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Rabbits and other Rodents: Health, Disease and Physiology
SUMMARIES OF ARTICLES ABOUT RABBITS AND OTHER RODENTS
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High fat diet leaves its mark on sperm
Diet changes can affect mouse sperm
source: Wendy Zukerman
New Scientist vol 212 no 2843, December 17 2011 p12
Obese mice fed on bad diets sire offspring that are likely to suffer from insulin resistance, which means that epigenetic changes resulting from diet may persist in sperm cells. Maria Ohlsson Teague with Michelle Lane from Adelaide University, Australia, has found that diet affects the rate of metabolic disorders in offspring.
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Ma's gene does different things to pa's copy
Function of mice gene may depend on which parent it comes from
source: New Scientist vol 209 no 2797, January 29 2011 p8
The function of imprinted genes in mice may differ according to which parent a gene comes from. The expression of most genes is in pairs, with both parents contributing a copy. Imprinted genes differ in that only a single copy is expressed, or turned on. Grb 10 is an imprinted gene, which is expressed in the brains of mice if a copy comes from the father, but elsewhere if it comes from the mother.
Maternal Grb 10 can curtail foetal growth. Mice which lacked the paternal gene were overzealous groomers, to the extent that they removed fur and whiskers from their mates. The paternal gene may thus moderate grooming behaviour, argue researchers Andrew Ward and team from Bath University, UK.
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Encephalitozoon cuniculi in pet rabbits
Encephaliitozoon cuniculi found among pet rabbits from North
Yorkshire, UK
source: F.M. Harcourt-Brown and H.K.R. Holloway
Veterinary Record vol 152 no 14, April 5 2003
starts p 427, 5 pages long
Encephalitozoon cuniculi is one of the Encephalitozoon species, and mainly
affects rabbits, usually infected by eating food contaminated with infected
urine. E cuniculi spores can survive at room temperature for four weeks minimum.
Spores multiply in cells, which rupture to release them, causing inflammation,
which in turn can lead to lesions. E cuniculi infections can affect other
animals such as guinea pigs, hamsters, cats, dogs and humans, with infections
reported for AIDs patients whose immune system is suppressed. Infected rabbits
may show no symptoms. The most common symptom in rabbits is a head tilt due
to vestibular disease. E cunicli can also cause kidney disease, cataracts
and uveitis. Laboratory rabbits undergo screening, with infected animals culled.
This study reports testing of 125 pet rabbits by a N Yorks veterinary practice,
England, from 1997 -2002, with subsequent treatment of affected rabbits. Rabbits
showing symptoms of E cuniculi accounted for 87 of the total. Rabbits living
with seropositive companions accounted for 12, and 26 of the sample underwent
tests during a health check.
Treatment varied according to the symptoms, with no parasiticidal treatment
initially given, until 1998, when fenbendazole and albendazole were used.
Fenbendazole alone was used from 2001, in line with a study published that
year. Owners decided whether rabbits with no symptoms should be treated.
Eight rabbits were seropositive of the 12 tested because a companion was
seropositive, while six (23%) were seropositive of the 26 tested during a
more general health check. Neurological signs affected 38 rabbits, and 20
of these lived over six months, with many still showing symptoms but less
severely affected. Five rabbits did not receive treatment for neurological
signs and still survived, three of them recovering completely. Seven rabbits
just suffered ocular lesions, and all of these survived. Three rabbits with
renal failure were euthanased.
Antibodies were found in 74 of the total of 125 rabbits, though the results
did not differentiate between rabbits with active or latent infections, and
those that had simply had an antibody response but no longer had an infection.
Little work has been carried out on treating rabbits with Encepalitozoonosis.
Some rabbits with neurological symptoms were treated with corticosteroids
to prevent an inflammatory response, though corticosteroids could hamper recovery,
since they are immunosuppressive.
