Two reports on epidemic mortality in frogs in the UK have been circulated by ProMED in September 2004. This is possibly due to the ranaviruses described by Cunningham et al (1996). Cause of the epidemic has not been confirmed.
Archive Number 20040912.2542
Published Date 12-SEP-2004
Subject PRO/AH/EDR> Red leg disease, frogs, fatal - UK
RED LEG DISEASE, FROGS, FATAL - UK
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A ProMED-mail post
http://www.promedmail.org
ProMED-mail is a program of the International Society for Infectious Diseases
Date: Sat, 11 Sep 2004
Killer virus could wipe out species
Sores erupt along frogs' legs, and limbs are lost
before the amphibians die, but scientists know
little else about the virus.
Although Red Leg has existed in Britain for many
years, it has now reached "crisis levels". It is
feared the disease has not yet reached its peak
and if unchecked could totally kill off the
species, says nature group Froglife.
Director of conservation Tom Langton said frogs
were the "hub" of the food chain. And he warned
that predators such as foxes, stoats and
buzzards, which rely on them as a food source,
would suffer.
He said: "We are staring into an abyss. This
could devastate our amphibians and once a
critical species like a frog disappears, then the
environmental impact has only just begun. It's a
waiting game, either they will bounce back or
face extinction -- we just don't know."
Froglife has urged the Government to fund a
nationwide survey to find out how many of the
creatures have been lost.
If the disease is caught early it can be treated,
but after several days of infection the mortality
rate is 90 percent. But the Environment Agency
said: "All we can do is take samples and confirm
the disease but if it occurs naturally there is
little we can do."
There is no evidence Red Leg can spread to humans or pets.
--
[The etiology of the frog pestilence was explained in our previous posting
(see ref. below) by Mod.PC as follows:
"The virus implicated in this outbreak is a member of the genus _Ranavirus_
of the family _Iridoviridae_. Iridoviruses are large complex viruses
possessing a large double-stranded DNA genome, which infect a variety of
hosts. Iridoviruses have only been isolated from poikilothermic [cold-
blooded] animals, usually those inhabiting damp or aquatic environments,
including marine habitats. None are known to infect warm-blooded vertebrates".
An explanation of the term "Red legs" in the
above news item may be found in the following
abstract of the paper by the Veterinary Science
Group, Institute of Zoology, London, U.K.:
Cunningham AA, Langton TE, Bennett PM, Lewin JF,
Drury SE, Gough RE, Macgregor SK. (1996).
Pathological and microbiological findings from
incidents of unusual mortality of the common frog
(Rana temporaria).Philos Trans R Soc Lond B Biol
Sci., 351(1347):1539-57.
"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 10 sites of unusual mortality
resulted in 2 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". - Mod.AS]
[see also:
Archive Number 20040914.2560
RED LEG DISEASE, FROGS, FATAL - UK (02)
Date: Tue, 14 Sep 2004
Red leg in frogs
Alberta Wildlife Status Report No. 9 (1997) says: "Mortality in
Northern Leopard Frogs has often been associated with the condition
of "red leg", which is not a disease itself but rather a condition of
kidney failure. It is often associated with infection by _Aeromonas
hydrophila_, a naturally occurring and widespread bacterium.
Ordinarily, this pathogen only affects individuals whose immune
systems have been weakened by stress, and not entire populations."
Other useful information is available in Greg Lewbart's review
"Amphibian Medicine", stating the following in the chapter Important
Diseases - Red Leg Disease:
"_Aeromonas hydrophila_ is considered an opportunistic pathogen of
amphibians. It is essentially ubiquitous in aquatic environments. It
establishes itself in stressed or immunosuppressed animals."
--
[see also:
Archive Number 20020201.3458
FROG MORTALITY, VIRUS - UK
Date: Fri 1 Feb 2002
Mystery virus ravages UK frogs
BBC Wildlife Magazine published the research showing that a virus is
responsible. The work of Froglife and the Institute of Zoology involved
investigation of more than 62 000 dead frogs. Writing in the magazine, Mr
Langton says one theory for the disease's origin is a change in the source
of imported goldfish. Until 20 years ago most goldfish imported to the UK
came from Italy, but since then Israel and the US have dominated the trade.
In the US, bullfrogs breed alongside the goldfish enclosures, and are often
attacked with shotguns to stop them competing for food pellets. Mr Langton
writes: "Bits of bullfrog could be eaten by a goldfish that is netted and
flown off for quick distribution to British garden centres."
"It's a complex situation and the exact causes are still not known. Slug
pellets, vehicle emissions, and changing weather patterns may play a role
in reducing frogs' resistance to the virus; the isolation of urban frogs
and in-breeding could also be a factor. More research is needed urgently."
Froglife says the disease was first seen to be increasing in suburban
London gardens in the late 1980s." Typically, adult frogs are seen to be
dying over several weeks, resulting in dozens, or even hundreds, of deaths,
"Reports of the virus reach a peak in July and August. Large-scale frog
mortalities also occur in late winter and are usually caused by a garden
pond freezing over, which can suffocate male frogs hibernating at the
bottom. We have found no evidence of the disease affecting people, pets or
other pond life; most people report that toads, newts and fish in a pond
where frogs are dying appear totally healthy."
[Byline: Alex Kirby]
--
[The virus implicated in this outbreak is a member of the genus _Ranavirus_
of the family _Iridoviridae_. Iridoviruses are large complex viruses
possessing a large double-stranded DNA genome, which infect a variety of
hosts. Iridoviruses have only been isolated from poikilothermic animals,
however, usually those inhabiting damp or aquatic environments, including
marine habitats. None are known to infect warm-blooded vertebrates.
