Lacaziosis (Lacazia loboi) is a chronic and slowly progressive, fungal skin disease occurring naturally only in humans and dolphins (Figure 1). The disease has been reported among three species of dolphins from various regions of the world. The first reported case of lacaziosis in a dolphin was from a bottlenose dolphin that died in Sarasota Bay in 1970 and was recovered and necropsied by Blair Irvine and Randy Wells. Although lacaziosis, previoulsy known as lobomycosis, has occurred in this region for more than three decades, the extent of the disease and aggression of the pathogen has been poorly understood. This year, my dissertation research goals were to use health assessment data to derive a prevalence estimate for lacaziosis occurrence in the Sarasota Bay dolphin community, as well as model and compare the progression of lacaziosis lesions among four cases using long-term photographic data.
Skin assessment records, photographs, and pathology reports were examined for all dolphins captured and released in the following time periods: 1) 1994; 2) 2001; 3) 1993-1995 and 2000-2002; 4) 1980-1989; and 5) 1990-1999. These time periods were chosen because the number of animals captured and released was sufficient to provide an 80% probability of detecting a lacaziosis prevalence equivalent to other published estimates. Results from the prevalence study revealed a lacaziosis prevalence of approximately 3%, and although lacaziosis is a rare disease among dolphins in Sarasota, the occurrence is comparable to other sites where it has been measured.
Long-term photographic studies of the dolphins in Sarasota Bay have revealed a sequential documentation of lacaziosis lesion spread. Methods to quantify the progression of lacaziosis and lesion growth rates were developed using image analysis tools in the latest version of Adobe Photoshop® and longitudinal photographic data from a bottlenose dolphin with a 16-year case history (Figure 2). These methods were applied to four male lacaziosis cases from Sarasota Bay (FB28, FB98, FB96, and FB40) (Figures 1, 3-4), and the progression of lesions over time was modeled using nonlinear growth modeling methods. Model comparisons revealed individual variability in disease progression and lesion growth among the infected dolphins, including statistically different growth rates between members of a male alliance (FB98 and FB96). Although individual variability in lacaziosis lesion progression is evident, the reason for the variation at this point is unknown.
This study has demonstrated that health assessment and long-term photographic data can be used as retrospective tools for epidemiologic studies of disease in a wild population. Furthermore, a mathematical framework (i.e. the growth models) has been established for future exploration of the influence of genetic, social, and environmental factors that may affect disease progression. To date, the pathogen responsible for lacaziosis has not been successfully cultured in vitro, and no long-term studies have documented the progression of disease in humans or other animals. Dolphins, with a documented and long-term case history, may serve as an ideal animal model to enhance our understanding of lacaziosis occurrence and pathogen aggression.
Funding for this project was provided by NOAA’s Center of Excellence for Oceans and Human Health at the Hollings Marine Laboratory.