Abstract

Phaeohyphomycosis

A stranded Atlantic bottlenose dolphin (Tursiops truncatus) (TMMSN# GA460) was recovered in May, 1992. Upon necropsy, lymph node enlargement, lungworms, a large protruding mass in the trachea, and a firm 3-4 mm discoloration on the base of the left frontal lobe of the brain were noted. Histological examination revealed a necrotizing granulomatous inflammation in the hilar and cervical lymph nodes, trachea, and brain. This inflammation was due to a melanin producing (black) fungus. The black fungi are known to cause disease in humans and other animals, particularly immunocompromised individuals. There was no evidence of morbillivirus infection and although bone marrow was not collected at the time of necropsy the lymph nodes were reactive, suggesting the presence of a competent immune system. While cultures were not obtained, the fungal infection was histologically classified as phaeohyphomycosis. To our knowledge, this is the first reported case of phaeohyphomycosis in a dolphin.

Lobomycosis

Another T. truncatus (TMMSN# GA710) stranded alive in October, 1995, was rehabilitated by the Texas Marine Mammal Stranding Network, and released on January 12, 1996. The animal stranded a second time and was recovered dead on January 31, 1996. A complete necropsy was performed. Several large chronic dermal lesions were present on the flukes. One was a deep ulcer with a rough base, bordered by nodular to pebbly white and black epidermis. Another lesion on the tail stock at the insertion of the flukes was partly healed, although elevated and granular to pebbly, with small ulcers. Similar lesions were present on both flippers. Samples of the lesions were placed in formalin and frozen at -70°C. Bacterial cultures of venous blood revealed Vibrio alginolyticus and Vibrio fluvialis. Histological examination of the skin lesions by methenamine silver stains demonstrated the characteristic "beads on a string" appearance of Loboa loboi, the presumed causative agent of lobomycosis.

Loboa loboi has never been successfully cultured in vitro, but the organism resembles a fungus in vivo. Other studies have suggested that L. loboi is a fungus, but the exact nature of this organism remains unknown. Therefore, we used molecular techniques to ascertain the taxonomic position of L. loboi. Primers targeted for highly conserved fungal genomic nucleic acid sequences were used in polymerase chain reactions (PCR) to amplify fungal ribosomal DNA from the dolphin lesion. Sequence alignments found extremely high homology to fungi in several genera including Cladosporium. These results suggest that L. loboi is indeed a fungus.

This is the second reported case of lobomycosis, or keloidal blastomycosis, from a western Gulf of Mexico dolphin. This disease has been reported in humans in Central and South America. There is a reported case of suspected transmission of lobomycosis from a T truncatus to an aquarium attendant in Europe.² In humans, treatment is typically achieved by surgical excision of the lesions. However, effective long term maintenance of lobomycotic lesions in an Atlantic bottlenose dolphin using itraconazole has been reported.¹ The zoonotic potential of lobomycosis should be considered by rehabilitation centers working with dolphins with skin lesions of unknown etiology.

We are planning to refine the molecular techniques developed in the characterization of L. loboi to better speciate organisms which are not cultured at necropsy such as the phaeohyphomycosis described previously. The development of molecular techniques for identification of microorganisms provides a powerful tool for pathologists when fresh tissue is not available for culture or the in vitro culture growth conditions are not yet established.

References

1.  Dalton, L.M., W.S. Mathey, R.R. Crawley, and W.G. Young. 1992. Lobomycosis in a bottlenose dolphin (Tursiops truncatus): diagnosis and treatment. Proceedings of the 23rd Annual IAAAM Conference, Hong Kong: p. 112.

2.  Symmers, W. St. C. 1983. A possible case of Lobo's disease acquired in Europe from a bottle-nosed dolphin (Tursiops truncatus). Bulletin de la Societe de Pathologie Exotique et de ses Filiales 76:777-784.