Ticks and Tick-borne Diseases

Rift Valley fever (RVF) is a zoonotic arboviral disease that causes adverse pregnancy outcomes and high mortality in domestic and wild ruminants. The disease is caused by the RVF virus (RVFV), which is transmitted by mosquitoes from several genera, mainly Aedes and Culex. However, whether ruminants can become infected by horizontal virus transmission remains unclear. In addition, how the route of RVFV inoculation may influence RVF pathogenesis and the host immune response in animals is still largely unknown. With this aim, we conducted a comparative experimental study in which young sheep were either inoculated subcutaneously (SC) or intranasally (IN) with the virulent RVFV 56/74 strain. We then evaluated disease dynamics, viremia, virus excretion, tissue damage, and the humoral immune response. We also aimed to determine whether RVFV can be transmitted from infected to in-contact animals, and to assess whether the inoculation route may influence virus excretion and the likelihood of subsequent horizontal transmission. The results showed that SC inoculated sheep had a shorter incubation period, an earlier onset of viremia, and an earlier seroconversion. In contrast, IN inoculated animals developed higher rectal temperatures, reached higher peak viremia, and developed a more robust neutralizing antibody response. They also exhibited increased concentrations of analytes indicative of moderate but more severe hepatic injury compared with the subcutaneous group, along with more pronounced histopathological damage in the central nervous system. These results demonstrate the influence of the route of inoculation on RVF pathogenesis and the host immune response. Our results also confirmed the horizontal transmission of RVFV between SC inoculated sheep and in-contact animals housed in the same room, a phenomenon not observed in the IN inoculated group. This finding underscores the influence of the inoculation route on virus transmission and the potentially significant role of horizontal transmission in RVF epidemiology and disease control. Author summaryAccording to the World Health Organization (WHO), RVFV is considered a priority pathogen due to its ability to strain animal and public health systems, especially in developing countries. RVF outbreaks have occurred across most of Africa and, since 2000, in the Arabian Peninsula. Evidence of RVFV circulation in North Africa further highlights the threat to Europe, where competent mosquito vectors are present. How the inoculation route shapes disease dynamics and hosts immunity is still largely unknown. Similarly, whether the virus can spread between infected and non-infected animals without competent vectors remains unclear. A comparative infection in which young sheep were inoculated SC or IN with the RVFV 56/74 strain showed that SC inoculated sheep had a shorter incubation period, an earlier onset of viremia, and earlier seroconversion. However, rectal temperature and peak viremia were higher in IN inoculated sheep, which also showed evidence of moderate but more severe hepatic damage, accompanied by greater central nervous system damage. Only the in-contact animals housed in the subcutaneous group became infected, demonstrating horizontal transmission. Our results show that the route of inoculation influences disease progression and that RVFV can be transmitted among sheep in the absence of mosquitoes.

AO_SCPLOWBSTRACTC_SCPLOWOrnithodoros phacochoerus are nidicolous soft ticks of the Ornithodoros moubata complex of species known to be vectors of the African swine fever (ASF) virus. These Ornithodoros ticks depend on endosymbionts to produce essential nutrients necessary for their development. However, endosymbionts are only a part of the complex microbiota hosted by the tick. This microbiota often includes primary or secondary endosymbionts, commensal species from the environment, and, most of the time, some pathogens. The present study was performed to understand the organization and spatial distribution of the microbiota of O. phacochoerus. One of the objectives was to investigate if the pathogen of interest (ASF virus) is involved in the organization of the microbiota through pathogen-induced dysbiosis or other interactions. For this purpose, 704 O. phacochoerus ticks were collected from two conservation areas in Mozambique. Sequencing was performed targeting the V3-V4 region of the 16S rRNA gene, and the resulting dataset was processed using FROGS to characterize the bacterial microbiota hosted by the ticks. The results indicate that the microbiota of Ornithodoros phacochoerus contains very low bacterial diversity, with one primary endosymbiont (Francisella-like endosymbiont), one potential secondary endosymbiont (Rickettsiella), and very few environmental or pathogenic bacterial species. We found a clear spatial structure of the microbiota, with ticks from the same sampling site showing similar patterns. On the contrary, no association with the infectious status for African swine fever virus was detected, suggesting that this pathogen does not shape Ornithodoros microbial communities. Our results on tick - microbiota - pathogen - environment interactions in nidicolous soft ticks, showed patterns that differ from most hard tick studies.

