Degenerative Rat Disease

Results of questionnaires concerning degenerative rat disease by Sally Clark

In the past few years three of my rats died from a degenerative disease that appears to affect the brain and neurological system. After writing an article in Pro-Rat-A I realised other people had lost rats with the same symptoms. I developed a questionnaire for owners of affected rats to fill in, in an attempt to find out more about it.

From the start it was clear that the symptoms the rats were showing could apply to more than one disease. So to be included in this survey the rats had to show symptoms in at least two out of three categories covering the rats’ awareness of their environment, their ability to eat and their ability to move and balance. This eliminated rats for example with spinal degeneration. Rats with this condition found it increasingly difficult to move around but didn’t score in the other two categories.

This gave me 54 questionnaires to analyse. There turned out to be an exactly equal number of bucks and does aged between 7 months and 3 years when they died. In the majority (46%) the symptoms increased in severity over a few weeks but for some it only took days or even hours, the average length of the illness was around a month. 4 does survived.
% Of Rats Showing Symptom Symptom
92.5% Lethargy
92.5% Inability to climb
85% Unable to hold food in front paws
83% Balance problems & tendency to fall off objects
81.5% Falling over whilst grooming
79.5% Becoming progressively more unaware/unconcerned about environment
79.5% Unable to eat solid food
74% Good appetite but problems eating
Table 1

Whilst it might be expected that a rat may show many of these symptoms when it is in a collapsed state at the end of a fatal or serious illness, in the diseases I was looking at these symptoms often appeared in the early stages when the rat looked healthy in ever other way.

Problems With Feeding
(74%) of rats kept a good appetite during their illness but had increasing problems feeding. The most obvious symptom was that they struggled and eventually were unable to pick up and hold food in their front paws. Various suggestions have been put forward as to why this happens.

The rat’s back legs and back are too weak for it to sit up and hold it’s food. Although the rats did have problems with their back legs, I’ve seen rats nearly paralysed in their back legs from spinal degeneration still manage to find ways of holding food in their front paws.
The rat’s front legs are rigid so the rat is unable to bend them to get the food to it’s mouth.

This is a symptom which has been connected to pituitary tumours, but in my survey only 18.5% of rats showed it. Even in those that did, it was often towards the end of the illness and they’d had problems feeding with their front paws from the start.
The rat can’t coordinate the paws to hold the food or feels pain, numbness or weakness in the front legs.

Whilst it’s difficult to know exactly what the rat feels this could be possible. Certainly the rats seemed to lose their ability or strength to grip with the front and back paws and this was the reason they couldn’t climb, tending to slide down the bars of their cage or down their owners’ front if they tried to climb onto a shoulder.

In 4 instances where the symptoms came on very quickly the rats’ front paws knuckled over when they moved as they pushed themselves along with their back feet, but often owners commented that even though they couldn’t feed the rats would still use their paws to clean their faces and walk around.

As well as having problems holding their food many rats progressively lost the ability to eat solid food, then lap and finally to swallow.

Problems With Movement & Balance
Many owners commented that the rat’s way of moving changed, they often appeared drunk or uncoordinated. As can be seen from the table, falling over whilst grooming or falling off objects featured for the majority of rats. 50% of rats were unable to get to their feet at all towards the end of the illness.

Problems With Awareness
For many owners the most distressing symptoms their rats had related to the fact that they became increasingly unaware and unconcerned about what was going on around them. It was often changes in behaviour that were the first symptoms to appear. Whilst some rats became withdrawn others appeared bolder because they lost their sense of danger, a few seemed to become claustrophobic in their cages.

61% of rats would move around in a purposeless way. Owners described their rats as moving like clockwork toys, if they bumped into something they would try and keep walking, needing the owner to pick them up and point them in another direction. Some got stuck in objects or tangled in their bedding.

61% of rats also seemed to be blind or deaf or unable to smell at times and 55.5% ceased to recognise or respond to their owners. At the end stages of the disease a couple of owners reported their rats squeaking out when touched as if they were startled, frightened or in pain. What was surprising considering all these neurological signs was that very few rats had seizures.

Possible Diagnosis’s
There are several diseases which could account for these many and varied symptoms.

Pituitary Tumours
This was the most common diagnosis by both vets and owners and could certainly account for many of the rats in this survey. Pituitary tumours most commonly effect older does and indeed 16 does died at over 18 months old. However pituitary tumours are considered to be far rarer in bucks and only likely to account for elderly ones yet 27 bucks had died and 13 of those were 18 months old or younger.

