Bacterial Infectious Diseases in Ferrets and Rabbits

Karen L. Rosenthal, DVM, MS, Diplomate ABVP-Avian
Director, Special Species Medicine
Clinical Studies-Philadelphia
University of Pennsylvania
School of Veterinary Medicine
Philadelphia, PA, 19104

Ferrets and rabbits, like all patients, are prone to bacterial infections. Ferrets react to bacterial infections the same way as dogs and cats. Rabbits are more likely to form walled off abscesses filled with a caseated, purulent material. Both gram positive and gram negative bacteria cause infection in small mammals. Most infections are due to aerobic bacteria but anaerobes can also cause disease.

Primary bacterial infections in pet ferrets are not common. If present, these bacterial infections are secondary to another primary disease process. Bacterial cystitis, not common, is usually noted in association with urolithiasis. An infrequent complication of adrenal gland disease in male ferrets is bacterial prostatitis. Signs include dysuria, mucoid urine, and hematuria. Diagnose bacterial prostatitis by exploratory laparotomy and the finding of a prostate filled with purulent material. Gram negatives are commonly isolated. The cystic nature of this disease and the resistant bacteria make this a difficult infection to treat. Treat cystic bacterial prostatitis by removing the affected adrenal glands, draining the cysts during surgery and administration of appropriate antibiotics. It is not uncommon to have to marsupilize the prostate to the body wall because the prostatic cysts persist past surgery. Bacterial prostatitis can endure even when there is no longer adrenal gland androgen influence over the prostate. Ferrets with prolonged bacterial prostatitis are hyperthermic, lethargic, and can become septic.

The ferret respiratory tract is an uncommon area for bacterial infection. Upper respiratory tract bacterial infection is very uncommon. Signs of upper respiratory tract bacterial infection include sneezing and nasal discharge. Culture of the nasal discharge is difficult to interpret as to which are normal bacterial inhabitants versus pathogenic bacteria. Both canine distemper (CDV) and influenza virus can be complicated by secondary bacterial respiratory disease. Realistically, bacterial pneumonia secondary to CDV infection is rarely treated as CDV itself is fatal in ferrets. Bacterial respiratory disease secondary to influenza virus infection is rare in immune competent ferrets. Bacterial pneumonia can also occur secondary to aspiration from megaesophagus. Ferrets with bacterial pneumonia cough, are lethargic, and are hyperthermic. Diagnose bacterial pneumonia by signs, thoracic radiographs, and a tracheal wash. Administer antibiotics and supportive care to ferrets with pneumonia.

Primary bacterial dermatitis is rare in ferrets but skin tumors are common in ferrets. Do not mistake a skin tumor, especially a mast cell tumor, as bacterial dermatitis. Diagnose bacterial dermatitis with cytology or biopsy and culture of the affected area.

Gastrointestinal disease is common in ferrets and bacterial infections likely account for some of these problems. The incidence of primary bacterial gastroenteritis is unknown. Possibly, the most common infection is caused by Helicobacter mustelae. It causes ulceration of the gastrointestinal mucosa and an active infection is characterized by lethargy, vomiting, anorexia, melena, and weight loss. Definitive diagnosis of helicobacter disease is best made on clinical signs, gastric biopsy, and response to treatment. Other gastrointestinal bacterial infections appear to be uncommon in ferrets. In practical terms, non-infectious etiologies are more likely a cause of diarrhea in ferrets. These would include foreign bodies, trichobezoars, and neoplasia. A fecal culture can be difficult to interpret.

Ferrets with bacterial infections have distinct alterations in their hematology profile. A rise in the white blood cell count above 8,000 with neutrophils the predominant cell is. In acute, severe infections, band cells are present. As the bacterial disease becomes chronic, an increase in monocytes is observed.

Diagnose bacterial infections in ferrets by history, signs, cultures, and response to treatment. Since bacterial infections in ferrets are usually a rare occurrence, this should be lower on a list of differential diagnoses. Treatment of bacterial infections in ferrets depends on the system involved and the severity of disease.

