WHAT CAUSES RESPIRATORY DISEASE IN RATS?

• The most common cause is Mycoplasma pulmonis, which is typically spread from mother to offspring at birth. Virtually all rats in the US are carriers of Mycoplasma unless bred in a specific pathogen free colony.
• Other bacteria and viruses can be involved and complicate infection. These include:
  • Streptococcus pneumoniae
  • Corynebacterium kutscheri
  • Cilia associated respiratory (CAR) bacillus
  • Sendai virus
  • Coronavirus (sialodacryoadenitis virus)
• Other causes such as cardiac disease, trauma, and neoplasia are possible but far less common
• Other contributing factors: poor hygiene leading to ammonia build up, improper bedding or caging, poor ventilation, nutritional deficiencies
• Pathologic changes from Mycoplasma include loss of cilia, suppurative bronchopneumonia, atelectasis, and/or abscesses along with pharyngitis, rhinitis, or tracheitis.
   

CLINICAL SIGNS

• Sneezing
• Wheezing or congested noises
• Porphyrin discharge from the eyes and/or nose (chromodacryorrhea)
• Labored breathing, wheezing or increased bronchovesicular sounds on auscultation 
• Progression to anorexia, weight loss, lethargy, etc. as severity of disease worsens
  
  

DIAGNOSIS

• Typically made based on clinical signs and history
• Radiographs are useful to rule out other causes and to evaluate the extent of disease which aids in prognosis, especially in chronic cases. Sedation with midazolam and butorphanol can aid both in positioning and easing the rat’s respiratory effort.
• While tests exist (mostly used in lab animal medicine) for various pathogens that can cause respiratory disease, these are rarely practical in the individual patient. The veterinarian is typically better off to assume a mixed infection exists and manage accordingly, and most all rats will test positive for Mycoplasma. Mycoplasma will not grow on traditional bacterial culture.
  
  

TREATMENT

• Treatment is focused on managing clinical signs and controlling the organism, but Mycoplasma cannot be eliminated.
• Antibiotics typically used to treat Mycoplasma include the fluoroquinolones, macrolides (azithromycin, tylosin), tetracyclines, chloramphenicol, or aminoglycosides. Widely used options include a combination of enrofloxacin and doxycycline or azithromycin. Tylosin can be administered in the drinking water for larger colonies.
• In mild cases, antibiotics alone will resolve the clinical signs, but the organism remains.
• Many rats will have flare ups of disease with stressful events, or if there is a lack of hygiene resulting in a buildup of ammonia in the cage. Maintaining a clean, dust free, well-ventilated environment and feeding a proper diet plays a large role in the prevention of signs.
• In more severe cases where breathing is more labored, nebulization therapy can be extremely useful. Various medications in saline can be delivered. Typically nebulization is performed twice daily until signs improve, then once daily until resolution. The recipe the author typically uses is:
  • 3ml of 100mg/ml gentamicin or 100mg/ml enrofloxacin 
  • 1.5ml 20% acetylcysteine
  • 36ml 0.9% saline
• Steroids have been shown to significantly decrease the inflammation associated with Mycoplasma infection. Despite the risk of immunosuppression with a chronic infection, steroids seem to help these rats breathe easier much faster than any other therapy other than nebulization. The author routinely uses prednisone 0.5mg/kg PO q12h x 3-5 days, then q24h x 3-5d, then q48h x 3-5 days. Rats seem to tolerate steroids exceptionally well with minimal to no side effects in the author’s experience, but owners should always be informed what to watch for. NSAIDs such as meloxicam can be used in milder cases.
• Over time many rats will develop recurrence of clinical signs on a frequent basis, or may have chronic symptoms that never fully resolve due to areas of chronic abscessation or fibrosis in the lungs. Radiographs are useful in communicating prognosis. Sometimes different therapies will need to be tried and adjusted to find the best regimen that keeps signs under control for an individual patient, realizing signs will never fully resolve.
• Oral antibiotics seem to be less useful in these cases, but they can be used long term or intermittently if they are helping. Most benefit more from other therapies such as intermittent or daily nebulization, low dose prednisone, or bronchodilators such as theophylline or terbutaline.
• Proper communication of prognosis and expectations with clients is important. If the patient cannot be kept comfortable with a good quality of life, euthanasia is reasonable.
  
  

Further Reading:

Graham JE, Schoeb TR. Mycoplasma pulmonis in rats. J Exot Pet Med 2011:20;270-276.

Benato L. Respiratory diseases in rats. Comp Anim 2012:17;47-50.

Dutton M. Respiratory disease in rats. Lafeber Vet 2010 https://lafeber.com/vet/respiratory-disease-in-rats/

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 About the Author: Stacey Leonatti Wilkinson, DVM, DABVP (Reptile and Amphibian)

Dr. Stacey Wilkinson graduated with her DVM from the University of Tennessee in 2006. Since graduation she has worked on exclusively exotic pets, first in Raleigh, NC, then in 2015 she opened Avian and Exotic Animal Hospital of Georgia in the Savannah area. In 2013 she became a diplomate of the American Board of Veterinary Practitioners in Reptile and Amphibian medicine. Dr. Wilkinson is also an adjunct assistant professor at North Carolina State University College of Veterinary Medicine. She has been published in scientific and non-scientific journals, written multiple textbook chapters, and lectures nationally on exotic animal medicine and care.