What You Need to Know About Rats

Tips from exotic veterinarians.

Originally published in the June 2015 issue of Veterinary Practice News

Exotics veterinarians who regularly handle rats say there are a few common ailments that general practitioners should be on the lookout for.

Skin ectoparasites (mites and lice), mammary tumors, pneumonia and upper respiratory infections are the four most common issues that Matthew S. Johnston, VMD, Dipl. ABVP (Avian), has come across in his rat patients.

Specialists like Dr. Johnston, an associate professor of avian, exotic, and zoological medicine at Colorado State University Veterinary Teaching Hospital, say general practitioners who have rat patients should get used to seeing and dealing with these common problems.

La'Toya Latney, DVM, head of exotics at the University of Pennsylvania’s Ryan Veterinary Hospital, warned that aggressive diseases seem to be commonplace among rats of all ages.

“It’s pretty common for us to see respiratory diseases in them across all ages,” Dr. Latney said, adding that the bacteria Mycoplasma pulmonis is often the cause of serious secondary respiratory infections in rats.

Latney, a consultant at the Brandywine Zoo in Delaware, also said rat owners tend to complain of ocular discharge, nasal discharge and sneezing.

Often these pet owners indicate that their rat’s eyes or nose are bleeding. This is because their tears are stained red, which is caused by porphyrin secreted by the Harderian gland, and this may indicate an upper respiratory infection, she said.

“When see this, we commonly start them on oral antibiotics that help treat Mycoplasma symptoms – doxycycline and enrofloxacin,” she said.

Doxycycline helps in two ways: to reduce bacterial infection and reduce inflammation in the lungs, she added.

Because rats are prey animals they tend to hide their symptoms.

That fact was noted by Stephen Divers, BVetMed, DZooMed, Dipl. European College of Zoological Medicine (Zoo Health Management, Herpetology), Dipl. American College of Zoological Medicine, and fellow of the Royal College of Veterinary Surgeons.

Dr. Divers, a professor of zoological medicine at the College of Veterinary Medicine at the University of Georgia, said general practitioners can spot rat ailments before they progress too far by training rat owners to be proactive.

He tells his rat-owning clients to buy an accurate gram scale and to weigh their rat on a regular basis, as often as two or three times per week.

“You will often pick up weight loss before you detect any obvious clinical signs,” Divers said.

If the owner reports a loss of, say, 10 grams, that will cue a veterinarian that there may be something wrong and prompt further investigation, he said.

Divers considers diagnostics an important tool that is not often enough used, with too many veterinarians instead going straight to antibiotics without attempting to find cause of the problem.

“Typically if we have any suspicion of respiratory issues we’re going to recommend radiographs; if there’s obvious nasal discharge, we will do culture and sensitivity testing; and if there’s no obvious discharge we’ll recommend blood collection and send out and get serological testing done,” Divers said. A rat panel to detect six agents that cause respiratory disease costs around $60.


In some cases antimicrobials may have little benefit, he said.

A rat’s respiratory disease may have a viral cause, such as Sendai virus (also called parainfluenza 1), which is often best managed by ensuring the animal has good husbandry conditions, an appropriate environment and is on a high-quality diet, Divers said.

“You’re trying to provide supportive measures,” he said.

Mammary tumors are another common ailment Latney sees in her rat patients.

They are mostly benign and typically easily removed by surgery, she said.

However, she recommends putting the patient on doxycycline before the procedure as a preventive measure against subclinical respiratory problems.

She noted that the stress of a surgery can cause Mycoplasma to overgrow.

Susan Kelleher, DVM, owner of Broward Avian & Exotic Animal Hospital in Deerfield Beach, Fla., treats lot of respiratory tract infections – both upper respiratory and pneumonia – and tumors.

“Respiratory tract infections are treated with systemic antibiotics and antibiotics delivered via a nebulizer,” Dr. Kelleher said. “Mammary masses are treated by surgically removing the masses.” 

Jeffrey R. Applegate Jr., DVM, a clinical veterinarian in the exotic animal medicine service at North Carolina State University College Veterinary Teaching Hospital, emphasized the importance of staying on top of and managing these ailments.

“Respiratory disease can be medically managed with antibiotics, oxygen and fluid therapy, but can sometimes be persistent or recurrent,” Dr. Applegate said. “Mammary gland tumors of rats, unlike dogs, cats and people, are typically benign. However, they tend to grow very quickly to a size that may compromise quality of life. Surgery to remove these tumors is usually curative for that particular tumor, though others may occur.”

Of the many common rat diseases, parasites are one of the simplest for any veterinarian to deal with, even if the practitioner has never had a rat for a patient before, Johnston said. 

