Fasciolosis is a parasitic disease caused by two trematode species of the genus
The prevalence of
The morphological identification of the two species of
Some studies have explored the genetic variability of
A recent study on
The present study aims to investigate the levels of genetic variability among specimens of
In the present study, 24 individuals of
Fig. 1
Map of the Algerian sample collection sites. The map shows the geographical origin of the sequences from Algeria isolated in the present study and those from GenBank and BOLD.

Sampling plan. The table reports data on the sampling collection, the GenBank accession numbers of the sequences obtained in the present study, and the haplotypes (Hap. type) found among individuals. The unique allelic variant isolated for the ITS fragment in all the samples analysed in the present study was deposited in GenBank under the accession number MZ292402. The presence of an identical host code for different samples indicates that flukes were isolated from the same host.
Sample code | Host code | Area | Site | Host | Sampling date | GenBank COI # | Hap. type |
---|---|---|---|---|---|---|---|
C1_142 | 142 | Algeria | Tipaza | Cattle | 03-29-2016 | MT920965 | 2 |
C2_142 | 142 | Algeria | Tipaza | Cattle | 03-29-2016 | MT920966 | 1 |
C1_170 | 170 | Algeria | Tipaza | Cattle | 04-06-2016 | MT920980 | 1 |
C1_858 | 858 | Algeria | Blida | Cattle | 10-03-2016 | MT920969 | 1 |
C2_858 | 858 | Algeria | Blida | Cattle | 10-03-2016 | MT920970 | 1 |
C1_903 | 903 | Algeria | Boumerdes | Cattle | 10-10-2016 | MT920978 | 1 |
C1_995 | 995 | Algeria | Algiers | Cattle | 11-02-2016 | MT920967 | 1 |
C2_995 | 995 | Algeria | Algiers | Cattle | 11-02-2016 | MT920968 | 2 |
C1_1000 | 1000 | Algeria | Algiers | Cattle | 11-02-2016 | MT920974 | 1 |
C2_1000 | 1000 | Algeria | Algiers | Cattle | 11-02-2016 | MT920975 | 1 |
C1_1110 | 1110 | Algeria | Boumerdes | Cattle | 11-26-2016 | MT920982 | 1 |
C1_1211 | 1211 | Algeria | Algiers | Cattle | 12-31-2016 | MT920976 | 1 |
C2_1211 | 1211 | Algeria | Algiers | Cattle | 12-31-2016 | MT920977 | 1 |
C1_1215 | 1215 | Algeria | Algiers | Cattle | 12-31-2016 | MT920981 | 1 |
C1_1230 | 1230 | Algeria | Algiers | Cattle | 12-31-2016 | MT920983 | 1 |
C2_1230 | 1230 | Algeria | Algiers | Cattle | 12-31-2016 | MT920984 | 1 |
C3_1230 | 1230 | Algeria | Algiers | Cattle | 12-31-2016 | MT920985 | 1 |
C4_1230 | 1230 | Algeria | Algiers | Cattle | 12-31-2016 | MT920986 | 1 |
C5_1230 | 1230 | Algeria | Algiers | Cattle | 12-31-2016 | MT920987 | 1 |
C6_1230 | 1230 | Algeria | Algiers | Cattle | 12-31-2016 | MT920988 | 1 |
C1_1279 | 1279 | Algeria | Algiers | Cattle | 01-18-2017 | MT920979 | 1 |
C1_1342 | 1342 | Algeria | Algiers | Cattle | 02-04-2017 | MT920971 | 1 |
C2_1342 | 1342 | Algeria | Algiers | Cattle | 02-04-2017 | MT920972 | 1 |
C4_1342 | 1342 | Algeria | Algiers | Cattle | 02-04-2017 | MT920973 | 1 |
FHLAC1 | LAC | Italy | Laconi | Cattle | 12-09-2013 | MT920989 | 1 |
FHLAC2 | LAC | Italy | Laconi | Cattle | 12-09-2013 | MT920990 | 1 |
FHLAC3 | LAC | Italy | Laconi | Cattle | 12-09-2013 | MT920991 | 1 |
