Parasitology

Anthropogenic changes to the environment, including altered food resource availability, influence host physiology, behaviour, and population dynamics, which can have strong downstream consequences on wildlife disease dynamics. Additionally, some individuals within a population contribute disproportionately to infection as super-shedders of infection, but the extent to which food availability alters the likelihood of super-shedding and overall parasite infection patterns is poorly understood. We conducted a three-year field experiment in southern Finland to investigate how food supplementation and parasite removal affect nematode infection measures and the relationship between nematode infection and fitness of wild bank voles (Clethrionomys glareolus). Using a factorial design across 12 populations, we manipulated food availability and administered anthelmintic treatments to assess effects on nematode infection status, intensity, and two measures of super-shedding (abundance super-shedding, intensity super-shedding). We also examined parasite impacts on host fitness, including apparent survival probability and reproductive status. Food supplementation did not affect likelihood of infection, intensity or intensity super-shedding, but did reduce the likelihood of abundance super-shedding, suggesting an effect of food availability on infection heterogeneity. We also identified an interaction between nematode infection status and host age on fitness. Notably, infected younger individuals had reduced survival and reproduction, but infected older individuals had greater survival and reproduction compared to their uninfected counterparts. Our study provides novel empirical evidence on how anthropogenic changes in food availability can influence parasite transmission dynamics and the fitness consequences of these sub-lethal parasites in a wildlife system.

Glutathione has important roles in diverse infections, yet its involvement in the interaction between the deadly fungal pathogen Batrachochytrium dendrobatidis (Bd) and its amphibian hosts is still unclear. Using in vitro assays and a cell infection model, we examined how glutathione influences Bd virulence traits and cellular host disease resistance. For Bd, inhibition of glutathione reductase rapidly killed zoospores, indicating that glutathione is essential for this pathogen. In addition, exposure to exogenous glutathione promoted the potential for virulence through accelerated and increased zoospore release. In host amphibian cells, Bd infection decreased intracellular glutathione content and increased reactive oxygen species, suggesting that chytridiomycosis pathogenesis may involve oxidative stress. Depletion of host glutathione before exposure to Bd increased infection severity and Bd growth, whereas amphibian cells with slightly elevated glutathione levels were partially protected against Bd. However, manipulation of host glutathione levels after the establishment of Bd infection did not impact its intracellular growth, implying that the host glutathione-mediated resistance only occurs during the initial Bd invasion process. Importantly, this effect of glutathione on host resistance is not a general response to pathogens, as it was not observed in cells exposed to viral pathogen FV3. As glutathione increased both infectious zoospore production and host resistance to zoospore infection, our study suggests that this antioxidant may play an important role in the host/pathogen interaction during chytridiomycosis. Thus, environmental conditions and therapeutic approaches that affect glutathione systems in the host and/or pathogen have the potential to alter chytridiomycosis dynamics and should be further explored.

Due to long co-evolutionary histories, many zoonotic pathogens are thought to exert little or no negative effects on their wildlife reservoir hosts. However, there remains a lack of rigorous investigations in natural settings. We conducted a 3-year factorial field experiment to investigate how survival of the Puumala hantavirus (PUUV) reservoir, the bank vole, is impacted by PUUV infection, nematode infections, and food availability. We hypothesized that PUUV would not impact survival, but that coinfection with nematodes would negatively impact survival, and that increased food availability would mitigate the negative effects of coinfection. Surprisingly, we demonstrated that PUUV infected voles had substantially reduced survival when compared to uninfected voles, and this strong negative effect manifested in young voles. Nematode removal increased survival of young voles and food supplementation interacted with movement rather than survival. Our results provide empirical evidence in a natural system for infection reducing survival of its reservoir host.

