The impact of macroparasites on their hosts is proportional to the number of parasites per host, or parasite abundance. Abundance values are count data, i.e. integers ranging from 0 to some maximum number, depending on the host–parasite system. When using parasite abundance as a predictor in statistical analysis, a common approach is to bin values, i.e. group hosts into infection categories based on abundance, and test for differences in some response variable (e.g. a host trait) among these categories. There are well-documented pitfalls associated with this approach. Here, I use a literature review to show that binning abundance values for analysis has been used in one-third of studies published in parasitological journals over the past 15 years, and half of the studies in ecological and behavioural journals, often without any justification. Binning abundance data into arbitrary categories has been much more common among studies using experimental infections than among those using naturally infected hosts. I then use simulated data to demonstrate that true and significant relationships between parasite abundance and host traits can be missed when abundance values are binned for analysis, and vice versa that when there is no underlying relationship between abundance and host traits, analysis of binned data can create a spurious one. This holds regardless of the prevalence of infection or the level of parasite aggregation in a host sample. These findings argue strongly for the practice of binning abundance data as a predictor variable to be abandoned in favour of more appropriate analytical approaches.

Anaplasmosis is a significant tick-borne disease (TBDs) caused by Anaplasma that affecting ruminant health and production worldwide. This study aimed to identify Anaplasma spp. infection using molecular as a fast diagnostic tool, perform a phylogenetic analysis and evaluate associated risk factors for combating Anaplasma spp. infection in small-scale livestock farms in Thailand. Total 963 blood samples from ruminants were collected from 125 farms across 4 regions of Thailand. Molecular diagnosis of Anaplasma spp. targeted the msp4 gene using conventional polymerase chain reaction (PCR) was performed and reported to the farmers within 14 days. Positive PCR products were purified, sequenced, and analysed the phylogenetic. Associated risk factor evaluations were conducted using R software. The overall prevalence of Anaplasma spp. infection in ruminants was 26.90%. The highest prevalence was observed in bullfighting cattle (47.06%), followed by beef cattle (35.75%), dairy cattle (21.73%), and goats (6.67%), with no infection in buffalo. Regionally, the Northern region had the highest prevalence (49.01%), followed by the Southern (25.88%), Central (22.01%), and Northeastern (13.81%) regions. Anaplasma spp. was commonly detected in Phrae, Chiang Rai, and Tak provinces. Sequencing confirmed A. marginale 99.64% to 99.76% identity to sequences in GenBank. Risk factors associated with A. marginale infection were history of TBDs on farm, animal illnesses, responsible person for treatment, and improper faeces removal practices. This study revealed a moderate to high Anaplasma infection across four regions. These findings underscore the need for enhanced tick control measures on farms, should be strictly implemented and promoted to reduce disease prevalence.

It is often postulated that natural systems are expected to suffer an increasing risk of infectious disease outbreaks as climate change accelerates. In the northern Argentine Sea, the rise of ocean temperature has produced a tropicalization of demersal megafauna since 2013. This rapidly warming hotspot provides an excellent model to test whether fish parasites have increased, declined, or remained stable in the region. Cardiocephaloides physalis a parasite of penguins Spheniscus magellanicus as adult and suspected to parasitize anchovies Engraulis anchoita as larvae is here used to compare their occurrence and abundance between samples composed by 1752 fish of variable age caught at different latitudes during 1993–1995 and 2022 and between 20 juvenile birds and literature data. In the present work, the identity of metacercariae as C. physalis is confirmed genetically, as well as a net decline of population parameters of the parasite to its effective disappearance in anchovies from northern areas and to extremely low levels in fish from southern regions and penguins. After analysing possible causes for such changes in a scenario of rapid regional tropicalization, a direct effect of increasing temperature on parasites arose as the main causal candidate for the observed decline in their populations over the last decades. Beyond the biological and ecological consequences of global change on them, parasites offer excellent systems for measuring and monitoring such effects. The almost local extinction of C. physalis in a marine hotspot of global warming seems to be one of the first examples of such processes.

