Large-Scale Molecular Epidemiological Survey of Blastocystis sp. among Herbivores in Egypt and Assessment of Potential Zoonotic Risk

Abstract

Given the proven zoonotic potential of the intestinal protozoan Blastocystis sp., a fast-growing number of surveys are being conducted to identify potential animal reservoirs for transmission of the parasite. Nevertheless, few epidemiological studies have been conducted on farmed animals in Egypt. Therefore, a total of 1089 fecal samples were collected from herbivores (sheep, goats, camels, horses, and rabbits) in six Egyptian governorates (Dakahlia, Gharbia, Kafr El Sheikh, Giza, Aswan, and Sharqia). Samples were screened for the presence of Blastocystis sp. by real-time PCR followed by sequencing of positive PCR products and phylogenetic analysis for subtyping of the isolates. Overall, Blastocystis sp. was identified in 37.6% of the samples, with significant differences in frequency between animal groups (sheep, 65.5%; camels, 62.2%; goats, 36.0%; rabbits, 10.1%; horses, 3.3%). Mixed infections were reported in 35.7% of the Blastocystis sp.-positive samples. A wide range of subtypes (STs) with varying frequency were identified from single infections in ruminants including sheep (ST1-ST3, ST5, ST10, ST14, ST21, ST24, ST26, and ST40), goats (ST1, ST3, ST5, ST10, ST26, ST40, ST43, and ST44), and camels (ST3, ST10, ST21, ST24-ST26, ST30, and ST44). Most of them overlapped across these animal groups, highlighting their adaptation to ruminant hosts. In other herbivores, only three and two STs were evidenced in rabbits (ST1-ST3) and horses (ST3 and ST44), respectively. The greater occurrence and wider genetic diversity of parasite isolates among ruminants, in contrast to other herbivores, strongly suggested that dietary habits likely played a significant role in influencing both the colonization rates of Blastocystis sp. and ST preference. Of all the isolates subtyped herein, 66.3% were reported as potentially zoonotic, emphasizing the significant role these animal groups may play in transmitting the parasite to humans. These findings also expand our knowledge on the prevalence, genetic diversity, host specificity, and zoonotic potential of Blastocystis sp. in herbivores.

Keywords: Africa; Blastocystis sp.; Egypt; herbivores; intestinal protozoa; molecular epidemiology; transmission; zoonosis.

Figure 1

Map of Egypt displaying the number of fecal samples collected from goats, sheep, camels, horses, and rabbits in each of the six governorates surveyed.

Figure 2

Maximum likelihood phylogenetic analysis of Blastocystis sp. isolates from animal groups based on SSU rDNA gene sequences. The phylogenetic tree is rooted using the reference sequences of the earliest diverging lineages ST15 and ST28 within the Blastocystis genus. Sequences from herbivores obtained in the current study (camel, sheep, goat, horse, and rabbit) are in bold, with the number of isolates from each animal type depicted by color-coded squares: red for camel, yellow for sheep, green for goat, blue for horse, and violet for rabbit. Isolates that are positioned within a specific ST are connected by black branches, while those whose ST designation is not confidently determined are connected by red branches (ND). Human-associated genotypes are indicated with white squares. Accession numbers for the reference sequences of known STs are provided. Bootstrap values are shown in black at the nodes of the tree, and values below 70% are not displayed. The likelihood of each sequence placement is indicated in blue next to the respective isolate.

Figure 3

SSU rDNA gene sequence polymorphism between genotypes of some of the most frequently STs and subgroups identified in the present study. The variable positions reported between sequences of isolates belonging to ST3, ST5, and ST26 as well as subgroups ST10a and ST10b are indicated above the alignment (vertical numbering) with respect to the arbitrarily selected reference sequences called genotype STX-1. Nucleotides identical to those of the reference sequences are represented by dashes, and gaps are represented by asterisks. The number of isolates for each genotype is indicated in parentheses on the right of the alignments.