Giardia duodenalis is a flagellated commensal protozoan that can infect both humans and animals. Infection can result in clinical signs such as diarrhea or, more often, the infection can be subclinical. Within the G. duodenalis species, there are several major genetic assemblages, A - H. Certain assemblages are species specific (C and D in dogs, F in cats) while assemblages A and B can infect humans as well as other mammals. This retrospective study used data collected from a commercial reference laboratory (Antech Diagnostics, Mars Petcare Science & Diagnostics). Real-time PCR data using fecal qPCR panel (KeyScreen™ GI Parasite PCR) for Giardia duodenalis and potential zoonotic assemblages A/B in 157,616 domestic cat stool samples from North America collected between March 8, 2022, to August 31, 2023, was used. Variables including age, sex, altered status, season, and geographic region were assessed to identify associations with cats that were detected for G. duodenalis and potential zoonotic assemblages A/B. The overall prevalence of G. duodenalis was 6.3% (9,962/157,616) and of those detected, 18.5% (1,840/9,962) were assemblages A/B. Cats that were G. duodenalis detected were more likely to be male, intact, less than one-year old, and in the Midwest. In general, lowest detection occurred during the summer months. Zoonotic potential detection was highest in cats aged less than one-year (19.7%; 1,011/5,137). These data highlight the importance of routine fecal screening in domestic cats to detect parasites, particularly those, like Giardia, of One Health concern, and provides prevalence, and risk factor information that aids clinical veterinary decision-making.

Giardiasis, caused by Giardia intestinalis, is a prevalent intestinal protozoan infection worldwide. Clinical manifestations are variable, and many infections remain asymptomatic. Disease pathogenesis is multifactorial, involving brush border enzyme deficiency, apoptosis, dysbiosis and increased intestinal permeability. Advances in genomics, genetic tools, and model systems have substantially improved our understanding of the parasite's virulence mechanisms. Giardia exhibits considerable genetic diversity, with distinct assemblages associated with differences in parasite biology. Attachment is mediated by the ventral disk, while the parasite's eight flagella contribute to motility and intestinal persistence. Antigenic variation of cysteine-rich surface proteins enables immune evasion and promotes chronic infection but the level of inflammation is low. The parasite releases a variety of proteins and extracellular vesicles containing proteins and small RNAs that play important roles in host-cell interactions and modulation of the gut microbiome. This review describes areas that need further research to connect pathogenesis to specific virulence mechanisms.

Giardia duodenalis is a ubiquitous enteric protozoan infecting humans, domestic animals, and wildlife worldwide. In Thailand, high densities of stray animals represent an important management challenge. However, molecular epidemiological data regarding stray cats remain limited. This study estimated the prevalence of G. duodenalis, characterized the identified genetic assemblages, and explored factors associated with PCR positivity in temple stray cats in Bangkok, Thailand.

A total of 100 fecal samples collected from cattle in the district of Viana do Castelo, northern Portugal, were molecularly screened for Cryptosporidium spp., Giardia duodenalis, and Blastocystis sp. This study represents the first molecular survey of enteric protozoa in cattle from the district of Viana do Castelo, northern Portugal. Blastocystis sp. was the most frequently detected protozoan and exhibited considerable subtype diversity, including the zoonotic subtype ST3 and the potentially zoonotic subtypes ST10a and ST14, a circumstance highlighting the occurrence in cattle of Blastocystis subtypes with potential public health relevance and the need to further investigate their cross-host transmission dynamics. Giardia duodenalis was detected at a relatively low occurrence, although unsuccessful multilocus sequence typing (MLST) amplification prevented assessment of its assemblages and zoonotic potential. Cryptosporidium spp. were not detected, likely reflecting the predominance of adult cattle in the sampled population. Overall, these findings contribute to the understanding of the molecular epidemiology of enteric protozoa in Portuguese cattle and provide updated baseline geographical data for northern Portugal. Continued molecular surveillance using optimized genotyping approaches and larger, more representative sample sets will be essential to better characterize the diversity, epidemiology, and zoonotic importance of these parasites within a One Health framework.

