Respiratory & Heart Disease in Rats
by Debbie "The Rat Lady" Ducommun

*This article is from my booklet Rat Health Care. I highly recommend you order a copy to have on hand.

Respiratory disease is the most common health problem and cause of death in pet rats. The most common organism causing this disease in rats is the bacteria Mycoplasma pulmonis. Mycoplasma is very contagious and incurable. There are different strains of mycoplasma that are more or less virulent and so can cause more or less severe disease. Different rats also seem to have differing resistance to the disease. The severity of a mycoplasma infection can be increased by cigarette smoke, ammonia from a dirty cage, vitamin A or E deficiency, pine or cedar shavings, and a concurrent respiratory infection of another type, as well as genetic susceptibility.

A mycoplasma infection makes a rat more susceptible to secondary respiratory bacterial infections as well. The respiratory symptoms that are common in rats can be caused either by the primary mycoplasma infection, or secondary infections, or both. In young rats, symptoms are more likely to be caused by secondary infection, so they need to be treated accordingly.

Most respiratory symptoms in rats are caused by respiratory infections or heart disease. It is very rare to find a lung tumor in rats. Since 1985 years I have done gross autopsies on more than 200 rats and I have only seen one possible lung tumor.

Mycoplasma typically causes a "blister" effect on the surface of the lungs, lung abscesses, and emphysema. It also causes inflammation and infection of the uterus. There is a special blood test, called a serology ELISA test, that can detect mycoplasma. (However, the disease is so common, you should just assume your rats have it.) Here are two labs which will perform serology testing on rat blood:
Research Animal Diagnostic and Investigative Lab
University of Missouri, College of Veterinary Medicine
1-800-669-0825; myco test is $6
Charles River Labs, 1-800-LABRATS; myco test is $8.20

Common Symptoms

Usually a mycoplasma infection is chronic, that is, it starts out slowly with mild symptoms that gradually get worse over a period of weeks or months. The first symptom of mycoplasmosis is usually frequent sneezing (healthy rats rarely sneeze), but then this often goes away and there can be a long period of time without symptoms. However, mycoplasma can cause lung damage even if there hasn't been any overt symptoms.
The infection generally begins in the upper respiratory passages. It can invade the inner ear and affect balance, causing a head tilt which can progress to rolling behavior. Mycoplasma can also cause damage to the nasal cavity and nasal bones resulting in fatal bleeding. Eventually, and especially if immunity is weakened due to stress, old age, or another disease, pneumonia occurs, usually causing wheezing. Any noise made while breathing can be a symptom of an infection.

Finally, the lungs will be permanently damaged and the rat will exhibit labored breathing. The heart may also be damaged. The rat may lose weight as his poor respiration makes it hard to eat or heart disease causes lack of appetite. The toes and tail tip may turn blue from lack of oxygen. The rat may experience respiratory distress, which causes a rat to gasp through her mouth, or dash about in panic when she can't get enough air. If treatment cannot prevent such attacks, euthanasia is the kindest action.

A rat infected with mycoplasma is usually active and eats normally until the disease is quite advanced. However, an acute secondary bacterial infection can cause a rapid onset of symptoms which can include any of the following: loss of appetite, lethargy, rough coat, hunched posture, runny eyes and nose, and difficulty breathing. Prompt antibiotic treatment will be necessary to save a rat with an acute respiratory infection. A rat that is extremely lethargic and refuses to eat or drink must receive antibiotics by injection. Gentamicin with one of the penicillin is recommended.

A number of secondary bacteria can be associated with mycoplasma infections including the Cilia-Associated Respiratory (CAR) bacillus, Pasteurella pneumotropica, and Corynebacterium kutsheri. Another common bacteria that can cause respiratory disease in rats is Streptococcus pneumoniae. Since strep can be transmitted from people to rats, I recommend anyone with a strep infection stay away from rats. Strep infections in rats are usually fatal within three days without vigorous antibiotic treatment. Rats cannot get human colds or flu.
For rats with an acute infection, a secondary infection, or a possible strep infection, the recommended treatment is amoxicillin.

Viral Infections

There are also two viruses that can cause respiratory symptoms in rats. Sendai virus causes sneezing and sometimes a stuffy nose, especially in babies which can prevent nursing and cause death. Sialodacryoadenitis (SDA) virus (also called rat corona virus) is an infection of the salivary glands, and symptoms can include any of the following: sneezing, runny eyes and nose, swelling under the throat, and bulging eyes. Treatment with ophthalamic ointment may be necessary to prevent permanent eye damage.

