Background

Ticks are considered to be the second most common vector of human diseases worldwide after mosquitoes, but they are the most important vectors of disease-causing pathogens in domestic and wild animals. Indeed, ticks transmit a wide variety of pathogens, including viruses, bacteria and protozoa, to their vertebrate hosts [1].

For instance, anaplasmosis is caused by a number of established and emerging tick-borne pathogens, including Anaplasma phagocytophilum, Anaplasma marginale, Anaplasma ovis, Anaplasma centrale, Anaplasma bovis, Anaplasma capra, Anaplasma platys, and ‘Candidatus Anaplasma camelii’, which are found worldwide, particularly in tropical and subtropical regions, including Iran [2,3,4,5,6]. Anaplasma spp. may infect humans and a broad range of wild and domestic mammals, including horses, dogs, cats, deer, goats, sheep, cattle, camel, and other ruminants [4, 6, 7]. Ehrlichiosis caused by Ehrlichia spp. is another tick-borne disease [8], and some Ehrlichia spp. have been identified as pathogens in humans. For example, Ehrlichia chaffeensis causes human monocytic ehrlichiosis and Ehrlichia ewingii is an agent of human granulocytic ehrlichiosis [9]. The zoonotic nature of the human ehrlichiosis is supported by reports of natural infections with the same Ehrlichia spp. in dogs, deer, horses, and rodents [10]. Granulocytic ehrlichiosis in humans has been described in immunocompromised and immunocompetent patients, causing headache, fever, myalgia, vomiting, nausea, acute renal failure, thrombocytopenia, leukopenia and increased liver enzyme activities [11,12,13].

Iran has a variety of climates: a mild cold climate in the high mountains; continental and arid climates in the plateau; a mild and damp climate on the Caspian coast; and a hot desert climate on the southern coast and in the south-east. Each climate may provide conditions suitable for the development of different tick species, which probably explains the difference in the epidemiology of anaplasmosis and ehrlichiosis in different regions [14]. Sistan and Baluchistan Province in the south-east corner of Iran has a long border with Pakistan and Afghanistan, where infectious diseases do not respect international boundaries [15]. Animal husbandry is one of the main activities of the people in the province, and every week thousands of head of livestock, including sheep, goats, cows, camels, and buffaloes, cross the borders between the countries [16].

Although Anaplasma spp. and Ehrlichia spp. have been identified by molecular assays in livestock in Iran, their presence in their vectors has been much less studied. There have been only a few studies on the detection of Anaplasma spp. and Ehrlichia spp. in ticks in Iran, which reported the presence of infected ticks in the north and other regions of Iran [14, 17, 18].

Ixodid ticks play an important role in maintaining Anaplasma spp. and Ehrlichia spp. in nature [19, 20]. Nonetheless, while Hyalomma spp. have been suggested as vectors of A. marginale [21], there has been little research on their possible involvement in Anaplasma spp. and Ehrlichia spp. transmission. Here, we report the occurrence of Hyalomma spp. infesting various domestic animals in the Iranian Province of Sistan and Baluchistan, with notes on Anaplasma spp. and Ehrlichia spp. infections in these ticks.

Methods

Sample collection and tick identification

The regions investigated include three districts of Sib & Suran County (Hiduj district; geographical coordinates 27°00′02″N, 62°07′01″E), Sarbaz County (Pishin district; geographical coordinates 30°35′5.31″N, 66°59′41.19″E) and Chabahar County (Negour district; geographical coordinates 25°23′20.84″N, 61°8′18.96″E), all of which are located in the south-east of Iran, close to the border with Pakistan. The collection of ticks was performed in three randomly selected major animal husbandry farms in each district, between November 2017 and late March 2018, i.e. at the season when adult ticks are most active in the region. In total, 1124 ticks were collected from goats (n = 80), cattle (n = 34), and camels (n = 12). Tick collection was arbitrarily conducted, depending upon the availability of the domestic animals for a 15-min examination per animal, but efforts were made to obtain a widespread representative sample from the different animal species included in the study. All ticks were transferred to vials and labelled according to their geographical origin and the animal from which they were obtained. The collected ticks were subsequently transferred to the Entomology Laboratory in the School of Public Health at the Tehran University of Medical Sciences and were identified to species level, based on microscopic observation of external morphological characteristics according to the identification keys [22,23,24].

DNA extraction

After species identification, the ticks were sterilized by immersion in 70% alcohol, washed in distilled water, dried on filter paper in a laminar-flow hood, and then stored at −80 °C until the DNA extraction.

