Reptiles and Amphibians: Health, Disease and Physiology
SUMMARIES OF ARTICLES ABOUT REPTILES AND AMPHIBIANS
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Newt superpower is regeneration
Newts can regenerate eye lenses
source: New Scientist vol 211 no 2821, July 16 2011 p15
Japanese newts (Cynops pyrrhogaster) can regenerate the lenses in their eyes, according to a team led by Panagiotis Tsonis from Dayton, who recorded the newts for 16 years. They excised lenses from six newts 18 times. Lens regeneration was carried out using pigment epithelial cells from the iris rather than from lens tissue remaining. The newts were aged 30 when the study ended, and regenerated lenses could not be distinguished from lenses that had not been regenerated. Efficient DNA repair may help explain the newts' regenerative abilities.
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Seroprevalence and significance of paramyxovirus titres in a zoological collection of lizards
Testing of lizards at London Zoo to determine exposure to paramyxovirus
source: C. Lloyd, R. Manwell, S. Drury, and A.W. Sainsbury
Veterinary Record vol 156 no 18, April 13 2005
starts p578, 3 pages long
Lizards as well as snakes can be infected with paramyxovirus (PMV). The infection was first detected in reptiles in London Zoo in 1999, when a rattlesnake with neurological problems tested positive. This project tested 59 lizards from 20 species from the crocodilia and squamata orders for PMV, through HI tests. 58 of the animals were clinically normal. Seven of the 59 animals tested positive. The positive animals were from three species, the rhinocerous iguana, blotched, blue-tobgued skink, and prehensile-tailed skink. The rhinocerous iguanas showed the highest titres. There appear to be different 'species' of reptile PMV, which makes testing difficult. Most of the lizards testing positive were clinically healthy. Many snakes previously testing positive, prior to this project, have stayed healthy. The route of infection affects whether PMV is virulent in birds, though the factors affecting virulence in reptiles are unclear.
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Frog fungus clue
Trade in amphibians as pets and food may have led to killer virus
source: New Scientist vol 212, no 2838, November 12 2011 P5
Trade in amphibians as pets and food may have led to the creation of a killer fungus, affecting amphibians in much of the world. The chytrid fungus is virulent, and affected frogs have a high death rate. A team led by Rhys Farrer from Imperial College, London, collected fungus samples from five continents. Sixteen of twenty samples were genetically identical. They were of the Bd GPL strain, formed from the union of two different fungus strains. This union was probably made possible by global trade in amphibians for food and pets. Quarantine could protect a country's amphibians. South east Asia and Madagascar both have rich amphibian diversity, and are free from Bd GPL. These areas need protection.
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Rescue bid to save frogs from fungus
Skin bacterium may help frogs affected with fungus
source: Linda Geddes
New Scientist vol 202 no 2711, June 6 2009 p14
A type of chytrid fungus called Bd may respond to a skin bacterium found naturally in some species of amphibians. The disease has spread rapidly, with the Philippines as the latest infected area. Reid Harris and team from James Madison University, Harrisonburg, Virginia, has discovered that infected frogs retained better weight of they were protected by a bacterium called Janthineobacterium lividum. They have also discovered that the bacterium can prevent deaths in infected frogs. They first coated 12 mountain yellow-legged frogs in J. lividum through bathing them, then infected six uncoated frogs with Bd, and six of the twelve coated frogs. After 20 weeks, all of the six coated frogs had survived, with some showing weight gains. Five of the six uncoated frogs had died. The J. lividum bacteria produce violacein, an antibiotic. The teams plans further research, with a long term goal of attempting to protect wild frogs through treating soil, water and animals themselves.
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Frog fightback starts now
Frog populations begin to recover from fungal disease
source Wendy Zukerman
New Scientist vol 208 no 2790, 11 December 2010 p14
Researchers in Australia and the US have found that some frog populations, which had dropped due to Chytrid fungal infections, have started to recover. The infections affected a range of species, which suffered major population falls from 1990 to 1998. Maichael Mahony from Newcastle University, New South Wales, has studied frogs along Australia's Great Dividing Range, and has found that barred river frogs, tusked frogs, and many species of tree frogs have returned. Meanwhile, tree frogs are returning to Queensland, according to Ross Alford of James Cook University, Queensland.