Enteric protozoan infections-cryptosporidiosis, giardiasis, microsporidiosis, and coccidiosis-constitute a significant global burden on human and animal health. Yet comprehensive parasitological surveys of wildlife in the eastern Tibetan Plateau, where anthropogenic, livestock, and wildlife activities extensively intersect, remain deficient. We collected 359 fecal specimens from wild carnivores across 98 random quadrats and employed molecular techniques for host identification and protozoan screening. Seven carnivore species were identified, with Tibetan fox (Vulpes ferrilata) predominating. Intestinal protozoa were exclusively recovered from Vulpes species, yielding a prevalence of 19.37% (68/351; 95% CI, 15.24%-23.51%). Eimeria falciformis (7.41%, 26/351) and Eimeria banffensis (7.12%, 25/351) were the most frequently detected, followed by Enterocytozoon bieneusi (3.70%, 13/351). Cryptosporidium was confirmed in one V. ferrilata, and Giardia intestinalis in 2 samples (V. ferrilata and Vulpes vulpes). This investigation furnishes the first molecular evidence that wild carnivores, especially V. ferrilata, harbor zoonotic protozoa including G. intestinalis assemblage AII and E. bieneusi genotypes PigEBITS5 and a D-like variant. The concurrent detection of Cryptosporidium yak genotype and E. bieneusi subgroup 1i in foxes, pikas, yaks, and sheep implies potential interspecies transmission at the wildlife-livestock interface. These findings fill knowledge gaps in regional parasite diversity and emphasize the need for enhanced surveillance of wildlife-borne protozoa under a One Health framework, thereby providing scientific evidence for zoonotic risk assessment and public health planning.

Phaeohyphomycosis is an uncommon fungal infection caused by dematiaceous (melanized) fungi, typically presenting as a localized subcutaneous nodule or cyst, and as systemic disease in immunocompromised individuals. It rarely involves the gastrointestinal tract. Esophageal candidiasis, a common fungal infection of the gastrointestinal tract, may cause dysphagia, whereas giardiasis is a protozoal infection, primarily associated with diarrhea and malabsorption. We report an unusual example of concomitant esophageal and gastric phaeohyphomycosis, esophageal candidiasis and duodenal giardiasis in an 8-year-old child, who presented with absolute dysphagia secondary to esophageal stricture and severe malnutrition. Histopathological examination established the diagnosis, and the patient was successfully managed with medical therapy, resulting in complete clinical, endoscopic, and histological resolution on follow-up.

Giardiasis is caused by the widespread intestinal parasite Giardia lamblia. The characterization of immunogenic proteins in G. lamblia has been investigated to identify potential vaccine targets, including members of the giardin family, variant-specific surface proteins (VSPs), cyst wall proteins (CWPs) and heat shock protein (HSP). The immunoglobulin-binding protein (BIP) is a HSP that has been described as immunogenic antigen; however, its role in this protozoan remains poorly characterized, particularly regarding its involvement in the humoral immune response activation, critical for parasite clearance. In this study, we evaluated the capacity of BIP to promote an antibody-mediated response through oral administration in mice. Additionally, we identified B-cell epitopes by integrated experimental and immunoinformatic approach. In mice, oral administration of BIP alone, without adjuvants, induced a specific humoral immune response at both systemic and mucosal levels, as well as, during Giardia infection, demonstrating its ability to disrupt the tolerogenic environment of the gut. Immunogenic regions of BIP were identified. A fragment around 7 kDa was recognized by specific-BIP polyclonal and monoclonal antibodies. This fragment contains two potential linear epitopes (the amino acids 64-132 and 176-190 of BIP protein) that are conserved in HSPs of other pathogens. Furthermore, in silico analyses identified additional B-cell epitopes distributed throughout the BIP sequence, reinforcing its antigenic potential. These findings support the ability of BIP to induce an efficient humoral immune response via the oral route, a key feature in infections such as giardiasis, thereby highlighting its potential as a target for vaccine development against Giardia.