E cunciuli appears to be an important cause of disease affecting pet rabbits
in the UK. More research is needed on how the disease spreads, and there is
a need for diagnostic tests as well as licenced products to prevent and treat
the disease, especially given its zoonotic potential.
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Anorexia in rabbits: 1. Causes and effects
Why rabbits may suffer from anorexia, and the effects
it has on them
source: Frances Harcourt-Brown
In Practice vol 24 no 7 July/Aug 2002
starts p358, 8 pages long
Pet rabbits are often taken to the vets with anorexia, which may have a number
of causes. They can die if the anorexia is left untreated, so it is important
to diagnose the condition promptly. Treatment and diagnosis will be discussed
in part 2.
Rabbits' digestive systems are geared to digesting a lot of fibrous food.
Their digestive strategies include ingesting caecotrophs, or pellets containing
vitamins, fatty acids, and amino acids, directly from the anus. Caecotrophs
are also called soft faeces, and are usually expelled when rabbits are resting,
while hard faeces are formed when rabbits are feeding. The excretion phases
follow circadian rhythms, which can be affected by a number offactors such
as stress, food type, lactation, and age. Caecal microflora are important
for absorbing and producing volatile fatty acids. They can be affected by
antibiotics. Gut motility is important for digestion, and can be affected
by several factors such as fat and carbohydrate levels in diet. High fibre
diets have a beneficial effect on gut motility, stimulate caecotrophy and
appetite. Giving rabbits hay to eat can prevent boredom, and help prevent
them from eating things that could harm them, like carpet fibre.
Stress can affect digestion in a number of ways, such as inhibiting gut motility.
Rabbits that are affected by slow gastric emptying may suffer dehydration,
and the stomach contents may become impacted. Slow gut motility can lead to
pain as gas is accumulated, and pain can in turn increase stress. Rabbits
may also suffer from acidosis, and anorexia and depression are common among
rabbits with ketoacidosis, which is stress-related. This can result in kidney
and liver failure if left untreated, and lactating and pregnant does are especially
vulnerable.
Rabbits may also suffer from problems with their teeth and gums, and dental
problems may lead to wounds on the rabbit's tongue. Dental problems may have
a number of causes, including teeth being clipped incorrectly.
Caecal impaction can result from rabbits eating cat litter. They may also
suffer from intestinal obsructions, especially breeds with long hair, which
may ingest hair as felted pellets while grooming themselves. The effect of
ingesting hair can be sudden. Dried pulses can also obstruct the intestine.
Young rabbits may also suffer from mucoid enteropathy, with diarrhoea and
mucus excreted, and the rabbit grinding teeth, possibly as a result of pain.
Enteritis can be found in lab rabbits, though is less often found among adult
pet rabbits. Kidney disease can also lead to anorexia, and may be caused by
parasites.
Lab investigations, exploratory surgery, and radiology may be needed to assess
the cause of anorexia, but these are the most common causes.
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Anorexia in rabbits: 2. Diagnosis and treatment
Diagnosing and treating anorexia in rabbits
source: Frances Harcourt-Brown
In Practice vol 24 no 8 September 2002
starts p450, 13 pages long
Rabbits need to be treated rapidly if they are suffering from anorexia, and
this applies especially to does that are pregnant or lactating. Rabbits that
look depressed and in pain and have suddenly stopped eating may have abdominal
obstructions and need an operation, since rabbits can't vomit. Rabbits also
need treatment rapidly if they have liquid diarrhoea, though if they just
have uneaten caecotrophs these are not life-threatening. Rabbits may also
go off their food if they lose a companion, or are deprived of water.
Wet or soiled fur may be a sign of digestive problems or urine infections.
Dehydrated rabbits have wrinkled skin. A rabbit's abdomen should be felt very
gently, since it's easy to damage the rabbit's abdominal organs. Rabbits with
dental disease tend to have wet chins, and may need an anaesthetic for a close
examination inside their mouths. X-rays can help in diagnosing problems. It's
possible to get some rabbits to keep still as though they were in a trance
by putting them on their backs and talking to them softly while stroking them
very gently. The rabbit can then be rolled on its side for an X-ray.
