Australasian Science: Australia's authority on science since 1938

Animals Spread Parasite Eggs in Water Catchments

A study of the prevalence of the Cryptosporidium in animals inhabiting 11 Australian water supply catchments has revealed higher than expected loads of the parasite’s eggs.

“Cattle, sheep, rabbits and kangaroos living in the area can shed faeces containing Cryptosporidium oocysts into raw water supply catchments, and so we were interested in understanding the sources, quantities and type of Cryptosporidium being shed by animals,” said Murdoch University PhD student Alireza Zahedi, who was lead author of the study published in Water Research (

“Cryptosporidium is one of the most common waterborne parasites throughout the world, causing gastroenteritis in humans, but there has been relatively little research on the levels of human-infectious Cryptosporidium shed by animals in Australian drinking water catchments,” Zahedi said.

“Cryptosporidium oocysts are shed into the environment in animal faeces but often don’t reach raw drinking water sources. If the eggs do enter raw drinking water sources, frequently they are no longer viable and therefore cannot cause infections. Despite this, the pathogen has been responsible for numerous waterborne outbreaks overseas and continues to represent a public health concern to water utilities in developed countries.”

Zahedi sampled 5774 animal faecal samples over 3 years to determine which animal species were infected with strains of Crypto­sporidium that could cause infection in humans. Results of the testing showed that the prevalence of infection with Crypto­sporidium was generally higher than previously reported in Australian catchments. While a Cryptosporidium hominis strain associated with outbreaks of human gastroenteritis worldwide was detected in samples from kangaroos and cattle, it was not possible to determine if it was still infectious in the samples screened.

Zahedi says that while the Cryptosporidium parasite was detected in water supply catchments, the parasite has not been detected in treated drinking water used for household consumption. All water utilities in Australia are required to meet the requirements of the Australian Drinking Water Guidelines in order to ensure the safety of the water supply, and this process is closely regulated by health departments in each state and territory.