Potential molecular tools for assessing the public health risk associated with waterborne Cryptosporidium oocysts

摘要

The use of multiple barrier stages at water and wastewater treatment facilities allows for the effective removal of the vast majority of coliforms and other enteric and non-enteric microbes. Subsequent disinfection steps (chlorine, ozone and UV irradiation) are utilized to inactivate microbes that escape the preceding treatment stages. Most viruses, bacteria and protozoa, such as Giardia, are effectively inactivated by chlorination; however, Cryptosporidium is relatively more resistant to environmental conditions and to chlorination. Therefore, UV disinfection has been introduced at many water and wastewater treatment plants to increase log inactivation. Any accidental treatment failure may pose a significant risk to public health. Waterborne transmission of coccidian parasites such as Cryptosporidium and Giardia continues to be a major public health concern. No effective therapies currently exist to treat cryptosporidiosis and the global increase in immunocompromised populations has emphasized the need for water utilities and public health laboratories to have immediate and reliable access to highly sensitive test methods that can determine the host specificity, viability and infectivity of protozoa in the water supply. The most common method used for monitoring Cryptosporidium oocysts and Giardia cysts at intermediate treatment stages and in finished drinking water is the US EPA Method 1623. Although Cryptosporidium species are morphologically indistinguishable, they differ greatly in their host specificity and infectivity. Method 1623 provides quantitative information about Cryptosporidium and Giardia contamination but cannot distinguish between species for intervention purposes in outbreak situations, nor is this method reliable for determining whether the oocyst on the slide is infective for humans. Molecular methods have proven valuable in diagnosing infectious diseases, especially those for which the causative agent is difficult to grow in culture, and similar tools would aid public health agencies to determine risk associated with Cryptosporidium. This review focuses on current methods for determining the host specificity (genotyping), viability and infectivity of Cryptosporidium oocysts.