1907
Tyzzer (1907, Proc Soc Exp Biol Med 5: 12-13) provides a brief but adequate description (at the time) of C. muris, the types species of the genus, from Mus musculus. He establishes the genus Cryptosporidium.

1910
Tyzzer (1910, J Med Res 23: 487-509) describes oocyst structure and endogenous development of Cryptosporidium muris from the gastric glands of experimentally infected mice. The use of control animals in his studies is noteworthy as it is not the norm at the time.

1911
Leger (1911, Arch Protistenkd 22: 71-88) establishes the family Cryptosporidiidae.

1912
Tyzzer (1912, Arch Protistenkd 26: 394-412) describes a second member of the genus, C. parvum, from mice as new. Morphological descriptions of both the oocyst and developmental stages are reported.

1913
Poche (1913, Arch Protistenkd 30: 125-321) also attempts to create the family Cryptosporidiidae but is two years too late.

1925
Triffit (1925, Protozoology 1: 19-26) names a new species, C. crotali from the rattlesnake, but it is now clear that this is a Sarcocystis sp.

1929
Tyzzer (1929, Am J Hyg 10: 269-383) reports the finding of "Cryptosporidium parvum" in the ceca of chickens. He is unsure whether his finding truly represents C. parvum, and provides no detailed information. It may or may not be considered a synonym of C. baileyi Current, Upton, & Hayes, 1986. Tyzzer also noted finding C. parvum in a rabbit which may be a separate species.

1938
Wetzel (1938, Arch Wiss Prakt Tierh 74: 39-40) describes C. vulpis as new from a fox. It is now considered to be a Sarcocystis sp. (Levine & Tadros, 1980 Syst Parasitol 2: 41-59).

1947
Matschoulsky (1947, Tr Buryat-Mongol Zoovet Inst 3: 93-101) reports C. baikalika as new from the woodcock. Line drawings reveal the parasite to represent gregarine oocysts.

1954
Bearup (1954, Aust Vet J 30: 185-186) erroneously reports a Sarcocystis sp. as Cryptosporidium sp. from a dog.

1955
Slavin (1955, J Comp Pathol Ther 65: 262-266) names C. meleagridis as new from the small intestine of the turkeys. A morphologic description of the oocyst, and descriptions of the developmental stages, are reported. This is still considered a valid species.

1961
Levine (1961, Protozoan Parasites of Domestic Animals and of Man. 412 pp) names the Cryptosporidiium sp. noted by Tyzzer (1929, Am J Hyg 10: 269-383) C. tyzzeri. Since a description is still lacking, the species remains a nomen nudum.

1963
Dubey & Pande (1963, Ind J Microbiol 3: 103-108) report a Cryptosporidium sp. from the Indian jungle cat, Felis chaus. This is now considered to represent a Sarcocystis sp.

1968
Anderson et al. (1968, J Parasitol 54: 577-581) name C. lampropeltis as new from the kingsnake, Lampropeltis calligaster. This is now termed Sarcocystis lampropeltis (Anderson, Duszynski, & Marquardt, 1968) Levine & Tadros, 1980.

1969
Arcay de Peraza & Bastardo de San Jose (1969, Acta Cient Venez 20: 125) name C. ameivae as new from the lizard, Ameiva ameiva, in Venezuela. Since no proper description has ever been published, this remains a nomen nudum.

Duszynski (1969, J Protozool 16: 581-585) names a new species, C. ctenosauris, from a Costa Rican lizard, Ctenosaura similis. This is now considered to be Sarcocystis ctenosauris (Duszynski, 1969) Levine & Tadros, 1980.

1971
Vetterling et al. (1971, J. Protozool. 18: 243-247; 248-260) names C. wrairi as new from guinea pigs. No morphological details about the oocyst are given.

1972
Gottschalk (1972, Beit Vogelkunde 18: 61-69) reports a Cryptosporidium sp. from the hawk, Accipiter gentilis. This is now considered to represent a Sarcocystis sp.

Pande et al. (1972, Acta Vet Acad Sci Hung 22: 231-234) report a new type of Cryptosporidium sp. from pups based on the "intracellular" location of the developmental stages. They term this species Hoareosporidium pellerdyi. This is now considered to represent a Sarcocystis sp.

1974
Barker & Carbonell (1974, Z Parasitenkd 44: 289-298) describe as new C. agni from lambs and C. bovis from calves. This, based solely on host specificity.