Individual ticks were frozen in liquid nitrogen and then ground in an Eppendorf microtube. The DNA was then extracted using the G-spin Genomic DNA Extraction Kit (iNtRON Biotechnology, South Korea), according to the manufacturer’s instructions. The precipitated DNA samples were quantified using a spectrophotometer (Thermo Scientific™ NanoDrop™ One, Wilmington, DE, USA), and their integrity was assessed using 1% agarose gel electrophoresis. Then, the extracted DNA was suspended in sterile distilled water and stored at −20 °C. Of the ticks collected, all the engorged ticks were analysed, and a subset (n = 50) of the unfed ticks were also tested for the presence of Anaplasma spp. and Ehrlichia spp.

Molecular detection of Anaplasma spp. and Ehrlichia spp. in ticks

The 16S rRNA gene of Anaplasma spp. and Ehrlichia spp. was amplified using the nested PCR protocol designed by Rar et al. [25]. The forward and reverse primers for initial reactions were Ehr1 (5′-GAA CGA ACG CTG GCG GCA AGC-3′) and Ehr2 (5′-AGT A(T/C)C G(A/G)A CCA GAT AGC CGC-5′) and for nested reactions were Ehr3 (5′-TGC ATA GGA ATC TAC CTA GTA G-3′) and Ehr4 (5′-CTA GGA ATT CCG CTA TCC TCT-3′). The size of final PCR products was 524 base pairs (bp). PCR reactions were performed in a 25 μl reaction mixture, containing 12.5 μl of the Hot Start Taq 2 \(\times\) Master Mix, 1 μl of each of the forward and reverse primers, 2 μl of DNA template and 7.5 μl of nuclease-free water to bring the volume to 25 μl. PCR reactions were performed in a DNA Mastercycler Personal PCR machine (Eppendorf, Germany) and PCR conditions were: 15 min at 95 °C for initial denaturation, then 60 s at 94 °C for denaturing, 60 s at 57 °C for annealing, and 60 s at 72 °C for extension for 35 cycles, and then a final extension for 10 min at 72 °C. The products (2 μl) of the first PCR were used as the template for the second PCR, which was carried out under the same conditions and reaction mixture as the first, except that nesting primers were used [25]. Two negative controls (one of double-distilled water and one of an un-infected tick DNA template) and a positive control (a confirmed sequenced A. bovis DNA isolated from a tick) were included in each PCR run. To ensure the presence of viable DNA, the barcoding region of the tick COI gene was used as endogenous control [26].

To assess the presence of expected bands for Anaplasma spp. and Ehrlichia spp., the PCR products were electrophoresed in a 1.5% agarose gel, and the size of each PCR product was estimated using a 100 bp ladder and visualized with a UV transilluminator.

DNA sequencing and phylogenetic analysis

The positive PCR products were purified, and bidirectional DNA sequencing was performed by the Sanger method, using the same inner PCR primers that were used for nested PCR amplification. The sequences obtained were edited and assembled using Chromas (http://www.technelysium.com.au/chromas.html) and BioEdit [27] software to construct consensus sequences, which were then analysed using the NCBI Blast database (Nucleotide collection) (https://www.ncbi.nlm.nih.gov/). The consensus high-confidence sequences were aligned with other sequences that were available in GenBank, using multiple sequence alignments available in CLUSTAL Omega (https://www.ebi.ac.uk/Tools/msa/clustalo). For phylogenetic analysis, the representative sequences of Anaplasma spp. and Ehrlichia spp. obtained in this study were combined with a subset of available representative sequences of all Anaplasma spp. and E. ewingii, using Spiroplasma sp. sequences as an outgroup [28-31]. Details of these sequences are shown as supplementary data (Additional file 1: Table S1). All the DNA sequences used for alignment were cut to obtain a consistent region (470 bp), and phylogenetic analyses were performed using the MEGA 7 software [32]. The data were aligned and the maximum likelihood method was employed to construct a phylogenetic tree. The same program was utilized to evaluate the stability of the obtained tree through bootstrap analysis with 1000 replicates.