FHLAC4 | LAC | Italy | Laconi | Cattle | 12-09-2013 | MT920992 | 1 |
FHLAC5 | LAC | Italy | Laconi | Cattle | 12-09-2013 | MT920993 | 1 |
FHLAC6 | LAC | Italy | Laconi | Cattle | 12-09-2013 | MT920994 | 1 |
FHLAC7 | LAC | Italy | Laconi | Cattle | 12-09-2013 | MT920995 | 1 |
FHLAC8 | LAC | Italy | Laconi | Cattle | 12-09-2013 | MT920996 | 1 |
FHGIA1 | GIA | Italy | Giara di Genoni | Goat | 11-28-2013 | MT920997 | 1 |
FHGIA2 | GIA | Italy | Giara di Genoni | Goat | 11-28-2013 | MT920998 | 1 |
FHGIA3 | GIA | Italy | Giara di Genoni | Goat | 11-28-2013 | MT920999 | 1 |
FHGIA4 | GIA | Italy | Giara di Genoni | Goat | 11-28-2013 | MT921000 | 1 |
FHGIA5 | GIA | Italy | Giara di Genoni | Goat | 11-28-2013 | MT921001 | 1 |
FHGIA6 | GIA | Italy | Giara di Genoni | Goat | 11-28-2013 | MT921002 | 1 |
FHGIA7 | GIA | Italy | Giara di Genoni | Goat | 11-28-2013 | MT921003 | 1 |
FHGIA8 | GIA | Italy | Giara di Genoni | Goat | 11-28-2013 | MT921004 | 1 |
Genomic DNA of the specimens was extracted using the kit Macherey-Nagel NucleoSpin Tissue (MACHEREY-NAGEL GmbH & Co. KG), following the protocol used by Cossu et al. (2015). Sample quality and DNA concentration were determined via spectrophotometry using a NanoDrop™ Lite (NanoDrop Technologies, Thermo Fisher Scientific Inc., Wilmington, DE). The DNA mean concentration obtained for the samples was 75 ng/μL.
PCR amplification of a partial fragment of the COI gene (441 bp) for samples from Algeria and Sardinia were performed using the primers, Ita 8 (forward; 5’-ACGTTGGATCATAAGCGTGT-3’) and Ita 9 (reverse: 5’-CCTCATCCAACATAACCTCT-3’) (Itagaki et al., 2005). Furthermore, PCRs were also performed for a fragment (900 bp) of the nuclear region including ITS-1, 5.8S rDNA, and ITS-2 (ITS) using the primers BD1 (forward: 5′-GTCGTAACAAGGTTTCCGTA-3′) and BD2 (reverse: 5′-TATGCTTAAATTCAGCGGGT-3′) (Luton et al., 1992). All PCRs were carried out in a total volume of 25 μl containing 10 ng of total genomic DNA on average which was combined with 0.6 μM of each primer and one pellet of PuReTaq Ready-To-Go PCR beads (GE Healthcare; 9900 West Innovation Drive, Wauwatosa, WI, USA). Each pellet of PuReTaq Ready-To-Go PCR beads contained reaction buffer, 2.5 units of PuReTaq DNA polymerase, bovine serum albumin (BSA), deoxynucleotide triphosphates (dNTPs) and stabilizers. For each bead reconstituted to a 25 μl final volume, the concentration of each dNTP was 200 μM and of MgCl2 was 1.5 mM. The PCR conditions were 4 min at 94 °C as an initial step, followed by 35 cycles of 30 sec at 94 °C, 30 sec at the annealing temperature (56 °C for COI and 57 °C for ITS), and 30 sec at 72 °C, with a final post-treatment of 5 min at 72 °C. Both positive and negative controls were used to test the effectiveness of the PCR protocols, and the absence of possible contamination. The PCR products were visualized on 2 % agarose gels (TAE 1×) and purified by ExoSAP-IT (USB Corporation). Sequencing was performed for both strands using the PCR primers by an external sequencing core service (Macrogen Europe).
