FACTORS INFLUENCING THE SURVIVAL OF CRYPTOSPORIDIUM OOCYSTS IN THE
Report No FR0456
E G Carrington, M E Ransome
These studies were carried out to determine if oocysts of Cryptosporidium parvum that had been stressed by environmental exposure were removed or inactivated during water treatment and disinfection to a greater extent than unstressed oocysts. The factors that influence the survival of oocysts in the environment were also investigated.
Observations reported by researchers in the USA have suggested that, with polluted waters, the viability of oocysts in the treated waters was lower than expected by comparison with studies using laboratory stored oocysts. Other workers have hypothesised that in the environment the survival of oocysts is poor and the numbers are maintained by continual inputs.
Unstressed oocysts were not removed to a greater extent during water treatment but they were slightly more susceptible to chlorine. Temperature and/or light had the greatest influence on their survival in the environment, with decline in numbers and viability being greater at the more extreme temperatures. Under these conditions the loss of viability was greater than the decline in total numbers.
The study has confirmed that although some oocysts may survive in the environment for long periods there is a continuing decline in numbers and a faster decay in the levels of viability.
This study was funded jointly by the Foundation for Water Research and the Department of the Environment as part of the National Cryptosporidium Research Programme.
Copies of the Report are available from FWR, price £15.00 less 20% to FWR Members