Volume 17, Number 12—December 2011
Ranavirosis in Invasive Bullfrogs, Belgium
To the Editor: Massive global declines in amphibians have been attributed to various causes, including infectious diseases such as chytridiomycosis and ranavirosis. Chytridiomycosis and ranaviral disease are international notifiable diseases because they have been listed by the World Organisation for Animal Health in its Animal Health Code.
Ranavirosis is caused by icosahedral cytoplasmic DNA viruses that belong to the family Iridoviridae, in particular by 4 species of Ranavirus: Frog Virus 3 (FV3), Bohle iridovirus, Ambystoma tigrinum virus, and a possible species Rana catesbeiana virus Z. In Europe, FV3 has been identified in several outbreaks of ranavirosis, characterized by mass deaths, notably in green frogs (Pelophylax sp.) in Denmark, Croatia, and the Netherlands (1,2); Rana temporaria and Bufo bufo in the United Kingdom (3,4); and Alytes obstetricans and Ichthyosaura alpestris in Spain (5). The invasive exotic bullfrog (Lithobates catesbeianus) has been introduced in several European countries and has established large breeding populations in France, Italy, Germany, Greece, and Belgium (6).
In addition to their direct effect on native amphibians through competition and predation, bullfrogs are thought to be carriers of chytridiomycosis (7,8) and, possibly, ranaviruses. Although mass deaths of L. catesbeianus tadpoles has been reported in aquaculture facilities, L. catesbeianus tadpoles are generally considered a subclinical reservoir of ranaviruses in the United States (9).
To assess the role of bullfrogs as carriers of ranaviruses in Europe, we collected 400 clinically healthy tadpoles of L. catesbeianus from 3 invasive bullfrog populations at Hoogstraten, Belgium (51°47′Ν, 4°75′Ε) during May–June 2010. All larvae were euthanized as part of an invasive species eradication project and stored at –20°C until further use. At necropsy, liver tissues were collected, and DNA was extracted by using the Genomic DNA Mini Kit (BIOLINE, London, UK). PCR to detect ranavirus was performed as described by Mao et al. (10).
Three samples showed positive results with this PCR. These samples were sequenced by using primers M4 and M5 described by Mao et al. (10) and blasted in GenBank. A 100% homology with the common midwife toad (A. obstetricans) ranavirus partial major capsid protein gene (GenBank accession no. FM213466.1) was found (5). Despite the low prevalence of Ranavirus infection (0.75%) in the bullfrog tadpoles examined, this study shows that invasive bullfrogs, a known reservoir of chytridiomycosis, are also a likely carrier of ranaviral disease in Europe.
This study was partly performed in the framework of European Union Interreg IVA project IVA-VLANED-2.31 “Invasieve exoten in Vlaanderen en Zuid-Nederland–INVEXO.”
- Ariel E, Kielgast J, Svart HE, Larsen K, Tapiovaara H, Jensen BB, Ranavirus in wild edible frogs Pelophylax kl. esculentus in Denmark. Dis Aquat Organ. 2009;85:7–14.
- Fijan N, Matasin Z, Petrinec Z, Valpotiç I, Zwillenberg LO. Isolation of an iridovirus-like agent from the green frog (Rana esculenta L.). Vet Arch Zagreb. 1991;3:151–8.
- Cunningham AA, Langton TES, Bennet PM, Lewin JF, Drury SEN, Gough RE, Pathological and microbiological findings from incidents of unusual mortality of the common frog (Rana temporaria). Philos Trans R Soc Lond B Biol Sci. 1996;351:1539–57.
- Hyatt AD, Gould AR, Zupanovic Z, Cunningham AA, Hengstberger S, Whittington RJ, Comparative studies of piscine and amphibian iridoviruses. Arch Virol. 2000;145:301–31.
- Balseiro A, Dalton KP, Del Cerro A, Marquez I, Cunningham AA, Parra F, Pathology, isolation and molecular characterisation of a ranavirus from the common midwife toad Alytes obstetricans on the Iberian Peninsula. Dis Aquat Organ. 2009;84:95–104.
- Ficetola GF, Coic C, Detaint M, Berroneau M, Lorvelec O, Miaud C. Pattern of distribution of the American bullfrog Rana catesbeiana in Europe. Biol Invasions. 2007;9:767–72.
- Schloegel LM, Ferreira CM, James TY, Hipolito M, Longcore JE, Hyatt AD, The North American bullfrog as a reservoir for the spread of Batrachochytrium dendrobatidis in Brazil. Anim Conserv. 2010;13(S1):53–61.
- Daszak P, Strieby A, Cunningham AA, Longcore JE, Brown CC, Porter D. Experimental evidence that the bullfrog (Rana catesbeiana) is a potential carrier of chytridiomycosis, an emerging fungal disease of amphibians. Herpetol J. 2004;14:201–7.
- Miller DL, Gray MJ, Rajeev S, Schmutzer AC, Burton EC, Merril A, Pathological findings in larval and juvenile anurans inhabiting farm ponds in Tennessee, USA. J Wildl Dis. 2009;45:314–24.
- Mao J, Hedrick RP, Chichar VB. Molecular characterization, sequence analysis, and taxonomic position of newly isolated fish iridoviruses. Virology. 1997;229:212–20.
Suggested citation for this article: Sharifian-Fard M, Pasmans F, Adriaensen C, Devisscher S, Adriaens T, Louette G, et al. Ranavirosis in invasive bullfrogs, Belgium [letter]. Emerg Infect Dis [serial on the Internet] 2011 Dec [date cited]. http://dx.doi.org/10.3201/eid1712.110236
- Page created: November 18, 2011
- Page last updated: November 18, 2011
- Page last reviewed: November 18, 2011
- Centers for Disease Control and Prevention,
National Center for Emerging and Zoonotic Infectious Diseases (NCEZID)
Office of the Director (OD)