Brazilian Purpuric Fever: Evolutionary Genetic Relationships of the Case Clone of Haemophilus influenzae Biogroup Aegyptius to Encapsulated Strains of Haemophilus influenzae

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Abstract
As a first step toward identifying the evolutionary origin of a pathogenic clone of Haemophilus influenzae biogroup aegyptius causing Brazilian purpuric fever, chromosomal variation and genetic relationships were indexed among 17isolates ofbiogroup aegyptius and 2209 previously characterized encapsulated H. influenzae strains recoveredfrom 30 countries on six continents. Biogroup aegyptius isolates form three distinct evolutionary lineages of the species H. inftuenzae and isolates of the case clone are genetically not closely related to other isolates classified as biogroup aegyptius. The Brazilian purpuric fever case clone was found to be genetically allied with H. infiuenzae isolates producing serotype c polysaccharide capsule. The population genetic evidence suggests that biogroup aegyptius isolates may represent cell lineages occasionally transmitted from nonhuman hosts or spawned from a much larger base population consisting of genetically diverse nonpathogenic precursor clones.