Tick-borne pathogens are transmitted by tick bites to cause infectious diseases in humans and domestic animals. To anticipate the occurrence of tick-borne diseases, it is required to understand high resolution distribution of infection risk and associated ecological factors. The aim of the present study is to reveal the spatial distribution of ticks and ticks infected with pathogens in central Hokkaido, Japan. Adult and nymphal ticks were collected with a constant effort at 171 sites from 13 May to 26 June 2024, followed by screening tick-borne pathogens. The potential suitable habitats of seven tick species and the endemic tick-borne pathogens in the study area (i.e. tick-borne encephalitis virus, Yezo virus, Beiji nairovirus, Lyme disease group borreliae, and relapsing fever group borreliae) were predicted using ecological niche modeling. Ixodes persulcatus and Ixodes ovatus were identified as the primary ticks to determine the distributions of all the pathogens. Besides, the predicted suitable habitats were specific to each pathogen/tick species. Among the environmental variables considered for modeling, snow depth appeared to significantly contribute to the distribution differences between ticks and pathogens. The findings of this study expand our understanding of the spatial risk distribution of tick-borne pathogen infections and its ecological context.

AimTo resolve the topological branching patterns, the timing of demographic events, and the effective population size changes associated with major demographic events. LocationMidwestern (eastern North Central) and Northeastern USA TaxonBlacklegged tick, Ixodes scapularis (Say, 1821) MethodsUsing three independent genomic datasets, single-nucleotide variants were analyzed for demographic inference. Maximum likelihood topologies and prior ecological knowledge were used to generate nested demographic hypotheses. The best-fit scenario and the associated demographic parameter estimates were determined using approximate Bayesian computation under a random forest statistical model. The topologies and parameters supported in the three independent datasets were compared to generate insights about the demographic history of blacklegged ticks in the region. ResultsThe emergence of extant northern populations of blacklegged ticks began between 10-15 k.y.a. (thousand years ago), with independent population splits from the common ancestor during the Early-Mid-Holocene, and never more recent than 4 k.y.a. All populations sustained moderately large population sizes without bottlenecks, with Michigan as the exception. Michigan appears to have an uncertain placement that depends on sampling, reflecting its admixed origin. Main conclusionsThere are multiple populations of northern blacklegged ticks that have persisted independently as deglaciated regions in the northern U.S. were recolonized following the Last Glacial Maximum (26.5 to 19 k.y.a.). The current ecological expansions across the northern U.S. are likely seeded by separate relictual populations with distinctive genomic ancestry rather than a range expansion from a single source, with important implications for vector-borne disease management.

Ehrlichia canis is primarily a Rhipicephalus sanguineus tick-borne rickettsial pathogen initially identified as causing canine monocytic ehrlichiosis, and infections in people have also been reported in Venezuela, Mexico, and parts of Europe. It is of high importance to have a vaccine suitable in protecting the canine host, which will aid in lessening E. canis infections also in people. Gene inactivation mutations in the phage head-to-tail connector protein genes (phtcp) from E. chaffeensis and A. marginale caused attenuated growth, and prior infection with the mutated bacteria induced protective immunity against wild-type bacterial infections in natural hosts, independent of blood-borne infection or tick-transmission infection. In the current study, we describe the development of targeted mutagenesis for the first time in E. canis genome and with a novel modification to avoid introducing antibiotic resistance cassettes to delete the phtcp ortholog from E. canis. The mutated E. canis was then assessed for its in vivo growth and the induction of host immunity exerted following the mutant infection aiding to protect against wild-type infection challenge in the canine host. We assessed systemic pathogen loads, hematological parameters, IgG immune responses, and plasma cytokines following the mutant infection relative to uninfected dogs. Similarly, the assessments were carried out following wild-type pathogen infections in dogs with or without prior mutant infection challenges. The study demonstrates that prior infection of dogs with the mutant induces immunity to prevent infection establishment by wild-type E. canis. Similarly, the mutant infection resulted in clear biological differences compared to the wild-type infection. This study establishes that the molecular genetic methods are broadly applicable to pathogens belonging to the family Anaplasmataceae and that the modified live vaccines with phtcp gene orthologs are valuable in reducing the diseases caused by the tick-borne rickettsial pathogens belong to Anaplasmataceae, including E. canis.

Filoviruses, particularly Ebola virus (EBOV), remain a major public health concern in Central Africa. However, their circulation in wildlife during inter-epidemic periods remains poorly documented. Non-human primates (NHPs) may serve as ecological sentinels of viral dynamics at human-forest interfaces, yet surveillance is constrained by the limitations of invasive sampling. We conducted a non-invasive investigation of EBOV exposure in free-ranging NHPs from the Mabali Forest Reserve (Equateur Province, Democratic Republic of Congo) for Ebola virus disease. A total of 630 fecal samples were collected and screened for active infection by PCR targeting the EBOV nucleoprotein gene; all samples tested negative. Molecular identification of host species was achieved in 569 samples (90.3%). Fecal serology using an automated capillary western blot platform (JESS), targeting EBOV nucleoprotein, glycoprotein and viral protein 40 antigens, identified four seropositive individuals (0.70%), including two Cercopithecus ascanius and two C. wolfi. The detection of discrete immunoreactive bands consistent with EBOV-specific antibodies suggests prior exposure despite the absence of active outbreaks. These findings provide the first serological evidence compatible with EBOV exposure in these two Cercopithecus species and support the hypothesis of low-level or cryptic viral circulation in forest ecosystems. The study highlights the feasibility and value of fecal serology as a non-invasive One Health surveillance tool for monitoring zoonotic pathogens at wildlife-human interfaces.