Parasitism is one of the key, structural, interspecific interactions in ecology. One remarkable parasitic strategy that has been documented in multiple systems is the behavioral manipulation of hosts to increase parasite fitness. While not yet documented in humans, we propose that a ubiquitous zoonotic parasite - Toxoplasma gondii - may change human behavior to favor the parasite by increasing the fitness of the parasites definitive host - cats. Specifically, we assess the possibility that human behavioral changes resulting from chronic, latent T. gondii infection lead to measurable changes in attitudes, actions and dopaminergic responses towards cats that function to increase domestic cat fitness. We assessed the potential role of humans in the T. gondii lifecycle by identifying and testing behavioral changes in humans that benefit the parasite; specifically, human affection for cats. We assessed T. gondii infection status in 68 participants using T. gondii serum antibody testing, and assessed their attitudes towards cats in three ways: i) surveys, ii) participant behavior in the presence of domestic cats, and iii) participant oxytocin levels before and after interactions with cats to assess dopaminergic changes. Only 2 of 68 participants were positive for T. gondii antibodies, limiting statistical power. However, our results indicated that T. gondii-positive participants both reported a greater affection for cats in surveys, and spent more time engaged with cats during behavioral trials than T. gondii-negative participants (87% of study time engaging with cats vs 75%). Oxytocin results were inconclusive.

Cetacean pathology is a cornerstone for population and marine ecosystem health monitoring, allowing clear differentiation among natural and anthropogenic threats. Previous studies in the Canary Islands reported natural causes of death in 59.4% (1999-2005) and 81% (2006-2012) of stranded cetaceans, versus anthropogenic causes in 33.3% and 19%, respectively. This study aimed to determine the causes of death (CD), pathologic findings, and epidemiological patterns of 316 cetaceans stranded in the Canary Islands between 2013 and 2018. The CDs were classified in pathologic entities (PEs) emphasizing natural versus anthropic origins. Of 316 animals, 224 (70.9%) from 18 species were suitable for pathological investigations. Among natural PEE, natural pathology associated with good nutritional status (NP-GNS) and natural pathology associated with significant loss of nutritional status (NP-LNS) represented 43/224 (19.2%) and 36/224 (16%) cases, respectively. Natural pathology with undetermined nutritional status (NP-UNS) occurred in 19/224 (8.5%) animals. Intra- and interspecific traumatic interactions (ITI) represented 30/224 (13.4%) cases, followed by neonatal/perinatal pathology (NPN) 19/224 (8.5%) and live-stranding stress and/or capture myopathy (LS-CM) 18/224 (8%). Infectious and parasitic diseases predominated in natural PEs. Anthropogenic PEs included interaction with fishing activities (IFA) in 17/224 (7.6%) cases, vessel collisions (VC) in 9/22 (4%) cases, and foreign body-associated pathology (FBAP) in 3/224 (1.3%) animals. Overall, anthropogenic causes accounted for 12.9% of deaths, natural causes for 73.6%, and the CD could not be established in 30/194 (13.4%) cases. This study reaffirms the trends concerning recognized PEs (NP-GNS, NP-LNS, NP-UNS, ITI, NPN, LS-CM, IFA, VC, and FBAP), expands the body of knowledge on cetacean pathology in the Canary Islands, and reports novel findings including mixed infections, clostridiosis in uncommon species, uremic syndrome secondary to urethral nematodiasis, gas embolism in unusual species, epibiont stomatitis, congenital musculo-skeletal malformations, or neoplastic processes. These findings advance understanding of cetacean mortality patterns and support conservation and management strategies.