Proctor & Kemp (1974, J Protozool 21: 664-666) name C. anserinum as new from the large intestine of a domestic goose, Anser anser. Oocyst sizes are never reported. Later, Levine (1984, J Protozool 31: 94-98) synonymizes this with C. meleagridis Slavin, 1955 even though the latter species develops in the small intestine. The species remains a nomen nudum.

1976
Nime et al. (1976, Gastroenterology 70: 592-598) and Meisel et al. (1976, Gastroenterology 70: 1156-1160) independently report Cryptosporidium from humans for the first time.

1977
Brownstein et al. (1977, Vet Pathol 14: 606-617) report pathology from snakes infected with a new Cryptosporidium sp. This is later named C. serpentis by Levine (1980, J Parasitol 66: 830-834), and is still considered a valid species.

1979
Inman & Takeuchi (1979, Vet Pathol 16: 89-95) name C. cuniculus from the ileum of a rabbit as new. Levine (1984, J Protozool 31: 94-98) attempts to synonymize this (erroneously) with C. muris.

Iseki (1979, Jap J Parasitol 28: 285-307) names C. felis from the domestic cat as new. More recent evidence will indicate this to be a valid species.

1980
Tzipori et al. (1980, Inf Immun 30: 884-886) suggest that Cryptosporidium may be a single-species genus (at least the species in mammals that they studied).

Levine (1980, J Parasitol 66: 830-834) creates the species C. rhesi for Crytosporidium reported to infect the Rhesus monkey, and C. serpentis for the species reported by Brownstein et al. (1977, Vet Pathol 14: 606-617) found to be pathogenic in snakes. The former species should be regarded as a synonym of C. parvum or C. hominis. The latter species, though considered valid, technically remains a nomen nudum in 1980 because of the lack of a proper definitive description.

1981
Hoover et al. (1981, J Fish Dis 4: 425-428) name C. nasorum for a new Cryptosporidium sp. found in Naso lituratus. Technically, since definitive morphologic details are lacking, this still remains a nomen nudum.

Bird (1981, in Parasitol Topics, Soc Protozool Spec Publ 1, 39-47) names C. garnharmi as new from humans. Although Levine (1984, J Protozool 31: 94-98) synonymizes this with C. muris, it should be regarded as a synonym of C. parvum or C. hominis.

1982
Tham et al. (1982, Avian Pathol 11: 619-626) reports a pathogenic Cryptosporidium sp. throughout the respiratory and digestive tract of quail. Although as yet unnamed and the life-cycle undetermined, this will probably be found to represent a distinct species.

1984
Levine (1984, J Protozool 31: 94-98) erroneously synonymizes C. parvum with C. muris. He also erroneously synonymizes C. rhesi with C. muris rather than C. parvum, "C. tyzzeri" with C. meleagridis, and C. serpentis with "C. crotali".

1985
Upton & Current (1985, J Parasitol 71: 625-629) "unsynonymize" C. parvum and C. muris. First published report of the large, abomasal C. sp. from cattle which is erroneously termed C. muris in the paper (eventually to be named C. andersoni). Complete morphologic descriptions of C. parvum and the abomasal C. sp. from cattle are provided. We now know there are many more species than described.

Qadripur & Klose (1985, Dermatol Monatsschr 171: 438-442) terms the species infecting humans as "C. enteritidis". This term is used later by several other european authors and should be considered a synonym of C. parvum.

1986
Current et al. (1986, J Protozool 33: 289-296) describe C. baileyi as a new species from the bursa and cloaca of chickens. Both a morphologic description and complete life-cycle are provided. Since "C. tyzzeri" remains a nomen nudum, and can be legally discarded by authors who present a proper description, "C. tyzzeri" is synonymized. Cryptosporidium baileyi remains a valid species.

Paperna et al. (1986, Proc 39th Ann Meet, Soc Protozool, Univ Rhode Island, Abstr 142) name Cryptosporidium villithecus as new from cichlid fish. They do not use the nomen triviale and simply refer to this species as C. sp. in their formal paper (Landsberg & Paperna, 1986, Dis Aquat Org 2: 13-20).

1987
Crawshaw & Mehren (1987, Erkrank Zoot, 1987, Cardiff, pp. 353-362) report a Cryptosporidium sp. from an amphibian (toad) for the first time.

