The prevalence and progression of lobomycosis in Sarasota Bay dolphins
By Leslie Burdett, PhD Student, Medical University of South Carolina

       Lobomycosis (Lacazia loboi) is a fungal skin disease that naturally occurs only in dolphins and humans. The skin disease is endemic in human populations inhabiting tropical areas in Central and South America, however, the mechanism for disease acquisition and transmission is uncertain. Currently, there are no effective treatments and although it is not known to cause death, it can be severely debilitating. The skin disease manifests in humans as wart-like lesions that proliferate on extremities such as the arm and leg. In dolphins, similar lesions are observed, which are characterized by light-gray/white nodular masses, often appearing on appendages such as the dorsal fin, pectoral fins, and tail flukes.
        In dolphins, lobomycosis has been reported in 3 species and among animals inhabiting Venezuela, Brazil, the coastal waters of Texas, and eastern and western Florida. The first reported North American case of lobomycosis in bottlenose dolphins occurred in Sarasota Bay in 1971, on a dolphin recovered by the SDRP founders Blair Irvine and Randall Wells. On the eastern coast of Florida, reports of lobomycosis in dolphins from the Indian River Lagoon have been documented since the mid-1970s. These documented cases in Florida provide evidence that lobomycosis may be a skin disease that is endemic to dolphins in this southern state.
        The prevalence of lobomycosis in the Sarasota population is unknown. Throughout the years of studying the Sarasota dolphin community, animals have been sighted with lobomycosis-like lesions, and the disease has been confirmed during health assessment projects. Because the lesions can occur on areas of the body that may not be visible during photo-id surveys, photo-id sighting data may not provide an accurate estimate of the disease prevalence. Our study goal is to determine the prevalence of lobomycosis in the Sarasota population using a retrospective analysis of historical health assessment data. In most cases, a thorough skin assessment is conducted by a veterinarian, and lesions are biopsied for histological analysis. These health assessment records will provide a confirmation of lobomycosis for lobomycosis-like lesions, and the full-body skin assessment resolves the issue of missing lesions that cannot be seen in the field. The disease confirmation paired with long-term abundance data will provide a precise estimate for the prevalence of lobomycosis in the Sarasota dolphin community.        

Figure 1: Grid overlay onto image from photo-id survey.

Lobomycosis has not been cultured in the laboratory, and little is known about the progression of the disease and the environment that supports its growth. The long-term sighting history of dolphins in Sarasota provides the perfect opportunity to examine the progression of the disease. Case studies will be identified from the health assessment data, and photographs of the lesions will be examined over time. The photographs are registered to a standard size using distinct reference points on the body. A grid overlay is applied to the photographs and grid blocks are classified according to the presence or absence of lesioned areas (Figure 1). The grid data are recorded onto a spreadsheet, and the proportion of lesion coverage on the body is calculated using the grid block assignments (Figure 2). Finally, the rate of lobomycosis progression is determined by using Poisson regression analysis.
       

Figure 2: Spreadsheet data from grid block assignments for two different years
(1989 and 2004 - same animal, FB28).

        This examination of lobomycosis highlights the importance and utility of long-term sighting and health assessment data. The incidence of lobomycosis has been documented in several dolphin species and populations around the globe, however, no long-term studies of the progression and prevalence have been conducted. As lobomycosis as been implicated in dolphins with suppressed immune systems, monitoring the prevalence and progression of the disease may serve as a proxy for overall health status.
        This work was funded by the Medical University of South Carolina’s College of Graduate Studies Student Assistantship. Future analysis will be supported by funding from South Carolina Sea Grant.