Schistosomiasis is a neglected tropical disease caused by parasitic flatworms of the genus Schistosoma, impacting hundreds of millions of people and animals globally. Disease pathology primarily originates from host immune responses to parasite eggs, which are produced only when female schistosomes are continuously paired with males. Past research focused on pairing-dependent female sexual maturation, while scarce data exist for the males reproductive biology. In this study, we characterized the G protein-coupled receptor Smgpcr9 (Smp_244240), an orphan Class A (Rhodopsin-like) GPCR with a testis-preferential and pairing-influenced expression profile in S. mansoni males. Previous bulk RNA-seq analyses of adult worms and their isolated gonads revealed that Smgpcr9 belongs to a subgroup of GPCR genes with abundant testis-preferential and pairing-influenced transcript levels in males but low and extremely low expression in unpaired and paired females, respectively. This male-/unpaired female-biased expression pattern mirrors that of neuropeptide (npp) genes of S. mansoni such as Smnpp26 and Smnpp41. In a deorphanization approach using yeast-two-hybrid analyses, GPCR internalization experiments, bioluminescence resonance energy transfer assays, and by modeling and docking analyses, we provide first evidence that both NPPs can interact with SmGPCR9. Furthermore, we optimized a GPCR RNAi approach and achieved efficient transcript knockdown (> 90%) enabling robust functional characterization of Smgpcr9. Following RNAi, physiological and morphological analyses revealed that SmGPCR9 regulates key aspects of male reproductive biology like testis morphology and spermatogenesis. Remarkably, ovary structure and egg production were also affected in paired females post RNAi. We observed similar phenotypes plus motility constraints and reduced stem-cell proliferation in both sexes upon RNAi of Smnpp26 and Smnpp41. In all cases, RNAi downstream analyses by RT-qPCR of marker genes substantiated the observed phenotypic effects. These results strongly indicate the importance of SmGPCR9, SmNPP26, and SmNPP41 for spermatogenesis and further physiological processes in male and female S. mansoni. Author SummaryResearch of the reproductive biology of schistosomes focused mainly on females so far, which upon pairing sexually mature to produce eggs that are important for the life cycle maintenance but also for the pathogenesis of schistosomiasis, the infectious disease caused by these parasites. We investigated a yet unknown G protein-coupled receptor, Smgpcr9, which showed a testis-preferential and pairing-influenced expression profile in Schistosoma mansoni males. To this end, we optimized an RNA interference (RNAi) approach for knockdown analysis, identified neuropeptides (NPPs) as potential ligands by different biochemical approaches and modeling and docking analyses, and we investigated the roles of SmGPCR9 and two interacting NPPs, SmNPP26 and SmNPP41, by physiological, microscopical, and molecular techniques. Our results strongly suggest that SmGPCR9 and both NPPs regulate spermatogenesis. Furthermore, we detected effects on ovary morphology, egg production, and stem-cell proliferation of paired females post RNAi. Taken together, we deorphanized SmGPCR9 and showed for the first time the essential role of a so far uncharacterized GPCR and two interacting neuropeptides for spermatogenesis. Our results shed first light on spermatogenesis regulatory processes controlled by GPCRs and neuropeptides in male S. mansoni and thus expand our understanding of the roles of GPCR-NPP signaling for schistosome reproductive biology.

BackgroundIn chronic asymptomatic Plasmodium vivax infections, the spleen accounts for more than 98% of total-body parasite biomass. Whether this splenic tropism also exists in acute infection and how the spleen influences pathogenesis have not been systematically explored. Materials and MethodsIn Papua, Indonesia, we compared plasma levels of P. vivax lactate dehydrogenase [PvLDH]) and circulating parasitemia in 24 spleen-intact and 25 previously splenectomized patients with acute uncomplicated vivax malaria. Clinical and hematology data were collected and plasma markers of intravascular hemolysis (cell-free hemoglobin [CFHb]), endothelial activation (angiopoietin-2), inflammation (interleukin [IL]-1 beta, IL-6, IL-18, IL-10, tumor necrosis factor-alpha) and neutrophil activation (elastase) were measured by ELISA. Giemsa-based histology in one spleen from an untreated patient splenectomized for trauma during an episode of acute vivax malaria enabled direct assessment of splenic and circulating parasitemia and biomass microscopically. ResultsCirculating parasitemia was 4-times higher in splenectomized compared to spleen-intact patients (median 21,100 vs 4,820 parasites/{micro}L, p=0.0002) but total-body P. vivax biomass (PvLDH) was 3-times lower in patients without a spleen (median 721 vs 2,140 ng/mL, p=0.026). Parasite staging and greater organ-specific symptoms suggest redistribution of parasites in the absence of a spleen. Linear regression modeling, adjusting for circulating parasitemia, patient age, sex and duration of fever, demonstrated an 8.1-fold higher PvLDH concentration in spleen-intact patients (95% confidence interval [CI]: 3.4-19.5-fold, p<0.0001), indicating a splenic biomass accounting for 89% (95%CI: 77.3-95.1%) of total-body parasites. Histopathology revealed a spleen-to-blood biomass ratio of 10.7, in-line with the PvLDH-based estimate. In spleen-intact patients, splenic P. vivax biomass correlated strongly with markers of disease intensity, endothelial activation and systemic inflammation, whereas circulating parasitemia correlated weakly or not at all. Compared to spleen-intact patients, CFHb, endothelial activation and systemic inflammation were higher in splenectomized patients while inflammasome-dependent responses were lower. ConclusionsP. vivax is predominantly an infection of the spleen, even in acute clinical vivax malaria. We conservatively estimate that 89% of total-body parasite biomass in acute infection is splenic. While the size of this hidden population correlates with disease intensity, the spleen likely regulates inflammatory pathways and heme-associated pathology.

