The Anaplasma genus includes a Gram-negative bacterium infecting the blood cells of wild and domestic mammals, causing tick-borne fever. Infection with pathogenic Anaplasma phagocytophilum strains may cause Human Granulocytic Anaplasmosis. Wild boars (Sus scrofa) may act as natural wild reservoir hosts for potentially zoonotic A. phagocytophilum strains; however, there is still little data to confirm this statement. The aim of this study was to verify whether wild boars can be classified as natural reservoirs of Anaplasma spp. and to compare the suitability of spleen and liver samples for such analysis.
Liver and spleen samples were collected from 59 wild boars (2017–2019). The organs were tested for Anaplasma phagocytophilum using short (partial) fragments of three markers: 16S rRNA, groEL, ankA.
Anaplasma spp. DNA was detected in 12 out of 59 samples, with a prevalence of 20.34%. The presence of A. phagocytophilum was confirmed by sequencing of the partial 16S rRNA gene. Positive individuals were tested for the characteristic markers: groEL and ankA. The analysis of the nucleotide sequences of 16S rRNA, groEL and ankA, indicated that the strains of A. phagocytophilum detected in these studies are potentially zoonotic for humans.
Wild boars from Poland can be classified as a natural reservoir of the zoonotic strain of Anaplasma phagocytophilum. Both the spleen and the liver tissues were found to be suitable materials for the detection of A. phagocytophilum.
The causative agent of Human Granulocytic Anaplasmosis (HGA), tick-borne fever (TBF) and granulocytic anaplasmosis in wild, domestic and farm animals is the parasitic bacterium Anaplasma phagocytophilum [1, 2]. Anaplasma spp. are gram-negative bacteria with a specific cell wall structure. Anaplasma phagocytophilum is an obligatory intracellular parasite that lives in neutrophils  and can be transmitted by ticks: Ixodes ricinus, I. persulcatus, I. scapularis and Dermacentor reticulatus [4,5,6]. Recent reports by Werszko et al. (2019)  show that the blood-sucking flies from Tabanidae family can act as carriers of A. phagocytophilum; however, more research is needed to confirm whether they can act as transmission vectors. Ticks and other hematophagous ectoparasites can easily transfer such bacterial intracellular parasites between natural animal reservoirs and humans [8, 9]. The considerable climate changes observed over the past 20 years have resulted in the spread of arthropods, such as ticks and flies, carrying pathogenic bacteria into new regions. Such an increase in annual temperatures has also led to a significant increase in the number of ectoparasites already present in the area, which significantly influences the spread of intracellular bacterial parasites, including Anaplasma spp., in the natural environment . Many wild animals, such as roe deer (Capreolus capreolus), red deer (Cervus elaphus), wild boar (Sus scrofa), red fox (Vulpes vulpes), raccoon dog (Nyctereutes procyonoides) and the European badger (Meles meles) are infected with A. phagocytophilum [11, 12]. Wild boars are likely to be natural wild reservoir hosts for potentially zoonotic A. phagocytophilum strains; however, there is still little data to confirm this statement [11, 13].
The aim of this study was to verify whether the wild boar populations in the north-east and central parts of Poland can be natural reservoirs of A. phagocytophilum, a bacterium potentially pathogenic to humans. It also determines which of the internal organs collected from wild boar, i.e., spleen or liver, is more suitable for the detection of Anaplasma phagocytophilum.
Materials and Methods
All materials were collected during the 2017/2018 hunting season in the Pisz Forest (Warmian-Masurian Voivodeship) and in the 2018/2019 hunting season in the Bolimów Forest (Łódź Voivodeship). In total, spleen and liver samples were collected from 59 adult wild boars.
DNA from both organs was isolated using a commercial DNA Mini Kit (Syngen). Anaplasma spp. was then detected using semi-nested PCR to amplify the partial 16S rRNA gene with primers specific to Anaplasma genus according to Szewczyk et al. (2019) . Positive samples for A. phagocytophilum were additionally tested for the presence of the partial groEL and ankA genes with nested PCR according to Alberti el al. (2005), Massung et al. (2007) and Rymaszewska (2014), respectively (Table 1) [14,15,16]. DNA amplification was performed using the DNA Engine T100 Thermal Cycler (BioRad, USA). The PCR products were visualized on a 1.2% agarose gel (Promega, USA) stained with SimplySafe (EURx, Poland). Visualization was performed using ChemiDoc, MP Lab software (Imagine, BioRad, USA). The obtained PCR products were purified with the QIAquick Purification Kit (Qiagen, Germany). The purified products were sequenced directly using ABI BigDye™ chemistry (Applied Biosystems, USA) on an ABI Prism 373xl or an ABI Prism 3100™ automated sequencer. The obtained sequences were submitted to the GenBank.
