Infections and genetic diversity of Cryptosporidium spp. and Giardia spp. in small wild mammals on the Eastern Tibetan plateau: public health implications.

Background: Cryptosporidium and Giardia are protozoan parasites that cause significant diarrheal diseases. Small mammals are potential reservoirs for their zoonotic transmission. The Tibetan Plateau alpine ecosystem harbors diverse and abundant small wild mammals, but their roles in the transmission of Cryptosporidium and Giardia remain inadequately studied.

Methods: Field sampling was conducted in Shiqu County, Sichuan Province, on the eastern Tibetan Plateau, in 2023. Small wild mammals were captured and morphologically identified. Fecal DNA was screened for Cryptosporidium and Giardia with nested-PCR targeting the small subunit ribosomal RNA (SSU rRNA) gene and the beta-giardin (bg) gene, respectively. Positive DNA samples were sequenced and analyzed phylogenetically. Differences in prevalence were assessed with the chi-square test.

Results: In total, 336 small wild mammals were collected, dominated by Neodon fuscus (175/336, 52.1%) and Ochotona curzoniae (106/336, 31.5%). Cryptosporidium infection was detected in 22.3% (75/336) of the small mammals, with marginally higher prevalence in N. fuscus (44/175, 25.1%) than in O. curzoniae (17/106, 16.0%; χ² = 3.220, p = 0.073). Six species/genotypes were identified: zoonotic C. suis (n = 25) and C. canis (n = 6), and non-zoonotic muskrat genotype II (n = 26), yak genotype (n = 10), muskrat genotype I (n = 4), and Cryptosporidium sp. MT524977 (n = 4). The overall prevalence of Giardia was 8.3% (28/336), with similar prevalence in N. fuscus (17/175, 9.7%) and O. curzoniae (10/106, 9.4%, χ² = 0.006, p = 0.938). Non-zoonotic G. microti (n = 3) and four unclassified Giardia spp.: Giardia sp. OR770651 (n = 13), Giardia sp. PQ604631 (n = 7), Giardia sp. MG676959 (n = 3), and Giardia sp. OP963933 (n = 2) were identified. Neodon fuscus harbored greater Giardia diversity (all five Giardia spp.) than O. curzoniae (only Giardia sp. OR770651).

Conclusions: This study demonstrates a high Cryptosporidium prevalence in small wild mammals on the eastern Tibetan Plateau, suggesting potential zoonotic risks to humans and livestock. Giardia exhibited host-specific infection patterns, indicating possible niche adaptation that warrants further investigation. These findings expand the host range and geographic distribution of these parasites and help elucidate their transmission dynamics in alpine ecosystems.