Pasteurellosis

This page is about clinical aspects of the disease.  For microbiologic aspects of the causative organism(s), see Pasteurella multocida.

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Danitza Lukac

Synonyms and keywords: Shipping fever; bovine respiratory disease complex; fibrinous pneumonia; pasteurella pneumonia; hemorrhagic septicemia; fowl cholera; snuffles

Overview

Pasteurellosis is an infection with a species of the bacterial genus Pasteurella, which is found in humans and other animals.

Pasteurella multocida (subsp. septica and subsp. multocida) is carried in the mouth and respiratory tract of various animals, including pigs. It is a small Gram negative bacillus with bipolar staining by Wayson stain. In animals, it can originate fulminant septicaemia (chicken cholera), but is also a common commensal.

Until taxonomic revision in 1999, Mannheimia spp. were classified as Pasteurella spp., and infections by organisms now called Mannheimia spp., as well as by organisms now called Pasteurella spp., were designated as pasteurellosis. The term "pasteurellosis" is often still applied to mannheimiosis, although such usage has declined.

Historical Perspective

• The genus Pasteurella is named after the French chemist and microbiologist, Louis Pasteur, who first identified the bacteria now known as Pasteurella multocida as the agent of chicken cholera.

Pathophysiology

• The mechanisms of pathogenesis of Pasteurella infection in its natural host species and in humans are still not completely understood, and further studies are needed.
• Pasteurella is usually transmitted via the cutaneous route to the human host.
• Pasteurella uses a number of mechanisms for avoiding or suppressing bactericidal responses:
  • Lipopolysaccharides (LPS) and the bacterias capsule probably play a substantial role in intracellular survival
  • P. multocida capsule has been shown in strains belonging to serogroups A and B to help resist phagocytosis by host immune cells and capsule type A has also been shown to help resist complement-mediated lysis
  • The LPS produced by P. multocida consists of a hydrophobic lipid A molecule (that anchors the LPS to the outer membrane), an inner core, and an outer core, both consisting of a series of sugars linked in a specific way
  • A study in a serovar 1 strain showed that a full-length LPS molecule was essential for the bacteria to be fully virulent in chickens
  • Strains that cause atrophic rhinitis in pigs are unique as they also have P. multocida toxin (PMT) residing on a bacteriophage. PMT is responsible for the twisted snouts observed in pigs infected with the bacteria. This toxin activates Rho GTPases, which bind and hydrolyze GTP, and are important in actin stress fiber formation
  • Formation of stress fibers may aid in the endocytosis of P. multocida
  • The host cell cycle is also modulated by the toxin, which can act as an intracellularmitogen
• Pasteurella needs iron to grow.
  • P. multocida has developed mechanisms acquire iron from hemoglobin, ferritin, lactoferrin and transferrin.

Causes

• Pasteurellosis is caused by an infection with Pasteurella spp.
• Pasteurella is a gram-negative, facultatively anaerobic bacteria.
• Pasteurella species are nonmotile and pleomorphic.
• Most Pasteurella species are catalase- and oxidase-positive.
• P. multocida is the most frequent causative agent in human.
• Pasteurella cells occur in many cats mouths, a large percentage of dogs mouths, and frequently in rabbits. This is in perfectly normal and otherwise healthy animals.
  • Cats oral cavity colonization of P. multocida is between 70%–90%
  • Dogs oral cavity colonization of P. multocida is between 50%–60%
• Several reports describe human infections by Pasteurella spp. that were acquired after close contact with pets, including sharing a bed, being licked by, kissing the pets, animal scratches or bites.
• Less commonly, pasteurellosis can be acquired by inhalating the bacteria, human-to human transmission or with non known source of infection.
• Pasteurella can be transmitted when exposed to animals that have been exposed directly or indirectly to the animals oropharyngeal secretions through licking or sniffing.