Zoos may serve as sentinel sites for zoonotic vector-borne diseases. West Nile virus (WNV) and Usutu virus (USUV) are closely related orthoflaviviruses transmitted between Culex mosquitoes and a bird reservoir. Both viruses can also infect mammals, including humans, where they may cause symptoms and, more rarely, hospitalization and death. However, serological cross-reactivity between WNV and USUV complicates their differential diagnosis. Here, we aimed to reconstruct the dynamics of emergence of WNV in a zoo located in a newly affected area in Europe, using ELISA and Virus Neutralization Test (VNT) serological analysis of 1707 animal sera collected between 2015 and 2024. Combining this data in a model accounting for cross-reactivity with USUV, we estimated yearly forces of infection (FOI) by both viruses, and thus found that WNV likely circulated in the area one year prior to the first cases reported to the passive surveillance system. Our results also showed that, in the zoo, mammals and reptiles had a lower risk of infection than birds (relative risk of 0.14 [0.05; 0.28]), and that the exposure of birds to water (aquatic lifestyle or proximity to stagnant water) affected the risk. Finally, we estimated diagnosis parameters, including the sensitivity of the VNT (80.4% [76.5%; 84.3%]), the expected VNT titer value, and the level of serological cross-reactivity between viruses during the VNT. To conclude, our modelling framework allowed to disentangle the co-circulation of two closely related viruses, a crucial point in ensuring the reliable sentinel surveillance of these vector-borne zoonotic pathogens.

BackgroundTegumentary leishmaniasis (TL) caused by Leishmania infantum has re-emerged in northern Italy, raising questions about the genetic diversity and population structure of circulating parasites and their potential role in shaping different clinical outcomes. Methodology/Principal findingsMultilocus microsatellite typing (MLMT) based on 15 polymorphic loci was applied to 44 L. infantum strains obtained from TL cases diagnosed between 2013 and 2024 in the Emilia-Romagna region. These strains were compared with sympatric isolates from VL cases, dogs and sand flies. MLMT revealed a considerable genetic variation among TL-associated strains, with 43 distinct multilocus genotypes identified. Population structure analyses using Bayesian clustering, multivariate approaches and phylogenetic reconstruction consistently identified three highly differentiated genetic populations (Fst >0.25). TL strains were divided into two main populations: one shared with VL-associated strains (PopB; 9/44) and a second population found exclusively among TL cases (PopC; 28/44). In contrast, the canine-associated population (PopA) showed no overlap with TL cases in this region. Populations also displayed divergent heterozygosity patterns, as indicated by positive and negative Fis values. Conclusions/SignificanceThese findings revealed previously unknown diversity within L. infantum in the study area and demonstrated that inclusion of tegumentary strains is essential to uncover hidden components of parasite population structure. The identification of a TL-associated population supports the existence of multiple evolutionary pathways and emphasises the importance of integrated One Health surveillance, which combines data from humans, animal hosts and vectors to improve understanding of the epidemiology of leishmaniasis in Italy. Author summaryLeishmania infantum is a parasite transmitted to humans through the bite of infected insect vectors. It can cause different forms of leishmaniasis, ranging from a systemic disease known as visceral leishmaniasis to a less common form that affects the skin and mucous membranes, called tegumentary leishmaniasis. Dogs are the main reservoir of the parasite and play a key role in maintaining its circulation in endemic areas. In recent years, cases of tegumentary leishmaniasis have re-emerged in northern Italy. This unexpected increase has raised questions about how the parasite is spreading and whether genetic differences among the parasites could explain these new patterns. To explore this, we examined parasitic DNA obtained from tegumentary leishmaniasis cases and compared it with DNA from patients with visceral leishmaniasis, from dogs and insect vectors from the same area. By examining multiple genetic markers, we found that parasites causing the tegumentary form of the disease are genetically diverse and belong to different groups. Notably, one parasite group was found only in cases of tegumentary leishmaniasis and not in visceral infections nor in infected dogs, suggesting that some parasite lineages may be more closely associated with skin and mucosal disease. Overall, our findings show that studying parasites from cutaneous and mucosal lesions provides important information that would otherwise remain hidden. By combining data from humans, animals and insect vectors, our study highlights the importance of integrated surveillance systems for improving our understanding of disease spread and supporting effective public health strategies.