The spread of any pathogen depends on the dynamics of its hosts, with transmission rates typically assumed to either scale linearly with host population density (density-dependent transmission) or to be independent of it (frequency-dependent transmission). For vector-transmitted pathogens, a key determinant of transmission scaling is whether vector abundance is constant or sensitive to host abundance, with the latter being consistent with density-dependent transmission. Here, we assess whether Culicoides vector abundance increases in a manner that indicates density-dependent transmission of Culicoides-transmitted pathogens. To test this, we conducted trapping of Culicoides midges on eight livestock operations across a wide range of cattle abundances, placing traps at varying distances from the host aggregation. We used hierarchical Bayesian models to estimate the effect of host abundance on the vector-to-host ratio while accounting for differences in trapping efficacy between locations. Our results indicate a positive linear effect of host abundance on the ratio of vectors to hosts, with a posterior probability of 0.83. Median posterior values of the effect of host abundance on vector density predict a 2.3% increase (95% credible interval: -0.8, 23.2%) in the vector-to-host ratio with every 1,000 additional hosts. The weight of evidence from our study suggests that Culicoides-transmitted pathogens are likely subject to density-dependent transmission, and that transmission may be amplified in high-concentration livestock environments.

Trichomonas gallinae is a protozoan parasite of major concern in avian medicine, particularly in domestic pigeons (Columba livia). This study investigated the risk factors associated with the frequency of nitroimidazole resistance and T. gallinae prevalence in domesticated pigeons from Eastern Spain, kept for different competitions. A total of 220 pigeons from 11 lofts were sampled and examined by microscopy and culture, revealing a 63.6% infection prevalence. Genotyping identified genotype C as predominant, with occasional detection of genotype A, mixed A/C infections, and one isolate of Lineage III. In vitro susceptibility testing of 42 isolates showed a high prevalence (81%) of metronidazole resistance (MIC values [&ge;] 20 {micro}g/ml), with minimum inhibitory concentrations (MICs) ranging from 5 to >100 {micro}g/mL in 9/11 pigeon lofts examined. Resistance was significantly associated with the use of metronidazole and was more frequent in young and non-reproductive birds. Biannual treatments and the combination of ronidazole and dimetridazole at higher doses were associated with lower infection rates than monotherapies or annual treatments. No significant associations were found between resistance and environmental or loft management parameters, although poor hygiene and high bird density were common in lofts with resistant strains. These findings highlight the urgent need for regulated treatment protocols, improved biosecurity, and the development of alternative trichomonacidal agents to combat the emergence of drug-resistant T. gallinae in pigeon populations.

