Rats are not as healthy as some other small mammals. If you are not prepared to spend money on vet care, please don't choose rats as your pet.
This is a fairly brief overview of some of the common illnesses. Although I've seen most of these problems, I'm not an expert and am usually guided by my vets.
It's not something you always think of when you choose rats as your pets, but it's as well to know where your vet is and what level of experience they have with rats before you need to visit in a hurry.
The following items are useful first aid items for your rat. This could be expanded greatly, but these are the basics.
Ill rats are generally less stressed when left with their cagemates, but there are occasions when they need to be removed to a hospital cage, either alone or with a gentle companion. If they feel cold to the touch, use a heat pad under one side of the hospital cage, but be sure to leave them the option of moving off the heat. If your rat is not grooming itself then you may need to wipe it down with a damp cloth, and wipe any urine away so it does not burn. Some rats seem to prefer to be with you when they are ill, so if this seems to be the case try to find a way to keep them comfortable with you, but don't forget to offer water.
I'm generally in favour of persuasion rather than force, but there are occasions when it just doesn't work. Liquid meds and pills that can be crushed can quite often be hidden in cream cheese, chocolate spread or other strong flavoured spreads, or my favourite method is to use a cube of bread and either drop liquid meds into it, or put a small amount of butter on top and pick up the powdered pill with it.
Liquid meds can also be syringed (with a needleless syringe) into the corner of your rat's mouth, if necessary while the rat is wrapped in a towel and held by someone else.
Bringing new rats into your home will always pose a risk to your current rats, but there are ways that you can reduce the risk. If you're bringing rats in from a friend who you know well and trust, and whose rats are known to be healthy, then the risk is low. If you have picked up pet shop or rescue rats from poor conditions then the risk is higher. In general, new rats should be quarantined for at least two weeks, preferably in a separate airspace, and always seeing to the new rats second. You may also wish to treat the new rats for parasites as a preventative measure. In practice, many of us don't have the space for strict quarantine and have to compromise.
Mites often appear with no apparent origin, but the assumption is that they find their way in via the substrate or food. Signs of mites include increased scratching, scabs and scratches around the neck, and sometimes flaky skin. You cannot see them with the naked eye. It often looks as though rats have been fighting when in reality they have mite infestations, so it's always worth treating for mites if your rats have bites but you haven't seen them fighting.
You may see the 'nits' or eggs as white specks in the fur, or just notice the lice as brown or orange specks marching along parted hairs.
These mites create bobbles and growths on the rats' ears and nose, spreading to the feet, tail and genitals. They are very infectious between rats.
The treatment I would recommend for all of the above parasites is Ivermectin, either in a 'spot on' form or injected by your vet. Bear in mind that this is a poison and can cause neurological damage if overdosed, so weigh your rat first and stick to the instructions on the packet.
For ordinary mites you generally only need to treat the affected rats. For lice and mange mites, I would recommend treating all of your rats.
Rats are unfortunately very good at producing abscesses. I'd advise an inexperienced rat owner to visit the vet with these, as they usually need draining before they will heal. If the vet decides to open up the abscess, it's useful to ask them to make a hole rather than a slit so that it won't heal up too quickly. A course of antibiotics can help to clear the infection, and flushing the abscess through with sterile water or an antibacterial will also help.
This is the one that everyone blames for respiratory disease, and is endemic in the pet rat population. It tends to be a slow progressive disease which lays the way for other secondary infections of the lungs. It can also be a cause of pyometra.
This is a nasty bacteria which can cause a very quick death when it infects the lungs. The symptoms are silent laboured breathing and weight loss, often after a trigger event such as an operation or treatment with steroids. It causes progressive lung abscesses and is often only diagnosed if a post mortem is done. If the rat does survive then it is left with permanent lung damage. This bacteria can also infect other organs, again producing numerous abscesses.
Sialodacryoadenitis or Rat Coronavirus is generally at a fairly low level in the pet rat population, but every now and then it flares up and gets passed around via pet suppliers and rat shows. Symptoms can include swollen eyes, respiratory distress and weight loss, sometimes leading to death.
This is another disease often passed on via pet suppliers and rat shows and produces flu-like symptoms and dehydration, sometimes leading to death. Antibiotics can be useful against secondary infections.
