PROTOZOAN PARASITES AFFECTING FOOD ANIMALS, FOOD SAFETY, AND PUBLIC HEALTH
Title: Cryptosporidiosis of Companion Animals
Submitted to: CRC Press
Publication Type: Book / Chapter
Publication Acceptance Date: June 6, 2007
Publication Date: January 1, 2008
Citation: Santin, M., Trout, J.M. 2008. Cryptosporidiosis of Companion Animals. In: Fayer, R. Xiao, L., editors. Cryptosporidium and Cryptosporidiosis. 2nd edition. Boca Raton, FL: CRC Press. p. 437-449.
Interpretive Summary: Pet ownership, particularly of dogs and cats, is common throughout the world. Gastrointestinal disorders in companion animals, especially diarrhea, are a common reason for pet owners to seek for veterinary advice. There is a modest prevalence of Cryptosporidium infections in companion animals. Although clinical disease is rare, severe clinical illness has been reported in dogs, cats and horses occasionally associated with concurrent infections such as canine distemper virus or feline leukemia virus, as well as in immunodeficient animals. Although pets offer significant benefits to our society, there may be health hazards associated with owning a pet, including the potential risk intestinal parasites. Cryptosporidiosis has been detected in dogs, cats, and horses and these animals may represent an important reservoir of infection for humans. The possible zoonotic implications should be borne in mind, and veterinarians need to recognize potentially zoonotic diseases in pets and provide accurate advice about these conditions to their clients. This is of particular importance to high risk populations, such as children, the elderly and those with weakened immune systems.
Cryptosporidium spp. was first reported in cats in Japan in 1979. Subsequently, asymptomatic and symptomatic Cryptosporidium spp. infections have been reported in cats worldwide. Studies using conventional methods to detect Cryptosporidium spp. oocysts found that 0% to 12.3% of cats were excreting oocysts. Three species of Cryptosporidium have been reported in cats, C. parvum, C. felis, and C. muris. However, only C. felis and C. muris have been confirmed by molecular analysis in naturally infected cats. Although C. parvum has been reported in cats, identification was made based on oocyst size not molecular characterization. Nevertheless, experimental infection with C. parvum was demonstrated in 8 adult domestic cats.
Cryptosporidiosis was first reported in dogs in 1981 and the first clinical case was reported 2 years later. Since then, cryptosporidiosis in dogs has been reported worldwide, involving both asymptomatic and diarrheic dogs. Coprology studies by microscopy showed that infection rates range from 0.23 to 40% in various countries. Only 36 isolates obtained from dogs have been genotyped. Of these samples, 26 were found to be C. canis, 9 C. parvum, and 1 C. meleagridis. Although these three species are known to be pathogenic to humans, C. canis and C. meleagridis have narrow host ranges, primarily infecting dogs and birds, respectively. Given the potential public health risk associated with cryptosporidiosis more specific and sensitive diagnostic methods should be selected over traditional methods such as microscopy. The dog genotype was designated as a new species, C. canis, in 2001, based of the results of cross-transmission experiments and genomic analysis. At the present, 30 cases of infection with C. canis have been reported in asymptomatic immunocompetent and immunocompromised humans in England.
Cryptosporidiosis in horses was initially described in 5 immunodeficient Arabian foals. Subsequently, however, cryptosporidiosis has been reported in immunocompetent horses worldwide. The prevalence of Cryptosporidium spp. in horses has shown wide variation in different geographic regions. Reported infection rates determined by microscopy varied from 1% to 47%. In a 5 year survey (1992-1996) of UK horses, the prevalence of Cryptosporidium spp. varied between years, fluctuating from 1.9% in 1994 to 24.7% in 1992. Foals are thought to be more susceptible to cryptosporidiosis than older animals. The major clinical sign of cryptosporidiosis in foals is diarrhea, but most Cryptosporidium infections in adult horses are asymptomatic. Cryptosporidium parvum appears to be the etiologic agent in most horse infections. However, reports are based on the size of the oocysts being consistent with that of C. parvum without molecular confirmation. There is little molecular data on Cryptosporidium spp. isolated from horses; only four published reports include gene sequence information to determine the Cryptosporidium species/genotype present in the specimens. In the first three C. parvum was identified and in the fourth, C. parvum and a novel Cryptosporidium horse genotype were reported.
Veterinarians need to be aware of the zoonotic potential of Cryptosporidium spp. when advising clients regarding infections in companion animals.