The sequences obtained for specimens of
The sequences of
Forty contiguous sequences for COI and 32 for the ITS, were aligned and inspected for errors using the package Clustal Omega (Sievers & Higgins, 2014) available at
The genetic variation within the datasets was assessed estimating the number of polymorphic sites (
Median-joining networks (Bandelt et al., 1999) were constructed using the software package Network 10.0.0.0 (
The Tajima’s
The best probabilistic model of sequence evolution was determined using jModeltest 2.1.1 (Posada, 2008), with a maximum likelihood optimised search. The Akaike Information Criterion (AIC) found “TPM3uf+I+G” as the best-fitting model, while the Bayesian Information Criterion (BIC) found the “HKY+G” model. The parameters of the more sophisticated model between the two which were detected were used for input files (i.e. TPM3uf+I+G). Phylogenetic relationships among different taxa (if any) were investigated using a species tree based on Bayesian Inference (BI) by means of the software MrBayes 3.2.7 specifying setting as model parameters: NST = 3, rates = invgamma, ngammacat = 4. Two independent runs, each consisting of four metropolis-coupled MCMC chains (one cold and three heated chains), were run simultaneously for 5,000,000 generations, sampling trees every 1,000 generations. The first 25 % of the 10,000 sampled trees was discarded as burnin. Runs were executed by means of the CIPRES Phylogenetic Portal (Miller et al., 2010). In order to verify the convergence of chains, it was checked that the average standard deviation of split frequencies (ASDSF), approached 0 (Ronquist et al., 2012), and the Potential Scale Reduction Factor (PSRF) was around 1 (Gelman & Rubin, 1992) following Scarpa et al. (2019a).
Phylogenetic trees were visualized and edited using FigTree 1.4.1 (available at
To verify the taxonomic assessment of every sequence in the dataset, four different methods of species delimitation, which are listed below, were used.
The ST-GMYC (Single Threshold-Generalized Mixed Yule Coalescent) method (Pons et al., 2006), which follows the phylogenetic species concept to delimit species, was applied by means of the SPLITS (SPecies LImits by Threshold Statistics) package (Ezard et al., 2009) implemented in the R statistical environment (available at
On the datasets obtained the principal coordinate analysis (PCoA) was performed using GenAlEX 6.5 (Peakall & Smouse, 2012). This analysis allows to distinguish genetic clusters running on a pairwise genetic distance matrix corrected with K2P (Kimura, 1980) model. The rate of variation among sites was modelled with a gamma distribution and all ambiguous positions were removed for each sequence pair.
The manuscript does not contain clinical studies or patient data. Sampling of parasites was not performed on live animals but only on tissues collected post-mortem in a slaughterhouse.
Twenty-four sequences of the central portion of the COI gene (441 bp) were obtained for the samples from Algeria in the present study (Table 1). Among them, only one polymorphic site was found that defined two haplotypes (type 1 and type 2, see Table 1 for details) that were shared by 92 % and 8 % of the samples, respectively (see Table 2 for details on the genetic divergence estimates). The two haplotypes diverged from one another for one neutral point-mutation (transition A → G ), which does not affect the protein structure since it produces a change between two non-polar aliphatic amino acids (isoleucine → valine). The mutation occurred at position 799 of the COI gene nucleotide sequence (reference sequence used for the
Indices of genetic variation. The table reports the estimates of genetic variation for the mitochondrial COI gene dataset. N: sample sizes; bp: fragment size;
N | bp | |||||
---|---|---|---|---|---|---|
24 | 441 | 1 | 2 | 0.159 | 0.00036 | |
32 | 441 | 7 | 7 | 0.393 | 0.00271 | |
187 | 441 | 42 | 32 | 0.753 | 0.00664 |
A COI dataset, which included the sequences from Algeria obtained in the present study and those of
A further COI dataset, including the sequences from Algeria (24) and Sardinia (16) obtained in the present study and those (147) corresponding to the same portion of the COI gene (441 base pairs of the central fragment of the gene) from
The network analysis based on sequences from Algeria (Fig. 2) showed a well-defined, star-like shape with a major and highly diffused haplotype that was found in 78 % of sequences and 6 derived haplotypes diverging for 1 to 4 point-mutations. Almost all the derived haplotypes were exclusive to single individuals, except for one lineage that was found in two individuals from Algiers (sample C2_995 in Table 1) and Tipaza (sample C1_142 in Table 1). Overall, 22 of the sequences from Algeria obtained in the present study belonged to the most frequent haplotype of the network.