Meanwhile, in the US, University of California's Roland Knapp has found that mountain yellow-legged frogs arecoming back. He and Mahony have discovered that frogs are co-existing with low levels of chytrid. The fungus could have weakened, and the frogs may have evolved to resist it. Knapp has found that recovered populations of frogs survuive exposure to infection better than frogs not previously exposed. This finding is echoed by results from Vanderbildt University, Nashville, where Louise and Alford Rollins Smith found higher levels of anti-fungal peptides on skins of frogs from recovered populations. In Europe, Ursina Tobler from Zurich University has shown that some tadpoles can survive the infection.
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Lizards will roast in a warming world
Global warming threatens the survival of reptiles
source New Scientist 21 Feb 2009 vol 201 no 2696 p11
Cold-blooded animals, such as reptiles, cannot produce heat, so migrate to cooler or warmer areas as a way to staying alive. Temperatures above 4 deg C can kill ectotherms, which prefer body temperatures from 30 to 35 deg C. A team led by Michael Kearney from Australia's Melbourne University, modelled expected changes in temperature, and found that temperature rises of 3 deg C in the shade could lead to ectotherm body temperatures of more than 40 deg C in tropical deserts in Australia. Ectotherms can take refuge in burrows, but the excess heat may still affect feeding and reproduction.
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Myiasis in two Hermanns' tortoises
Tortoises infected with fly larvae
source: M.J. Sales et al
Veterinary Record vol 153 no 19, November 8 2003
starts p600, 2 pages long
Two adult Hermann's tortoises, a female and a male, some 70-years-old, were
taken to a vet surgery in Barcelona, Spain, suffering from wounds in their
limbs. They lived in a garden enclosure. Both tortoises were found to have
Dipteran larvae in their limbs, and hundreds of these larvae were taken out
of the tortoises. The female tortoise had more severe wounds, and more larvae
were removed from her. Wound debridement was carried out, followed by disinfection
with povidone iodine, and then an antibiotic pomade was applied. One of the
tortoises, the female, died, despite treatment. The larvae were probably of
the Calliphora vicina blowfly. The cause of death was probably severe destruction
of the tissues by carnivorous maggots.
This sort of infestation has been reported in wild tortoises, mostly in the
US. Surgical removal is needed if maggots are in swellings under the skin,
and forceps can be used to take maggots out of open wounds. Infestation can
be prevented by bringing tortoises indoors if keepers notice that they have
wounds, or by using screened hutches at the time of year when flies tend to
be active. Animals infested in this way should preferably be prevented from
hibernating until their wounds have healed. The article describes the infestation
and treatment in further detail.
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Tests improve odds in frog fungus flight
New tests developed to detect chytrid fungus infections in
frogs
source: Rachel Nowak
New Scientist no 2382, February 15 2003 p18
A new test has been developed that can detect chytrid fungus infections in
frogs. The fungus has led to nine or more species of frogs becoming extinct
since the 1940s, and testing for the fungus has hitherto only been possible
once frogs have started to sicken. The new test was developed at Canterbury
University, New Zealand, by ecologist, Bruce Waldman. The test uses DNA analysis
of skin cells from frogs thought to be at risk.
The new test should help protect frogs in New Zealand, where one species
from the Leiopelma genus is threatened with extinction. The old-style test
involved removing a frog's toe for a sample.
Another new test, which resembles that of Waldman, has been developed by
biotech company, Pisces Molecular, while Australian Animal Health Laboratory's
Alex Hyatt has developed a further test, that detects proteins from the fungus.
The fungus may have come from South Africa, where the African clawed from
can harbour infections while not falling ill.
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Explaining frog deformities
Causes of deformities in frogs
source: Andrew Blaustein and Peter Johnson
Scientific American vol 288 no 2 February 2003
starts p48, 6 pages long
Amphibians throughout the US have been affected by deformities, noted in
over 60 species, and 46 US states since 1995. Elsewhere in the world, missing
and extra legs and other deformities have been noted. There appears to have
been an increase in these deformities, and one suspect is an excess of ultraviolet
radiation, leading to genetic mutations and damaged immune systems. Some researchers
have found a link between missing legs and ultraviolet radiation, but this
fails to explain extra legs, and why animals are affected when they are nocturnal,
or hide from the sun in shade and mud.
