Epizootic of multi-centric, squamous cell carcinomas in populations of Indo-Pacific humpbacked dolphins Sousa chinensis in Thai waters.

Over the span of several years, 3 Indo-Pacific humpbacked dolphins died and were necropsied in Thailand. These 3 animals were all captive-bred at Oasis Sea World (Chanthaburi, Thailand), and displayed similar macroscopic progressive cutaneous lesions diagnosed as squamous cell carcinomas. In 2 of the 3 animals, necropsy revealed a severe fibrinosuppurative tracheitis and pneumonia secondary to metastasis of a cutaneous squamous cell carcinoma which extended from the head throughout the trunk and flippers. The tumors were characterized by coalescing botryoid masses with severe areas of cutaneous erosion, ulceration and necrohemorrhagic dermatitis. There was evidence of metastasis to the lungs and hilar lymph nodes. Necropsy of the third animal revealed similar progressive cutaneous squamous cell carcinomas but without evidence of metastasis. DNA molecular analysis of homogenized neoplastic tissue was conducted using polymerase chain reaction for both herpesvirus and papillomavirus in 2 of the 3 cases. In the first case, the tissues were positive for a herpesvirus alone, and this was phylogenetically classified as an alphaherpesvirus. This new herpesvirus has been tentatively named Sousa chinensis alphaherpesvirus. The second animal was negative for this novel herpesvirus and the third was not analyzed. In addition to the captive population, there is photographic evidence from 2 separate wild populations of Indo-Pacific humpbacked dolphins in the Gulf of Thailand, of a macroscopically identical proliferative and ulcerative process suspected to be squamous cell carcinomas.