Acta parasitologica · 2026
Multilocus Characterization of Human Ascaris in Pakistan Indicates Ongoing Introgression and Shared Global Haplotypes.
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Khan Amjad Ullah, Shan Tayyaba, Khalid Mashal, Firasat Sabika, Afshan Kiran
Аннотация
BACKGROUND: Understanding the molecular epidemiology of Ascaris is essential for clarifying species boundaries and transmission dynamics within regions where human-animal interfaces may influence parasite dispersal. This study provides a comprehensive multilocus characterization of Ascaris populations in Pakistan using nuclear (partial 5.8 S, ITS2, partial 28 S) and mitochondrial (cox1) markers.
METHODS: A total of 1675 children were enrolled across six districts of Khyber Pakhtunkhwa, and expelled adult worms were collected following single-dose anthelmintic treatment; genomic DNA from morphologically confirmed specimens was analysed using standard rDNA and cox1 sequencing workflows.
RESULTS: Nuclear rDNA analysis revealed extremely low intraspecific variation among Pakistani Ascaris isolates, with only a few variable sites detected across the partial 5.8 S, ITS2, and partial 28 S regions. Most sequences (Pk_01, Pk_02, Pk_04, Pk_05) were nearly identical, while Pk_03 and Pk_06 showed slightly higher but still limited divergence, clustering within mixed A. lumbricoides/A. suum lineages. The haplotype network placed Pk_01 in the dominant global ITS2 haplotype, with Pk_02 and Pk_06 only one mutational step away, indicating strong global connectivity. Mitochondrial cox1 sequences showed similarly shallow divergence (< 1%), with PK_03 and PK_04 identical and PK_06 exhibiting the greatest but still modest variation. Phylogenetic analysis positioned all Pakistani cox1 haplotypes within a well-supported monophyletic Ascaris clade (bootstrap = 100%) showing intermixing of both species, consistent with incomplete lineage sorting and historical introgression. The cox1 haplotype network identified multiple maternal lineages, including globally common types and one divergent Pakistani haplotype (PK_06).
CONCLUSIONS: The intermixing of A. lumbricoides-A. suum sequences supports the concept of a genetically interconnected species complex rather than clearly separated species. The presence of slightly divergent haplotypes further indicates ongoing microevolutionary processes within Pakistani Ascaris populations.
METHODS: A total of 1675 children were enrolled across six districts of Khyber Pakhtunkhwa, and expelled adult worms were collected following single-dose anthelmintic treatment; genomic DNA from morphologically confirmed specimens was analysed using standard rDNA and cox1 sequencing workflows.
RESULTS: Nuclear rDNA analysis revealed extremely low intraspecific variation among Pakistani Ascaris isolates, with only a few variable sites detected across the partial 5.8 S, ITS2, and partial 28 S regions. Most sequences (Pk_01, Pk_02, Pk_04, Pk_05) were nearly identical, while Pk_03 and Pk_06 showed slightly higher but still limited divergence, clustering within mixed A. lumbricoides/A. suum lineages. The haplotype network placed Pk_01 in the dominant global ITS2 haplotype, with Pk_02 and Pk_06 only one mutational step away, indicating strong global connectivity. Mitochondrial cox1 sequences showed similarly shallow divergence (< 1%), with PK_03 and PK_04 identical and PK_06 exhibiting the greatest but still modest variation. Phylogenetic analysis positioned all Pakistani cox1 haplotypes within a well-supported monophyletic Ascaris clade (bootstrap = 100%) showing intermixing of both species, consistent with incomplete lineage sorting and historical introgression. The cox1 haplotype network identified multiple maternal lineages, including globally common types and one divergent Pakistani haplotype (PK_06).
CONCLUSIONS: The intermixing of A. lumbricoides-A. suum sequences supports the concept of a genetically interconnected species complex rather than clearly separated species. The presence of slightly divergent haplotypes further indicates ongoing microevolutionary processes within Pakistani Ascaris populations.