Multilocus genotypic analysis of Cryptosporidium parvum isolates from different hosts and geographical origins

Abstract

The genetic analysis of oocysts recovered from the stools of humans and animals infected with Cryptosporidium parvum has consistently shown the existence of two distinct genotypes. One of the genotypes is found exclusively in some human infections, whereas the other genotype is found in human as well as in animal infections. On the basis of these observations and the results of published epidemiological studies with single polymorphic markers, the existence of two separate transmission cycles has been postulated, one exclusively anthroponotic and the other involving both animals and humans. To test this hypothesis, C. parvum isolates of different geographic and host origins were analyzed by using unlinked genetic polymorphisms. A total of 28 isolates originating from Europe, North and South America, and Australia were examined. Isolates clustered into two groups, one comprising both human and animal isolates and the other comprising isolates only of human origin. The absence of recombinant genotypes is consistent with two reproductively isolated populations within the species C. parvum.

FIG. 1

Chromosomal locations of three C. parvum RFLP markers. Oocyst DNA (a, c, and e) was fractionated by CHEF electrophoresis (COWP and TRAP-C1) or PFGE [poly(T)] in parallel with S. cerevisiae DNA standards (a and c, left lanes; e, right lane) and Hansenula wingei chromosomes (e, middle lane). The locations of C. parvum chromosomal bands are indicated with horizontal lines. The molecular sizes of these bands are 1.54, 1.44, 1.24, 1.08, and 1.03 Mb from top to bottom, respectively (2). Panels b, d, and f show the results of Southern analyses with the corresponding probes.

FIG. 2

PCR and PCR-RFLP fingerprints of three C. parvum isolates obtained with five markers. Isolates MD and H78 are of ovine and human origin, respectively, and are examples of isolates displaying the C genotype, whereas isolate P12 is a human isolate of genotype H. Fractionation of DNA fragments was performed in 3.5% agarose (lane M, 100-bp DNA ladder).