Actinobacillosis is caused by the bacteria [[Actinobacillus suis| '''''Actinobacillus suis'''''. In piglets aged 1 to 8 weeks old the organism causes acute and rapidly fatal septicaemia, and localized infections such as endocarditis, polyarthritis, and respiratory distress may also been seen with additional neurological signs. Adult pigs can suffer pneumonia like symptoms, see [[Actinobacillus suis#Clinical Signs| clinical signs]] for more details. Although ''A.suis'' mainly affects pigs it has also been linked to septicaemia, acute haemorrhagic pulmonary infarction and necrotizing pneumonia in horses, airsaculitis in waterfowl, neonatal calf pneumonia and localised infections and polyarthritis in alpacas. It is not considered a zoonosis but there has been a report of human infection after a pig bite <ref>Escande, F., Bailly, A., Bone, S., Lemozy, J. (1996)'''Actinobacillus suis infection after a pig bite'''. '''''Lancet''''' (British edition), 348(9031):888; 5 ref</ref>.
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==Signalment==
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High health status herds with lower immune challenges are more at risk then conventional herds. Piglets from high health status herds can suddenly die without any premonitory signs. Excessive temperature fluctuation, high humidity, mixing of pigs of different ages and overcrowding may also have an important role in the development of disease.