Amphibians in
trouble.
Ranavirus - what is and
how does it affect amphibians?
Viral pathogens belonging to the ranavirus genus and family
Iridoviridae have had a devastating
impact globally on amphibian populations.
It is thought the disease reached the UK as a result of transmission
from non native species to native populations. All amphibian species in the UK
are at risk of the disease however the common frog and the
common toad, are the species most reported suffering from the
disease. Reptiles and fish are also at risk.
Ranavirus can infect numerous hosts in both adult and larval
form, and is capable of surviving outside of a host for a period of several
weeks or more in water systems. The
disease can be transmitted via both direct and indirect routes such as becoming
exposed to water or soil which has become contaminated with the disease. Direct
transmission occurs as result of contact with already infected animals and the
consumption of infected tissue during acts of predation, cannibalism and
necrophagy.
Symptoms – Signs of ranavirus include the swelling of limbs or body, ulcerations, lethargic behaviour and reddening of the body. It is not unusual to find large numbers of animals with no obvious external cause of death however this is likely to be the result of the disease having lethal internal affects.
Symptoms – Signs of ranavirus include the swelling of limbs or body, ulcerations, lethargic behaviour and reddening of the body. It is not unusual to find large numbers of animals with no obvious external cause of death however this is likely to be the result of the disease having lethal internal affects.
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| A fatality of ranavirus. Picture courtesy of Amanda Duffus/ZSL. |
Chytridiomycosis -What is it and how does it affect amphibians ?
Also known as chytrid, it is a disease caused
by batrachochytrium dendrobatidis otherwise known as bd - a non-hyphal, zoosporic chytrid fungus.
It has been described as being the worst recorded infectious disease
known to affect vertebrates due to the sheer number of species affected and its
tendency to force them into extinction. The disease targets the skin of adults
and mouthparts of tadpoles, and has been recorded in all amphibian species in
the UK having first been detected on these shores in 2004.
When infected with chytrid, the skin of the amphibian
becomes thick as a result of changes taking place invisible to the naked eye.
These changes become lethal to amphibians due to their unusual physiology which
enables them to absorb water and salts through their skin a trait uncommon to
most other animals. Chytrid damage to the skin causes electrolyte levels to
alter abnormally and subsequently cardiac arrest occurs.
Symptoms - In some cases adults may show signs such as reddening of the skin and ulcerations.
Behaviours may also differ for example nocturnal species adapting a diurnal
lifestyle. The majority of the time however dead animals are found with no
visible reason for the cause of death.
What you can do – To lessen the risk of the disease being
transferred it is vitally important not to move anything which may have been
contaminated for example spawn, adults, water and water plants from one are to
another. The disinfecting of equipment and boots which may come into contact
with more than one water source is another step which can be taken to lessen
the risk of transmission.
The Adder - a
victim of fear.
A quick search on the
internet is all it takes, the fear evident the misunderstanding of a maligned
species even more so. People are
terrified to go on holiday, dog walkers convinced that the menace in the grass is only to ready
to strike, the occasional reported
encounter only helps to further taint their reputation. Look a little harder and the real nature of
the adder becomes apparent many residents of Cornwall have lived twenty years
thirty years, maybe more and have encountered an adder less than a handful of
times. The descriptions of these encounters predominantly describe the
beautifully camouflaged reptile swiftly moving away seeking sanctuary from the
human invaders into their world as contrary to popular belief, a bite is a last resort. Venom is a valuable resource only to be used
in essential situations. The last human fatality as a result of an adder bite
was almost forty years ago with only a handful occurring over the last century.
Adders should be admired and treated with a healthy respect not feared and
maligned.
Fact File
Description - Females
are larger, growing up to 75cm while males grow up to 60cm. Females weigh
between 80-100 gm while males range between 50-60 gm. The guideline when distinguishing between
males and females is the colouration of the trademark zig zag pattern on their
backs. If the markings are black it’s a
male, brown it’s a female. It should be
noticed if the snake has not sloughed its skin for a period of time, this can
complicate differentiation.
Life span – Estimated
up to twenty years.
Habitat - Adders
prefer heathland but are adaptable to a
variety of habitats including sand dunes, grassland, woodlands and quarries.
Slopes are preferable for basking while scrub is utilised as cover.
Reproduction – With the arrival of Spring, males participate
in a dance consisting of tangles, twists, and rolls competing for the right to
mate. In August and September, females give birth to up to twenty live young
which are roughly seven inches in length.
Hibernation – Once Autumn begins, adults start to return to
their hibernation sites using the scent trails left by other adults as a
guide. These areas can be leaf piles,
brush wood, compost heaps or hollow tress with groups of up to as many as
twelve individuals. Adders will often return to the sites they were born, their
survival hanging on the conditions of the upcoming winter.
Diet – The diet of the adder consists of small mammals,
young birds, lizards and amphibians. Britain’s only venomous species victims
are injected with venom, after which the adders wait for them to succumb before
beginning to feed. Adder’s have
remarkable physiology- their jaws have extensible connective tissue
which allows their main jaw bones to move independently, enabling them to
swallow prey whole which may be larger than their heads width. Once swallowed, powerful digestive fluid gets
to work with just the hair and teeth of rodents being passed through
unaffected.
Threats and protection – Habitat loss and human persecution have had serious
implications on adder populations which can become isolated as a result of
countryside development and high intensity agriculture. The implications of
this mean reduction in numbers of adders, limited genetic diversity leading to inbreeding
which consequently impacts on the adders ability to fight off diseases. Natural
disasters such as fires, a variety of predators including buzzards, ravens,
herons and hedgehogs and the impact of non native species such as pheasants all carry a constant threat. All snakes in
England, Scotland and Wales are protected under the 1981 Wildlife and
Countryside Act offering protection from being caught, collected, sold, injured
or killed.
A fascinating new find from Africa.
Oldest fossil evidence of modern African venomous snakes
found in Tanzania.
And that concludes our first blog, we hope you enjoyed it
and be sure to keep an eye out for the next one !
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