# Food and Drinking Water as Sources of Pathogenic Protozoans: An Update
## 4 _Cryptosporidium_ spp. The genus _Cryptosporidium_, clade Sar Alveolata, phylum Apicomplexa, class Conoidasida, subclass Coccidia, family Cryptosporidiumidae [2] comprises 44 validated species and more than 120 genotypes [87; 88]. The species _C. hominis_ and _C. parvum_ are responsible for nearly 95% of human infections, and one or the other was reported to be dominant in different countries [89; 90; 91; 92; 93; 94; 95; 96]. _C. meleagridis_ can infect both birds and mammals, and it is the third-most common species involved in human cryptosporidiosis [97]. _Cryptosporidium_ chipmunk genotype I, associated with rodents, was the third cause of human cryptosporidiosis in Sweden [98]. Other species and genotypes reported in humans are _C. andersoni, C. bovis_, _C. canis, C. anticellus, C. dirtichi, C. erinacci, C. fajeri, C. felis, C. meleagridis, C. mortiferum, C. muris, C. scridrum, C. suis, C. tyzzeri, C. ubiquittum, C. viatorum, C. xaioi, C. occultus, Cryptosporidium chipmunk genotype I, skunk genotype, horse genotype and mink genotype [10; 88; 91; 93; 95; 99; 100]. _Cryptosporidium_ subtype families are distinguished based on glycoprotein (gp60) gene sequences. Five subtype families of _C. hominis_ with very divergent sequences, Ia, Ib, Id, le, and If and _C. parvum_ subtype family IIc--followed by IIa, and IId--are common in different countries [101]. _C. hominis_ subtype IfA12G1R5, also common in Australia and New Zealand, was associated with increased incidence of cryptosporidiosis in the USA and became dominant over the _C. hominis_ subtype IbA10G2, which was involved in a massive outbreak with more than 400,000 infections and 69 deaths in Milwaukee, Wisconsin, in 1993 caused by insufficiently sanitized drinking water caught from Lake Michigan [4; 102; 103; 104]. The latter was found to be dominant in the American continent [104], together with _C. hominis_ subtype IeA11G3T3, and in other countries [90; 91]. _C. parvum_ subtype family IIa was frequently reported in dairy calves, and subtype family IId in sheep and goats [94; 97]. The _C. parvum_ subtype IIaA15G2R1, associated with calves, predominated in the Americas, UK, and Jordan [89; 93; 95; 104] and became increasingly prevalent in China with the diffusion of intensive farming [94]. The _C. parvum_ subtype IIaA18G3R1 predominated in New Zealand [91], IIaA19G1R1 predominated in Norway [10], and the _C. parvum_ subtype IIdA20G1b predominated among asymptomatic food handlers in Qatar [97]. In Sweden, the new subtype families IIy and IIz were identified for _C. parvum_, and the new subtype families IIIk and VId were identified for _C. mortiferum_, which was involved in foodborne outbreaks [100]. _Cryptosporidium_ life cycle comprises an asexual and a sexual phase. The thick-walled oocyte represents the infectious stage of this organism shed with the feces of infected hosts. The oocyte contains four sporozoites that, once ingested, are released in the host gastrointestinal tract. These attach to the enterocyte surface and are incorporated in para-stiophora vacuoles derived from the host-cell membrane. Here the sporozoites divide asexually, giving rise to trophozoites, and then to type-1 meronts, which contain eight merozoites that either reproduce asexually in the epithelial cells or initiate the sexual cycle by differentiating into type-II meronts. These give origin to four merozoites via asexual division, which infect other enterocytes and differentiate into micro- and macro-gametes. The mature micro-gametes leave their host cell and fertilize the macrogametes forming a zygote that goes through meiosis and gives rise to theocysts. Theocysts are either thin- or thick-walled; the thin-walledocysts cause autoinfection, while the thick-walledocysts are excreted and can infect new hosts. One infected host can shed up to one thousand oocysts [10]. The infective dose calculated in healthy volunteers was 132 oocysts for _C. parvum_ and 10 to 83 oocysts for _C. hominins_[90]. The thick-walled oocysts are resistant to all the available anti-coccidal drugs.