Endemic and introduced haplotypes of Batrachochytrium dendrobatidis in Japanese amphibians: sink or source?

Abstract

The global emergence of the amphibian chytrid pathogen Batrachochytrium dendrobatidis (Bd) is one of the most compelling, and troubling, examples of a panzootic. Only discovered in 1998, Bd is now recognized as a proximate driver of global declines in amphibian diversity and is now widely acknowledged as a key threatening process for this ancient class of vertebrates. Moreover, Bd has become a member of a small group of highly virulent multihost pathogens that are known to have had effects on entire vertebrate communities and the ecosystem‐level effects of Bd‐driven amphibian declines are starting to emerge as a consequence of regional decreases in amphibian diversity. Despite the speed at which this species of aquatic chytrid has become a focus of research efforts, major questions still exist about where Bd originated, how it spreads, where it occurs and what are Bd’s effects on populations and species inhabiting different regions and biomes. In this issue, Goka et al. (2009) make an important contribution by publishing the first nationwide surveillance for Bd in Asia. Although previous data had suggested that amphibians in Asia are largely uninfected by Bd, these surveys were limited in their extent and few firm conclusions could be drawn about the true extent of infection. Goka et al. herein describe a systematic surveillance of Japan for both native and exotic species in the wild, as well as amphibians housed in captivity, using a Bd‐specific nested PCR reaction on a sample of over 2600 amphibians. Their results show that Bd is widely prevalent in native species across Japan in at least three of the islands that make up the archipelago, proving for the first time that Asia harbours Bd.

Germ Tube Mediated Invasion of Batrachochytrium dendrobatidis in Amphibian Skin Is Host Dependent

“…Moreover, the ability of Bd to enter amphibian skin and to spread in the skin, or its invasiveness, appears to coincide with the susceptibility of the studied species to chytridiomycosis, e.g. low in X. laevis [21], [28], [41], moderate in A. muletensis [23], [37] and high in L. caerulea [24]–[26]). …”

“…this species can be colonized by Bd but is able to limit the impact of Bd on its health and to maintain a low-level infection [21], [28]. Unfortunately, reports of chytrid infections in X. laevis rely merely on PCR-detection [21], [29], [30] and there is no conclusive histological evidence of how chytrid infections manifest in this species under natural conditions.…”

Is Chytridiomycosis an Emerging Infectious Disease in Asia?

“…A more thorough historical analysis of museum records through space and time is needed to determine the historical presence of Bd throughout the region but our preliminary study indicates that if Bd is endemic to Asia, epidemiologically it does not explain the lack of declines there. It will also be important to compare the genetic strains of Bd found in Asia with those found at sites associated with mass die-offs to determine if strain difference in the pathogen can explain the difference in disease prevalence in Asia [50], [51].…”

Chytridiomycosis risk among Central European amphibians based on surveillance data

“…These differences appear to be influenced by geography, life history and habitat (Becker et al 2012, Murray & Skerratt 2012. The pathogen's original host and biogeography context remains an unresolved issue that has received a great deal of attention (Weldon et al 2004, Fisher 2009, Schloegel et al 2012. It nevertheless seems clear that the major part of the pathogen's impact is caused by novel genetic lineages that have recently spread around the world (James et al 2009, Farrer et al 2011, Schloegel et al 2012.…”