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

Abstract

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. KEY WORDS: European eel · Herpesvirus anguillae · HVA · Pathogenesis · Virus isolation · PCR · Immunohistochemistry · Histopathology Resale or republication not permitted without written consent of the publisherDis Aquat Org 78: [13][14][15][16][17][18][19][20][21][22] 2007 dexamethasone was reported, and the antibody response to HVA was studied. Rijsewijk et al. (2005) reported the antigenic relationship of the Dutch and Japanese isolates to H. anguillae. Shih et al. (2003) experimentally infected Japanese eels A. japonica with HVA by injection, and this resulted, after only > 7 wk, in gill and liver disease. To our knowledge, no pathogenesis studies in European eel infected with HVA by bath immersion have been published so far.The present study investigated the susceptibility of juvenile European eel Anguilla anguilla to infection with a European strain of HVA by bath immersion, and its pathogenesis in these eels. We successfully induced an experimental clinical HVA infection in post-larval (glass) eels via bath immersion with a HVA strain isolated from diseased farmed European eel. An immunohistochemical technique was established to study the pathogenesis of HVA. We used PCR (Rijsewijk et al. 2005) and virus isolation techniques to confirm the presence or absence of virus in experimentally exposed eels. The results of these techniques were compared in a time-course study. Furthermore, we studied the histopathological changes caused by HVA infection in glass eels. Clinical pathology, virus isolation, and PCR were found to be the most suitable methods for diagnosis of HVA infections. MATERIALS AND METHODS Cells and virus.The eel kidney cell line, EK-1, developed by Chen et al. (1982) was used throughout this study. EK-1 cells were cultured at 26°C according to Davidse et al. (1999). The Dutch HVA virus isolate no. 500138 (Van Nieuwstadt et al. 2001) was replicated in EK-1 cells at 26°C. After 100% cytopathic effect (CPE) developed, th...

First examination of the Lough Neagh European eel (Anguilla anguilla) population for eel virus European, eel virus European X and Anguillid Herpesvirus‐1 infection by employing novel molecular techniques

“…The Lough Neagh European eel population has been intensively studied (Allen, Rosell, & Evans, ; Bornarel et al., ; Rosell, Evans, & Allen, ) during which no eels have been observed as displaying either acute or chronic viral signs. However, viral infections have been suggested to play a contributory role in the decline of the worldwide eel stock (Esteve & Alcaide, ; ICES, ; Van Ginneken et al., ) and husbandry practices associated with eel farming including stress induced by high stocking densities, water quality and unfavourable water temperatures have been identified as key factors influencing viral disease outbreaks (AHAW Scientific Panel, ; Hangalapura, Zwart, Engelma, & Haenen, ). In wild eels, migration and maturation represent significant stresses (Haenen, van Ginneken, Engelsma, & van den Thillart, ; Van Ginneken et al., ) that may contribute to viral disease aeitology (Haenen et al., ) and it has been suggested that viral infections may have a detrimental effect on the swimming abilities and stamina of migrating silver eels (Bureau du Colombier, Bolliet, Lambert, & Bardonnet, ; Van Ginneken et al., ), accentuated further by the stresses incurred during this 6,000‐km spawning migration (ICES, ).…”

Viral diseases of wild and farmed European eel Anguilla anguilla with particular reference to the Netherlands

“…In the larger eels in fected by gill arch injection, after 21 d, slight necrotic lesions were observed in gill filaments, but AngHV1 was not reisolated. Hangalapura et al (2007) infected post-larval Anguilla anguilla (~5.1 g) by bath immersion with AngHV1. During the 21 d rearing period at 24°C, 15% of the inoculated eels showed clinical signs, such as haemorrhages extending from the lower jaw, throat, operculum and pectoral fins, ventrally down to the tail.…”

First detection of a viral agent causing disease in farmed sturgeon in Russia

“…This varied from microscopically observed alterations in European eel with Anguillid herpesvirus 1 (Hangalapura et al 2007) to grossly recognisable catarrhal inflammation of the posterior intestine in CCV-infected channel catfish (Wolf et al 1972) and rainbow trout with Salmonid herpesvirus 1 (Wolf & Smith 1981), and haemorrhagic inflammation found in coho salmon having both natural or experimental infection with Salmonid herpesvirus 2 (Kumagai et al 1994). The latter virus belongs to the same Subgroup 3 as the SbSHV.…”

“…Although relevant data are scarce in the literature, various degrees of heart pathology have been described in other herpesvirus-infected fishes: from those recognisable only at the histopathological level -in rainbow trout, coho salmon Oncorhynchus kisutch and European eel (Wolf & Smith 1981, Kumagai et al 1995, Hangalapura et al 2007) -to ones found both grossly (flaccid and mottled heart) and microscopically (degenerative cardiomyopathy and inflammatory response) -in carp Cyprinus carpio L. with koi herpesvirus (Haenen et al 2004, Wada et al 2004). More attention should be paid in the future to examination of the sturgeon heart, particularly in the age groups most susceptible to infection and disease.…”

“…(2) weakly virulent viruses causing chronic systemic infections without specific involvement of the integument: Salmonid herpesvirus 1 (Eaton et al 1989 (Hedrick et al 1991), white sturgeon herpesvirus 2 (Watson et al 1995), Salmonid herpesvirus 2 (Kimura, Yoshimizu 1989), carp pox herpesvirus (Sano et al 1990), koi herpesvirus (Hedrick et al 2000), epizootic epitheliotropic disease virus of lake trout Salvelinus namaycush (Bradley et al 1989, McAllister & Herman 1989, herpesvirus of Japanese flounder Paralichthys olivaceus (Iida et al 1989), herpesvirus of angelfish Pterophyllum altum (Mellergaard & Bloch 1988), herpesvirus of blue-eyed plecostomus Panaque suttoni (Yanong 1995), and other viruses; (4) weakly virulent viruses causing or associated with mild to benign conditions accompanied by the abovementioned integumentary manifestations: walleye Stizostedion vitreum vitreum diffuse epidermal hyperplasia herpesvirus (Kelly et al 1983), spawning papillomatosis herpesvirus of European smelt Osmerus eperlanus (Anders & Möller 1985), Atlantic salmon Salmo salar papillomatosis herpesvirus (Shchelkunov et al 1992), northern pike Esox lucius herpesvirus (Yamamoto et al 1984), sheatfish Silurus glanis herpesvirus (Békési et al 1984), European eel Anguilla anguilla herpesvirus (Békési et al 1986), Anguillid herpesvirus 1 (Hangalapura et al 2007), and other viruses.…”