Pesticides may also be a contributory factor, but again, they do not appear
to be the only cause of deformities. Trematode parasites have, however, been
linked to the development of extra limbs. Amphibians can become infected with
Ribeiroia ondatrae parasites, which spend part of their lives in snails, which
can infect frogs. Affected tadpoles do not develop properly, and can be more
easily caught by herons and other birds. The parasites mature within the bird,
and are excreted, and then infect snails.
An increase in infections by parasites could, then, explain why deformities
have become more common, and increased fertilizer run-off from farmed land
into wetland may be the reason why infections of amphibians with this parasite
have become more common. The run-off promotes the growth of algae, which can,
in turn, boost the population of snails. Amphibians may also become more vulnerable
to the parasites because of excess radiation, or pollution.
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The frog doctor
Froglife helps frogs in ponds in London, England
source: Virginia Ironside
Independent on Sunday Review May 18 2002
starts p13, 2 pages long
Froglife is an organization that provides advice on caring for frogs in garden
ponds, and even sends a frog doctor to help people worried about their ponds.
There are around 150,000 ponds in the Greater London area, and these ponds
are important for the survival of amphibian species, especially since many
rural ponds have been polluted by pesticides.
The frog doctor, Nick Meade, gives free visits, funded by the Bridge House
Estates Trust, which is an important funder of London environmental charities.
He estimates that 95% of London ponds he knows of house frogs, while 75% have
newts, and 20% are homes to toads. Frogs like ground cover round ponds, so
they can escape from predators. They can also use ramps to get out of ponds.
An excess of nutrients can turn water green with algae, which is not a good
environment for frogs. Leaves should be removed before they sink, and left
once they have sunk. Rainwater is better than tap water, and ponds should
be at a distance from compost heaps.
Water fleas and oxygenating plants can help provide a good environment for
frogs. The fleas can be found in ponds, and feed algae, so clean up ponds
affected by an excess of nutrients.
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Thermal shock in a colony of South African clawed frogs (Xenopus
laevis)
Captive frogs die after rapid rise in water temperature
source S.L.Green et al:
Veterinary Record vol 152, no 11, March 15 2003
starts p336, 2 pages long
The sudden death of South African clawed frogs at Stanford University, US,
led to an investigation into possible causes. There were 200 adult, female
frogs housed in a 300 litre laboratory tank, and 22 of these frogs were found
dead, followed by a further 17 found dying or dead eight days later. No pathogens
were found, histological examinations showed no abnormalities, and the water
quality did not appear to be at fault. Four moribund frogs were euthanased
and found to have haemotological profiles of cold-adapted amphibians. The
39 affected frogs had all come from a holding tank kept at 16 degrees C to
boost oogenesis. The profiles fit with data on cold adaptation in amphibians
from other studies. This species of frog prefers a water temperature of 21
deg C to 24 deg C, but can tolerate variations in temperature up to between
31 deg C and 39 deg C, so long as the change in temperature occurs over some
hours. The frogs had been transferred from water at 16 deg C to 23 deg C,
and had suffered from acute thermal shock. Other species of frogs have been
affected by sudden, small temperature rises between 2 deg C and 5 deg C.
Laboratory practice was changed, allowing the frogs to acclimatise overnight
in a 3 litre bucket, with a 23 deg C - 25 deg C ambient temperature. After
this change in practice, there were no more deaths from thermal shock.
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Popular herbicide may gender bend wild frogs
Toxicologists concerned that atrazine can feminize male frogs
Source: Jay Withgott
New Scientist November 2 2002 p13
Toxicologists are concerned that atrazine, commonly used on corn crops in
the US, can feminize male frogs. Forty per cent of herbicides used in the
US are atrazine-based, and the Enviromental Protection Agency (EPA) could
restrict their usage.
