Ajellomycetaceae

Ajellomycetaceae is a family of fungi in the order Onygenales, within the class Eurotiomycetes of the phylum Ascomycota. The group is best known for containing several thermally dimorphic genera that are medically important due to their ability to cause systemic infections in humans and animals. Taxonomic relationships within Ajellomycetaceae have been clarified by molecular phylogenetics, and the family includes genera such as Histoplasma, Blastomyces, Paracoccidioides, Emmonsia, and Emergomyces, as well as teleomorphic genera linked to the sexual states of some environmental species.

Most ajellomycetaceous fungi exhibit temperature-dependent dimorphism: they grow as filamenteous molds in the environment and switch to yeast-like forms at host temperature. This dimorphism is a central feature linked to their pathogenic potential, enabling replication and tissue invasion in hosts. Ecologically, many species are associated with soil or organic matter rich in bird or bat guano, and human infection generally occurs through inhalation of propagules or fungal fragments.

Clinical relevance is significant, as members of Ajellomycetaceae can cause a spectrum of diseases ranging from mild pulmonary illness to disseminated infections, particularly in individuals with weakened immune systems. Notable diseases historically associated with the family include histoplasmosis, blastomycosis, and paracoccidioidomycosis, with additional reports of emmonsiosis and disseminated infections by emergent species. Diagnosis typically relies on culture, histopathology, antigen or antibody testing, and molecular methods, while treatment depends on the specific pathogen and disease severity.

In summary, Ajellomycetaceae comprises pathogenic, dimorphic fungi linked to important human diseases, united by phylogenetic relationships and a shared propensity for environmental molds that convert to yeast forms in the host.