Soil-transmitted helminths (STHs) are intestinal parasitic worms that present a significant global health challenge. Traditionally, the diagnosis of STH infections has relied on microscopy; however, molecular tests such as quantitative PCR (qPCR) are now widely adopted for their greater sensitivity, increasingly reduced cost and higher throughput. Recent evidence highlights genetic diversity in both coding and non-coding DNA regions of STHs routinely targeted by molecular diagnostics. Most qPCR assays have been developed using a limited selection of parasite isolates, thus likely overlooking the substantial genetic variation present within and among STH populations worldwide. Such genetic diversity can significantly impact the diagnostic targets of molecular tests, potentially reducing their sensitivity and leading to false-negative results. Therefore, there is growing recognition of the need to develop diagnostic tools that account for this genetic variation. In this Chapter, we outline current advances in STH genomics and review recent work on the assessment of genetic diversity directly from fecal samples, especially as access to adult worms becomes increasingly difficult. These studies emphasize the importance of thoroughly evaluating current and future diagnostic methods prior to their implementation to effectively guide control measures and policy decisions regarding the cessation of STH deworming. Together, these findings lay the groundwork for genomic epidemiology and the sustainable control of STHs as a public health issue.
Sarcocystosis is an emerging zoonotic disease caused by apicomplexan parasites of the genus Sarcocystis, which can infect a wide range of hosts, including humans, animals, reptiles, and birds. Humans may serve as either definitive or intermediate hosts, depending on Sarcocystis species. Consumption of undercooked beef containing mature sarcocysts of Sarcocystis hominis or Sarcocystis heydorni, or of raw or partially cooked pork containing Sarcocystis suihominis zoitocysts, may lead to intestinal sarcocystosis in humans. In contrast, muscular sarcocystosis follows ingestion of food or water contaminated with zoonotic Sarcocystis spp. sporocysts, as evidenced by infection outbreaks by Sarcocystis nesbitti among travelers returning from exotic destinations in Malaysia. Further, Sarcocystis fayeri, which cycles between horses and dogs, has been implicated in cases of food poisoning in humans following consumption of raw horse meat. Clinical features range from asymptomatic cases to acute symptoms, such as muscle pain, fever, and, in severe cases, neurological complications. Diagnosis relies on clinical presentation supported by microscopy, histopathology, serology, and advanced molecular techniques. Therapeutic options are limited; antiprotozoal agents including sulfadiazine, pyrimethamine, decoquinate, clindamycin, and triazine derivatives have shown high efficacies. Preventive measures focus on hygienic meat handling, thorough cooking, and restricting carrion scavenging by stray carnivores. Increasing human-wildlife interactions elevate the risk of cross-species transmission of novel Sarcocystis species. Adopting a One Health approach is fundamental for understanding the epidemiology and transmission dynamics of zoonotic sarcocystosis and reducing future outbreaks through effective diagnostics, therapeutics, and preventive interventions.
Cyathostomins (also known as small strongyles or small redworms) are ubiquitous parasites of equids. They are found in a wide range of climatic regions, and inhabit the large intestine of their hosts. While infections are often sub-clinical, clinical consequences ranging from chronic to acute, and most notably, acute larval cyathostominosis, can occur in specific circumstances. Control of cyathostomin infection is complicated by widespread drug resistance. This Chapter provides a broad review of cyathostomin biology and host-parasite relationships, and also highlights significant knowledge gaps, for example relating to immune response, and the community dynamics of mixed populations of cyathostomins within the host, that complicate the development of sustainable parasite control strategies.
Parasitic platyhelminths (Trematoda, Monogenea, and Cestoda) are responsible for widespread disease in wild and cultured fish in both freshwater and marine environments globally, impacting both human health and the sustainability of aquaculture industries. Research into these parasites primarily aims to understand the impact of infections on host species, as well as developing management strategies to reduce or eliminate disease. -Omics-based research can assist in uncovering the biology of these parasites across a range of key areas, including understanding host-pathogen interactions, identifying novel drug and vaccine targets, and recognizing the overall diversity of parasite species. To date, the application of -omics technologies to piscivorous platyhelminths has been limited. This Chapter focuses on the current availability of -omics research in fish platyhelminths, with a primary focus on parasites with definitive fish hosts, and argues that the application of these technologies may provide unprecedented opportunities for the development of novel sustainable strategies for infection and disease management and control.
