Cyclospora: potential reservoirs and occurrence in irrigation waters

Cyclospora has recently been implicated in outbreaks associated with U.S. produce imported from Mexico. Outbreaks have also been linked to drinking water. Information on the sources and occurrence of this organism are very limited. Currently, only humans and possibly primates are believed to be infected by this parasite. Our goal is to determine if produce in the United States is at risk of contamination from irrigation waters contaminated with human sewage (e.g., from faulty/leaky septic systems or compromised sewer pipes) and treated wastewater effluents that could potentially be discharged into surface waters used for the irrigation of food crops. Our specific objectives are to: a) determine the occurrence of C. cayetanensis in irrigation waters in Arizona and Texas. This will allow a determination of any risk from C. cayetanensis and to identify areas of potential risk; and b) to determine the occurrence of C. cayetanensis in raw sewage and treated wastewater effluents in produce producing areas such as Yuma, AZ and El Paso, TX. This data will allow for an assessment of the incidence of C. cayetanensis infection among these communities. In addition, treated wastewater effluents are sometimes released into watersheds and could potentially impact irrigation waters. This study will allow us to determine if any risks exist from Cyclospora in irrigation waters from these two regions.

Cyclospora cayetanensis has been implicated over the last several years in outbreaks associated with fresh produce in the United States imported from Mexico. Outbreaks have also been linked to drinking water. Information on the sources and occurrence of this protozoan parasite are very limited. It is believed that only humans and possibly primates can be infected by this organism. Recently, we have identified the presence of C. cayetanensis in treated and raw sewage in Tucson, Arizona. In addition, a recent study in Italy found C. cayetanensis in treated wastewater used for irrigation. The goal of the proposed study is to determine if produce in the United States is at risk of contamination from irrigation waters contaminated with human sewage (e.g., from faulty/leaky septic systems or compromised sewer pipes) and treated wastewater effluents potentially discharged into surface waters used for the irrigation of food crops. Our specific objectives are a) to determine the occurrence of C. cayetanensis in irrigation waters in Arizona and Texas, and b) to determine the occurrence of C. cayetanensis in raw sewage in produce producing areas such as Yuma, AZ and El Paso, TX. To meet these objectives, we will collect five 100-liter irrigation water samples monthly over a 2-year period from Yuma, AZ and the Upper Rio Grande Valley in Texas/New Mexico for a total of 240 samples collected over the project period (120 per region). C. cayetanensis will be concentrated from Irrigation water samples using Envirochek high-volume (HV) filters. To determine the incidence of C. cayetanensis in influent (raw sewage) and effluent (treated wastewater) in these produce growing areas in Arizona and Texas, 1-liter raw sewage and treated wastewater grab samples will be collected monthly over a 2-year period from three wastewater treatment plants near agricultural fields in Yuma, AZ and El Paso, TX for a total of 288 samples collected over the project period (144 samples per region). C. cayetanensis will be concentrated using an electronegative filter method attached to a glass filter holder to a final volume of 1.5 ml. All water and wastewater concentrates will be examined for the presence of C. cayetanensis using a SYBR-Green quantitative polymerase chain reaction (qPCR) method. This study will allow us to determine if any risks exist from C. cayetanensis in irrigation waters in Arizona and Texas. It will also allow us to determine that if such risks exist, what sources may be present, and potential options for reducing the risk. The occurrence of C. cayetanensis in raw sewage and in treated wastewater in produce growing areas such as Yuma, AZ and El Paso, TX will allow an assessment of the incidence of C. cayetanensis infection in these communities and the potential for contamination of watershed water that could have an impact on irrigation water quality.

1. Determine the occurrence of Cyclospora cayetanensis in irrigation waters in Arizona and Texas. (This will allow a determination of any risk from C. cayetanensis and to identify areas of potential risk.) 

2. Determine the occurrence of C. cayetanensis in raw sewage and treated wastewater effluents in produce-growing areas such as Yuma, AZ, and El Paso, TX. (This data will allow an assessment of the incidence of C. cayetanensis infection among these communities. Treated wastewater effluents are also sometimes released into watersheds and could potentially impact irrigation waters.)

This study showed that even though Cyclospora cayetanensis is presumptively present in irrigation waters in Arizona and Texas the risk from C. cayetanensis seems to be relatively low, given that no outbreaks have been linked to fresh produce grown in these two regions. These findings do not determine the viability or the infectivity of the presumptive positive samples. No relationship was observed between coliform and E. coli data in connection with C. cayetanensis presumptive positive samples. No seasonality pattern was noticed with C. cayetanensis for the presumptive positive samples; however, a trend was observed with the increase of coliform levels in irrigation water samples during the summer months. The study also showed that C. cayetanensis is presumptively present in influent (raw sewage) and effluent (treated wastewater) in the produce producing areas of Yuma, AZ, and the Upper Rio Grande Valley, TX. These findings indicate that there is a presumptive incidence of C. cayetanensis infection among both the Arizona and Texas communities. However, no determination was made of the potential source of contamination of C. cayetanensis in irrigation waters. Although effluent is released into watersheds no connection was made to impacting irrigation waters in these growing regions. These findings also suggest that persons involved in the production and harvesting of fresh produce and who live in these communities might pose a potential risk through some cross-contamination pathway. The project findings lead to three recommendations. First, further research should be conducted to determine the similarity between the C. cayetanensis–presumptive positive irrigation water samples and WWTP samples. Second, for persons in the community who are involved in the production and harvesting of fresh produce, precautionary measures should be considered to reduce the potential for cross-contamination of fresh produce by infected persons. And third, effluent (treated wastewater) released into watersheds that flow to fresh produce growing regions in Mexico should be investigated to determine the risk of C. cayetanensis.