Results and discussion
Of the 59 wild boar from which spleen and liver samples were taken, DNA of Anaplasma spp. were detected in 12 individuals, i.e., a prevalence of 20.34%. Anaplasma spp. genetic material was detected in seven individuals in the spleen samples, and in six individuals in the liver samples (Table 2). All positive samples were obtained from boars in the Pisz Forest; no positive samples were found in the Bolimów Forest. Four positive samples were selected for sequencing, and the results indicated the presence of A. phagocytophilum.
A number of studies in various countries have been performed on wild boars with the aim of identifying natural reservoirs of zoonotic strains of A. phagocytophilum [2, 17, 18]. Most of these tests are based on analyses of blood and spleen samples [1, 2, 17, 19, 20] and, very rarely, liver samples [18, 21]. Although some individual studies have used both the spleen and liver [21, 22] none indicate which is more suitable for this type of analysis. Our findings clearly show that, in wild boars, both these tissues are suitable (Table 2). However, as only one examined individual demonstrated positive results for both organs (1/59), it is advisable that both organs should sampled to maximize the detection possibilities when there is no access to blood, which is the best material for this type of analysis .
The prevalence of Anaplasma phagocytophilum in wild boars varies across Europe and elsewhere, ranging from 0.97% in Belgium  to 44.8% in France . In addition, one study reports that genetic material of A. phagocytophilum was not detected in the tested wild boar in Slovakia . Although the prevalence of A. phagocytophilum identified in wild boars in the present study (20.34%) is consistent with the results of those carried out in Germany (12.5%) , Czech Republic and Japan (14.3%) [22, 27], Slovakia (28.2%)  and Hungary (39.2%) ; however, it is nevertheless one of the higher rates. By comparison, A. phagocytophilum was found to be present in 12% (39/325) of wild boars examined in west-central Poland (Mazovian Voivodeship) in 2012 .
Comparing the prevalence of A. phagocytophilum in wild boars in three regions of Poland, it can be seen that it is much more widespread in the west-central (12%)  and north-central (20.34%) regions than in the central (no positive samples) region (this study). The higher prevalence in the west-central and north-central regions may be due to the high afforestation density , which favors an increased incidence of ticks, these being known vectors of A. phagocytophilum . The presence of increased numbers of vectors in an environment enables a faster spread of A. phagocytophilum among hosts. A similar correlation between geographic distribution and an increase in host prevalence has been shown by Szewczyk et al. .
Our sequencing of selected positive 16S rRNA partial gene samples (n = 4) confirmed the presence of A. phagocytophilum in the tested wild boars (MT510541). The identified nucleotide sequences are 100% identical to each other and to the 16S rRNA gene sequence of A. phagocytophilum isolates from various wild animals including carnivores (Vulpes vulpes MH328211, Meles meles MH328207, Nyctereutes procyonoides MH328209), wild boar (KM215225), cervids (Capreolus capreolus MN170723, Cervus elaphus KM215243) and small rodents (Apodemus agrarius KR611718, Myodes glareolus KC583437), as well as tick and flies (Ixodes ricinus HQ629922, JX173651, Haematopota pluvialis MH844585, Tabanus distinguendus MH844584), farm animals (Bos taurus taurus KP745629, Equus caballus AY527212), domestic animals (Canis lupus familiaris MN453474, MK814406) and humans (Belgium KM259921, Austria KT454992, USA AF093788, South Korea KP306518).
The two most common markers used to describe the genetic diversity of A. phagocytophilum strains are the groEL and ankA genes . Based on our analysis of the groEL gene sequences (MT731760, MT731761, MT731762) the detected strains of A. phagocytophilum were classified into ecotype I [10, 30]. In the groEL gene, one nucleotide sequence (MT731760) showed 100% similarity to a groEL sequence from the human strain of A. phagocytophilum (AF033101), while another two (MT731761, MT731762) showed only 99.78%. However, despite the point change observed in the latter two sequences, all three encode the same protein as in human strains of A. phagocytophilum. Regarding ankA, two sequences (MT534241, MT731758), obtained from two wild boar individuals, are 100% complementary to human isolates (AF100886, AF100887, GU236800). The third isolate from wild boar (MT731759) showed 99.4% similarity to human markers. From all obtained ankA gene sequences, only two of them (MT534241 and MT731758) encode the same protein as human A. phagocytophilum strains: the third one (MT731759) is significantly different from the protein detected in humans. The analysis of the nucleotide sequences of 16S rRNA, groEL and ankA indicates that the strains of A. phagocytophilum detected in samples in this study can be classified as potentially zoonotic for humans.
