Pathological and microbiological findings from incidents of unusual mortality of the common frog ( Rana temporaria )

Abstract

In 1992 we began an investigation into incidents of unusual and mass mortalities of the common frog (Rana temporaria) in Britain which were being reported unsolicited to us in increasing numbers by members of the public. Investigations conducted at ten sites of unusual mortality resulted in two main disease syndromes being found: one characterized by skin ulceration and one characterized by systemic haemorrhages. However, frogs also were found with lesions common to both of these syndromes and microscopic skin lesions common to both syndromes were seen. The bacterium Aeromonas hydrophila, which has been described previously as causing similar lesions, was isolated significantly more frequently from haemorrhagic frogs than from those with skin ulceration only. However, as many of the latter were euthanased, this may have been due to differences in post mortem bacterial invasion. An iridovirus-like particle has been identified on electron microscopical examination of skin lesions from frogs with each syndrome and iridovirus-like inclusions have been detected in the livers of frogs with systemic haemorrhages. Also, an adenovirus-like particle has been cultured from one haemorrhagic frog. A poxvirus-like particle described previously from diseased frogs has now been found also in control animals and has been identified as a melanosome. Both the prevalence of the iridovirus-like particle and its association with lesions indicate that it may be implicated in the aetiology of the disease syndromes observed. Specifically, we hypothesize that primary iridovirus infection, with or without secondary infection with opportunistic pathogens such as A. hydrophila, may cause natural outbreaks of 'red-leg', a disease considered previously to be due to bacterial infection only.

A Synergism between Temporins toward Gram-negative Bacteria Overcomes Resistance Imposed by the Lipopolysaccharide Protective Layer

“…Among these bacteria is Aeromonas hydrophila, which is associated with the global decline of amphibians (44,45), and which is resistant to the majority of natural AMPs (36,45). Our data suggest that temporin L prevents the aggregation of temporins A and B within LPS, thus allowing their translocation across the outer membrane into the cytoplasmic membrane.…”

“…Note that the strongest synergism was observed against A. hydrophila, considered to be part of the natural flora of a multiplicity of animals including humans (46,(72)(73)(74). A. hydrophila is an opportunistic pathogen found in healthy frogs, but capable of inducing diseases, such as the natural outbreaks of "red-leg" in Amphibia (45), including the species of R. temporaria (44). Beside causing high mortality in amphibian populations, this bacterium is also responsible for variety of infections in humans (75)(76)(77), especially in immunocompromised individuals, and it has been found to be insensitive to several classical antibiotics (72,74,78).…”

Xenopus Laevis: A Possible Vector of Ranavirus Infection?

“…Ranaviruses (Iridoviridae) are becoming increasingly associated with diseases in wild and cultured fishes, frogs, salamanders, and reptiles (Cunningham et al, 1996;Zupanovic et al, 1998;Hyatt et al, 2000;Zhang et al, 2001;Chinchar, 2002;De Voe et al, 2004;Pearman et al, 2004;Greer et al, 2005). Frog virus 3 (FV3), the best-characterized member and type species of the Ranavirus genus, is a large (165-169 nm) double-stranded DNA icosahedral virus that was originally isolated from the North American leopard frog, Rana pipiens (Chinchar, 2002).…”

Behavior of an Aeromonas hydrophila aroA Live Vaccine in Water Microcosms

“…Aeromonas hydrophila is a gram-negative enterobacterium widely distributed in aquatic environments (22,24,26,45), and it has long been known as a pathogen of amphibians, reptiles, and fish (4,19,52,(55)(56)(57)66). Also, this bacterial species has been reported to cause a wide variety of human infections (2,28,29,42,70).…”