Microsporidia (syn. microsporida) is a highly diverse phylum with which approximately 150 genera and over 1200 species are associated. These eukaryotic parasites infect mainly arthropods and fish, but have gained relevance in the medical community in the past few decades because of their increased infection of humans suffering from compromised immune symptoms, mainly associated with HIV. It is very common in pigs and seems to be a natural pathogen in animals such as pigs.
At this time there are 13 microsporidians which are known to infect humans, primarily affecting those with immunocompromised disorders. The most prevalent pathogens of humans include Enterocytozoon bieneusi, whose clinical manifestations include diarrhea and pneumonia; Encephalitozoon cuniculi, whose symptoms include encephalitis and nephritis; Nosema sp., which affect the cornea; and Encephalitozoon intestinalis, which causes diarrhea and nephritis.