Parasites harbor diverse microbial ecosystems that include not only bacteria but also archaea, fungi, viruses and microbial eukaryotes. These parasite-associated microbiomes, long overlooked, are now recognized as important determinants of parasite development, fitness, virulence and interactions with hosts across medical, veterinary, agricultural and ecological systems. However, current understanding of parasite-associated microbiomes remains fragmented, with most studies focusing on a narrow set of human parasites, relying heavily on bacterial surveys and rarely capturing the full multi-kingdom diversity of microbial partners. Important challenges include expanding research to encompass neglected parasite groups and their non-bacterial associates, establishing causal links between microbiome members and parasite phenotypes, and overcoming the technical barriers posed by low-biomass, host-contaminated and/or experimentally intractable systems. Progress will also depend on developing robust reference genomes and analytical tools that can resolve multi-kingdom communities and integrate parasite and symbiont biology. This chapter synthesizes current knowledge across helminths, protozoa, ectoparasites and plant-infecting parasites. We consider how microbiome manipulation may contribute to parasite control while recognizing the evolutionary and ecological complexities involved in altering host-parasite-microbiome interactions. Embracing an explicitly multi-kingdom, holobiont-focused perspective promises to illuminate fundamental aspects of parasitism. Such knowledge may contribute to new avenues for mitigating the impact of parasitic diseases on human and animal health, food security and ecosystems.
Entamoeba is a genus of anaerobic protists that infect humans and a wide range of animal hosts worldwide, and that are also detected in environmental reservoirs. Of particular importance is Entamoeba histolytica, the causative agent of amoebiasis, which accounts for more than 55,000 deaths each year and remains a major public health concern. Given this substantial burden, and the fact that pathogenic and non-pathogenic species of Entamoeba cannot be distinguished based on morphology alone, molecular approaches have become essential for accurate diagnosis, taxonomy, and epidemiological surveillance. In this Chapter, we systematically review the impact of DNA sequencing technologies on Entamoeba research from 1987 to 2025. A bibliographic search was conducted using PubMed and Google Scholar, combining the names of all recognized Entamoeba species with keywords related to sequencing technologies, spanning from first- to fourth-generation platforms. Original research articles employing DNA sequencing for molecular identification, phylogenetic analyses, and genomic investigations were included. The literature illustrates a clear transition from morphology-based classification to Sanger sequencing of the small subunit of the ribosomal RNA (SSU rRNA) gene, which established the molecular taxonomic framework of the genus and enabled the recognition of numerous new species and ribosomal lineages. The expansion of diversity revealed by high-throughput sequencing is also addressed, together with the contribution of long-read technologies to resolving highly AT-rich and repetitive genomes. Despite these advances, challenges remain in species delineation and marker-associated biases, highlighting the ongoing need for integrative genomic approaches in Entamoeba research.
Neglected tropical diseases (NTDs) encompass 20 conditions or groups of diseases that affect almost exclusively the rural poor in low- and middle-income countries (LMIC). NTDs cause severe and chronic disabilities, from disfigurement and cognitive defects to death, and present substantial public health and socioeconomic burdens. Amongst NTDs, infections by parasitic protozoans, helminths and arthropod and non-arthropod ectoparasites, are of critical importance, with soil-transmitted helminths (STHs) representing the most widespread and prevalent NTDs globally. Whilst mass drug administration is the current strategy for control of helminth (STH and schistosomiasis) infections, treatment alone is inadequate due to the absence of lasting immunity against reinfections and the persisting concern of emerging drug resistance. The prevention and ultimate elimination of parasitic NTDs would avoid unnecessary suffering and significantly reduce poverty; hence, the potential of effective antiparasitic vaccines offers hope to billions, particularly those in sub-Saharan Africa. Given the strong links between NTDs and poverty - both regarding the demographics of the most affected communities and the socio-economic impact that these diseases exert - vaccines for these conditions are often referred to as "antipoverty vaccines". Here, a comprehensive analysis of the current state of antipoverty vaccine development is provided, with a focus on the potential for antiparasitic vaccines. This encompasses both a review of the current scientific literature and an assemblage of key stake-holder perspectives obtained through semi-structured interviews, all aimed to assess the future directives, utility and acceptability of these vaccines. The causes behind the current paucity of antipoverty vaccines are explored and global policy recommendations to assist their development and acceptance addressed. There was unanimous agreement among stakeholder interviewees on the importance and value of antipoverty vaccines, although it was felt that this sentiment does not extend to funders or policymakers from the Global North. Such findings highlight the scientific challenges in/of creating these vaccines, and how such challenges are amplified by financial constraints. The lack of funding reflects low profitability and biases against diseases largely of morbidity rather than mortality, as well as potentially the issues of poor people in poor countries and race/ethnicity. Solutions to how barriers affecting vaccine uptake on the ground can be addressed are proposed, primarily involving increased access to healthcare infrastructure, enhanced compliance through education, and involvement of local communities in all stages of development and rollout.