Vector-borne diseases represent a growing public health issue nationwide. Nebraska reports a sustained burden of mosquito-borne diseases and expanding tick-borne disease risk. This study aims to assess trends in vector abundance, vector infection rates, and human vector-borne disease reports using retrospective surveillance data and to examine the relationship between vector factors and human risk across the state. Vector abundance and pathogen infection rates were mapped alongside presence and incidence of key vector-borne diseases. Mosquito surveillance and mosquito-borne disease data were available from 2012-2024, while tick surveillance and associated tick-borne disease data were available from 2021-2024. Statistical models and comparative tests were used to explore associations between vector factors and disease reports. Overall, the current vector-borne disease surveillance suggests that mosquito-borne disease remains the primary concern in Nebraska, with notable geographic variation in mosquito species distribution and human cases. Tick surveillance indicates established populations of clinically relevant tick species in distinct regions of the state, with pathogen detections generally aligning with areas where human cases have been reported. Differences in the level of human case reporting and data availability affected interpretation of long-term trends and limited strong conclusions regarding direct relationships between vector factors and human disease. Nebraska maintains comprehensive vector-borne disease surveillance systems that support understandings of vector abundance, vector pathogen infection rates, and human risk. Continued integration of entomological surveillance with human case information may help clarify patterns of vector-borne disease risk and inform efforts to address current and emerging threats in Nebraska.

BackgroundTreatment response in canine leishmaniosis is driven by the dog host, the Leishmania parasite, and pharmacological factors, with drug resistance increasingly undermining the effectiveness of therapy. A direct quantitative PCR test (LeishGenR) was applied to 104 clinical samples from 95 dogs in the Mediterranean area diagnosed with leishmaniosis in veterinary clinical settings and testing positive for Leishmania infantum by PCR. The assay enabled rapid detection of genetic drug-resistance biomarkers for allopurinol (metk), meglumine antimoniate (mrpa), and miltefosine (LdMT), providing a clinically relevant, timely alternative to culture-based approaches by directly analyzing circulating Leishmania infantum amastigotes. ResultsThe assay (LeishGenR) showed high specificity (100%) and sensitivity (>87.5%) for genetic drug-resistance profile assignment and a strong correlation with whole-genome sequencing for gene copy number assessment (metk: r = 0.878; mrpa: r = 0.943 and LdMT = 0.691). Genetic drug-resistance biomarkers were detected in 24.3% of L. infantum DNA from clinical samples analyzed (20/82; 95% CI 16.3-34.6)), most commonly for allopurinol (13.4%; 95% CI 7.6-22.4), then meglumine antimoniate (9.4%; 95% CI 4.6-18.2), and for miltefosine (5.4%; 95% CI 1.8-14.8). Prevalence was higher in dogs previously treated for leishmaniosis. ConclusionThis study demonstrates the ability to detect genetic biomarkers of drug resistance in L. infantum directly from clinical samples of dogs with leishmaniosis. This method enables rapid, precise detection of genomic biomarkers, circumventing delays associated with culture-based methods and supporting more effective clinical management and surveillance. Among dogs with high parasitemia referred to clinics in Mediterranean regions sampled in this study, the findings reveal a significant prevalence of circulating L. infantum strains carrying genomic drug resistance biomarkers to standard treatments for canine leishmaniosis.