Unlike ferrets, bacterial infections are common in rabbits. Bacterial infections in rabbits incite an inflammatory reaction characterized by caseated pus and walled-off abscesses which makes antibiotic treatment alone usually unsuccessful.

Possibly the most common area for rabbit bacterial infection is the respiratory tract. Signs of upper respiratory disease include nasal discharge, sneezing, and difficulty breathing. The lay term for upper respiratory disease in rabbits is "snuffles". Bacterial pneumonia, both clinical and subclinical, is common in pet rabbits. Bacterial pneumonia is characterized by dyspnea, tachypnea, and hyperthermia. Diagnosis of respiratory bacterial disease in rabbits is based on signs, history, and radiographs. Ideally, diagnosis is further based on culture and sensitivity if a tracheal wash is attempted. Pasteurella multocida is commonly implicated as the cause of respiratory disease in rabbits but likely many species of bacteria are the cause of this problem. Bacterial infections of the respiratory tract likely act as the nidus for which bacteria spread to other areas of the body.

Bacterial otitis is common in rabbits. Bacterial respiratory infection leading to local invasion of the ear canal may be the cause of otitis. Aural discharge and inflammation along with head tilt are the most common signs of bacterial otitis. It is possible that aural bacterial infections may seed from the ear following the cranial nerves into the central nervous system.

Ocular bacterial infections are also common in rabbits. Presentations of ocular bacterial infection include blephrospasm, excessive tearing, discharge, reddening, and swelling of the ocular tissues. Intraocular infections are characterized by hypopion and abscesses that can be attached to intraocular tissue. Diagnosis is based on physical examination, corneal staining, flushing of the naso-lacrimal duct, and culture.

The rabbit urinary tract is another frequent site of bacterial infections. Bacterial cystitis is common and is thought to be one of the pre-disposing causes for urolithiasis in rabbits. Signs of bacterial cystitis include stranguria, dysuria, hematuria, anorexia, and lethargy. Diagnose rabbit urinary tract bacterial infections with urinalysis, urine culture or culture of the bladder wall, and response to treatment. When urolithiasis is present, some feel it is best to assume an underlying bacterial infection is present and part of urolithiasis treatment should include culture for bacterial antibiotics.

Bacterial dermatitis in rabbits, characterized by subcutaneous abscess formation, is common. Likely, the etiology of these spontaneous abscesses is a bacterial nidus of infection somewhere else in the body. Superficial bacterial dermatitis is usually secondary to other conditions such as perineal ulceration due to urine scald. Diagnose bacterial dermatitis with cytology, biopsy, and culture.

Bacterial infection of the reproductive tract in rabbits is uncommon. In males, bacterial infection of the scrotal area and surrounding tissue is a consequence of improper surgical technique. Infection of the female reproductive tract is uncommon. Infection of the ovariohysterectomy surgical site occurs as a consequence of improper surgical technique.

Bacterial osteomyelitis is most commonly observed in the mandible of the rabbit. This is usually due to dissemination of bacteria from other areas of the body, especially from diseased tooth roots. This infection appears as a firm swelling on the jaw of a rabbit. Use radiographs to determine the extent of the lesion. Most mandibular abscesses are non-resectable and therefore carry a poor prognosis.

Rabbits with bacterial infections may not show an increase in total white blood cell count. Instead, the relative heterophil count may increase and account for more than 90% of the total white blood cell count. Nucleated red blood cells may also be seen in acute bacterial infections. Blood chemistry changes may reflect organs that are affected. Possibly, inappropriately, much bacterial disease in rabbits is attributed to Pasteurella multocida. There are tests other than cultures to assess pasteurella infection in rabbits. Titers of antibodies to pasteurella must be interpreted with caution. They are only measurement of exposure, not infection. This may make them less useful as measurement of infection.