Pathological changes and viral antigen distribution in tissues of Iberian hare (Lepus granatensis) naturally infected with the emerging recombinant myxoma virus (ha-MYXV)

Abstract

Background:A cross-species jump was confirmed in 2018, when a novelrecombinant myxoma virus (MYXV) (ha-MYXV) caused high mortality inIberian hare (Lepus granatensis) in the Iberian Peninsula.Method:The aim of this study was to evaluate the main lesions, tissular dis-tribution and target cells of ha-MYXV in Iberian hare. Gross postmortemexaminations and histological and immunohistochemical studies to detectha-MYXV were carried out in 28 animals that were confirmed as ha-MYXVpositive by PCR.Results:The main macroscopic lesions were bilateral blepharoconjunctivi-tis, epistaxis, intense congestion and oedema in several organs and someinternal haemorrhages. Visible myxomas were not found. Histopathologicalexamination revealed hyperplastic epidermis with predominant hyperker-atosis and myxoid matrix in the dermis. ha-MYXV-positive keratinocytesshowed hydropic degeneration and cytoplasmic inclusion bodies. Alveolaroedema, interstitial pneumonia, dramatic lymphoid depletion in the spleenand necrosis in the liver and testis were observed. ha-MYXV was mainlydetected in epithelial and myxoma cells in the skin, and also in macrophages,lymphocytes, fibroblasts and endothelial cells in several organs, as well as inhepatocytes and Leydig cells.Limitations:A non-homogeneous number of samples were included inall the animals. Future experimental studies with controlled variables arenecessary.Conclusion:These findings correspond to an unusual form of myxomatosis,characterised by an acute or hyperacute presentation.