Blood samples can give useful clues. Rabbits with anaemia may have abscesses
or dental trouble. Changes in blood glucose levels can be caused by a number
of conditions, such as stress, or intestinal obstruction, though it is uncommon
for rabbits to suffer from diabetes mellitus.
There are some general guidelines that should help rabbits with anorexia,
such as providing hay, fresh grass, and tempting fibrous foods, and keeping
the rabbit warm and quiet to help keep stress levels down. Painkillers, such
as carprofen, can also help. Rabbits need syringe feeding if 24 hours have
passed without their eating.
Specific treatments depend on the cause of the anorexia. Pineapple juice
can help rabbits with hairballs, both by providing energy, and by helping
the stomach contents to move through the digestice system. Dental problems
should be treated very carefully, to avoid damaging the rabbit's mouth. Rabbits
with kidney disease have a poor prognosis, but restricting calcium levels
in their diet can help.
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Polyomavirus infection in hamsters and trichoepitheliomas/cutaneous
adnexal tumours
Tumours in hamsters linked to polymavirus infection
source: A.P. Foster et al
Veterinary Record vol 151 no 1, July 6 2002
starts p13, 5 pages long
Hamsters sometimes suffer from hair follicle tumours, which are usually seens
as non-metastatic and benign, though the hamster may be adversely affected
if there are several growths, and/or they are large. A link has been discovered
in laboratory hamsters between these lesions and hamster polyomavirus infection.
This study investigates tumours found in 22 pet hamsters living in five colonies.
Two of these hamsters were also affected by lymphomas. Electron microscopy
failed to reveal virus particles, though immunoblot analysis and ELISA found
virus-specific antibodies in all the affected hamsters. The hamsters seemed
to be suffering from multiple skin tumours as a result of a polyomavirus ,
though it is not clear where the infection came from.
The incubation period can vary between four and eighteen months, from when
the hamster is infected to when nodules develop. There is no cure for this
sort of infection, and hamsters can be infected without actually showing skin
lesions. It appears to be spread through urine, and disinfection products
can be used to deal with it, for example products used to tackle parvovirus.
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Degrees of aversion shown by rats and mice to different
concentrations of inhalational anaesthetics
Study of effects of inhalational anaesthetics used on
small rodents
source: M.C. Leach et al
Veterinary Record vol 150 no26, June 29 2002
starts p808, 8 pages long
It is important to assess how humane anaesthetics are that are used with
rodents, since many procedures require a general anaesthetic. Little work
has been carried out on distress suffered by animals and how they initially
react to anaesthetics. This research was carried out at Birmingham University,
England, using 60 mice and 60 rats. Their levels of aversion were measured
using different agents at high, medium and low concentrations in test chambers.
The animals were able to enter and leave the test chambers when they wanted
to. The rodents' aversion levels were measured by how long they spent in these
chambers, and their initial withdrawal.
Both mice and rats showed most aversion to carbon dioxide. Rats showed least
aversion to halothane, and mice showed least aversion to enflurane and halothane.
Their reactions to isoflurane were also tested, and they were less aversive
to this agent than to carbon dioxide. Rats showed greater levels of aversion
the higher the concentrations, though mice tended not to show more aversion
to agents at high than at medium concentrations.
Some aversion was found for all four agents. Medium concentrations of halothane
(rats) or halothane or enflurane (mice) appear to provide the best balance
in terms of minimizing distress, and rapid induction.
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Epidemiology of viral haemorrhagic disease and myxomatosis
in a free-living population of wild rabbits
Study of mxymatosis and VHD in Spanish rabbits
source: C Calvete et al
Veterinary Record, vol 150, no 25 June 22 2002
starts p 776, 7 pages long
Wild rabbits are important in Spanish ecosystems, and are also hunted for
sport. The population dropped after mxymatosis arrived in the 1950s, then
rose until the 1980s, when viral haemorrhagc disease (VHD) led to many local
populations being wiped out, and numbers overall to drop. There have been
efforts to restock, but their success or otherwise is not clear, and research
on these diseases has tended to focus on domestic rabbits.
