Actinobacillus suis

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Also known as: A. suis

Actinobacillus suis
Kingdom Bacteria
Phylum Proteobacteria
Class Zymobacteria
Sub-class Alphaproteobacteria
Order Pasteurellales
Family Pasteurellaceae
Genus Actinobacillus
Species Actinobacillus suis


Actinobacillus suis Gram stain

A.suis is a beta-haemolytic Gram-negative bacterium. It has many strains due to differences in their lipopolysaccharides (LPS), which are known as 'O' antigens and are referred to as O1,O2 and O3 and capsules (CPS), refered to as K antigen with variants described as K1, K2 and K3. More than 95% of A. suis clinical isolates are cross-reactive with O1/K1 or O2/K3 antiserum and more severe infection were noted with O2/K2 strain [1]. This opportunistic bacteria mainly causes actinobacillosis in pigs, but has also been linked to diseases in neonatal calves, waterfowl, alpacas, horses and various other species.

Other haemolytic strains of Actinobacillus species have been linked to various diseases in horses such as Actinobacillus equuli and Actinobacillus ligneresii. The latter species also causes wooden tongue in cattle.

A. suis-like organism may cause acute haemorhagic pulmonary infarction and necrotizing pneumonia as well as septicaemia in horses.

A. suis are able to resist bile and serum and have genes that encode toxins similar to apxI and apxII of A. pleuropneumoniae, but they are less virulent. Once an animal is infected with A. suis it can provide partial cross protection against A. pleuropneumoniae.


A.suis can infect all ages of pigs and it is thought that incidence of the disease is increasing, especially in North American high-health-status herds.

Wild hosts include anatidae (ducks, geese and swans) and coypu but A. suis can also affect domestic species including cattle, sheep, goats, alpacas, zebu, dogs, cats and tenuous links to equine disease have been recorded (although this is thought to be an A.suis-like microorganism rather than A. suis itself). A. suis is not considered to be a zoonosis, but there is a report of a human infection after a pig bite [2].

Clinical signs

For clinical signs in pigs see actinobacillosis in pigs. In other species, A. suis causes pneumonia like symptoms and localised infections in neonatal calf, airsaculitis in waterfowl, and polyarthritis in alpacas and acute haemorrhagic pulmonary infarction and necrotizing pneumonia in horses.


The epidemiology of A. suis is poorly understood, although it can be found in the tonsils and upper respiratory tract of both healthy and diseased pigs, and isolates are genetically and biochemically similar. It is believed to be spread via aerosol infection and invasion of the upper respiratory tract. Systemic disease can be seen when infected emboli spread haematogenously throughout the body adhering to the endothelium of blood vessels or becoming trapped in smaller vessels. It is thought to colonise piglets in the first three weeks of life but not all piglets become clinically affected and some can become carriers.


A. suis is difficult to culture and most of the O1 strains analysed possess pustulan (1-6,beta-D-glucan) which is a major component of fungal and lichen cell walls. Therefore, many animals have antibodies to this polysaccharide in the absence of exposure to A. suis. These antibodies may provide naive pigs with some level of protection against the O1 strains [3], [1].

For more information see actinobacillosis in pigs.



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  1. 1.0 1.1 Slavic, D., DeLay, J., Hayes, M.A., MacInnes, J.I. (2000) Comparative pathogenicity of different Actinobacillus suis O/K serotypes. Canadian Journal of Veterinary Research, 64(2):81-87
  2. Escande, F., Bailly, A., Bone, S., Lemozy, J. (1996) Actinobacillus suis infection after a pig bite. Lancet (British edition), 348(9031):888; 5 ref.
  3. MacInnes, J.I., Desrosiers, R. (1999) Agents of the "suis-ide diseases" of swine: Actinobacillus suis, Haemophilus parasuis, and Streptococcus suis. Canadian Journal of Veterinary Research, 63(2):83-89; 52 ref.


This article was originally sourced from The Animal Health & Production Compendium (AHPC) published online by CABI during the OVAL Project.

The datasheet was accessed on August 08, 2011.

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