Exotoxins of Actinobacillus Pleuropneumoniae

Abstract

Actinobacillus pleuropneumoniae (previously Haemophilus pleuropneumoniae) is the etiological agent of swine pleuropneumonia, a severe, contagious disease of swine causing important economic losses in industrialized swine production worldwide. The disease is either acute and often fatal or chronic localized and necrotizing. It seems to be mainly transmitted via the respiratory route from pig to pig (Nicolet and Konig, 1966; Nicolet, 1968; Nicolet et al., 1969; Nicolet, 1992; Shope, 1964). Two different biovars, the ß-NAD dependent biovar 1 and the ß-NAD independent biovar 2 (Niven and O’Reilly, 1990), and twelve serotypes of A. pleuropneumoniae have been described (Nicolet, 1988; Nielsen, 1988). The chemical composition of the capsular polysaccharides (K-antigens) and lipopolysaccharides (O-antigens) of all serotypes is known (Perry et al., 1990; Beynon et al., 1993). Among the twelve serotypes, significant differences in virulence have been observed. In particular, serotypes 1 and 5 and to some extent also 9 and 11 are involved in severe outbreaks with high mortality and severe pulmonary lesions. Serotypes 2,4,6,7,8 and 12 are less virulent, although some of these serotypes are frequently isolated. In spite of the fact that serotypes 2,4,6,7,8 and 12 cause virtually the same lesions as serotypes 1, 5, 9 and 11, they cause lower mortality (Fales et al., 1989; Rapp et al., 1985; Brandreth and Smith, 1985; Martineau et al., 1984; Nicolet, 1992; Rosendal et al., 1985). In addition some serotypes, in particular serotype 3, seem to be of very low virulence and of no epidemiological importance in many countries. Serotyping is therefore one of the most important and most frequently used tools in epidemiology and sanitation programmes to control porcine pleuropneumonia (Nicolet, 1992; Nielsen, 1990).