• Cryptosporidium species are apicomplexan protozoan parasites. Members of this genus have been isolated from more than 150 mammalian species, as well as a broad range of birds, fish, and reptiles. • Cryptosporidium preferentially infect enterocytes; however, other epithelial surfaces may become infected. • Taxonomy among members of this genus is in constant flux; however, at the time of writing, 22 species are considered valid. Additionally, some 40 genotypes have been reported in the literature. • The term genotype is synonymous with the term cryptic species. Historically, most genotypes were reported as C. parvum genotypes. For example, the cervine genotype was frequently recorded as C. parvum cervine genotype. Such genotypes are now reported as Cryptosporidium spp. cervine genotype. • C. cuniculus is synonymous with Cryptosporidium rabbit genotype. • Cryptosporidium species have been isolated from more than 30 avian species. The predominant species affecting birds are C. meleagridis and C. baileyi, with the former demonstrating zoonotic potential, particularly among immune compromised individuals. C. galli was first reported in 1999 in chickens; the pathologic significance of this species is largely unknown in both birds and humans. This species has since been identified in a small number of psittacine and passerine birds. • Several Cryptosporidium genotypes have been discovered among birds, particularly psittacines and passerines. The zoonotic potential of these genotypes is undetermined at this stage but is considered relatively low owing to the lack of confirmed human cases associated with these genotypes. • C. meleagridis is most commonly observed among turkeys. The organism has also been isolated from chickens, game birds, and waterfowl. Recently, C. meleagridis has been reported in a small number of psittacine species. • Cryptosporidiosis has been identified in chinchillas for over 20 years. However, to the author’s knowledge, no human cases of cryptosporidiosis have been attributed to chinchillas. Thus, the relative zoonotic risk posed by chinchillas to humans may be considered low. • Molecular data are also lacking among cases of cryptosporidiosis in chinchillas. Such investigations would be useful in better characterizing the zoonotic risk posed by cryptosporidial infections in chinchillas. • Reports of cryptosporidiosis among ferrets have appeared in the literature for over 20 years. However, as with chinchillas, no human cases of cryptosporidiosis have been attributed to ferrets, to the author’s knowledge. • Recent molecular investigations have demonstrated that the ferret has a unique genotype of Cryptosporidium that is conserved across wide geographic ranges. This genotype has not been identified in molecular epidemiologic studies of human cryptosporidiosis to date, further supporting the notion that Cryptosporidium ferret genotype is not zoonotic. • Although immune competent and immune compromised gerbils (Meriones unguiculatus) are commonly used in the study of cryptosporidiosis, spontaneous infection with Cryptosporidium spp. has not been reported in this species, to the author’s knowledge. Therefore, the zoonotic potential of gerbils with reference to Cryptosporidium is considered low. • Reports of Cryptosporidium spp. among guinea pigs have appeared in the literature for over 40 years. The guinea pig was proposed to be the definitive host of C. wrairi, which received official species designation in 1971. • Although it has been associated with clinical and subclinical infections in guinea pigs for over 40 years, C. wrairi is not known to cause disease in humans and is not considered a zoonotic species of Cryptosporidium. • Infection with Cryptosporidium spp. has been reported in pet and laboratory hamsters (Mesocricetus auratus, Phodopus sungorus, and Phodopus roborovskii) for over 25 years. Molecular techniques have been applied to investigate the zoonotic potential of the cryptosporidial species and genotypes affecting hamsters. • For example, in a recent Chinese study, zoonotic C. parvum was identified in 8 of 136 hamsters of various species obtained from a pet market in Zhengzhou. Other hamster isolates obtained in this study included C. muris, C. andersoni, and a newly defined hamster genotype. Therefore, hamsters should be considered as a potential source of human cryptosporidiosis. • A few reports have described cryptosporidiosis in European hedgehogs (Erinaceus europaeus). Recently, Cryptosporidium spp. genotype belonging to the VIIa subtype family was identified in wild juvenile hedgehogs rescued and brought to rehabilitation