Effect of reagents used during detection and quantification of Ascaris suum in environmental samples on egg viability

Abstract

Soil-transmitted helminths (STHs) are a major health concern globally. Infection is mostly through contact with contaminated water, food or soil. Therefore to break the cycle of viable transmission STH eggs must be quantitatively detected in the environment. The effect of different reagents on the viability of Ascaris suum eggs during laboratory detection and quantification was assessed and different incubation solutions compared. Sulphuric acid gave a slightly higher recovery percentage of viable eggs (91.2%) than distilled water (90.0%) and 0.5% formalin (87.6%), although the difference was not statistically significant (p > 0.05). Acetoacetic acid, ethyl acetate, ammonium bicarbonate, zinc sulphate, magnesium sulphate and Tween 80, are reagents widely used in test protocols for the detection and quantification of STH eggs. Eggs were exposed to these reagents for different time durations. Acetoacetic acid resulted in the highest loss of viability (3.4 ± 0.7% viable), while magnesium sulphate resulted in the least effect (88.5 ± 1.2% viable). In conclusion the use of the selected reagents in the detection of these eggs was found to affect the viability of exposed eggs, especially during prolonged exposures. Therefore we recommended that eggs be exposed for ≤5 minutes, to reduce the risk of viability loss.

Figure 1

Images of potentially viable eggs at different stages of development. (a) Egg at the one cell stage; (b) decorticated egg undergoing embryonation; (c) decorticated egg at multicellular stage (>7 cells); (d) eggs with visible larvae (indicated by the arrow).

Figure 2

Images of non-viable eggs after incubation. (a) Decorticated eggs with visible globules (indicated by arrows); (b) dead egg.

Figure 3

Viability of A. suum eggs with different incubation solutions (n ¼ 6).

Figure 4

Reduction in percentage viability of eggs after prolonged exposure to treatments of acetoacetic acid (AA) and combination of acetoacetic acid and ethyl acetate (AA þ EA).

Figure 5

Reduction in percentage viability of eggs after prolonged exposure to treatments of ethyl acetate (EA) and Tween 80 (T8).

Figure 6

Reduction in percentage viability of eggs after prolonged exposure to treatments of magnesium sulphate (MS) and combination of acetoacetic acid and formalin (AA þ F).