This review article summarizes the history of amoebic dysentery (entamoebiasis) caused by Entamoeba histolytica. Initially, Entamoeba species were thought to be the most primitive extant eukaryotes, but more recent research revealed that they emerged relatively late in evolutionary history. Paleoparasitological data suggest that E. histolytica has been a parasite of humans since ancient times and was probably spread throughout the world by man during early human migration. By the end of the 19th century, it was established that E. histolytica was the etiological agent of amoebic dysentery and liver abscess. The issue over pathogenic and non-pathogenic strains of E. histolytica was resolved in the 1980s by the discovery of the morphologically indistinguishable harmless sister species Entamoeba dispar. Being mainly a disease of tropical and subtropical low-income countries, entamoebiasis cases have increased among travellers and immigrants arriving from endemic regions in recent years.

Freshwater parasitic copepods appear to exhibit great taxonomic diversity. However, little is known about gene flow between species or whether there is incongruence between morphological and phylogenetic species definitions. Additionally, little is known about what evolutionary factors may contribute to speciation across various lineages. The copepod genus Salmincola, which includes common ectoparasites of fishes in the family Salmonidae, is distributed throughout the northern hemisphere and is a good model to demonstrate limited taxonomic understanding. Much of the regular scholarly output regarding Salmincola copepods comes from fisheries management agencies, where they are considered a pest species. Within a geographic region, Salmincola copepods of the same species are often found infecting their hosts at substantially different rates across different water bodies. However, present taxonomic definitions of Salmincola are based on decades old morphological descriptions, which were limited in geographic scope and number of specimens examined. There is a strong possibility that traditional species definitions in this genus, based on host species along with morphology, are missing cryptic diversity that may explain differences in infection intensity across environments. This review outlines the current scientific limitations of understanding of this genus and provides suggestions for how adding genetic data could inform taxonomic revisions, as well as clarifying connections between genetic differentiation and infection dynamics across localities.

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.

Spirometra is a genus of zoonotic cestodes with an ambiguous species-level taxonomic history. Previously, Spirometra mansonoides was considered the only species present in North America. However, recent molecular data revealed the presence of at least three distinct species in the USA: Spirometra sp. 2 and 3, and Spirometra mansoni. This study aimed to elucidate the diversity and potential host associations of Spirometra species among companion animals in the USA. Samples (N = 302) were examined from at least 13 host species, including mammals, amphibians and reptiles. Sample types included eggs isolated from faeces (n = 222), adult specimens (n = 71) and plerocercoids (n = 9) from 18 different states and 2 territories across the USA. Extracted genomic DNA was subjected to PCR targeting a fragment of the mitochondrial cytochrome c oxidase subunit 1 (cox1) gene. Generated sequences (n = 136) were included in a phylogenetic analysis. Spirometra mansoni was detected in domestic cats (n = 76), dogs (n = 12), a White’s tree frog (n = 1), a Cuban knight anole (n = 1), a green iguana (n = 1) and a serval (n = 1) across 15 states and Puerto Rico. Spirometra sp. 2 was found only in dogs (n = 3) from Florida and Spirometra sp. 3 was found only in cats (n = 41) from 17 states. All plerocercoid samples were consistent with S. mansoni. The results confirm that at least three distinct Spirometra species are present and established in companion animals, such as dogs and cats, and likely are using various native and exotic species as paratenic hosts within the USA.

The dinoflagellates Hematodinium spp. are important endoparasites of a wide range of decapod crustaceans from across the globe. High prevalences of infection have been reported particularly in decapods of commercial importance including crabs and some lobster species. While such infections usually result in their death, the dynamics of these differ widely depending on location, the genotype of Hematodinium and host. This review aims to explore the interaction between these parasites and their hosts with particular emphasis on the diversity of host range, methods of detection, impact on fisheries and how this parasite multiplies within hosts without causing any apparent cellular immune response. Emphasis is placed on evaluating the future directions required to solve key unanswered questions of this increasingly important parasite.

