OVERVIEW
Pasteurella haemorrhagicus is a normal flora of the oral cavity of cats and dogs and a common cause of respiratory infections in many animals and birds. Pasteurella haemolytica is a common cause of human cellulitis from dog and cat bites. The bacterium can cause respiratory infections in humans, leading to Pasteurella pneumonitis, but it is rarely reported.
Epidemiology
Pasteurella haemorrhagicus is a normal flora of the oropharynx or digestive tract of many domestic and wild animals and birds, and Pasteurella haemorrhagicus cellulitis is associated with animal bites. Pneumonia due to this organism in humans occurs mostly in individuals with chronic respiratory disease, especially in patients with bronchiectasis and chronic bronchitis. It is widely believed that the organism is transmitted from animals to humans, but the exact mode of transmission of pneumonia caused by the organism is not known. The organism can remain latent in patients with chronic pneumonia for a long time without symptoms and becomes pathogenic when the resistance of the organism decreases, resulting in pulmonary infection.
Etiology
The genus Pasteurella includes Pasteurella haemorrhagicus septicaemia, also known as Pasteurella multocida, which is the causative agent of fowl cholera, mammalian hemorrhagic septicemia and many infectious diseases in humans. Pasteurella haemorrhagicus is a small bipolar coloring gram-negative cocci that grows well in serum-containing agar, but growth is inhibited in MacConkey’s medium. This bacterium produces pods that interfere with leukocyte phagocytosis.
Symptoms.
Increased cough, increased pus and sputum, increased dyspnea, and in patients with bronchiectasis, increased hemoptysis or even hemoptysis. In addition to the aggravation of the symptoms of the underlying disease, the patient may have fever, even high fever, and chest pain may occur when the pleura is involved.
Examination
1. Laboratory examination
Gram-negative cocci can be found in sputum, pleural fluid or blood specimen, and bacterial culture is positive.
2. Other auxiliary examinations
X-ray shows uneven infiltrative changes in one lobe, multiple lobes or diffuse, involving the lung bases, upper lobe involvement is rare, 20% of cases may involve the pleura, and pleural reaction occurs, but pyothorax occurs less frequently.
Diagnosis.
Hemorrhagic septic Pasteurella pneumonia has no characteristic changes in clinical manifestations, about 50% of cases have a history of animal contact, and it occurs in patients with chronic lung disease, manifesting as further aggravation of the original underlying disease. In suspicious cases, sputum, pleural fluid or blood specimens should be made for gram staining and bacterial culture.
Differential diagnosis
The organism is morphologically similar to Brucella, Yersinia, Francisella, and Haemophilus influenzae, and final differentiation depends on history and bacterial identification.
Complications
Complications include lung abscess, emphysema and sepsis.
Treatment
Most strains are highly susceptible to penicillin or ampicillin. Ampicillin should be preferred in gram-negative cocci infections. Chloramphenicol is also effective, especially in patients who are allergic to penicillins. Third-generation cephalosporins are also effective. Closed drainage and intrathoracic injection of effective antibiotics should be performed in the presence of pyothorax formation.