Polymorphism of eimerian oocysts can be a problem in naturally infected hosts: an example from subterranean rodents in Bolivia.

Since 1986, 364 tuco-tucos (Ctenomys spp.) representing 7 species were collected from 16 major collecting areas representing at least 4 distinct ecological habitats in Bolivia, South America. All were examined for coccidia, and 125 (34%) had oocysts in their feces including 84 of 236 (36%) Ctenomys boliviensis from tropical palm/savanna habitats; 1 of 3 (33%) Ctenomys conoveri from a chaco thorn forest; 3 of 7 (33%) Ctenomys frater from medium altitude grass habitats; and 6 of 8 (75%) Ctenomys lewisi and 31 of 35 (88%) Ctenomys opimus from high altitude/puna habitats. None of 3 Ctenomys leucodon (high altitude/puna) or 72 Ctenomys steinbachi (tropical palm/savanna) were passing oocysts when examined. The 5 infected host species all had oocysts of Eimeria opimi Lambert, Gardner, and Duszynski, 1988, in their feces. These oocysts and their sporocysts varied greatly in size, both within and between host species, but qualitative characters (e.g., residua and wall texture) remained constant. Our conclusion, that all oocysts seen were E. opimi, was supported by multigroup discriminant analysis of 256 individual oocysts, 30-67 selected randomly from each Ctenomys sp. Minimum polygons enclosing the centroid (= multivariate mean) and the spread of individuals for each species group (OTU) showed significant overlap in discriminant space, and Geisser classification showed a 55% miss rate of individuals being classified into the wrong OTUs. Thus, oocyst and sporocyst lengths and widths cannot be used to separate morphotypes of E. opimi from different Ctenomys spp. from different geographic regions of Bolivia.