Does can suffer from pus or blood in the uterus, showing as bleeding or as a swollen abdomen. Antibiotics can sometimes clear up bleeding, but spaying is the only sure treatment.
Rats' tears contain a red stain called porphyrin, which acts as a useful sign when they are having eye problems or upper respiratory infections. If this persists then a visit to the vet is in order.
This is due to a problem with insulin production, with the symptoms being increased drinking, and weight loss. The rat should have access to water at all times and be fed a diet with as little sugar and refined carbohydrate as possible. It is possible to use injected insulin to treat this, under a vet's advice.
The symptoms, fairly obviously, are the head tilted to one side and 'rolling' or circling when trying to walk. This is usually an inner ear infection and generally responds to steroids and antibiotics, although the sooner it's treated the more chance of the tilt going away. Often the underlying infection is cured but the tilt remains, although it sometimes improves over time.
These are generally just fatty lumps under the legs or on the lower neck. They don't tend to be cancerous and can be removed fairly routinely if they're not left to become enormous and are not too close to the genitals. In my experience they don't always come back if removed and if the rat is otherwise fit and healthy I see no reason why they shouldn't be removed.
There are, of course, other tumours that are found to be cancerous. Again, if the rat is fit and healthy and the vet feels there is a good chance of removing the tumour, I would go for removal. If the tumour looks cancerous or returns quickly, then it's time to think again.
These cause neurological problems such as progressive loss of grip with the hands, and can be detected at an early stage by touching the rat's head and seeing if they 'head bump', pushing up against the pressure.
The Zymbal's gland sits at the base of the ear canal. The tumour often shows up as a fairly ordinary abscess just below and behind the ear, or sometimes as a pus discharge from the ear. The abscess doesn't clear, and if operated on then a malignant tumour is found beneath that is producing the infected material, and is impossible to remove entirely.
Hind leg degeneration is usually a disease of older rats, usually coming on slowly with just a slight weakness and knuckling under of the back feet at first, progressing to paralysis of the legs. When it comes on quickly I would suspect an injury or a brain problem. There are various ideas for treatment, none of which seems to work on all cases. NSAIDs can help some rats, but can hasten kidney disease in others.
Rats' teeth are normally orange, so this is nothing to worry about. The most common problems are broken or overgrowing teeth. If your rat breaks a tooth, you may have to have the opposing teeth trimmed until the broken tooth regrows. Sometimes teeth become misaligned as rats grow older and may have to have regular trims every two or three weeks.
Diseases that you and your other pets can share with your rats)
This is a fungal infection that can give your rats a circular patch of bare skin, and on you produces a circular inflammation on the skin that spreads outwards like a toadstool ring. It's passed easily from person to person and from person to rat and back again, so you can never be really sure who brought it home, but you're the one who's been out in the infectious world.
Cuts or scratches on both humans and rats can pick up staph infections, and you can pass them to each other, so be aware that this is what a skin infection may be.
Rats have been known to pick up Bordatella from live vaccine used on dogs, so it's a good idea to keep your rats quarantined from your dogs when they've had their kennel cough vaccination.
Some pet rats in the UK have been found to carry Hantavirus. This doesn't seem to cause the rats any problems, but can cause fever, headaches and renal problems in humans. It seems to usually be a mild infection but can cause serious illness and is probably passed on by inhaling dust while cleaning cages.
You're not likely to know whether or not your rats have this, but again it's something that you're more likely to catch from a pet that goes outdoors than from a caged pet rat. In humans this is a mild infection that is only really a problem if you're pregnant. The usual advice is to avoid handling pet faeces while pregnant, or use it as a good excuse to get someone else to clean cages for you.
I've included this because it's something that people think of in connection with wild rats. It is not commonly found in pet rats.
This is a bacterial disease which crosses the species barrier to affect many animals, including rats and humans and also cattle, dogs, horses and pigs. Pet rats have very little opportunity to contract this disease, and you are probably more likely to catch it from a pet dog that has been swimming in the local river than from your pet rat.
The symptoms in humans are a 'flu-like' illness which can last from a few days to a few weeks, and which like flu is very occasionally fatal. There are around 2 or 3 human deaths from Leptospirosis each year in the UK, and it is mostly a danger to farmers and cavers who can come into contact with the urine of infected animals.