From the literature, we have hypothesized that helminth parasite could be present in the soil. In this regard the guidance of learned community of Parasitologists is saught.
I am not a parasitologist but having worked with nematodes including their eggs and cysts, we used an elutriator which separates these structures from soils using a washing-sieving method. You might consult the following for the method to determine if this might be adapted for your particular needs:
Niblack, T. L., R. D. Heinz, G. S. Smith, and P. A.Donald. 1993. Distribution, density, and diversity of Heterodera glycines in Missouri. Supplement to Journal ofNematology 25:880–886.
Iam expert in detection parasite eggs in wastewater and sludge, you can refer to the following:
Hindiyeh, M. (2004). "Integrated Guide in Sanitary Parasitology: Theoretical and Practical Aspects". WHO/CEHA, a book 108 pages. Arabic and English, French, and Portuguese Languages, http://www.emro.who.int/ceha/publication.asp.