Common Health Problems in Rats – Part 1: Myco, Respiratory Problems & Heart Disease

One of the downsides to keeping pet rats is that they are prone to illness. Although it is possible to breed against a lot of rat health problems, this requires expertise, effort, and careful record-keeping. That generally doesn’t happen where rats are being bred en-masse for sale. As a result, many rat owners will see health problems in their pets well before old age. 

Today we’ll take a look at one of the most common sets of rat health issues – respiratory problems and their underlying causes: infections; husbandry and allergies; and heart disease. 

Disclaimer – this article should not be used to replace veterinary advice. If you suspect your rat to be ill, you should always seek advice from a qualified vet.

Respiratory disease / chest infections in rats

Looking for the signs and symptoms of respiratory disease in rats? Check our list here.

Myco in rats – Mycoplasma infections

The main cause of respiratory issues in rats is infection with Mycoplasma bacteria, commonly referred to as “myco” in the rat community. All rats (and most humans) carry these bacteria in their noses from birth. Most of the time, that doesn’t cause a problem – the immune system and the rest of the bacterial flora in the body keep them under control. However, if a rat’s immune system isn’t very good at this – because of another medical problem, stress, or just because the rats in their line haven’t been selected for resistance to respiratory problems – then the infection can flare-up. This often starts in the nose, but can move rapidly to the lungs, causing life-threatening pneumonia if not caught and treated appropriately. The most obvious symptom is a snotty or grunty noise on breathing, but some infections can be silent without a stethoscope so it is also important to keep an eye out for behavioural changes, lethargy, labored breathing or abdominal breathing, and gasping. 

Myco infections come with a nasty twist: although we most often become aware of them as acute flare-ups causing pneumonia or other obvious symptoms, they also act as a chronic infection, often at a sub-clinical level. This type of infection doesn’t show many symptoms, but it does cause inflammation of the lung tissue, creating tissue damage, scarring, and consolidation (areas of scarring in the lungs that can’t absorb oxygen). Over time this reduces the ability of the lungs to absorb oxygen. That’s why a rat who has had one myco flare-up will often go on to have more, and why the disease usually worsens in older rats. It’s also why early treatment is very important.

Treatments for myco

The number one line of defence against mycoplasma is an antibiotic course prescribed by a vet and given early in the first flare-up to nip it in the bud before pneumonia develops. It’s important to treat before the issue becomes life-threatening as rats are very good at hiding pain, so by the time they look lethargic and seriously ill, they have lungs full of fluid and may not survive. Early treatment also reduces the risk of lung-scarring and future flare-ups.

If you believe your rat has a chest infection it is important to get them examined by a qualified vet as soon as possible.

There are a lot of different antibiotics out there and they don’t work equally well for all bugs. Myco is unusual, because unlike a lot of bacteria it doesn’t have a cell wall. That means that drugs like clavamox and trimethoprim sulfa, which are common veterinary antibiotics that work by disrupting bacterial cell walls, aren’t effective against it.

The most commonly prescribed drug for myco infections is enrofloxacin, often sold under the name of baytril. In more severe infections, this is often used in combination with doxycycline, as the two drugs have complementary effects. Doxy has a secret weapon – as well as preventing the bacteria from reproducing, it also has an anti-inflammatory effect which helps prevent long-term scarring.

For difficult infections that don’t respond to baytril and doxy, your vet may use drugs such as azithromycin (sold as Zithromax and most effective in young rats), pradofloxacin (sold as veraflox – a more recently developed drug in the same family as baytril), and tulathromycin (a drug originally developed to treat myco and pasturella in farm animals, sold as draxxin and given by injection). They may also choose to combine a drug that treats myco with a broad-spectrum antibiotic like amoxycillin to address secondary mixed infections such as pasturella. 

Each vet will have their own preferred approach to medicating rats, depending on what they have seen work before. Our vets mostly use one or a combination of enrofloxacin, doxycycline and tulathromycin depending on the medical history of the rat and the severity of the infection. They like to combine the antibiotics with meloxicam, an anti-inflammatory painkiller, both to reduce inflammation in the lungs and to provide symptom relief. Where the rat has a lot of mucus, they often also prescribe a bronchodialator such as ventolin or nuelin.

Regardless of what drugs are used, there are some rules of thumb:

• Antibiotics should never be given in the water bottle, as this prevents accurate dosing of the sick animal and may result in healthy animals receiving unnecessary antibiotics. That encourages drug resistance and is a very bad thing.
• Antibiotics should also always be given for the full length of time your vet tells you, no matter how quickly the rat recovers. If you don’t complete the full course, the bacteria that are more resistant to the drug are likely to survive and cause a new, harder to treat, infection. We never do a course of less than 10 days and it is usually 3-4 weeks.

Myco can only be effectively treated with antibiotics. Other treatments such as bronchodialators, nebulisers, and anti-inflammatories can be very helpful in managing symptoms, reducing long-term damage, and providing the rats with relief, but they can’t cure the underlying infection. Use of “immune-boosting” foods and herbs is fine (as long as they are rat safe of course), but again, if the rat already has a chest infection, they can’t cure it. If you are giving your rats any supplements, remember to tell your vet.

