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Pathogen Page

Actinobacillus pleuropneumoniae

I. General Information

1. NCBI Taxonomy ID:

2. Disease:

porcine pleuropneumonia

3. Introduction

The bacterium Actinobacillus pleuropneumoniae (App) was previously called Haemophilus pleuropneumoniae and there are at least twelve different strains, some of which produce no disease and are non pathogenic, but others cause very severe disease. Strains 1, 5, 9, 11 and 12 are highly virulent and strains 3 and 6 are very mild. The organism is carried in the tonsils and respiratory tract and the incubation period is very short, from as little as 12 hours through to three days. It is transmitted by droplet infection between one pig and another. The organism may survive in discharges, serum etc. for up to 5 days. Contact with dead stock is therefore important from biosecurity. It dies quickly if dried, but it may persist in water for 20 days or more. App can survive in the lungs and tonsils for long periods of at least 4 months. It is probably airborne for only 5 to 10 metres. Disease is dose dependent i.e. the more bacteria the pig is exposed to the more severe will be the disease. Infection is spread from one pig to another by nose to nose contact. Pigs may be infected with different serotypes simultaneously. PRRS and EP can make the disease worse. In a naïve herd up to 30% of animals may be affected. When App attacks the lungs the toxins produced cause severe damage to the tissues which turn blue to black (necrosis) with extensive pleurisy. The chest cavity rapidly fills up with fluid.

The organism may affect the pig from weaning through to slaughter but usually the age is from 8 to 16 weeks, once maternal antibody has disappeared. Sudden death is often the only sign with blood and froth discharged from the nose. In the live pig a short cough may be heard with signs of severe breathing difficulties and blueing of the ears. Badly affected pigs are severely depressed. Body temperature is often high. Death is due to a combination of heart failure and the toxins produced by the organisms (ThePigSite Pig Health).

4. Microbial Pathogenesis

Actinobacillus pleuropneumoniae interacts closely with epithelial cells in the lower respiratory tract and toxins produced during infection are delivered directly to the cell surface. This close association between A. pleuropneumoniae and respiratory epithelial cells may impair the binding of specific antibodies to the Apx toxins, resulting in development of necrosis and hemorrhage (Haesebrouck et al., 2004).

5. Host Ranges and Animal Models

Pigs are the main host, and mice can serve as a model of infection (Shin et al., 2007).

6. Host Protective Immunity

Protection is mediated by antibodies and mucosal immunity (Shin et al., 2007).

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