Plasmodium vivax transmission from humans to mosquitoes depends on the density of gametocytes that in turn depends on asexual parasite replication and gametocyte commitment. These processes are often analyzed separately, despite being biologically linked and measured with substantial uncertainty. We used a joint Bayesian latent-variable model to simultaneously analyze parasite density, gametocyte density, and mosquito infectivity while accounting for measurement error and propagating uncertainty across linked processes. The model was applied to individual-level data from three P. vivax transmission studies conducted in Ethiopia (n = 455). A tenfold increase in gametocyte density was associated with more than a twofold increase in the odds of mosquito infection (odds ratio [OR] = 2.32, 95% credible interval [CrI]: 2.12-2.54). Asexual parasite density was also positively associated with infectivity after accounting for gametocyte density (OR = 1.74, 95% CrI: 1.60-1.90), and inclusion of parasite density improved predictive performance. Pathway decomposition within the joint model indicated that approximately 41% of the parasite-infectivity association operated through gametocyte density. Increasing age was associated with lower asexual parasite density but higher gametocyte density, resulting in minimal overall association with infectivity. Predicted infection probability increased sigmoidally with gametocyte density, remaining low at lower densities before increasing sharply and approaching a plateau at higher densities. Gametocyte density produced the largest predicted changes in the proportion of infected mosquitoes, while asexual parasite density added predictive information not fully captured by measured gametocyte density alone. This approach links molecular parasite measurements with mosquito infection risk while accounting for measurement uncertainty and provides an interpretable framework for studying the P. vivax infectious reservoir. Author SummaryMalaria transmission occurs when mosquitoes ingest sexual-stage parasites, called gametocytes, during a blood meal. In Plasmodium vivax infections, human-to-mosquito transmission depends on linked biological stages, including asexual parasite replication, gametocyte production, and mosquito infection. These processes are closely connected and often measured with uncertainty, making them difficult to study using standard approaches that analyze them separately. In this study, we applied a joint Bayesian model that analyzes parasite density, gametocyte density, and mosquito infectivity together while accounting for uncertainty in laboratory measurements. Using data from three studies in Ethiopia, we quantified how parasite density, gametocyte density, and host characteristics relate to mosquito infection. The analysis showed that measured gametocyte density alone did not fully explain variation in infectivity, and that asexual parasite density provided additional predictive information. We also found that age was associated differently with asexual parasite and gametocyte densities, resulting in little overall association with infectivity. This approach helps link molecular parasite measurements with transmission outcomes and improves understanding of the P. vivax infectious reservoir in endemic settings.

BackgroundLeishmania donovani (LD) is an obligate intracellular parasite that survives and replicates within macrophages. Leptomonas seymouri (LS), a traditionally monoxenous trypanosomatid, has been repeatedly co-isolated with LD from visceral leishmaniasis (VL) and post-kala-azar dermal leishmaniasis (PKDL) patients in India, often together with Leptomonas seymouri narna-like virus 1 (Lepsey NLV1). Whether LS can survive and replicate within mammalian macrophages, and how co-infection influences parasite and viral dynamics, remains unresolved. Methods and FindingsUsing murine (RAW 264.7) and human (THP-1) macrophages, we systematically evaluated intracellular survival, replication, and revival of LS alone and during co-infection with LD. Quantitative ITS1 PCR demonstrated significant increases in intracellular parasite DNA over 48-168 h post-infection, with mean intracellular loads rising up to [~]7.6-fold, indicating active replication rather than persistence. Reduced extracellular parasite load suggested restricted cell lysis and enhanced macrophage survival in co-infection compared to mono-infections. In co-infection scenario, generally LS displayed higher persistence compared to LD. Giemsa staining confirmed intracellular localization of LS. Parasites recovered from infected macrophages remained viable and revived as motile promastigotes, whereas extracellular parasites failed to survive beyond 48 h, confirming macrophages as the exclusive niche for prolonged viability. Interestingly, co-infection dampened macrophage IL-12 production, suggesting altered host immune activation. Lepsey NLV1 RNA accumulated predominantly within macrophages and persisted up to 168 h post-infection. Virus load within LS in co-infection state was [~]2.5-4 and [~]7.5-23 fold higher (for RAW 264.7 and THP-1 respectively) compared to LS mono-infection. Purified virus alone failed to enter macrophages, indicating LS-dependent viral delivery. ConclusionsOur findings question the prevailing view of LS as a strictly non-infective parasite, demonstrating its capacity to replicate within mammalian macrophages and persist during mono-or LD co-infection. The identification of a stable LD-LS-virus interaction highlights a previously underappreciated "triple-pathogen" biology with potential implications for VL and PKDL pathogenesis.

