Parasitology

Bivalve diseases caused by protozoan parasitic infection are monitored by coordinated surveillance programs across European member countries. These routine monitorings of bivalve health, however, only survey a few relatively well known parasites, which may leave undetected a range of lesser known opportunistic protozoan agents. Under increased stress, for example due to shifting environmental conditions affecting water quality and nutrient access, these opportunistic parasites may develop pathogenicity impacting reproduction or growth and therefore decreasing the success and future development of aquaculture or wild population sustainability. During routine histopathological surveillance of blue mussels in Sweden, we noticed cryptic lesions in the adductor muscle in high prevalence over a period ranging from 2017 to 2022. These lesions suggested cell infiltration and degenerative changes in the muscle tissues. In this study, we report on the isolation, identification, and culture of the protistan cells likely responsible for at least some of these lesions. Using histology and cytology, molecular phylogeny, and catalyzed reporter deposition fluorescence in situ hybridization (CARD-FISH), we show that the cells correspond to the H. nelsoni sequence initially isolated from oysters. We also reveal the presence of H. nelsoni in the digestive glands and mantel, and that this parasite might be horizontally transmitted from adult to larvae via infections within gonads, ovaries. This study represents the first report of H. nelsoni in blue mussel.

Culicoides biting midges are significant vectors of various pathogens, impacting both human and animal health globally. Understanding their host feeding patterns is crucial for deepening our understanding of disease transmission dynamics and developing effective control strategies. While several studies have identified the sources of blood meals in Culicoides, a quantitative synthesis of their host preferences and the factors influencing these behaviours is lacking. A systematic literature search focused on gathering data on (1) host selection and (2) host preference. For reviewing host selection we focused on studies reporting the identification of blood meal sources in individual Culicoides. When reviewing host preference we focused on studies comparing the number of Culicoides caught on or nearby different host species at the same location. Analysis revealed that some Culicoides species exhibit fixed host preferences, consistently feeding on specific hosts such as cattle and horses, while others display more opportunistic feeding behaviours. Notable variations were observed across different geographic regions. The findings indicate that host availability significantly influences Culicoides feeding patterns. This study highlights the complexity of host selection in Culicoides biting midges, which has implications for disease transmission. The variability in feeding behaviours underscores the need for regional assessments to inform targeted vector control strategies.

Seasonality is a ubiquitous feature of wildlife disease ecology, but is determined by a complex interplay of environmental, parasitological and host factors. Gastrointestinal parasites often exhibit strong seasonal dynamics in wild vertebrate populations due to, for example, environmental influences on free-living or vectored life stages, and variation in the physiological and immune status of hosts across their annual cycle. At the same time, wild populations are typically infected with multiple parasites. The seasonal dynamics of co-infecting parasites may differ depending on age and reproductive status, and associations among parasites may be driven by short-term within-individual changes or longer-term interactions that are consistent among hosts. Here, we used faecal samples and egg counts collected repeatedly from individually marked and monitored wild Soay sheep that were part of a long-term study to investigate seasonal dynamics of six gastrointestinal parasite groups (strongyle nematodes, coccidian protozoa, Capillaria, Strongyloides, Nematodirus, and Moniezia). Prevalence and abundance generally tended to be higher spring and summer, and burdens were higher in lambs than adults. Within the highly prevalent strongyle nematode group, we found differences in seasonality of egg counts depending on adult reproductive status. Reproductive ewes had increased counts in spring around the time of birth followed by a drop in abundance in summer, while barren ewes showed little evidence of seasonality. Males showed a sustained rise in egg counts through spring and summer, and sex differences were only strongly apparent in summer. In contrast, in similarly prevalent coccidia we found a peak in faecal oocyst counts in spring but no differences in seasonality among males, barren and pregnant ewes. Using multivariate mixed-effects models, we went on to show that both strongyle and coccidia counts are moderately repeatable across seasons among individuals. We further show that apparent positive correlation between strongyle and coccidia counts was driven by short-term within-individual changes in both parasite burdens rather than long-term among-individual covariation. Overall, our results demonstrate that seasonality varies across demographic and parasite groups and highlight the value of investigating fluctuating susceptibility and exposure over time for understanding epidemiology of a population.

