Detection of Cryptosporidium and Giardia in environmental waters

Cryptosporidium and Giardia, both enteric parasites, have been shown to cause waterborne disease. Methods were developed to investigate the occurrence of Cryptosporidium and Giardia in large volumes of water. Environmental waters were filtered, eluted from a filter and concentrated using centrifugation. Antifoam was employed after homogenization of the resultant pellet suspension for faster oocyst recoveries. This suspension was then layered onto a density gradient to separate the parasites from the sediment. The gradient layer containing any potential parasites was directly labeled on the membrane filter with fluorescein labeled monoclonal antibodies. These filters were then examined by immunofluorescence. Using this technique, Cryptosporidium oocysts were detected in raw sewage, treated sewage, backflush waters, and surface waters. Cryptosporidium was three magnitudes higher in concentration than Giardia in raw sewage. Since Cryptosporidium is frequently present in environmental waters, and in significantly higher numbers than Giardia, it potentially could be transmitted by this route.