On the structural organization of the bacillary band of Trichuris muris under cryopreparation protocols and three-dimensional electron microscopy

Simultaneous recording of the surface and internal structures of helminth parasites by fluorescence stereomicroscopy and light-sheet fluorescence microscopy (LSFM)

The study of helminth parasites has been carried out using different microscopy tools such as bright-field, fluorescence, confocal, and electron microcopies, providing morphological and ultrastructural information, which are important for morphological taxonomy. However, these microscopy techniques are unable to visualize both surface and internal structures simultaneously at high resolution in a single analysis. Consequently, researchers must use different tools to enhance the knowledge of helminths and other parasites. The present work highlights the importance of using a fluorescence stereomicroscopy based in the structured illumination to visualize simultaneously the surface and internal structures of helminth and other metazoan samples. Our results using a single equipment showed the surface topography and internal structures of the whole parasite simultaneously. In addition, the series of images can be applied to produce a three-dimensional (3D) model of the samples. These advanced methods can indeed open new frontiers for obtaining better morphological data, enriching the knowledge in helminthology, and enhancing studies of other invertebrates, especially where thick samples, which are common, are present. Recent studies with large and thick helminths have provided 2D and 3D visualization of the whole parasite. This represents an important advance in the investigation of helminth parasitology, invertebrate morphophysiology, and other areas of microanatomy study in metazoans.

Structural insights into Trichuris muris eggs through 3D modeling, Cryo-SEM, and TEM of samples prepared with HPF-FS

Trichuriasis - a disease caused by Trichuris trichiura - affects underserved communities. Infection occurs by the ingestion of embryonated eggs, a resilient structure against environmental fluctuations - an essential feature for the survival and transmission of trichurids. This study aims to enhance our comprehension of the trichurid eggs by providing a characterization of the ultrastructure of eggshell and first-stage (L1) larvae of T. muris, a key experimental model for trichuriasis. We employed the following microscopy techniques: light, fluorescence, confocal, Cryo-SEM, and Transmission electron microscopy (TEM), analyzing unfixed, chemical and cryofixed samples. Light microscopy revealed the structure of the eggshell, consisting of three main layers: Pellicula ovi (PO), chitinous layer (CHI), and the electron-dense parietal coating (EdPC). Fluorescence microscopy showed the calcein's high affinity for the eggshell and polar plugs, while the DAPI distinctly stained the L1 larval cells. Using confocal microscopy and 3D modeling, we quantified an average of 151 larval cells. TEM of high-pressure frozen and freeze-substituted samples revealed that the PO and the EdPC layers lacked sublayers, while the CHI layer was composed of 12-14 sublayers. The CHI also contained continuous distinct organization structure forming the polar plugs. The combination of different sample fixation methods and advanced imaging techniques was crucial for revealing structural details of both the eggshell and L1 larva, including the arrangement of cells, cuticle, and an anterior pointed structure. These findings provide deeper insights into the structural biology of T. muris and offer valuable information for advancing parasite control strategies in both human and veterinary context.

Experimental trichuriasis: Changes in the immune response and bacterial translocation during acute phase development illustrated with 3D model animation

Trichuriasis, a well-known type of soil-transmitted helminthiasis, is a neglected gastrointestinal nematode disease predominantly affecting children in tropical regions and is caused by Trichuris trichiura. The potential zoonotic transmission of this disease is indicated by its presence in nonhuman primates. Chronic infection leads to mucosal damage, bacterial translocation, and intense inflammatory infiltration; however, the progression of these processes remains poorly understood. This study tracks the acute phase of experimental trichuriasis, providing detailed insights into nematode tissue migration stages, inflammatory infiltration, cytokine production, and 2D/3D imaging of the bacterial translocation process. We showed a mixed immune response (Th1, Th2, and Th17) initiated by larval-induced lesions in the intestine tissue and modulated by L4 larvae and adult worms in the cecum, with systemic changes observed in the mesenteric lymph nodes, peritoneal macrophages, and spleen. Despite the disruption of the intestinal mucosa within the first 10 days post-infection (d.p.i.), bacterial invasion becomes evident only after the development of the nematode into the L3 larval stage (17 d.p.i.), intensifying with lesions caused by the L4 larvae (22 d.p.i.) and adult worms (35 d.p.i.). Our multidimensional approach, which incorporates microscopy tools, micro-CT, physiological evaluations, tissue/organ assessments, and immunological parameters, demonstrates the ability of larvae to breach the intestinal mucosa, further indicating the timing of extensive bacterial infiltration. Additionally, a 3D animation illustrates how adult worm attachment mechanisms may facilitate bacterial translocation. This study provides significant insights into the immunological and pathological mechanisms of trichuriasis progression, highlighting the complex interplay among host immune responses, the gut microbiome, and parasite survival strategies, all of which are crucial aspects for future therapeutic development.

