Upper Respiratory Infection in Rats

What Is an Upper Respiratory Infection in Rats?

Upper respiratory infection (URI) is a common ailment in rats. URIs can be viral or bacterial in origin, and in some cases, rats may have more than one organism causing their illness. These infections can lead to pneumonia, urogenital disease, neurological problems, and even death if not treated. Once the more advanced signs of the disease are noticed it is considered a medical emergency.

Symptoms of Upper Respiratory Infection in Rats

Early Onset: Initial signs of URI in rats can be subtle.  At first you may hear an occasional sneeze or see small reddish crusts near the eyes or nose.  As the disease progresses over the next few days you may also notice:  

• Frequent sneezing

• Squinting

• Rust colored tears and/or nasal discharge

• Decreased appetite

• Lethargy

• Ruffled hair coat

• Behavioral changes—avoidance, irritability, biting when handled

Advanced Signs: Within days to a week after initial signs are noticed, rats can become very ill with further symptoms such as:

• Weight loss

• Hunched posture

• Distended abdomen

• Discharge from the genital area

• Bloody urine

• Head tilt or loss of balance

• Coughing

• Wheezing or crackling sounds when breathing

• “Flank breathing” (using abdominal muscles to breathe)

•  Open mouth breathing

Causes of Upper Respiratory Infection in Rats

Most rats naturally carry a species-specific bacteria called mycoplasma pulmonis. This particular bacterium colonizes in the cells of the reproductive system and the respiratory tract. M. pulmonis is one of the most common causes of URI in rats, and is contagious from one rat to another. Because it is so common, purchasing a rat free of m. pulmonis is nearly impossible. Therefore, it is a recommended to quarantine new rats for 2 weeks to monitor for symptoms before introducing them to your other rats.

Other bacteria that can cause URIs are known as “secondary invaders.” These are opportunistic bacteria that will invade the body while the rat's immune system is weakened from the primary disease. If left untreated, bacterial infections can lead to pneumonia (fluid accumulation in the lungs) or an abscess (pocket of infection) in the lungs.

Upper respiratory infections can also be caused by viruses. Viral infections will weaken a rat's immune system, leaving them vulnerable to secondary bacterial infections.

Poor sanitation can also contribute to a rat’s development of an upper respiratory infection. Ammonia odor can build up in a dirty cage and irritate airways, leaving the tissue of the respiratory tract exposed to bacterial and viral pathogens. Proper care of pet rats is essential to their livelihoods.

Risk Factors for Upper Respiratory Infection in Rats

Advanced age: Rats as young as 2-6 months old may have microscopic lesions in their respiratory tract from m. pulmonis, but sometimes symptoms may not become apparent until the rat reaches 12-18 months of age. Like people, as rats age their immune system becomes weaker making them more prone to infections.

Underlying conditions: When the immune system is busy dealing with another health condition (such as obesity, heart disease, or cancer), the body becomes more susceptible to other illnesses like respiratory infections.

Inhaled irritants: Rats are very sensitive to fumes from smoking or vaping, scented soaps, cleaning chemicals, burning candles, etc. Inhaling these types of fumes can cause small lesions in the respiratory tract where infection can set in.

Stress: As prey animals, rats are sensitive to their surroundings and may stress easily. Since stress can weaken the immune system, a rat's habitat should be in a clean, quiet, and draft-free environment. Excessive or improper handling can cause stress as well, so teaching children proper handling techniques is important.

Overcrowding: Since both bacterial and viral respiratory infections are contagious between rats, it is important to not have too many in one environment to avoid a multi-pet outbreak.

Obesity: Being overweight puts extra strain on a rat's respiratory system–weakening it and leaving them vulnerable to a URI.

How Veterinarians Diagnose Upper Respiratory Infection in Rats

Your veterinarian will begin with a physical exam and listen to the lungs for sounds of wheezing or crackling that might indicate fluid buildup (pneumonia). A healthy rat has a respiratory rate of 70-100 breaths per minute, and your vet will note if your rat’s respiratory rate is elevated. A vet will also look for any discharge from the eyes, nose, mouth, and genital area. Your rat will be weighed, and his body condition assessed for signs of weight loss or unhealthy hair coat.