Results

Tick species and abundance

A total of 1124 hard ticks were collected which were classified into three genera: Hyalomma (n = 1020, 90.7%), Rhipicephalus (n = 68, 6.1%), and Dermacentor (n = 36, 3.2%). All of the 1020 ticks collected were morphologically identified as belonging to one of six Hyalomma spp., with Hyalomma anatolicum being the most common species in all three districts. In detail, the tick species were found to be H. anatolicum (n = 462; 228 from cattle and 234 from goats), Hyalomma asiaticum (n = 143; 87 from camels, 25 from goats, and 31 from cattle), Hyalomma marginatum (n = 203; 134 from cattle, 66 from goats and three from camels), Hyalomma dromedarii (n = 188; 46 from goats and 142 from camels), Hyalomma schulzei (n = 17 from goats), and Hyalomma detritum (n = 6 from camels) (Table 1). The average number of ticks on camels, cattle, and goats were 19.8, 11.6, and 4.9, respectively. The collected tick specimens were mix of unfed (75%), partially fed (15.1%), and fully engorged (9.9%). Unfed were very small, often black or brown colour, partially engorged (partially swollen), which means the tick has had a partial blood meal, and engorged (swollen, usually blue-grey in colour) (Table 1).

Table. 1 Details of Hyalomma spp. specimens collected from animals in Sistan and Baluchistan Province, south-east corner of Iran, 2017–2018
Full size table

Anaplasma spp. and Ehrlichia spp. infections in ticks

Using generic EHR primers, a subset (n = 50) of non-engorged tick specimens, and all of the 255 fully or partially engorged tick specimens, comprising 63 males (25%) and 192 females (75%), were tested for the presence of Anaplasma spp. and Ehrlichia spp. The tested specimens were representatives of the ticks collected from different animals in the three regions. The positive results were obtained with 68.6% (175 out of 255) of the engorged specimens, whereas non-engorged specimens were all negative. The species, number, and percentage of pathogen infection in Hyalomma spp. ticks at each collection site are shown in Table 2. A sub-set of positive PCR amplicons was sequenced and the consensus sequences were deposited in GenBank (accession numbers shown in Table 3). Details of the Anaplasma spp. and Ehrlichia spp.-positive samples are provided in Table 3.

Table. 2 Details of Anaplasmataceae infections in different Hyalomma spp. collected from Sistan and Baluchistan Province, south-east corner of Iran, 2017–2018
Full size table
Table. 3 Details of Anaplasma spp. and Ehrlichia spp. infections in Hyalomma spp. from three districts of Sistan and Baluchistan Province, south-east corner of Iran, 2017–2018
Full size table

Sequence and phylogenetic analysis

Analysis of the sequence data showed that the highest percentage of sequences obtained corresponded to A. ovis (18 out of 22, 81.8%). All of the strains of A. ovis detected in this study were identical, both to each other and to the other Iranian strains, and to the strains from China (GenBank: MG869525) and Russia (GenBank: KC484563). In addition to A. ovis, two A. marginale (9.1%) and two E. ewingii (9.1%) positive samples were detected. Sequences of A. marginale found in this study were identical to sequences from the USA, Brazil, Cuba, Iraq and China (GenBank: CP000030, CP023731, MK804764, MH551233, and KU586075, respectively). Similarly, the detected strains of E. ewingii obtained in this study were identical or highly similar to the isolates from Australia, the USA, Brazil, Thailand, and China (GenBank: NR_044747, NR_044747, HQ908082, NR_044747, and MN148615, respectively). The detected strains of A. marginale and or E. ewingii showed sequence similarities of 99–100% with sequences available in GenBank.

Phylogenetic analysis revealed that the Anaplasma/Ehrlichia spp. detected in this study clustered into four different clades, including (I) A. ovis, (II) A. marginale, (III) A. platys-A. phagocytophilum-A. odocoilei, and (IV) A. centrale-A. capra (Fig. 1). Both E. ewingii sequences obtained herein were associated with the branches of clade III.

Fig. 1
figure 1

Phylogenetic relationships inferred from 470 bp of 16S rRNA gene sequences of Anaplasma spp. and Ehrlichia spp. detected in this study and others available in GenBank. The representative sequences obtained in this study are marked with red circles. The tree was computed by maximum likelihood (MEGA 7.0 software). Bootstrap values (> 50%) are shown on nodes. For sequences from Iran, the county or province name is also provided

Full size image

Discussion

This is the first comprehensive study of the Hyalomma spp. ticks from domestic animals and their associated Anaplasma spp. and Ehrlichia spp. along the Iran-Pakistan border. The results show that domestic animals in this area are infested with at least six Hyalomma spp., in addition to ticks belonging to other genera, which were not identified to species level herein. Moreover, at least two Anaplasma spp. and one Ehrlichia sp. were detected in the collected ticks. These results are generally in agreement with previous observations in Pakistan and in other parts of Iran [17, 33,34,35,36].