Three molecularly undescribed filarial species were co-detected, while screening animals for Brugia malayi, the agent of lymphatic filariasis. Single microfilariae (Mf) isolated from blood samples of crab-eating macaques (Macaca fascicularis) from Belitung, Indonesia, and from pet dogs and cats in Sabah, Malaysia, were analyzed. Among 163 macaques, 33 (20.2%) were positive for large Mf (mean length 498.9 {micro}m) similar to Dirofilaria ( Belitung I). One macaque was infected with small Mf (mean length 150.4 {micro}m) ( Belitung II), with a high density of 17,150 Mf/mL. In two cats co-infected with B. malayi, Mf of a Dirofilaria species ( Sabah) with an average length of 299.1 {micro}m were detected. Morphometric analysis of Mf showed distinct differences between these three species and other Mf described in the area. Whole genome amplification and genome sequencing of 24 individual Mf enabled phylogenetic analysis of mitochondrial genomes, and analysis of specific mitochondrial and nuclear barcode regions. The three Mf groups formed distinct clusters and did not match any currently available reference sequence. Cluster Belitung I from macaques formed a sister group to all other Dirofilaria. Cluster Belitung II included bird filariae and primate filariae of the genus Mansonella as close relatives. The cluster Sabah formed a monophyletic group with the zoonotic species D. asiatica and Dirofilaria sp. Thailand. DNA of Wolbachia endobacteria was detected in Mf of Belitung I and Sabah, but not in Belitung II. These findings highlight the limited understanding of filarial diversity in macaques and cats in Asia and underscore the need for a more comprehensive approach that combines morphological and molecular data to identify and assess the pathogenicity and zoonotic potential of these parasites. Author summaryFilarial worms are parasitic nematodes that infect humans and animals and are often transmitted by the same vector mosquito. We identified three molecularly undescribed filarial species while investigating animals as reservoirs for the agent of lymphatic filariasis, Brugia malayi on Belitung Island, Indonesia, and in Sabah, Malaysia. Blood samples were collected from Indonesian macaques and Malaysian pet cats. Out of 163 macaques, 20.2% tested positive for exceptionally large microfilariae (Mf) of an unclassified Dirofilaria-like species (Belitung I). Another filarial species ( Belitung II) with very small Mf, but with a remarkably high density of 17,150 Mf/mL was detected in one macaque. Two cats harbored medium sized Mf of a Dirofilaria species (Sabah). Genetic analysis revealed unique phylogenetic clusters that did not match any reference sequence. Dirofilaria sp. Sabah was closely related to the zoonotic D. asiatica complex, whereas Belitung I clustered as a sister group to Dirofilaria. Belitung II Mf clustered next to but not within the Mansonella spp. cluster. DNA of Wolbachia endobacteria was only detected in Mf of Belitung I and Sabah. These findings highlight the limited understanding of filarial diversity in animals and underscore the need for a comprehensive approach that combines morphological and molecular data to identify and assess the pathogenicity and zoonotic potential of these parasites.

Dengue transmission is strongly influenced by climatic conditions that affect mosquito population dynamics and virus circulation. In Southern Brazil, where dengue historically occurred at low levels, recent climatic anomalies may be contributing to the expansion of Aedes vectors and an increase in local dengue incidence. This study investigated the spatiotemporal association between climatic variables, Aedes mosquito infestation and dengue cases in Porto Alegre (Southern Brazil, 2018 to 2025). Entomological, surveillance and climatic data were analyzed using Morans I and LISA for spatial association, Kendall correlation, polynomial regression and LASSO to identify relevant drivers and develop predictive models of mosquito infestation and dengue incidence. A strong spatial association between Aedes aegypti and Aedes albopictus was observed, with persistent local clusters detected across all years. Annual climatic variables were associated with mosquito abundance in several districts. Overall, rainfall frequency had a stronger effect on Aedes aegypti abundance than accumulated rainfall. Temperature and lagged infestation indices showed strong association with both species and dengue incidence, with effects observed up to four weeks prior. Predictive models demonstrated good agreement between observed and predicted values, particularly within low to moderate infestation levels. Lagged variables were consistently retained in both mosquito infestation abundance and dengue incidence models, highlighting the importance of temporal predictors for anticipating vector dynamics and dengue risk. This approach is generally applicable for predicting Aedes infestation and disease incidence and emphasizes the importance of integrating entomological and climatic surveillance data to improve anticipation and detection of dengue risk periods and support more effective public health interventions.

Chronic Wasting Disease (CWD) is a transmissible spongiform encephalopathy (TSE) of cervids (elk, deer, moose, and reindeer) that is increasing in prevalence and expanding to new geographical areas. TSEs, commonly referred to as prion diseases, are fatal neurodegenerative diseases that occur in a variety of mammals, including humans, and typically exhibit species-specific characteristics. This study reports the sequencing of the prion protein gene (PRNP) in retropharyngeal lymph node samples from 358 Montana mule deer (Odocoileus hemionus) and the identification of 36 PRNP genetic variants, many of which have not been reported previously. Further investigations tracked spatiotemporal characteristics of variants to hunting districts, year of harvest, and CWD status. PRNP polymorphisms V12F, D20G, R40Q, and S225F were examined with EmCAST computational predictions to determine the relationship between sequence and structural variations providing further insights into mechanisms affecting CWD outcomes. EmCAST predictions suggest the novel variant V12F phenotype is attributable to functional changes such as altered protein-protein interactions that might be linked to the CWD positive status of the samples. Notably, the analysis of S225F by EmCAST predicted that S225F is a neutral mutation for folded PrP and incompatible with fibril PrP, suggesting a potential structural mechanism for why this previously known variant may provide protection against CWD based on reduced fibril PrP formation. The CWD-positive samples harboring PRNP variants were examined with the prion RT-QuIC assay, including the novel variant V12F, which resulted in prion seeding activity. Author SummaryChronic Wasting Disease (CWD) is a fatal disease of cervids, which include deer, elk, and moose. Since its discovery in 1967, CWD has spread to 36 U.S. states and four Canadian provinces, with prevalences exceeding 20% in select free-ranging populations. With the popularity of hunting big game animals and the role of these species in the ecosystem, concerns have arisen regarding the transmission of disease to humans, as well as how to mitigate long term consequences of disease on animal populations. Given the significant risk of species spillover and the limitations of current management, innovative genetic research is essential. Our study identified novel PRNP genetic variants in Montana mule deer, cataloging their regional distribution and CWD status across several hunting seasons. By investigating the impact of these polymorphisms on protein stability and seeding activity, we provide critical insights into the genetic factors that influence disease phenotypes and transmissibility in wild cervid populations.

