Long-term study of Borrelia and Babesia prevalence and co-infection in Ixodes ricinus and Dermacentor recticulatus ticks removed from humans in Poland, 2016–2019

Abstract

Background Lyme borreliosis (LB) is the most common vector-borne disease in Europe. Monitoring changes in the prevalence of different Borrelia species in ticks may be an important indicator of risk assessment and of differences in pathogenicity in humans. The objective of our study was to assess the prevalence, co-infection and distribution of Borrelia and Babesia species in ticks removed from humans in a large sample collected during a study period of 4 years. Methods The ticks were collected throughout Poland from March to November over 4-year period from 2016 to 2019. All ticks (n = 1953) were morphologically identified in terms of species and developmental stage. Molecular screening for Borrelia and Babesia by amplification of the flagellin gene (flaB) or 18S rRNA marker was performed. Pathogen identity was confirmed by Sanger sequencing or PCR–restriction fragment length polymorphism analysis. Results The ticks removed from humans in Poland during this study belonged to two species: Ixodes ricinus (97%) and Dermacentor reticulatus (3%). High Borrelia prevalence (25.3%), including B. miyamotoi (8.4%), was confirmed in Ixodes ricinus ticks removed from humans, as was the change in frequency of occurrence of Borrelia species during the 4-year study. Despite Babesia prevalence being relatively low (1.3%), the majority of tested isolates are considered to be pathogenic to humans. Babesia infection was observed more frequently among Borrelia-positive ticks (2.7%) than among ticks uninfected with Borrelia (0.8%). The most frequent dual co-infections were between Borrelia afzelii and Babesia microti. The presence of Borrelia was also confirmed in D. reticulatus (12.7%); however the role of these ticks in spirochete transmission to susceptible hosts is still unclear. Conclusions Although the overall risk of developing LB after a tick bite is low in Europe, knowledge of the prevalence and distribution of Borrelia and Babesia species in ticks might be an important indicator of the risk of both these tick-borne diseases. Graphical abstract

Abundance of Ixodes ricinus Ticks (Acari: Ixodidae) and the Diversity of Borrelia Species in Northeastern Poland

“…In I. ricinus of the Warmia and Mazury region, the current study did not confirm the occurrence of the pathogenic B. spielmanii previously detected in I. ricinus in Poland in the forested city areas of Warsaw [ 40 ] or in I. ricinus removed from humans [ 54 ]. However, B. bavariensis (formerly B. garinii OspA serotype 4) [ 79 ] was identified in I. ricinus males from the central subregion of Warmia and Mazury.…”

“…In the studied population of I. ricinus ticks, a higher mean density of nymphs (7.8 ticks per 100 m 2 ) than adult ticks was noted. The higher density of nymphs compared to adult ticks is consistent with the fact that most reported tick bites on humans are from nymphs [ 54 , 55 , 56 , 57 ]. Nymphs are therefore considered the most important life stage involved in transmitting Borrelia spirochetes to humans.…”

“…Despite suggesting the presence of a genetically specific Polish strain of B. miyamotoi [ 40 ], the genetic analysis in the current study revealed a lack of polymorphism in the flaB gene and glpQ gene sequences and full nucleotide identity to the European type of B. miyamotoi . Despite the low prevalence of B. miyamotoi in I. ricinus in northeastern Poland, the authors strongly agree with the conclusion [ 40 , 54 , 55 ] that B. miyamotoi disease (BMD) should not be underestimated. The number of confirmed symptomatic and asymptomatic cases of BMD in Europe is steadily increasing and has been diagnosed so far in 50 patients, including one patient in Poland [ 20 , 26 ].…”

“…It has been observed that B. miyamotoi is constantly circulating in European populations of questing I. ricinus , although its prevalence is low and ranges between 0.2% and 8.9%, depending on the region and the developmental stage of ticks [ 20 ]. A relatively high B. miyamotoi prevalence was detected in I. ricinus ticks removed from humans in Poland (8.4%) [ 54 ] and Germany (7.3%) [ 55 ]. In Poland, B. miyamotoi was also identified in I. ricinus in recreational areas in Szczecin [ 47 ] and Warsaw [ 40 ], and in natural habitats of Lower Silesia [ 85 ] and eastern Poland [ 40 ], with a prevalence ranging from 0.5–3.9%.…”

The Risk of Exposure to Ticks and Tick-Borne Pathogens in a Spa Town in Northern Poland

“…From an epidemiological point of view, the I. ricinus tick has greater importance than D. reticulatus . I. ricinus dominated among ticks removed from human skin in Europe [ 24 , 25 , 26 ] and it is considered to be a main vector of Lyme borreliosis [ 27 ]. In our study, spirochaetes from the B. burgdorferi complex were detected only in I. ricinus .…”