Fig. 2
Median-joining network analysis. The network includes COI sequences from Algeria obtained in the present study along with those from GenBank. The small red plot on one node shows a median vector representing the hypothetical connecting sequence that was calculated using the maximum parsimony method. The number of mutations between sequences that are greater than 1 are reported on network branches. As well, the number of individuals showing the same haplotype that is greater than 1 is reported inside the spot.

The neutrality tests performed on the same dataset of sequences from Algeria showed non-significant negative values of
The network analysis performed on the COI dataset, including sequences from all over the world (Fig. 3), showed evidence of the occurrence of three highly diffused haplotypes, which are surrounded by many derived lineages that diverged for a single point mutation from the central ancestor and are generally exclusive to single individuals. Two of the three most frequent haplotypes of the network were diffused across nearly every country included in the analysis, while the third most frequent haplotype was exclusive to sequences from Spain, aside from one sequence from Austria. Furthermore, 10.7 % of the haplotypes included in the dataset were exclusive to single individuals, and one haplotype found in three flukes from China was highly divergent (more than 20 point-mutations) from the others.
Fig. 3
Median-joining network analysis. The network includes all COI sequences from the present study along with those from GenBank. The small red plots on one node show a median vector representing the hypothetical connecting sequence that was calculated using the maximum parsimony method. The number of mutations between sequences that are greater than 1 are reported on network branches. As well, the number of individuals showing the same haplotype that is greater than 1 isreported inside the spot. The MP calculation post-processing option, that uses only the shortest trees sufficient to generate the graphic output, has been applied for drawing the network. This option allows to obtain a network without showing the reticulations. All Sardinian sequences in the network are form the present study.

The neutrality tests performed on this dataset of sequences showed a significant departure from the equilibrium, with a significant negative value for Tajima’s
For phylogenetic inferences, one sequence of
The phylogenetic tree (Fig. S1 in Supplementary Materials) showed a unique, well-supported monophyletic cluster that included all
Consistently, every species delimitation method that was used showed that all the COI sequences of
Principal coordinate analysis (PCoA) was performed on all the COI sequences of
Fig. 4
Principal coordinates analysis performed on the COI gene dataset. Bi-dimensional plots show the genetic differentiation among populations due to the base differences per site found in the dataset. Percentage of variation explained by the first three axes for the COI dataset: 1st = 40.96, 2nd = 13.80, 3rd=9.31.

Group A mainly spread in western Europe and Africa, with only a few sequences isolated on other continents; individuals of
For both Algerian and Sardinian flukes, 32 identical sequences (see Table 1 for details) were obtained for the nuclear ITS fragment in the present study (GenBank accession number: MZ292402). It was not possible to obtain good and scorable sequences for 8 samples, which were not included in the analyses.
A dataset was constructed that included all 32 identical ITS sequences obtained in the present study, along with those (137) from GenBank that exactly matched the ITS fragment used in the present research (see supplementary Table S3 for the GenBank accession numbers and further details). The dataset included 169 sequences of
Because of the low level of genetic variability found among ITS variants, neither the network nor phylogenetic tree and neutrality tests analyses were informative (data not shown).