Wildlife in cities can act as reservoirs for parasites that can infect domestic pets and have implications for human health. For example, the Coccidian parasite Toxoplasma gondii can infect all mammalian species, with felids acting as the only definitive hosts. Rodents, such as squirrels, could play an important role in urban infection dynamics of T. gondii, as squirrels occur at higher densities in cities than in natural environments and regularly share their territories with cats. In urban and suburban areas squirrels can encounter infectious oocysts shed in cat feces in contaminated soil or in the food they eat. They are also preyed upon by cats making them a potentially important species for completing the T. gondii life cycle in cities. We hypothesized that due to increased exposure to cats, urban squirrels would be more susceptible to T. gondii infection relative to squirrels in more natural areas. We investigated this using molecular and serological methods on samples collected from American red squirrels (Tamiasciurus hudsonicus), eastern grey squirrels (Sciurus carolinensis), northern flying squirrels (Glaucomys sabrinus), and least chipmunks (Tamias minimus) in and around the city of Winnipeg, Manitoba, Canada. We tested a total of 230 tissue samples from 46 squirrels for T. gondii DNA using quantitative PCR and supplemented these data with analyses of 13 serum samples from grey squirrels (Sciurus carolinensis) testing for T. gondii antibodies by indirect ELISA. We found no evidence of T. gondii infection in any squirrel. This suggests that squirrels may not be important intermediate hosts of T. gondii in cities and do not need to be considered as sources of infection to cats.

Seasonal variation strongly influences honey bee colony dynamics, leading to time-dependent changes in behavioral and physiological phenotypes. However, the extent to which seasonal fluctuations affect the susceptibility and tolerance of honey bees to viral infection remains largely unexplored. To address this, we conducted a longitudinal study in which adult honey bee workers were collected monthly from research colonies and experimentally infected with Israeli acute paralysis virus (IAPV) over the course of a year. Our results showed significant seasonal variation in the mortality and IAPV load of inoculated bees, with bees challenged during the pre-overwintering period (i.e., fall) exhibiting the highest susceptibility and lowest tolerance to IAPV infection compared to bees challenged in spring, summer, or winter. To investigate factors underlying these seasonal differences, we conducted nutrition-based studies that determined: 1) the variation in lipid content of colonies throughout the year and its potential link to our observed trends in IAPV tolerance, and 2) the impact of seasonally collected pollen on the survivorship of IAPV-challenged bees. Our findings support that seasonal changes in honey bee physiology and nutritional status play key roles in influencing honey bee viral tolerance. We conclude that honey bee colonies are particularly vulnerable to viral infection during the pre-overwintering period, most likely as a result of reduced tolerance to pathogen stress when transitioning from a summer to winter worker population. We further hypothesize that this period of increased vulnerability to viral infection, in correlation with other disease factors such as Varroa mite abundance and available forage, likely contributes to the relatively high overwintering losses experienced by beekeepers. Given the recent reports of severe colony losses attributed to honey bee viruses, understanding the relationship between seasonality and viral tolerance in honey bees is crucial for better informing management strategies and improving overwintering success. AUTHOR SUMMARYWe explored how seasonal changes affect the ability of honey bees to withstand viral infections. Previous research has shown that there are physical and behavioral differences between summer and winter bees, but its unclear how these seasonal differences affect a honey bees ability to withstand viral infection. To investigate this, we collected honey bee workers monthly and infected them with Israeli acute paralysis virus (IAPV) over the course of a year. Our results showed that honey bees were most vulnerable to IAPV in the fall (i.e., prior to overwintering), as they showed the highest mortality rates and lowest viral tolerance, based on their IAPV loads, during this time. By following up with nutrition-based studies, we found that seasonal changes in bee nutrition in part explained the seasonal differences we observed in honey bee virus tolerance. Overall, our findings suggest that bees are less tolerant to viral infection during the pre-overwintering period when colonies transition from a summer to a winter worker population. This vulnerable period may help explain the high rates of colony losses experienced by beekeepers nationwide and demonstrates the importance of developing seasonally-dependent disease management strategies.

Helminths are common parasites of wild ungulates that can have substantial costs for growth, mortality, and reproduction. While 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 an important 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 faecal samples non-invasively from known individuals and used them to count propagules of three helminth taxa (strongyle nematodes, Fasciola hepatica, and Elaphostrongylus cervi). Using generalised linear models, we investigated associations between parasite counts and overwinter survival for calves and yearlings. Strongyles were associated with reduced survival in both age class, and F. hepatica was associated with reduced survival in yearlings, while 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.

