Actinobacillus Pleuronpneumoniae (APP)

General

Actinobacillus pleuropheumoniae is a highly contagious, often fatal, respiratory disease of weaned, growing and finishing pigs in which infection with Actinobacillus pleuropneumoniae causes fibrinous pleurisy, pneumonia and sudden death.

Actiology

Actinobacillus pleuropneumoniae is a bacteria which has the ability to attach to respiratory cells, evade the immune system and release toxins. Actinobacillus pleuropneumoniae is a delicate bacteria, but can survive for 5 days at 18ºC, particularly in nasal discharge. It is however, sensitive to many antimicrobials.

Pathogenesis

Actinobacillus pleuropneumoniae infects by entering the upper respiratory tract, or oral cavity, (where it only adheres to the tonsils). Infection of the respiratory tract results in the diaphragmatic, caudal and accessory lobes being most severely affected.

Actinobacillus pleuropneumoniae secretes toxin which kill macrophages, the cells which normally kill bacteria. Other phagocytic cells are unable to attack the pathogen, due to these toxins and its protective capsule. Infection continues rapidly, with necrosis of lung occurring within 4-5 days.

Passive maternal antibodies protects against infection for up to 4 weeks. Active immunity can be first seen 5-10 days after infection and peaks 3-4 weeks later. Cross protection between serotypes varies, although serotype 2 infection seems to give rise to protection against other serotypes.

Clinical Signs

The disease may be seen as three different forms; acute, subacute and chronic.

Acute disease signs include depression, anorexia, fever and laboured respiration. Cyanosis (blue ears and membranes), pyrexia (high temperature) and sudden death may occur 4-6 hours later. Up to 50% mortality may occur.

In the subacute form, groups of pigs are anorexic and show respiratory distress, especially when disturbed. Exercise intolerance is evident and animals have reduced appetites, appear hairy and are depressed. Subsequent decreases in average daily gain and feed conversion efficiency occur. Non-immune animals of all ages may be affected and abortions may be induced in gilts or sows. Where infection is constantly present the most common problem is amongst pigs of 6-12 weeks of age. Medication can alter the clinical signs and mortality.

Chronically affected animals show signs of very poor body condition, continued exercise intolerance and respiratory distress and may be humanely destroyed.

Upon post mortem, lesions occur mainly in the thoracic cavity, with frothy blood in trachea, congested, swollen lungs and yellow stringy material on the pleural surface of lung. Inflammation of the lymph nodes and fibrous pericarditis also occur.

Epidemiology

The organism spreads from animal to animal by contact, particularly during the oral contact associated with fighting after mixing. The organism survives in water, but does not survive long in aerosol.

Spread is mainly by the movement of carrier pigs and transmission on people and other objects.

Diagnosis

Diagnosis is performed by post mortem examination and confirmed by laboratory techniques.

Treatment

Clinically affected animals should be treated injecting with an effective antibiotic. In water medication can also be used, if monitored. In feed medication is ineffective as affected pigs have reduced feed and possibly water consumption.

Vaccination

Vaccination programs often require both vaccination of the sow to give passive protection to the suckers and subsequent vaccination of the piglets. Where passive immunity is present, best results are by vaccinating piglets after the disappearance of maternal immunity. This is usually at 4-6 weeks of age.

Eradication

Only possible when de-stocking of farm and replacement with disease-free pigs or pigs derived by hysterectomy that are free of Actinobacillus pleuropneumoniae.