In mycoplasma-free rats these viruses are not usually fatal to post-weaning rats and the rats recover in a week or two. Both viruses will die out in a population if breeding and new introductions are discontinued for at least two months. However, if a rat is already infected with mycoplasma (which most pet rats are these days), a viral infection on top of it can be fatal. Aggressive supportive therapy, including fluids, and antibiotic treatment for secondary bacterial infections will be necessary. (Gentomicin with one of the penicillin is recommended.)
Most rat respiratory diseases, especially mycoplasma and the viruses, are infectious and can be spread both through direct contact and through the air. Viruses can also be transmitted on hands, clothing, and other inanimate objects. Mycoplasma is not known to be transmitted in this way. To protect your rats from the viruses, it is always a good idea for new rats or rats returning from a show to be quarantined for at least 2 weeks before exposing them to your other rats. Ideally there should be no air-flow between your rats' room and the quarantine area. Wash thoroughly and change your clothes after being with the quarantined rats.
(None of the organisms causing respiratory infections in rats are infectious to humans. The only disease I know of that can be transmitted from domestic rats to humans is "rat-bite fever," a rare bacterial infection similar to cat-scratch fever. Symptoms can occur several weeks after a bite and include a rash and flu-like symptoms. I have personally heard of only 2 cases. You can find out more about rat-bite fever at

Antibiotic Treatment

Although mycoplasmosis in rats is basically incurable, treatment with antibiotics can help control the damage. Antibiotics are also vital in treating secondary bacterial infections.

A head tilt caused by an inner ear infection requires early and aggressive treatment if the symptoms are to be reversed. Since this can also be caused by a secondary bacterial infection, Baytril, chloramphenicol, or gentamicin which tend to be effective against most other bacteria as well as mycoplasma, are recommended. Treatment with a steroid, along with the antibiotics, is also vital to help reduce inflamation. A head tilt can also be caused by a pituitary tumor or stroke, and in this case the primary treatment is with steroids. But an antibiotic should also be given since steroids depress the immune system, and can also help shrink a tumor.

The best antibiotics to use against mycoplasma, in general order of weakest to strongest, are erythromycin, tylosin, tetracycline, azithromycin, doxycycline, Baytril, and gentamicin. Different strains of mycoplasma are varyingly susceptible to different antibiotics so if one doesn't work, try another. Some combinations seem to work well. Baytril or gentamicin can be used in combination with amoxicillin or cefadroxil, tylosin can be used with tetracycline, and Baytril with doxycycline can be quite effective. One rat breeder claims that repeated treatment with tylosin can eventually eliminate mycoplasma from rats under 10 months old, but this claim has not been proven.

Tylosin is available by mail order from the Omaha Vaccine Company (800-367-4444) under the brand name Tylan as 100 g of powder (item #02941) for about $32 or as 100 ml of injectable liquid (item #00012) for $10.50. Tylan is also available in some feed stores.
Erythromycin and tetracycline are available in pet shops as Ornacyn and Ornacycline. Tetracycline is also available in fish capsules and in feed stores as Terramycin Soluble. Amoxicillin is available as fish capsules in some pet shops and feed stores and by mail order from Doctors Fosters & Smith (see sources below). Amoxicillin is recommended for an acute infection, a secondary infection, or a possible strep infection. Other antibiotics that have been successful at treating secondary infections are trimethoprim-sulpha, cefadroxil, and chloramphenicol.

If a particular antibiotic is effective against the infectious organism, you should see an improvement in acute symptoms within 2-3 days, or in chronic symptoms within a week. If you don't see any improvement within this time, you must try a different antibiotic. When treating respiratory infections, antibiotics should be continued for at least a week after all the symptoms disappear to prevent an immediate relapse. That means sometimes the treatment must be continued for several months. Treatment should be reinstated if the symptoms come back. If an antibiotic is no longer effective, try another one.

Other Prescription Drugs

Two prescription drugs that can be very helpful in rats with advanced mycoplasmosis are aminophylline, which is a broncodialator, and predisone, which reduces inflamation. The dose for aminophylline is 1.36mg/lb. twice a day. The dose for prednisone is 1 mg/lb. once a day. Both can be given either orally or by injection. (Primatene (guaifensin) is a bronchodialator available over the counter. I do not have a dose for it, but you might try 1/10 the human dose.)

If the lungs are congested, a diuretic is called for. I've had good results with Lasix at a dose of 1-2 mg/lb. 1-3 times/day.

I have found that rats with advanced mycoplasmosis often have heart disease as well. The recommended treatment for heart failure is a low sodium diet, a diuretic (to reduce fluid in the lungs), and enalapril (dose 0.25 mg/lb. SID), which lowers the blood pressure and makes it easier for the heart to beat. Enalapril is so safe it can be used as a diagnostic tool. If giving enalapril makes the rat feel better, then you know he has congestive heart failure.

Another recommended medication is a beta-blocker. (The American Heart Association recently announced it was recommending the use of beta-blockers for most patients with congestive heart failure.) The one that I have used is atenolol, at a dose of 1 mg/lb. twice a day. It took about a week for the improvement to occur.
If the symptoms include skin edema or if it can be determined by x-ray that the heart is dilated, rather than hypertrophic, digoxin, which helps the heart beat more strongly, can be added to the treatment. The dose for digoxin is 0.001-0.0025 mg/lb. twice a day. As time goes on, you often have to increase the dose. I once had a rat with congestive heart failure live to 38 months with digoxin and Lasix treatment!

Studies have also found that some supplements can help people with congestive heart failure. These include the omega-3 oils in flax oil (25 mg/day), co-enzyme Q10 (10-30 mg/day), L-carnitine (25 mg/day), and taurine (50 mg/day). The doses I've recommended here for rats are 1/10 the human doses. I have been giving these to 5 of my rats with good results. They take them eagerly in peanut butter balls.

I lost the rest of this article.

Go back to the info page.

Girls Myths Fun Home

Hosted by