**1. Introduction**

*Cryptosporidium* spp. are important diarrheal pathogens in humans and various animals [1]. Currently, 45 *Cryptosporidium* species and over 100 genotypes have been recognized [2]. Among them, *C. parvum*, *C. ubiquitum*, and *C. xiaoi* are common species in sheep and goats. *C. parvum* and *C. ubiquitum* are zoonotic species that infect a wide range of hosts, while *C. xiaoi* appears to be adapted to ovine and caprine animals [3]. *C. xiaoi*, previously known as the *C. bovis*-like genotype, is the most common species in sheep and goats in most areas except Europe [4–8].

Sequence analysis of the 60-kDa glycoprotein (*gp60*) gene has been used extensively in subtyping *C. parvum*, *C. ubiquitum,* and other zoonotic species due to its high sequence heterogeneity and relevance to parasite biology. The unique distribution of subtype families and subtypes have significantly improved our understanding of host adaptation and transmission dynamics within these *Cryptosporidium* spp. [2,9–15]. Recently, *gp60* genebased subtyping tools have been developed for molecular epidemiological studies of some non-human pathogenic *Cryptosporidium* spp., such as the bovine-adapted *C. ryanae* and the

**Citation:** Fan, Y.; Huang, X.; Guo, S.; Yang, F.; Yang, X.; Guo, Y.; Feng, Y.; Xiao, L.; Li, N. Subtyping *Cryptosporidium xiaoi*, a Common Pathogen in Sheep and Goats. *Pathogens* **2021**, *10*, 800. https:// doi.org/10.3390/pathogens10070800

Academic Editor: Luiz Shozo Ozaki

Received: 2 June 2021 Accepted: 22 June 2021 Published: 24 June 2021

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marsupial-adapted *C. fayeri* [16,17]. However, such a tool is not available for *C. xiaoi*, which is occasionally found in humans [18].

In this study, we sequenced the genome of *C. xiaoi*, identified its *gp60* gene, and developed a subtyping tool for genetic characterizations of isolates from sheep and goats.
