A Novel Uncultivated Fungus May Cause Cutaneous Granulomas in Dolphins

A study recently published in Emerging Infectious Diseases reported the identification of a novel uncultivated strain of the fungus Paracoccidioides brasiliensis, the probable etiologic agent of chronic granulomatous skin infections in dolphins.

Lacaziosis, formerly known as lobomycosis, is a chronic granulomatous skin infection endemic to Latin America, primarily Brazil. Caused by the fungus Lacazia loboi, lacaziosis presents as cutaneous keloidal lesions in humans, accompanied by pruritus, pain, and burning sensations. Lacaziosis has also been identified in bottlenose dolphins in the Gulf of Mexico and off the coasts of Florida and Japan.

Because of clinical and histologic similarities of lacaziosis in dolphins and humans, this disease in dolphins was once thought to also be caused by L. loboi. This thought was challenged by results of a molecular study analyzing L. loboi DNA from a bottlenose dolphin with cutaneous granulomas; molecular analysis revealed near 100% identity between DNA sequences of P. brasiliensis and L. loboi.

Paracoccidioidomycosis (PCM), which is endemic to Latin America, is caused by P. brasiliensis and P. lutzii. PCM has two clinical forms in humans: juvenile (acute) and adult (chronic). Severe cases of juvenile PCM present with significant weight loss (≥10% body weight), tumor-like skin lesions, and enlarged lymph nodes. Severe adult PCM affects numerous organs in addition to the skin, including the central nervous system, lungs, and adrenal glands.

The current study’s authors obtained skin samples from six bottlenose dolphins with cutaneous granulomas; the dolphins were captured in the Indian River Lagoon off Florida’s eastern coast. To determine the presence and quantity of chains of yeast-like cells, samples were stained with Gomori methenamine silver. The authors then isolated DNA from the samples and performed PCR to amplify the Kex gene, which is found in yeast cells.

Phylogenetic analysis was performed using the Kex gene, along with DNA sequences from two genes (gp43, CHS4) and several fungi (P. brasiliensis, P. lutzii, L. loboi, Ajellomyces capsulatus, Ajellomyces dermatitidis).

Silver staining revealed yeast-like cells that were arranged in branches and connected by short isthmuses. This branching pattern resembles that of P. brasiliensis.

Using the GenBank database, the authors determined alignment among Kex gene sequences from the dolphins’ fungi and those of human P. brasiliensis and L. loboi. The dolphin Kex gene sequences were more similar to those of P. brasiliensis than L. loboi. Only a single nucleotide differentiated the P. brasiliensis and dolphin gene sequences; this nucleotide was present in the P. brasiliensis gene sequence but absent in the dolphin gene sequence. In contrast, a 13-nucleotide gap differentiated L. loboi and dolphin gene sequences.

BLAST analysis, which identifies similarities in nucleotide sequences, demonstrated 100% homology between the dolphin and human P. brasiliensis Kex gene sequences; homology was less with P. lutzii (93%) and L. loboi (73%).

Phylogenetic analysis indicated the dolphin Kex gene sequence could be clustered in the same group with human P. brasiliensis. L. loboi was not placed in the same cluster as P. brasiliensis, suggesting the evolutionary paths of these two fungal organisms are different, despite their clinical and phenotypic similarities.

According to the authors, this study’s findings “added support to the notion that a novel uncultivated P. brasiliensis, which is different from the cultivated P. brasiliensis causing human [PCM] and L. loboi causing parakeloidal-like lesions in humans, is the causative agent of lacaziosis/lobomycosis in dolphins.” Based on the findings, the authors propose “paracoccidioidomycosis ceti” as the name for chronic cutaneous granulomatous disease caused by uncultivated P. brasiliensis in dolphins.

Dr. JoAnna Pendergrass received her doctorate in veterinary medicine from the Virginia-Maryland College of Veterinary Medicine. Following veterinary school, she completed a postdoctoral fellowship at Emory University’s Yerkes National Primate Research Center. Dr. Pendergrass is the founder and owner of JPen Communications, LLC.