Like other cells, parasitic and other trypanosomatids sense and regulate Zn2+ transport, but the mechanisms involved remained unknown. Here we identify a trypanosome RNA-binding protein which specifically eliminates ZIP3 Zn2+-transporter mRNA in Zn2+-replete conditions. We first demonstrated that Trypanosoma brucei ZIP3 mRNA abundance is subject to 3-untranslated region (3-UTR) and Zn2+-dependent negative control. A genome-wide RNA interference library screen, using a reporter associated with the ZIP3 3-UTR, identified Tb927.11.9510 as a candidate Zn2+-sensor. We name this protein Zinc Nuclear Knuckles 1 (ZNK1) since it localises to the nucleus and contains several Zn2+-knuckle motifs. ZNK1 is conserved among trypanosomatids, and a PIN-domain suggests a ribonuclease-based mechanism. We validate ZNK1 as a ZIP3 3-UTR dependent negative regulator and identify a GU-repeat motif in the ZIP3 3-UTR that is predictive of negative control by ZNK1. We use Cas9-editing to knockout ZNK1, and RNA-seq to assess the consequences, revealing highly specific accumulation of ZIP3 transcripts in znk1-null cells. We conclude that ZNK1 senses Zn2+-abundance and eliminates ZIP3 mRNA in a Zn2+-dependent manner. We suggest that trypanosomatid ZNK1 is an RNA-specific zinc finger nuclease that binds ZIP3 3-UTRs and degrades ZIP3 mRNA only when the tandem sensor modules are coordinated with Zn2+. Key pointsO_LITrypanosome Zinc Nuclear Knuckles 1 (ZNK1) is a zinc-sensor that eliminates zinc transporter mRNA. C_LIO_LIZNK1 negative control operates via the transporter mRNA 3-untranslated region. C_LIO_LIThe findings indicate that trypanosomatid ZNK1 is a conserved RNA-specific zinc finger nuclease. C_LI

Parasites occur in every ecosystem, although their dispersal is often constrained by the availability of hosts or vectors. Here, we explore how variation in parasite life history traits, particularly transmission strategy, may influence their distributions. Specifically, we test whether a variety of parasites ad-here to the rules of island biogeography, and whether their distributions vary with transmission strategy. We utilised broad-spectrum parasite detection from existing Whole Genome Sequence (WGS) data to characterise parasites with varying transmission strategies from the blood of a passerine bird, the silvereye (Zosterops lateralis), sampled across 25 islands in the South Pacific and from five of the states in mainland Australia. Overall, parasite richness was higher on mainland Australia compared to islands and decreased with distance of islands from the Australian continent. However, these patterns were dependent on transmission strategy. For parasites transmitted by flying insect vectors, richness decreased on islands compared to the mainland. However, increasing isolation from the mainland among islands had little further impact. On the other hand, richness of directly transmitted parasites and those requiring another intermediate host declined sharply with increasing distance from the mainland. While islands may act as an initial barrier to colonisation for parasites relying on flying insect vectors, their highly dispersive vectors may subsequently reduce the impact of increasing isolation distance on richness. Our work underscores the importance of considering parasite life-histories and their transmission strategies for understanding the processes that shape parasite communities on islands.

Triatomine bugs are blood feeding insects that transmit the parasite Trypanosoma cruzi, causative agent of Chagas disease. The bugs are found primarily in the Americas with a few species in Asia and Africa. Here we report the first case of a live triatomine bug in Europe, found in a Lisbon hotel room. In August, 2025, the hotel room occupants discovered a triatomine bug perched on the headboard of their bed. Upon capture, bright red blood emerged from the bug; the occupants suspected that it had bitten them during the night. The bug was identified morphologically as triatomine species Hospesneotomae protracta, which was confirmed molecularly. Hospesneotomae protracta is native to the southwestern United States where it is a competent T. cruzi vector. Trypanosoma cruzi was not detected in this specimen. Although this case likely represents an accidental importation, it illustrates the ease with which disease vectors can be unknowingly transported globally. Ergo it is crucial to document and share these findings to prevent introductions of non-native arthropods of medical importance.

BackgroundUnderstanding population dynamics is fundamental to predicting species persistence and extinction, yet remains challenging due to the complex interplay between ecological, environmental and anthropogenic factors. Population dynamics are regulated by intrinsic factors such as negative density-dependence and Allee effects. While negative density-dependence is a well-understood process, Allee effects have received less attention but can have important implications for conservation and species management. For control of disease vectors, negative density-dependence and Allee effects can drive vectors to elimination or to rebound after control. For malaria mosquitoes, negative density-dependence at the larval stages is well known to limit population growth, but the implications of Allee effects and the trade-offs between negative density-dependence and Allee effects remain unknown. It is hypothesised that, depending on the vector control strategy, Allee effects could be triggered and push populations closer to extinction. MethodsA stochastic state-structured population simulation model was developed, which followed a simplified mosquito life cycle. Negative density-dependence and Allee effects were included as parameters influencing larval survival and total fecundity, respectively. The aims were addressed by varying the strength of negative density-dependence and Allee effects parameters, independently and simultaneously, under different vector control scenarios: control, sustained and shorter-term interventions (here, immolating larvicides) that reduced the larval population. ResultsWhile in isolation, the strength of negative density-dependence and Allee effects did not have a long-term impact on the population dynamics, their combination accelerated population extinction as both the strength of negative density-dependence and Allee effects increased. As Allee effects act on small population sizes, sustained interventions were able to activate Allee effects, increasing the probability of population extinction, but short-term interventions can lead to populations rebounding, driven by negative density-dependence. ConclusionUnderstanding less-studied regulatory processes like Allee effects can support vector control by highlighting aspects of the vectors life cycle that are either resilient or vulnerable to interventions. If present, Allee effects could potentially be harnessed to accelerate the elimination of vectors and diseases such as malaria.

