Elimination of the amphibian chytrid fungus Batrachochytrium dendrobatidis by Archey's frog Leiopelma archeyi

Department of Zoology, University of Otago, PO Box 56, Dunedin 9054, New Zealand.
Diseases of Aquatic Organisms (Impact Factor: 1.75). 04/2009; 84(1):9-15. DOI: 10.3354/dao02028
Source: PubMed


Archey's frog Leiopelma archeyi is a critically endangered New Zealand endemic species. The discovery of the emerging infectious disease, chytridiomycosis, in wild populations of this frog raised concern that this disease may drive the species to extinction. Twelve wild-caught Archey's frogs naturally infected with the amphibian chytrid fungus Batrachochytrium dendrobatidis were monitored in captivity by observing clinical signs, measuring weight gain, and performing repeated PCR tests. Eight frogs were treated with topical chloramphenicol, without PCR results being available, for B. dendrobatidis at the day of entry of the frog into the trial. Eleven of the 12 frogs (92%) cleared their infection within 3 mo of capture, even though they were held at 15 degrees C and in high humidity, conditions that are ideal for the survival and propagation of B. dendrobatidis. B. dendrobatidis in the remaining frog tested positive for the fungus was eliminated after treatment with topical chloramphenicol. None of the 8 frogs exposed to chloramphenicol showed any acute adverse reactions. Archey's frog appears to have a low level of susceptibility to the clinical effects of chytridiomycosis. Individual frogs can eliminate B. dendrobatidis and Archey's frog can apparently be treated with topical chloramphenicol with no acute adverse reactions. However, the small number of specimens treated here requires that more extensive testing be done to confirm the safety of chloramphenicol. The significance of the amphibian chytrid fungus for wild populations of Archey's frog needs to be determined by a longitudinal study in an infected wild population to correlate the presence of B. dendrobatidis in individual frogs. Such a study should occur over a period of at least 3 yr with clinical assessment and monitoring of survival, growth and body condition parameters.

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    • "However, there is dramatic variation in the outcome of Bd 63 infection: some populations are decimated by Bd (e.g., Schloegel et al. 2006; Crawford et 64 al. 2010; Vredenburg et al. 2010), while others persist (Retallick et al. 2004; Woodhams 65 et al. 2007; Lam et al. 2010). This variation in infection outcome is affected by three 66 interacting factors: environmental conditions such as temperature (Voyles et al. 2012; 67 Spitzen-van der Sluijs et al. 2014), intrinsic differences in host susceptibility (e.g., 68 Bishop et al. 2009; Searle et al. 2011; Voyles et al. 2011; Ghal et al. 2012; Gervasi et al. 69 2013), and differences in virulence among Bd isolates (e.g., Berger et al. 2005; Retallick 70 & Miera 2005; Fisher et al. 2009; Farrer et al. 2011; Voyles 2011). 71 Here we focus on variation in virulence caused by intrinsic differences among Bd 72 isolates. "
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    ABSTRACT: Emerging infectious diseases pose a significant threat to global health, but predicting disease outcomes for particular species can be complicated when pathogen virulence varies across space, time, or hosts. The pathogenic chytrid fungus Batrachochytrium dendrobatidis (Bd) has caused worldwide declines in frog populations. Not only do Bd isolates from wild populations vary in virulence, but virulence shifts can occur over short timescales when Bd is maintained in the laboratory. We leveraged changes in Bd virulence over multiple generations of passage to better understand mechanisms of pathogen virulence. We conducted whole-genome resequencing of two samples of the same Bd isolate, differing only in passage history, to identify genomic processes associated with virulence attenuation. The isolate with shorter passage history (and higher virulence) had higher chromosome copy numbers than the isolate maintained in culture for longer, suggesting that virulence attenuation may be associated with loss of chromosome copies. Our results suggest that genomic processes proposed as mechanisms for rapid evolution in Bd are correlated with virulence attenuation in laboratory culture within a single lineage of Bd. Moreover, these genomic processes can occur over extremely short timescales. On a practical level, our results underscore the importance of immediately cryo-archiving new Bd isolates and using fresh isolates, rather than samples cultured in the lab for long periods, for laboratory infection experiments. Finally, when attempting to predict disease outcomes for this ecologically important pathogen, it is critical to consider existing variation in virulence among isolates and the potential for shifts in virulence over short timescales. Copyright © 2015 Author et al.
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    • "Chytridiomycosis is the only explanation, for which supporting evidence is available, for the global ''enigmatic'' declines and disappearances of frog populations and species (Skerratt et al., 2007; Fig 1: Bd Global Mapping project www.bd-maps.net). The high prevalence of Bd fungus amongst native frog species in Australia and New Zealand (Skerratt et al., 2007; Bishop et al., 2009) in all habitats suggest that it could be widespread in the Pacific Islands region. Fig. 1. "
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    • "There are other naturally produced antimicrobial compounds found to be inhibitory to B. dendrobatidis, such as chloramphenicol. Bishop et al54 applied chloramphenicol topically to the skin of adult frogs to remove B. dendrobatidis. After treatment with chloramphenicol, symptoms of chytridiomycosis dissipated and the infected frogs recovered. "
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