Identification of a new sp. in marsh deer () from wetlands of Argentina.

The marsh deer () is the largest South American native deer species and is listed as "Vulnerable" by IUCN due to the population reduction. As part of a conservation and disease surveillance program, muscle samples from 14 marsh deer found dead in 2016 and 2017 in northeast Argentina were obtained at necropsy. Samples from each animal were processed as pooled muscles (heart, diaphragm, tongue and hindlimb) by homogenization and direct microscopical observation to detect intracellular spp. cysts. Sarcocysts were observed in six samples, and several cysts recovered from two samples were processed by transmission electron microscopy. The cysts were thin-walled and showed a cyst-wall ultrastructure with ribbon-like protrusions similar to other species using cervids as intermediate host and canids as definitive hosts. Genomic DNA from individual sarcocysts from three marsh deer were successfully amplified by PCR of and gene fragments and further sequenced. Sequence comparison revealed a 99.3-100% identity among them and only 93.7-96.6% and 88.8-89.7% identity at and markers, respectively, with other spp. Despite morphological similarities, the high sequence divergence at and fragments allowed the assumption that sp. from marsh deer is a different species from others using cervids as intermediate hosts. Therefore, we propose the name n. sp. for the species infecting marsh deer.