Other respiratory infections in rats

Mycoplasma is not the only bacteria that can cause a respiratory infection in a rat – plenty of other bugs can flare-up too. An important one to be aware of is Corynebacterium kutscheri (CK). This is another bacteria that most rats carry, and which flares-up opportunistically when a rat has experienced physical stress. It’s an especially nasty infection as it causes hard abscesses in the lungs. As the pus is thick, it doesn’t make the wet grunty noises we usually associate with respiratory infection, and so can go unnoticed until the rat develops laboured breathing. It develops rapidly, and is hard to treat, as antibiotics struggle to penetrate the abscessed tissue. CK has a high fatality rate in rats as even when the bacteria are successfully treated, the damage done to the lungs is severe. We have had most success with a combination regime of doxycycline and amoxycillin, and supportive oxygen.

Respiratory issues caused by viruses

Another source of infection is viruses. The prevalence of these depends on what country you live in – Australia has very few problematic viruses circulating in the pet rat population, whereas the US and Europe have several that require management. The most common are are SDAV and Sendai. SDAV causes swollen glands as well as respiratory issues and infected rats may show bulging eyes.

Unlike the common bacterial infections, which are normally active flare-ups of bugs all rats carry, viruses are contagious between rats. Transmission is usually by airborne droplets, and unfortunately, you can’t make rats wear masks! Outbreaks most often occur when rats from different origins are mixed together, for example at shows, or by the sale of rats from an infected pet shop, breeder, or rodent farm. Just like humans with flu or covid, a rat with a virus can be infectious well before symptoms become obvious, meaning that the virus can infect your whole group before you know it is there. 

If you live in a country where outbreaks occur, the only effective defence against the spread of these viruses is conscientious quarantine of new rats brought into the house (they need to be isolated in a completely separate airspace to the main group), of rats who are going to mix at shows or visit other owner’s homes, and of any rats who have been infected. The recommended quarantine period is usually 2-3 weeks.

Viruses themselves are hard to treat in rats, so the main approach is supportive therapy with anti-inflammatories, fluids, easy to digest foods, and oxygen as necessary, along with medication for secondary bacterial infections (myco flare-ups during viral infections are extremely common). In a viral outbreak it is normal for several rats to get sick at once.

Respiratory problems and allergies from husbandry

Rats have very sensitive respiratory systems, which means they can be susceptible to external triggers – a bit like humans with hay-fever and asthma. The biggest husbandry issue causing respiratory problems in rats is ammonia build up. This results from:

• urine, faeces and soiled litter not being cleaned away regularly,
• or from the cage being poorly ventilated.

This is why rats should not be kept in tanks. Exposure to ammonia can both trigger myco flare-ups and cause respiratory scarring in its own right. The rule of thumb is that if you can smell your rats pee, then they will be breathing in ammonia. A rat cage should not smell – if it does, it needs cleaning.

Another source of problems is artificial fragrance, either added to bedding and litter, or otherwise used round the house. Some rats, just like some humans, react badly to these, so it is best to buy litter that is fragrance-free, and to keep air fresheners and scented candles for use elsewhere in the home. It is also important to avoid dusty products as dust can irritate the airways and again trigger respiratory flare ups. Want to know what to look for in bedding products? Check our guide here.

Sometimes a respiratory problem caused by a husbandry issue can be reversed simply by removing the trigger – cleaning the cage, or changing the bedding. This is particularly true where the symptom is only sneezing. However, it is always important to get a rat with RI symptoms checked by a vet, even if you think you’ve identified the cause, as environmental irritations can quickly turn to myco flare-ups in susceptible rats.

Heart disease in rats

I’ve included heart disease in this article because, although it isn’t technically a respiratory problem, it often presents as one in rats. Frequently the first warning we get are classic respiratory symptoms – grunting noises, more laboured breathing – that don’t respond to normal antibiotic treatment. Examination by an experienced vet can often pick-up abnormalities in the heart beat, although this isn’t always the case; rat hearts are small, fast, and the beat can’t always be heard well if there is a lot of respiratory noise overlaying it. Quite often, if we have a rat with suspected heart issues, our vet trials heart medication to confirm the diagnosis. They first give frusemide, a diuretic that relieves congestive heart failure, and if a rat shows response to that, we add in pimobendan, which supports the heart’s action. Other drugs a vet might use include ACE inhibitors such as forketor.

Heart disease can’t be cured in rats, but with a carefully dosed medication regime, it can often be managed, with some of my rats living for many months after diagnosis. Rats with heart issues tire easily, but still benefit from the opportunity to exercise, so a good-sized cage set out in easy stages is helpful. Just as in humans, heart issues in rats are partly genetic, but also partly influenced by environmental factors, so keeping rats a healthy weight and fed a healthy diet can help stave off serious problems.

I hope you’ve found this article useful for demystifying respiratory problems and their treatments in rats. It’s always worrying when one of our pets gets ill, but with timely and appropriate veterinary treatment, these problems can be managed, if not fully cured.