The objective of this study was to assess the potential role of aquatic biofilms as natural reservoirs for Blastocystis. For this purpose, surface water (n = 4) and biofilm samples (n = 8) were collected from a stream nearby an urban area characterized by limited sanitation infrastructure and a high prevalence of Blastocystis in humans. Blastocystis cysts were detected in three of the four water samples and seven of the eight biofilm samples using fluorescence microscopy. Furthermore, viable cysts were identified exclusively in biofilm samples (five of the eight), while no live cysts were detected in water samples. These findings indicate that aquatic biofilms provide a habitat where Blastocystis cysts can adhere and remain viable, potentially contributing to their environmental accumulation. In addition, molecular characterization of the five isolates identified subtypes ST8 (allele 21) and ST3 (allele 36). This study is the first to report the detection and identification of viable Blastocystis subtypes in aquatic biofilms. The analysis of biofilms by fluorescence microscopy, as demonstrated here, offers a promising approach for monitoring Blastocystis and could serve as an alternative to traditional water sampling methods.

The presence of parasites can elicit host responses even in the absence of infection. These risk-induced trait responses include altered host behaviours, morphology, and/or physiology, which can trade off with other fitness-related traits. Studies of predator-induced non-consumptive effects (NCEs) have demonstrated that exposure at one life stage can lead to NCEs in the next stage, but no studies to date have examined such an effect of parasite exposure. Numerous NCEs have been demonstrated in larval, pupal and adult stages of Drosophila nigrospiracula exposed to ectoparasitic mites (Macrocheles subbadius). Here we experimentally investigated whether parasite-induced NCEs carry over into subsequent developmental stages (i.e. interstadial effects). We tested the prediction that when flies are exposed to mites during the larval and pupal stages, the subsequent adult stage will exhibit decreased body mass, fecundity and longevity. However, we did not detect downstream effects of parasite exposure on adult body mass, fecundity or longevity. The probability of survival and lifetime fecundity were comparable for previously exposed and unexposed groups. We suggest that when parasite exposure is confined to one developmental stage, and the risk of infection is removed in the subsequent stage, the long-term effects of parasite exposure dissipate. The potential to recover from the interim costs of parasite exposure may provide an added benefit to host dispersal.

We present four cases of male genital schistosomiasis (MGS) within children and adolescents opportunistically encountered as part of a wider screening programme for imported schistosomiasis in Germany and community outreach screening in Mali. Such genital manifestations in young children and adolescents are often overlooked but can include hydrocele, hypogonadism, varicocele, cutaneous granulomata on the penis and scrotum, echogenic spots in the prostate and the epididymis, alongside testicular masses. Though these cases appear sporadic, from our scoping literature review, they draw fresh attention on MGS in young children and highlight wider confusion with other congenital, neoplastic and infectious disease. These might include an insufficient closure of the tunica vaginalis, malignancies or lymphatic filariasis. Frequently haematuria is not present. One typical sign indicating MGS in adults, i.e. haematospermia is not present before puberty. Another reason of missing MGS cases may be that screening with scrotal or transabdominal ultrasonography are not easily accepted unless the reason for it is not extensively explained beforehand and that transabdominal ultrasonography is less sensitive for revealing prostatic lesions than transrectal ultrasonography.

Aplectana membranosa is a cosmocercid nematode that shows affinity with various amphibian and reptile hosts, being considered a generalist species. To date, no studies have investigated the influence of host and locality in the morphological variation of this species. Thus, we analysed morphological and morphometric characters of 260 specimens of A. membranosa collected from 9 host species and 7 different localities. To complement the metric studies, we conducted phylogenetic analyses using the ribosomal genes 28S and internal transcript spacer 1 (ITS1) to determine the phylogenetic position of the species and its divergence. In the present study, it was possible to observe the cloacal papillae pattern of the species through scanning electron microscopy, and we found no morphological variation in the specimens of A. membranosa from various hosts in different localities in Brazil. The study showed low variation in all data. However, despite the low variation, we found that external environmental conditions, such as climate and latitude, influence its variation. Molecular analyses highlighted that the separation of Cosmocercidae members may be related to geographic distribution and population genetic divergence. Thus, the results illustrated in this study reiterate the importance of using integrative data to better elucidate the family’s taxonomic and evolutionary history.

