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Cryptosporidium spp. are protozoan parasites that belong to subphylum apicomplexa and cause diarrhea in humans and animals worldwide. Data on the prevalence of Cryptosporidium spp. and its subtypes among calves in the Republic of Korea (KOR) are sparse. Hence, our study aimed to investigate the prevalence and association between the age of calf and the identified Cryptosporidium spp. and to determine the genotypes/subtypes of Cryptosporidium spp. in pre-weaned calves with diarrhea in the KOR. A total of 460 diarrheic fecal samples were collected from calves aged 1−60 days and screened for Cryptosporidium spp. by the 18S rRNA gene. Species identification was determined using the sequencing analysis of the 18S rRNA gene, and C. parvum-positive samples were subtyped via the sequence analysis of the 60-kDa glycoprotein (gp60) gene. Sequence analysis based on the 18S rRNA gene revealed the presence of three Cryptosporidium spp., namely, C. parvum (n = 72), C. ryanae (n = 12), and C. bovis (n = 2). Co-infection by these species was not observed. The infection rate was the highest in calves aged 11−20 days (26.1%, 95% CI 17.1−35.1), whereas the lowest rate was observed in calves aged 21−30 days (7.7%, 95% CI 0.0−16.1). The prevalence of C. parvum was detected exclusively in calves aged ≤20 days, and the highest infection rate of C. ryanae was seen in calves ≥31 days of age. The occurrence of C. parvum (χ2 = 25.300, P = 0.000) and C. ryanae (χ2 = 18.020, P = 0.001) was significantly associated with the age of the calves. Eleven different subtypes of the IIa family that belonging to C. parvum were recognized via the sequence analyses of the gp60 gene. Except for two (IIaA18G3R1 and IIaA15G2R1) subtypes, nine subtypes were first identified in calves with diarrhea in the KOR. IIaA18G3R1 was the most frequently detected subtype (72.2% of calves), followed by IIaA17G3R1 (5.6%), IIaA15G2R1 (4.2%), IIaA19G4R1 (4.2%), IIaA16G4R1 (2.8%), IIaA17G4R1 (2.8%), IIaA19G3R (2.8%), IIaA14G1R1 (1.4%), IIaA14G3R1 (1.4%), IIaA15G1R1 (1.4%), and IIaA19G1R1 (1.4%) These results suggest that the prevalence of Cryptosporidium spp. is significantly associated with calf age. Furthermore, the findings demonstrate the high genetic diversity of C. parvum and the widespread occurrence of zoonotic C. parvum in pre-weaned calves. Hence, calves are a potential source of zoonotic transmission with considerable public health implications.

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Bovine viral diarrhea virus (BVDV) is an economically important pathogen that causes development of mild to severe clinical signs in wild and domesticated ruminants. We previously showed that mice could be infected by BVDV. In the present study, we infected mice intraperitoneally with non-cytopathic (ncp) BVDV1 or ncp BVDV2, harvested the blood and organs of the infected mice at days 4, 7, 10 and 14 postinfection (pi), and performed immunohistochemical analyses to confirm BVDV infection. Viral antigens were detected in the spleens of all infected mice from days 4 through 14 and were also found in the mesenteric lymph nodes, gut-associated lymphoid tissue (GALT), heart, kidney, intestine, and bronchus-associated lymphoid tissue (BALT) of some infected mice. In ncp BVDV2-infected mice, flow cytometric analysis revealed markedly fewer CD4(+) and CD8(+) T lymphocytes and lower expression of costimulatory molecules CD80 (B7-1) and CD86 (B7-2) and major histocompatibility complex (MHC) class II (I-A/I-E) than those in ncp BVDV1-infected mice. Production of the cytokines interleukin (IL)-6 and monocyte chemotactic protein (MCP)-1 was higher in the plasma of ncp BVDV2-infected mice than that in that of ncp BVDV1-infected mice. Our results demonstrate that ncp BVDV1 and ncp BVDV2 interact differently with the host innate immune response in vivo. These findings highlight an important distinction between ncp BVDV1 and ncp BVDV2 and suggest that ncp BVDV2 impairs the host's ability to control the infection and enhances virus dissemination.

Korean water deer (Hydropotes inermis argyropus) are widespread in the Republic of Korea (ROK). Mostly, Korean water deer are essential hosts for maintaining ticks and tick-borne diseases (TBDs). Here, we investigated the prevalence of tick-borne pathogens (TBPs) among rescued Korean water deer. Anaplasma phagocytophilum (21.4%, 6/28), Anaplasma capra (14.3%, 4/28), Babesia capreoli (3.6%, 1/28), and Coxiella burnetii (3.6%, 1/28) were detected, but Borrelia burgdorferi, Ehrlichia, Rickettsia, and Theileria infections were not found. A. phagocytophilum was the most commonly detected pathogen, and co-infection with A. capra and B. capreoli was also noted in one Korean water deer. To our knowledge, this is the first article of B. capreoli infection in Korean water deer in the ROK. The infecting isolate of A. phagocytophilum was genetically characterized by 16S ribosomal RNA (rRNA) gene and ankyrin-related protein (ankA) gene. Although the 16S rRNA gene alone may not be informative enough to delineate distinct host species, ankA-based phylogeny revealed a high identity of Korean water deer sequences with those of the causative agent of human granulocytic anaplasmosis. A. capra was detected by using citrate synthase gene (gltA), heat-shock protein (groEL), and major surface protein 4 (msp4) genes. Phylogenetic tree based on these gene markers revealed that there were at least two distinct variants within A. capra circulating in the ROK. One variant originated from different hosts including humans, ticks, goats, and sheep, whereas the other variant was reported recently in Korean water deer in the ROK. Consequently, these sequences were identified to belong to a zoonotic species. Sequencing analysis of the 18S rRNA gene revealed that our isolate belonged to B. capreoli and was distinct from Babesia divergens and Babesia venatorum. Moreover, our isolate showed 92.2% homology with B. capreoli sequences, indicating that these differences may be attributed to the different tick species that transmit B. capreoli or to different host species. Genotyping and phylogenetic analysis of C. burnetii based on 16S rRNA and IS1111 genes revealed that our isolate was grouped with several strains of C. burnetii and was genetically distant from Coxiella-like bacteria isolates. The present results highlight that Korean water deer act as potential reservoir hosts for zoonotic TBPs, and thus play an important role in the transmission of TBDs in humans, animals, and livestock.