Dog, Cat, and Horse

Cryptosporidiosis in companion animals such as dog, cat, and horse is most common in younger animals and has been reported worldwide with clinical signs ranging from asymptomatic to symptomatic (Santín and Trout 2008a). Usually, the course of disease of dogs infected with C. canis is asymptomatic, though severe diarrhea, malabsorption, and weight loss have occasionally been reported (Irwin 2002; Santin 2013). Also in cats, cryptosporidiosis is mostly asymptomatic and commonly associated with C. felis infection (Yoshiuchi et al. 2010). Clinical disease may develop with immunosuppressive conditions like feline leukemia virus infection or when coinfected with another enteric parasite (Monticello et al. 1987; Rambozzi et al. 2007; Santin 2013). Immunocompetent foals and to a lesser degree adult horses can develop cryptosporidiosis, but not always excretion of oocysts is accompanied with diarrhea (Xiao and Herd 1994; Majewska et  al. 2004). However, a case where infection of foals resulted in severe morbidity, and three animals died, has been reported (Grinberg et al. 2003). In this case and in most other studies where the infecting species has been determined, the presence of C. parvum has been reported. Foals and horses that are immunosuppressed seem to attract the infection relatively easily and have been observed to develop severe diarrhea and shedding of oocysts, suggesting that the severity of the M.L. Tomazic et al. 39 disease varies according to the immune status of the horses (Snyder et al. 1978; Bjorneby et al. 1991). After an experimental infection of immunodeficient foals with C. parvum, a severe, persistent, and watery diarrhea developed which was associated with oocyst excretion that lasted between 2 and 5  days (Table  2.4) (Bjorneby et al. 1991).