Retrospective analysis of clustered neuroinflammatory and neurodegenerative diseases in captive lions in the early 1970s

Rustrela virus (RusV), a recently discovered pathogen for domestic and wildlife animals, was identified as the causative agent of meningoencephalomyelitis in domestic cats and various zoo animals including lions. To analyze a past outbreak of increased mortality in lions and to reveal its possible etiological relationship with an RusV infection, this retrospective study re-evaluates 20 cases of lions originating from a zoo in Western Germany using archived formalin-fixed paraffin-embedded (FFPE) tissues. Animals with different neurologic signs were submitted for necropsy between December 1970 and April 1971. Eight lions (40%) suffered from non-suppurative meningoencephalomyelitis with RusV RNA and antigen detectable in the central nervous system (CNS). Twelve animals (60%) were negative for RusV. Eleven animals had an etiologically undetermined degenerative encephalomyelopathy characterized by dilated myelin sheaths, myelinophages, and spheroids. Eight of these 12 lions suffered from an erosive, lymphohistiocytic enteritis with nuclear inclusion bodies in enterocytes associated with parvoviral antigen and nucleic acid in the intestines, lymph nodes, and spleen, but not in the CNS. Five of the parvovirus-infected animals had a granulomatous inflammation in mesenteric lymph nodes that was also the only detectable lesion in one other lion. Acid-fast bacilli and <i>Mycobacterium bovis</i> DNA confirmed the diagnosis of tuberculosis. In summary, this study provides convincing evidence of the usefulness of long-term stored FFPE material for further investigations using immunohistochemistry, reverse transcription quantitative polymerase chain reaction, and in situ hybridization for resolving past disease outbreaks. It provides further insights into the epidemiology of infectious agents like RusV and parvovirus.