Standard- and large-sized eggs of Trichuris trichiura in the feces of schoolchildren in the Yangon Region, Myanmar: Morphological and molecular analyses

Standard- and large-sized eggs of Trichuris trichiura were found in the feces of schoolchildren in Yangon, Myanmar during epidemiological surveys and mass deworming with albendazole in 2017–2019. The standard-sized eggs were identified as those of T. trichiura, but it was necessary to exclude the possibility of the large-sized eggs belonging to Trichuris vulpis, a dog whipworm. We conducted morphological and molecular studies to determine the species of the 2 types of Trichuris eggs. Individual eggs of both sizes were isolated from Kato-Katz fecal smears (n=20) and mechanically destroyed using a 23G injection needle. Nuclear DNA was extracted, and the 18S rRNA region was sequenced in 15 standard-sized eggs and 15 large-sized eggs. The average size of standard-sized eggs (T. trichiura) was 55.2×26.1 μm (range: 51.7–57.6×21.3–28.0 μm; n=97), whereas the size of large-sized eggs was 69.3×32.0 μm (range: 65.1–76.4×30.1–34.5 μm; n=20), slightly smaller than the known size of T. vulpis. Regarding standard-sized eggs, the 18S rRNA nucleotide sequences exhibited 100% homology with T. trichiura deposited in GenBank and 88.6–90.5% homology with T. vulpis. Regarding large-sized eggs, the nucleotide sequences showed 99.8–100% homology with T. trichiura in GenBank and 89.6–90.7% homology with T. vulpis. Both standard- and large-sized eggs of Trichuris spp. found in Myanmar schoolchildren during 2017–2019 were morphologically and molecularly confirmed to belong to T. trichiura. The conversion of eggs from smaller to large sizes might be due to anthelmintic treatments with albendazole.