Pathogenesis of Herpesvirus anguillae (HVA) in juvenile European eel Anguilla anguilla after infection by bath immersion.

A clinical infection in post-larval (glass) European eels Anguilla anguilla was successfully induced after artificial bath immersion with Herpesvirus anguillae (HVA), isolated from diseased European eel. HVA caused a clinical infection after 7 d post-inoculation (pi); virus was detected by polymerase chain reaction (PCR) from Day 1 pi; virus isolation was positive from Day 7 pi, and HVA antigen was detected by immunohistochemistry in gills and stomach from Day 4 pi. Tissue changes were found by histological examination in gills and skin from Day 4 pi. In general, there was good correlation in the timing of the clinical signs, PCR, virus isolation, immunohistochemistry and histopathology results, although PCR, histopathology and immunohistochemistry were the first positive tests. HVA was first detected in skin and stomach, followed by gills, and later heart and intestine, whereas HVA was detected persistently in gills and skin. Koch's postulates were fulfilled. For diagnosis of HVA infections, clinical pathology combined with virus isolation and/or PCR are recommended.