Cutaneous papillomas associated with a herpesvirus-like infection in a herd of captive African elephants

Proliferative cutaneous lesions developed in a herd of captive African elephants (33 from an animal importer in Texas [group 1], and 63 young elephants collected in Zimbabwe [group 2]). Group-1 elephants were purchased 8 months before the arrival of the group-2 elephants. On arrival, 7 group-1 elephants had raised nodular fibrous growths, located predominantly on their trunks. Lesions were not observed in the group-2 elephants until approximately 3 months after they were acquired. Lesions on group-2 elephants began as small focal proliferative growths that regressed or that progressed into large nodular fibrous growths that were similar in appearance to those seen in the group-1 elephants. Lesions at various stages of development were biopsied and examined. Histologically, early lesions were inverted papillomas, with hyperplastic and hypertrophic epithelial cells containing amphoteric intranuclear inclusions in the lesion center. Older, large, nodular fibrous growths were ulcerated and were composed predominantly of a thickened dermis containing fibroblasts, collagen, and a mixed inflammatory cell infiltrate; inclusions were not observed in adjacent epidermal cells. Using a peroxidase-antiperoxidase technique, we did not detect group-specific papillomavirus antigens. Southern blot hybridization analysis of DNA from lesion specimens did not indicate papillomavirus-specific genomes. Electron-microscopically, inclusions consisted of aggregates of virus particles. The particles had electron-dense and electron-lucent cores and were 95 to 103 nm in diameter. Virions developed envelopes from nuclear membranes. Mature particles were seen within the cytoplasm and filled the intercellular spaces. On the basis of size, location, conformation, and envelopment, the particles most closely resembled those of herpesviruses.