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Ticks are a significant cause of illness globally. The tick Ixodes ricinus is commonly found across Europe and is a significant vector of Tick-Borne Encephalitis virus (TBEv), Borrelia burgdorferi s.l. (causative agent of Lyme borreliosis), Babesia divergens, Anaplasma phagocytophilum, and several Rickettsia bacteria, among others. The Tick Surveillance Scheme (TSS) administered by the UK Health Security Agency (UKHSA) contains validated reports from the general public of tick encounters over the last twenty years. We modelled the probability of I. ricinus tick presence across England and Wales using the locations of TSS reports from 2013 to 2023 and a combination of biotic and abiotic factors. An ensemble of statistical and machine learning models was trained to classify points as presence (true tick report locations) or background (points generated randomly and by target-group sampling). The ensemble model had a continuous Boyce index of 0.99 and area under the receiver-operator curve (ROC AUC) of 0.84 on out-of-sample 2024 data. Variables relating to roe deer (Capreolus capreolus) distribution and land cover type were most important. Most of southern England, as well as other areas with known tick populations such as the New Forest and the Lake District, are modelled as highly probable tick presence areas. Unstructured citizen science data was suitable for creating a high-performing species distribution model for I. ricinus after addressing spatial and demographic biases. This model is now being used to inform local public health awareness showing the advantage of passive surveillance through to modelling and public health awareness.

Background Free-living ungulates are hosts of ixodid ticks and reservoirs of tick-borne microorganisms in central Europe and many regions around the world. Tissue samples and engorged ticks were obtained from roe deer, red deer, fallow deer, mouflon, and wild boar hunted in deciduous forests of south-western Slovakia. DNA isolated from these samples was screened for the presence of tick-borne microorganisms by PCR-based methods. Results Ticks were found to infest all examined ungulate species. The principal infesting tick was Ixodes ricinus, identified on 90.4% of wildlife, and included all developmental stages. Larvae and nymphs of Haemaphysalis concinna were feeding on 9.6% of wildlife. Two specimens of Dermacentor reticulatus were also identified. Ungulates were positive for A. phagocytophilum and Theileria spp. Anaplasma phagocytophilum was found to infect 96.1% of cervids, 88.9% of mouflon, and 28.2% of wild boar, whereas Theileria spp. was detected only in cervids (94.6%). Importantly, a high rate of cervids (89%) showed mixed infections with both these microorganisms. In addition to A. phagocytophilum and Theileria spp., Rickettsia helvetica , R. monacensis , unidentified Rickettsia sp., Coxiella burnetii , “ Candidatus Neoehrlichia mikurensis”, Borrelia burgdorferi ( s . l .) and Babesia venatorum were identified in engorged I. ricinus . Furthermore, A. phagocytophilum , Babesia spp. and Theileria spp. were detected in engorged H. concinna. Analysis of 16S rRNA and groEL gene sequences revealed the presence of five and two A. phagocytophilum variants, respectively, among which sequences identified in wild boar showed identity to the sequence of the causative agent of human granulocytic anaplasmosis (HGA). Phylogenetic analysis of Theileria 18S rRNA gene sequences amplified from cervids and engorged I. ricinus ticks segregated jointly with sequences of T. capreoli isolates into a moderately supported monophyletic clade. Conclusions The findings indicate that free-living ungulates are reservoirs for A. phagocytophilum and Theileria spp. and engorged ixodid ticks attached to ungulates are good sentinels for the presence of agents of public and veterinary concern. Further analyses of the A. phagocytophilum genetic variants and Theileria species and their associations with vector ticks and free-living ungulates are required.

Ticks prefer specific feeding sites on a host that are influenced by host–tick and tick–tick interactions. This study focused on the spatiotemporal distribution of ticks in Hokkaido sika deer, an important tick host in Hokkaido, Japan. Tick sampling was performed on the sika deer in the Shiretoko National Park between June and October 2022. Ticks were collected from 9 different body parts of the deer to compare their attachment site preferences. Interspecific and intraspecific relationships among ticks were examined using co-occurrence analysis. The collected ticks were nymphal and adult stages of 4 species: Ixodes ovatus , Ixodes persulcatus , Haemaphysalis japonica and Haemaphysalis megaspinosa . Seasonal variations in tick burden were observed, with I. persulcatus and I. ovatus peaking in June and declining towards October; H. japonica showing low numbers in July and August and increasing from September; and H. megaspinosa appearing from September onwards with little variation. Attachment site preferences varied among species, with a significant preference for the pinna in I. ovatus and I. persulcatus . Haemaphysalis japonica was mainly found on the body and legs between June and August, and shifted to the pinna from September. Haemaphysalis megaspinosa showed a general preference for areas other than the legs. Co-occurrence analysis revealed positive, negative and random co-occurrence patterns among the tick species. Ticks of the same genus and species exhibited positive co-occurrence patterns; I. ovatus showed negative co-occurrence patterns with Haemaphysalis spp. This study revealed the unique attachment site preferences and distinct seasonal distributions of tick species in the Hokkaido sika deer.

