Despite being endemic in the pet rat population Corynebacterium kutscheri (CK) is a bacterial infection that rarely gets talked or written about, and I personally, had owned rats for a number of years before even hearing mention of it. Many breeders have post mortems carried out on their rats to try to clearly determine the cause of death. All the breeders I have spoken to who do post mortems admit to having seen rats from their colonies with signs of this condition at autopsy.
CK (also called pseudotuberculosis or pseudoTB) is a bacterial infection that occurs naturally within populations of rats at a subclinical or latent level. The latent infection does not cause any actual symptoms of disease and active infection may never be triggered throughout a rat’s life. The lung lesions of CK have a characteristic multiple abscessed appearance on PM.
The disease is airborne (in droplets from the respiratory systems of other rats) or can be picked up (orally) from the faeces of an infected rat. It is also passed from mother to babies in utero.
Triggering the active disease
Any major trauma that weakens a rat’s immune system has the potential to trigger active CK in a rat with a latent infection. The problem for pet owners is that it is not possible to know which rats are affected until symptoms occur (once the rat has moved to the active stage). Stressors include treatment with immunosupressants such as steroids, malnutrition, surgery, major trauma, other infections and pregnancy.
Symptoms of the active infection
- Increasingly laboured breathing which, unlike many respiratory infections in rats is often completely silent. Respiratory rate increases and abdominal breathing is common.
- Weight loss and anorexia.
- Hunched position and spiky ‘staring’ coat.
- May have abnormal ‘creeping’ gait.
- May have increased porphyrin discharge.
- May drool saliva
Progression and treatment
Unlike active mycoplasma respiratory infection in rats, which is a progressive and chronic disease, CK once active is acute and often rapidly fatal. CK is reported as a deadly disease, which without treatment will generally lead to death within one week. Sadly treatment may not be effective, since the disease moves so quickly, and may only lead to a slower deterioration. Thus the pattern of illness in a rat with active CK is sudden onset (usually after an identifiable stressful event) severe, but generally silent respiratory illness and weight loss.
Treatment with antibiotics should be aggressive, and these can be given by injection at least initially. CK is sensitive to ampicillin/amoxyxillin and tetracycline/oxytetracycline or doxycycline. Amoxycillin and doxycycline can be given concurrently for maximum effect. Some people also report success with Septrin (co-trimoxazole). As well as antibiotics a stress free environment is essential and nutritional support (soft nutritious foods and supplements) should be given.
Research has shown that SDA and Sendai viruses do not trigger latent CK into an active disease, at least not in a lab!
Endemic – a disease that occurs regularly within a particular population.
Pseudo – a thing that resembles something that it isn’t.
Subclinical – referring to the early stages of a disease before it has any noticeable symptoms.
At the age of 18 months Tabikit had some kind of fall/trauma in her cage, which caused her to lose the use of her back legs/tail. She was seen by a vet and was treated with a steroid injection followed by regular Metacam. She was nursed in a one level cage without any levels and only an igloo as ‘furniture’. Within a couple of days she was recovering the use of her legs and was moving about the cage with increasing strength. 6 days after the steroid injection she died despite making good progress. I found her dead in her cage one morning. She had not had notable respiratory symptoms the previous evening. On PM her lungs were completely abscessed.
At the age of 22 months Revelet had surgery for the removal of a typical mammary lump. The surgery was uncomplicated and she seemed to be recovering well. She was an apparently fit, healthy rat. Our rats have routine antibiotic cover post operatively for 5 days, so she was already on Baytril. At the time of her wound check with the vet (5 days) it was clear she was ‘declining’. Her breathing was increasingly laboured and she was losing weight rapidly. We extended her treatment to include cephalexin, but she continued to decline and died a few days later. PM showed completely abscessed lungs.
Author: Alison Campbell