldwide, is transmitted by sheep, which usually carry the virus asymptomatically. However, in some rare occasions, sheep also develop MCF when infected with OvHV-2. Here we report a case of a 4-year-old, female, mixed-breed sheep that presented respiratory discomfort for at least one-month, progressive emaciation and was euthanized due to poor prognosis. Based on clinical and pathological manifestations and supported by radiographical, immunohistochemical, and molecular findings the diagnosis of OvHV-2-induced MCF was confirmed in this sheep. MCF in carrier species can be challenging to diagnose since the causative agent is frequently present in healthy animals. In these cases, it is important to use a variety of diagnostic methods, including a newly developed immunohistochemistry for detection of MCF viruses that allows detection of viral proteins within lesions, which is critical for a definitive diagnostics of MCF in reservoir species, such as sheep.

Technical Abstract: Sheep Associated-Malignant Catarrhal Fever (SA-MCF) is severe, frequently lethal, lymphoproliferative disease predominantly of ruminants, that is caused by ovine gammaherpesvirus-2 (OvHV-2), a member of the MCF virus (MCFV) complex. However, SA-MCF in sheep is a rare entity with few demonstrations of natural diseases worldwide. This report documents the clinical, radiographical, pathological, immunohistochemical, and molecular findings of SA-MCF in a sheep. A 4-year-old, female, mixed-breed sheep with progressive emaciation for at least one month was humanely euthanized due to poor prognosis. Clinically, the animal had tachypnea, ruminal hypomotility, productive coughing with bilateral muffling sounds during pulmonary auscultation. Radiographical evaluation revealed alveolar opacity of the cranioventral pulmonary region. Grossly, there were distinct rib impressions on the pleural surface of the lungs, suggestive of interstitial pneumonia. Histopathologic evaluation of the lungs revealed several disease patterns including 1) chronic interstitial pneumonia with vasculitis and proliferating vascular lesions, and thrombosis; 2) pulmonary abscesses associated with embolic dissemination of Corynebacterium pseudotuberculosis from superficial lymph node due to caseous lymphadenitis, CLA; 3) granulomatous pneumonia associated with pulmonary nematodes; and 4) chronic pleuritis, probably due to caseous lymphadenitis. Additional significant histologic findings included widespread lymphocytic vasculitis and proliferating vascular lesions in multiple tissues, atrophic enteritis, segmental degeneration of myocardial fibers with lymphocytic pericarditis, lymphocytic interstitial nephritis, and non-suppurative encephalitis. An immunohistochemistry (IHC) assay, based on the monoclonal antibody 15A (MAb-15A), that is specific to all MCFV known to cause MCF, revealed positive, intracytoplasmic, intralesional immunoreactivity, predominantly within bronchial and bronchiolar epithelial cells of the lungs and cryptal epithelial cells of the small intestine, followed by the renal tubular epithelium, cardiomyocytes, and with patchy immunolabelling within neurons of the cerebral cortex. Molecular testing done to detect a wide range of bacterial and viral agents of ruminant diseases, only amplified OvHV-2 DNA from fresh tissue fragments of the lungs, kidney, liver, spleen, and cerebrum. Direct sequencing confirmed that the PCR amplicon derived from the pulmonary fragments had 99.2–99.7% nucleotide sequence identity with OvHV-2 reference strains and strains of OvHV-2 from Brazil. The clinical, radiographical, gross, histopathologic, IHC, and molecular findings in the lungs are consistent with chronic interstitial pneumonia associated with infection by OvHV-2. Furthermore, the non-detection of other viral agents associated with pulmonary diseases in ruminants suggest that OvHV-2 was directly associated with the development of chronic pneumonia in this sheep. Additionally, the dental alterations, CLA, and the pulmonary nematode may have contributed towards the reduced immunological statue of the animal and facilitated the occurrence of SA-MCF. These findings may indicate that OvHV-2 may be a major participant in the pathogenesis of pulmonary disease of sheep under special conditions. Moreover, the proliferating vascular lesions identified in multiple tissues are additional evidence of chronic manifestations of OvHV-2 infections as described in chronic SA-MCF of cattle, while the widespread vasculitis is consistent with SA-MCF. Additionally, the IHC findings using the MAb-15A confirmed that this diagnostic approach is efficient to identify intralesional antigens of OvHV-2.