Haemonchosis is a major gastrointestinal parasitic infection in sheep caused by Haemonchus contortus. An abattoir-based cross-sectional study was conducted from January to September 2024 to assess the Haematobiochemical alterations and lesion characterization induced by Haemonchosis in sheep slaughtered at the Gondar ELFORA abattoir. The study involved 60 male local breed sheep, divided into 30 infected and 30 non-infected controls. The selection process involved postmortem examination of the abomasum tissues, incision, palpation, and visual inspection. Blood samples were taken for hematology and serum biochemical profiles, and a three cm tissue sample with typical Haemonchus contortus lesions was also taken. The study found significant reductions in hemoglobin, hematocrit, corpuscular volume, hemoglobin, and red blood cell counts in the infected group compared to the non-infected group. However, white blood cells, monocytes, neutrophils, and eosinophils were significantly higher in the infected group. Biochemical parameters showed significant reductions in total protein, albumin, globulin, and albumin to globulin ratio in the infected group. Erythrocyte indices indicated microcytic normochromic anemia. Gross examination revealed hemorrhages, dark brown abomasal contents, blood streaks, and a nodular lesion. Microscopic analysis revealed tissue-dwelling worms, submucosal hemorrhage, mucosal gland hyperplasia, thickened muscularis, and hyperplastic abomasal glands. The alterations in haematobiochemical parameters support the findings from gross and microscopic lesions. Thus, integrating haematobiochemical analysis with gross and microscopic lesion characterization improves the diagnosis of haemonchosis. Due to hypoproteinemia observed, it is advisable to supplement helminth-infected animals with protein-rich feeds, such as legumes.

BackgroundIn vector-borne diseases, invertebrate hosts are exposed to highly variable quantities of parasites during their blood meal. This heterogeneity may partly explain the overdispersed distribution of parasites within the vector population, as well as the variability in the extrinsic incubation period (EIP) of the parasite. Indeed, the quantity of parasites ingested is often considered as a good predictor of the quantity of parasites that will develop within the vectors, as well as the speed at which they will develop (EIP). However, density-dependent processes can strongly influence the relationship between parasite burden in the vertebrate host and in vectors, making this relationship not always clear. MethodsHere, we used the avian malaria system to investigate whether the proportion of red blood cells infected by sexual and/or asexual stages of malaria parasite influences the intensity of malaria infection and the EIP of Plasmodium within the invertebrate vectors. For this purpose, we have experimentally infected twelve vertebrate hosts in order to generate a range of intensity of infection. More than a thousand mosquitoes took a blood meal on these hosts and the development of Plasmodium within the vectors was followed for more than 20 days. ResultsThe main finding presented in this study reveals a negative relationship between the intensity of infection in the vertebrate host and the EIP. Four days were sufficient for 10% of infected mosquitoes fed on the most infected hosts to become infectious. However, the number of transmissible stages did not significantly vary according to the vertebrate host intensity of infection. ConclusionWhile the quantity of ingested parasites had no impact on the density of transmissible stages in infectious mosquitoes, the EIP was affected. Studies have demonstrated that small changes in the EIP can have a significant effect on the number of mosquitoes living long enough to transmit parasites. Here, we observed a difference of 4-6 days in the detection of the first transmissible stages, depending on the intensity of infection of the bitten vertebrate host. Considering that a gonotrophic cycle lasts 3-4 days, the shortened EIP observed here may have significant effects on Plasmodium transmission.

BackgroundGastrointestinal parasitic (GIP) infections can decrease the survival and reproductive performance of humans and livestock. Even so, the immediate and delayed fitness consequences of GIP in unmanaged wild mammal populations, particularly during the sensitive and energetically demanding early life stage, remain largely unknown. MethodsWe investigate non-invasively the effects of GIP during early life on the survival to adulthood, age at first reproduction and longevity of 68 individually known female spotted hyenas in the Serengeti National Park, Tanzania. We also test whether a high investment in gastrointestinal local immunity (i.e. faecal mucin and immunoglobulin A) and an elevated allostatic load (i.e. faecal glucocorticoid metabolites) decrease these measures of performance, when controlling for resource availability and maternal effects (i.e. maternal social rank) using logistic regression and Cox proportional hazards models. ResultsAncylostoma sp. infections and the level of immunoglobulin A both negatively associate with survival to adulthood, probably because of the damage caused by the parasite and resource allocation trade-off between immunity and maintenance. Conversely, maternal social rank has a positive influence on survival to adulthood and longevity. Immune responses, allostatic load and GIP do not affect the age at first reproduction, suggesting either no effect, a complex interaction between different life stages, or a more immediate time-dependent effect. ConclusionOur study highlights the critical role of GIP infections and maternal effects on early-life fitness and long-term outcomes in females of a wild carnivore, thereby contributing to our understanding of ecological dynamics in unmanaged ecosystems.