A team from University of California, Berkley, headed by Tyrone Hayes, an
endocrinologist, first studied Xenopus laevis, a species from Africa, used
in laboratories, and then went on to look at native wild frogs in the US.
Both the African frogs, and Tana pipiens, or northern leopard frogs, develop
ovaries and their voice boxes shrink. His initial research found that even
a dose of one thirtieth the EPA standard for safe drinking water could have
this effect. Low doses could affect the frogs more severely than higher ones,
which may be because they appear similar to hormones at low levels. The research
has been reported in Nature, vol 419 p895. Syngenta, which makes atrazine,
has funded other research, and these researchers argue that their research
shows that, while atrazine does feminize frogs, it only does so at high doses.
Atrazine has been banned in many countries in Europe.
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Salmonella septicaemia in a beauty snake
Case of beauty snake found dead with Salmonella septicaemia
infection
source: S. Tellez et al
Veterinary Record vol 151 no 1, July 6 2002
starts p 28, 2 pages long
Salmonella species are often found in reptile intestines, and they may be
carriers, ad suffer from minor infections. However, Salmonella species can
also cause serious problems for reptiles, such as septicaemia and gastroenteritis.
Malnutrition, stress, and poor husbandry can make reptiles more vulnerable
to such infections, and the seriousness of the infection depends on how virulent
the serotype is, the reptile's innate immunity, and the type of lesions resulting
from the infection.
In this case, Madrid University researchers have studied a female beauty
snake from a private collection of reptiles, which died suddenly, though she
had not appeared to be ill. The snake was found to have renal congestion,
nodules on the liver, and the small intestine showed haemorrhagic contents.
The systemic infection was found to be the result of one S enterica strain
of the houtenae subspecies, with isolates found in the gall bladder, liver
and kidney. This subspecies is usually linked to septicaemia in lizards, not
snakes. S enterica diarizonae isolates were also found in the snake's intestines.
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No defence
Frogs’ immune systems affected by pesticides
source: Kurt Kleiner
New Scientist May 4 2002 p12
Frogs’ immune systems can be affected by small amounts of pesticides,
according to Brian Dixon from Canada’s University of Waterloo, Ontario.
He injected DDT, dieldrin and malathion into northern leopard frogs, and discovered
that their antibody production fell dramatically, sometimes to zero, following
these injections, which were nearly as powerful as immunosuppressants as a
drug used for this purpose, cyclophosphamide.
Dixon also studied wild frogs in polluted locations in Ontario. These frogs
suffered the same sort of immune system damage as the injected froms, and
the psticide levels are similar. Canada has banned usage of dieldrin and DDT,
but these pesticides break down slowly, while malathion is still in use.
The wild frogs were still able to produce antibodies in response to antigens
they had been in contact with prior to their exposure to pesticides, and they
also underwent some recovery eight weeks after a transfer to clean water.
These findings, which are to be published in Environmental Toxicology and
Chemistry, may help explain a world-wide drop in frog numbers. Affected frogs
may also be more susceptible to infection by parasites.
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Disease killing frogs is linked to goldfish from US
British frogs hit by infection
source: Paul Brown
Guardian January 29 p7
Frogs in London and south east England have been hit by an infection which
begins with sores, and is eventually fatal. An estimated 62,000 frogs have
died in 3,500 outbreaks, with 2,000 frogs dying in one case. Froglife Trust
director, Tom Langton, sees the disease as worst south of a line from Norfolk
to Dorset, though there have also been cases in Scotland, Wales, and the Midlands.
The cause appears to be a ranavirus imported from the US with goldfish that
have been put into British garden ponds. North American bullfrog tadpoles
were also imported during the 1980s, and may have been another source of the
virus. Reptiles can also catch the disease.
The affected frogs may have been more vulnerable to infection because of
poisoning by slug pellets. Their livers have been found to contain extremely
high levels of copper, used to colour slug pellets. Frogs may have eaten poisoned
slugs, and even pellets attached to the slugs, which would damage the frogs’
immune systems, so leave them more open to infections.
