Vestibular Syndrome Associated to Ranavirus in Farmed American Bullfrogs

Abstract— Frog farming is a consolidated aquaculture activity in Brazil. American bullfrogs (Lithobates catesbeianus) are raised in high densities and fed artificial diets, conditions that favors the emergence of diseases. A common disease affecting farmed frogs is a nervous syndrome characterized by postural and locomotive alterations resembling a vestibular disease in other species. Ninety-one sick frogs were analyzed from two different farms located at Goiás State in Central-Western Brazil. Frogs were first clinically assessed and further necropsied to identify lesions. Samples from the whole head, liver, kidney, spleen, stomach, intestine, lungs, gonads, skin and blood were obtained for histopathology, immunohistochemistry (IHQ), bacteriology, transmission electron microscopy (TEM) and real-time PCR. Macroscopic lesions affecting the inner ear region were collected for histopathology. Inflammatory lesions with necrosis and lymphocytic infiltrate affecting the labyrinthine endorgans, with necrotic foci, abundant macrophages and cellular debris associated with inflammatory infiltrates and acidophilic inclusion bodies were observed. No bacteria were isolated or identified in these lesions. IHQ showed positive staining for Iridoviridae and TEM confirmed viral particles. qPCR also detected a virus from Ranavirus genus. These findings indicate that Ranavirus cause frog vestibular syndrome. As far as we know this is the first report of Ranavirus producing nervous lesions