Neorickettsia risticii is an obligate intracellular pathogen, primarily of horses, that is currently part of the family Anaplasmataceae. Vectors include a number of adult aquatic insects that are infected with encysted N. risticii-infected trematodes, which are ingested by feeding horses. The IFA test uses infected cells, where the N. risticii are seen in custers of cytoplasmic valuoles (morulae), much like Ehrlichia canis in appearance.