This study of the epidemiology of VHD and mxymatosis in wild rabbits was
carried out from January 1993 until June 1996. The location was 250 hectares
in the Ebro valley, an area with a semi-arid climate, small fields, and scrub
on hillocks where burrows are common. Rabbits were trapped and blood samples
taken, and dead rabbits were also examined. Rabbits were also radiotagged.
Rabbits were most likely to die from predation or disease, though some died
from flooding. The incidence of disease may be masked by diseased animals
being caught more easily by foxes and raptors.
All adult rabbits had antibodies to mxymatosis, and only young rabbits were
found with clinical signs of the disease, and this only in spring and winter.
Most young rabbits were infected before reaching a year old, and probably
caught the disease through fleas.
The population density increased during the study, as did the prevalence
of antibodies to VHD. This could be because a less lethal form of the disease
had appeared, or it may be that there were fewer predators, with foxes having
been affected by sarcoptic mange. Adult rabbits did die from VHD, especially
during the winter. This may be because they tended to use their burrows more
during the winter, and were more likely to be infected in their burrows.
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Rise and shine
Research on hibernating squirrels may explain why they
wake for short periods
source: Stephen Leahy,
New Scientist May 4 2002 p16
Research on ground squirrels has helped to explain a mystery relating to
hibernation, why chipmunks, marmots, ground squirrels, and other true hibernators
wake up regularly. This is difficult to understand since waking up costs the
hibernators a lot of stored energy. They apparently need to wake up as a way
of boosting their immune systems, and checking themselves for pathogens and
parasites.
Hibernation is a way of conserving energy at a time when there is little
food about. Badgers and bears have short drops in temperature, while true
hibernators can have temperatures at five deg C for several consecutive weeks.
The golden-mantled ground squirrel from California hibernates for some five
to six months, and its heart beat slows, beating only twice a minute. This
squirrels wakes up around once a week, and undergoes a temperature rise to
37 deg C during 12 to 16 hours. These periods of wakefulness can account for
some 80% of the squirrels’ energy budget for a winter.
Ohio State University’s Brian Prendergast and his team studied 31 squirrels,
some of which were injected with a lipopolysaccaride, the constituent of dead
bacterial outer cells. The squirrels did not react with a temperature rise
until they awoke, indicating that their immune systems were not operational
while they hibernated. The temperature rise only occurred once the animals
awoke, and then their bodies responded as if they had only just received the
injection.
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Wildlife
Rabbits infested by coccidial parasites
source: Veterinary Record vol 150 no 3, January 19 2002 p64
A population of several hundred wild rabbits in Penrith, UK, has been infested
by coccidial parasites. Some 10% of the rabbits are affected, probably the
young rabbits from these warrens. The affected animals have rough coats. Two
of these rabbits have been shot for further investigation, and liver lesions
have been found, with serious infestation by parasites, probably Eimeria stiedae.
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Fast breeders
Climate change could lead British rabbits to become more
susceptible to rabbit haemorrhagic disease
source: Deborah MacKenzie
New Scientist July 28 2001 p15
Rabbit haemorraghic disease (RHD) can affect both captive and wild rabbits,
and was linked to the deaths of 64 million farmed rabbits in Italy in 1986.
It is thought to have spread from Central Europe, and had reached China by
1984, with 140 million domestic rabbits dying in an outbreak there. Spain
has also been affected, and wild rabbits have been imported into Spain due
to a shortage for hunters.
RHD has yet to make much impact in Britain, though it was first noted there
in 1994. Stirling University’s Peter White argues that this may be due
to a natural vaccine in the British rabbit population, in the form of a variant
of the RHD virus that does not have much effect on rabbits. Populations with
a high average age tend to have more rabbits with immunity from this natural
vaccine. Slower rates of reproduction tend to mean a higher average age for
rabbits.