“For lice, I prefer a good old-fashioned flea comb and carbaryl powder dusting, as the lice are chewing lice, so systemic medications don’t work nearly as well,” Johnston said.

In cases of mammary tumors, which Johnston said are typically benign fibroadenomas, removal is usually indicated because they can get large and bother the rat. 

“Simple removal is not a difficult surgery, but because these tend to happen in geriatric rats, there are often co-morbidities such as pneumonia that have to be considered when planning the anesthesia and surgery,” Johnston said.  “Additionally, we know that these tumors are hormonally mediated – specifically prolactin – so they will recur with a high frequency unless efforts are made to prevent hormonal stimulation.” 

Pneumonia, due to a number of different factors including various infectious agents, is common in older rats and treatment options are limited.

“In most cases, we are unable to cure pneumonia, but with antibiotics, bronchodilators, NSAIDs, and nebulization, we are able to improve quality of life for several months while owners of these pets come to grips with difficult decisions,” Johnston said.

Upper respiratory infections, typically viral in origin, are commonly found in young rats. “With supportive care they are usually self-limiting,” Johnston added.


When is it time to call in a specialist?

Rat experts said most general practitioners can handle the majority of ailments they will see without seeking a referral.

In Johnston’s view, the time to seek expert advice or send a patient to a specialist is when practitioners feel they are in over their heads.

However, depending on where a clinic is located, seeking a referral may be easier said than done as access to small-mammal specialists is limited in some areas, forcing veterinarians to try to work through tough cases on their own, he acknowledged.

“Thankfully, with telemedicine, VIN (the Veterinary Information Network) and other similar consulting services, in most cases, vets can feel that they at least have some backup available,” Johnston said.

Applegate, of NCSU, used the phrase “comfort zone” as a dividing line for when practitioners handle a case.

“General practitioners can easily manage rats as patients without difficulty, provided rats are within the veterinarian's comfort zone,” Applegate said. “An exotics specialist can often be a help when the diseases being managed are refractory to treatment, have an unusual presentation or require specialized surgery or equipment to manage.”

Divers, of the University of Georgia, also used “comfort zone” as his standard for when a general practitioner should seek a referral.

And if a rat isn’t responding to treatment, a specialist can then take further steps, he added.

“Some of the things that we might do are CT evaluations or high Tesla MRIs of rodents,” he said. “There’s a high level that we can do in referral practice including microsurgery, endoscopy, radiation therapy, etc.”

Put another way, the time for seeking a referral is when things aren’t going as planned, Kelleher said.

“Rats should be referred to a veterinarian experienced with their care if the respiratory tract infection is not responding to management,” she said. “Rats with mammary masses should be referred if the mass is located in an area that would make removal complicated. Examples of complicated sites would be masses that are very close to or involving the genitals.”

Certain surgeries, and diagnostics like a CT or MRI imaging, can be tricky and may require a consult, Latney agreed.

Like Johnston, she also encouraged general practitioners to seek out specialists like her, who are available for a phone consult.

She also recommends calling on a specialist when pituitary tumors are suspected. Indications of a pituitary tumor include issues with balance, a wide stance and occasionally blindness.

“That’s when we recommend people refer to us,” she said.

In this case the rats are given cabergoline, a dopamine agonist that inhibits secretion of prolactin and growth hormone, as there are reported case studies that this can dramatically improve a rat’s recovery, and is the same treatment used in human medicine, Latney said.


Not all experts were in full agreement about neutering rats as a preventive measure.

“We know that ovariectomy and ovariohysterectomy will prevent mammary tumor occurrence in females, and we also think neutering will prevent mammary tumor occurrence in males,” Johnston said. 

He said it should “definitely be offered” to rat owners when they come in.

“The difficulty is that anesthesia and surgery in these animals is not as straightforward as a dog or cat, so I believe that many clients are never offered this as a possibility,” Johnston said.

Kelleher, on the other hand, believes there isn’t enough solid scientific data to support that spaying rats decreases their chance of developing mammary tumors.

But many owners do opt to neuter their rats in hopes of decreasing the hormone levels that may contribute to mammary masses, she added.  

“Neutering male rats is most commonly done to decrease their body odor and to calm their behavior down,” Kelleher said.

Latney’s take is that neutering rats at a young age is a good preventive step.

“It reduces the chances of them getting these mammary tumors as they get older,” she said.

For Divers, the chance of preventing fibroadenomas is a good reason to get a rat spayed.

“If you sterilized these female rats then we can prevent the occurrence of those tumors,” Divers said.

Johnston too said prevention of mammary tumors is most easily accomplished by performing an ovariectomy or ovariohysterectomy.

However, since it lengthens the time a patient must spend under anesthesia, this method may not be appropriate for every patient, he said, adding, “Drug therapy to block hormones has been used with variable success.”

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