SIGNIFICANCE OF THE HOST-PARASITE-INTERAC TION FOR COLONIZATION AND INFECTION WITH HAEMOPHILUS-INFLUENZAE

The following overview describes the conditions of the host-parasite r elationship which are important for the infection with Haemophilus inf luenzae (H.I.). New epidemiological data point out that the general va ccination of infants and children with the HIB-conjugate vaccine has b een followed by a shift from encapsulated H.I. type B to unencapsulate d, low-virulent strains. However, unencapsulated H.I. strains have bee n cultured increasingly from blood samples of patients with severe sep ticemic infections. Elderly patients with underlying chronic lung dise ase as well as children are affected. It is well accepted that in the pathogenesis of H.I.-infection bacterial adherence to mucosal epitheli al cells of the oropharynx precedes colonization. However, bacterial p ill as special virulence factors that promote binding to epithelial ce ll receptors (=bacterial adherence) have been especially demonstrated in vitro on the low virulent, unencapsulated H.I.-strains and are lack ing on most in vitro grown encapsulated strains. Nevertheless, unencap sulated strains were taken from oropharyngeal swaps while encapsulated strains originated from blood and/or cerebrospinal fluid. The publish ed controversial data on the adhesive capacity of H.I.B./H.I. as a vir ulence property are discussed. We propose to analyze systematically th e host-parasite interaction with unencapsulated H.I.-strains in order to protect patients at risk from infections with these bacteria showin g increasing clinical virulence. lt would be desireable to develop H.I .B./H.I. vaccines that contain ''common'' antigens of unencapsulated H .I.-strains in addition to the type B-capsular antigens.