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.
