Comparative analysis of microscopic methods for diagnosing intestinal helminthiasis (Ascaris lumbricoides)

Introduction: Despite significant improvements in laboratory diagnostic methods, direct parasitological methods remain the gold standard for diagnosing parasitic diseases of the gastrointestinal tract. The purpose of our work was to conduct a comparative analysis of the effectiveness of methods for direct diagnosis of parasitoses of the gastrointestinal tract, most often used in clinical practice in Russia. Methods: The study was carried out in the laboratory of the clinic of infectious and parasitic diseases of the Rostov Research Institute of Microbiology and Parasitology in 2021-2023. The following methods were used: native and stained smears, Kato-Katz thick smear, flotation method with NaNO₃, ether-formalin sedimentation (EFS). The material was also studied by sedimentation method using an intestinal parasite concentrator containing ethyl acetate.Under experimental conditions, 180 fecal samples were studied. The model was Ascaris lumbricoides eggs due to the possibility of obtaining a large amount of material (240,000 eggs from 1 female roundworm). Previously, the feces from patients of Clinic were examined for all types of helminths and protozoan cysts. Using a laboratory pipette, a suspension of Ascaris lumbricoides eggs in the amount of 500 ± 10 eggs was added to each sample (15 grams of feces,), and the material was thoroughly mixed. Each method was carried out in 30 replicates. Results: Analysis of the results showed that the sensitivity of the stained and native smear method was 10% (out of 30 samples, eggs were found in only 3), in an amount of 0.1 egg in 1 field of view. The sensitivity of the flotation method with NaNO₃ was 46.7% - eggs were found in 14 samples, 1 egg in 1 field of view. The sensitivity of the Kato-Katz thick smear was 60%, eggs were found only in 18 samples out of 30, 2 eggs in 1 field of view. The sensitivity of the EFS method was 100% eggs were detected in all samples in the amount of 4 eggs in 1 field of view. When using a concentrator for intestinal parasites, eggs were detected in 100% of samples, but in the amount of 3.5 eggs in 1 field of view. Discussion: Currently, Russian laboratories use sedimentation methods in various modifications, flotation methods (with NaCl and NaNO₃) to detect helminth eggs and cyst of pathogenic protozoa. Also the Kato-Katz thick smear kits are used, as well as the study of stained and native smears. The use of direct microscopic methods is attractive due to its low cost, but the main problem of these methods is the need for highly qualified laboratory diagnostic specialists. Conclusion: Analysis of the data obtained led to the conclusion that the most effective method for detecting A. lumbricoides eggs in feces is the ether-formalin sedimentation method.