Leishmaniasis, caused by vector-borne Leishmania spp., continues to cause a significant burden of disease around the world. These sand fly-transmitted protozoan parasites, of which numerous species exist, are responsible for cutaneous (CL), mucocutaneous (MCL), and visceral leishmaniasis (VL) - diseases which can be debilitating or even fatal, especially in immunocompromised individuals. In many areas, dogs serve as a reservoir for Leishmania. Treatment of leishmaniasis relies on a minute arsenal of chemotherapeutic drugs that are toxic, costly, or difficult to source. Meanwhile, an effective vaccine formula remains elusive, although vaccines for the prevention of canine leishmaniasis (CanL) have been in use for decades. Treatment failure (TF) is an important concern for leishmaniasis. Incomplete cure or relapse is relatively common in cases of VL and CL. When it comes to CanL, TF or relapse is typical; host immunity and drug characteristics play a major role. Meanwhile, drug resistance (DR) has also become a major issue in some regions and may play an important role in TF. Leishmania parasites possess an impressively plastic genome and utilize copy number variations (CNVs) and single-nucleotide polymorphisms (SNPs) to escape drug pressure. Futhermore, studies have shown that they deploy extracellular vesicles (EVs) with a variety of key molecules as cargo, contributing not only to host-pathogen interaction & pathogenesis, but also to spread of DR. TF and DR are discussed here in detail, as well as the current state of vaccine development and available and prospective therapies for CL, MCL, VL, and CanL. Variables affecting the course of disease are addressed. Finally, the role of dogs as a reservoir for Leishmania parasites, as well as their potential to contribute to the spread of DR parasites, is considered.
Anisakidosis is a fish-borne zoonosis characterised by mild to severe gastrointestinal (GI) symptoms and potentially linked to the onset of allergic reactions and cancer. The disease follows the ingestion of marine products infected with third-stage (L3) larvae of the genera Anisakis and Phocanema. Epidemiologically, anisakiasis is most prevalent in countries where fish consumption is high, such as Japan and the Mediterranean regions; however, the globalization of dietary habits has contributed to the expansion of its incidence worldwide. In this Chapter, we provide an overview of aspects related to the disease, from the description of the biological features of L3 and fourth-stage (L4) larvae, to the mechanisms likely responsible for allergic reactions and GI lesions. Multiple factors contribute to the allergenicity of Anisakis spp., including exposure time, GI and endo-lysosomal stability and antigenic structure. A growing body of research focuses on the parasite excretory/secretory (E/S) products, including extracellular vesicles, encompassing proteolytic enzymes, immunomodulatory molecules, and potential virulence factors. E/S products play key roles in host-parasite interactions, such as tissue invasion, immune evasion, and allergic sensitization. Both in vivo and in vitro studies (conducted in murine models of infection and human epithelial and dendritic cell cultures, respectively) have enhanced current understanding of anisakidosis pathophysiology, elucidating mechanisms of mucosal damage, cytokine production, and adaptive immune responses. These models also offer insights into chronic disease outcomes, that include formation of eosinophilic granulomas, chronic abdominal pain, and a potential correlation between anisakidosis and the occurrence of a tumorigenic microenvironment in the GI tract.