One sequence of
PCoA was performed on 167 sequences of
Fig. 5
Principal coordinates analysis performed on the ITS fragment dataset. Bi-dimensional plots show the genetic differentiation among populations due to the base differences per site found in the dataset. Percentage of variation explained by the first three axes for the ITS dataset: 1st = 36.71, 2nd = 23.37, 3rd=11.22.

The mitochondrial and nuclear markers used in this study identified all flukes from Algeria as
In this context, the most common COI haplotype found in Algerian isolates (from GenBank and the present study) may correspond to one of the oldest mitochondrial variants present in this country and may be representative of the first lineages introduced from Europe (Walker et al., 2007). The few haplotypes found to be exclusive to single individuals may have recently derived
Interestingly, according to what other authors have already reported (Walker et al., 2007; Elliot et al., 2014), the two new COI haplotypes found in the present study for
Since a low level of genetic divergence was found for the COI fragment analyzed among isolates on every continent, the present study suggests a common origin of flukes sharing the same haplotype, as it was also suggested by other authors (Le et al., 2000; Lotfy et al., 2008; Amor et al., 2011; Simsek et al., 2011; Martinez-Valladares & Rojo-Vazquez, 2014; Mucheka et al., 2015). Accordingly, a unique taxonomic entity corresponding to the monophyletic clade of
The results obtained in the present study also suggest a lack of association between the genetic structuring of the COI gene and host species. Similarly, Santos (2012), who analysed a different and more variable fragment of the COI gene than the present study examined, reported the same haplotype diffused in different hosts (cattle and sheep) from the same geographic Portuguese region. Additionally, Elliot et al. (2014) revealed that many haplotypes are shared between cattle and sheep from Australia, indicating that there is no host selection. Furthermore, present results are also consistent with Bozorgomid et al. (2019), who used the mitochondrial NADH gene to demonstrate low levels of gene flow between
The intergenic spacers (ITS1 and ITS2) located between the 18S, 5.8S and 28S rRNA regions generally showed a low level of genetic variability among
In conclusion, the present study reports two new mitochondrial COI lineages for
The general low level of genetic variation retrieved for COI and ITS fragments is a frequent genetic pattern of
Fig. 1

Fig. 2

Fig. 3

Fig. 4

Fig. 5

Indices of genetic variation. The table reports the estimates of genetic variation for the mitochondrial COI gene dataset. N: sample sizes; bp: fragment size; S: number of polymorphic sites; H: number of haplotypes; hd: haplotype diversity; π: nucleotide diversity.
N | bp | |||||
---|---|---|---|---|---|---|
24 | 441 | 1 | 2 | 0.159 | 0.00036 | |
32 | 441 | 7 | 7 | 0.393 | 0.00271 | |
187 | 441 | 42 | 32 | 0.753 | 0.00664 |
Sampling plan. The table reports data on the sampling collection, the GenBank accession numbers of the sequences obtained in the present study, and the haplotypes (Hap. type) found among individuals. The unique allelic variant isolated for the ITS fragment in all the samples analysed in the present study was deposited in GenBank under the accession number MZ292402. The presence of an identical host code for different samples indicates that flukes were isolated from the same host.
