Microsporidia

Microsporidia are a group of spore-forming unicellular parasites. They were once considered protozoans or protists, but are now known to be fungi, or a sister group to fungi. Loosely 1500 of the probably more than one million species are named now. Microsporidia are restricted to animal hosts, and all major groups of animals host microsporidia. Most infect insects, but they are also responsible for common diseases of crustaceans and fish. The named species of microsporidia usually infect one host species or a group of closely related taxa. Several species, most of which are opportunistic, also infect humans (Wikipedia).

Microsporidian fungus species have been found associated with the following ants:

Plowes et al. (2015) - While microsporidian parasites are extremely diverse and pervasive within the animal kingdom, only four species have been described from ants to date, all from the host genus Solenopsis. The evolutionary adaptation of microsporidia as intracellular parasites has resulted in the evolution of highly reduced genomes in some species and loss of mitochondria and associated metabolic functionality (Keeling and Fast, 2002), yet these remarkable parasites exhibit intricate life cycles with multiple spore types (Andreadis, 2007; Becnel and Andreadis, 2014). A clear phylogeny has only recently been developing which has included their placement within the fungi (Capella-Gutiérrez et al., 2012; Keeling, 2014) and comparative relationships between the taxa (Smith, 2009; Vossbrinck and Debrunner-Vossbrinck, 2005; Vossbrinck et al., 2014). Of note are the apparent aquatic origins of most microsporidian clades within which some recent acquisitions of terrestrial hosts have occurred and this appears to be the case with the four previously described species of microsporidian parasites of ants (Kneallhazia solenopsae, K. carolinensae, Vairimorpha invictae and Burenella dimorpha).