Quantitative risk assessment for zoonotic transmission of Cryptosporidium parvum infection attributable to recreational use of farmland.
Cryptosporidiosis caused by Cryptosporidium parvum infection is a major cause of enteric illness in man and there is a significant reservoir in animals, particularly young ruminant species. To preliminary assess the magnitude of the risk posed by contact with faeces produced by infected livestock, two microbiological risk assessments have been developed: one for the risk of human infection with C. parvum while camping on contaminated land recently grazed by infected suckler cattle and a comparable risk assessment for camping on land recently spread with contaminated cattle slurry. Using a worst-case scenario approach, the upper level of risk was estimated to be one infection in every 6211 person-visits for a camping event on land recently grazed by infected cattle. Translated into camping events of 100 persons, this risk estimate would most likely lead to zero (98% likelihood) or one infection (1% likelihood). The results for cattle slurry model are similar despite different pathways. Sensitivity analysis was conducted for the grazing cattle model only. This suggested that the time between grazing and camping was the most important control strategy, but increasing hand-washing frequency and the removal of cattle faeces before camping would also be beneficial. If the upper level of risk were to be judged unacceptable then further data would be required to more accurately estimate the risk of infection through these scenarios. Further research would also be required to assess the fraction of cases attributable to camping and/or environmental contact with Cryptosporidium oocysts.
Hill
A
A
Centre for Epidemiology and Risk Analysis, Veterinary Laboratories Agency - Weybridge, New Haw, Surrey, UK.  a.hill@vla.defra.gsi.gov.uk
Nally
P
P
Chalmers
R M
RM
Pritchard
G C
GC
Giles
M
M
D000818:Animals; D002165:Camping; D002417:Cattle; D002418:Cattle Diseases / Q000453:epidemiology / Q000469:parasitology / Q000635:transmission*; D003198:Computer Simulation; D003457:Cryptosporidiosis / Q000453:epidemiology / Q000469:parasitology / Q000635:transmission*; D016785:Cryptosporidium parvum / Q000302:isolation & purification*; D004197:Disease Reservoirs / Q000469:parasitology; D004777:Environment; D005243:Feces / Q000469:parasitology; D005759:Gastroenteritis / Q000469:parasitology*; D006801:Humans; D058751:Livestock / Q000469:parasitology*; D008297:Male; D008954:Models, Biological; D033661:Oocysts; D012044:Regression Analysis; D018570:Risk Assessment / Q000379:methods; D012680:Sensitivity and Specificity; D013997:Time Factors; D014881:Water Supply