Subtyping Cryptosporidium ubiquitum,a Zoonotic Pathogen Emerging in Humans

Na Li, Lihua Xiao, Keri Alderisio, Kristin Elwin, Elizabeth Cebelinski, Rachel Chalmers, Monica Santin, Ronald Fayer, Martin Kvac, Una Ryan, Bohumil Sak, Michal Stanko, Yaqiong Guo, Lin Wang, Longxian Zhang, Jinzhong Cai, Dawn Roellig, Yaoyu Feng

, and BohumilSakYaqiongGuoJinzhongCai

Author affiliations: East China University of Science and Technology, Shanghai, China (N. Li, Y. Guo, L. Wang, Y. Feng);Centers for Disease Control and Prevention, Atlanta, Georgia, USA (N. Li, L. Xiao, Y. Guo, D. Roellig); New York City Department of Environmental Protection, Flushing, New York, USA (K. Alderisio);UK Cryptosporidium Reference Unit, Swansea, UK (K. Elwin, R. Chalmers); Minnesota Department of Health, St. Paul, Minnesota, USA (E. Cebelinski); US Department of Agriculture, Beltsville, Maryland, USA (M. Santin, R. Fayer); Academy of Science of Czech Republic, České Budějovice, Czech Republic (M. Kvac, B. Sak); Murdoch University, Perth, Australia (U. Ryan); Slovak Academy of Sciences, Košice, Slovakia (M. Stanko); Henan Agricultural University, Zhengzhou, China (L. Zhang); Qinghai Academy of Veterinary Medicine and Animal Science, Xining, China (J. Cai)

Abstract

Cryptosporidium ubiquitum is an emerging zoonotic pathogen. In the past, it was not possible to identify an association between cases of human and animal infection. We conducted a genomic survey of the species, developed a subtyping tool targeting the 60-kDa glycoprotein (gp60) gene, and identified 6 subtype families (XIIa–XIIf) of C. ubiquitum. Host adaptation was apparent at the gp60 locus; subtype XIIa was found in ruminants worldwide, subtype families XIIb–XIId were found in rodents in the United States, and XIIe and XIIf were found in rodents in the Slovak Republic. Humans in the United States were infected with isolates of subtypes XIIb–XIId, whereas those in other areas were infected primarily with subtype XIIa isolates. In addition, subtype families XIIb and XIId were detected in drinking source water in the United States. Contact with C. ubiquitum–infected sheep and drinking water contaminated by infected wildlife could be sources of human infections.

Cryptosporidium infection is a leading cause of diarrhea in humans (1). Five Cryptosporidiumspecies—C. hominis, C. parvum, C. meleagridis, C. felis, and C. canis—are responsible for most cases of cryptosporidiosis in humans. Among them, C. hominis and C. parvum are the most common etiologic agents, and the latter is responsible for most zoonotic infections (2). In recent years, C. ubiquitum, previously known as the cervine genotype, has been emerging as another major zoonotic species that infects persons. It has been found in humans worldwide, primarily in industrialized nations (3–11). In the United Kingdom, more human cases of cryptosporidiosis have been attributed to C. ubiquitum than to C. canis (9).

C. ubiquitum is of public health concern because of its wide geographic distribution and broad host range. Of all Cryptosporidium spp. identified by molecular diagnostic tools, it infects the greatest variety of host species (12). C. ubiquitum has been commonly detected in domestic and wild ruminants (sheep, goats, mouflon sheep, blesboks, nyalas, white-tailed deer, Père David’s deer, sika deer, ibexes, buffalos, and yaks), rodents (squirrels, chipmunks, woodchucks, beavers, porcupines, deer mice, house mice, and gerbils), carnivores (raccoons), and primates (lemurs and humans) (12–16). It has also been found in drinking source water, storm water runoff, stream sediment, and wastewater in various geographic locations (17–22).

Thus far, showing an association between human and animal cases of C. ubiquitum infection has not been possible because of the lack of suitable genetic markers for subtyping. For C. parvum,C. hominis, and some genetically related species, the most commonly used marker for subtyping is the 60-kDa glycoprotein gene (gp60, also called gp40/15). Sequence analysis of the gp60 gene has been used in studies of the genetic diversity, host adaptation, infection sources, and transmission dynamics of these Cryptosporidium spp. (2). However, it has been suggested that a single locus, such as gp60, is not a reliable marker of C. parvum and C. hominis population structure because genetic recombination may occur (23).

Because C. ubiquitum is genetically distant from C. hominis and C. parvum, its homologue of the gp60 gene has thus far not been identified (24). In this study, we identified the gp60 gene of C. ubiquitum by whole-genome sequencing and used it to develop a subtyping technique to characterize specimens from humans, various animals, and drinking source water.