Birds possess the most diverse assemblage of haemosporidian parasites, although the true diversity is unknown due to high genetic diversity and insufficient sampling across all avian clades. Waterfowl (Order Anseriformes) are an ideal group to discover hidden parasite diversity and examine the role of host ecology in parasite transmission. Waterfowl contain 2 distinct feeding guilds, dabbling and diving, which differ in niche utilization that likely alters vector encounter rates and haemosporidian parasite risk. To determine the role of feeding guild in haemosporidian parasitism we analysed 223 blood samples collected by hunters from the upper Midwest of the United States from 2017 to 2019. Fifty-four individuals were infected by haemosporidian parasites (24·2% prevalence). Infection prevalence differed significantly between dabbling (34·9%, n = 109) and diving (14·0%, n = 114) ducks. Feeding guild was the only host trait that could predict haemosporidian infection risk, with a significantly higher risk in dabbling ducks. Twenty-four haemosporidian lineages were identified, with 9 identified for the first time. Thirteen lineages were found only in dabbling ducks, 5 only in diving ducks and 6 in both feeding guilds. Community analysis showed that each feeding guild harboured a unique parasite community. There was no phylogenetic signal of feeding guild within a phylogenetic reconstruction of North American waterfowl haemosporidian lineages. Our results demonstrate that waterfowl contain a diverse and distinct community of haemosporidian parasites. The unique composition of each feeding guild determines not only haemosporidian infection risk but also community structure. This is the first report of such an impact for waterfowl feeding guilds.

Scabies is a neglected tropical disease caused by the ectoparasitic mite, Sarcoptes scabiei var. hominis (S. scabiei). Common scabies, the most prevalent clinical subtype of scabies, is characterized by pruritus, multiple skin lesions and low mite burden. In contrast, crusted scabies, an extremely contagious variant, is characterized by hyperkeratosis and high mite burden, with or without pruritus. Scabies can be diagnosed based on clinical manifestations, with confirmation obtained through microscopic identification of diagnostic features of S. scabiei. However, owing to the diversity and non-specific nature of its clinical manifestations and insufficient knowledge regarding early-stage clinical manifestations, the diagnosis of crusted scabies continues to be delayed. Herein, we present three cases of scabies with varying degrees of crusting and mite burden. Three patients with physical and microscopic results suggesting scabies were selected for this study. Case 1 had mild crusting and low mite burden, case 2 had severe crusting and high mite burden and case 3 had mild crusting and high mite burden. In this case report, ‘the initial stage of crusted scabies’ refers to the progression from common to crusted scabies. The discussion regarding the diagnostic characteristics of the initial stage of crusted scabies is expected to aid the early diagnosis of crusted scabies.

Copepods of the genus Pennella parasitize a wide range of marine animals, including cetaceans, teleosts, and cephalopods worldwide. Their taxonomy is unclear, as there is incongruence between morphological and genetic data and incomplete species coverage. This study provides new morphological and genetic (COI) data from 23 specimens of Pennella cf. filosa (syn. P. balaenoptera) from western Mediterranean whales and a swordfish. First, their position in the phylogeny of Pennella was assessed and species delimitation revisited using all available Pennella COI sequences (n = 189), obtained from Mediterranean and north Pacific specimens from 18 host species (including multiple cetaceans and teleosts). Second, it was investigated whether the geographic location, degree of host vagility, or host taxonomic identity help explain genetic differentiation. Five distinct haplotype groups with varying genetic divergence were distinguished. Although the presence of sibling species cannot be ruled out, species delimitation methods could not find interspecific genetic differences, leaving the taxonomy of the genus unresolved. The observed genetic differentiation could not be attributed to geography or host type. This suggests that members of the genus Pennella show low specificity for definitive hosts and interoceanic dispersal mediated by some vagile definitive hosts. The use of more genetic markers for addressing these questions in the future is encouraged.

In this first report of endoparasites from endemic land-mammals of the Galápagos Islands, we describe a new species of cestode of the genus Raillietina (Cyclophyllidea: Davaineidae) from a species of Nesoryzomys and summarize the extent of helminth parasitism in both oryzomyine endemics and introduced species of Rattus. Up to the current time, no helminth parasites have been reported from rodents of the Galápagos, and little work has yet been done describing and synthesizing Galápagos parasite diversity. In historical times, several species of autochthonous rodents have occupied the islands including: Nesoryzomys narboroughi Heller 1904, N. fernandinae Hutterer and Hirsch 1979, N. swarthi Orr, 1938, and Aegialomys galapagoensis (Waterhouse, 1839). Colonization of the islands by humans brought 3 known species of synanthropic rodents: Rattus rattus, R. norvegicus, and Mus musculus which are suspected to have caused the extinction of at least 3 other oryzomyines in historical times.