Intestinal protozoan infections remain highly prevalent among children and women of reproductive age, particularly across low- and middle-income countries. However, their impact on maternal-child outcomes-including birth weight, prematurity, intrauterine growth restriction (IUGR), and/or childhood stunting remains largely undetermined. Here, we conducted a systematic literature search across six databases for studies published between 1976 and 2024 that examined potential associations between gastrointestinal (GI) protozoan infections, and childbirth and growth outcomes. A total of 99 cross-sectional and longitudinal studies were included. Cross-sectional studies reporting odds ratios (ORs) or adjusted odds ratios (AORs) for stunting, unadjusted and adjusted mean differences (MD) in height-for-age z-score (HAZ), and those reporting regression coefficients for HAZ differences were included in meta-analysis. Meta-analyses of cross-sectional data revealed significant associations between child protozoan infections and stunting, with the strongest evidence for Cryptosporidium spp. (AOR = 2.38, 95 % CI: 1.55 to 3.64). Giardia spp. infections were also associated with higher odds of stunting (AOR = 1.70, 95 % CI: 1.12 to 2.58) and reduced HAZ (MD: -0.42, 95 % CI: -0.53 to -0.30). Narrative synthesis of longitudinal studies supported these associations, providing robust evidence that asymptomatic infections are significantly associated with reduced growth. Five studies examined maternal protozoan infections and birth/stunting outcomes, revealing mixed evidence. Findings underscore the need for improved detection, treatment strategies, and targeted public health interventions, including better access to water, sanitation and hygiene (WASH), to address both symptomatic and asymptomatic protozoan infections. Further research is needed in particular to disentangle the relationship between maternal GI protozoan infections and child health outcomes, and to encompass a broader range of protozoan species to elucidate their impact on childhood stunting.
Epithelial barriers are critical in our interaction with the outside world. They mediate gas exchange in the lung, nutrient absorption in the gut and provide a barrier against pathogen entry throughout the body. Until relatively recently, these mechanical barrier functions were thought to represent the primary mechanism by which the epithelium protects against infection; however, current research is unveiling a broad range of interactions between epithelial barrier cells and the immune response. This Chapter reviews current evidence that the epithelium is central to the immune response to soil-transmitted helminths, with a focus on the cytokines and other mediators that epithelial cells produce. We compare and contrast the cellular sources and initiating factors that lead to epithelial cytokine production, the role of the epithelium in ejecting and killing parasitic worms, and the techniques by which these parasites counteract the activities of the epithelium.
A myriad of diseases can be treated by efficacious and potent drugs, yet the delivery efficiency is often hindered due to absorption issues, loss during first-pass metabolism, non-specific delivery, degradation before action and failure to comply to treatment. This has motivated researchers to develop novel methods for drug delivery, including live biotherapeutic products, notably transgenic bacteria delivering foreign therapeutic molecules. Recent advancements demonstrate that controlled experimental human helminth infections are tolerated and safe and may have natural protective attributes for other maladies. Helminths continuously release a cocktail of excretory/secretory proteins (ESP) during infection to aid migration and feeding, and to modulate the host's immune system. Genetic modification, and most specifically Clustered Regularly Interspaced Palindromic Repeats (CRISPR) and CRISPR-associated nucleases, has transformed the study and manipulation of the eukaryotic genome. Using these approaches to target regions of the helminth genome, it is now possible to genetically modify parasitic helminths to constitutively release therapeutic biologics. This approach could be applied to targeting diseases such as Inflammatory Bowel Disease, metabolic diseases such as type 2 diabetes, Coeliac Disease and arthritis, all of which represent a severe burden on both patients and the community. Here, we review the current evidence that wild type and genetically engineered helminths could serve as novel drug-delivery platforms. We specifically focus on species of human hookworms and schistosomes, following published controlled human infections and clinical trials in healthy and diseased human subjects.