Within the research conducted in the years 2016–2022 in the area of Volovsky Mountains in Slovakia, 63,950 biting midges were collected during 74 trapping sessions. The aim of the study was to identify species composition of biting midges, their host preference and potential transmission of parasites by these insects under natural conditions. The collected biting midges fell into 29 species and the most common were the Culicoides ( C. obsoletus / C. scoticus / C. montanus ) that accounted for 47.9% of the collected biting midges. Identification of species was based on the morphology of biting midges and the use of molecular methods. We confirmed positive suckling results on red deer in three samples namely C. montanus , C. scoticus and C. deltus . We examined these samples for the presence of Onchocerca worm DNA. We confirmed the presence of O. flexuosa DNA in one C. deltus sample. The host preference of biting midges was identified by molecular technique that involved sequencing a 350-bp sequence of the mitochondrial cytochrome b gene (cyt b). The presence of Onchocerca flexuosa DNA in C. deltus was confirmed by sequencing of fragments of mitochondrial genes cox1. The sequences matched the previously published sequences for O. flexuosa . Data on high prevalence of infections caused by Onchocerca worms in red deer in Slovakia have already been published and indicated favourable conditions for the vectors and a suitable environment for parasite circulation in Slovakia. According to the authors’ knowledge, this was the first ever detection of O. flexuosa in C. deltus in wild nature.

Exsheathment is crucial in the transition from free-living to parasitic phase for most strongyle nematode species. A greater understanding of this process could help in developing new parasitic control methods. This study aimed to identify commonalities in response to exsheathment triggers (heat acclimation, CO 2 and pH) in a wide range of species ( Haemonchus contortus , Trichostrongylus spp., Cooperia spp., Oesophagostomum spp., Chabertia ovina , and members of the subfamily Ostertagiinae) from sheep, cattle and farmed deer. The initial expectation of similarity in pH requirements amongst species residing within the same organ was not supported, with unexpected pH preferences for exsheathment of Trichostrongylus axei , Trichostrongylus vitrinus , Trichostrongylus colubriformis and Cooperia oncophora. We also found differences between species in their response to temperature acclimation, with higher exsheathment in response to heat shock observed for H. contortus , Ostertagia ostertagi , T. axei , T. vitrinus and Oesophagostomum sikae . Furthermore, some species showed poor exsheathment under all experimental conditions, such as Cooperia curticei and the large intestinal nematodes C. ovina and Oesophagostomum venulosum . Interestingly, there were some significant differences in response depending on the host from which the parasites were derived. The host species significantly impacted on the exsheathment response for H. contortus , Teladorsagia circumcincta, T. vitrinus and T. colubriformis . Overall, the data showed variability between nematode species in their response to these in vitro exsheathment triggers, highlighting the complexity of finding a common set of conditions for all species in order to develop a control method based on triggering the exsheathment process prematurely.

Our analysis covers 122 scientific publications about health issues in free-ranging Neotropical ungulates produced between 1990 and 2022, with an emphasis on the epidemiology of infectious diseases and parasites. Most studies focus on parasitology (43.4%) and bacteriology (15.6%), while body condition (0.8%), toxicology (1.6%), virology (6.6%), and health assessments (6.6%) are less studied. Brocket deer (Mazama americana and M. gouazoubira), followed by peccaries (Pecari tajacu and Tayassu pecari), and the lowland tapir (Tapirus terrestris) were the most frequent species surveyed (61.4% of all publications). We detected considerably higher numbers of studies and health topics covered in Brazil (n = 64; 52.5% of the total) compared to other Latin American countries. We emphasize the need for further research focused on poorly known health aspects of Neotropical ungulates that have received little attention in the past, especially the Chacoan peccary (Catagonus wagneri), taruca deer (Hippocamelus antisensis), Northern pudu (Pudu mephistopheles), and the least known Mazama species. Ecotoxicology and pathology studies are necessary to evaluate the impact of agrochemicals and other human disturbances on Neotropical ungulate populations in the wild. We encourage further research on the human impacts and trends of change in the epidemiology of infectious diseases, parasites, and health status of Neotropical wild ungulate populations.

To assess the role of white-tailed deer ( Odocoileus virginianus , WTD) in the epidemiology of toxoplasmosis, we conducted a national survey of WTD across the USA for Toxoplasma gondii infection. To do this, we combined serology with parasite isolation to evaluate the prevalence and genetic diversity of T. gondii in this game species. From October 2012 to March 2019, serum and tissues were collected from 914 WTD across the USA. Serum samples were screened for antibodies to T. gondii , and then the tissues of seropositive WTD were bioassayed in mice. Antibodies were detected in 329 (36%) of 914 WTD tested by the modified agglutination test (positive reaction at 1:25 or higher). Viable T. gondii was isolated from the heart of 36 WTD from 11 states. Three of the 36 isolates were pathogenic but not highly virulent to outbred Swiss Webster mice and all 36 isolates could be propagated further in cell culture and were genotyped. For genotyping, DNA extracted from cell culture-derived tachyzoites was characterized by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) using the genetic markers SAG1, SAG2, SAG3, BTUB, GRA6, c22-8, c29-2, L358, PK1 and Apico. Genotyping revealed seven ToxoDB PCR-RFLP genotypes, including 24 isolates for genotype #5 (haplogroup 12), four isolates for #2 (type III, haplogroup 3), three isolates for genotypes #1 (type II, haplogroup 2), two isolates for genotypes #3 (type II, haplogroup 2) and one isolate each for #39, #221 and #224. Genotype #5 was the most frequently isolated, accounting for 66.6% (24 of 36) of the isolates. Combining the 36 isolates from this study with previously reported 69 isolates from WTD, 15 genotypes have been identified. Among these, 50.4% (53/105) isolates belong to genotype #5. Our results indicate moderate genetic diversity of T. gondii in WTD. The results also indicate that undercooked venison should not be consumed by humans or fed to cats.

