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Microscopic and Molecular Identification of Sarcocystis Species in Wild Brown Rats (Rattus norvegicus) in Lithuania and Latvia
State Scientific Research Institute Nature Research Centre, Akademijos Str. 2, 08412 Vilnius, Lithuania
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Animals 2026, 16(2), 331; https://doi.org/10.3390/ani16020331
Submission received: 24 December 2025
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Revised: 17 January 2026
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Accepted: 20 January 2026
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Published: 21 January 2026
(This article belongs to the Section Veterinary Clinical Studies)
Simple Summary
The brown rat, an invasive and synanthropic rodent, exhibits highly opportunistic omnivorous feeding habits and plays an important role in the transmission of a wide range of pathogens to humans and domestic animals. Sarcocystis spp. are protists that alternate between two hosts, forming sarcocysts in muscle tissue of the intermediate hosts and developing sporocysts in the intestine of definitive hosts. Information on the role of brown rats as definitive hosts of Sarcocystis parasites under natural conditions is limited, with only S. cymruensis (syn. S. rodentifelis) having been experimentally confirmed to complete its life cycle in this rodent. Intestines of 27 brown rats were collected in Lithuania and Latvia and examined for Sarcocystis spp. The results of a light microscopy examination indicated that seven rats were positive for Sarcocystis spp. sporocysts and oocysts. Based on nested PCR and sequencing of several different genetic regions, more than half of the samples were positive for these parasites. Molecular analysis revealed the presence of DNA of several different Sarcocystis species that use rodents, ungulates, and birds as intermediate hosts. Overall, the study suggests that brown rats might be involved in the transmission of Sarcocystis species in nature.
Abstract
Sarcocystis is a genus of heteroxenous, globally distributed apicomplexan parasites found in reptiles, birds, and mammals. Typically, sarcocysts develop in muscles of intermediate hosts, and oocysts sporulate in intestines of definitive hosts. The parasite’s life cycle is based on prey–predator relationships and usually involves two distinct host species. However, some Sarcocystis spp. can complete their full development within a single host species. Brown rats (Rattus norvegicus) are invasive, synanthropic, highly adaptable rodents that are true omnivores and opportunistic feeders. Therefore, it is possible that they can act as definitive hosts of Sarcocystis parasites. This study provides the first comprehensive assessment of Sarcocystis protists in brown rat intestinal samples under natural conditions, combining microscopy and molecular analyses. Of 27 brown rats investigated, 25.9% (7/27) of animals harbored oocysts/sporocysts of Sarcocystis spp. Based on nested PCR and sequencing of four genetic loci (18S rRNA, 28S rRNA, ITS1, and cox1), 59.3% of samples were positive for Sarcocystis spp. Parasites identified were genetically similar to Sarcocystis spp. using bird–bird, bird–Carnivora, rodent–Carnivora, or ungulate–Carnivora as their intermediate–definitive hosts. The present study suggests that synanthropic rodents may facilitate cross-ecosystem transmission of these parasites, increasing infection pressure on livestock, companion animals, and wildlife in human-dominated environments. Future molecular and dietary ecological studies are needed to assess the role of synanthropic and opportunistic hosts, such as the brown rat, in the transmission of Sarcocystis spp.