Sample code | Host code | Area | Site | Host | Sampling date | GenBank COI # | Hap. type |
---|---|---|---|---|---|---|---|
C1_142 | 142 | Algeria | Tipaza | Cattle | 03-29-2016 | MT920965 | 2 |
C2_142 | 142 | Algeria | Tipaza | Cattle | 03-29-2016 | MT920966 | 1 |
C1_170 | 170 | Algeria | Tipaza | Cattle | 04-06-2016 | MT920980 | 1 |
C1_858 | 858 | Algeria | Blida | Cattle | 10-03-2016 | MT920969 | 1 |
C2_858 | 858 | Algeria | Blida | Cattle | 10-03-2016 | MT920970 | 1 |
C1_903 | 903 | Algeria | Boumerdes | Cattle | 10-10-2016 | MT920978 | 1 |
C1_995 | 995 | Algeria | Algiers | Cattle | 11-02-2016 | MT920967 | 1 |
C2_995 | 995 | Algeria | Algiers | Cattle | 11-02-2016 | MT920968 | 2 |
C1_1000 | 1000 | Algeria | Algiers | Cattle | 11-02-2016 | MT920974 | 1 |
C2_1000 | 1000 | Algeria | Algiers | Cattle | 11-02-2016 | MT920975 | 1 |
C1_1110 | 1110 | Algeria | Boumerdes | Cattle | 11-26-2016 | MT920982 | 1 |
C1_1211 | 1211 | Algeria | Algiers | Cattle | 12-31-2016 | MT920976 | 1 |
C2_1211 | 1211 | Algeria | Algiers | Cattle | 12-31-2016 | MT920977 | 1 |
C1_1215 | 1215 | Algeria | Algiers | Cattle | 12-31-2016 | MT920981 | 1 |
C1_1230 | 1230 | Algeria | Algiers | Cattle | 12-31-2016 | MT920983 | 1 |
C2_1230 | 1230 | Algeria | Algiers | Cattle | 12-31-2016 | MT920984 | 1 |
C3_1230 | 1230 | Algeria | Algiers | Cattle | 12-31-2016 | MT920985 | 1 |
C4_1230 | 1230 | Algeria | Algiers | Cattle | 12-31-2016 | MT920986 | 1 |
C5_1230 | 1230 | Algeria | Algiers | Cattle | 12-31-2016 | MT920987 | 1 |
C6_1230 | 1230 | Algeria | Algiers | Cattle | 12-31-2016 | MT920988 | 1 |
C1_1279 | 1279 | Algeria | Algiers | Cattle | 01-18-2017 | MT920979 | 1 |
C1_1342 | 1342 | Algeria | Algiers | Cattle | 02-04-2017 | MT920971 | 1 |
C2_1342 | 1342 | Algeria | Algiers | Cattle | 02-04-2017 | MT920972 | 1 |
C4_1342 | 1342 | Algeria | Algiers | Cattle | 02-04-2017 | MT920973 | 1 |
FHLAC1 | LAC | Italy | Laconi | Cattle | 12-09-2013 | MT920989 | 1 |
FHLAC2 | LAC | Italy | Laconi | Cattle | 12-09-2013 | MT920990 | 1 |
FHLAC3 | LAC | Italy | Laconi | Cattle | 12-09-2013 | MT920991 | 1 |
FHLAC4 | LAC | Italy | Laconi | Cattle | 12-09-2013 | MT920992 | 1 |
FHLAC5 | LAC | Italy | Laconi | Cattle | 12-09-2013 | MT920993 | 1 |
FHLAC6 | LAC | Italy | Laconi | Cattle | 12-09-2013 | MT920994 | 1 |
FHLAC7 | LAC | Italy | Laconi | Cattle | 12-09-2013 | MT920995 | 1 |
FHLAC8 | LAC | Italy | Laconi | Cattle | 12-09-2013 | MT920996 | 1 |
FHGIA1 | GIA | Italy | Giara di Genoni | Goat | 11-28-2013 | MT920997 | 1 |
FHGIA2 | GIA | Italy | Giara di Genoni | Goat | 11-28-2013 | MT920998 | 1 |
FHGIA3 | GIA | Italy | Giara di Genoni | Goat | 11-28-2013 | MT920999 | 1 |
FHGIA4 | GIA | Italy | Giara di Genoni | Goat | 11-28-2013 | MT921000 | 1 |
FHGIA5 | GIA | Italy | Giara di Genoni | Goat | 11-28-2013 | MT921001 | 1 |
FHGIA6 | GIA | Italy | Giara di Genoni | Goat | 11-28-2013 | MT921002 | 1 |
FHGIA7 | GIA | Italy | Giara di Genoni | Goat | 11-28-2013 | MT921003 | 1 |
FHGIA8 | GIA | Italy | Giara di Genoni | Goat | 11-28-2013 | MT921004 | 1 |
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