Although many symptoms fitted the diagnosis of a pituitary tumour very well, other symptoms which are expected to be noticed with pituitary tumours were rarely seen. These included rigidity of the legs with the rat unable to flex them, only (18.5%) and walking in circles (31%).

A head tilt was only seen in a few rats and aggressiveness, another sign sometimes seen with these tumours in only one. Some owners reported a staring coat and weight loss, but an equal number noticed the coat stayed in good condition and some rats even increased in weight.

Other Brain Tumours
Of the other tumours of the brain, Astrocytomas of the brain stem are considered the most common brain tumour in younger rats. The symptoms seen could certainly be caused by this kind of tumour, however without post mortem examinations it isn’t possible to tell which, if any tumour is present.

Older rats are most likely to get strokes and some of the symptoms would overlap with those seen in the survey. Strokes are usually sudden in onset and the body shows varying degrees of paralysis, often on one side of the body. There can be improvement although it may be painstakingly slow.

15% of rats showed one sided paralysis so strokes are a possibility. The fact that in this survey usually the symptoms came on gradually and didn’t improve and that a lot of younger rats were effected means strokes couldn’t account for many of the rats.

An infection did look possible for a few of the rats. 4 rats in one household came down with very acute symptoms within 24 hours of each other. They were all treated with antibiotics, first Baytril and then the last surviving rat was switched to a penicillin based antibiotic.

She seemed to recover but succumbed to pneumonia a few days later. These rats were knuckling over on their front paws and close to collapse from the start and it’s possible they had a form of meningitis. A viral or bacterial infection could also account for the 4 does who survived. Mycoplasma which is often responsible for respiratory disease in rats and can cause inner ear disease, although it can be treated the rat is often left with a head tilt which one doe was.

The symptoms of ivermectin toxicity are very similar to the symptoms seen in these rats. 39% of the rats had been given ivermectin to treat mites during their lifetime. However animals that react to ivermectin usually do so within hours of being dosed with it and only a few rats were dosed with it close to the time they were ill. So far ivermectin has not been reported to have a delayed or cumulative effect.

Common Factors
Some of the questions on the survey were to see if rats affected by symptoms had anything in common. The most significant similarities between the rats were the age at which they died and where they originally came from.

Age Of Affected Rats
For does these illnesses were more common in either old age or at least over 18 months old, only 6 died younger. However just under half the bucks died at under 18 months. What illness these young bucks had is far more difficult to explain.

Source Of Affected Rats
As can be seen from Table 2 rats the majority of rats showing these symptoms came from pet shops. In fact in the young rats aged 18 months and under only one came from a breeder. If you consider that many of the rescued rats may have originally come from pet shops and the homebred rats may have had parents who also came from there, pet shops are accounting for most of the rats.

Although I had replies from owners who had bought their rats from breeders. I had very little response from breeders themselves, so these figures may not be completely accurate. However of the breeders I spoke to, the opinion was that they occasionally saw this problem in elderly rats and this was backed up by the survey.

Source of Rats Percentage
Pet Shop 59%
Rescue 16.5%
Breeder 13%
Home Bred* 9%
Laboratory 5%
*Homebred – the rat was bred by the owner who breeds the occasional or accidental litter but doesn’t breed to show.
Table 2

There could be an inherited susceptibility to this disease. There are strains of laboratory rat which have been deliberately bred to be more susceptible to pituitary tumours, and it would be easy to accidentally breed in a weakness in pet rats by breeding for numbers rather than sound health. Rodent farms who stock many of the pet shops have no incentive to breed healthy and long lived rats.

In fact they are unaware of the fate of their rats once they’ve left them. They also may not be careful about how inbred their rats are. Most owners were unable to find out what had happened to other members of their rat’s family but 5 owners did report that siblings or mothers had died of the same disease.

The early environment the rats were in could also have contributed to their susceptibility to this disease. It could well be that it takes a combination of factors to trigger these problems.

No other significant similarities showed up between the rats. They tended to be fed one of the commercial rat or rabbit mixes along with fresh food. Their bedding was usually paper based or shavings.

The rat’s colour and markings doesn’t appear to be significant either, most colours were represented, although some of this data was difficult to interpret because not all owners used the standard names of colours and markings to describe their rats.

Probably one of the most common illnesses rats get is respiratory infections. Within the survey 37% of rats had had respiratory problems at some point in their life. Only 9% of the does had had mammary tumours removed which is a low number, but some of the does in the survey were quite young and the chances of mammary tumours increase as does get older. Of the drugs given prior to the illness, 33% had had Baytril which is the most usual antibiotic to be given to rats and 20% had had an anaesthetic.

