Removal of parasitic protozoa from water using a mobile water filtration apparatus intended for field use by military or emergency personnel

Military Medicine, Jan 2003 by Robertson, Lucy J

Parasitological Analysis of Water Samples

The analytical method used is based on a standard technique, U.S. Environmental Protection Agency (EPA) Method 1623.(12) Rather than using capsule filtration, membrane filtration of the sample was used.(13) Although membrane filtration is more cumbersome than capsule filtration, it is considerably less expensive and has been used successfully by the Section of Parasitology at The Norwegian School of Veterinary Science14,15 as well as various other laboratories worldwide.

Before the analytic procedure was commenced, the sample was shaken thoroughly, and a small volume was removed for turbidity measurement (Hach turbidimeter 2100A).

In brief, the analytical technique is divided into five sections: (a) membrane filtration, (b) elution from the membrane filter, (c) concentration by centrifugation, (d) isolation of the parasites by immunomagnetic separation, and (e) detection and identification by immunofluorescence assay, using light microscopy with Normaski (differential interference contrast) optics for confirmation of identity,

For the control samples, microscopic examination and counts were made on 10% (1-L equivalents) of the sample concentrate. For the filtered samples, the whole of the final sample was screened by microscopy (10-L equivalents).

The timing of the sequence of analytical procedures followed those stipulated in U.S. EPA Method 1623 with the exception of storage of samples prior to filtration (U.S. EPA Method 1623 stipulates that sample processing should begin within 24 hours of sample collection). Whereas the filtered water samples were stored overnight (approximately 20 hours) before processing commenced, the control water samples were stored for approximately 56 hours before processing commenced. However, previous research has indicated that water samples may be stored in plastic carboys for up to 2 weeks without any significant effect on oocyst or cyst recovery.16

Results

Turbidity Measurements

The turbidity of the inoculated, unfiltered water was 1.0 nephlometric turbidity units (NTU). Following filtration, turbidity initially increased to 4.0 NTU, then increased further to 11.0 NTU, before decreasing again to similar levels to those of the unfiltered water (Table I). The increase in turbidity was presumably attributable to particles of the filter material being carried into the filtered water. These particles could be clearly seen following concentration of the membrane filter eluate. Although the turbidity increased in the filtered water, the amount of some particulate matter decreased as would be expected. This meant that the membrane filtration of the filtered water could be completed much more rapidly than for the control samples of unfiltered water.

Parasitological Analysis

The mean concentrations ( /-SD) of both parasites per 1-L equivalent of unfiltered water were calculated to be 273.5 /- 23.5 for Cryptosporidium and 191.8 /- 8.1 for Giardia. Calculations of removal efficiency were based on calculated means in 10 L of unfiltered water (2,735 Cryptosporidium oocysts per 10 L and 1,918 Giardia cysts per 10 L; Table I).