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Introduction
The genus Cryptosporidium comprises obligate protozoan parasites that predominantly inhabit the gastrointestinal epithelium of humans and other vertebrate animals (Fayer, 2010). Cryptosporidium has been under intensive investigation for more than 40 years and the enormous diversity in the genus has been revealed by genotyping studies conducted over the past 20 years. Studies on Cryptosporidium in humans and livestock have predominated due to the clinical and economic importance of cryptosporidiosis in these hosts (Robertson et al., 2014; Kváč et al., 2014b). Research on Cryptosporidium spp. in wild animals has increased significantly in the last decade, expanding our knowledge of genetic diversity in the genus, but the biological properties of these parasites in wildlife remain poorly studied (Ren et al., 2012; Li et al., 2015; Kváč et al., 2018; Tan et al., 2019; Wei et al., 2019). Recent studies indicate that rodents, which represent about 40% of the mammalian diversity, are predominantly parasitized by host-specific Cryptosporidium spp. with unknown biology (Lv et al., 2009; Feng et al., 2011; Ng-Hublin et al., 2013; Stenger et al., 2017; Čondlová et al., 2019). Today, 45 valid Cryptosporidium species and a similar number of genotypes have been reported (Holubová et al., 2020). Cryptosporidium muris and C. proliferans have a broad host range in the order Rodentia. In contrast, a narrow host specificity has been reported for C. alticolis and C. microti in voles, C. apodemi and C. ditrichi in apodemus mice, C. homai and C. wrairi in guinea pigs, C. tyzzeri in house mice, C. rubeyi in ground squirrels and C. occultus in rats (Tyzzer, 1910; Vetterling et al., 1971; Ren et al., 2012; Li et al., 2015; Kváč et al., 2016, 2018; Zahedi et al., 2017; Čondlová et al., 2018; Horčičková et al., 2018). Additionally, a large number of Cryptosporidium genotypes have been reported in rodents (Kváč et al., 2014b).
Representatives of the genus Rattus, which are globally distributed, with the exception of the polar region (Reid, 2007; Thomson et al., 2018), have been reported as hosts of several Cryptosporidium spp. (Table 1). The recently described C. occultus is specific for...