Pleuropneumonia is a severe respiratory infection caused by Actinobacillus pleuropneumoniae. Clinical signs include fever, anorexia, reluctance to move, respiratory distress, and sudden death. Diagnosis is confirmed by bacterial culture. Sick animals may be treated with antibiotics, but control is achieved by elimination of the bacteria at the breeding stock level.
Pleuropneumonia is a severe and contagious respiratory disease, primarily of young pigs (≤6 months old), although in an initial outbreak, adults also may be affected. It has a sudden onset, short course, and high morbidity and mortality. It occurs worldwide and appears to be increasing in incidence, although some reports suggest that severity is declining in countries where it has been long established.
Etiology of Pleuropneumonia in Pigs
The causal organism of pleuropneumonia is Actinobacillus pleuropneumoniae. Historically, serotypes 1, 5, and 7 have been prevalent in the USA. Transmission is mainly by nose-to-nose contact, and many recovered pigs are carriers. Clinical signs develop within 4–12 hours in experimental infections. Aerosol transmission is limited.
Clinical Findings of Pleuropneumonia in Pigs
Onset of pleuropneumonia is sudden, and in herds that have not been infected previously, spread is rapid. Some pigs may be found dead without having shown clinical signs. Respiratory distress is severe; there are “thumps,” and sometimes open-mouth breathing with a blood-stained, frothy nasal and oral discharge. Fever up to 107°F (41.5°C), anorexia, and reluctance to move are typical signs.
Although primarily a disease of growing pigs, A pleuropneumoniae infection may be fatal in adults or cause sows to abort. The course of the disease varies from peracute to chronic. Morbidity may reach 50%, and in untreated cases, mortality is high. Survivors generally show reduced growth rates and persistent cough.
Once established in a herd, the disease may be evident only as a cause of reduced growth rate and pleurisy at the abattoir, although acute disease exacerbations may occur. However, severe lesions may not always be accompanied by equally severe clinical signs. Deaths in transit and carcass condemnation may result. Concurrent infection with mycoplasma, pasteurellae, porcine reproductive and respiratory syndrome, or swine influenza virus is common.
Lesions
Courtesy of Dr. Bruce Lawhorn.
The pneumonia is usually bilateral. The characteristic lesion is a severe fibrinonecrotic and hemorrhagic pneumonia with accompanying fibrinous pleuritis. Fibrinous pleuritis and pericarditis may be severe. In acute cases, the lungs are dark and swollen and ooze bloody fluid from the cut surface; hemorrhagic, even necrotic, bullae of various sizes may be present. The trachea may contain bloodstained froth. In chronic cases, the lesions are more organized and localized. Extrathoracic lesions are uncommon.
Diagnosis of Pleuropneumonia in Pigs
Based on clinical signs and confirmed by serology or bacterial culture
An explosive disease onset is suggestive and, when combined with clinical signs and gross lesions, often justifies a tentative diagnosis of pleuropneumonia. Concurrent infections, eg, with pasteurellae, may complicate diagnosis. In herds that have been exposed and have developed at least a degree of immunity, the pattern may be less distinctive. Many serologic tests, including complement fixation and ELISA, have been used to confirm a herd diagnosis or detect carriers, but results are not always straightforward. A definitive diagnosis depends on isolation and identification of A pleuropneumoniae, a gram-negative coccobacillus that requires V factor (NAD) supplementation for growth. A Staphylococcus aureus nurse colony can provide the necessary factor. PCR testing is also available and provides better sensitivity than direct culture.
Treatment and Control of Pleuropneumonia in Pigs
Sick animals can be treated with injectable antibiotics
Elimination of the organism is the primary means of control
Rapidity of onset and persistence in infected herds make treatment of pleuropneumonia difficult. Ceftiofur, tilmicosin, tetracyclines, synthetic penicillins, tylosin, and sulfonamides have been used. The first treatment should be parenteral, followed by medication given in water or feed, which also may protect contact pigs.
Segregated early weaning, “all-in/all-out” management, reduced stocking rates when possible, and improved ventilation are recommended for prevention. In herds free of the disease, replacements should be purchased from herds free of A pleuropneumoniae; if the disease proves difficult to control, herd depopulation and repopulation should be considered. Due to elimination programs at the breeding stock level, pleuropneumonia is rarely encountered in today's modern confinement swine production systems.
Key Points of Pleuropneumonia in Pigs
Actinobacillus pleuropneumoniae causes severe respiratory disease in pigs.
Because vaccination and medication provide little benefit, A pleuropneumoniae should be eliminated from swine herds.
