Pasteurellosis (Pasteurella multocida)

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Description:

Pasteurella is a type of bacterial that commonly infects the respiratory tract of calves causing bovine respiratory disease. Pasteurella multocida is one of the most common bacteria isolated from calves suffering from shipping fever pneumonia. Pasteurella is usually a secondary bacterial invader, meaning that a virus or some other disease first weakens the immune system thus allowing Pasteurella to invade. Pasteurella is found throughout the environment and within the upper respiratory tract of cattle, but it usually does not cause disease in otherwise healthy animals.

Etiology:

Pasteurella multocida is considered part of the normal bacterial flora of the upper respiratory tract of most cattle. Pasteurella can cause disease when it is inhaled into the deeper portions of the respiratory tract and the animal’s normal defense system is impaired. Normally, inhaled bacteria like Pasteurella is killed and removed by the body’s antibodies and macrophages. When a calf’s immune function is impaired by stress or diseases such as bovine rhinotracheitis virus (IBR), parainfluenza virus (PI-3), or bovine respiratory syncytial virus (BRSV). the bacteria can invade and cause disease. This is when you can see necrotizing, fibrinous pleuropneumonia. Pasteurella is spread via direct contact, or by ingestion of feed and water contaminated by nasal and oral discharges from infected cattle. Transmission of these bacteria is especially efficient when calves are crowded (as in shipment) or closely confined (as in a dairy calf nursery).

Symptoms:

The severity of disease depends on the pathogenisity of the bacteria and on the associated infections (IBR, PI-3, BVD, and BRSV, other viruses or bacteria). P. multocida is often associated with the longer-lasting cases of bovine respiratory disease. The clinical signs of infection start with depression, and decreased appetite. This progresses to complete loss of appetite, lowered head and ears, mucopurulent nasal discharge and a high fever (107F) and labored breathing. Breathing is painful for these animals and they will often show a moist cough, rapid shallow respiratory rate and reluctance to move around. If the animal is not treated by this stage of infection, the lungs can become irreversibly damaged, and the calf will often die.

Diagnosis:

On physical exam, the above clinical signs will be noted. Auscultation of the cranioventral lung field often reveals increased bronchial sounds, crackles, and wheezes. Necropsy of an affected animal will show small amounts of fibrin exudation, some thromboses, limited lung necrosis, and suppurative bronchitis and bronchiolitis. A diagnosis of Pasteurellosis relies on bacterial culture. Given that pasteurella multocida is a normal inhabitant of the upper respiratory tract, it is helpful to collect bacterial culture samples from within the lung tissues of a dead calf being necropsied. Otherwise, bacterial culture samples can be collected via transtracheal wash, bronchoalveolar lavage, or tracheal swab.
 

Treatment:

The outcome of treatment depends significantly on the stage at which disease is detected. Early recognition of pasteurellosis is critical and is associated with a better outcome. Antibiotic treatment is necessary to stop the progression of disease caused by bacterial invasion of the lungs. Bacterial culture and sensitivity can help select an appropriate antibiotic, but the antibiotic of choice is usually one effective against the three gram-negative bacteria most often associated with bovine respiratory disease (P. multocida being one of the three). Long-acting antibiotics have been developed specifically to treat bacterial pneumonia in cattle because it is very important that the antibiotic treatment continue beyond the point at which the animal has apparently recovered. NSAIDS can be a beneficial ancillary treatment to help reduce inflammation and pain.

Prevention:

The most important measure in preventing pasteurellosis is preventing stress and viral disease associated with shipping fever. Measures to take include minimizing stress, providing adequate nutrition and internal parasite control, establishing an effective and early immunization program (preconditioning), and maintaining biosecurity by minimizing exposure to diseased and unfamiliar cattle. The calf’s immune system, when functioning properly can prevent most infection with Pasteurella multocida. There are some newer vaccines available that can help prevent disease. There vaccines include live bacterial cultures and subunits. Vaccination should be done 3 weeks prior to shipping calves to a feedlot and in dairy cows, vaccination of the dam prior to calving can help increase antibodies within the colostrum.
 

Sources: 

Anderson, D.E., Rings M.D. Current Veterinary Therapy: Food Animal Practice, 5th Ed. Saunders, St. Louis MO. 2009. pp. 164-170.

Smith, B.P. Large Animal Internal Medicine, 3rd Ed. Mosby-Elsevier Publishing. St. Louis, MO. 2009. pp.559-561.

Merck Veterinary Manual Online: http://www.merckvetmanual.com/mvm/index.jsp?cfile=htm/bc/121216.htm
 

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