Rabbits tend to reproduce faster when it is warm, and this may explain why
rabbits are worse affected in southern Europe than in Britain. They are also
worse affected in southern England than in Scotland. There will be a smaller
percentage of immune, older rabbits in warmer areas, allowing the disease
to spread more easily. Global warming could, thus, lead to a decline in rabbit
numbers in Britain. White’s research is reported in ‘Philosophical
Transactions of the Royal Society B’, volume 356, p1087.
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Fire crew’s oxygen mask saves hamster
Hamster saved by firemen after suffering smoke inhalation
source: Paul Kelso
Guardian June 11 2001 p9
A hamster called Pikachu has been saved by firefighters after suffering smoke
inhalation at a house blaze in Nottingham, England. He was carried out from
his home unconscious after a fire in the kitchen, caused by a washing machine
exploding. The fire was contained in the kitchen because the family closed
the kitchen door. The firefighters gave Pikachu a heart massage using fingertips,
and put him in an oxygen mask. Pikachu’s previous adventures have included
eating rat poison, which made his teeth go blue, and a five-day absence from
his cage, after which he returned covered in black dirt.
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What does a rat dream about?
Research on how animals such as rats dream and form memories
source: Sanjida O'Connell
Independent, Review section February 23 2001 p
Research has been carried out on the way that rats and other animals sleep. Massachusetts Institute of Technology professor, Matthew Wilson, and Kenway Louie, a graduate student, trained rats to run round a track. They measured that rats' brain activity while they performed the task, and also while the rats were asleep. Some half the rats exhibited the same type of brain patterns while they were asleep as while they were awake. The researchers could even guess what the rats were dreaming about, such as their location and whether they were standing or running. The brain activity was found to be concentrated in the hippocampus, which is linked to memory formation. Sleep appears to play a role in the way that memories are formed. Memory formation takes place in two stages, while animals are undergoing experiences, and then through consolidation, which is important for forming long term memories. Other research on the way animals dream backs up these findings on rats.
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Tom dreams of Jerry
Research on memory formation and dreaming in rats
source: Alison Motluk
New Scientist February 3 2001 p19
Matthew Wilson and Kenway Louie from Massachusetts Institute of Technology have carried out research on rats' neuronal activity while performing a task, and while asleep. They used four male rats with microelectrodes implanted into their hippocampi. The rats had learnt to run along a track, with food rewards at checkpoints. Patterns of spikes could be seen that could be linked to the rats' location on the track. The rats were also monitored when they were asleep, and their brain activity during REM sleep was found to resemble their activity while on the track on 50 per cent of the recording sessions. The memories were replayed at the same speed as the original experiences. Wilson argues that his work shows that animals can re-evaluate experiences while asleep, and he believes that mamories may be laid down in REM sleep through animals reactivating experiences. Dreams may allow animals to bring together related experiences occurring at different times. This work was reported in 'Neuron', vol 29 p145.
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Bugs for bunnies
Research on viruses that can infect rabbits
source: Joanna Marchant
New Scientist August 26 2000 p21
Researchers in Australia and Spain have been working on two different viruses which can infect rabbits. The Spanish researchers have developed a genetically modified virus that can immunise rabbits against myxomatosis and rabbit haemorrhagic disease. Spanish researchers are concerned that their rabbit population is low, which threatens natural predators. The Spanish Federation of Hunters has part-funded the work. The virus can be passed from from the first infected rabbits to other rabbits, but is not passed on a second time. The work has been carried out by the Centre for Investigation into Animal Health, Madrid, and reported in 'Vaccine', vol 19, p174. Meanwhile, Australian researchers have developed a virus that can make rabbits infertile, or kill them - reported in New Scientist, October 7 1995, p8. Australian researchers see rabits as a pest, in contrast to Spanish researchers, who want to increase their rabbit population.
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