Kristin Claricoates, DVM
Pasteurella is a gram negative rod bacteria. It is an opportunistic bacteria when in the body, which means that the bacteria is normal and in certain parts of the rabbit’s body. If, however, it relocates to another part of the body, it is capable of causing disease. In rabbits, pasteurella is a major cause of respiratory diseases. If your rabbit has a respiratory disease, pasteurella multocida should be considered but never assumed to be the cause of a respiratory disease. Several other causes of respiratory disease are Bordetella bronchiseptica, Staphylococcus, Pseudomonas, or Pasteurella multocida. Pasteurella is one of the common causes of rabbit “snuffles” or respiratory infections. Interestingly, some rabbits exposed to pasteurella resisted the infection, spontaneously eliminated the infection, became subclinical carriers, developed acute disease (a bacteremia or pneumonia) or developed chronic disease.
There are several serotypes of this bacteria, labeled A, B, C, D, E, or F. The way this bacteria is more or less virulent depends on properties of the bacteria, such as adhesions, phagocyte resistance, endotoxins, exotoxins, and iron regulation. The type A strains are more likely to cause infection in the respiratory tract and are commonly seen. The type D strains are significantly more pathogenic and cause bacteremia (bacterial infection that goes to the bloodstream and spreads through the entire body) more often. One of Pasteurella’s properties is that it has developed a thick capsule which prevents the bacteria from being eaten. Type D actually can avoid being broken down because it can resist bactericidal activity.
Transmission of pasteurella is by aerosol from acutely affected rabbits, by direct contact with affected rabbits, or by fomites (things like towels, blankets, or other things that are carried between the affected rabbit and a healthy rabbit). The bacteria enters the body through the nares or wounds. Rarely, venereal (sexual) transmission can occur with genital infections. If the body does not resist the infection, then the bacteria colonizes the nares and may cause production of a nasal discharge. The period of time between infection and showing signs of that infection is difficult to define because many rabbits are subclinical carriers of the infection, which means they may not show signs of the infection at all. In experimental studies, rhinitis (inflammation and infection of the nasal passages) occurred 1-2 weeks after intranasal inoculation, suggesting that the incubation time of this infection is 1-2 weeks. Once the bacteria becomes established in the nasal passages, the infection spreads to nearby tissues. Spreading hematogenously (by bloodstream) also can account for infection that reaches the internal organs, lungs, and middle ears.
Pasteurella is a commensal organism on mucous membranes, but can exhibit pathogenicity (infectious nature) under conditions of immunodeficiency and stress in the host. Nutritional, environmental, managerial, or social changes may predispose a rabbit to disease, as may infection from something else at the time of pasteurella infection, and physical or chemical injury to the mucosa. In disseminated pasteurellosis (pasteurella that is spread widely over the whole body), fever enhances the immune system response and increases survival. At this time, there is no vaccine available for rabbits.
Forms of pasteurellosis are varied. They can be signs of an upper respiratory tract disease (rhinitis, sinusitis, conjunctivitis, lacrimal duct infection), otitis, pleuropneumonia, bacteremia, abscesses of subcutaneous tissues or internal organs, bones, joints, and genitalia.
Affected rabbits present with audible respiratory noises, infection of nasal lacrimal duct may extend to the conjunctiva. Affected rabbits make audible noises and have bouts of sneezing. Conjunctivitis may sometimes be present. Infection can spread from the nares to the middle ears through the eustachian tubes. Otitis can also present where there is purulent white debris. The more pathogenic strains of pasteurella are likely to spread by the bloodstream (hematogenously) causing acute generalized disease, fever, and sudden death.
Diagnosis is made by isolation of the bacteria. This requires a culture before using antibiotics. Once antibiotics have begun, bacteria may be difficult to grow. A swab of the nasal cavities is taken. Also, serologic testing from a sample of blood is used. It is helpful in detecting internal infections or subclinical carriers. After the culture returns, we will determine what antibiotic is the best to treat pasteurella based on what the bacteria is sensitive to.
Once the culture returns, your pet is placed on the appropriate antibiotic based on the sensitivity and your pet is rechecked several weeks later to determine if the infection is gone or still present.
Works Cited:
Quesenberry, Katherine E., and James W. Carpenter. Ferrets, Rabbits and Rodents: Clinical Medicine and Surgery. Missouri: Saunders, 2004. Print.