Differentiating Pasteurellosis from other Diseases

Pasteurellosis must be differentiated from:

• Cat scratch disease
• Abscesses:
  • Abdominal
  • Brain
  • Liver
  • Lung
  • Perinephric
  • Due tu amebas, streptococcus, staphylococcus, and anaerobic bacteria
• Cellulitis
• Animal Bites
• Pneumonia:
  • Bacterial
  • Comminuty-adquired
• Abdominal Sepsis
• Haemophilus spp. infections
• Actinobacillus actinomycetemcomitans infection
• Cardiobacterium hominis infection
• Eikenella corrodens infection
• Kingella spp infection
• Peritonitis
• Meningitis

Epidemiology and Demographics

• It is difficult to establish the true prevalence and incidence of pasteurellosis because disease reporting is not required.
• P. multocida oral cavity colonization in cats, dogs and other animals is common worldwide.
• An estimated 4.4 million animal bites occur each year in the United States
• The annual incidence of dog and cat bites has been reported as 300 bites per 100,000 population
• The mortality rate of pasteurellosis is approximately 25-30%.
• The mortality rate of pasteurellosis patients with meningitis and neurological manifestations is approximately 17-29%.
• The mortality rate of pasteurellosis patients with bacteremia is approximately 40-63%.

Risk Factors

• Animal exposure
• Children: Among children, the rate of dog-bite–related injuries is highest for those 5 to 9 years old. Children are more likely than adults to receive medical attention for dog bites.
• Men: Men are more likely than women to be bitten by a dog.
• Elderly
• Pregnant women
• Immunosuppressed individuals

Natural History, Complications and Prognosis

If left untreated, patients with pasteurellosis may progress to develop soft tissue inflammation. Common complications of pasteurellosis include cellulitis, septic arthritis, and osteomyelitis. Patients with cutaneous infection have the most favorable prognosis with adequate treatment.

Natural History

• Pasteurellosis incubation period occurs within 24 hours.
• Initial presentation usually shows as soft tissue inflammation.
• If left untreated, patients with pasteurellosis progress to develop complications.

Complications

• Pasteurellosis complications include:
  • Cellulitis
  • Subcutaneous abscesses
  • Septic arthritis
  • Lower respiratory tract infections
  • Upper respiratory tract infections
  • Osteomyelitis
  • Bacteremia
  • Endocarditis
  • Meningitis
  • Peritonitis

Prognosis

• The prognosis varies with the type of infection; cutaneous infections have the most favorable prognosis with adequate treatment.
• Prognosis is generally poor for patients who develop bacteremia, endocarditis and meningitis.

History and Symptoms

There are several forms of the infection:

• Skin/subcutaneous tissue disease is a septic phlegmon that develops classically in the hand and forearm after cat bite. Inflammatory signs are very rapid to develop; in 1 or 2 hours, edema, severe pain and serosanguineous exudate appear. Fever, moderate or very high can be seen along with vomiting, headache and diarrhea. Lymphangitis is common. Complications are possible, in the form of septic arthritis, osteitis or evolution to chronicity.
• Sepsis is very rare, but can be as fulminant as septicaemic plague, with high fever, rigors and vomiting, followed by shock and coagulopathy.
• Pneumonia disease is also rare and appears in patients with some chronic pulmonary pathology. It usually presents as bilateral consolidating pneumonia, sometimes very severe.

Other locations are possible, such as septic arthritis, meningitis and acute endocarditis, but are very rare.

Diagnosis

• Diagnosis is made with isolation of Pasteurella multocida in a normally sterile site (blood, pus or CSF)
• P. multocida has been observed invading and replicating inside host amoebae, causing lysis in the host. P. multocida will grow at 37 °C on blood or chocolate agar
  • Colony growth is accompanied by a characteristic "mousy" odor due to metabolic products
• Being a facultative anaerobe, it is oxidase-positive and catalase-positive, and can also ferment a large number carbohydrates in anaerobic conditions

Treatment

As the infection is usually transmitted into humans through animal bites, antibiotics usually treat the infection, but medical attention should be sought if the wound is severely swelling. Pasteurellosis is usually treated with high-dose penicillin if severe. Either tetracycline or chloramphenicol provides an alternative in beta-lactam intolerant patients. However, it is most important to treat the wound.

Prevention

Preventing dog bites:

• Do:
  • Remain motionless (e.g., "be still like a tree") when approached by an unfamiliar dog.
  • Curl into a ball with your head tucked and your hands over your ears and neck if a dog knocks you over.
• Don't:
  • Approach an unfamiliar dog.
  • Run from a dog.
  • Panic or make loud noises.
  • Disturb a dog that is sleeping, eating, or caring for puppies.
  • Pet a dog without allowing it to see and sniff you first.
  • Encourage your dog to play aggressively.
  • Let small children play with a dog unsupervised.

See also

• Hemorrhagic septicemia
• Pasteurellaceae

External links

• Pasteurella multocida-related diseases in sheep and goats