1989
Upton et al. (1989, J Wildlf Dis 25: 20-30) report oocyst measurements for C. serpentis for the first time. Measurements of various isolates suggest multiple Cryptosporidium spp. exist in reptiles.

Lindsay et al. (1989, Proc Helminthol Soc Wash 56: 91-92) presents formal measurements for C. meleagridis that agree well with those published earlier by Slavin (1955, J Comp Pathol 65: 262-266). This clearly demonstrates that the species is similar in size to C. parvum and smaller than C. baileyi.

1991
Tilley et al. (1991, Can J Microbiol 37: 949-952) first report oocyst measurements for C. wrairi, which are indistinguishable from C. parvum, and establish low level infections in mice. It is unknown whether C. wrairi should be regarded as a distinct species, or a form of C. parvum.

1993
Gajadhar (1993, Can Vet J 34: 115-116) and Bezuidenhout et al. (1993, J South Afr Vet Assoc 64: 156-158) independently report a Cryptosporidium sp. from ostriches.

1994
Gajadhar (1994, Parasitol Res 80: 316-319) presents morphologic evidence to suggest that the Cryptosporidium sp. in ostriches is a species distinct from others and smaller than other known avian Cryptosporidium spp.

1995
Morgan et al. (1995, Am J Trop Med Hyg 52: 539-564) uses RAPD analysis and suggests two distinct genotypes infecting humans.

Pavlasek et al. (1995, Gazella 22: 99-108) describe Cryptosporidium varani n. sp. for the intestinal Cryptosporidium sp. commonly found in reptiles, particularly lizards. The type host is Varanus prasinus (Emerald monitor). Later, Pavlasek (1997, Veterinarstvi 2: 63-65; 1998, Gazella 25: 163-170) reported the parasite from additional hosts. Koudela and Modry (1998, Folia Parasitologica 45: 93-100), unaware of the work of Pavlasek, later decribe this same species as Cryptosporidium saurophilum n. sp.

1996
Paperna & Vilenkin (1996, Dis Aquat Org 27: 95-101) create a new genus and species, Piscicryptosporidium reichenbachklinkei for a species of Cryptosporidium in the gourami, Trichogaster leeri. It is unknown as this time whether this species is distinct from C. nasorum and whether piscine Cryptosporidium spp. deserve generic status.

1997
Peng et al. (1997, Emerg Inf Dis 3: 567-573) also reports two distinct genotypes, and perhaps species, of Cryptosporidium exist that may infect humans. Suggests 1993 Milwaukee outbreak may not be due to bovine fecal contamination.

1998
Koudela & Modry (1998, Folia Parasitol 45: 93-100) describe C. saurophilum as new from the skink, Eumeces schneideri. Oocysts are smaller than for C. serpentis. This species should be regarded as a synonym of Cryptosporidium varani Pavlasek, Lavickova, Horak, Kral, and Kral, 1995.

Champliaud et al. (1998, Appl Environment Microbiol 64: 1454-1458) use molecular techniques to reveal C. meleagridis and C. parvum to be similar. Nonetheless, previous studies have shown that the two species generally do not cross transmit between avian and mammalian hosts.

Sargent et al. (1998, Vet Parasitol 77: 221-227) present morphologic and molecular evidence to support the supposition that C. felis is a distinct species.

Morgan et al. (1998, Parasitology 117: 31-37) present molecular evidence that distinct porcine and murine genotypes exist that are morphologically indisinguishable from C. parvum.

1999
Bornay-Llinares et al. (1999, Appl Environment Microbiol 65: 1455-1458) present molecular and morphological evidence suggesting C. felis to occur in a cow.

Pieniazek et al. (1999, Emerg Inf Dis 5: 444-449) present molecular evidence suggesting C. felis to occur in an AIDS patient.

Carreno et al. (1999, Parasitol. Res. 85: 899-904) present molecular evidence suggesting Cryptosporidium spp. are more closely allied to the gregarines than to the coccidia proper.

Morgan et al. (1999, J. Parasitol. 85: 1126-1133) present molecular evidence suggesting that Cryptosporidium spp. from marsupials, and some isolates from swine, may represent distinct species.

Patel et al. (1999, Int. J. Parasitol. 29: 1241-1247) report an unusual genotype of Cryptosporidium from a single human, which eventually turns out to be similar or identical to C. meleagridis (Pedraza-Diaz et al. 2000, FEMS Microbiol Lett 189: 189-194).