As animals age they often exhibit substantial physiological and behavioural changes that can drive changes in infection status over the lifespan. Generally, immunosenescence is expected to lead to greater infection in older individuals, but this process could be confounded or counteracted by changes in behaviour, selective disappearance of certain individuals, or a range of immune processes. Here, we uncover contrasting age-related patterns of infection across three different helminth parasites in wild adult red deer (Cervus elaphus). Counts of strongyle nematodes (order: Strongylida) increased with age, while counts of liver fluke (Fasciola hepatica) and tissue worm (Elaphostrongylus cervi) decreased. These relationships could not be explained by selective disappearance of certain individuals or changes in behaviour, suggesting that immune changes could be responsible. Additionally, we found a positive relationship between social connectedness and strongyle infection, implying that previously documented age-related decreases in social behaviour may minimise exposure, reducing the negative effects of immunosenescence. These findings demonstrate that burdens of different parasites can show contrasting changes over an individuals lifespan depending on a complex suite of intrinsic and extrinsic factors.

Multiple populations of resident ecotype killer whales (Orcinus orca ater) inhabit the Northeast Pacific, but the southern resident killer whale (SRKW) population is the most at-risk. SRKWs were listed as endangered in the United States in 2005 and have since shown little sign of recovery. Several factors have been identified as key threats to this population, and previously published studies suggest the population may be energetically stressed. Underlying health risks, such as parasitism, may be contributing to this populations failure to recover, but little is known about parasite infections in living individuals from natural killer whale populations. To assess the prevalence of internal parasite infections in Northeastern Pacific killer whales, we examined scat from endangered SRKW (n = 25) compared to two conspecific populations of resident killer whales that are not in decline: northern resident (NRKW, n = 2) and southern Alaska resident killer whales (SARKW, n = 7), and one offshore killer whale (OKW, n = 1). We analyzed 35 fecal samples collected from 27 wild killer whales using both microscopic identification of parasite eggs and genetic detection of parasites through DNA metabarcoding. We used body condition indices derived from concurrent aerial photogrammetry to evaluate whether parasite infection status was associated with individual body condition. We found that most individuals sampled (94%) were positive for Anisakis spp. - a parasitic nematode known to inhabit the intestines of cetaceans. These infections were detected across populations, and were not correlated with body condition, based on limited paired data. These results suggest that Anisakis infection is widespread among resident killer whales of the Northeast Pacific. The widespread detections of Anisakis among the samples examined here emphasizes the need for further work to understand the potential health impacts of parasitic infections on individual killer whales, and potential synergistic effects with other environmental stressors.

Treponema pallidum subsp. pertenue (TPE) causes yaws, a chronic, nonvenereal treponematosis characterized by contagious cutaneous lesions in early stages and destructive bone involvement in the tertiary stage. In the latency stage, the infection is asymptomatic with only serologic markers. A retrospective analysis of health, demographic, and behavioral records using a Generalized Linear Mixed Model (GLMM) with binomial distribution, conducted through R software to assess disease risks and trends from January 2019 to December 2024 of wild baboons at Gombe, revealed an overall clinical prevalence of 11.24% (2018/17946) across the eight studied troops. Age was a strong predictor where infants (OR = 0.05, p < 0.001), juveniles (OR = 0.27, p < 0.001), and subadults (OR = 0.65, p < 0.01) had significantly reduced odds of displaying Treponema signs compared to adults. Troops B.C and D.D exhibited elevated infection risk (OR = 2.74 and 2.63, respectively). Pregnant females (OR = 0.19, p < 0.001), wounded baboons (OR = 0.45, p < 0.001), and male immigrants (OR = 0.47, p < 0.001) were less likely to show signs. Infection signs were also lower during wet seasons (OR = 0.81, p < 0.001). Notably, the odds of infection increased consistently over time (Year OR = 1.73, p < 0.001). Understanding the ecological and demographic determinants of Treponema transmission is essential for disease surveillance, conservation, and One Health initiatives. This study presents the first long-term dataset on (TPE) infection in wild baboons from Tanzania and East Africa. Author SummaryTreponema pallidum subspecies pertenue (TPE) bacteria can cause debilitating disease in both humans and animals, yet little is known about how it spreads among wild Non-Human Primates. We studied a large population of habituated baboons and analyzed how various factors like Age, Troop, Pregnancy, Wounds, male immigration, Treatments and Interactions affect the likelihood of catching and showing signs of Treponema infection. Our analysis found that younger baboons are much less likely to show symptoms, but infection risk increases with Age. Some troops had significantly higher infection rates compared to others. Pregnant females and immigrants (Males) were less likely to show symptoms, possibly due to behavioral or biological differences. The risk of infection has also been increasing year after year. These findings suggest Treponema is becoming more common and highlight the importance of targeted monitoring and control in high-risk groups. Understanding these dynamics helps us protect wild primates and prevent cross-species transmission and potentially spill over to humans.

