A putative new Besnoitia species in the southern black-eared opossum Didelphis aurita

<i>Besnoitia</i> spp. are cyst-forming coccidian parasites with a broad host range, infecting various wild and domestic animal species. Northamerican opossums (<i>Didelphis virginiana</i>) are severely affected by the infection with <i>B. darlingi</i>. This study presents a case of infection with <i>Besnoitia</i> in a road-killed female southern black-eared opossum (<i>Didelphis aurita)</i> in Misiones, Argentina. Many 0.5-1 mm cysts were observed in several muscles and visceral organs and were microscopically identified in skeletal muscles, tongue, and heart. Histological analysis disclosed multiple spherical cysts with a myriad of bradyzoites like-cells and a well-defined cyst wall. A small number of degenerate and ruptured cysts, surrounded by mild to moderate inflammation were observed. Genomic DNA from an individual cyst and muscle was extracted and ITS1 marker and <i>18S rRNA</i> gene fragments from sarcocystid protozoa were successfully amplified by PCR and sequenced. The <i>18S</i> sequence exhibited 100% identity with sequences of <i>B. darlingi</i> and <i>B. oryctofelisi</i>. Comparison of the complete ITS1 sequence (259 bp) revealed an identity of 99.2% with <i>B. oryctofelisi</i> and 97.7% with <i>B. darlingi.</i> This result together with the phylogeny positioning, suggest that the <i>Besnoitia</i> sp. in the present case differ from <i>B. darlingi</i>, being closely related with <i>B. oryctofelisi</i>.