Background Venezuelan haemorrhagic fever (VHF), caused by Guanarito virus (GTOV), is a zoonotic disease endemic to the western plains of Venezuela. Despite decades of recognition, its epidemiology and clinical profile remain poorly characterised. Methodology We analysed individual level data from standardised case report forms submitted to the Venezuelan National Epidemiological Surveillance System between 2017 and 2024 for suspected VHF cases in Barinas, Apure, and Portuguesa. Demographic, clinical, and laboratory variables were examined to characterise temporal and geographical patterns and to define the clinical profile of VHF compared with endemic arboviral infections. Principal Findings Among 480 suspected cases, 72 (15.0%) were laboratory confirmed GTOV infections. Confirmed cases occurred predominantly in men engaged in agricultural or service related occupations, with the highest prevalence among individuals aged 46 to 90 years. A marked seasonal pattern was observed, with most cases occurring between September and January. The most frequently reported symptoms included headache, haemorrhage, sore throat, and diarrhoea. Compared with other endemic arboviral infections, GTOV was more strongly associated with headache, myalgia, sore throat, haemorrhage, and abdominal pain, delineating a distinct clinical phenotype relative to diseases caused by encephalitic alphaviruses, chikungunya virus, dengue virus, and Zika virus. The case fatality ratio among laboratory confirmed cases was 36.1% (95% CI: 25.1 to 48.3). GTOV infection was independently associated with mortality (adjusted relative risk [aRR] 3.66; 95% CI 2.28 to 5.87; p < 0.001), underscoring its substantial clinical severity. Conclusion GTOV remains endemically transmitted in western Venezuela, disproportionately affecting older men engaged in agricultural and service related occupations. Its seasonality and clinical phenotype, characterised by haemorrhage, sore throat, and gastrointestinal symptoms, highlight the need for clinical awareness and improved differential diagnosis, particularly in remote endemic settings with limited access to laboratory testing.

In 2025 Guinea was validated as achieving elimination as a public health problem for the highly pathogenic, vector-borne infection, gambiense human African trypanosomiasis (gHAT) after reaching several years of low-level case reporting. gHAT cases in Guinea have overall seen a large decrease between 2000 and 2024, however there have been notable fluctuations. Transmission modelling was used to assess these trends in observed cases for the foci Boffa East, Boffa West, Dubreka, and Forecariah and evaluate transmission changes. This study quantifies the impact of interruptions due to Ebola and the introduction of new interventions (particularly the rapid diagnostic tests in the passive health system and vector control) in each focus. The model suggests that transmission of gHAT has fallen 97% (83-100%) between 2000 and 2024, with disease burden measured in disability-adjusted life years (DALYs) reduced by 94% (63-100%). We estimated that Ebola interruptions caused an additional 1,147 gHAT DALYs due to the suspension of gHAT activities, however passive screening improvements and the introduction of vector control likely averted 1,719 and 9,038 DALYs respectively. This study quantifies the impact of Ebola related interruptions on gHAT transmission and disease burden and highlights the success of medical and vector control interventions in Guinea.

