Prevalence and Subtype Distribution of Blastocystis sp. in Senegalese School Children

Abstract

Blastocystis sp. is an enteric protozoan that frequently colonizes humans and many animals. Despite impacting on human health, data on the prevalence and subtype (ST) distribution of Blastocystis sp. remain sparse in Africa. Accordingly, we performed the first multicenter and largest epidemiological survey ever conducted on Blastocystis sp. for this continent. A total of 731 stool samples collected from healthy school children living in 10 villages of the northwestern region of Senegal were tested for the presence of Blastocystis sp. by real-time polymerase chain reaction followed by subtyping of positive samples. Considerable variation in prevalence between villages (51.7 to 100%) was evident with the overall prevalence being 80.4%. Mixed infections were identified in 23% of positive individuals. Among 453 school children with a single infection, ST2 was predominant, followed by ST1, ST3, ST7, ST10, and ST14; this is the first report of ST10 and ST14 in humans. Genetic polymorphisms were evident at the intra-ST level with the identification of numerous ST1 to ST3 genotypes. ST1 showed the greatest intra-ST diversity followed by ST2 and ST3. The prevalence and distribution of STs and genotypes varied among target villages, pointing to several potential infection sources, including human-to-human, zoonotic, and waterborne transmission.

Keywords: Africa; Blastocystis sp.; SSU rDNA sequence; Senegal; intestinal parasites; molecular epidemiology; real-time quantitative PCR; subtyping; transmission; zoonosis.

Figure 1

Detailed location of the 10 villages in Northwestern Senegal screened for the presence of Blastocystis sp. by qPCR. Geographic coordinates and total population (TP) of each of the villages are indicated.

Figure 2

Alignment of partial SSU rDNA gene sequences from Blastocystis sp. ST1 (A), ST2 (B), and ST3 (C) isolates. Only the variable positions identified in the compared domain of the gene for these STs are shown in this alignment. The positions of variable nucleotides with respect to the reference sequences (genotypes ST1-1, ST2-1, and ST3-1) are indicated above the alignment (vertical numbering). Nucleotides identical to those of the reference sequences are represented by dashes and gaps are represented by asterisks. All the genotypes identified for each ST are indicated on the left of the alignment. On the right of the alignment is reported the total number and percentage of isolates identified in our study for each genotype followed by their repartition per village (number of isolates in parentheses). Abbreviations: MB, Mbakhana; MD, Maka Diama; NM, Ndiol Maure; LR, Lampsar; NE, Ndiawdoune; MT, Malla Tack; FS, Foss; ME, Mbane; DT, Diokhor Tack; MA, Malla. The abbreviations of the villages located in the area of Lake Guiers are underlined, which is not the case of those located in the area of Saint-Louis.