Biology subjects

Bajer, A.

Publications and source records attributed to Bajer, A..

7 recordsLinked to original sources

bioRxiv2026

Co-circulating TBEV lineages and evidence for vertical transmission in wild bank voles from Poland

Tick-borne encephalitis virus (TBEV) is a zoonotic flavivirus maintained in complex enzootic cycles involving ticks and vertebrate hosts. While vector-mediated transmission has been extensively studied, host-associated mechanisms, including vertical transmission and prolonged viral carriage in natural reservoir populations, remain poorly understood. Here, we investigated TBEV circulation, genetic diversity, and evidence for vertical transmission in bank voles (Clethrionomys glareolus) from a highly endemic region of North-eastern Poland. A total of 258 wild rodents were screened using molecular and serological approaches. TBEV RNA was detected in 14.3% of individuals, whereas seroprevalence was substantially lower (6.6%), revealing limited concordance between viral presence and humoral response under natural conditions. Near-complete genome sequences were obtained from 10 TBEV-positive individuals, representing the first near-complete TBEV genomes generated from wild rodents in Poland. All isolates belonged to the European subtype (TBEV-Eu), and phylogenetic analysis revealed two genetically distinct viral clades co-circulating within a narrow spatiotemporal window. Importantly, TBEV RNA and/or envelope protein were detected in embryos from naturally infected females, providing evidence consistent with vertical transmission in a wild reservoir host. Together, these findings suggest that vertical transmission and complex host infection dynamics may be underappreciated components of TBEV maintenance in natural reservoir populations. Our results highlight the need to integrate vertebrate host dynamics into models of TBEV ecology and support expanded wildlife-based surveillance to better understand and predict zoonotic risk.

microbiology↗

bioRxiv2026

Does Borrelia afzelii outer surface protein E coevolve with complement factor H of its rodent host? Insights from GxG and spatial associations

BackgroundLyme borreliosis is a common tick-borne disease in Europe caused by spirochetes of the Borrelia burgdorferi sensu lato complex, including Borrelia afzelii, which is maintained in nature through interactions with rodent reservoir hosts. These spirochetes have evolved several surface proteins to manipulate rodent host immunity, some of which remain polymorphic in Borrelia populations. Among these proteins, OspE, which binds the host complement-regulating factor CFH to evade destruction by complement, is one of the most variable. Yet, what evolutionary forces maintain this polymorphism is not well understood. Motivated by a recent discovery of CFH polymorphism in the bank vole (Clethrionomys glareolus), the main reservoir host of B. afzelii, we hypothesized that the polymorphism is maintained by host-parasite coevolution involving specific associations between host and parasite genetic variants. MethodsWe analyzed associations between bank vole CFH alleles and B. afzelii OspE variants across three datasets sampled in Poland. Selection acting on OspE was evaluated using omegaMap. Host-pathogen genotype associations were tested using partial redundancy analysis (RDA), and co-structure was assessed using co-correspondence analysis (CoCA). ResultsWe found that OspE evolves under positive selection, however, we found no evidence for an association between OspE and host CFH variants at the individual level based on RDA or at the population level based on CoCA. ConclusionsDespite evidence of positive selection acting on OspE, we found no support for specific genetic matching between B. afzelii and its bank vole host at the CFH-OspE interface. These results suggest that the evolution of CFH and OspE may be shaped by broader selective pressures, potentially including interactions with multiple host species.

evolutionary biology↗

bioRxiv2026

Species-specific responses of helminths to temperature and moisture: long-term and multi-scale analyses in a free-living rodent

Parasite infections in wildlife vary across time and space due to interactions among host biology, ecological processes, and climatic variability. Under ongoing climate change, understanding how temperature, precipitation, or humidity influences parasite dynamics is important for predicting shifts in infection patterns and host-parasite interactions. Here, we examine how variation in climatic conditions is associated with helminth infections in a free-living rodent, the bank vole (Myodes glareolus), across 17 years and multiple spatial scales. Using zero-inflated generalised linear models, we quantified the effects of climatic variables on individual parasite burden. Climatic conditions (temperature and humidity or precipitation) affected helminth infections across all analysed scales, though the strength and direction of these effects differed among parasite species and between temporal and spatial scales. In the temporal dataset, parasite load was associated with seasonal variation in weather conditions, whereas in the spatial datasets, infection levels were linked to yearly average climatic variables. The differences reflect species-specific parasites life histories and transmission strategies. Our findings highlight the importance of analysing individual parasite species rather than overall parasite load or aggregated infection indices when assessing the impacts of climatic variation on host-parasite dynamics.

ecology↗

bioRxiv2021

Cytokine gene polymorphism and parasite susceptibility in free-living rodents: importance of non-coding variants

