Rabbits and Rodents: Health, disease and physiology


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Diseases in pet guinea pigs: a retrospective study in 1000 animals

Dental and skin diseases most common health problems in Czech guinea pig study

Source: Minarikova, A., K. Hauptman, E. Jeklova, Z. Knotek, and V. Jekl
Veterinary Record Volume 177: 200, July 2015

A study by a team from the University of Brno, Czech Republic, of records for 1,000 pet guinea pigs taken to a vet clinic from 2008 to 2013 has found dental and skin diseases to be their most common health problems. The guinea pigs were divided into three groups, less than two years’ old, from two to five, and more than five years’ old. Dental problems affected 363, or 36% of the guinea pigs, with males and guinea pigs of middle age most likely to be affected.  A third (33.3%) of the guinea pigs had skin problems, mainly due to mites and other parasites, with males and the youngest group most affected. They may have been infected at pet stores, where guinea pigs from different sources are mixed, making it more likely that infections can spread. Female guinea pigs more than two years old were more likely to suffer from  reproductive disorders, in particular, ovarian cysts. Reproductive disorders affected 16% of the total, or 158 guinea pigs, of which only ten were males. Fatty eye, and other eye problems were also common, affecting 150 guinea pigs. Other diseases included gastrointestinal problems, and osteoarthritis.

These guinea pigs appeared to be generally well-cared for, so there were only 40 cases of respiratory problems, which tend to be linked to poor housing. Scurvy arising from lack of vitamin C, was also less common than other researchers had previously found, in fact these owners often fed Vitamin C supplements and risked overdosing their pets.   More vet checks could help avoid undetected conditions becoming serious, and this especially applies to guinea pigs just bought from pet shops, which could have skin infections. Preventive neutering of female guinea pigs, involving removal of the ovaries, would avoid ovarian cysts. Fresh fruit and vegetables, pellets, grass and hay, can also help keep guinea pigs healthy. The calcium-phosphorous ratio is important for teeth and bones, as is exposure to UVB light or natural light, to help with metabolising Vitamin D.


Health survey of 167 pet rabbits (Oryctolagus cuniculus) in Finland

Adult pet rabbits need regular vet check-ups

Source: J. Mäkitaipale, F. M. Harcourt-Brown, O. Laitinen-Vapaavuori
Veterinary Record, Vol. 177, Nº. 16, 2015, p418

A survey of 167 pet rabbits which owners thought were healthy has been carried out at the Small Animal Teaching Hospital, Helsinki University, Finland, and has uncovered many hidden problems. The rabbits were handled by a vet in clinical examinations, and were X-rayed. Health problems were found in 118 rabbits, or 70.7% of the total of 167 rabbits. Dental problems were the most common health problem, affecting 67 rabbits, or 40.1% of the total. Spinal column problems affected 52 rabbits, or, 31.1 % of the 167 rabbits, and skin problems affected 28 rabbits, or 16.8% of the total. There were also 12 rabbits, 7.2% of the total, with eye problems. Dwarf lop rabbits were found to be especially prone to spinal deformities. Rabbits older than three-years-old were more likely to have a health problem of some sort. This applied to 51 older rabbits, or 82.3% of the older rabbits.

Rabbits are prey animals. Prey animals tend not to show distress when they are ill because it would make them vulnerable to predators, so it is easy for owners to miss symptoms of illnesses that vets can diagnose at a routine check-up. These Helsinki check-ups of rabbits that seemed healthy uncovered a high percentage of rabbits with problems. This result suggests that pet owners should take their rabbits for regular vet checks, especially older adult rabbits, so that any problems can be treated before they become serious.


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.



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. 


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. 


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.


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.


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.


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.


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. 


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.



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.


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.


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.


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.


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.


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.