BackgroundLeishmaniasis is endemic in southern Europe with high risks of outbreaks and geographical spread. However, the risk factors for human leishmaniasis are understudied in this region. MethodologyTo evaluate these risk factors, we tested associations between leishmaniasis incidence and an array of variables related to socioeconomics, immunocompetence, climate, land use, biodiversity, and ecology (i.e., the pathogen and its vectors and reservoirs). FindingsSocioeconomic factors, such as demography, occupation, and housing conditions, were strongly associated with leishmaniasis incidence in endemic regions. The specific factors and the magnitude of their impacts varied among the five countries studied. Human immunosuppressive condition was highly correlated with leishmaniasis risk in Spain and Italy. Climate likely delineated leishmaniasis-free regions from endemic regions in France. Our results suggest that climate change alone may not drive the spread of leishmaniasis within this century. Pathogen hazard and reservoir abundance affected leishmaniasis risk more than vector hazard in countries where data were available. Biodiversity was weakly, negatively related to leishmaniasis. SignificanceOur results highlight the importance of socioeconomic risk factors and immunosuppression for human leishmaniasis, suggesting potential implications for disease control and prevention policies. Surveillance of Leishmania spp. in humans, vectors, and reservoirs; assessment of reservoir abundance; and data accessibility are crucial for disease prevention and preparedness. Because of possible biodiversity regulation, efforts to understand and control leishmaniasis could benefit from a One Health approach that involves epidemiologists, social scientists, and ecologists, among others. Author summaryLeishmaniasis is a common disease in tropical and subtropical regions, but it also occurs in southern Europe. While some infectious disease experts are concerned that climate change might lead to the emergence of new diseases in new areas, the main factors shaping leishmaniasis in Europe are not well understood. This study considered a wide array of potential risk factors in a variety of categories, ranging from climate and nature to how people live and work. We found that the risk for leishmaniasis is mostly related to occupation, housing type, age, and sex, though the exact risk factors change from country to country. People with weakened immune systems face high risk, and infected animals pose a major threats, but climate change alone may not drive the spread of leishmaniasis as much as once feared. Interestingly, a healthy variety of wildlife may help keeping the disease in check. To limit the impacts of leishmaniasis, we need to protect the most vulnerable populations, such as people living with weakened immune systems, working in high-risk sectors, residing in single-dwelling buildings, or experiencing or facing homelessness. We need to monitor the parasite in people and animals and share those surveillance data openly. Ultimately, we need a "One Health" approach where doctors, social workers, and scientists work together to keep our ecosystems healthy and our communities safe.

BackgroundOnchocerciasis remains a public-health challenge in the Democratic Republic of the Congo (DRC). The Kakoi-Koda focus, Ituri Province, exhibited high endemicity in the early 2000s and received community-directed treatment with ivermectin (CDTI) in some health zones (e.g., Nyarambe), but not in others (e.g., Logo). Moxidectin clinical trials were conducted in these health zones, alongside onchocerciasis-associated epilepsy studies. MethodologyWe synthesised epidemiological (including nodule prevalence), entomological and CDTI programmatic data. We collated anti-Ov16 serological data from epilepsy-related studies (community, cohort, case-control designs, 2015-2021) and skin-snip microscopy results from two moxidectin trial screenings (2009-2011; 2021-2023) and epilepsy-related studies (2015-2017). Geospatial analyses were used to describe land-cover change relevant to vector ecology and to identify areas with recent transmission. Principal findingsOnchocerca volvulus transmission declined markedly over time. In CDTI-naive Logo villages, microfilarial prevalence fell from 69-79% (first trial, 2009-2011) to 9% (second trial, 2021-2023), and mean infection intensity from 17-26 to 1 microfilariae per skin snip, similar to declines observed in Nyarambe villages under CDTI (72% to 3% and 11 to 0.4, respectively). Anti-Ov16 seroprevalence among children aged 3-10 years was low (0-5%) from 2016 onwards, and seropositivity was geographically circumscribed, mirroring contemporary skin-snip results. Human landing catches and breeding-site prospections (2015-2017) identified Simulium dentulosum and S. vorax as the current anthropophagic species, with no evidence of S. neavei after 2009. Progressive deforestation and canopy opening provide a plausible mechanism for a shift from crab-associated S. neavei habitats towards more open-habitat vectors. SignificanceConsistent parasitological, serological, entomological and geospatial evidence indicates substantially reduced transmission across Kakoi-Koda, with spatially-circumscribed residual transmission. Whether the current simuliid species can sustain transmission above elimination thresholds remains uncertain. Targeted, integrated surveillance is warranted to guide CDTI and stop-CDTI decisions. The dataset assembled here can be used to inform transmission modelling of these dynamics. Author SummaryOnchocerciasis, also known as river blindness, is a parasitic disease of public health concern in sub-Saharan Africa, transmitted by blackfly vectors. The disease is responsible for skin and eye clinical manifestations and is associated with neurological complications. We investigated an area in north-eastern Democratic Republic of the Congo called the Kakoi-Koda onchocerciasis focus, where the infection was once common. We reviewed and assembled data from past studies on infection in humans and blackflies, and analysed satellite imagery to assess the loss of tree cover that can affect where blackflies live and breed. We found that the prevalence of onchocerciasis in Kakoi-Koda has declined markedly in recent years. This decline appears linked to the disappearance (by deforestation) of the habitat suitable for some blackfly species, and to ivermectin distribution to treat onchocerciasis in parts of the focus. Our findings help to understand why onchocerciasis has decreased across the Kakoi-Koda focus and highlight a small number of fast-flowing river segments where other blackfly species may allow small pockets of local transmission. These results support continued, targeted monitoring to determine whether the disease is still transmitted in specific locations where elimination interventions may be needed.