BackgroundTrypanosoma rangeli is a non-virulent hemoflagellate protozoan parasite that infects mammals, including humans, in Central and South America. It is primarily transmitted through the bites of triatomine bugs and shares an overlapping geographical distribution with T. cruzi, as well as triatomine vectors and mammalian hosts, and various shared surface antigens. The life cycle of T. rangeli differs from those of other human-infecting trypanosomes, such as T. cruzi and T. brucei, and the molecular mechanisms underlying host-parasite and host-vector interactions are not well understood, demanding improved molecular and genomic resources. ResultsThe use of a hybrid approach to sequence and assemble the T. rangeli genome, complemented by transcriptomics and proteomics for functional gene annotation, led to the generation of the near-complete genome sequence of the parasite. Detailed intra- and inter-specific comparative genomics allowed analysis of polymorphisms, genome structure and improved resolution of genes coding for important surface molecules such as Mucins, TASV and GP63. ConclusionsThe improved T. rangeli genome assembly, combined with comparative genomics has yielded novel biological insights. These included the first description of a metalloprotease activity, attributed to specific GP63 genes that are absent in Leishmania species. In addition, a TASV gene family that is absent in T. cruzi was identified, which indicates a possible role in the T. rangeli infection process.

Parasite prevalence varies in time and space. Thus, hosts may escape infection by dispersing out of habitats where parasites are present. However, it is not clear if the advantage of avoiding parasites outweighs the cost of dispersing. Juvenile hosts are expected to be relatively protected from environmentally-transmitted parasites, and we hypothesize that this age bias in transmission could magnify the benefits of juvenile (i.e., natal) dispersal. We tested these ideas in the model nematode Caenorhabditis elegans, a host with discrete life stages and natal dispersal, and its environmentally transmitted microsporidian parasite Nematocida parisii. We found that under standardized exposure conditions, larger C. elegans individuals (corresponding to older life stages) acquired many more parasites than smaller (younger) individuals. We found this same bias during multigeneration epidemics, especially during early stages of the epidemics. We also found that C. elegans dispersal larvae were less likely to be infected and harbored less severe infections than the population mean. We conclude that the early stages of an epidemic can provide young hosts with a window of opportunity to escape infection by dispersing.

Equine endometrosis is a major cause of subfertility in mares characterized by fibrotic remodeling of the endometrium. Although transforming growth factor beta 1 (TGF-{beta}1) is implicated in fibrogenesis, the relationship between endometrosis severity and transcripts associated with tissue maintenance and proliferation remains incompletely defined. Present study evaluated endometrial mRNA expression of IGF1, MKI67, TGFB1, and ACTA2 in relation to endometrosis severity and defined histopathological features. Forty-seven endometrial samples were graded according to the modified Kenney and Doig (KD) categories. Relative mRNA expression was quantified by RT-qPCR and histopathology was extended using a standardized feature-based assessment. TGFB1 mRNA expression was higher in category I+ than in categories I and III (p = 0.041) and in samples with glandular basal lamina disruption (p = 0.020). MKI67 mRNA expression was lower in samples with luminal epithelial erosion (p = 0.049). IGF1 mRNA expression correlated negatively with KD category ({rho} = -0.401, p = 0.015), glandular degeneration ({rho} = -0.340, p = 0.043), overall inflammatory infiltration ({rho} = -0.387, p = 0.020), lymphocytic infiltration ({rho} = -0.426, p = 0.010), and neutrophilic infiltration ({rho} = -0.448, p = 0.006). MKI67 correlated positively with ESR1 ({rho} = 0.887, p < 0.001). These findings indicate that early endometrosis-compatible lesions are associated with increased TGFB1 transcription and that epithelial damage is accompanied by reduced MKI67 expression. The inverse associations between IGF1 expression and both lesion severity and inflammatory infiltration support a link between progressive histopathological changes and reduced expression of a growth factor involved in tissue maintenance.

