ABSTRACT
Haemophilus Species ..................................................................................................................... 519 Collection, Transport, and Identication ....................................................................................... 520
Identication ....................................................................................................................... 520 Clinical Associations ..................................................................................................................... 523
Haemophilus influenzae ..................................................................................................... 523 Diagnostic Tests for Haemophilus influenzae ......................................................... 524 Pathogenesis of Haemophilus influenzae Infection ................................................. 524
Haemophilus parainfluenzae .............................................................................................. 525 Haemophilus ducreyi .......................................................................................................... 526
Diagnostic Tests for Haemophilus ducreyi .............................................................. 526 Pathogenesis of Haemophilus ducreyi Infection ..................................................... 526
Other Haemophilus Species ............................................................................................... 527 Treatment ....................................................................................................................................... 527 Genomes and Genetic Diversity .................................................................................................... 527 References ...................................................................................................................................... 528
The genus Haemophilus currently includes 12 species: Haemophilus aegyptius, H. ducreyi, H. felis, H. haemoglobinophilus, H. haemolyticus, H. influenzae, H. paracuniculus, H. parahaemolyticus, H. parainfluenzae, H. paraphrohaemolyticus, H. parasuis, and H. pittmaniae (International Committee on Systematics of Prokaryotes, 2006). Pfeiffer rst described the type species, H. influenzae, during the 1889-1892 inuenza pandemic and, until 1918, it was incorrectly presumed to be the etiologic agent of these infections. The taxonomy of the genus has evolved rapidly since sensitive genotyping methods have become available. The most recent changes include the recognition that H. aphrophilus and H. paraphrophilus are synonymous, and that these strains, along with H. segnis, are more appropriately classied within a distinct genus Aggregatibacter gen. nov., as Aggregatibacter aphrophilus comb. nov., and Aggregatibacter segnis comb. nov., respectively (Norskov-Lauritsen, 2006). Genotypic and phenotypic studies have also prompted the reassignment of H. paragallinarum and H. (Pasteurella) avium to a novel genus, Avibacterium gen. nov., as A. paragallinarum comb. nov., and A. avium comb. nov., respectively (Blackall, 2005). The signicant phenotypic and genotypic differences between H. ducreyi and other Haemophilus species indicate that, while currently still included in the genus, H. ducreyi would be more properly recognized as a distinct member of the Pasteurellaceae (Sturm, 1981). The taxonomy of H. parainfluenzae, H. haemoglobinophilus, H. parahaemolyticus, H. parasuis, H. paraphrohaemolyticus, H. paracuniculus, and H. felis has also been questioned. H. aegyptius and nonencapsulated H. influenzae may be indistinguishable by standard phenotypic tests but are genetically distinct and continue to be regarded as separate species. Haemophilus species causing human disease include H. influenzae,
H. aegyptius, H. ducreyi, H. haemolyticus, H. parahaemolyticus, H. parainfluenzae, H. paraphrohaemolyticus, and H. pittmaniae.
