Preliminary testing of a rapid coupled methodology for quantitation/viability determination of helminth eggs in raw and treated wastewater

The use of raw and treated wastewater for irrigation of crops is a common practice in Mexico. In force since January 1997, the Water Quality Norms for helminth ova refer only to the number of eggs that can be present in the irrigation water, and ignore the assessment of viability because the conventional techniques are not suitable for routine application. However, since viability is of prime importance in the epidemiology of parasitic infections, work was done for the development of a rapid and reliable method to detect a metabolic activity or a physiological characteristic related to viability. As a result, a vital staining procedure was developed and validated, and it was coupled with two rapid quantitative procedures previously assessed, therefore, permitting the determination of the total number of helminth eggs and, simultaneously, the viable and non-viable fraction. The average recovering efficiency of the rapid quantitative methods is 54% for raw wastewater and 77% for treated wastewater; the staining technique for viability is equally reliable (within the 95% confidence limits) as the conventional in vitro procedure; the overall test takes from 4 to6 h to be completed when processing up to four samples at the same time, and the cost per sample (for unrecoverable materials) ranges from US$2.50 to $4.00.