First identification of Sarcocystis spp. in synanthropic and wild rodents from Argentina

Abstract

Sarcocystis spp. are cyst-forming intracellular protozoan parasites with an obligate two-host prey-predator type life cycle. Sarcocystis spp. in muscles of different rodent species have been described in several countries. The objective of this study was to determine the presence of Sarcocystis spp. in synanthropic and wild rodents from rural areas in the Humid Pampa Region, Argentina. A total of 158 rodents were captured, euthanized and sampled from dairy cattle farms between 2021 and 2022. The animals were 107 synanthropic (103: Mus musculus, 3: Rattus rattus, and 1: R. norvegicus) and 51 wild rodents (28: Oxymycterus rufus, 12: Necromys lasiurus and 11: Akodon azarae). Samples of different skeletal muscles (tongue, masseter, heart, and semitendinosus) were collected and assessed by histopathological analysis and homogenization followed by direct microscopic examination. Also, PCR targeting a 18S rRNA gene fragment and the internal transcribed spacer 1 (ITS1) were performed from muscles homogenates from Sarcocystis spp. microscopically positive samples. The positive amplicons were further sequenced and analysed. Histopathology and direct microscopy revealed the presence of thin-walled cysts consistent with Sarcocystis spp. in 12.6% (20/158) of rodents. Sarcocysts were more frequently observed in semitendinosus muscle (8 M. musculus, 6 O. rufus, 2 A. azarae, 2 N. lasiurus), followed by the masseter (5 O. rufus, 3 M. musculus, 1 N. lasiurus), heart (1 M. musculus, 1 N. lasiurus) and tongue (1 M. musculus). By 18S rRNA fragment PCR 16/20 samples were positive, and seven were selected for further ITS1 PCR and sequencing. Six of the 18S rRNA sequences showed a 99.48-99.64% identity with S. dispersa (3 M. musculus, 1 A. azarae, 1 N. lasiurus and 1. O. rufus) a species with a rodent-owl cycle, and one (O. rufus) was only 95.5-96.6% similar to other Sarcocystis spp. The last sample showed a 100% identity with S. attenuati at ITS1 sequence fragment (954bp), a species with snakes as putative definitive hosts. The remaining ITS1 sequences (around 1450 bp) showed a high similarity among them and a 100% identity with several Sarcocystis spp. but with a low coverage (10-13%), possible due to the lack of ITS1 sequences in the database. Our results indicate a relatively high proportion of S. dispersa-like in different rodents from Argentina, potentially related with an owl predation of rodents. In addition, a S. attenuati-like species was detected in a O. rufus, suggesting a potential rodent-snake cycle. This is the first study to identify Sarcocystis spp. by molecular methods in rodents from Argentina and probably the first report of ITS1 sequences for S. dispersa-like. Further studies are needed to unravel the role of synanthropic and wild rodents in the epidemiology of cyst forming coccidia parasites.