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.

Wildlife are increasingly common in suburban environments as towns and cities spread into surrounding rural areas. Many wildlife species have adapted to these new environments; however, we know comparatively little about how parasites respond urbanization of host habitats. Parasites are important members within ecological communities and alterations to transmission dynamics are known to alter host population dynamics. For complex life cycle parasites (parasites that use multiple different host species), suburban environments are thought to decrease transmission. Here, infection metrics of two parasites of white-tailed deer, giant liver flukes and thin-necked bladderworms, are examined to determine how successful these parasites are in a suburban environment. Additionally, land cover variables within suburban deer hunting areas are used to test if infection prevalence is associated with certain landscape level metrics. Results indicate that both parasites are common across the suburban landscape and are commonly found coinfecting the same hosts. Prevalence of neither parasite was strongly related to landscape variables within deer hunting areas, but fluke intensity was negatively correlated with the proportion of human development on the landscape. Overall, the scale of transmission events and host-parasite biology may explain why landscape metrics are weak predictors of infection risk in this system.

Marine fishes often suffer detrimental effects of parasitism, which can affect multiple life-history traits, such as maturity, growth, fecundity, and mortality. Rockfishes (genus Sebastes), in the northeast Pacific Ocean, are commonly parasitized by copepods in the genus Sarcotaces. These copepods form large cysts within the body cavity, or in the musculature of individuals. There is a lack of baseline data on the prevalence of Sarcotaces sp. infection and the effect of infection on rockfish health and life-history. Here, we present data on Sarcotaces sp. infection in 23 rockfish species (including two thornyhead species, genus Sebastolobus) that includes over 37,000 individual records collected on Fisheries and Oceans Canadas (Pacific Region) groundfish research surveys. Sarcotaces sp. were found in all geographic areas covered by the surveys (the coastal waters of British Columbia), and at all depths fish were encountered. Infection rates in the various species ranged from 0% to 10%, and were highest for Pacific Ocean Perch (POP), Silvergray, Rougheye/Blackspotted Complex (REBS), Yellowmouth, and Yelloweye rockfishes. We found that Sarcotaces sp. infection shifted the length-at-maturity ogive, with infected individuals maturing at larger sizes--particularly for males, who exhibited a 22.3 mm increase (95% CrI [credible interval]: 5.5, 39.8) in length-at-maturity across species. For most species, this effect was greater in males than in females, and the effect was most pronounced in POP, Silvergray, and REBS rockfish. Moreover, we found that immature males were 2.5 times more likely to be infected than mature males (95% CrI: 1.3, 4.7) and immature females were 1.7 times more likely to be infected than mature females (95% CrI: 0.9, 3.0). While speculative, this is consistent with Sarcotaces sp. infection acting as a co-morbidity, possibly affecting fish health and the probability of perishing before reaching maturity. Body condition was largely unrelated to infection status; however, a slight increase ({approx} 5%) in condition was associated with infection in REBS, Yelloweye, and Yellowmouth rockfishes. To our knowledge, this is the first large-scale report on Sarcotaces sp. infection within rockfishes and on rockfish life-history traits. Future work is needed to elucidate how infection influences other life-history traits and, importantly, whether these changes affect key stock assessment parameters and, ultimately, catch advice provided to fisheries managers.

