A Layman's Guide to the Health and Nursing Care of Rats
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NOTE:Being a prey species, rats often will not show signs of illness until they are very sick. Clinical signs would indicate the need for immediate treatment by a veterinarian.
CAR bacillus is highly contagious. It occurs naturally in a percentage of both domesticated, as well as wild rats. It also occurs in several species of mice and in rabbits.
CAR bacillus resides among and parallel to the cilia throughout the respiratory system. Cilia are tiny hair-like protrusions that extend from the surface of some cells and move in a wave-like fashion. Through a continuous beating movement, they function to move mucus and fluid that included entrapped contaminants out of the respiratory tree. Being mechanisms that have not been elucidated, CAR bacillus infection may disrupt this function resulting in accumulation of airway mucus airways and possible destruction of cilia. When cilia are damaged or missing, the bodyââ¬â¢s natural defenses against invading bacteria and ability to handle infection are decreased.
As a natural defense the body will send neutrophils (a type of white blood cell) in an attempt to envelope and destroy the invading bacteria. Unfortunately, not only are these neutrophils unable to destroy the CAR bacillus but they also produce antibacterial compounds and pus that can damage the host.
When clinical signs of disease are present, bronchopneumonia, bronchiectasis (dilatation of one or more bronchioles with filling of bronchi with mucus and pus) and atelectasis (failure of lung to inflate leading to consolidation of lungs, obstruction and prevention of air intake) may be found.
CAR bacillus can act as a primary pathogen and result in a chronic progressive respiratory disease. More typically it is seen as a co-pathogen, often in association with Mycoplasma pulmonis. It may increase the severity of disease caused by M. pulmonis and other respiratory pathogens. The host produces antibodies to CAR bacillus, however, these antibodies are ineffective at clearing the infection. (1)
Antibiotics can be used to help manage the clinical signs of CAR bacillus infection, but will not eradicate the pathogen.
Serology (ELISA; enzyme-linked immunoabsorbent assay) can be used to test for CAR bacillus. ELISA measures antibodies produced by the host (must be at least 6 weeks old) and found in the serum. An animal with an intact immune system exposed to CAR bacillus will produce antibodies (for testing purposes) within 7-10 days. Serology serves as a good screening tool because it is inexpensive, relatively sensitive, and can be performed on blood collected from a live rat. However, as with most bacterial ELISAs, this test is subject to false positive results. As a result, all positive serology results should be confirmed by other means. Negative serologic results likely indicate that CAR bacillus is not a problem; however repeat testing may be warranted in some cases due to the aforementioned delay between infection and antibody production.
PCR (polymerase chain reaction) is a fast and specific test for this bacterium. It can be performed on nasal swabs (use small uro-genital swabs). To collect a nasal swab, you will need to have your rat anesthetized during the collection.
The cost of an individual PCR test can range from approximately $50.00 - $80.00. The University of Missouri’s RADIL, Research Animal Diagnostic Laboratory, charges $55.00 per PCR assay test.
Microscopic examination of tissues is very specific test for CAR bacillus as the presence of the organism can be verified in the lung tissue. Tissue sent in for testing should be stained using both hematoxylin and eosin (a general stain for tissue lesions) and a silver stain such as Warthin-Starry or Steiner (used to identify bacteria colonizing the respiratory mucosa). Specific immunohistochemical techniques may also be employed, but these are often expensive and do not provide sufficient additional information to be cost effective (6). CAR bacillus spreads through the respiratory system in a descending manner. Therefore, the nasal passages and trachea will usually show infection first. This testing is restricted to postmortem examinations.
Electron microscopic examination of affected areas of the respiratory tract tissue will show the CAR bacillus residing amongst the ciliated regions.
Electron microscopy is very expensive and used primarily as a research tool.
Charles Rivers Laboratories: (800)338-9680
http://www.criver.com/research_models_and_services/research_animal_diagnostics/
UGA Veterinary Diagnostic Lab:
http://www.vet.uga.edu/dlab/
Since CAR bacillus infection is often seen in conjunction with M. pulmonis infection, it may help to treat the rat with broad-spectrum antibiotics that typically help to control the signs of that disease. If the rat is not responding then switching to a different antibiotic(s) may be appropriate. Nebulized antibiotics, or a combination of nebulized and oral antibiotics, may prove to be more effective in threating this bacteria.
For a listing of antimicrobials and broad-spectrum antibiotics see the Rat Medication Guide. Also refer to listings in the Rat Health Guide articles: Mycoplasmosis, or Pneumonia, for additional therapies based on severity of signs.
NOTE: In Japan, research studies on mice have shown some success in controlling, preventing, and even eradicating CAR bacillus using sulfamerazine (3). Ampicillin has also been reported to have successful results in treating mice with CAR bacillus (2). It is unknown whether these treatment regimens will also work with rats.
CAR bacillus can not be spotted in a quarantine situation unless ongoing disease is severe enough to result in clinical disease. When combined with M. pulmonis infection, which unfortunately infects many pet rat populations, it may pose additional health issues. When combined with viral infections (such as SDA or Sendai) it can cause an increase in morbidity and mortality. CAR bacillus infection may also be sub clinical, with little or no obvious impact.
In a colony or sub group, with a high prevalence of infection, testing may help to determine if the group is infected.
In a pet scenario, with good husbandry practices, an infection with the CAR bacillus may not cause overt clinical signs. If rats are kept in a healthy manner, have no immune deficiencies, and/or have adequate resistance, then signs relating to CAR bacillus infection may not be a major issue. On the other hand, if these scenarios are not in place, CAR bacillus may amplify, speed up, and complicate new or existing respiratory diseases.
If a rat has tested positive for CAR bacillus it is best not to add it to a colony that is CAR bacillus free. In the event it is decided to add the rat, it will need to be caged separately so as not to spread the pathogen to the rest of the colony.
Use proper basic hygiene methods and allow no contact between an infected rat and the uninfected rats to help contain the disease.
Breeding sick or positive rats will spread the CAR bacillus. To establish whether a breeding colony is contaminated, multiple rats (over 6 weeks of age) from separate cages should be tested.
Posted on December 24, 2003, 15:16,
Last updated on December 23, 2008, 12:39
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