Common Diseases of Rats

This article looks at each body system one by one and discusses common diseases that can occur in rats systematically.

The typical ‘sick rat’ appearance, of a hunched back, unkempt hair and loss of appetite and thirst is described, as a non specific sign of disease.

Rats can also produce ‘red tears’, which is an indicator of stress or illness too.

Diseases such as diarrhoea, dental disease, kidney disease, mange and tumours are discussed.

The disease is described, along with its most common symptoms, and a brief description of what your vet may do to treat the particular disease, and the prognosis for your rat.



The Common Rat (Rattus norvegucus) is a very common and popular pet in the UK. They make excellent pets for children as they rarely bite and are relatively intelligent and easy to train.

This article will take you through a number of common diseases of the pet rat categorised in body systems and the most common symptoms seen with each disease.

Most diseases in rats are displayed unanimously as the ‘sick rat’ appearance. You will find your pet sitting quietly with a hunched appearance and showing little interest in their surroundings. Your rat’s coat will be ruffled and ungroomed and they will begin to lose weight as they are eating and drinking less.

If you see your pet rat behaving in this manor, then you would be advised to take your pet to see his/her veterinarian.

Another sign of generalised disease in addition to the ‘sick rat appearance’ can be the presence of ‘red tears’ (Chromodacryorrhoea). This is red ocular and nasal discharge which is produced as a non-specific response to stress and disease.

Other symptoms specific to the disease are listed below under the disease heading.

Digestive System

Dental Disease

The incisors are generally the only teeth in the rat to cause a problem. They can overgrow due to malocclusion; meaning they do not meet so they cannot then be worn down. Causes of malocclusion include cage gnawing or it is an inherited disposition.


–       weight loss

–       reluctance to eat/food left in bowl

–       difficulty eating

–       saliva staining on face

Your vet may advise you to have your pet’s teeth trimmed regularly in order to prevent difficulty in eating and pain.


As in humans and other animals, enteritis is characterised by diarrhoea.

The most common cause of enteritis in rats is a sudden change in diet or an increased amount of rich food.

Other causes include Salmonella and other bacteria. These produce very severe diarrhoea and a very sick rat and your vet may recommend that your pet be euthanased, as Salmonella also poses a risk to human health.

Small worms that are residing inside your rats’ guts may also cause mild diarrhoea.

Most veterinarians will prescribe a short course of antibiotics and some electrolytes to go into your rat’s water to provide rehydration.

Respiratory system

Respiratory disease is very common in rats, particularly as they get older.

The cause is often viral but then bacteria can colonise following the initial viral attack on the lungs.

High levels of ammonia also contribute to the incidence of respiratory disease as it is a respiratory irritant. Ammonia levels can be reduced by regular cage cleaning, with special attention being paid to your rat’s toilet area.

Respiratory disease is more commonly seen in groups of rats, but is not unseen in the individual pet.


–       runny nose (rhinitis)

–       difficulty breathing (dyspnoea)

–       sneezing

–       noise on breathing

–       weight loss

–       red tears

On noticing these signs, it is necessary to visit your veterinarian.

You will likely be prescribed a short course of antibiotics. If the disease progresses, other drugs to help your pet breath easier such as a bronchodilator may also be prescribed.

Rats can often live for some time, even with the chronic form of the disease, with symptoms being treated as and when they occur.

Urogenital System

Kidney Disease

This is again, another fairly common disease seen in ageing pet rats. Chronic kidney disease is not one that can be treated and cured, but rather, can be managed by your vet.

Dietary factors including high protein diets are known to help contribute to progression of disease.


–       Increased drinking/ Thirsty (Polydispsia)

–       Increased urination (Polyuria)

Some ways of managing this disease include decreasing the protein in the diet of your pet rat, which your vet will advise you on and trying to increase the water which your rat drinks.

Mammary Tumours

High percentages (up to 50% in laboratory rats) of female rats develop mammary tumours in later life. These tumours are usually benign, but can still grow to become rather large.

The treatment option your vet will advise you on is surgery to remove the mass.

The surgery offers a good prognosis if the whole of the mass is excised.

If surgery is not chosen, then your vet will advise that your rat be put to sleep when the mass becomes too large and begins to restrict movement, or if it becomes ulcerated, as both of these will reduce the animals’ quality of life.

Skin Disease


The infestation of your rats’ skin by mites is more commonly known as mange.


–       itching

–       hair loss

–       thinning of hair

–       papules

Your vet will usually prescribe you Ivermectin, which will kill all stages of the mites’ lifecycle. This can be given as a one off injection by your vet or can be put into your rats’ drinking water or applied onto their back as a spot on treatment every one to two weeks.


These often occur following a bite wound or from another trauma causing a small wound.

You will see abscesses as a lump under your rat’s skin, or as a ruptured abscess with pus exuding from the hole.

Don’t try and treat these yourself with salt water or similar, as a high degree of bacteria is contained within these that need antibiotics to treat.

Your vet may advise you to clean the site of the abscess if it is ruptured, but it is likely they will give you some suitable cleaner to do this with.

If the abscess has not ruptured then your vet may advise that surgery is necessary to excise it.

Neurological Disease


This is characterised as a continuous circling, caused by a lesion in the brain or internal that can occur in rats of all ages, but is fairly uncommon.

Treatment is usually unrewarding, but your vet, depending on your wishes, may like to try with a large dose of steroids as this has been found to be effective treatment in some acute cases.


Occur quite commonly in pet rats, mostly of the tail and limbs. These can occur if the animal is trapped in the cage door or accidentally dropped.

It is usually obvious when a rat has a fractured leg as it will be limping. If a tail is fractured then it may appear to be at a crooked angle and may have notable bruising/abrasions.

Amputation of a leg or of the tail is usually well tolerated and will likely be the treatment of choice that your vet will recommend.


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