Phlebotomine sand flies are major vectors of Leishmania parasites, yet the mechanisms underlying their blood-feeding behavior remain poorly understood. In Lutzomyia longipalpis, the primary vector of Leishmania infantum in the Americas, feeding occurs via telmophagy, a pool-feeding method which is known by involving dermal laceration, salivation, and the creation of a blood pool. While the biochemical effects of sand fly saliva on host hemostasis, inflammation, and immunity are well studied, the dynamics of mouthpart movements and saliva at the feeding site remain to be systematically explored. Using intravital microscopy, fluorescent saliva labelling and image analysis, we characterized the mechanical actions of mouthparts and the spatial-temporal patterns of salivation during feeding on mammalian skin. Our recordings indicate that the labrum and hypopharynx are the most prominent mouthparts during feeding and exhibit scissor-like movements during probing. At specific moments, these structures close forcefully, generating small blood splashes in multiple directions. Feeding occurred in two distinct phases: an initial probing phase, often distinguished by ineffective blood intake, and a subsequent engorgement phase that was initiated exclusively upon the activation of small dermal "feeder vessels."Acridine Orange labelling showed abundant early salivation that penetrated progressively deeper into the dermis and remained detectable for over an hour, reflecting both the tissue damage and enzymatic effects. The analysis of images demonstrated the sequential salivation events, highlighting an initial high-frequency phase followed by a more gradual pattern during engorgement. These findings provide the first real-time, detailed view of the coordinated interactions between mouthpart mechanics, targeted salivation, and host microvascular responses in Lu. longipalpis. This study redefines sand fly telmophagy as a non-passive and coordinated process integrating mouthpart mechanics, salivation, and modulation of host vasculature. This work advances our understanding of sand fly vector-host interactions and underscores the potential of salivary molecules as targets for transmission-blocking strategies. Author SummaryPhlebotomine sand flies are the main vectors of Leishmania infantum, the parasite responsible for visceral leishmaniasis in the Americas. Although sand flies are traditionally classified as "pool feeders," meaning they lacerate the skin and feed from small pools of blood, the mechanics of how they obtain blood and deliver saliva into host skin have remained poorly understood. In this study, we used image analysis, intravital microscopy and fluorescent labeling of saliva to visualize, in real time, the feeding behavior of Lutzomyia longipalpis on mammalian skin. We show that blood feeding is not a passive process based solely on blood pooling. Instead, it involves coordinated movements of the mouthparts, modulation of host microvessels with the saliva contribution, and the recruitment of small dermal "feeder vessels" that supply blood directly to the insect. Our findings reveal that sand fly feeding is a highly orchestrated interaction between vector and host, integrating mechanical tissue disruption, salivary secretion, and vascular responses. These processes likely create a favorable microenvironment for Leishmania establishment and transmission. By providing a detailed characterization of mouthpart and salivation dynamics, this study advances our understanding of sand fly biology and highlights salivary components and feeding-site events as potential targets for transmission-blocking strategies.

This report describes lethal Nannizziopsis-associated dermatomycosis in a breeding colony of the family Diplodactylidae (Correlophus ciliatus and Rhacodactylus auriculatus). After introducing one gecko from overseas, three with indirect contact history died due to severe skin lesions. Extensive lesions were observed on the toe pads and ventral surface, along with necrotic dermatitis and cellulitis associated with fungi forming hyphae. Subsequently, four geckos developed diarrhea, melena, emaciation, and fungal dermatitis of the toe pads and died. Histopathologically, the fungal morphologies observed in the skin lesions of the seven geckos were consistent, and Nannizziopsis arthrosporioides was isolated and identified in two of them. To our knowledge, this is the first report of a fatal outbreak of N. arthrosporioides in geckos.