Curiously, however, there is a weak amino acid sequence homology of the
major capsid protein with a corresponding protein of African swine fever
virus, a vertebrate virus of uncertain phylogeny - Mod.CP]
[Although reports concerning viruses, which are not associated with
outbreaks of disease in humans and domestic animals, are not normally
posted on ProMED-mail, the epidemiology of how this ranavirus gets
transported around the world is a lesson to us all. Today frogs, tomorrow ??
Frogs are eaten by humans, and the major trade, which is out of Southeast
Asia, could be used to explain some movement of _Vibrio cholerae_ 'El Tor'.
With the collapse of the US rural population we don't catch the number of
frogs that we used to, but the culinary demand for 'frog legs' is as high
as ever. Many years ago I had my students here in Louisiana study the
survival of _V. cholerae_ in frozen frog legs -- they do very nicely, thank
you -- It is the only paper in the literature on irradiated frog legs in
Louisiana. -
Mod.MHJ].
[The following background information on this outbreak has been supplied by
Dr Peter Daszak,Executive Director, Consortium for Conservation Medicine,
Lamont-Doherty Earth Observatory, Palisades, New York 10964-8000, USA
The facts behind this story originate in the work of Dr Andrew A.
Cunningham, Head of Wildlife Epidemiology, Institute of Zoology, London and
Dr Alex Hyatt at CSIRO. Cunningham has been working on the UK frog
mortality events for a decade. His work convincingly implicates a ranavirus
(Genus _Ranavirus_ Family _Iridoviridae_) as the causative agent.
Ranaviruses have been isolated from a range of amphibian, fish, and reptile
hosts in America, Europe, Australia, and Asia.
Cunningham has published solid epidemiological data to support this. He has
also replicated clinical signs (skin ulceration and systemic hemorrhage)
experimentally and fulfilled Koch's postulates for a ranavirus isolate from
common frogs (_Rana temporaria_) (Phil Trans Roy Soc London B. 1996, 351:
1539-1557). This is an important disease. It is implicated in amphibian
population declines in the UK and has received a great deal of scientific
and public interest not least because of widespread mass die-offs and the
striking lesions (the feet don't strictly "drop off", but there often is
extensive necrosis of the digits).
The hypothesis that this is an introduced pathogen is based on a recent
phylogeny paper (Arch Virol 2000, 145: 301-331). Major coat protein DNA
sequences from UK ranavirus isolates (one from a common frog, the other
from a toad) group with sequences of isolates from North American
amphibians including the bullfrog (_Rana catesbeiana_), suggesting it could
have been introduced from North America.
The bullfrog is a recent introduction to the UK and is now resident there,
but the first reports of this easily noticeable disease pre-date the
bullfrog's introduction. Langton suggests goldfish may be involved, and
although this hypothesis seems like a tabloid dream, it also is not
unreasonable. The global trade in aquarium fish is huge: it represents the
largest live animal trade globally and the largest portion of the import of
live animals into the UK.
Many ranaviruses have a wide host range experimentally, and experimental
infections of fish with amphibian ranaviruses (and vice versa) have been
published. Another potential source of introduction is the significant pet
trade in amphibians. Of course, hand-in-hand with import of aquarium fish
is import of aquarium water and its constituent microbial flora and fauna.
Ranaviruses are generally hardy outside the host, especially at cool
temperatures, and previous authors have proposed transport on fishing nets,
by waterbirds, and during fish stocking as means of pathogen introduction
to new sites (reviewed in EID 1999, 5: 735-748). The dimensions of the
aquarium fish and amphibian pet trade, the hardiness of the virus, and lack
of knowledge of amphibian pathogens (let alone surveillance, quarantine and
control measures) all suggest that this hypothesis is worth testing, and
that the disease outbreaks in the UK may represent yet another example of
"pathogen pollution."]
Updated 19 September, 2004
From: ProMED-mail
Source: Mirror, UK, 11 Sep 2004 [edited]
-----------------------------------
Frogs could be wiped out by a deadly disease
sweeping the UK, wildlife experts warned
yesterday. Millions [of frogs] have died over
the summer from Red Leg and the species is now
facing extinction.
2002
----
Frog mortality, virus - UK 20020201.3458]
Published Date 14-SEP-2004
Subject PRO/AH> Red leg disease, frogs, fatal - UK (02)
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A ProMED-mail post
ProMED-mail, a program of the
International Society for Infectious Diseases
From: Hugh Baker
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In the early 1970s it was common practice to ship live amphibians by
rail or bus to rural high schools in western Canada for use in the
biology curriculum. If the bus was delayed, or if the heating system
allowed the frogs to become chilled, there were large die-offs due to
"red leg". At the time (I was, of course, a student then) we were
told that red-leg was caused by a virus that was dormant in frogs
unless they were "cold-shocked".
H.J.Baker, DVM
Etobicoke, Ontario
Canada
Red leg disease, frogs, fatal - UK 20040912.2542
2002
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Frog mortality, virus - UK 20020201.3458]
Published Date 01-FEB-2002
Subject PRO/AH/EDR> Frog mortality, virus - UK
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A ProMED-mail post
ProMED-mail is a program of the
International Society for Infectious Diseases
From: ProMED-mail
Source: BBC News Online, Mon 28 Jan 2002 [edited]
------------------------------
Scientists say they are now certain that the disease that has killed
millions of British frogs is caused by a virus. The disease, which began in
south-east England, has crossed the Scottish border, hundreds of kilometres
to the north. Tom Langton, the director of the Froglife Trust, stated that:
"The ends of their limb extremities, their hands and feet, drop off, they
haemorrhage, open sores develop, they get thin and emaciated, and then they
die."
ProMED-mail
................mpp/mhj/cp/pg/es
Rick Speare