Our findings suggest that wild boars from Poland can be classified as a natural reservoir of the zoonotic Anaplasma phagocytophilum strains. In addition, both the spleen and liver were found to be suitable for the detection of A. phagocytophilum. However, further research is needed in other areas of Poland to comprehensively analyze the issues of A. phagocytophilum natural reservoirs throughout the country, and such studies should include other animals, which may demonstrate different tissue predilection than wild boars.
The datasets generated during and/or analysed during the current study are available from the corresponding author on reasonable request.
Hornok S, Sugar L, Fernandez IG et al (2018) Tick- and fly-borne bacteria in ungulates: the prevalence of Anaplasma phagocytophilum, haemoplasmas and rickettsiae in water buffalo and deer species in Central Europe. Hungary Vet Res 14:98. https://doi.org/10.1186/s12917-018-1403-6
Kazimirova M, Hamsikova Z, Spitalska E et al (2018) Diverse tick-borne microorganisms identified in free-living ungulates in Slovakia. Parasites Vectors 11:495. https://doi.org/10.1186/s13071-018-3068-1
Lin M, Rikihisa Y (2003) Ehrlichia chaffeensis and Anaplasma phagocytophilum Lack Genes for Lipid A Biosynthesis and Incorporate Cholesterol for Their Survival. Infect Immun 1(9):5324–5331. https://doi.org/10.1128/IAI.71.9.5324-5331.2003
Karbowiak G, Vichová B, Slivinska K et al (2014) The infection of questing Dermacentorreticulatus ticks with Babesiacanis and Anaplasma phagocytophilum in the Chernobyl exclusion zone. Vet Parasitol 204(3–4):372–375. https://doi.org/10.1016/j.vetpar.2014.05.030
Karbowiak G, Biernat B, Stańczak J et al (2016) The role of particular ticks developmental stages in the circulation of tick-borne pathogens in Central Europe. 4. Anaplasmataceae. Ann Parasitol. 62(4):267–284. https://doi.org/10.17420/ap6204.62
Wirtgen M, Nahayo A, Linden A (2011) Detection of Anaplasma phagocytophilum in Dermacentor reticulatus ticks. Vet Rec 168(7):195. https://doi.org/10.1136/vr.d1053
Werszko J, Szewczyk T, Steiner-Bogdaszewska Ż, Laskowski Z, Karbowiak G (2019) Molecular detection of Anaplasma phagocytophilum in blood-sucking flies (Diptera: Tabanidae) in Poland. J Med Entomol 56(3):822–827. https://doi.org/10.1093/jme/tjy217
Andersson MO, Marga G, Banu T et al (2018) Tick-borne pathogens in tick species infesting humans in Sibiu County, central Romania. Parasitol Res 117:1591–1597. https://doi.org/10.1007/s00436-018-5848-0
Atif FA (2015) Anaplasma marginale and Anaplasma phagocytophilum: Rickettsiales pathogens of veterinary and public health significance. Parasitol Res 114:3941–3957. https://doi.org/10.1007/s00436-015-4698-2
Matei IA, Estrada-Pena A, Cutler SJ et al (2019) A review on the eco–epidemiology and clinical management of human granulocytic anaplasmosis and its agent in Europe. Parasites Vectors 12:599. https://doi.org/10.1186/s13071-019-3852-6
Adamska M (2020) The role of different species of wild ungulates and Ixodes ricinus ticks in the circulation of genetic variants of Anaplasma phagocytophilum in a forest biotope in north-western Poland. Ticks Tick Borne Dis 11(5):101465. https://doi.org/10.1016/j.ttbdis.2020.101465
Szewczyk T, Werszko J, Myczka AW et al (2019) Molecular detection of Anaplasma phagocytophilum in wild carnivores in north-eastern Poland. Parasites Vectors 12:465. https://doi.org/10.1186/s13071-019-3734-y
Dugat T, Zanella G, Véran L et al (2016) Multiple-locus variable-number tandem repeat analysis potentially reveals the existence of two groups of Anaplasma phagocytophilum circulating in cattle in France with different wild reservoirs. Parasit Vectors 9(1):596. https://doi.org/10.1186/s13071-016-1888-4
Alberti A, Zobba R, Chessa B et al (2005) Equine and canine Anaplasma phagocytophilum strains isolated on the island of Sardinia (Italy) are phylogenetically related to pathogenic strains from the United States. Appl Environ Microbiol 71(10):6418–6422. https://doi.org/10.1128/AEM.71.10.6418-6422.2005