Pavlasek (1999, Remedia-Klinicka Mikrobiol. 3: 290-301) describes a large Cryptosporidium sp. from the proventriculus of chickens as Cryptosporidium galli n. sp. He later provides more data on this parasite (2001, Veterinarstvi 51: 103-108).

2000
Morgan et al. (2000, Parasitology 120: 457-464) present molecular evidence showing Cryptosporidium muris and C. andersoni to be genetically distinct.

Lindsay et al. (2000, J. Euk. Microbiol. 47: 91-95) present morphologic, molecular, and in vivo evidence that demonstrates the large abomasal species in cattle to be distinct from C. muris (researchers in Japan have been saying this for over a decade). The name C. andersoni sp. n. is proposed.

Morgan et al. (2000, Appl. Environ. Microbiol. 66: 2220-2223) present molecular evidence showing that dogs can be infected with a distinct genotype of Cryptosporidium in addition to the classic genotype 2.

Katsumata et al. (2000, Am. J. Trop. Med. Hyg. 62: 70-72) present evidence of Cryptosporidium muris infecting humans. Multiple reports since have confirmed that the parasite may infect some people.

2001
Fayer et al. (2001, J. Parasitol. 87: 1415-1422) describe Cryptosporidium canis sp. n. from canids.

2002
Alvarez-Pellitero and Sitja-Bobadilla (2002, Int. J. Parasitol. 32: 1007-1021) describe Cryptosporidium molnari sp. n. from marine fish.

Xiao et al. (2002, J. Inf. Dis. 185: 1846-1848) identify the pig genotype in a human patient.

Morgan et al. (2002, J. Eukaryot. Microbiol. 49: 433-440) describe Cryptosporidium hominis sp. n. from humans. This has been termed "C. parvum genotype I" previously.

2003
Ryan et al. (2003, J. Parasitol. 89: 809-813) redescribe Cryptosporidium galli Pavlasek, 1999 from birds.

2004
Ryan et al. (2004, J. Parasitol. 90: 769-773) provide genetic and biological data to support their description of Cryptosporidium suis n. sp. for one of the two genotypes of Cryptosporidium spp. found in swine.

2005
Fayer et al. (2005, J. Parasitol. 91: 624-629) provide genetic and biological evidence for Cryptosporidium bovis n. sp., which has previously been referred to as bovine genotype B and infects older ruminants. This parasite was apparently first reported by Panciera et al. (1971, Vet. Pathol. 8: 479-484).

2006
Slapeta, J. (2006, Trends Parasitol. 22: 469-474) proposes that Cryptosporidium pestis n. sp. be subsituted for C. parvum of most mammals.

2008
Ryan et al, (2008, J Euk Microbiol 55: 22-26) propose Cryptosporidium fayeri n. sp. for the isolate from the red kangaroo.

Jirku et al. (2008, Folia Parasitol. Praha, 55: 81-94) propose C. fragile n. sp. for the species in toads. This may or may not be the same species reported in 1987.

Fayer et al. (2008, Vet. Parasitol. 156: 191-198) propose C. ryanae n. sp. for another species in cattle.

Pavlasek and Ryan (2008, Exper. Parasitol, 118: 434-437) show (once again) that C. varani takes precedence over C. saurophilum.

2009
Fayer and Santini (2009, Vet. Parasitol. 164: 192-200) propose C. xiaoi as a new species in sheep.

As you will note from the above, the taxonomic history of the genus Cryptosporidium is a bit confusing and incomplete, and the taxonomic positions of several species remain unclear. In order to help resolve taxonomic issues, and keep species from falling as synonyms, nomen nuda, or nomen dubia, the following guidelines for establishing new species are proposed:

1. Provide adequate morphologic measurements of viable oocysts using light microscopy and a well calibrated ocular micrometer. Provide photomicrographs of these oocysts in the published description. This may not be important to the molecular biologists, but it is very helpful for microscopists. Also, taxonomy is based on morphology and not genetic information.

2. Whenever possible, provide an adequate description of the life-cycle, which should include descriptions of the endogenous stages and transmission studies. Cross-transmission studies between hosts other than the type host, and the use of TEM, are important as well.

3. Sequence accepted genetic loci and make the information available in an internationally accessible database.

4. Send samples of your oocysts or DNA to other researchers who can later perform their own genetic analysis on other loci. The availability of this material to others will certainly be found to be important in future taxonomic studies.

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