Pasteurella multocida is a small, gram-negative, nonmotile, non–spore-forming coccobacillus with bipolar staining features. The bacteria typically appear as single bacilli on Gram stain; however, pairs and short chains can also be seen. P multocida often exists as a commensal in the upper respiratory tracts of many livestock, poultry, and domestic pet species, especially cats and dogs. In fact, Pasteurella species are some of the most prevalent commensal bacteria present in domestic and wild animals worldwide. P multocida infection in humans is often associated with an animal bite, scratch, or lick, but infection without epidemiologic evidence of animal contact may occur. See the image below.
Wound infections associated with animal bites usually have a polymicrobial etiology, mandating the empiric use of broad-spectrum antimicrobials targeted at both aerobic and anaerobic gram-negative bacteria. Nevertheless, Pasteurella species are commonly isolated pathogens in most animal bites, especially in dog- and cat-related injuries. These injuries can be aggressive, with skin manifestations typically appearing within 24 hours following a bite. These wounds can exhibit a rapidly progressive soft-tissue inflammation that may resemble group A β-hemolytic Streptococcus pyogenes infections.
Deeper soft tissue can also be affected, manifesting as tenosynovitis, septic arthritis, and osteomyelitis. More-severe disseminating infections may also develop, including endocarditis or meningitis, the latter mimicking Haemophilus influenzae or Neisseria meningitides infections in young children. Fortunately, Pasteurella species are fairly sensitive organisms and can be treated with a penicillin-based regimen.
Local: P multocida infection usually presents as an infection that complicates an animal bite or injury. Complications include rapidly progressive cellulitis, abscesses, tenosynovitis, osteomyelitis, and septic arthritis.  The latter two are particularly common following cat bites because of their small, sharp, penetrative teeth. 
Respiratory: P multocida may cause upper respiratory tract infections, including sinusitis, otitis media, mastoiditis, epiglottitis,  pharyngitis, and Ludwig angina.  In rare cases, P multocida may also cause lower respiratory tract infections, including pneumonia, tracheobronchitis, lung abscess,  and empyema,  usually in individuals with underlying pulmonary disease.
Cardiovascular: P multocida has been reported to cause native-  and prosthetic-valve endocarditis,  pericarditis, mycotic aneurysms,  vascular graft infections,  central venous catheter infections, bacteremia, sepsis, septic shock,  and disseminated intravascular coagulation. 
Central nervous system: P multocida is an uncommon cause of meningitis,  subdural empyema, and brain abscess.  P multocida meningitis has been associated with cat licks and bites occurring on the face in persons at the extremes of age. 
Gastrointestinal: P multocida rarely causes gastrointestinal problems but has been associated with appendicitis, hepatosplenic abscesses, and spontaneous bacterial peritonitis. P multocida has been isolated in patients with polymicrobial peritoneal dialysis catheter–associated peritonitis. 
According to the American Pet Products Association, approximately 180 million dogs and cats live in the United States, cats currently outnumbering dogs by 12 million. Animal bites account for 1% (300,000) of annual emergency department visits. The estimated cost in health care expenditures has been reported to be $30 million per year. Approximately 10% of animal bites require medical attention; 1-2% eventually require hospitalization.
Approximately 5 million animal bites are reported annually. The vast majority of animal bites involve dogs (85-90%), followed by cats (5-10%).
Infectious complications occur in approximately 15-20% of dog-related bites and more than 50% of cat-related ones. Dog bites are associated with younger animals engaging in playful activities, mostly with children. German shepherd, pit bull, Staffordshire terrier, and mixed breeds are most commonly involved with human bites, while the golden retriever and Labrador retriever are least. Cat bites are usually provoked, typically by female felines, and occurring on the upper extremities or face. Sharp and long teeth of cats can easily penetrate human skin and create a deep puncture wound and even inoculate the periosteum component of bones. Indeed, cat-related wounds more commonly progress to more serious and deeper-tissue infections, including osteomyelitis and meningitis.
P multocida infections occur worldwide. Cats are involved in 60-80% of human P multocida infections. Moreover, P multocida is isolated in 50% of dog bites.
It is estimated that 10-20 human deaths per year occur following an animal bite.
Infectious complications occur in approximately 15-20% of dog-related bites and more than 50% of cat-related ones. Following a bite, a rapidly progressive cellulitis may develop; deeper structures, including tendons, joints, and bones, can become affected, especially in cat-related injuries. Dissemination can occur.
Chronic obstructive pulmonary disease is a risk factor for P multocida respiratory tract infection,  which carries a mortality rate of approximately 30%. Diabetes mellitus  and liver dysfunction  are predisposing conditions associated with pasteurellosis and associated bacteremia.
Localized P multocida infections carry an excellent prognosis. Significant morbidity has been associated with musculoskeletal P multocida infections, especially those involving the hand. Disseminated P multocida infections carry a 25-30% overall mortality risk.
All age groups can be affected by P multocida infections. Young children seem to be frequently involved in nonfatal dog bites. P multocida meningitis typically occurs in persons at the extremes of age.
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