The giant roundworm Ascaris is an important nematode parasite of humans and pigs worldwide. Ascariasis, the disease associated with Ascaris infection, is classified as a neglected tropical disease and has been targeted for elimination as a public health problem by 2030. Despite increased efforts to control Ascaris in humans, it remains highly prevalent. A major challenge is the long-term viability of Ascaris eggs in the environment, resulting in a significant reservoir. Here, we review present understanding of Ascaris environmental contamination, and existing and emerging approaches for surveillance and control. Another potential challenge is represented by the emergence of resistance to the drugs (benzimidazoles) used for Ascaris control and treatment. We describe the current evidence for resistance in Ascaris and related ascarid parasites and recent work to understand mechanisms of resistance, which may be different to those described for other nematodes. There has been much recent progress in the availability and use of 'omic resources for Ascaris. We review how 'omic data is being employed to provide insights into Ascaris population structure, drug pressure and transmission dynamics at different scales. We also describe how 'omic data is being exploited through reverse vaccinology to identify new vaccine targets for Ascaris, offering a possible alternative avenue for control. We conclude by highlighting some emerging research areas which could be applied to Ascaris and reflecting on how recent advances can impact on progress towards achievement of the WHO 2030 target.
Resistance to chemotherapy continues to limit the ability to cure infectious diseases and cancer. Resistance to antiparasitic drugs is affecting control of many pathogens in human and veterinary medicine. In veterinary medicine, particular attention has been focused on resistance to parasites of livestock, including helminths, ectoparasites and protozoa, as an effect of intensive treatment regimens that promote economic sustainability of production systems. Less attention has been given to drug resistance in parasites of companion animals. We provide a comprehensive review of current knowledge of drug resistance in ectoparasites, helminths and protozoa of importance in dogs and cats to establish a baseline assessment of the field and provide recommendations for research priorities and therapeutic alternatives.
Alveolar echinococcosis (AE) caused by Echinococcus multilocularis is a rare but serious animal and human disease in the northern hemisphere. We review published data and reports of E. multilocularis in animals and humans in Europe and North America since 2015. New findings in Europe include the first detection of AE in a wild canid (golden jackal, Canis aureus) and brown hare (Lepus europaeus); evidence for and against the role of domestic and wild felids as definitive hosts of E. multilocularis; new reports in wildlife in 2 countries and human AE in 8 countries; slow range expansion in France, Italy, and Sweden; and increased prevalence in red fox (Vulpes vulpes) in endemic regions of Austria, Italy, and Germany. New findings in North America include rapid range expansion to the west, south, and east (from 5 to 9 of the 13 provinces/territories in Canada, and from 13 to 24 of 50 states in the USA); an unprecedented number of canine and human cases of AE associated with European haplotypes, especially in Alberta, Canada; the first detection of the parasite in a new rodent intermediate host (eastern chipmunk, Tamias striatus); and the first detections in dogs as definitive hosts. Surveillance in wild canids (red fox in Europe, as well as coyotes, Canis latrans, in North America) is key to determining local risk in endemic areas, and to maintain country freedom status in Europe; in addition, recent findings suggest that large-scale screening of livers of horses and pigs may also be useful. From a One Health perspective, control of AE would benefit from voluntary case registries, regulation to prevent introduction of novel strains or hosts into new areas, increased clinical suspicion and access to early diagnoses, broad application of standardized disease staging approaches, standardized molecular classification schemes to enable source attribution and tracing between animals and humans, and increased access to established and novel chemotherapeutic options.
Parasitic worms (helminths) release extracellular vesicles (EVs) -membrane-surrounded, nanosized structures loaded with a repertoire of active biomolecules- as part of their excretory/secretory products. These particles play key roles in intercellular communication, not only within multicellular organisms but also between organisms that establish stable biological associations, as it occurs during parasitism. Since their "rediscovery" in 2012, the field of helminth EVs has expanded significantly, with a wealth of research conducted both in model organisms and parasites of human and veterinary importance. These investigations have revealed that helminth EVs play active roles in host-parasite interactions. In this article, we review milestone literature on helminth EVs and point out remaining knowledge gaps regarding several aspects of their biogenesis, composition, and interaction with the host. Furthermore, we outline current perspectives on the potential application of these bio-nanoparticles to the theragnostic of helminth infections, highlighting the main challenges hindering the translation of experimental evidence into actual EV-based tools for the control of human and livestock helminthiases.
