Diversity of mitochondrial genes and predominance of Clade B in different head lice populations in the northwest of Iran

Abstract

Background: The head louse, Pediculus humanus capitis, is the most important ectoparasite causing many health problems. Several linkages are presented for this parasite, each representing a particular geographical distribution, prevalence rate, vector competence, susceptibility to pediculicides, and infestation rate. Determining the genetic nature of these linkages is necessary to identify the population structure and also to develop and monitor control programmes against head lice. This study was designed to analyse cox1 and cytb genes and determine the mitochondrial clades in head lice populations in the northwest of Iran.

Methods: Adult head lice were collected from infested females of Ardabil, East and West Azerbaijan, and Zanjan Provinces from 2016 to 2018. Partial fragments of the mitochondrial genes cox1 and cytb were amplified by PCR and some of the amplicons were sequenced. All confirmed sequences were analysed, and the frequency of each mitochondrial clade was determined in the studied areas.

Results: A total of 6410 females were clinically examined, and 897 adult head lice were collected from 562 infested cases. Genomic DNA was extracted from 417 samples, and fragments of cox1 and cytb genes were amplified in 348 individuals. Analysis of the 116 sequences showed the 632-bp and 495-bp fragments for cox1 and cytb genes, respectively. The nucleotide and haplotype diversities of cytb and cox1 genes were 0.02261 and 0.589 and 0.01443 and 0.424, respectively. Sequence analysis indicated 6 haplotypes clustered in two clades, A and B. The relative prevalence of clade B was 73% for cytb and 82% for cox1 gene. Haplotypes of clade B were found in all the studied areas, while those of clade A were observed only in rural and suburban areas.

Conclusions: To our knowledge, this is the first study investigated deeply the field populations of Pediculus and documented two clades in the Middle East. The considerable prevalence of pediculosis in the studied areas requires authorities' attention to establish effective control and preventive measures. Given the role of cytb in monitoring population groups, application of this marker is suggested for future epigenetic studies to evaluate the factors affecting the abundance of these clades.

Keywords: Mitochondrial clade A; Mitochondrial clade B; Pediculosis; Pediculus humanus capitis; cox1 gene; cytb gene.

Fig. 1

Alignment of the nucleotide sequences of the mitochondrial cytb gene fragment in different haplotypes in head lice populations in the northwest of Iran. The numbers in parentheses are the representative accession numbers of the haplotype groups

Fig. 2

TCS network tree of head lice mitochondrial genes, based on all polymorphic sites. Each dash represents one single nucleotide difference between two neighbouring haplotypes. The numbers in the parentheses after the name of each haplotype denote the number of samples belonging to each haplotype

Fig. 3

Alignment of the nucleotide sequences of the mitochondrial cox1 gene fragment in different haplotypes in head lice populations in the northwest of Iran. The numbers in parentheses are the representative accession numbers of the haplotype groups

Fig. 4

Alignment of the amino acid sequences of the mitochondrial cox1 gene fragment in different haplotypes in head lice populations in the northwest of Iran. The numbers in parentheses are the representative accession numbers of the haplotype groups

Fig. 5

Alignment of the amino acid sequences of the mitochondrial cytb gene fragment in different haplotypes in head lice populations in the northwest of Iran. The numbers in parentheses are the representative accession numbers of the haplotype groups

Fig. 6

Phylogenetic relationships between different population groups of P. humanus capitis. Phylogenetic tree was inferred with Neighbor-Joining and Maximum Likelihood methods in fragments of the cytb (a) and cox1 (b) genes in different haplotypes of the present study and their homologues in P. humanus humanus and P. humanus capitis populations. The percentage of replicate trees in which the associated taxa clustered together in the bootstrap test (500 replicates) is shown next to the branches. The scale-bar indicates the Kimura 2-parameter distance