Plant secondary metabolites (PSMs) may improve gastrointestinal health by exerting immunomodulatory, anti-inflammatory and/or antiparasitic effects. Bark extracts from coniferous tree species have previously been shown to reduce the burden of a range of parasite species in the gastrointestinal tract, with condensed tannins as the potential active compounds. In the present study, the impact of an acetone extract of pine bark (Pinus sylvestris) on the resistance, performance and tolerance of genetically diverse mice (Mus musculus) was assessed. Mice able to clear an infection quickly (fast responders, BALB/c) or slowly (slow responders, C57BL/6) were infected orally with 200 infective third-stage larvae (L3) of the parasitic nematode Heligmosomoides bakeri or remained uninfected (dosed with water only). Each infection group of mice was gavaged for 3 consecutive days from day 19 post-infection with either bark extract or dimethyl sulphoxide (5%) as vehicle control. Oral administration of pine bark extract did not have an impact on any of the measured parasitological parameter. It did, however, have a positive impact on the performance of infected, slow-responder mice, through an increase in body weight (BW) and carcase weight and reduced feed intake by BW ratio. Importantly, bark extract administration had a negative impact on the fast responders, by reducing their ability to mediate the impact of parasitism through reducing their performance and tolerance. The results indicate that the impact of PSMs on parasitized hosts is affected by host's genetic susceptibility, with susceptible hosts benefiting more from bark extract administration compared to resistant ones.

Avian Plasmodium parasites can be pathogenic to their vertebrate hosts. Although cases of anaemia are frequently reported in parasitized birds, the potential damage caused by the parasite during the exoerythrocytic reproduction phase remains poorly investigated. Here, we report 2 individuals of red-legged seriemas (Cariama cristata) infected with 2 different lineages of Plasmodium huffi, one of them exhibiting potential malarial-compatible tissue lesions in the spleen, liver, brain and lungs, alongside molecular confirmation of parasite presence in the spleen. Previously classified as specific to birds from the order Piciformes, this parasite has shown different associated lineages amplified across diverse host orders in South America (Anseriformes, Charadriiformes, Columbiformes, Galliformes, Pelecaniformes and Passeriformes). Those infections, however, were defined as abortive due to the absence of gametocytes visualized in blood smear slides. Herein, we confirm P. huffi as a generalist parasite based on the first morphological characterization in the peripheral blood of a bird outside the Piciformes order. This is also the first morphological and molecular description of a Plasmodium species in Cariamiformes. In addition to the morphological analyses, we have also proposed a novel phylogenetic hypothesis based on the partial cytb gene and the near-complete mitochondrial genome of this parasite. Our findings support that the division of the genus Plasmodium into subgenera is not monophyletic, as P. (Huffia) huffi and its associated lineages cluster more closely with Plasmodium (Haemamoeba) gallinaceum than with Plasmodium (Huffia) elongatum.

Coinfection of a host by more than 1 parasite is more common than single infection in wild environments and can have differing impacts, although coinfections have relatively rarely been quantified. Host immune responses to coinfection can contribute to infection costs but are often harder to predict than those associated with single infection, due to the influence of within-host parasite–parasite interactions on infection virulence. To first quantify coinfection in a common bird species, and then to test for immune-related impacts of coinfection, we investigated the prevalence and immune response to avian haemosporidian (genera: Plasmodium, Haemoproteus and Leucocytozoon) coinfection in wild blackbirds. Coinfection status was diagnosed using a 1-step multiplex polymerase chain reaction, immune response was quantified through white blood cell counts and heterophil: lymphocyte ratios, and parasitaemia was quantified for each infected sample. We detected high rates of haemosporidian infection and coinfection, although neither impacted immune activity, despite a significantly higher parasitaemia in individuals experiencing double vs single infection. This suggests that immune-related costs of haemosporidian single and coinfection are low in this system. This could be due to long-term host–parasite coevolution, which has decreased infection virulence, or a consequence of reduced costs associated with chronic infections compared to acute infections. Alternatively, our results may obscure immune-related costs associated with specific combinations of coinfecting haemosporidian genera, species or lineages. Future research should investigate interactions that occur between haemosporidian parasites within hosts, as well as the ways in which these interactions and resulting impacts may vary depending on parasite identity.