Distinguishing between Stomylotrema bijugum and S. vicarium is challenging due to their phenotypic plasticity. In this study, adult specimens were recovered from 9 host species in the Mexican tropical lowlands. To explore the morphological differences, 32 morphological characteristics were evaluated in 54 specimens. Linear discriminant analysis provided enough evidence to differentiate the 2 species. Additionally, a principal component analysis (PCA) was performed for each species. The PCA of S. bijugum revealed 3 groups separately corresponding to specimens from the 3 hosts, suggesting host-induced phenotypic plasticity, whereas the PCA of S. vicarium revealed that the specimens from 3 host species were clustered together, indicating morphometric homogeneity. To confirm the morphological differences between the 2 species of Stomylotrema, we sequenced 2 molecular markers: the D1–D3 domains of the large subunit (LSU) from nuclear DNA and nicotinamide adenine dinucleotide dehydrogenase subunit 1 (Nad1) from mitochondrial DNA. Sequences of the LSU were aligned and compared with the LSU sequences of other congeneric species available in GenBank. Phylogenetic analyses supported the monophyly of Stomylotrema, with 2 main subclades that corresponded to S. bijugum and S. vicarium. A haplotype network was predicted with 25 Nad1 sequences, revealing the presence of 2 clusters representing the 2 species separated from each other by 98 substitutions. The current studies on S. bijugum and S. vicarium revealed new hosts and geographical regions in the Americas, suggesting that both species addressed in the current study can complete their life cycle in the Neotropical region of Mexico.

Dioecious species that reproduce by internal fertilization typically carry an associated risk of exposure to sexually transmitted parasites and pathogens. When hosts intermingle for procreation, certain protist and helminth parasites, for example, transfer successfully between individuals and then navigate across various life history traits of their hosts, often probing dimensions in both sex and gender, respectively. In humans, there are many sexually transmitted infections as well as sexually transmitted diseases. A well-known sexually transmitted infection is the flagellated protist Trichomonas vaginalis that causes trichomoniasis, with over 150 million new cases reported annually. By contrast, the schistosome blood fluke Schistosoma haematobium, though not a sexually transmitted infection, causes significant damage to the male and female genital tracts. Such overt damage raises risks of spreading and acquiring Human Immunodeficiency Virus and Human Papilloma Virus. In Africa, over 50 million women continue to suffer from female genital schistosomiasis, alongside a poorly quantified global burden of travel-related infections. In conjunction with male genital schistosomiasis, urogenital schistosomiasis causes much suffering, within and between afflicted households, inclusive of stigmatization. Both trichomoniasis and schistosomiasis expose several public health needs currently addressed inadequately by routine sexual and reproductive health services. This preface to the Parasitology Special Issue entitled ‘Parasites of the genital tract: short- and long-term consequences’, introduces 19 papers that explore the short – and long-term impacts of parasitic infections within the genital tract. While current parasitological research is weighted towards human medicine, we encourage future studies that explore veterinary contexts and analogous parasitic diseases within wildlife.

Population dynamics of aquatic parasites respond to factors like host availability, habitat age and quality. Amphipods are intermediate hosts for Acanthocephala, a widespread group of parasitic worms. Acanthocephalan infections of amphipods can easily be detected, and the widespread occurrence of amphipods makes their infection status an attractive potential proxy for the ecological status of their aquatic environment, including stressors introduced by urbanization. This study investigated the prevalence and the species-level and genetic diversity of Acanthocephala in the stream amphipod Gammarus fossarum. The study streams cross forested, agricultural and urban landscapes in the eastern foothills of the European Alps. Parasite prevalence ranged from 0% to 8.8% and increased towards downstream reaches independent of surrounding land use. Oxford Nanopore Technology was used to sequence the mitochondrial cytochrome oxidase I barcoding locus to identify parasite species and assess their genetic diversity. The majority of the parasites were Pomphorhynchus tereticollis, which use fish as definitive hosts. Despite their relative abundance in the studied streams, their genetic diversity was low and the most common haplotype was found at all sampling sites, which might indicate population expansion. Amphipods also hosted P. laevis and Polymorphus sp. type 1, the first evidence of this cryptic species within Polymorphus cf. minutus in Austria. Genetic diversity was high in Polymorphus sp. type 1, possibly reflecting a large effective population size due to gene flow maintained by the avian final hosts. The low and downstream-biased prevalence suggests that definitive hosts may be a limiting factor for Acanthocephala populations in small streams.

