Genotyping of Cryptosporidium parvum With Microsatellite Markers

Recent outbreaks of cryptosporidiosis caused by
Cryptosporidium parvum
in the United States and other countries (
1
,
2
), as well as the emergence of cryptosporidiosis as a frequent cause of morbidity and mortality in immunodeficient individuals (
3
), have raised the interest of the research community in this parasite. The genus
Cryptosporidium
, phylum Apicomplexa, comprises an undefined number of species, of which only
C. parvum
is of public health concern. Cryptosporidiosis is contracted through the ingestion of oocysts, the stage of the parasite produced in large numbers by infected hosts. Because the oocysts are small, typically about 5 �m in diameter, and lack species-specific morphological features, there is a need for molecular markers to distinguish between human-infectious
C. parvum
and other species that do not (or only infrequently) cause disease in humans. Genetic characterization of
Cryptosporidium
oocysts using restriction fragment length or sequence polymorphism has revealed host-associated genotypes, that are often referred to as species (
4
–
6
). In addition,
C. parvum
was found to include two genotypes, designated type 1 and type 2 (
see
Note 1 ). Type 1 is almost exclusively found in humans, whereas type 2 infects humans and various mammalian hosts (
7
–
9
). The frequent occurrence of
Cryptosporidium
oocysts in untreated surface water and the potential for contamination of drinking water (
10
,
11
) have emphasized the need for molecular markers to track the source of oocysts within a watershed or water distribution system, and to discriminate between oocysts infectious to humans and nonpathogenic species. Genetic markers are also needed to study the taxonomy of
Cryptosporidium
.