The nematode parasites of Australasian macropodoid and vombatoid marsupials (kangaroos, wallabies and wombats) comprise a variety of endemic species, dominated by members of the superfamily Strongyloidea. Thus far, more than 300 species of strongyloid nematodes have been described from the gastrointestinal tracts of macropodoid (kangaroos, wallabies, rat-kangaroos and potoroos) and vombatoid (wombats) marsupials. These nematodes belong to the family Cloacinidae which is subdivided into two subfamilies, the Cloacininae and Phascolostrongylinae. This chapter reviews the historical and current understanding of their morphology, biology, ecology and recent advances in molecular phylogeny. Knowledge gaps in the systematics, phylogenetic relationships and evolutionary origins of the cloacinid nematodes and possible avenues for future research are also discussed.
The Neotropical region stands out as a megadiverse area in terms of herpetofauna, hosting more than 4457 species, 2233 of which are distributed across South America. Reptiles are recognized as amplifiers and reservoirs of several pathogens, yet their role in disease cycles and the vectorial potential of their mites and ticks remain poorly understood. These hosts are infested by over 500 species of mites and ticks, classified into 61 genera across 13 families within the orders Trombidiformes (Acariformes), Mesostigmata, and Ixodida (Parasitiformes). Some of these arthropods may serve as vectors of reptile vector-borne diseases (RVBDs), that include bacterial, viral and protozoal pathogens of zoonotic concern. In this article, we explore the main groups of mites and ticks that infest reptiles in the Neotropical region, with a particular focus on vector-borne zoonotic pathogens of reptiles. In addition, we discuss the intricate relationships between these animals, arthropod vectors, and the zoonotic pathogens they may transmit.
Cystoisospora suis, the cause of suckling piglet coccidiosis, is an intestinal protozoan pathogen of worldwide distribution and major economic and animal health significance in swine industry. It is closely related to cyst-forming, facultatively heteroxenic Coccidia like Toxoplasma gondii and Neospora caninum, but its biology resembles more that of the non-cyst-forming, homoxenic genus Eimeria. Lately, a unique in vitro cultivation system for C. suis was developed by which sporozoites infect monolayer cell cultures to produce merozoites which can in turn be propagated in a host-cell free system and develop into sexually differentiated gamonts, gametes and finally oocysts. This system has been used to produce and analyse developmental stages throughout the life cycle of C. suis. Transcriptomic, proteomic and secretomic data are now available, providing information for fundamental and applied research not only on this coccidian species but extrapolation to related parasites. In addition, antiparasitic compounds can be tested in this in vitro model, and further upscaling will provide a higher-throughput system for (pre-clinical) compound screening and in vitro efficacy testing for anticoccidial drugs, supporting the early detection of anticoccidial resistance in C. suis field strains. With these developments, C. suis can be considered a "non-model model" for the Coccidia, bridging the gap between the cyst-forming Sarcocystidae and the non-cyst-forming Eimeriidae, and between parasites of One Health relevance, such as T. gondii, and those members of the Coccidia that are of relevance in veterinary medicine and animal health.
The development of parasite cultures has long been pivotal in advancing parasitology, with broad applications in medicine, veterinary science, and biology. Laboratory cultures are invaluable tools for studying parasite biology, host-parasite interactions, and the development of treatments and vaccines. However, cultures of digenean trematodes under laboratory conditions remain a challenging yet critical endeavour in parasitology. These parasites hold significant importance to both human health and ecological systems. Nevertheless, trematodes exhibit a complex life cycle involving multiple hosts, which demands innovative culture methods. This review aims to provide a comprehensive overview of laboratory culture techniques for digenean trematodes, covering in vitro, in vivo, and in ovo approaches. These techniques are discussed in order across the different parasitic life stages of trematodes, from sporocyst/redia to adults, as well as the handling of trematode eggs, with a focus on optimising media composition, host-cell integration, and environmental parameters. In vitro approaches, particularly those using host-cell-based media or host-derived sera, have shown promise for certain zoonotic species. However, cultures of marine trematodes often face limitations due to suboptimal media protocols. On the other hand, in vivo and in ovo methods, while generally achieving higher success rates, raise ethical and logistical concerns. Despite notable progress, the standardisation of protocols and the adaptation of techniques for a broader range of species remain significant challenges in digenean trematode cultures. Future research should prioritise the development of host-cell-based media, innovative culture technologies, and integrative molecular and proteomic tools to address these limitations and further our understanding of trematode biology.
