Prevalence of Batrachochytrium dendrobatidis in Amphibians in Northwestern Italy's Protected Areas

Abstract

Chytridiomycosis, caused by the fungus Batrachochytrium dendrobatidis (Bd), is a significant threat to global amphibian populations, leading to widespread declines and extinctions. In the spring of 2023, Bd presence was detected in different amphibian species within two protected areas near Turin, Piedmont, Italy, following an unusual mortality event among the common toad (Bufo bufo). Histological and molecular analyses confirmed Bd infection in a deceased Pelophylax sp. specimen, prompting further investigation. Sampling of 166 individuals across seven amphibian taxa revealed an overall Bd occurrence of 38.6%, with Pelophylax sp. showing the highest detection rate (50.5% of 93 individuals). A marked difference in the positivity rate was observed between the two locations, with La Mandria (67.2% of 58) exhibiting significantly higher rates than Vauda (22.9% of 35). While Bd was identified in the sampled amphibians, the exact cause of the observed mortality remains unclear and may involve other pathogens or multifactorial causes, including but not limited to Bd. These findings represent the first documented case of Bd presence in Piedmont after an 18-year gap, highlighting the potential influence of local environmental factors on infection dynamics. The study emphasises the need for expanded, standardised field sampling and further investigation into the various factors affecting amphibian health to guide conservation efforts for vulnerable amphibian species.

Keywords: Anurans; EIDs; La Mandria; Pelophylax; Piedmont; Vauda; animal diseases; chytridiomycosis; emerging infectious diseases.

Figure 1

Map of Northern Italy. On the left, the red rectangle highlights the area of Piedmont (region coloured in dense white) where the two Natural Parks involved in the study are located. On the right, in detail, is the location of La Mandria (light green) and Vauda (dark green) to the north of the city of Turin. Map credits: left—Google Earth [Data SIO, NOAA, U.S. Navy, NGA, GEBCO; Image Landsat/Copernicus], modified; right—OpenStreetMap contributors, available under the Open Database License.

Figure 2

Histological section with PAS staining. Amphibian epidermis affected by Batrachochytrium dendrobatidis, exhibiting hyperkeratosis and epidermal hyperplasia with corneal pearl (blue arrow). The black arrow identifies the enlarged area in the insert, where several zoosporangia (red arrow) containing zoospores are visible.

Figure 3

Bd positivity rates after grouping Rana spp. and newts to strengthen the analysis (top: overall data, considering the whole study area; bottom left: data related to La Mandria; bottom right: data related to Vauda). Red values: rate of Bd positives relative to the total sample in each specific locality. Blue values in brackets: rate of Bd positives in each locality relative to the total sampled for that taxon across both localities.