Molecular Epidemiology and Genetic Diversity of the Enteric Protozoan Parasite Blastocystis sp. in the Northern Egypt Population

Abstract

Blastocystis sp. is currently reported as the most frequent single-celled eukaryote inhabiting the intestinal tract of humans and a wide range of animal groups. Its prevalence is especially higher in developing countries linked with fecal peril. Despite a growing interest in this enteric protozoan, certain geographical regions potentially at high risk of infection, such as North Africa, remain under-investigated. Therefore, a large-scale molecular epidemiological survey, including 825 participants presenting digestive disorders or not, was conducted in five governorates located in Northern Egypt. A real-time polymerase chain reaction (qPCR) assay was performed to identify the parasite in stool samples, followed by direct sequencing of the positive PCR products for subtyping and genotyping of the corresponding isolates. The overall prevalence was shown to reach 72.4% in the Egyptian cohort, coupled with a variable frequency depending on the governorate (41.3 to 100%). Among the 597 positive participants, a large proportion of them (39.4%) presented mixed infections, as determined by sequencing. The remaining individuals with single infection were predominantly colonized by subtype 3 (ST3) (48.3%) followed by ST1 (39.5%), ST2 (10.8%), ST14 (1.1%), and ST10 (0.3%). This was the first report of ST10 and ST14 in North Africa. Age, sex, digestive symptoms, and health status of the participants or contact with animals were not identified as significant risk factors for Blastocystis sp. occurrence or affecting the ST distribution. In contrast, substantial variations in the prevalence and ST distribution of the parasite were reported according to the governorate. Genotyping of isolates revealed the lower intra-ST diversity for ST3, followed by ST1 and then ST2. By combining subtyping and genotyping data, a widespread inter-human transmission was strongly suggested for ST3 within the Egyptian cohort. Regarding ST1 and ST2, additional animal or environmental sources of infection by these STs have been proposed, whereas the few cases of colonization by ST10 and ST14 were likely the result of zoonotic transmission from bovid. These investigations clearly emphasized the active circulation of Blastocystis sp. in Northern Egypt and the necessity for health authorities to implement prevention campaigns towards the population and quality control of drinking water, with the aim of reducing the burden of this enteric protozoan in this endemic country.

Keywords: Blastocystis sp.; Egypt; humans; molecular epidemiology; transmission sources; zoonosis.

Figure 1

Variable positions identified between partial SSU rRNA gene sequences obtained in the present study from isolates of ST1 (A), ST2 (B), and ST3 (C). The positions of variable positions are indicated above the alignment (vertical numbering) with respect to the arbitrarily selected reference sequences called genotypes ST1-1, ST2-1, and ST3-1. Nucleotides identical to those of these 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 alignments. The total number and percentage of isolates identified in our study for each genotype, followed by their repartition per governorate (number of isolates in parentheses), are reported on the right of the alignments. Abbreviations: D, Dakahlia; B, Beheira; A, Alexandria; I, Ismailia; C, Cairo.

Figure 2

Detailed location of the 5 governorates in Northern Egypt screened for the presence of Blastocystis sp.