Potentials and challenges in the isolation and detection of ascarid eggs in complex environmental matrices

Ascarid infections constitute a major concern for both human and animal health risk assessment. Although being effectively transmitted by soil, water and contaminated food, reliable detection of ascarid eggs in environmental media often remains challenging. However, contamination of the environment with ascarid ova has gained more attention as a decisive part of proper risk assessment in recent years. Due to various factors, such as sample matrices, dissociation detergents and flotation solutions, defined and standardised protocols for the isolation of eggs from complex environmental matrices are difficult to establish and therefore limited. Thus, this study reviews common techniques used for the recovery of ascarid eggs from environmental media with special emphasis on sampling strategies, purification procedures and microscopic as well as molecular detection of egg contamination. Despite various advancements, mainly in the field of molecular methods leading to more reliable and sensitive detection, it can be concluded that there is still a need for unified guidelines for sampling and recovery of ascarid eggs derived from complex environmental matrices.

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Standardised methods to assess environmental ascarid egg contamination are needed.

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The environmental sampling strategy has to be adapted to the study hypothesis.

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Egg detection mostly relies on matrix homogenisation, filtration, sedimentation and flotation.

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Microscopic detection is still frequently applied.

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Molecular methods enable more reliable and sensitive detection.

Accuracy and precision of McMaster and Mini-FLOTAC egg counting techniques using egg-spiked faeces of chickens and two different flotation fluids

Faecal egg counting techniques (ECTs) are useful tools for assessing anthelmintic efficacy and selecting hosts resistant to parasite infection. McMaster (MM) is one of the most commonly used ECTs, but it suffers from low sensitivity and precision. Mini-FLOTAC (MF) has been proposed to replace MM, but so far has not been evaluated for gastro-intestinal nematode infections in chickens. This study compared sensitivity, precision, and accuracy of MM and MF with two trials using egg-spiked faecal samples ranging from 50-1250 eggs per gram of faeces (EPG). In addition, effects of two flotation fluids with different specific gravities (SG), namely salt (SG = 1.20) and sucrose solutions (SG = 1.32), on accuracy and time-spent for both ECTs were evaluated. Overall sensitivity based on the composite reads across all EPG-levels was 97.1 % for MM and 100 % for MF. MF was, however, more sensitive (P = 0.003) or tended to (P = 0.087) be more sensitive than MM at only the lowest EPG-level (i.e. 50 EPG) using one of the duplicate reads, whereas there was no significant difference at any EPG-level using composite reads. Overall average precision of MF (79.5 %) was higher (P < 0.001) than that of MM (63.4 %) across all EPG-levels. Precision of MM increased from 22 to 87 % with increasing EPG-levels from 50-1250 EPG. Corresponding precision estimates for MF ranged from 76 to 91 %. Overall recovery rate of MM (74.6 %) was significantly higher (P < 0.001) than that of MF (60.1 %). There was no significant difference in recovery rate of spiked-eggs among different EPG-levels (P = 0.833). Recovery rate of MM ranged from 64 % to 79 % across different EPG-levels, while it ranged from 54 % to 64 % with MF without an interaction between ECT and EPG-level (P = 0.701). It took more time (P < 0.001) to process (prepare and read) samples with MF than with MM using the same flotation fluid. The sugar solution tended to (P = 0.100) increase egg-recovery with both ECTs, while increasing (P < 0.001) time-spent for processing the samples. Our data collectively suggest that MM is less sensitive than MF only at around minimum detection level of MM when using unrepeated reads. We conclude that McMaster is faster, relatively more accurate but less precise than Mini-FLOTAC. The sugar solution with higher SG increases accuracy of both techniques at the expense of increased labour time.