New figures show New Zealand has some of the highest rates in the developed world for two common stomach infections.
Research by the University of Otago in Wellington, published in the New Zealand Medical Journal, shows New Zealand has almost three times more cases of cryptosporidium than Britain and about nine times more cases of giardia.
Cryptosporidium is three times more prevalent in rural areas and preschoolers are eight times more likely than other age groups to be infected.
Associate Professor Michael Baker says a spike of cases in spring has led scientists to believe children handling lambs and calves is the most likely cause.
Nappy changing is a major source of infection for giardia.
Mr Baker says careful handwashing and improvements to the quality of drinking water would help stop the spread of infection.