MONITORING OPHIDIOMYCES OPHIDIICOLA IN A HIGH-SUSCEPTIBILITY EUROPEAN SNAKE SPECIES

Ophidiomycosis (snake fungal disease) is a skin disease associated with the fungus Ophidiomyces ophidiicola (Oo). While Oo has been increasingly reported across continents, robust field data on prevalence, disease expression, and ecological correlates in free-ranging European snakes are still limited. In our new study, we investigated Oo infection and ophidiomycosis in dice snakes (Natrix tessellata) along the northern shore of Lake Como (Northern Italy), combining field observations with molecular diagnostics and histopathology.

Dice snake, Natrix tessellata (©Matteo di Nicola)

How common was Oo, and when does infection translate into disease?

Across a season-long survey, we screened live snakes and opportunistically collected skin sheds. After accounting for recaptures, we analysed 92 records (69 live snakes plus 23 sheds).

We found that:

• Oo was detected in 53.3% of all analysed records.

• “At least apparent” ophidiomycosis was recorded in 23.9% of the total sample set.

• Skin lesions were a strong predictor of Oo detection and ophidiomycosis.

• Smaller snakes were more frequently Oo-positive, suggesting age-linked susceptibility.

• All sequenced samples belonged to Oo clade II.

• Oo-positive snakes had lower body temperatures, but did not clearly select warmer substrates, suggesting limited or absent behavioral fever in this setting.

• Oo-positive snakes were significantly less likely to exhibit musking, suggesting possible sublethal effects of pathogen presence on antipredator responses.

  
  

Dice snake, Natrix tessellata, With lesions (©Matteo di Nicola)

Why does it matter?

Understanding how often Oo occurs in wild European snake populations, and which host traits and behaviours are associated with infection and disease, is essential to design targeted surveillance and risk-based monitoring. Our results show that Oo can be common and that a substantial fraction of individuals may exhibit clinically relevant skin disease, with potential implications for individual fitness and broader consequences for wild snake populations.

For more information about this study, you can read the full scientific article here.