Evidence that Cryptosporidium parvum Populations Are Panmictic and Unstructured in the Upper Midwest of the United States

Abstract

e Cryptosporidium parvum is a zoonotic protozoan parasite that causes cryptosporidiosis, an infectious diarrheal disease primarily affecting humans and neonatal ruminants. Understanding the transmission dynamics of C. parvum, particularly the specific contributions of zoonotic and anthroponotic transmission, is critical to the control of this pathogen. This study used a population genetics approach to better understand the transmission of C. parvum in the Upper Midwest United States. A total of 254 C. parvum isolates from cases of human cryptosporidiosis in Minnesota and Wisconsin and diarrheic calves in Minnesota, Wisconsin, and North Dakota were genotyped at eight polymorphic loci. Isolates with a complete profile from all eight loci (n ‫؍‬ 212) were used to derive a multilocus genotype (MLT), which was used in population genetic analyses. Among the 94 MLTs identified, 60 were represented by a single isolate. Approximately 20% of isolates belonged to MLT 2, a group that included both human and cattle isolates. Population analyses revealed a predominantly panmictic population with no apparent geographic or host substructuring.

Host Association of Cryptosporidium parvum Populations Infecting Domestic Ruminants in Spain

“…In France, the C. parvum structure ranged from basic clonality (humans) to epidemic clonality (livestock) (22), while a predominantly clonal structure was seen in Italy (39). In contrast, the C. parvum population in humans and cattle was predominantly panmictic in the upper Midwest of the United States, with limited geographic or host substructuring (40). Population analysis in the current study confirmed the evolutionary divergence of C. parvum isolates infecting domestic ruminants in our geographical area.…”

“…Multilocus studies of isolates from humans and livestock with VNTR markers have also identified C. parvum groups apparently restricted to humans in the United Kingdom, France, or Haiti, which supports the anthroponotic characteristics of these isolates or the occurrence of cycles that do not involve livestock (20,22,34). In contrast, no apparent host association was seen in the upper Midwest of the United States, with C. parvum being transmitted freely between cattle and humans (40). Data on the existence of specific C. parvum subpopulations within livestock species are limited.…”

“…None of the six markers alone improved the discriminatory power previously reported by GP60 sequencing (23), but the multilocus analyses substantially increased the HGDI value and identified up to 56 MLTs within 140 isolates. This finding indicates an extensive genetic diversity, which has been related to regions where Cryptosporidium transmission is assumed to be intense (38) and was proportionally higher in goat kids ( (19,20,22,39,40).…”

Is Predominant Clonal Evolution a Common Evolutionary Adaptation to Parasitism in Pathogenic Parasitic Protozoa, Fungi, Bacteria, and Viruses?

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Next Generation Sequencing uncovers within-host differences in the genetic diversity of Cryptosporidium gp60 subtypes

“…The relative contribution of each type of population structure appears to vary between regions and hosts, and may reflect the prevailing ecological transmission dynamics (Mallon et al, 2003;Tanriverdi et al, 2008;Widmer and Sullivan, 2010;Herges et al, 2012;Widmer et al, 2015). The finding of only one C. hominis subtype by both Sanger and NGS in the kangaroo-derived DNA samples may reflect a clonal population structure operating locally in kangaroo populations from the main Sydney drinking water catchment.…”