Actinobacillus suis

Also known as: A.suis

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

Introduction

A.suis is a beta-haemolytic Gram-negative bacterium. Strains of A.suis vary 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 srain . This opportunistic bacteria mainly causes actinobacillosis in pigs, but has also been linked to neonatal calf pneumonia and localised infections, airsaculitis in waterfowl, and polyarthritis in alpacasand, to septicaemia, acute haemorrhagic pulmonary infarction and necrotizing pneumonia in 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 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 strains are able to resist bile and serum.

Signalment

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 pigs, cattle, sheep, goats, alpacas, zebu, dogs, cats and tentive links to equine disease have been recorded (although this is thought to be 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 (Escande et al., 1996).

Epidemiology

The epidemiology ofA.Suis is poorly understood. A.Suis 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 aerososl infection and invasion of the upper respiratory tract. 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.

Diagnosis

A.Suisis difficult to culture and most of the O1 strains analyzed 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. Thses antibodies may provide naive pigs with some level of protection against the O1 strains , . For more information see actinobacillosis in pigs.

Distribution

Worldwide

References

Actinobacillus suis Learning Resources
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