Herein, more than 90% of livestock-infesting adult ticks belonged to the genus Hyalomma, which agrees with the result of other researchers in Baluchistan of Pakistan where 525 out of 529 (99.2%) of the ticks belonged to this genus [37]. Among Hyalomma spp., H. anatolicum was the most common species and presented the widest geographical range. This three-host tick species was previously reported to be the most prevalent hard tick from different parts of Pakistan and Iran [17, 18, 33,34,35, 38,39,40,41,42,43].

The ecology of different Hyalomma spp. ticks may influence the risk of tick-borne diseases in the region [39, 41, 44,45,46]. The intense animal movements across Iranian regions and neighbouring countries may also facilitate the spread of these ticks. The infected ticks found in this study were feeding on the animals at the time of collection and were, therefore, potentially transmitting (or ingesting) Anaplasma spp. and E. ewingii while feeding. Therefore, the possibility that these ticks play a role in the transmission of these agents to domestic animals in the study area requires further investigation.

Except for E. ewingii, the pathogens found herein have previously been detected in ticks in several regions of Iran [14, 18, 33, 41,42,43]. However, we found the prevalence of Hyalomma spp. ticks carrying Ehrlichia spp. or Anaplasma spp. to be 68%, which is higher than previously reported from other parts of the country, including 4.6% in the south-eastern and north-western regions [33], 25% in the north [35], 43.84% in Meshkin-Shahr, Ardebil Province [43], and 55.5% in the four provinces of East Azerbaijan, Gilan, South Khorasan and Yazd [14]. These differences in tick infection rates could be related to several factors, including sampling methods, diagnostic methods, season, tick species, and feeding status of the ticks. Here, although the nested PCR technique used is known to be highly sensitive and specific, more nested PCR-positive samples should have been sequenced to determine the actual prevalence of Anaplasma spp. and Ehrlichia spp. infection in the ticks.

The results of this study, taken together with the above literature, have shown that different Hyalomma spp. could be involved in the transmission of pathogens to cattle, goats and camels in different regions of Iran. In addition to the Hyalomma spp. ticks, other ticks, including Rhipicephalus bursa, Rhipicephalus sanguineus sensu lato, Dermacentor marginatus, Haemaphysalis erinacei, and Ixodes ricinus have been reported as proven or putative vectors of different bacteria of the family Anaplasmataceae in Iran [17, 18, 33, 43].

The fact that no Anaplasma spp. or Ehrlichia spp. DNA was detected in the non-engorged specimens may suggest that there is little or no transovarial transmission of the bacteria in Hyalomma spp. ticks. Moore et al. [47] showed some evidence of transovarial transmission of A. ovis in Dermacentor nuttalli, although they did not detect any A. ovis DNA in larvae or nymphs. Another study [48] demonstrated the transovarial transmission of A. marginale in Rhipicephalus microplus, and that infected larvae can transmit the infection to susceptible hosts.

In this study, A. ovis was detected in five tick species: H. anatolicum, H. asiaticum, H. marginatum, H. dromedarii, and H. detritum, which were collected from cattle, goats, and camels. On the other hand, A. marginale and E. ewingii were found only in H. schulzei and H. dromedarii collected from goats and camels, respectively. Both A. ovis and A. marginale are important livestock pathogens [49], whereas E. ewingii is an important human pathogen [10, 50, 51] and is reported for the first time in Iran. However, the presence of E. ewingii should be confirmed by sequencing other genes (e.g., groEL), which was not possible in this study. Anaplasma ovis is distributed worldwide and is an important agent of anaplasmosis in small ruminants [52, 53]. For instance, bovine anaplasmosis is hyper-endemic in Sistan and Balouchestan Province, where 80% of goats have been shown to be infected with A. ovis [54]. Indeed, both A. ovis and A. marginale are established as the main agents of goat anaplasmosis in Iran [54].

In addition to A. ovis and A. marginale, other studies at the borders of Iran with Afghanistan and with Pakistan have reported the presence of different Ehrlichia spp. and Anaplasma spp. [18, 36, 40, 55] including A. marginale, A. centrale, A. ovis, A. platys-like organism, and Ehrlichia minasensis, and two uncharacterized species, namely, Ehrlichia sp. (Multan) and Anaplasma spp. (BL099-6) [18, 36, 40].

Conclusions

In conclusion, we confirmed the presence of A. ovis, A. marginale and E. ewingii in Hyalomma spp. ticks collected from cattle, goats and camels on the Iran-Pakistan border. Further research is needed to confirm the role of these Hyalomma spp. and other ticks in the transmission of these pathogens in this region.