Disseminated human Lyme borreliosis (LB) is traditionally associated with invasive spirochete species from the Borrelia burgdorferi sensu lato (s.l.) complex. The Borrelia burgdorferi sensu lato complex consists of 23 spirochete species worldwide, with additional species being proposed. Interactions between the host immune system and Borrelia species have been studied for a diverse range of vertebrate reservoirs of LB spirochetes, including lizards and snakes, as well as the widely recognized rodent and bird reservoirs. Humans are the vertebrate species most susceptible to B. burgdorferi s.l. spirochetes, as demonstrated by the increasing number of diagnosed LB cases worldwide. However, few studies have evaluated differences in the borreliacidal action of human complement against specific Borrelia species. Using the serum sensitivity test, we analyzed whether complement-mediated killing of 10 spirochete species from the B. burgdorferi s.l. complex varies among healthy human individuals of different ages and sexes. Our results show that the 10 genospecies exhibit varying sensitivities to human complement and can be classified into three statistically distinct groups: high, medium, and low sensitivity. Complement sensitivity did not correlate with the known human health impact of these genospecies; similar resistance to the killing effects of human serum was found among Borrelia species that are major causes of LB worldwide and species with unclear pathogenicity to humans. Additionally, females showed reduced complement-mediated Borrelia killing compared to males for all Borrelia species in almost all age groups. Age and biological sex interacted for the Borrelia species most sensitive to human complement. Overall, the effectiveness of complement-mediated killing of the different Borrelia species tended to decrease with age, with more complex age-dependent changes observed for some Borrelia species.

Borealpox virus (BRPV; formerly Alaskapox) is an orthopoxvirus that has caused seven reported human infections in Alaska since 2015, including a fatal case in 2023. The natural reservoir of BRPV is unknown, although previous investigations have raised the possibility of wild small mammals transmitting the virus to humans, either through direct contact or via domestic cats and dogs. To understand which species may be involved in the maintenance and/or spillover of BRPV in Alaska, we trapped and sampled wild small mammals (including voles, shrews, and squirrels) in 2021 and 2024 near reported human case locations in Fairbanks and the Kenai Peninsula, respectively. We found evidence of previous exposure to orthopoxviruses in five species (including the House Mouse, Mus musculus) and detected BRPV DNA as well as viable virus in Northern Red-backed Voles (Clethrionomys rutilus). Further, screening of tissues from historical museum specimens revealed BRPV DNA in C. rutilus specimens collected in Denali National Park and Preserve in 1998 and 1999, 17 years before the first reported human case of BRPV. Phylogenomic analysis of all human and animal BRPV isolates strongly supports the hypothesis of local human infections through multiple spillover events. These findings suggest C. rutilus as a possible reservoir species for BRPV and indicate that BRPV has been present in Alaskan wild small-mammal populations for at least 25 years. Our study highlights the potential of museum collections to elucidate the temporal, spatial, and host ranges of emerging pathogens. Further museum- and field-based sampling will clarify the true geographic range of BRPV, which is closely related to Old World orthopoxviruses and may be circulating beyond North America.

Wildlife surveillance is critical for tracking disease emergence, characterizing pathogen diversity, and assessing spillover risks. Blood-borne pathogens are of particular interest for such efforts due to their global distribution, broad host taxa, and zoonotic potential. Despite the need to monitor blood-borne pathogens, blood collection efforts are costly for both biologists and the wildlife being sampled (i.e., time-consuming and stressful), hindering our ability to expand and enhance surveillance efforts. There is thus a pressing need for reliable methods for detecting blood-borne pathogens that minimize sampling efforts and wildlife stress. Vascular tissues can contain enough blood to detect infections while minimizing sampling effort and stress on wildlife, but it is unclear how pathogen detection and characterization from these tissues compared to blood. To evaluate the reliability of using vascular tissues for detecting blood-borne pathogens in wildlife, we collected paired samples of blood and wing biopsies from individual common vampire bats (Desmodus rotundus) and molecularly screened them for bartonellae, hemotropic mycoplasmas (hemoplasmas), and trypanosomes. The probability of detection was consistently lower in wing tissues than in blood for all pathogens, possibly due to blood vessel avoidance when collecting the former. However, we detected infection in wing tissues of at least two individual bats for each blood-borne pathogen. Paired-positive individuals mostly showed high sequence concordance between tissues, indicating frequent detection of the same infections. Estimated sample sizes needed to detect a single infection and the reported prevalences were similar (i.e., n = 10-39). Due to the lower probability of infection in wing tissues compared to blood, we suggest that using these samples to estimate infection prevalence of blood-borne pathogens is not ideal. However, our results demonstrate that vascular tissues are viable for initial pathogen assessment and discovery to help target surveillance efforts in the future.