Validierung ausgewählter koproskopischer Untersuchungsmethoden zum direkten Nachweis parasitärer Stadien verschiedener Parasitenspezies der Haussäugetiere

Increasing demand on quality assurance and management systems in parasitological laboratories makes new and standardised validation of the methods used in those laboratories necessary. The goal of this project is to yield relevant data to contribute toward the validation of coproscopic methods used in veterinary-parasitological diagnostics for detecting parasitic stages according to their sensitivity, efficiency and variability. The validation of the combined Sedimentation-Flotation-method using zinc sulfate as flotation medium and the modified McMaster-method was performed by using eggs of A. caninum, U. stenocephala, C. oncophora, Cyathostominae, A. suum, T. leonina, T. canis, T. cati, T. vulpis, M. expansa and A. perfoliata. For the validation of the sedimentation method and the Baermann larval migration method eggs and larvae respectively of F. hepatica and D. viviparus were used as those methods are the special analytical procedures for them. With an egg count of 80 epg feces all parasites could be reproducibly detected, using the combined sedimentation-flotation method. The method sensitivity lacks measurably in variances when performed with lower numbers of eggs. The method efficiency improves with increasing egg numbers. The efficiency showed significant deviation at all concentration levels, e.g. at 80 epg, 1.5 % of eggs were retrieved. Since this method is used primarily for qualitative and semi-quantitative detection this comparatively low efficiency is of less importance. Using the McMaster-method no false-negative samples were detected, in egg counts of 500 epg. The variance in sensitivity of the method decreases with increasing egg count per gram feces. The method efficiency resulted in a mean of 49 % and showed relatively large variances. It can be assumed from the literature, that the method efficiency can be markedly improved with larger egg counts, such as 1000 epg, leading to a decrease in variance. Differences among parasites as well as parasitic groups led to results that were in hard to interpret. Various complicating factors could have contributed to this situation, such as variations in the characteristics of the eggs – surface conditions (e.g. electrostatic charge), density, maturity, interaction with flotation media – as well as the small sample sizes of some subpopulations. Differences in the sensitivity of the different methods exist between species at lower dilution levels near the detection limit. All parasites showed a 100 % sensitivity at certain concentrations of epgs used in this investigation. Employing the sedimentation method, eggs of F. hepatica, starting at 20 epg, could be reproducibly found. The efficiency was highly variable, and the maximum re-collection rate increased to 19,7 %. According to the Baermann migration method detecting D. viviparous, a 100 % detection rate was observed beginning with 6,3 larvae per gram feces in a thoroughly mixed-feces sample. The examination of unmixed fecal samples resulted in lower sensitivity, though sample sizes have been too low for statistically proven statements (n=120). The highest larval count was found in the unmixed fecal sample but showed large variation and (partly high inhomogeneous) readings, suggesting an uneven distribution of larvae in the sample. The results show that the combined sedimentation-flotation method is the method of choice for the qualitative diagnosis of the parasites investigated and also should be used as a quantified modification for low concentration egg counts in epidemiological studies. Whether or not this method can be improved and what properties other parasites may show is substance for further study. The McMaster-method shows little validity for egg counts below 1000 epg due to the method´s low efficiency for a reliably quantitative determination in this range. A number of authors have made suggestions for improving and standardizing the efficiency of the McMaster-method. Both, sedimentation and Baermann migration are methods of choice with sufficient sensitivity in qualitative diagnostics for the detection of trematode stages and nematode larvae, respectively.