Clinical diagnosis and treatment of epidermal chytridiomycosis in African clawed frogs (Xenopus tropicalis).
ABSTRACT An investigation was conducted to determine the cause of morbidity and mortality in a collection of 55 adult male Xenopus (Silurana) tropicalis at the University of California, Berkeley. More than 80% of affected frogs died during the epizootic. All frogs were anorectic and lethargic, had dark pigmentation and excess skin sloughing, and lacked a slime layer. Histologic examination revealed severe hyperplastic and spongiotic dermatitis associated with colonization of the stratum corneum by large numbers of zoosporangia diagnostic of Batrachochytrium dendrobatidis. Treatment with a commercial formalin/malachite green solution at a dilution of 0.007 ml/L of tank water for 24 h, repeated every other day for four treatments, eliminated the organism and was curative. These findings are indicative of epidermal chytridiomycosis as a primary cause of death in this collection of X. tropicalis.
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ABSTRACT: The skin secretion of many amphibians contains an arsenal of bioactive molecules, including hormone-like peptides (HLPs) acting as defense toxins against predators, and antimicrobial peptides (AMPs) providing protection against infectious microorganisms. Several amphibian taxa seem to have independently acquired the genes to produce skin-secreted peptide arsenals, but it remains unknown how these originated from a non-defensive ancestral gene and evolved diverse defense functions against predators and pathogens. We conducted transcriptome, genome, peptidome and phylogenetic analyses to chart the full gene repertoire underlying the defense peptide arsenal of the frog Silurana tropicalis and reconstruct its evolutionary history. Our study uncovers a cluster of 13 transcriptionally active genes, together encoding up to 19 peptides, including diverse HLP homologues and AMPs. This gene cluster arose from a duplicated gastrointestinal hormone gene that attained a HLP-like defense function after major remodeling of its promoter region. Instead, new defense functions, including antimicrobial activity, arose by mutation of the precursor proteins, resulting in the proteolytic processing of secondary peptides alongside the original ones. Although gene duplication did not trigger functional innovation, it may have subsequently facilitated the convergent loss of the original function in multiple gene lineages (subfunctionalization), completing their transformation from HLP gene to AMP gene. The processing of multiple peptides from a single precursor entails a mechanism through which peptide-encoding genes may establish new functions without the need for gene duplication to avoid adaptive conflicts with older ones.PLoS Genetics 08/2013; 9(8):e1003662. · 8.17 Impact Factor
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ABSTRACT: Chytridiomycosis, caused by the chytridiomycete fungus, Batrachochytrium dendrobatidis, is an important pathogen of amphibians in captivity and is a major concern for global conservation of amphibians. The organism infects keratinized epithelial cells of amphibian skin and causes disease and mortality by interfering with important skin functions, especially electrolyte balance. Primary treatments are with antifungal medications applied in a topical bath solution, and itraconazole is the most commonly used agent, although several different options are available. Supportive treatment of the clinically ill patient is necessary for success, with particular attention to electrolyte therapy.Veterinary Clinics of North America Exotic Animal Practice 09/2013; 16(3):669-85.
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ABSTRACT: Chytridiomycosis, an amphibian skin disease caused by the emerging fungal pathogen Batrachochytrium dendrobatidis, has been implicated in catastrophic global amphibian declines. The result is an alarming decrease in amphibian diversity that is a great concern for the scientific community. Clinical trials testing potential antifungal drugs are needed to identify alternative treatments for amphibians infected with this pathogen. In this study, we quantified the minimal inhibitory concentrations (MIC) of chloramphenicol (800 μg/ml), amphotericin B (0.8 - 1.6 μg/ml), and itraconazole (Sporanox®) (20 ng/ml) against B. dendrobatidis. Both chloramphenicol and amphotericin B significantly reduced B. dendrobatidis infection in naturally-infected southern leopard frogs [Rana (Lithobates) sphenocephala], although neither drug was capable of complete fungal clearance. Long-term exposure of R. sphenocephala to these drugs did not inhibit antimicrobial peptide (AMP) synthesis indicating that neither drug is detrimental to this important innate skin defense. However, we observed that chloramphenicol, but not amphotericin B or itraconazole, inhibited the growth of multiple R. sphenocephala skin bacterial isolates in vitro at concentrations below the MIC against B. dendrobatidis. These results indicate that treatment with chloramphenicol might dramatically alter the protective natural skin microbiome when used as an antifungal agent. This study represents the first examination of the effects of alternative antifungal drug treatments on amphibian innate skin defenses, a crucial step to validating these treatments for practical applications.Applied and Environmental Microbiology 04/2014; · 3.95 Impact Factor