Parker, J. M., Mikaelian, I., Hahn, N. & Diggs, H. E. Clinical diagnosis and treatment of epidermal chytridiomycosis in African clawed frogs (Xenopus tropicalis). Comp. Med. 52, 265-268
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.
- SourceAvailable from: Edward Narayan
Acta Herpetologica 03/2014; 6:261-266. · 0.81 Impact Factor
- "Low prevalence has been recorded in some terrestrial breeding species such as Microhylids (Kriger and Hero, 2006a) and the Pouched Frog (Assa darlingtoni) record in Kriger and Hero (2007b) but not others i.e. the Eleutherodactylids in Central and South America (Beard and O'Neill, 2005); 5. the FGF on Viwa have been exposed to Bd but they have skin defences that prevent Bd infection (Woodhams et al. 2003; Woodhams and Alford, 2005). This is unlikely as most species that are resilient still have Bd positive individuals within the population – however no clinical sign of disease (Parker et al., 2002). Many other anuran species are resilient to the pathogen and either do not become susceptible to it or have some level of population-level resistance (e.g. "
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- "The findings of the diagnostic characteristics of chytridiomycosis (Lane, Weldon & Bingham , 2003), and patterns of mortality and infection resembling a die-off (Hopkins & Channing, 2003), call for further investigations, but do not contradict an endemic presence of Bd in the region. Information on the susceptibility of African amphibians to Bd under controlled conditions is limited to pipids and indicates susceptibility in the western African species Silurana tropicalis but resistance in Xenopus laevis (Reed et al., 2000; Parker et al., 2002; Fisher & Garner, 2007). This has not yet been verified by experimental infection challenges but is solely based on observations of mortality and aclinical infection in captive populations. "
ABSTRACT: Amphibians at the global scale are dramatically declining and the pathogenic fungus Batrachochytrium dendrobatidis (Bd) has been suggested to be an important driver in this biodiversity crisis. Increasing evidence points towards the global emergence of Bd being a panzootic caused by pathogen pollution. Africa has been suggested to be the origin of the pathogen but remains one of the least-studied areas. We have conducted the most comprehensive survey on the continent to date focusing on Kenya for investigating taxonomic and environmental components in the distribution of Bd in tropical Africa. Eleven sites along a 770 km transect from the coast up to the border of Uganda were surveyed. Using quantitative PCR, we screened 861 samples from 23 different species in nine genera. The pathogen was confirmed at all studied sites, with an overall prevalence of 31.5%. No dead or symptomatic specimens were found and no declines have been reported in the region so far. Both prevalence and parasite load ranged from the detection limit to some of the highest ever reported. The parasite load showed a significant taxonomic bias and a strong inverse correlation with temperature. Our findings suggest that Bd may be enzootic in the region. We recommend that further research should focus on comparative experimental studies of susceptibility to Bd in African species. Moreover, we stress the need for improved knowledge on the conservation status of the tropical African amphibian fauna to confirm the enzootic nature of widespread Bd infections.Animal Conservation 11/2010; 13:36 - 43. DOI:10.1111/j.1469-1795.2009.00297.x · 2.52 Impact Factor
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- "Batrachochytrium dendrobatidis has a broad host range (Speare & Berger, 2004) but does not cause disease or death in every species that it infects. The survival rate of individuals exposed to B. dendrobatidis differ with host species (Parker et al., 2002; Davidson et al., 2003; Daszak, 2004; Blaustein et al., 2005; Woodhams et al., 2007) and lifehistory stage at exposure (Lamirande & Nichols, 2002; Carey et al., 2006) and research has focused on identifying the host traits causing these differences (Rollins-Smith et al., 2002b; Harris et al., 2006; Rowley & Alford, 2007; Woodhams et al., 2007). However, the effects of host species and life stage on the steps leading from exposure to disease have not been investigated. "
ABSTRACT: Introduced pathogens are increasingly being implicated in population declines and their effects are difficult to manage. In the absence of methods to eradicate pathogens acting as threatening processes, intervention before population decline is necessary. Such an intervention requires an ability to predict when population declines will occur, and therefore, an understanding of when exposure will lead to infection, disease, death and population decline. This study investigates when pathogen exposure leads to disease for the amphibian chytrid fungus Batrachochytrium dendrobatidis, which has been implicated as a causal agent in the global amphibian decline. Susceptibility studies were conducted on two anuran species, the green and golden bell frog Litoria aurea and the striped marsh frog Limnodynastes peronii, when exposed to the fungus as either tadpoles or juveniles. Host species was found to significantly affect the outcome of exposure, with infection loads in L. aurea increasing over time and resulting in significantly lower survival rates than unexposed. By comparison, infection loads in L. peronii remained the same or decreased over time following the initial infection, and survival rates were no different whether exposed to B. dendrobatidis or not. These outcomes were independent of the life stage at exposure. Individuals with higher infection loads were not found to have lower survival rates; rather, an infection load threshold was identified where individuals with infection loads that crossed this threshold had high likelihoods of showing terminal signs of chytridiomycosis. Therefore, host species determined whether infection load crossed this threshold and the crossing of the threshold determined the incidence of disease and survival. The quantification of infection load thresholds for survival, along with the time it takes to reach them, will enable infection loads in wild populations to be related to the likelihood of disease and is the first step in the understanding and prediction of when exposure will result in population decline.Animal Conservation 11/2010; 13(s1):62 - 71. DOI:10.1111/j.1469-1795.2010.00407.x · 2.52 Impact Factor