This hypothesis has been proposed for Bd within Asia as well, due to the fact that a high diversity of lineages is found in eastern Asia 13, 14 and, throughout this region Bd has a low prevalence with no signs of disease outbreak in many amphibian species 15, 16, 17, 18, 19, 20. The presence of Bsal in several urodelan species in Thailand, Vietnam and Japan, coupled with clinical infection trials indicating three Asian salamander species were capable of persisting with the infection or clearing the infection completely, gave rise to the hypothesis that Bsal is endemic to eastern Asia and the salamander species inhabiting this area may act as a reservoir for the fungus 12. A recent screening for Bsal revealed the presence of the fungus during disease outbreaks in wild salamander populations within the Netherlands, Germany and Belgium 9, and in captive animals from the UK and Germany 10, 11. Bsal appears to be restricted to urodelan hosts, causing erosive skin lesions with subsequent death in diseased individuals, and the type strain has lower thermal growth tolerance limits than its sister species Bd 8. salamandrivorans (Bsal), which is causing massive declines in salamander populations in Europe 8, 9. Globalization has led to the emergence of infectious diseases that threaten biodiversity and contribute to the current 6 th mass extinction, a recent example being amphibian chytrid fungi: Batrachochytrium dendrobatidis (Bd), which has caused declines and extinctions within Anura, Urodela and Gymnophiona throughout many parts of the world 1, 2, 3, 4, 5, 6, 7 and B. Therefore, this study provides support for the hypothesis that these chytrid fungi may be endemic to Asia and that species within this region may act as a disease reservoir. Bsal was more widespread than Bd, and occurs at temperatures higher than tolerated by the type strain, suggesting a wider thermal niche than currently known. Combined with a complete lack of correlation between infection and individual body condition and absence of indication of associated disease, this suggests low level pathogen endemism and Bsal and Bd co-existence with Vietnamese salamandrid populations. The globalized pandemic lineage of Bd was found within one pond on one species with a prevalence of 0.69%. Bsal was found within 14 of the 55 habitats (2 of which it was detected in 2013), in 5 salamandrid species, with a prevalence of 2.92%. We sampled 583 salamanders from 8 species across Vietnam in 55 locations for Bsal and Bd, determined scaled mass index as a proxy for fitness and collected environmental data. Recent evidence suggests Southeast Asia as a potential cradle for both fungi, which likely resulted in widespread host-pathogen co-existence. salamandrivorans (Bsal), pose a major threat to amphibian biodiversity. The amphibian chytrid fungi, Batrachochytrium dendrobatidis (Bd) and B.
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