1. Introduction
Neonatal calf diarrhea caused by intestinal pathogens including bacteria, viruses and parasites is a leading cause of morbidity and mortality in pre-weaned calves (Gomez & Weese, 2017). Rotavirus, coronavirus, Escherichia coli , andCryptosporidium spp. are considered the most important causes for calf diarrhea (Meganck, Hoflack, & Opsomer, 2014). Synergistic infections of these pathogens were often identified during outbreaks of diarrhea in calves (Foster & Smith, 2009; Gomez & Weese, 2017). Among them,Cryptosporidium spp. and rotavirus are the most frequently observed pathogens in fecal specimens from neonatal calves worldwide (Mohamed, Mansour, El-Araby, Mor, & Goyal, 2017; Thomson et al., 2017). In addition, moderate-to-severe diarrhea caused by Cryptosporidiumspp. is of the leading causes for morbidity and mortality in young children in developing countries (Kotloff et al., 2013).
Cryptosporidium spp. are especially common in dairy calves. The cumulative infection rate of Cryptosporidium spp. in pre-weaned dairy calves in the United States is 100.0% (Santin, Trout, & Fayer, 2008; Xiao & Herd, 1994). In China, the average infection rate of Cryptosporidium spp. in dairy calves with diarrhea was 45.8%, much higher than that in cattle overall (14.5%) (Wang, Zhao, Gong, & Zhang, 2017). Numerous cryptosporidiosis outbreaks have been reported in neonatal calves in the United States, European countries, Australia, India, and China, causing serious harms to the dairy industry (Brar et al., 2017; Cui et al., 2014; Izzo et al., 2011; Li et al., 2019; Ouakli et al., 2018; Randhawa, Randhawa, Zahid, Singla, & Juyal, 2012).
Among the over 40 established Cryptosporidium species (Feng, Ryan, & Xiao, 2018), C. parvum , C. bovis , C. ryanae and C. andersoni are commonly found in cattle (Ryan, Fayer, & Xiao, 2014). Among the latter, C. parvum is the only major pathogenic and zoonotic species (Thomson et al., 2017). The distribution of Cryptosporidium spp. in cattle in China, however, is very different from other countries, with C. bovis being the most common species in pre-weaned calves rather than C. parvumelsewhere (Feng & Xiao, 2017). In addition, subtyping of C. parvum based on sequence analysis of the 60 kDa glycoprotein (gp60 ) gene indicates that calves in China are exclusively infected with IId subtypes (Feng & Xiao, 2017). Elsewhere, IIa subtypes are mostly identified in calves, while IId subtypes are usually seen in lambs and goat kids (Xiao, 2010).
Thus far, almost all investigations of cryptosporidiosis outbreaks in humans and calves caused by C. parvum have focused on its IIa subtype family in industrialized nations. The clinical importance of the IId subtype family of C. parvum is less clear. Two recent outbreaks, however, have been reported in dairy calves in China, responsible for substantial mortality (Cui et al., 2014; Li et al., 2019). They were caused by IIdA15G1 and IIdA19G1 subtypes, two dominant C. parvum subtypes in calves and other animals in China (Feng & Xiao, 2017).
Here, we report the results of an investigation of a cryptosporidiosis outbreak in neonatal calves on a large cattle farm in Hebei Province, China caused by another IId subtype of C. parvum . Approximately 20% of neonatal calves on the farm died of watery diarrhea during the outbreak period.