Alternaria alternata as emerging threat for Hoplobatrachus tigerinus and Phrynoderma hexadactylum in southern West Bengal, India

Abstract

Amphibians are facing a global decline for the last few decades due to habitat loss, pesticide pollution, diseases and some other reasons. Fungal disease called chytridiomycosis has been emerged as one of the major causes of anuran extinction and decline in many parts of the globe. As the causal fungi Batrachochytrium dendrobatidis (Bd) were reported to have ubiquitous distribution on Earth, a survey was being conducted in districts of southern West Bengal, India, to assess probable anuran damage by the Bd in this region. A significant percentage of the common frogs Hoplobatrachus tigerinus and Phrynoderma hexadactylum were found to carry disease symptoms like redness of ventral skin, rashes, skin lesions, sluggish movements followed by death within 2 months. Investigation pointed the causal factor as Alternaria alternata. Liver and lungs were the primarily affected organs. Histopathology identified the presence of spores in TS of infected lungs along with hepatocellular steatosis. Elevation of serum SGPT and triglyceride (~ tenfold and ~ threefold, respectively, compared to healthy groups) was also key findings in infected individuals. Infection prevalence was highest in South 24 Parganas (more than 7%). A common plant pathogen shifting host to anurans in a trans-kingdom way may be a significant evolutionary finding, but the infection being detrimental to two local frogs will have severe impacts. As the frogs are food web intermediates of their habitats, a collapse in local food web will be the primary ecological impact along with higher incidence of mosquito-borne diseases.