Herpesvirus like particles were identified associated with cutaneous Papillomas in captive koi carp (Cyprinus carpio) housed in indoor aquaria at the Prospect Park Wildlife Conservation Center. Twenty-two koi (6 scale less and 16 scaled), obtained from two sources, were combined into two groups. During an 11 month period cutaneous Papillomas developed in 50% of scale less koi and 25% of scaled koi. Lesions occurred in both groups and were first noted within 6 months of arrival. Papillomas spontaneously resolved in l to 3 weeks or persisted for >3 months and recurred in 1 to 5 months in several koi. Lesions developed in the months of January, March, July, and November.

Typically, single to multiple Papillomas were present on the fins (caudal, dorsal, pectoral, or anal). One fish developed a maxillary lip mass. Lesions consisted of 2 to 10 mm, raised (1 to 4 mm), white, poorly circumscribed, fleshy plaques which were most often associated with fin rays. Prominent blood vessels frequently radiated from the papillomas. The koi were otherwise asymptomatic.

Koi were anesthetized by immersion in tricaine methanesulfonate (approximately 100 ppm)for evaluation. Gill, fin, and skin wet mount preparations were unremarkable. Papillomas were biopsied and preserved in Davidson's solution or EM fixative for histopathologic and electron microscopic examination. Wet mount preparations of lesions were densely cellular, with normal cellular morphology, and no pathogens or inflammatory cells were evident. Viral and bacterial cultures were not performed. Histologically the lesions were characterized by marked epidermal hyperplasia. Ultra structurally, virions typical of herpesviruses were evident.

Although the clinical, histologic, and ultrastructural findings are characteristic of Herpesvirus cyprini infection,^2,3 viral cultures were not performed for confirmation. Herpesvirus cyprini has a worldwide distribution^2,3 but has uncommonly been reported in koi from the United States.

References

1.  Hedrick, R.P., J.M. Groff, M.S. Okihiro, and T.S. McDowell. 1990. Herpesviruses detected in papillomatous skin growths of Koi carp ( Cyprinus carpio ). J. Wild. Dis. 26(4):578581.

2.  McAllister, P.E. 1993. Goldfish, Koi, and Carp Viruses In: Fish Medicine, Stoskopf,M.(ed.), W.B. Saunders, Inc. Phila, Pa., Pp 478-486.

3.  Wolf, K. 1988. Fish Pox In: Fish Viruses and Fish Viral Diseases, Comstock Publishing Associates, Ithaca, N.Y., Pp 253-263.