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Mighty muscles help chameleons grab a quick bite
Chameleons have supercontracting tongue muscles
source: New Scientist October 13 2001 p27
Northern Arizona researchers have found supercontracting muscles in chameleons’
tongues, unknown in other species. These muscles mean that chameleons can
exert maximal force, allowing them to reel in prey they have caught, even
large prey like birds, and even when the chameleons’ tongues are extended
to their full length. This research is described in The Journal of Experimental
Biology, vol 204, p3621.
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Lego wheels for overfed tortoises
Lego wheels provide mobility for disabled tortoises
source: Martin Wainwright
Guardian November 23 2000 p11
Vet, Stuart McArthur, from Leeds, England, has developed a way of treating disabled tortoises to give them mobility through attaching Lego wheels. Tortoises sometimes become disabled if they are overfed when they are young. This means that their shells may set too deeply for them to be able to walk properly. Other tortoises may have spinal, or leg injuries. McArthur is a tortoise specialist who has researched the best type of Lego wheel, and this is not a treatment that should be carried out by pet owners on their own, or used for tortoises that are not disabled.
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Got it licked
Chameleons' tongues act as suction pads
source: Ian Sample
New Scientist October 21 2000 p24
Anthony Herrel is a researcher from Antwerp University, Belgium, who has studied the way that chameleons use their tongues. Chameleons can eat birds and lizards, which means their tongues have to work in a special way, for them to catch such large prey. Herrel's research was carried out with Northern Arizona University researchers, and involved filming feeding chameleons with high-speed cameras. He discovered that the end of a chameleon's tongue takes the shape of a suction pad, around two milliseconds prior to hitting its prey. After the tongue hits the prey, the tongue muscles contract, which pulls back the cup, and makes the suction effect stronger. Further information can be obtained from 'Journal of Experimental Biology', vol 203, p3255.
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Snakes use night sights to stalk their prey
Snakes may use night-vision
source: New Scientist March 27 1999 p29
Researchers from Wright-Patterson Air Force Base, Ohio, have found a protein in pythons' sensory organs found in their jaw linings. The researchers think that pythons may be able to sense infrared radiation using this protein. The same organs are present in boas, while similar structures are found below the eyes of pit vipers. The protein may allow these snakes to locate warm-blooded prey, even if it is totally dark.
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Salamander power
Salamander skin contains substance that kills bacteria
source: New Scientist September 23 2000 p21
University of Southern Louisiana researchers have found that red-backed salamander skin contains a substance that kills bacteria. The peptides were more effective than most antibiotics at killing staphylococci. Salamanders do not appear vulnerable to infections, despite biting and wounding each other. This finding could help with developing antibiotics. The findings were reported in 'Journal of Experimental Zoology', vol 287, p340.
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Grown astray
Chemical pollution could cause deformities in frogs in North America
source: Kurt Kleiner
New Scientist April 3 1999 p26
Scripps Research Institute's James La Clair is a molecular biologist who claims that frogs may suffer deformities in North America due to chemicals interfering with an enzyme, acetylcholinesterase (AChE), that affects a neurotransmitter. La Clair is unsure which chemicals are responsible. There have been discoveries of tens of thousands of frogs suffering from deformities in the US and Canada since 1995. La Clair used water from four locations in Vermont. Malformed frogs had been discovered at these sites. La Clair tried to raise tadpoles in his water samples, but they became too malformed to survive. Tadpoles from clean water started twitching if they were placed in the sample water, which indicated that neurotransmitter function was affected. La Clair was able to reproduce the malformations by using tacrine, a drug that inhibits the enzyme AChE. Embryos exposed to AChE inhibitors were found to have little fibroblast growth factor, without which they cannot develop.
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Multiple killers
Possible reasons for drop in world amphibian population
source: Kurt Kleiner
New Scientist February 26 2000 p16
There are a number of possible reasons for a worldwide drop in the population of amphibians. High levels of ultraviolet radiation, and Chytrid and other types of infections could be causes. Amphibians may have become more susceptible to infection as a result of weakened immune systems. Amphibians have previously adapted to climate change, though changes in climate may make them more vulnerable to diseases.
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See also:
Reptiles
and Amphibians: General
Books
on snakes
Books
on lizards
Books on tortoises, turtles and terrapins
Books on amphibians
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