Pasteurella Multocida Infection in Cats

Abstract

Overview:

Pasteurella species are part of the normal oral flora of cats. They are also a common cause of infection in this species and an important zoonotic agent.

Infection in cats:

Pasteurella species are commonly isolated from subcutaneous abscesses and pyothorax in cats. They may also cause secondary lower respiratory tract infection and have been associated with spinal empyema and meningoencephalomyelitis.

Infection in humans:

Disease in humans mainly occurs after a cat bite or scratch, but may also be transmitted via respiratory secretions from cats in close contact with a person. Signs of local infection after a cat bite appear in a few hours (3–6 h). Severe disease and a fatal outcome mostly occur in immunocompromised people, but have also been reported in immunocompetent healthy individuals. Cat ownership by immunocompromised people may carry a risk.

Bacterial properties

Pasteurella multocida, a Gram-negative, facultative anaerobic, non-spore-forming pleomorphic coccobacillus, is a commensal bacterium and part of the natural flora in the nasopharynx and upper respiratory tract of the cat.^1,2 In one study, a 90% carrier state in gingival margins was shown. ¹

Several subtypes have been associated with human infections: P multocida subspecies multocida, P canis, P multocida subspecies septica, P stomatis and P dagmatis. ³

Epidemiology and pathogenesis

Cat bites frequently become infected (20–80%), and P multocida is the most commonly cultured bacterium from infected bite wounds. ¹ Apart from bites, scratches and licks, close contact has also been sufficient for infection. Bacteria usually enter through skin wounds, but inhalation of secretion droplets from the upper respiratory tract is another possible source. ⁴

Clinical presentation

P multocida is one of the most frequent pathogens in infected skin wounds and subcutaneous abscesses. ⁵ It is also one of the common bacteria producing pyothorax in cats.^6–8 Pasteurella species may also cause secondary lower respiratory tract infection and have been associated with spinal empyema and meningoencephalomyelitis.^9,10

Diagnosis

Diagnosis is made on the basis of bacterial culture from infected tissues or secretions. Pasteurella grows readily on chocolate and sheep-blood agar media, but fails to grow on MacConkey agar, the usual medium for Gram-negative bacteria. Strains are usually catalase-, oxidase-, indole- and sucrose-positive.

Treatment

Penicillins and potentiated beta-lactams (amoxicillin-clavunalate potassium) are first-line antibiotics for the treatment of Pasteurella species infections [EBM grade II].^1,5,12 Quinolones, cephalosporins and modern macrolides are also indicated. ¹ In severe cases, therapeutic decision making must be based on antibiotic susceptibility tests.

Key Points

• Pasteurella species are commensal bacteria present in the oral cavity of most cats.

• Cat bites, scratches or even simply close contact may transmit Pasteurella species to humans.

• Local infections are common in persons after a cat bite.

• Severe infections, septicaemia and peritonitis may occur in immunocompromised people, and less frequently in immunocompetent individuals in contact with cats.

• Pasteurella is common in subcutaneous abscesses and pyothorax in cats.

• Diagnostic confirmation of Pasteurella species infection is not difficult, as it grows readily in routinely used bacterial culture media.

• Penicillins and potentiated beta-lactams are first-line antibiotics in both humans and cats.

• The zoonotic potential is important, especially in immunocompromised people, and cat ownership in these situations must be discussed.