In cases of chronic or re-occurring respiratory infections, a culture and sensitivity test can be performed to determine what organism(s) is causing your rat’s specific illness. This test is non-invasive and involves swabbing a sample of either respiratory or genital discharge and sending it to a lab. Within days, the test results will help a veterinarian to determine which medication(s) should be used to treat the infection.

Additional diagnostic tests are available but are best performed under sedation to be less stressful on a sick rat. Bloodwork can test for the presence of m. pulmonis in the body, and x-rays can show evidence of tumors or pneumonia in the lungs. If needed, an ultrasound guided biopsy can be performed while the rat is sedated to obtain samples of suspect tumors in the body.

Treatment of Upper Respiratory Infection in Rats

There are no effective home remedies or over-the-counter treatments for URIs in rats, so your veterinarian will likely prescribe an antibiotic. Upper respiratory infections that do not respond to antibiotics within 7 days are generally considered to be viral. Viral infections can potentially resolve in 3-4 weeks, however supportive care is necessary if your rat stops eating, grooming, or develops a secondary bacterial infection.

Bacterial URIs in young rats are typically treated with oral antibiotics for at least 7-10 days. Your vet may recommend trimethoprim sulfa, enrofloxacin, or doxycycline. In cases of severe infections more than one antibiotic may be prescribed.

Since there is currently no cure for m. pulmonis, rats with chronic re-occurring respiratory infections may need to be medicated for 6-8 weeks at a time. Long-term intermittent dosing (also known as “pulse therapy”) can help a rat with chronic URI since the medication will keep the symptoms manageable and provide a good quality of life.

Medications can be administered orally, by injection, or via a nebulization chamber. Corticosteroids (prednisone, dexamethasone) will reduce inflammation in the respiratory tract. Bronchodilators such as albuterol, aminophylline, or theophylline will open the airways to allow easier breathing. For very sick or debilitated rats, a vet may recommend fluid replacement injections and may also utilize an oxygen chamber if breathing is labored.

Recovery and Management of Upper Respiratory Infection in Rats

It can take weeks to months for a rat to recover from an upper respiratory infection. During that time, it is important to monitor your rat closely. If he is not eating or drinking on his own, you can use a needle-less syringe to feed your rat vegetable baby food and water. Vitamin supplements can be given orally, and electrolyte replacement solutions such as Pedialyte® or Gatorade® may help. Plain yogurt can also be offered to help prevent the destruction of normal digestive bacteria while your rat is prescribed antibiotics. Alternatively, a gel option may be used. 

During recovery from a respiratory infection, allow your rat to rest in a stress-free environment. Keep handling to a minimum except for medicating or feeding. Provide extra warmth with a warm water bottle wrapped in a towel or a heating pad under one corner of the cage. Some rats benefit from a humidifier or steam from a hot shower to loosen congestion. For overweight rats, proper diet, and mild exercise (not forced) will promote weight loss and allow easier breathing.

Upper respiratory infections can often cause permanent damage to a rat's lungs and airways, leaving scars or lesions that make a rat more susceptible to re-infection. Reoccurrence is common, especially if m. pulmonis is present. Some rats need to be on long-term intermittent medication for the rest of their lives.

While upper respiratory infections are not contagious to people, they are very contagious between rats. Always wash your hands well after handling a sick rat to prevent spreading disease to other rats. Keep the cage clean and avoid using wood-based bedding as it can harbor and grow bacteria. Paper-based bedding, such as Carefresh small animal bedding is a safer option than pine, cedar, or corn-based substrates. House your rats in a draft free area and avoid inhaled irritants such as smoking, burning candles, or spray disinfectants near your rat. Quarantine new rats for a minimum of 2 weeks before introducing them to your existing pets to avoid the spread of disease.