Avaliação comparativa de técnicas parasitológicas no diagnóstico de Blastocystis sp. e determinação de seus subtipos

Abstract

Blastocystis sp. has been the most common intestinal protist in humans. In Brazil, nine parasite subtypes with varying frequencies are described. Microscopic parasitological techniques in faecal samples are generally those used in routine parasitological laboratories for the diagnosis of intestinal parasites, since they are low cost and fast to process. However, when it comes to a Blastocystis sp. infection, the technique to be used is not yet consensual, since studies on the subject consider that parasitological techniques not specific for parasite identification may lead to underestimation of positive samples. In this way, this study aimed to compare microscopic parasitological techniques for the diagnosis of Blastocystis sp. on fresh or preserved fecal samples from children and day care workers and identify subtypes. The study was conducted in three basic kindergarten units located in Niteroi, totaling 419 children and 101day care workers. Each participant delivered a fresh fecal sample that was processed by direct examination, modified Ritchie, trichrome stained smear, with and without chemical preservative, and culture. Blastocystis sp. positive samples in the culture were subjected to polymerase chain reaction (PCR) and subsequent sequencing to identify subtypes. The adhesion rate of fecal sample delivery was 34.4%. Blastocystis sp. was the most frequent parasite among the participants, being evidenced in 24.5% (44/179) of these. The most effective isolated technique was culture (81.8%), followed by the trichrome stained smear (43.2%). The association between culture and stained smear detected the parasite in 93.2% of positive samples and direct examination with stained smear in 79.5% of these. The McNemar test shows evidence of disagreement between the different techniques used. The techniques evaluated in this study presented high sensitivity and except for culture, all other techniques presented low sensitivity values. The use of chemical preservative resulted in greater diagnostic effectiveness. Among the 44 positive participants for Blastocystis sp., 26 (59.1%) reported gastrintestinal symptoms, and in 16 (36.4%) Blastocystis sp. was the only pathogen detected. By sequencing of 26 samples, subtypes were identified: ST1 (n=19), ST2(n=2), ST3(n=4) and ST6(n=1), with ST1 being the most frequent subtype. For children, the only risk factor identified was the supply of untreated water to the house and living in a home with up to four people was considered a protection factor. Considering the results obtained, it is suggested that for the diagnosis of Blastocystis sp. that culture should be considered as the gold standard and the second most effective technique is the trichrome stained smear in samples without preservative.