Not knowing exactly what is wrong with these rats makes them difficult to help. Just under half the vets consulted thought it could be a brain/ pituitary tumour. Other diagnosis’s were inner ear infections or strokes but one poor rat was put under the cold tap by the vet as she thought he had heatstroke. The most common treatment was Baytril and steroids or just steroids. This sometimes improved the rats symptoms but only for a very short time, usually days.

It is unlikely to do any harm to try these two drugs as early on in the illness as possible if you have an affected rat. They may ease some of the symptoms for a short time. One rat also seemed more comfortable on the painkiller Meloxicam (Metacam). If you suspect a bacterial infection and Baytril isn’t effective it may be worth switching to a different antibiotic.

All the owners had tried hard to find foods their rats could manage to eat. It was also necessary as the rats became more unaware of their environment to monitor them closely as there were reports of rats falling off objects, or getting stuck or tangled in their cages sometimes fatally.

Apart from 4 rats who recovered all the rats were either euthanased or died naturally. Some rats were obviously suffering whilst with others it was more difficult to tell because they became so oblivious to everything they didn’t look distressed. My own bucks came into this category and died in their sleep. However since doing this research I would favour euthanasia as the neurological symptoms are difficult to interpret. Whilst it’s easy to tell if a rat is distressed with the symptoms of something like respiratory disease. It’s very hard to tell if they are suffering with head pain or whether the way they are experiencing the world has become distressing.

Clearly a lot more needs to be known about these diseases before we will know how to prevent them occurring. However from the research I did three general points emerged.

With such a high proportion of affected rats, particularly the ones who died young coming from pet shops. It would be advisable to buy from a breeder who keeps good health records of their stock and keeps their own rats for their full life span.

If you do have an affected rat from a breeder it is probably worth letting them know, however don’t automatically blame the breeder. Only if a breeder starts to have several rats from one family or strain affected, especially if they die young would they need to be suspicious of an hereditary condition.

In laboratory rats it has been repeatedly shown that overweight animals are more likely to develop tumours and pituitary tumours develop slower on a restricted diet. Whilst comparisons can’t always be made between pet and lab rats and very few of the rats in the questionnaire were reported to be overweight. It seems sensible to try and keep pet rats at their correct weight as there are so many health problems associated with obesity.

It’s worth being cautious in the use of ivermectin as it’s very easy to overdose an animal the size of a rat. There is also a much higher risk of toxicity if the rat is unhealthy or on any other medication.

These diseases are clearly distressing for both the rats and their owners trying to help them. My hope in doing this survey is that the more these conditions are discussed, the more clues can be found as to what they are and how to treat and prevent them. Whilst the most common diagnosis is a pituitary tumour, because post mortems are rarely done there is often little evidence as to whether this is the correct diagnosis.

To give useful information a post mortem needs to be done by a specialist who is familiar with examining rats as opposed to other species like dogs and cats. This can be expensive. The survey brought to light that there are a number of bucks suffering from this problem at 18 months old or younger and it is not known exactly which disease they are suffering from.

The NFRS has a fund for pathology investigations into unidentified diseases, and is willing to arrange and pay the cost of post mortems on bucks showing these symptoms who are 18 months old or younger, if they are owned by NFRS members. If you are unfortunate enough to have a buck affected in this way and are willing for a post mortem to be carried out please contact Ann Storey in advance for consent and advice on how to proceed. Tel: 01322 285788 Email:

Many thanks to all the owners who helped me in this research by filling in questionnaires and to Ann Storey for her advice.


Common tumours of the rat Ann Storey Pro-Rat-A supplement 1999
Rat Health Care Debbie Ducummon
Pro-Rat-A 99 pp17-18 Letter from Andrea Withers & advice from Esther Rawlinson MRCVS concerning possible bacterial infections in the CNS.
Rat & Mouse Gazette Jan/Feb 2000 Weakness in older rats: A paralysis primer. Kathy Barrett available at
Modulation of estrogen action in the rat pituitary and mammary glands by dietary energy consumption. Thomas J. Spady et al. The American Society For Nutritional Sciences Journal of Nutrition 1999 available at
Effect of diet or reproductive status on the histology of spontaneous pituitary tumours in female Wistar rats. P.H. Berry Veterinary Pathology Vol 23 Issue 5 pp610-618 1986 Available at
Genetic separation of tumor growth & hemorrhagic phenotypes in an estrogen-induced tumor. Douglas L.Wendell, Allison Herman, Jack Gorski 1996
Available on photograph of pituitary adenoma & brief description Brief info on diagnosis & treatment of pituitary tumours information on ivermectin for reported reactions to ivermectin

Sally Clark can be contacted via email at: