Bronchopneumonia caused by Pasteurella multocida or Mannheimia haemolytica has a cranioventral lung distribution and affects sheep and goats of all ages worldwide. It can be particularly devastating in young animals. It is a common cause of morbidity and mortality in lambs and kids, especially in those that have not received adequate colostrum or in which passive colostral immunity is waning. The disease appears to occur most often in animals that have undergone recent stress such as transportation, weaning, or commingling with animals from unrelated farms. (Also see Pasteurellosis of Sheep and Goats.)

Etiology

P multocida and M haemolytica are gram-negative rods that can cause pneumonia either alone or in conjunction with other organisms. Primary infections with respiratory pathogens such as parainfluenza-type 3, adenovirus, respiratory syncytial virus, Bordetella parapertussis, or Mycoplasma spp appear to predispose to secondary infection with Pasteurella and Mannheimia. Both organisms are normal inhabitants of the upper respiratory tract of sheep and goats; however, pneumonia caused by M haemolytica biotype A occurs more frequently than infection with P multocida. Similar to the infection in calves, P multocida in sheep and goats produces a milder disease with a shorter course than M haemolytica-associated pneumonia. In sheep and goats, serotype A₂ is the most common serotype isolated. Important but less prevalent serotypes found in sheep are A₁, A₆, A₇, A₈, A₉, A₁₂, and in goats, serotypes A₁ and A₆.

Pathogenesis

Stress appears to be an important factor in the breakdown of respiratory defense mechanisms, allowing Pasteurella, Mannheimia, Mycoplasma spp, other bacteria, and viruses to invade lung tissue and cause pneumonia. In some laboratory animal species and calves, alveolar macrophage function is impaired after viral pneumonia. This results in decreased clearance of inhaled bacterial pathogens, allowing them to become established. Pathogen-host interactions result in tissue damage, especially because of massive influx of neutrophils. As these neutrophils are lysed, enzymes are released that cause more lung tissue damage. This mechanism may be similar to that of Pasteurella and Mannheimia pneumonias in sheep and goats.

Clinical Findings

M haemolytica-associated pneumonia occurs in both young stock and mature animals, usually during times of stress such as lambing/kidding, weaning, dramatic changes in environmental temperatures, inadequate ventilation situations, and less than ideal stocking densities, especially in confinement housing. Outbreaks in groups of sheep and goats usually occur 10–14 days after a stress. For example, in feedlots, outbreaks are expected ~2 wk after arrival in the feedlot.

Early clinical signs can be dramatic and reflect the endotoxemia that often occurs with infection. Sudden death may occur without observation of clinical signs. The disease usually has a rapid onset accompanied by respiratory distress, including open-mouth breathing, anorexia, depression, poor perfusion (prolonged capillary refill time and cool extremities), fever of 104–106°F (40–41.1°C), serous (early) to mucopurulent (later) ocular and nasal discharges, coughing, and lethargy. Harsh lung sounds, especially in the cranioventral portions of the lung field, may be auscultated. Morbidity and mortality rates are variable. Animals that survive the acute phase may develop secondary problems that result in chronic ill health.

Lesions

Lesions are usually confined to the cranioventral lung lobes on both sides. These areas may appear red to purple and feel firm from consolidation. The pleural cavity may contain variable amounts of straw-colored fluid, and yellow fibrin may cover the pleural surface of affected lung lobes from pleuritis. Chronic cases may have extensive pleural adhesions and multiple abscesses of variable size.

Diagnosis

In acute cases, cultures obtained from tracheal swabs or washes or from lung tissue or associated lymph nodes are diagnostic. Histopathologic examination is useful, especially if other types of pneumonia (eg, retrovirus interstitial pneumonia in adult sheep and goats) are also suspected. In chronic cases, bacterial cultures may be less rewarding; Pasteurella or Mannheimia may have been the initial problem, but results of cultures taken later may reveal Arcanobacterium pyogenes, a common causative agent of lung abscesses.

Treatment and Control

Whenever possible, treatment should be based on bacterial culture and sensitivity, especially in herd or flock outbreaks, when valuable animals are involved, or in acute or chronic cases when initial therapeutic attempts have failed. Commonly recommended antibiotics include ceftiofur (1.1–2.2 mg/kg, sid), oxytetracycline (10 mg/kg, sid, of non-long-acting product, or 20 mg/kg once of the long-acting product), ampicillin (20 mg/kg, bid), flor-fenicol (20 mg/kg, every 48 hr), and tylosin (10–20 mg/kg, sid-bid). Therapy should continue for at least 24–48 hr after body temperature has returned to normal. Duration of treatment usually is 4–5 days. Acute cases may also benefit from the use of NSAID (eg, aspirin, flunixin meglumine, or ketoprofen) in conjunction with antibiotic therapy for control of endotoxemia and inflammation. Treatment with NSAID should be of short duration because prolonged use may result in gastric ulceration or renal complications. In the USA, use of some of the above antibiotics and NSAID is extra-label, and appropriate withdrawal times to slaughter should be followed.

Inadequate ventilation, crowding, commingling of animals from various farms (feedlot or sale barn situations), poor nutrition, failure of passive transfer of antibodies, transportation, and other stresses have all been associated with pneumonia outbreaks. Control and prevention lies with correction of the predisposing factors whenever practical. At present, there are no bacterins that have proved effective for control of these pneumonias.

Last full review/revision March 2012 by Michelle Kopcha, DVM, MS