The disease can occur in a peracute, acute or chronic form. In its peracute form, death occurs within 24 to 36 hours, and treatment can rarely be administered in time to save the animal. The severity of the signs depends on age, immunity status and involved serotype. Symptoms include fever, lethargy, listlessness, and varying degrees of respiratory distress. In more chronic cases, the animals may have few if any systemic signs, but will suffer from cough and diminished appetite.

Saliva droplets projected by carrier animals transmit the disease. Sows infect piglets at 2 weeks of age, and these infected piglets propagate the infection throughout the group once their maternal immunity has disappeared after weaning. The microorganism is secreted in large quantities through the nose, and, once in the environment, can survive more than 3 days in the mucus. It can survive in 4°C water for up to 30 days.

The diagnosis of infection is based on characteristic clinical signs, results of postmortem examinations and APP cultures of material taken from the pulmonary lesions.

• It is necessary to establish a biochemical profile in order to distinguish between the APP isolate and other, very similar commensal species.
• Isolating the microorganism in the tonsillar samples taken in the farm is not enough to diagnose the disease because of the existence of non-virulent APP strains (which, just to complicate matters, can still contain toxic genes) in the upper respiratory tract.
• The isolates can be serotyped, but the predictive value of this test as concerns virulence is uncertain.
• PCR identification can target toxic or serotype determinant genes.
• Serology (ELISA test) aimed at identifying specific anti-APP antibodies in the entire farm is largely used, but difficult to interpret. This test screens for antibodies targeted at different specific serotypes (based on capsular antigens) or at the Apx IV toxin (common to all members of the APP group), for example. However, the presence of anti-APP antibodies does not make it possible to assess the virulence potential of the strain in question.

Early administration of antibiotic treatment is essential for lowering the mortality rate. Since infected animals eat little if anything, it is important that they be treated by parenteral route (intramuscular injection). The choice of antibiotic must be based on a sensitivity analysis of the APP strain isolated during the epidemic. Consult your veterinarian before administering antibiotics and vaccines to animals. Your veterinarian is the best person to talk to for recommendations that are right for your farm.

Disease-free units: maintain the disease-free status by controlling incoming animals (disease status of incoming animals, systematic isolation of incoming breeding stock).

Actively infected units: implement an all-in all-out system, plus drug treatment when pigs are transferred to a new site. If this is impossible, control must be based on strategic drug treatment administered repeatedly, a vaccination program (commercial or autogenous vaccines), better ventilation, and a reduction in population density, as well as thorough cleaning and disinfection of the buildings.

REFERENCES:

¹ Gottschalk M, Taylor D. 2006. Actinobacillus pleuropneumoniae. In: Diseases of swine. eds, Straw B, Zimmerman JJ, D’Allaire S, and Taylor D. 9th Edn. Blackwell Publishing. Oxford.

² Bosse J, Janson H, Sheehan B, Beddek A, Rycroft N, Kroll S, Langford P. 2002. Actinobacillus pleuropneumoniae : Pathobiology and pathogenesis of the infection. Microbes and Infection 4: 225-235. Anon. 2004. VLA Quarterly Surveillance Report: 8: 5-6.

³ Andersen LV, Gram S. 2004. Successful elimination of A. pleuropneumoniae, M. hyopneumoniae, and PRRS V by partial depopulation, early weaning, and tilmicosin treatment. Proceedings of the 18th Congress of the International Pig veterinary Society, Hamburg, p179.

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