Updated November 28, 2020
- A rat with sneezing, watery eyes or wheezing should always see the vet
- Once a rat develops breathing problems or gasping, it’s urgent
- Rat respiratory infections are preventable and respond best to early treatment
Now dive deeper…
Rats make great pets. They’re smart, affectionate, odourless and easy to look after. They’re also healthy, with just one exception.
Everyone who keeps rats needs to be familiar with their most common disease: Murine Respiratory Mycoplasma (MRM). If you understand it, you can avoid serious problems and prevent heartache.
What Is Rat Mycoplasma?
Mycoplasma pulmonis is a tiny bacteria that lives in the respiratory tract of nearly all wild and pet rats. It’s often present without causing obvious illness. When it does it causes nasal and middle ear infections, bronchitis and pneumonia.
Mild or early infections just look like a simple head cold with sneezing, watery eyes or noisy breathing. This is when experienced rat owners will come to me, and when the disease is easiest to control.
More advanced disease is marked by the appearance of breathing problems. These rats now have a severe and life-threatening illness with some or all of the following:
- Breathing faster than normal
- Making more effort, i.e. heavy breathing
- A wheeze or click during respiration
- Breathing through the mouth
- Quietness and lethargy
- Hunched posture and ruffled coat
- Eating less and weight loss
Red porphyrin staining around the eyes and nose is often seen in stressed rats like these. A head tilt or a twisted neck is a sign of infection in the middle ear.
So it’s clearly serious. Let’s talk about the causes and prevention, then how we can treat MRM.
Causes Of Rat Mycoplasma
To prevent MRM, you need to ask this: if M. pulmonis is everywhere, why do only certain rats get sick? Here are some possibilities:
- Stress causes suppression of the immune system. That allows the disease to ‘break out’ in a normally healthy carrier. Examples of stressful things for rats are overcrowding, incompatible groups, transport, and sale. Therefore, it’s important to be especially vigilant when bringing in new rats.
- Introducing a new rat can also cause a disease outbreak due to the other rats not having been exposed before. That’s why I prefer a month of quarantine in a separate room before bringing rats together. Mycoplasma will spread in the air, on hands, clothes, bowls, sippers and foodstuffs.
- Other diseases often make it worse, especially cilia-associated respiratory bacillus (CARB). You have less control over these but the vet needs to keep them in mind.
- Environment is the most important factor, and the one you can manage most easily. It’s so important that I’m going to give it a heading all of its own.
Rat Air Quality 101
A good environment is essential for a strong respiratory tract. There are three important considerations:
- Temperature should be neither hot or cold. Rats like the same Goldilocks zone as us from 20 to 28 degrees C.
- Humidity is again similar to ours. Rats like the humidity to be from 30 to 70%.
- Good air quality is even more important. This is the one rat owners struggle with the most.
The reason for this is urine. When it sits around, it releases ammonia gas, which is highly toxic to the lining of the airways. Worse still, ammonia tends to settle on the cage floor unless it’s disturbed.
In laboratory rat colonies, the importance of ammonia clearance has been understood for over 40 years. Ammonia damages the defences of the airways, and shuts down the tiny hairs called cilia that carry mucus and bacteria away. It increases respiratory disease at even the lowest concentrations tested.
That’s the message: it’ll never be perfect, but you need to do the best you can. Try the ’sniff test’. Get your nose right down to rat level- if you can smell ammonia or urine, something needs to be done. If it makes your eyes water, it’s critical. Here are some suggestions:
- Change litter frequently.
- Use the largest enclosure you can.
- Have wire, not solid sides at floor level.
- Avoid wood or soft furnishings if you can’t clean them.
- Create 3-D environments so rats can live well above the litter floor.
- Encourage gentle air movement without causing chilly drafts.
I also think the single greatest thing you can do to prevent rat respiratory infections is choose your breeder carefully. Now you see the effort required, it’s easy to imagine that not all sellers have good rat husbandry. Too often I see rats who were affected from the very beginning.
Treatment of Rat Mycoplasma
It’s not hopeless. Many rats live normal lifespans despite an early diagnosis. They may require further visits but most can expect long disease-free periods in between.
The aim isn’t to eliminate Mycoplasma, which is thought to be nearly impossible, but to control its effects on your rat.
Mild cases go on a course of doxycycline antibiotic paste. We use a product made for cats, and repackage it into 1mL syringes so you can dose it accurately.
As the severity increases, we add the following:
- Anti-inflammatory drugs
- A second antibiotic
- Nebulisation to loosen airway secretions
If things are getting serious, we will recommend a chest X-ray using our dental X-ray unit. It won’t help us with the treatment, but if we see the shadow of lung abscesses we know things are bad. Sometimes it’s best to find this out early to avoid unnecessary treatment.
However, with early detection and the support of your vet, the future is anything but grim. Rat respiratory infections are usually easy to treat, but that’s not all. They also lead us to make changes that will improve your rat’s every-day life.
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By Andrew Spanner BVSc(Hons) MVetStud, a vet in Adelaide, Australia. These help topics are from a series regularly posted on email and Twitter. Subscribe via email here to never miss a story! The information provided here is not intended to be used as a substitute for going to the vet. If your pet is unwell, please seek veterinary attention.