centers in Europe. This genotype is closely related to C. parvum but is genetically distinct and is probably a hedgehog-specific Cryptosporidium spp. genotype with unknown zoonotic potential. One case of fatal cryptosporidiosis identified as C. parvum in an African hedgehog (Atelerix albiventris) from a U.S. zoo has been described. No human cases of cryptosporidiosis have been attributed to hedgehogs, to the author’s knowledge. • Pet, wild, and laboratory mice (Mus domesticus) are definitive hosts for C. muris, which has been isolated infrequently from humans and is considered to be of minor zoonotic concern. • To the author’s knowledge, genetically confirmed, zoonotic C. parvum has been reported in mice only once. In this report, five mice from Victoria, Australia, were shown to carry this organism. The mice might have obtained this organism from sheep with which they shared close proximity. • Recent studies have demonstrated that mice also carry Cryptosporidium mouse genotypes I and II. To date, genotype I has been isolated from one human with clinical cryptosporidiosis in the Middle East. Genotype II has not been isolated from humans. • The overall zoonotic risk of cryptosporidiosis posed to humans by mice is considered relatively small. • C. cuniculus was first reported in 1979 in an asymptomatic adult female rabbit. • C. cuniculus has subsequently been identified in laboratory, commercial, and wild rabbits. • Prevalence among wild rabbits (Oryctolagus cuniculus) is approximately 7% based on studies conducted in Australia and the United Kingdom. • The zoonotic potential of C. cuniculus was demonstrated in a 2008 waterborne outbreak in the United Kingdom. • Pet and laboratory rats may be infected by a number of genotypes of Cryptosporidium, including rat genotypes I, II, and III and mouse genotype I. Based on current molecular epidemiologic studies, the three rat genotypes are not thought to be zoonotic. However, mouse genotype I may have zoonotic potential. • Cryptosporidium infections have been reported in at least 57 species of reptiles. Cryptosporidium serpentis and C. varanii predominate in snakes and lizards, respectively. • Occasionally C. parvum and C. muris are isolated from reptile feces. It is widely believed that these instances stem from passive transmission of Cryptosporidium spp. affecting rodent prey species, rather than true infections of the reptile hosts. • To date, C. serpentis and C. varanii have yet to be identified from humans with cryptosporidiosis. Therefore, reptiles are not considered to pose a significant zoonotic risk to humans with reference to cryptosporidiosis. • Fecal-oral transmission directly from the host or indirectly via multiple routes such as drinking of recreational water, food, or fomites. • Oocysts have relatively thick walls and are environmentally resistant. This feature enhances the organism’s ability to spread via indirect routes and its ability to cause large, often waterborne, outbreaks. • Cryptosporidium meleagridis is most commonly observed among turkeys. The organism affects the epithelial cells of the small intestine and causes a severe diarrheal disease, particularly in poults. Additionally, birds may present with lethargy, anorexia, and huddling, and moderate flock mortality rates may be observed. • C. baileyi causes bursitis and cloacal infection in chickens that may be detected histologically. However, this organism rarely leads to clinical disease. • C. baileyi has, however, been reported to cause moderate to severe ocular and respiratory disease in more than 30 species of birds, including chickens, turkeys, and a number of caged, aviary, and pet bird species from multiple genera. Affected birds may present with oculonasal discharge, sneezing, and/or cough. Histopathologic evaluation of these birds may demonstrate sinusitis, air sacculitis, tracheitis, and/or pneumonia. • Occasionally, Cryptosporidium species have been identified as a cause of nephritis and ureteritis in a variety of avian species. Clinical signs vary but may include anorexia, weight loss, and weakness characterized by pelvic limb paresis. Affected birds are typically immune suppressed by concurrent viral infections.
Cryptosporidiosis
Basic Information
Definition and Infectious Agent
Synonyms
Organism
Epidemiology
Animal Species—hosts And/Or Carriers
Birds
Chinchillas
Ferrets
Gerbils
Guinea pigs
Hamsters
Hedgehogs
Mice
Rabbits
Rats
Reptiles
Modes of Transmission
Clinical Presentation of Animals
Birds
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Cryptosporidiosis
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