Background Plasmodium odocoilei , the only nonhuman Plasmodium parasite of native mammals in North America, infects white-tailed deer (WTD) throughout the eastern USA. Although deer malaria is not a significant cause of disease in healthy deer, infection with P. odocoilei may increase susceptibility to infection with and mortality due to epizootic hemorrhagic disease virus in deer fawns. The incrimination of the vector(s) of deer malaria is an essential step in developing management plans for reducing the incidence of deer malaria. Methods At a deer farm in Gadsden County, FL, with previously documented evidence of deer malaria transmission, mosquitoes were collected using carbon-dioxide-baited light traps, aspirators, and resting shelters. White-tailed deer host use and P. odocoilei infection rates were quantified in potential vector mosquito samples using polymerase chain reaction and Sanger sequencing. Results Diverse mosquito species ( n  = 38) were active at the deer farm. Four mosquito species or species complexes specialized in feeding on WTD were observed, taking at least 75% of blood meals from this one host species: Anopheles quadrimaculatus s.l. (88.9%), Anopheles punctipennis (83.3%), Anopheles crucians s.l. (81.4%), and Culex erraticus (87.7%). The highest infection rate of P. odocoilei was found in An. quadrimaculatus s.l. (4.1%), followed by An. punctipennis (3.1%), and An. crucians s.l. (0.47%). No other mosquito species were found to be infected with P. odocoilei . Conclusions Anopheles quadrimaculatus s.l., An. punctipennis , and An. crucians s.l. met three of the criteria for vector incrimination. These species were present in areas inhabited by WTD, specialized in feeding on WTD, and were naturally infected with P. odocoilei . Anopheles quadrimaculatus s.l. and Anopheles punctipennis are the most likely natural vectors of deer malaria in Florida, as indicated by their high percentages of WTD blood meals (> 83%) and relatively high infection rates (> 3%). To fully incriminate the vector(s) for P. odocoilei , laboratory vector competence studies are needed to determine their ability to biologically transmit the parasites. Graphical Abstract

Lyme disease is the most prevalent vector-borne disease in North America, and both the annual incidence and geographic range are increasing. The emergence of Lyme disease has been attributed to a century-long recovery of deer, an important reproductive host for adult ticks. However, a growing body of evidence suggests that Lyme disease risk may now be more dynamically linked to fluctuations in the abundance of small-mammal hosts that are thought to infect the majority of ticks. The continuing and rapid increase in Lyme disease over the past two decades, long after the recolonization of deer, suggests that other factors, including changes in the ecology of small-mammal hosts may be responsible for the continuing emergence of Lyme disease. We present a theoretical model that illustrates how reductions in small-mammal predators can sharply increase Lyme disease risk. We then show that increases in Lyme disease in the northeastern and midwestern United States over the past three decades are frequently uncorrelated with deer abundance and instead coincide with a range-wide decline of a key small-mammal predator, the red fox, likely due to expansion of coyote populations. Further, across four states we find poor spatial correlation between deer abundance and Lyme disease incidence, but coyote abundance and fox rarity effectively predict the spatial distribution of Lyme disease in New York. These results suggest that changes in predator communities may have cascading impacts that facilitate the emergence of zoonotic diseases, the vast majority of which rely on hosts that occupy low trophic levels.

Helminths are common parasites of wild ungulates that can have substantial costs for growth, mortality and reproduction. Whilst these costs are relatively well documented for mature animals, knowledge of helminths' impacts on juveniles is more limited. Identifying these effects is important because young individuals are often heavily infected, and juvenile mortality is a key process regulating wild populations. Here, we investigated associations between helminth infection and overwinter survival in juvenile wild red deer (Cervus elaphus) on the Isle of Rum, Scotland. We collected fecal samples non-invasively from known individuals and used them to count propagules of 3 helminth taxa (strongyle nematodes, Fasciola hepatica and Elaphostrongylus cervi). Using generalized linear models, we investigated associations between parasite counts and overwinter survival for calves and yearlings. Strongyles were associated with reduced survival in both age classes, and F. hepatica was associated with reduced survival in yearlings, whilst E. cervi infection showed no association with survival in either age class. This study provides observational evidence for fitness costs of helminth infection in juveniles of a wild mammal, and suggests that these parasites could play a role in regulating population dynamics.