Respiratory Disease in Rats

THE PROBLEM
Respiratory disease in rats is caused by a combination factors:

• Genetic susceptibility of individual rats

• An immune system compromised by stress (for example, a recent move to a pet store or new home, overcrowding, and dusty, dirty housing)

• Infection

Infection is not usually just one bacteria or one virus causing trouble; most often it is a combination of one bacteria, called Mycoplasma, along with other bacteria and viruses.

And then, once infection is established:

• Respiratory secretions of fluid and mucus increase, obstructing the nasal passages and potentially filling the lungs and chest

• Mucus secretions create a biofilm lining the respiratory tract, where bacteria live protected from antibiotics

• Abnormally vigorous inflammation occurs, leading in the short term to swelling in the airways and in the long term to the lungs changing from soft, supple air-filled space to hard, dense tissue with little room for air

• Additionally, occasionally the problem spreads to the inner ears, causing problems with balance, head tilt, and circling

• And less commonly the problem can involve the heart or its external lining, the pericardium

SIGNS OF ILLNESS

• Breathing difficulties: sneezing, wheezing, severely increased respiratory rate and effort

• Nose bleeds

• Decreased appetite

• Debility: weight loss, poor fur quality

• Sudden death

DIAGNOSIS
Our diagnosis of respiratory disease is most commonly based on the history, physical exam, and trial antibiotic therapy. X-rays are often useful to determine the extent and severity of the problem, and an echocardiogram can help us determine if the heart is involved.

TREATMENT
In severe cases, when a rat is having obvious breathing difficulty that has developed quickly, we hospitalize it in order to treat with an oxygen cage, and both injectable and nebulized medications.

We typically treat rats that are stable (eating and acting well despite respiratory signs) as outpatients with oral antibiotics and sometimes other medications.

It’s critical to recognize that most cases respiratory disease becomes chronic and require repeated treatment with antibiotics and other medications over the rat's lifetime.

We believe, and it has been shown repeatedly in studies that it is extremely important for the owner to provide an excellent environment to reduce symptoms:

• Recycled pelleted paper bedding instead of fragrant wood chips

• An open cage rather than a closed aquarium-type one

• Cage cleaned frequently to avoid urine build-up

• Avoid fragrant cleaning agents, dusty environments, and tobacco smoke

PROGNOSIS
For rats that have a rapid onset of severe signs the death rate is high unfortunately.
Rats that milder signs of slower onset usually recover mostly but will develop chronic breathing problems. These problems fluctuate from mild to severe, and usually they require medical treatment, either occasionally or persistently.

CONTAGION
Most rats carry Mycoplasma and other bacteria and viruses in their respiratory tracts normally. These microorganisms are shed in their respiratory secretions, so rats kept in close contact with each other, especially young rats, are inevitably exposed to them.

Exposure to bacteria and/or viruses is very likely to occur but whether or not a rat becomes ill, and how ill it becomes, depends on other factors combining with infection. The most important other factors are the genetic susceptibilty of the individual rats and whether or not the rat's immune system is depressed by environmental stresses.

The microorganisms that are involved in rat respiratory disease are extremely unlikely to affect people, but people with poor immune system health are at increased risk. There is one report of transmission of Mycoplasma to healthy laboratory personnel.