"The sudden appearance of chytridiomycosis, the cause of amphibian deaths and population declines in several continents, suggests that its etiologic agent, the amphibian chytrid Batrachochytrium dendrobatidis, was introduced into the affected regions. However, the origin of this virulent pathogen is unknown. A survey was conducted of 697 archived specimens of 3 species of Xenopus collected from 1879 to 1999 in southern Africa in which the histologic features of the interdigital webbing were analyzed. The earliest case of chytridiomycosis found was in a Xenopus laevis frog in 1938, and overall prevalence was 2.7%. The prevalence showed no significant differences between species, regions, season, or time period. Chytridiomycosis was a stable endemic infection in southern Africa for 23 years before any positive specimen was found outside Africa. We propose that Africa is the origin of the amphibian chytrid and that the international trade in X. laevis that began in the mid-1930s was the means of dissemination."



Source: Origin of the amphibian chytrid fungus



and



"Regarding to adverse effects that contribute to amphibian declines, the effects of atrazine on sex differentiation can negatively affect amphibian populations. The effects of the pesticide mixture on growth can have an even more rapid negative effect on populations, as described above. The immunosuppressive effects are likely even more relevant. Most significantly, the nine-pesticide mixture increased plasma corticosterone levels. Corticosterone can produce all the effects observed with the pesticide mixtures, including retarded growth (Hayes 1995a, 1995b; Hayes and Wu 1995; Hayes et al. 1993, 1997), retarded development (Glennemeier et al. 2002a, 2002b; Hayes 1995a, 1995b, 1997b; Hayes and Wu 1995; Hayes et al. 1993, 1997), and immunosuppression (Belden and Kiesecker 2005; Hayes 1995b). Given these adverse effects and the continued increase and use of pesticides in agriculture over the last 50 years, it is likely that pesticides have played and will continue to play a role in amphibian declines. In particular, the effects described here are very important. Pesticide-induced declines in populations as a result of decreased prey availability and increased susceptibility to predators (as a result of decreased size and the negation or reversal of the relationship between time to metamorphosis and size at metamorphosis) may be difficult to discern in the wild. Perhaps more important, emergent diseases caused by agents such as ranavirus (Brunner et al. 2005; Green and Muths 2005; Jancovich et al. 2005; Pearman et al. 2004) and chytrid (Berger et al. 1998; Green and Muths 2005; McCallum 2005; Ouellet et al. 2005; Rollins-Smith et al. 2002; Weldon et al. 2004) are considered major contributors to amphibian declines. Given the present findings with the flavobacteria in the present study, perhaps these diseases are not emergent at all. As suggested by Burkhart et al. (2003), perhaps what is emergent is the inability to mount proper immune responses as a result of pesticide exposure. As Sparling et al. (2003) pointed out, “Unfortunately, almost all research on amphibian population declines has focused on single factors or multiple factors considered individually with little consideration for interactions.” This approach has to change if problems are to be identified and solutions formulated."



Source: Pesticide Mixtures, Endocrine Disruption, and Amphibian Declines: Are We Underestimating the Impact?



Emphasis in bold is mine.

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