Willis Method Modification With a View to Improving Routine Coproparasitological Diagnosis

Abstract

Intestinal parasites still cause high morbidity and mortality, due to poor hygiene and sanitaryconditions, and therefore indiscriminate treatment has been routine practice advocated by thePublic Health staff. Although there is a consensus regarding the need to diagnose such diseases,this is not performed with the necessary care, due to great demand and the lack of a wide rangedand highly sensitive technique. In this sense, most clinical laboratories use routine methods forfecal examination such as the Lutz sedimentation or modified Ritchie methods, which are completeand easy to execute, but do not have adequate sensitivity to detect low density eggs and protozoancysts, especially when there is a predominance of low parasite burdens. In contrast, there aremethods that are based on the flotation of low density developmental forms, namely, the Willismethod (NaCl flotation d=1.120), which is rapid, easy to perform and allows high density eggflotation but with low sensitivity for protozoan cysts; and the Faust method, which is based oncentrifugal flotation of developmental forms in a 33% ZnSO4 (d=1.200) solution, but with thedisadvantage of being lengthy and requiring a centrifuge. In this study, we verified the applicabilityof introducing an alteration in the Willis method, which consisted in the substitution of NaCl byZnSO4 in order to combine the advantages of this method with the Faust method. 208 samples wereassessed by the Willis and Ritchie methods and by the proposed method (modified Willis). Thelatter proved superior to the other two (ρ <0,0001 – X2) regarding the detection of protozoan cysts,but similar to the Ritchie method in regard to other diagnosed parasites, therefore demonstratingthe high potential for the introduction of this modified method in the routine of fecal diagnosis.