Pasteurella pneumotropica Infection

Pasteurella pneumotropica frequently infects mice, often without clinical disease. It is associated with a number of lesions in mice as an opportunistic pathogen, but its true nature as a primary pathogen is questionable.

Although mice are experimentally susceptible to Pasteur- ella multocida, naturally occurring disease due to P. mul- tocida is rare in mice.

Epizootiology and Pathogenesis

Pasteurella pneumotropica is a ubiquitous commensal bacterium in nearly all, if not all, wild mice, and is common among laboratory mouse populations. Elimi­nation of P. pneumotropica from a mouse population allows some other Gram-negative bacterium, such as K. oxytoca, to fill its opportunistic niche. Infection is typically inapparent, but the bacterium has a propensity to complicate or cause disease in tissues that have been perturbed by other factors. Pasteurella pneumotropica is shed from upper respiratory secretions and feces and is spread by direct contact. The vagina and uterus are often colonized without disease, and thus it is transmitted from dam to pups during or shortly after birth. Fetuses can also be infected in utero, which may explain why P. pneumotropica is a frequent agent in failure of cesarean rederivation. Seroconversion normally occurs only in mice with overt disease.

Pathology

Disease associated with P. pneumotropica is varied, including conjunctivitis, panophthalmitis, dacryoade- nitis, periorbital abscessation, rhinitis, otitis (externa, media, and interna), and cervical lymphadenitis. It is also associated with suppurative lesions and abscesses of preputial glands, bulbourethral glands, and muscles.

Diagnosis

Culture of the organism from lesions, with subsequent identification, is required. In live animals, oral swabs or fecal culture appear to be sites of choice for sample collection. Although most strains will grow in conven­tional media (e.g., blood agar plates), NAD growth factor­requiring strains of P. pneumotropica have been identi­fied, as have closely related Pasteurellaceae, including Actinobacillus muris and Haemophilus influenzaemurium. Pasteurella ureae may also cause abortion, metritis, and stillbirths and can be discriminated from P. pneumotrop- ica biochemically as indole negative and mannitol posi­tive. PCR assay and DNA extraction are other techniques used to identify the organism. In screening mouse colonies for P. pneumotropica, serology is not particularly helpful, since Subclinically infected mice are normally seronegative. Differential diagnoses include infections from other pyogenic organisms. The primary cause for P. pneumotropica opportunism should be sought, such as predilection for conjunctivitis in BALB mice, fighting injuries, and respiratory tract infections due to M. pulmonis, Pneumocystis, and Sendai virus.