Advances in experimental and theoretical work increasingly suggest that parasite interactions within a single host can affect the spread and severity of wildlife diseases. Yet empirical data to support predicted co-infection patterns are limited due to the practical challenges of gathering convincing data from animal populations and the stochastic nature of parasite transmission. Here, we investigated co-infection patterns between micro- (bacteria and protozoa) and macroparasites (gastrointestinal helminths) in natural populations of the multimammate mouse (Mastomys natalensis). Fieldwork was performed in Morogoro (Tanzania), where we trapped 211 individual M. natalensis and tested their behavior using a modified open-field arena. All animals were checked on the presence of helminths in their gastrointestinal tract, three bacteria (Anaplasma, Bartonella, and Borrelia) and two protozoan genera (Piroplasma and Hepatozoon). Besides the presence of eight different helminth genera (reported earlier), we found that 21% of M. natalensis were positive for Anaplasma, 13% for Bartonella, and 2% for Hepatozoon species. Hierarchical modelling of species communities was used to investigate the effect of the different host-related factors on these parasites infection probability and community structure. Our results show that the infection probability of Anaplasma and Bartonella was higher in adults than juveniles. We also observed that females and less explorative individuals had a higher infection probability with Bartonella. We found limited support for within-host interactions between micro-and macroparasites, as only animals infected with Bartonella were significantly more likely to be infected with Protospirura, Trichuris, and Trichostrongylidae helminths.

High levels of infection and severe liver fibrosis in schistosomiasis appear only in a few cases of infected people with high susceptibility. Tissue damage is caused by the inflammatory response to eggs trapped in the liver. The genetic background influences susceptibility to schistosome infection. To assess the genetic basis of susceptibility to schistosomiasis and identify the chromosomic regions involved, we used a backcross strategy to generate a mouse cohort with high variation in schistosomiasis susceptibility. Thus, we crossed the resistant C57BL/6 mouse strain with the susceptible CBA one; and later; the F1 females (C57 x CBA) were backcrossed with CBA males generating the F1BX cohort. The spectrum of phenotypes in the F1BX mice showed gradation from mild to severe disease, lacking a fully resistant group. We differentiated four levels of infection intensity using cluster and principal component analyses and K-means based on parasitological, pathological and immunological trait measurements. Mice were massively genotyped with 961 informative SNPs. We identify 19 new quantitative trait loci (QTL) associated with phenotype indicators of parasite burden, liver lesion, white blood cell populations, and antibody responses evaluated in the backcross cohort. Two QTLs on chromosomes 15 and 18 were simultaneously linked to the number of granulomas, grade of liver lesion and IgM levels. The human syntenic regions are located in chromosomes 8 and 18. None of the significant QTL identified coincided with previously reported mice association or were syntenic with human chromosomes. Author summaryHigh number of cases of infection and high levels of infection and liver fibrosis in schistosomiasis appear only in a few cases of people with high susceptibility, because the genetic background influences this susceptibility. To assess this, we used a backcross strategy crossing a resistant strain of mouse C57BL/6 with another susceptible CBA, and later F1 females were backcrossed with males susceptible, generating the F1BX cohort, which showed gradation from mild to severe disease. We differentiated four levels of infection according to cluster, principal component analysis and K-means, and based on parasitological, pathological and immunological measurements. Mice were massively genotyped and 19 quantitative trait loci (QTL) were identified, associated with phenotype indicators evaluated in backcross cohort. Two QTLs on chromosomes 15 and 18 were simultaneously linked to the number of granulomas, grade of liver lesion and IgM levels. None of the significant QTL identified coincided with previously reported mice association or were syntenic with human chromosomes.

