The chytrid fungal pathogens Batrachochytrium salamandrivorans (Bsal) and B. dendrobatidis (Bd) are driving amphibian extinctions and population declines worldwide. They are thought to have originated in East/Southeast Asia, and hence Asia remains crucial for understanding the ecology of these pathogens. However, Bsal screening is relatively limited in this region, particularly in hotspots where Bd lineage diversity is high. To address this gap, we conducted an extensive survey across the Guangxi region of Southern China, now considered a Bd hotspot. We examined 1230 individuals from 38 amphibian species and 36 environmental water bodies sampled during mostly the middle spring and summer months of 2019-21. However, PCR testing revealed absence of Bsal in our samples. A subsequent niche modeling analysis for Bsal suggested that the bioclimatic conditions of much of the region may not be conducive to Bsal. Although our findings show absence of Bsal in the surveyed habitats, periodic monitoring in amphibians is still needed, particularly across seasons. This is because Bsal pathogenicity could increase at relatively lower temperatures, and Bsal may be partitioning its niche with Bd across seasons. Our results suggest that the climatic conditions of the karstic Guangxi plains and perhaps competition from other Bd lineages may suppress Bsal establishment in the region. Our study provide interesting insights into Bsal niche dynamics and the knowledge generated will facilitate the conservation efforts in amphibian populations devastated by chytrid pathogens across other regions of the world.

Ranaviral infections, a malady of ectothermic vertebrates, are becoming frequent, severe, and widespread, causing mortality among both native and cultured species, raising odds of species extinctions and economic losses. This turn of events is possibly due to the broad host range of ranaviruses and the transmission of these pathogens through regional and international trade in Asia, where outbreaks have been increasingly reported over the past decade. Here we focus attention on the origins, means of transmission, and patterns of spread of this infection within the region. Infections have been recorded in both cultured and wild populations in at least twelve countries/administrative regions, together with mass die-offs in some regions. Despite the imminent seriousness of the disease in Asia, surveillance efforts are still incipient. Some of the infections transmitted within Asia may transmit across host-taxon barriers, posing a significant risk to native species. Factors such as rising temperatures due to global climate change seem to exacerbate ranaviral activity, as most known outbreaks have been recorded during summer; however, data are still inadequate to verify this for Asia. Import risk analysis, using protocols such as Pandora+, pre-border pathogen screening, and effective biosecurity measures, can be used to mitigate introduction to uninfected areas and curb transmission within Asia. Comprehensive surveillance using molecular diagnostic tools for ranavirus species and variants will help in understanding the prevalence and disease burden in the region. This is an important step towards conserving native biodiversity and safeguarding the aquaculture industry.