Medical Corner - Respiratory Infections in Pet Rats

Virginia Simpson
From the November/December 1997 Rat & Mouse Gazette

Mycoplasma pulmonis is a bacteria present in the nasal passages of rats. The only rats guaranteed to be free of the mycoplasma bacteria are labratory rats kept in a perfectly sterile environment. For this reason, mycoplasma pulmonis is the most common cause of respiratory infections in rats. Although there are several other bacteria that can cause the same symptoms, the usual culprit is mycoplasma.

When a rat gets old, or gets stressed, the mycoplasma bacteria has a chance to take hold and multiply. Pneumonia is when the infection gets into the lungs. With rats, a "cold" (i.e., sneezing and sniffling), can quickly lead to pneumonia which can cause permanent damage to the lungs and even death if left untreated.


If your rat is sneezing more than usual, listen closely to his breathing. If the nasal passages and chest sound clear, keep a very close watch on him, but it shouldn't be necessary to start treatment unless he starts acting more tired than usual, or stops eating or drinking. Allergies and dust are also possible causes of sneezing.

If there is a clicking sound from the sinuses, he is congested. This could progress further, so treatment would be a good precaution at this point.

If there is a gurgling, congested sound from the chest, you have a sick rat. Get him to a vet immediately! Rats succumb to these infections with amazing swiftness. A rat with no symptoms one day can have full blown pneumonia the next. This is partially because of their high metabolic rate, and because there is often a secondary infection caused by a different bacteria or virus.

Does your rat have red stuff on his nose, or around his eyes? This is called porphyrin. Porphyrin is a red mucous that is produced by a gland behind the eye (the Harderian Gland) which dries the color of blood. It's often mistaken for dried blood by people unfamiliar with rats. Porphyrin staining is often associated with mycoplasma infections because the infection puts stress on the rat, and stress will cause the discharge of porphyrin from the eyes and nose. This doesn't always occur when a rat is suffering from an infection. If you have a really laid-back rat, he may not get stressed out! There is also the possibility that your rat is being stressed by something else.

If your rat's fur is standing somewhat on end making him look puffy (a bit like a cat when it's been treed by a dog) and he's hunched up, he's feeling sick, uncomfortable, possibly in pain. Get him to a vet immediately!


The standard treatment for mycoplasma infections is a round of antibiotics. If the antibiotic is going to work, you will see an improvement in about three days. If there is no improvement, you should go back to the vet for a different antibiotic. Antibiotics commonly used for mycoplasma infections are:

  • Tylan (the powdered form of tylosin)
  • Tetracycline
  • Cefadroxil (for secondary infections - best used in combination with Gentocin)
  • Chlorampenicol
  • Baytril (enrofloxacin)
  • Doxycycline
  • Baytril and Doxycycline in combination
  • Gentocin in combination with Cefadroxil
  • Amikacin in combination with Cefadroxil

Although rats are commonly used as research animals, there is little information available about proper dosages for medicating them. When Baytril first came on the market, the mg/lb dose given to rats was too low, so it appeared that Baytril didn't work very well for them. Even today, several years later, the proper Baytril dosage for rats is not commonly available to vets. Very few reference books list dosages for rats for any medication. If your vet seems unsure, the RMCA has a Drug Usage Chart for Rat Respiratory Illnesses and Other Conditions by Mary Ann Isaksen and Daryl Mabley, D.V.M. available on their web site (www.rmca.org). The Drug Usage Chart can be found on the Gazette page as a sample article from the May/June 1997 Rat & Mouse Gazette.

In addition to the antibiotics, there are a few other things you can do for your rat.

  • Make sure his cage is sheltered from drafts.
  • Humidity in the room is as good for stuffed up rats as it is for stuffed up humans. A humidifier is a definite plus! Steaming him occasionally can also help (i.e., take him in the bathroom when you take a shower).
  • The ammonia smell from old bedding irritates the nasal passages, and makes the rat more susceptible to infections, so changing the bedding in his favorite sleeping area daily may help.
  • If you have several rats, you may want to move the sick one to a private cage or tank if he is really, really ill. This way, he won't have to compete for his food, and won't have buddies jumping on him trying to get him to play. Whether or not it's best to do this will depend a lot on the rats' personalities. Normally, the company is good for them, even when they are sick.
  • A heating pad set on low under one end of the cage or tank so that he can sleep in a warm spot if he wants is a good idea.
  • Echinacea can help boost the immune system. There is a liquid echinacea which is made for children that is fruit flavored and alcohol-free. Give one or two drops twice daily. Echinacea shouldn't be given all the time, so one week on, and two or three off could be used as a schedule. There are no hard and fast guidelines yet on how to best use this herbal supplement, but it can help with sneezes. Goldenseal is a similar herb which helps boost the immune system, and works well when given along with the echinacea.


This is not always as easy as it sounds! Some antibiotics taste awful, or smell awful, and some rats simply won't take them. You can give the antibiotics to your rat by squirting them into the side of the rat's mouth. I haven't had much success with this method, and it upsets both me and the rat! What I've found works best is mixing the medicine with baby food.

I've had doxycyline that my rats absolutely refused to touch! It smelled like raspberries, so I got a bottle of Heinz strained Apple Raspberry, and a bottle of Heinz Strawberry Dessert baby foods. The flavors seemed to mix well with the doxycycline (I tasted it and I couldn't taste medicine), and had no trouble administering it after that.

Baytril I've mixed with baby food vegetables with quite good success. A lot depends on what your rat likes, and what the antibiotic can be mixed with. Be creative! Mashed avocado, melted ice cream, chocolate pudding, shepherd's pie, cheese whiz, anything to get the medicine down! Be cautious with dairy products, though. The calcium in them neutralizes some antibiotics such as doxycycline. Ask your vet or local club to be sure.

If your rat is so ill he's refusing to eat or drink, you may be forced to use injections to medicate and hydrate him.


The bacteria which helps both rats and people digest food can be killed off by antibiotics. When they are prescribed for your rat, ask if you can give him yogurt while he's on them. If the gut flora gets wiped out by the antibiotic your rat could develop diarrhea which can quickly lead to dehydration. Dehydration is very serious for a rat.

Pedialyte, for human babies, is good for rats with diarrhea or dehydration. Once opened, however, a can/bottle of pedialyte only lasts 24 hours, so make ice cubes out of any you don't need immediately, and melt them as you need them.

An injection of lactated ringers solution can help immensely when a rat is dehydrated. Any rat with diarrhea should be taken to the vet as soon as possible.


When a rat is really sick he may not feel like eating, and can lose weight very quickly. This is not good. You should try to get some high calorie, nutritious food into him if at all possible. Nutri-cal, mashed avocado, some particular favorite of the rat in baby food form. Use a needleless syringe to try to force some food into his mouth (a larger syringe can be used to fill a smaller one). Usually a rat will swallow the food rather than spit it out once you've managed to get it into his mouth.

Nursing a rat through a bout of pneumonia can be a challenge, but is very much worth the effort. Depending on the age of the rat, he could have years of life to look forward to! Hopefully, this is something you will never have to do.