There is growing interest in using avermectins in livestock as a vector control tool for mosquitoes involved in the transmission of human malaria in sub-Saharan Africa (SSA). If implemented, the potential health and productivity impacts across the livestock sector would need to be considered, as avermectins are already commonly used in veterinary medicine to treat gastrointestinal helminths and parasitic insects. Here we present the results of a restricted systematic review that summarizes what is known about the effects of avermectins on cattle and swine productivity in SSA and the presence of avermectin resistance in endo- and ectoparasites of importance in these species. A total of 583 unique journal articles were identified using key search terms in 3 databases: Agriculture, Life, and Natural Sciences Databases from ProQuest, CAB Abstracts and Scopus. Ten articles met the criteria for inclusion on impacts on productivity and 4 met the inclusion criteria related to avermectin resistance. All studies documenting impacts of avermectins on productivity were performed using ivermectin in cattle. Generally, these showed a positive significant effect on growth rates. Resistance to avermectins was documented in 2 of the 4 included articles. Considering the extensive literature documenting resistance to avermectins in other areas of the world, our findings may reflect a paucity of studies on the subject in SSA. The authors conclude that additional research is needed to quantify the potential benefits and challenges to the livestock sector of using avermectins for malaria control across different production systems, and in a variety of ecological settings.

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.

The Nippostrongylinae is a group of strongylid nematodes that includes species typically associated with coprophagous mammals; in the New World, it is represented by 82 species within 11 genera. Two main morphological features, the synlophe and the caudal bursa, are used to evaluate the characteristics that allow identification and classification of the organisms in the taxon. However, the analysis of these characters often requires a partial or total destruction of specimens and therefore morphological variation is studied in only a very small subset of organisms per species. To evaluate the phylogenetic signal from these characteristics, we use genetic data to reconstruct the first phylogeny for the Nippostrongylinae using nuclear and mitochondrial genes and include representatives of the most common and diverse genera. The reconstructed phylogeny features five distinct clades and allows us to identify three non-monophyletic taxa including Carolinensis, Vexillata and Hassalstrongylus. From these, Carolinensis s. l. is divided into four genera including Carolinensis, Boreostrongylus, Neoboreostrongylus n. gen. and Tepalcuanema n. gen. Stunkardionema is resurrected to include Vexillata noviberiae and Hassalstrongylus is divided into two, establishing Lovostrongylus n. gen. to include species that are closely related to Guerrerostrongylus and Trichofreitasia. Organisms in these three genera feature a caudal arrangement of type 2-2-1. Furthermore, species in Hassalstrongylus sensu stricto are more closely related to species in Malvinema and Stilestrongylus. Our results reveal the existence of an additional unnamed genus and underscore the usefulness of framing morphological characters in a comparative framework. A key for genera from the Americas is proposed.

Both sex (biological) and gender (socio-cultural) are increasingly recognized as important factors in disease risks and outcomes, including parasitic infections and especially those of the genital tract. Many funding agencies now require these dimensions be incorporated into research proposals, though little guidance is given regarding how, leading to confusion among those who do not specialize in this area. In this commentary, I review instances of the use of the word ‘gender’ in the archives of Parasitology (174 articles) to assess how parasitologists are progressing in the incorporation of this dimension and identify what can be done to improve efforts. Use of the term has increased since 1990, reflecting an enthusiasm among parasitologists for including this dimension to their work. Examination of articles which use this term reveals that correct and thorough incorporation of the gender dimension has also increased, but that these articles only account for 8.0% of all articles using the term, demonstrating widespread persistent confusion around terminology regarding sex and gender and how to best account for gender in parasitological research. Parasitologists studying animals should only refer to sex and should incorporate sex into their research design and report whether there are differences in baseline or response between sexes. Parasitologists studying humans should incorporate sex, but then also consider whether any observed differences are due to biological factors like sex hormones and immunity or gendered social variables like behavioural norms and healthcare access. These considerations will further our understanding of host–parasite interactions and improve health outcomes.