The widespread mass mortality of the noble pen shell (Pinna nobilis) has occurred in several Mediterranean countries in the past seven years. Single-stranded RNA virus affecting immune cells and leading to immune disfunction have been widely reported in human and animal species. Here we present data linking P. nobilis mass mortality events (MMEs) to haemocyte picornavirus (PV) infection. This study was performed on 30 specimens, from wild and captive populations. We sampled P. nobilis from two regions of Spain, Catalonia [24 animals] and Murcia [two animals]), and one region in Italy (Venice [four animals]). The low number of analyzed specimens was due to the scarcity of remaining individuals in the Mediterranean Sea. In 100% of our samples, ultrastructure revealed the presence of a virus (20nm diameter), capable of replicating within granulocytes and hyalinocytes, leading to the accumulation of complex vesicles of different dimensions within the cytoplasm. As the PV infection progressed, dead haemocytes, infectious exosomes, and budding of extracellular vesicles were visible, along with endocytic vesicles entering other cells. The THC (total haemocyte count) values observed in both captive (eight animals) (3.5 x 104 - 1.60 x105 ml-1 cells) and wild animals (14 samples) (1.90 - 2.42 x105 ml-1 cells) were lower than those reported before MMEs. Sequencing of P. nobilis (six animals) haemocyte cDNA libraries revealed the presence of two main sequences of Picornavirales, family Marnaviridae. The highest number of reads belonged to animals that exhibited active replication phases and abundant viral particles from Trasmission Electron Microscopy (TEM) observations. These sequences correspond to the genus Sogarnavirus - a picornavirus identified in the marine diatom Chaetoceros tenuissimus (named C. tenuissimus RNA virus type II). Real time PCR performed on the two most abundant RNA viruses previously identified by in silico analysis revealed positive results only for the sequences similar to C. tenuissimus RNA virus. These results may not be considered conclusive of picornavirus identification in noble pen shell haemocytes, and require further studies. Our findings suggest that picornavirus infection likely causes immunosuppression, making individuals prone to opportunistic infections which is a potential cause for the MMEs observed in the Mediterranean.

The single flagellum of African trypanosomes is essential in multiple aspects of the parasite development. The FLAgellar Member 8 protein (FLAM8), localised to the tip of the flagellum in cultured insect forms, was identified as a marker of the locking event that controls flagellum length. Here, we investigated whether FLAM8 could also reflect the flagellum maturation state in other stages. We observed that FLAM8 distribution extended along the entire flagellar cytoskeleton in mammalian infective forms. Then, a rapid FLAM8 concentration to the distal tip occurs during differentiation into early insect forms, illustrating for the first time the remodeling of an existing flagellum in trypanosomes. In the tsetse cardia, FLAM8 further localizes to the entire length of the new flagellum during an asymmetric division. Strikingly, in parasites dividing in the tsetse midgut and in the salivary glands, the amount and distribution of FLAM8 in the new flagellum was seen to predict the daughter cell fate. We propose and discuss how FLAM8 could be considered as a meta-marker of the flagellum stage and maturation state in trypanosomes. Summary statementThe trypanosome protein FLAM8 displays a dynamic and stage-specific distribution during the entire parasite cycle, representing a novel marker of the flagellum stage and maturation state.

Parasites primarily rely on the host to survive, and have evolved diverse survival strategies. In the present study, we report a specific survival strategy of a dipteran parasite Exorista sorbillans (Diptera: Tachinidae), which is a potential biological control agent for agricultural pests and a pest in sericulture. We found that the expression levels of host nitric oxide synthase (NOS) and nitric oxide (NO) production were increased after E. sorbillans infection. Reducing NOS expression and NO production with a NOS inhibitor (L-NAME) in infected hosts significantly impeded the growth of E. sorbillans larvae. Moreover, the 20-hydroxyecdysone (20E) biosynthesis of infected hosts was elevated with increasing NO production, and inhibiting NOS expression also lowered 20E biosynthesis. More importantly, induced NO synthesis was required to eliminate intracellular bacterial pathogens that presumably competed for shared host resources. Inhibiting NOS expression down-regulated the transcription of antimicrobial peptide genes and increased the number of bacteria in infected hosts. Collectively, this study revealed a new perspective on the role of NO in host-parasite interactions and a novel mechanism for parasite regulation of host to support its development. Author summaryParasites are ubiquitous on earth and diverse, and have evolved various strategies to match their own specific requirements for survival within the host. In this study, we found that Exorista sorbillans, an endoparasite of many agricultural pests and the main insect pest in sericulture, used a novel strategy to manipulate its host NO synthesis for survival within its host Bombyx mori. Specifically, NOS expression and the production of NO in the host were up-regulated by E. sorbillans infection, which benefited larval E. sorbillans development. Meanwhile, increased NO production in host activated 20E synthesis of parasitized hosts and triggered the expression of AMPs against the invasion of pathogenic bacteria to avoid nutritional competence in the host. Our study provides innovative insights into the mechanisms by which a parasite manipulates host NO production for development and may help to expand our knowledge of other parasitic systems.