The crayfish plague pathogen Aphanomyces astaci (Oomycota: Saprolegniales) is native to North America but expanded with its crayfish hosts to other regions. In most of its invaded range, A. astaci haplotypes are associated with specific American crayfish, probably due to introduction bottlenecks, but haplotype diversity is higher and clear host-specific associations are lacking in its native range. However, little is known about the infection rate and load of this pathogen in North America. We investigated the distribution, prevalence and genetic variation of A. astaci in Pennsylvania (eastern USA), where multiple native and introduced crayfish species (family Cambaridae) occur. We used A. astaci-specific quantitative PCR to screen 533 individuals representing 8 crayfish species (2 Cambarus and 6 Faxonius) from 49 sites. Faxonius limosus, an American species first introduced to Europe and carrier of A. astaci genotype group E, was of particular interest. We confirmed A. astaci infections in 76% of sites in all but 1 host taxon, with the pathogen infection rate and load comparable to established populations of North American crayfish studied in Europe and Japan. Despite the absence of highly infected hosts, we genotyped A. astaci from 14 sites. We only detected 2 mitochondrial haplotypes, but nuclear markers indicated the presence of at least 4 distinct pathogen genotypes, none documented from invaded areas in Europe or Asia. Genotype group E was not detected in F. limosus, possibly due to limited spatial distribution of the original strain. Our results highlight both benefits and limitations of combining multiple pathogen genotyping methods.

Sulfadoxine-pyrimethamine (SP) is the standard of care for Plasmodium falciparum malaria chemoprevention among pregnant women, infants and children. Developing alternative chemoprevention products and other prevention products, such as vaccines and monoclonal antibodies, requires significant investment. However, knowledge gaps surrounding the activity of SP and resistance put these investments at risk. Therefore, we reviewed SP’s combined antimalarial action, including the individual antiplasmodial components, other antimicrobial effects, impact on malaria immunity development and continued effectiveness in settings with high SP resistance. We created a roadmap of non-clinical and clinical evidence to better understand the effectiveness of SP for chemoprevention and inform the development of new prevention tools.

Different agencies have emphasized the need to evaluate current serological methods for screening patients with suspected urogenital schistosomiasis. However, there is still a lack of evidence regarding the most appropriate methods for this purpose. Here we assessed the diagnostic efficacy of a newly developed serological technique that utilizes the recombinant protein Sh-TSP-2, applied to the urine and serum of migrants suspected of having urogenital schistosomiasis. The sensitivity, specificity, positive and negative predictive values of an in-house enzyme-linked immunosorbent assay (ELISA) using the recombinant protein Sh-TSP-2 were analysed and compared with other commercial serological methods. Due to the limitations of microscopy as a perfect reference method, a latent class analysis (LCA) and composite reference standard (CRS) approach was used to determine the sensitivity and specificity of each test. According to the LCA model, the commercial tests NovaLisa® and immunochromatography test (ICT) immunoglobulin G–immunoglobulin M (IgG–IgM) presented the highest sensitivity (100%), whereas the Sh-TSP-2 serum ELISA test had 79.2%. The Sh-TSP-2 urine and serum ELISA tests had the highest specificities among the serological methods (87.5 and 75%, respectively). CRS modelling showed that the ICT IgG–IgM, NovaLisa® and Sh-TSP-2 serum tests led in sensitivity at 97.1, 88.6 and 71.4%, respectively, with all tests except that the ICT IgG–IgM test having a specificity >90%. Sh-TSP-2 has been validated as a screening tool for patients suspected of having urogenital schistosomiasis. Although commercial serological tests have shown higher sensitivities, Sh-TSP-2 could be valuable for confirming results from tests with lower specificity. Nevertheless, further studies with larger patient cohorts are necessary to fully verify its potential.