Pasteurella multocida, formerly known as Pasteurella
septica, was renamed P multocida or “killer
of many” because it affects many different animal species.1 The
first report of human infection caused by P multocida was
published in 1919.2 The primary importance of the organism
in pediatrics is in animal bites in which P multocida, alone
or in concert with other organisms, is the most common infecting
There are several species in the genus Pasteurella. The
most common human pathogen is P multocida, but
infection also can be caused by one of the related species such
as P canis or P dagmatis. There
are 3 subspecies of P multocida: multocida, septica, and gallicida. More
than one half of human infections are caused by P multocida subspecies multocida. Defining
the subspecies aids in epidemiologic investigation, but is not necessary
in the usual clinical setting.
The organism is found as a component of the oral flora of 70% to
90% of cats and at least 25% to 50% of
dogs. Other animals, including rabbits, rats, or pigs, also can
harbor the organism in respiratory tract or oral secretions. Carriage
of P multocida by humans is uncommon, but commensal
carriage can occur as a consequence of frequent animal contact.3 The
usual mode of transmission is direct inoculation from the bite or
scratch of a colonized animal. P multocida has
been implicated as causal in 50% of dog and 80% of
cat bite wound infections.
The pathogenesis of infection caused by P multocida is
dependent upon the portal of entry of the organism. The three major
clinical expressions of disease are focal infection, respiratory
tract infection, and invasive infection.4 Focal
infection is initiated by direct inoculation of the organism into
the subcutaneous tissue, bone, or joint space after a cat scratch
or bite or a dog bite. Inoculation is likely to be deeper after
a cat bite than a dog bite. The organism produces endotoxin, which
may promote the inflammatory reaction that is observed, often within
hours, after inoculation.
Respiratory tract infection occurs as the result of inhalation
of P multocida. Animal-to-human but not human-to-human
spread has been documented. The organism has low pathogenicity in
the respiratory tract, and infection has been documented almost
exclusively in the setting of altered host resistance from disease
processes such as bronchiectasis or chronic bronchitis.
Invasive infection occurs when hematogenous dissemination complicates
primary soft tissue or pulmonary infection. Bacteremic infection
is a particular risk for children with hepatic dysfunction and reduced
efficiency of reticuloendothelial clearance mechanisms.
Focal infection, usually manifested as cellulitis, develops rapidly
after inoculation of P multocida. The average time
of onset of erythema, swelling, and pain is within 24 hours after
an animal bite or scratch. Infections due to P multocida...