TRANSMISSION
• Cryptosporidium is transmitted via the faecal-oral route. Zoonotic cryptosporidiosis may be transmitted through direct contact, and indirectly through ingestion of contaminated food or water. Aerosol transmission of oocysts has been reported. 6 • Cryptosporidium oocysts are immediately infective after being passed in faeces. • Cryptosporidium spp. can tolerate a range of environmental conditions, surviving in water
and soil for months if the moisture and temperatures are suitable. 6,7 • As few as 10 oocysts can cause disease in healthy individuals. 7,8
IN HUMANS
PREVALENCE AND RISK FACTORS • Cryptosporidiosis is an important waterborne protozoal disease globally. Australia has a higher rate of reported cryptosporidiosis than other similarly developed countries. 9 • The majority of human cases in Australia (>85%) are caused by C. hominis (formerly known as C. parvum anthroponotic genotype) and to a lesser extent C. parvum . 10 • The majority of cases of cryptosporidiosis in humans can be attributed to contaminated water – drinking from natural bodies of water or recreational water activities (e.g. camping, community swimming pools). 6,11 Occupational risk factors include working with young children (e.g. daycare centres) or animals (e.g. veterinarians, farmers). 6 In Australia, reports of cryptosporidiosis peak in summer, with an additional peak in spring in NSW and Queensland (thought to be associated with increased numbers of young livestock, in particular calves). 9
Calves are the primary source of C. parvum . It is estimated that a single calf excretes approximately 6×10 11 oocysts in the first month after birth. 12 • The burden of cryptosporidiosis has been reported to be significantly higher in Aboriginal versus non-Aboriginal communities in Australia, with notification rates in Aboriginal people up to 50 times higher. 13 The proportion of infections with zoonotic Cryptosporidium species has been reported to be higher in non-Aboriginal individuals than Aboriginal individuals. 13 • Human infections with both C. canis and C. felis have been reported in both immunocompetent and immunocompromised individuals, including children. A review of Cryptosporidium species isolated from more than 22,000 cases in 20 industrialised nations included only 59 cases (0.26%) of C. felis and 4 cases (0.02%) of C. canis infection. 14
CLINICAL DISEASE • Cryptosporidiosis can result in damage to the intestinal epithelium, disrupting absorption and
barrier function and leading to mild to severe diarrhoea. A dose-dependent prepatent period of 3 to 12 days is reported in humans. 15 • A significant proportion of cases are asymptomatic. Development of signs is related to infecting strain or species, host age (more common in young children, particularly under five years of age), immunocompromise or alterations in GIT microbiota. 15 • Clinical signs include profuse watery diarrhoea, abdominal pain, vomiting and mild fever. Uncomplicated cases typically resolve within two weeks, however relapse is reported to occur in approximately a third of cases. 15 In children and infants, Cryptosporidium infections are sometimes associated with failure to thrive, stunted growth and malnutrition. 16
Cryptosporidium parvum oocysts in a faecal sample from a human with cryptosporidiosis (Public Health Image Library, CDC)
CONTENTS
34 Companion Animal Zoonoses Guidelines
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