Clinical and Diagnostic Findings in Dogs Infected with Trichuris vulpis: A Retrospective Study

Trichuris vulpis is a parasite of the large intestine of canids and has a global distribution. Despite its well-established epidemiology, the question of its pathogenicity in dogs remains debated. It has been suggested that younger age and concurrent infection with Ancylostoma caninum may be responsible for more severe clinical presentations. This retrospective study aimed to describe the clinical and diagnostic features of T. vulpis-infected dogs and to compare these findings with dogs infected with both T. vulpis and other intestinal parasites (poly-infected dogs). Forty-five dogs were included, with twenty-five being solely infected by T. vulpis and twenty poly-infected dogs. Only weight loss was more frequent (p = 0.006) in poly-infected dogs compared to T. vulpis mono-infected dogs. No significant differences were observed in laboratory abnormalities between mono-infected and poly-infected dogs. Only diarrhea was more frequent (p = 0.007) in younger dogs compared to adults. The egg shedding pattern was significantly higher (p = 0.04) among adult dogs compared to young ones, and there was a significant positive correlation between egg shedding and age (r = 0.41; p = 0.005). These findings suggest that T. vulpis might be responsible for both clinical signs and laboratory abnormalities in dogs, irrespective of the host's age and the presence of other intestinal parasites.

A Structural Analysis of Host-Parasite Interactions in Achatina fulica (Giant African Snail) Infected with Angiostrongylus cantonensis

Angiostrongylus cantonensis is a nematode parasite that resides in the pulmonary arteries of rodents, serving as its definitive hosts. The life cycle involves several species of non-marine gastropods as intermediate hosts, and the African giant snail Achatina fulica is considered one of the most important around the world. Experimental data concerning A. cantonensis infection in the African giant snail remains notably limited. This helminth causes eosinophilic meningitis or meningoencephalitis in humans, representing an emergent zoonosis in Brazil. Understanding the host-parasite relationship through the application of new tools is crucial, given the complex interaction between zoonosis and the intricate mechanisms involving wild/human hosts, parasite adaptation, and dispersion. The objective of this study was to employ SEM as a novel methodology to understand the structural organization of the host tissue, particularly the granuloma formation. This sheds light on the complex balance between A. fulica and A. cantonensis. Nine three-month-old snails were randomly selected and exposed for 24 h to a concentration of 2000 L1/dose of A. cantonensis. A necropsy was performed 37 days after the infection, and the samples were examined using light and scanning electron microscopy (SEM). The histopathological results revealed third-stage larvae of A. cantonensis associated with granulomas distributed throughout the head-foot mass, mantle, and kidney. Scanning electron microscopy of the histological section surface showed that the granuloma is surrounded by a cluster of spherical particles, which are distributed in the region bordering the larvae. This reveal details of the nematode structure, demonstrating how this methodology can enhance our understanding of the role of granulomas in molluscan tissue. The structural characteristics of granuloma formation in A. fulica suggest it as an excellent invertebrate host for A. cantonensis. This relationship appears to provide protection to the parasite against the host's immune defense system while isolating the snail's tissue from potential exposure to nematode antigens.

Another decade of Trichuris muris research: An update and application of key discoveries

The mouse whipworm, Trichuris muris, has been used for over 60 years as a tractable model for human trichuriasis, caused by the related whipworm species, T. trichiura. The history of T. muris research, from the discovery of the parasite in 1761 to understanding the lifecycle and outcome of infection with different doses (high versus low dose infection), as well as the immune mechanisms associated with parasite expulsion and chronic infection have been detailed in an earlier review published in 2013. Here, we review recent advances in our understanding of whipworm biology, host-parasite interactions and basic immunology brought about using the T. muris mouse model, focussing on developments from the last decade. In addition to the traditional high/low dose infection models that have formed the mainstay of T. muris research to date, novel models involving trickle (repeated low dose) infection in laboratory mice or infection in wild or semi-wild mice have led to important insights into how immunity develops in situ in a multivariate environment, while the use of novel techniques such as the development of caecal organoids (enabling the study of larval development ex vivo) promise to deliver important insights into host-parasite interactions. In addition, the genome and transcriptome analyses of T. muris and T. trichiura have proven to be invaluable tools, particularly in the context of vaccine development and identification of secreted products including proteins, extracellular vesicles and micro-RNAs, shedding further light on how these parasites communicate with their host and modulate the immune response to promote their own survival.

