Actinobacillus suis infections

M M HENTON

GENERAL INTRODUCTION: FACULTATIVELY ANAEROBIC GRAM-NEGATIVE RODS Actinobacillus spp. infections

Actinobacillus suis is a rare cause of a rapidly fatal septicaemia particularly in piglets younger than two months of age. Adult sows, especially those in minimal-disease herds, may also succumb to septicaemic disease, and may show signs very similar to those of acute erysipelas.^{6, 7, 13} Pathogenic Escherichia coli infections may occur together with A. suis in piglets. The highest prevalence in infected herds occurs in pigs aged 16 weeks, after a decline in maternally derived antibody levels between 8 and 12 weeks.⁵ Clinical signs and lesions in affected animals are similar to those that occur in foals suffering from Actinobacillus equuli septicaemia (see Actinobacillus equuli infections).

Horses may carry A. suis in the upper respiratory and genital tracts, but the role of the organism in the production of disease—if indeed there is a role—is unclear.⁴

Actinobacillus equuli and A. suis have similar biochemical properties; earlier publications have not always differentiated clearly between the two species.^{11, 14} Serological cross-reactions in pigs have been demonstrated between A. suis and Actinobacillus pleuropneumoniae, Pasteurella multocida and Haemophilus parasuis.⁹ There are also similarities between the RTX (repeats in structural toxin) toxins produced by A. pleuropneumoniae and A. suis. These toxins are cytolysins and are found in a variety of Gram-negative bacteria. Actinobacillus suis produces toxins very similar to Apx I (A. pleuropneumoniae endotoxin) and Apx II but not Apx III.^{1, 3, 12} Two different lipopolysaccharide O-antigen types, O1 and O2 and three capsular types (K1, K2 and K3) have been described and virulence has been associated with types O2/K3 but not O1/K1.^{8, 9}

Only 18 cases of A. suis infection in pigs were diagnosed at the Onderstepoort Veterinary Institute, South Africa, in the period from 1991 to 2000.²

Actinobacillus suis is susceptible to ampicillin, chloramphenicol, trimethoprim-sulphonamide combinations, tetracyclines and streptomycin, and treatment at recommended dosages with any of these remedies is usually effective.^{7, 10}

References

1. BURROWS, L.L. & LO, R.Y., 1992. Molecular characterization of an RTX toxin determinant from Actinobacillus suis. Infections and Immunity, 60, 2166–2173.
2. HENTON, M.M., 2001. Onderstepoort Veterinary Institute, South Africa. Unpublished observations.
3. KAMP, E.M., VERMEULEN, T.M., SMITS, M.A. & HAAGSMA, J., 1994. Production of Apx toxins by field strains of Actinobacillus pleuropneumoniae and Actinobacillus suis. Infection and Immunity, 62, 4063–4065.
4. KIM, B.H., PHILLIPS, J.G. & ATHERTON, J.G., 1976. Actinobacillus suis in the horse. The Veterinary Record, 98, 239.
5. LAPOINTE, L., D’ALLAIRE, S., LACOUTURE, S. & GOTTSCHALK, M., 2001. Serologic profile of a cohort of pigs and antibody response to an autogenous vaccine for Actinobacillus suis. Veterinary Research, 32, 175–183.
6. MACINNES, J.I. & DESROSIERS, R., 1999. Agents of the ‘suis-ide disease’ of swine: Actinobacillus suis, Haemophilus parasuis, and Streptococcus suis. Canadian Journal of Veterinary Research, 63, 83–89.
7. MINIATS, O.P., SPINATO, M.T. & SANDFORD, S.E., 1989. Actinobacillus suis septicaemia in mature swine. Two outbreaks resembling erysipelas. Canadian Veterinary Journal, 30, 943–947.
8. 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, 81–87.
9. SLAVIC, D., TOFFNER, T.L., MONTEIRO, M.A., PERRY, M.B. & MACINNES, J.I., 2000. Prevalence of O1/K1- and O2/K3-reactive Actinobacillus suis in healthy and diseased swine. Journal of Clinical Microbiology, 38, 3759–3762.
10. TAYLOR, D.J., 1986. Miscellaneous bacterial infections. In: leman, a.d., straw, b., glock, r.d., mengeling, w.l., penny, r.h.c. & scholl, e., (eds). Diseases of Swine. 6th edn. Ames,Iowa: Iowa State University Press.
11. VAN DORSSEN, C.A. & JAARSVELD, F.H.J., 1962. Actinobacillus suis (novo species). A bacterium occurring in swine. Tijdschrift voor Diergeneeskunde, 87, 450–458.
12. VAN OSTAAIJEN, J., FREY, J., ROSENDAL, S. & MACINNES, J.I., 1997. Actinobacillus suis strains isolated from healthy and diseased swine are clonal and carry apxICABDvar.suis and apxIICAvar.suis toxin genes.Journal of Clinical Microbiology, 35, 1131–1137.
13. WILSON, R.J. & MCORIST, S., 2000. Actinobacillus suis infection in pigs in Australia. Australian Veterinary Journal, 78, 317–319.
14. WINDSOR, R.S., 1973. Actinobacillus equuli infection in a litter of pigs and a review of previous reports on similar infections. The Veterinary Record, 92, 178–180.