Associations between genetic variants and susceptibility to infections have long been studied in free-living hosts to infer contemporary evolutionary forces shaping genetic polymorphisms of the immunity genes. Despite extensive studies of receptors, such as MHC or TLR, little is known about efferent arm of the immune system. Cytokines are signalling molecules that trigger and modulate the immune response, acting as a crucial link between innate and adaptive immunity. In the present study we investigated how genetic variation in cytokines affects susceptibility to parasitic diseases in bank voles. We focused on three cytokines: tumour necrosis factor (TNF), lymphotoxin alpha (LT), and interferon beta (IFN{beta}1). Two SNPs in LT and two in IFN{beta}1 significantly affected susceptibility to nematodes, and was of them was also associated with susceptibility to microbial pathogen Bartonella. All these variants displayed signatures of selection. One of the variants was synonymous, and one was located in an intron. Our study shows that cytokines are prone to parasite-driven selection, and non-coding variants may play an important role in susceptibility to infections in wild systems.

evolutionary biology↗

bioRxiv2021

Seroprevalence of Toxoplasma gondii among sylvatic rodents in Poland

Toxoplasma gondii is a significant pathogen affecting humans and animals. We conducted seromonitoring for T. gondii in four sylvatic rodent species in Poland. We report an overall seroprevalence of 5.5% (3.6% for Myodes glareolus and 20% for other vole species). Seroprevalence in bank voles varied significantly between host age and sex.

microbiology↗

bioRxiv2020

Impact of Babesia microti on the initiation and course of pregnancy in murine model of vertically transmitted infection

Genus Babesia groups tick-transmitted protozoa causing babesiosis, a malaria-like disease. Vertical transmission of Babesia spp. was reported in mammals, however, the exact timing and mechanisms involved in this mode of transmission are not currently known. In this experimental study we evaluated: 1) the reproductive success, and success of vertical transmission of Babesia microti in mice mated in acute and chronic phases of the infection and in pregnant mice infected during early and advanced pregnancy; 2) possible influence of the pregnancy on the course of parasite infection (parasitaemia) in females; and 3) pathological changes in females and their embryos induced by infection. Blood smears and PCR targeting the 550 bp 18S rRNA gene fragment were used for the detection of B. microti. Histopathological examination was performed on collected tissues. Successful development of pregnancy was recorded only in females in the chronic phase of infection. The success of vertical transmission of B. microti in this group was 63% (71/112). In females mated in the acute phase of infection or on the 4th day of pregnancy, no evidence for pregnancy development were observed. In the group infected on the 12th day of pregnancy, numerous complications including pregnancy loss and stillbirth were recorded. During the acute phase of infection, parasitaemia was lower in pregnant females in comparison to infected, non-pregnant control females. Acute B. microti infection prevents pregnancy initiation and development of pregnancy at a very early stage, and causes severe complication in BALB/c mice in the second and third trimester of pregnancy. Chronic B. microti infection has no negative impact on the initiation and development of pregnancy, but resulted with congenital infections. Further study is required to determine to what extent maternal antibabesial immune responses and potential placental accumulation of parasites contribute to compromised pregnancy in the murine model of congenital Babesia infection. Author summaryThe mouse is the most common mammalian model for studying human parasitic diseases, including malaria, toxoplasmosis, Chagas disease, and babesiosis. Babesiosis is an emerging intraerythrocytic infection caused by protozoal parasites, mostly Babesia microti. Our previous work in murine model proved that vertical transmission of Babesia microti, is a third way - after tick-bite and blood/organ transfusion - to acquire babesiosis. In this study we focused on investigating how the infection influences the course of pregnancy. We were interested in how variations in infection acquisition time and infection phase influence the reproductive success of mice and vertical transmission of parasites. We expected that the infection causes severe pathological changes in the organs of infected females and their offspring. Results obtained in this study have shown that vertical transmission of B. microti was only possible in chronically infected mice, in which health status and reproductive success were not compromised by the infection. Acute infection made successful reproduction impossible, however, the infection had no significant effect on the histopathological condition of tissues. We hope that these insights into B. microti vertical transmission will lead to the better understanding of congenital babesiosis.

pathology↗

bioRxiv2020

Zoonotic viruses in three species of voles (Microtus spp.) from Poland

Rodents are known to be reservoir hosts for a plethora of zoonotic viruses and therefore play a significant role in the dissemination of these pathogens. We trapped three vole species (Microtus arvalis, M. oeconomus and M. agrestis) in N.E. Poland, all of which are widely distributed species in Europe, and, using immunofluorescence assays, we assessed serum samples for the presence of antibodies to hantaviruses, arenaviruses and cowpox viruses (CPXV). We detected antibodies against CPXV and Puumala virus (PUUV), overall seroprevalence of combined viral infections of 18.2% [10.5-29.3] and mostly attributed to CPXV. Antibodies to Tula hantavirus, typical for Microtus voles, are known to cross-react strongly with the PUUV antigen used in PUUV screening, but we detected only one PUUV/TULV cross-reaction in Microtus arvalis (1.3% [0.1-7.9]). We found antibodies against CPXV in all three Microtus spp. Seroprevalence was similar in all vole species. There were no significant differences in seroprevalence between the sexes and among host age categories. Our results contribute to the increasing understanding of CPXV abundance in voles in Europe, and confirm that CPXV circulates also in Microtus spp. voles in NE Poland.

microbiology↗