Cryptosporidium spp. and Giardia duodenalis are protozoan parasites that cause diarrhea in humans and animals. Molecular data on Cryptosporidium spp. and G. duodenalis in calves in the Republic of Korea (ROK) is limited; thus, we investigated the prevalence of Cryptosporidium and Giardia in pre-weaned calves, analyzed the association between these parasites and diarrhea, and identified their zoonotic potential for human infection. Fecal samples were collected from 315 pre-weaned calves aged 1-60 days from 10 different regions in the ROK and screened for Cryptosporidium spp. and G. duodenalis using PCR. Overall prevalence of Cryptosporidium spp. and G. duodenalis was 4.4% (n = 14) and 12.7% (n = 40), respectively. Co-infection was not detected. All Cryptosporidium-positive samples were identified as C. parvum after sequence analysis of a small subunit rRNA fragment and further subtyped into zoonotic IIaA15G2R1 (n = 13) and IIaA18G3R1 (n = 1) by DNA sequencing of the 60-kDa glycoprotein gene. To our knowledge, this is the first report of C. parvum IIaA15G2R1 subtype in calves in the ROK. Based on β-giardin (bg) gene, G. duodenalis-positive samples belonged to assemblages E (n = 36) and A (n = 4), with the latter belonging to subtype A1, the zoonotic genotype. Six subtypes of assemblage E were identified at the bg locus: E1 (n = 6), E2 (n = 3), E3 (n = 13), E5 (n = 1), E8 (n = 1), and E11 (n = 1). The occurrence of C. parvum and G. duodenalis was not associated with diarrhea in pre-weaned Korean native calves. The present results suggest that the prevalence of C. parvum is not related to calf age; in contrast, the prevalence of G. duodenalis was significantly higher in 41-50-day-old calves (odds ratio = 9.90, 95% confidence interval 2.37-41.34; P = 0.001) than in 1-10-day-old calves. Therefore, calves are a potential source of zoonotic transmission, which may have significant public health implications.
Keywords: Cryptosporidium parvum; Giardia duodenalis; Pre-weaned calves; Zoonotic potential.