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 characteristically
develop watery gray or serosanguineous drainage. Infection in the
subcutaneous space can result in abscess formation and regional
lymphadenopathy. Infection also can present as tenosynovitis, septic
arthritis, or osteomyelitis. These expressions of infection usually
occur after cat bites, which tend to penetrate tissue spaces more
deeply than do dog bites. Joint stiffness with cellulitis of the
hand is a finding suggestive of tendon sheath involvement.
When P multocida infection is not related to an
animal bite, the most common focus of infection is the respiratory
tract. The clinical manifestations are those expected for children with
exacerbations of chronic underlying conditions, such as bronchiectasis
or chronic bronchitis. Several cases of pleural empyema and of lung
abscess have occurred may occur.
Meningitis, with or without bacteremia, is the most common manifestation
of invasive infection caused by P multocida. Most
children diagnosed as having Pasteurella meningitis
are younger than 1 year of age, and most have had contact with a
pet within the household.1 Usually, these infections
develop after animal contact, such as licking, that does not violate
cutaneous barriers. The presenting features include lethargy, irritability,
and fever, similar to bacterial meningitides.
P multocida urinary tract infection has occurred
in children with obstructive uropathy, and peritonitis can occur
in patients with chronic renal disease who are receiving peritoneal
dialysis.5 The organism has been isolated from children
with periappendiceal abscess or with peritonitis in association
with appendicitis. It is not known whether these infections result from
hematogenous spread or from ingestion of the organism. There are
also case reports of other unusual manifestations of infection
by due to P multocida such as include tonsillitis, endocarditis,
brain abscess, or infection of a ventriculoperitoneal shunt.6-8 Brain
abscess has resulted from a dog bite that penetrated a small child’s
Isolation of the organism from the drainage of skin lesions caused
by bite wounds or from other sites of focal infection, such as joint
fluid or aspirate of the subperiosteum, is diagnostic.9 Pleural
fluid or sputum can yield the organism in patients with pulmonary
infection. In disseminated infection, P multocida can
be isolated from cultures of blood or, with meningeal involvement,
from the cerebrospinal fluid.
P multocida is a small, nonmotile gram-negative
rod that grows well on standard media, including blood, chocolate,
and Mueller-Hinton agars. Colonies resemble those of enterococci
on blood agar plates. If P multocida is suspected, laboratory
personnel should be alerted so that appropriate confirmatory biochemical
testing can be performed.
Laboratory differentiation from morphologically similar organisms,
such as Haemophilus influenzae, is not difficult.
Penicillin is the drug of choice for P multocida infection.
Other effective oral agents include ampicillin, ampicillin-clavulanate, cefuroxime,
cefpodoxime, doxycycline, and fluoroquinolones.9 Susceptibility
testing should be performed, but β-lactamase–producing strains have
been recovered only rarely.10 Because polymicrobial
infection should be assumed after an animal bite, empirical therapy consisting
of oral amoxicillin-clavulanate or intravenous ampicillin-sulbactam
should be initiated in this setting while culture results are pending.
Parenterally administered broad-spectrum cephalosporins such as
cefotaxime and ceftriaxone have good activity and have been used
successfully to treat invasive P multocida infection.
In children who are allergic to β-lactam agents, the
optimal treatment for P multocida infection is problematic.
Doxycycline is effective, but tetracyclines should be administered
to children younger than 8 years of age only after assessment of
the risk-to-benefit ratio. Azithromycin exhibits good activity against P
multocida.11 A recommended oral alternative
for empiric treatment of dog or cat bite wounds in penicillin-allergic children
is an extended-spectrum cephalosporin or trimethoprim-sulfamethoxazole plus
clindamycin.12 Trimethoprim-sulfamethoxazole is
effective against P multocida as well as Staphylococcus
aureus. Clindamycin is active against anaerobes, as well
as streptococci and most S aureus. This combination
can be employed parenterally for wounds of severity warranting hospitalization.
The usual duration of therapy is 7 to 10 days for focal soft-tissue
infections. A longer treatment course can be required for septic
arthritis and osteomyelitis. For pulmonary or disseminated infection,
including meningitis, 10 to 14 days of therapy is usually required.
Infected animal bite wounds should be adequately debrided. Infected
collections of fluid should be drained, and devitalized tissue should
be removed. Consultation with a specialist in hand surgery is appropriate
for tendon sheath involvement. Preventive treatment for rabies (see Chapter 321) should be instituted
only if clinical circumstances warrant.
Educational interventions regarding appropriate interactions
with domestic animals and limiting interactions with wild animals
can help to prevent P multocida infections.