Massung RF, Levin M, Munderloh UG et al (2007) Isolation and Propagation of the Ap-Variant 1 strain of Anaplasma phagocytophilum in a tick cell line. J ClinMicrobiol 45(7):2138–2143. https://doi.org/10.1128/JCM.00478-07
Rymaszewska A (2014) Genotyping of Anaplasma phagocytophilum strains from Poland for selected genes. Folia Biol (Krakow) 62(1):37–48. https://doi.org/10.3409/fb62_1.37
Masuzawa T, Uchishima Y, Fukui T et al (2011) Detection of Anaplasma phagocytophilum from wild boars and deer in Japan. Jpn J Infect Dis 64:333–336
Michalik J, Stanczak J, Cieniuch S et al (2012) Wild boars and hosts of human-pathogenic Anaplasma phagocytophilum variants. Emerg Infect Dis 18(6):998–1001. https://doi.org/10.3201/eid1806.110997
Reiterová K, Špilovská S, Blaňarová L et al (2016) Wild boar (Sus scrofa)—reservoir host of Toxoplasma gondii, Neospora caninum and Anaplasma phagocytophilum in Slovakia. ActaParasitol 61(2):255–260. https://doi.org/10.1515/ap-2016-0035
StrasekSmrdel K, Bidovec A, Malovrh T (2009) Detection of Anaplasma phagocytophilum in wild boar in Slovenia. ClinMicrobiol Infect 15(Suppl 2):50–52. https://doi.org/10.1111/j.1469-0691.2008.02174.x
Kiss T, Cadar F, Krupaci FA et al (2014) Prevalence of Anaplasma phagocytophilum infection in European wild boar (Sus scrofa) population from Transylvania. Romania Epidemiol Infect 142:246–250. https://doi.org/10.1017/S0950268813000812
Petrovec M, Sixl W, Schweiger R et al (2003) Infections of wild animals with Anaplasma phagocytophilum in Austria and Czech Republic. Ann N Y AcadSci 990:103–106. https://doi.org/10.1111/j.1749-6632.2003.tb07345.x
Rikihisa Y (2011) Mechanisms of obligatory intracellular infection with Anaplasma phagocytophilum. ClinMicrobiol Rev 24(3):469–489. https://doi.org/10.1128/CMR.00064-10
Nahayo A, Bardiau M, Volpe R et al (2014) Molecular evidence of Anaplasma phagocytophilum in wild boar (Sus scrofa) in Belgium. BMC Vet Res 10:80. https://doi.org/10.1186/1746-6148-10-80
Stefanidesova K, Kocianova E, Boldis V et al (2008) Evidence of Anaplasma phagocytophilum and Rickettsia helvetica infection in free-ranging ungulates in central Slovakia. Eur J Wildl Res 54:519–524. https://doi.org/10.1007/s10344-007-0161-8
Silaghi C, Pfister K, Overzier E (2014) Molecular investigation for bacterial and protozoan tick-borne pathogens in wild boars (Sus scrofa) from southern Germany. Vector Borne Zoonotic Dis 14(5):371–373. https://doi.org/10.1089/vbz.2013.1495
Matsuo K, Moribe J, Abe N (2017) Molecular Detection and Characterization of Anaplasma Species in Wild Deer and Boars in Gifu Prefecture, Japan. Jpn J Infect Dis 70(3):354–356. https://doi.org/10.7883/yoken.JJID.2016.368
Statistical Yearbook of Forest (2019) Statistic Poland
Welc-Falęciak R, Kowalec M, Karbowiak G (2014) Rickettsiaceae and Anaplasmataceae infections in Ixodes ricinus ticks from urban and natural forested areas of Poland. Parasit Vectors 24(7):121. https://doi.org/10.1186/1756-3305-7-121
Jahfari S, Coipan EC, Fonville M et al (2014) Circulation of four Anaplasma phagocytophilum ecotypes in Europe. Parasites Vectors 7:365. https://doi.org/10.1186/1756-3305-7-365
The authors would like to thank the management and staff of Strzałowo Forest District and Hunting Club No. 9 “Knieja” from Warsaw.
The authors received no financial support for the research, authorship, and publication of this article.
Conflict of interest
The authors declare that they have no conflict of interest.
This article does not contain any studies with human participants or animals performed by any of the authors.
All authors consent to the publication.
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
About this article
Cite this article
Myczka, A.W., Szewczyk, T. & Laskowski, Z. The Occurrence of Zoonotic Anaplasma phagocytophilum Strains, in the Spleen and Liver of Wild Boars from North-West and Central Parts of Poland. Acta Parasit. 66, 1082–1085 (2021). https://doi.org/10.1007/s11686-021-00368-6
- Anaplasma phagocytophilum
- Sus scrofa
- Tick–borne disease