Morphological variability in the mucosal attachment site of Trichuris muris revealed by X-ray microcomputed tomography

Parasitic infections can be challenging to study because two dimensional light and electron microscopy are often limited in visualising complex and inaccessible attachment sites. Exemplifying this, Trichuris spp. inhabit a tunnel of epithelial cells within the host caecum and colon. A significant global burden of this infection persists, partly because available anthelminthics lack efficacy, although the mechanisms underlying this remain unknown. Consequently, there is a need to pioneer new approaches to better characterize the parasite niche within the host and investigate how variation in its morphology and integrity may contribute to resistance to therapeutic intervention. To address these aims, we exploited three-dimensional X-ray micro-computed tomography (microCT) to image the mouse whipworm, Trichuris muris, in caeca of wild-type C57BL/6 and SCID mice ex vivo. Using osmium tetroxide staining to effectively enhance the contrast of worms, we found that a subset exhibited preferential positioning towards the bases of the intestinal crypts. Moreover, in one rare event, we demonstrated whipworm traversal of the lamina propria. This morphological variability contradicts widely accepted conclusions from conventional microscopy of the parasite niche, showing Trichuris in close contact with the host proliferative and immune compartments that may facilitate immunomodulation. Furthermore, by using a skeletonization-based approach we demonstrate considerable variation in tunnel length and integrity. The qualitative and quantitative observations provide a new morphological point of reference for future in vitro study of host-Trichuris interactions, and highlight the potential of microCT to characterise enigmatic host-parasite interactions more accurately.

Immunoregulatory molecules secreted by Trichuris muris

Trichuris, whipworm nematode infections are prevalent in humans, domestic livestock and mammals. All share an epithelial dwelling niche and similar life cycle with the chronic infections that follow implying that immune evasion mechanisms are operating. Nematode excretory secretory (ES) products have been shown to be a rich source of immunomodulatory molecules for many species. The Trichuris muris model is a natural parasite of mice and has been used extensively to study host–parasite interactions and provides a tractable platform for investigation of the immunoregulatory capacity of whipworm ES. The present review details progress in identification of the composition of T. muris ES, immunomodulatory components and their potential mechanisms of action. The adult T. muris secretome is dominated by one protein with modulatory capacity although remains to be completely characterized. In addition, the secretome contains multiple other proteins and small molecules that have immunomodulatory potential, certainly by comparison to other Trichuris species. Moreover, T. muris-derived exosomes/exosome-like vesicles contain both protein and multiple miRNAs providing an alternate delivery process for molecules with the potential to modulate host immunity.

Trichuris muris as a tool for holistic discovery research: from translational research to environmental bio-tagging

Trichuris spp. (whipworms) are intestinal nematode parasites which cause chronic infections associated with significant morbidities. Trichuris muris in a mouse is the most well studied of the whipworms and research on this species has been approached from a number of different disciplines. Research on T. muris in a laboratory mouse has provided vital insights into the host–parasite interaction through analyses of the immune responses to infection, identifying factors underpinning host susceptibility and resistance. Laboratory studies have also informed strategies for disease control through anthelmintics and vaccine research. On the contrary, research on naturally occurring infections with Trichuris spp. allows the analysis of the host–parasite co-evolutionary relationships and parasite genetic diversity. Furthermore, ecological studies utilizing Trichuris have aided our knowledge of the intricate relationships amongst parasite, host and environment. More recently, studies in wild and semi-wild settings have combined the strengths of the model organism of the house mouse with the complexities of context-dependent physiological responses to infection. This review celebrates the extraordinarily broad range of beneficiaries of whipworm research, from immunologists and parasitologists, through epidemiologists, ecologists and evolutionary biologists to the veterinary and medical communities.