Giardiasis caused by the intestinal protozoan Giardia lamblia is a major global cause of diarrheal disease and malabsorption particularly affecting young children and populations in low- and middle-income countries. Despite evidence of immunity after infection, no human vaccine is available. Induction of effective mucosal immunity is critical for protection against this lumen-dwelling pathogen, but has been hampered by the lack of suitable adjuvants. We show here in a murine model that cyclic di-(3',5')-guanosine monophosphate (CDG) is a potent mucosal adjuvant for immunization against G. lamblia with a defined antigen, α1-giardin. Based on this observation, we developed a novel nanovaccine strategy that employs metal-organic framework (MOF) nanoparticles loaded with CDG and cloaked with native G. lamblia membranes. These particles enable simultaneous delivery of multiple antigens in their native form together with a powerful mucosal adjuvant. CDG-loaded MOFs exhibited efficient cargo encapsulation and controlled release and strong immune-stimulatory activity in dendritic cells. Intranasal immunization of mice with G. lamblia membrane-coated CDG-MOFs elicited robust parasite-specific IgG responses and conferred profound protection against G. lamblia infection that was superior to that achieved with a single defined antigen. Immunization-induced protection was dependent on the CDG receptor STING and required CD4[+] T cells but was independent of secretory IgA. These findings demonstrate that MOF-based nanovaccines incorporating a cyclic dinucleotide represent an effective platform for inducing protective mucosal immunity against giardiasis. More broadly, this approach offers a versatile strategy for delivering hydrophilic adjuvants and multivalent antigens for vaccination against mucosal pathogens of the gastrointestinal tract.

Giardiasis remains a significant global health issue, and its treatment is increasingly hampered by the emergence of drug resistance and cross-resistance between nitroimidazoles and nitazoxanide. In this study, we evaluated the in vitro antigiardial activity, cytotoxicity, and potential mechanisms of action of seven structural analogs (CLB 1-7) derived from a hybrid structure combining nitazoxanide and clofibric acid. Among them, compounds CLB-3 and CLB-5 emerged as the most potent candidates, demonstrating exceptional efficacy against a nitazoxanide-resistant (NTZr) strain of Giardia lamblia, with potencies up to 43 and 60 times higher than that of the reference drug, respectively. Furthermore, both compounds demonstrated high selectivity for the parasite, exhibiting low cytotoxicity in human Caco-2 cells. To investigate the mechanism of action, functional biochemical assays revealed that treatment with these derivatives significantly reduced the intracellular ATP levels and altered the ADP/ATP ratio, indicating a direct impact on the parasite's energy metabolism. These functional findings correlate closely with RT-qPCR transcriptional analyses and in silico molecular dynamics simulations; collectively, the data suggest a multi-target mechanism of action that may involve the disruption of energy homeostasis and the possible inhibition of key enzymes in the glycolytic pathway (PFOR, G6PD::6PGL, PK, and PPDK). In summary, these results identify compounds CLB-3 and CLB-5 as highly promising chemotherapeutic candidates for combating refractory giardiasis.

Objectives: This study aimed to evaluate the intestinal mucosal alterations in lambs naturally infected with Giardia duodenalis at both histopathological and molecular levels, focusing on the relationship between infection severity and gene expression. Materials and Methods: A total of 24 lambs were categorized into four groups (control, mild, moderate, and severe) based on histopathological assessment of intestinal tissue sections. The tissues were examined for villus morphology, epithelial integrity, inflammatory cell infiltration, crypt morphology, and hyperemia. Additionally, the expression levels of FABP2, TFF3, ALPI, CLDN3, and ACTG2 genes were quantified using real-time PCR (qPCR). Results: Histopathological examination revealed progressive villus atrophy, epithelial degeneration, crypt hyperplasia, and lymphoplasmacytic infiltration in the lamina propria, which intensified with infection severity. Molecular analysis showed significant upregulation of FABP2 and TFF3 in the mild and moderate groups, suggesting early activation of mucosal repair. In contrast, ALPI expression decreased in the moderate and severe groups, indicating impaired epithelial detoxification. CLDN3 expression was significantly elevated across all infected groups, reflecting a compensatory response to tight junction disruption, while ACTG2 expression remained unchanged. Conclusions: Giardia duodenalis infection in lambs induces complex mucosal pathogenesis. The results demonstrate that the disease involves a simultaneous activation of destructive and regenerative molecular mechanisms, with distinct gene expression patterns correlating with the severity of intestinal damage.

Giardia duodenalis is a common intestinal parasite that infects children and adults worldwide. Of its eight known assemblages (A-H), assemblages A and B are the predominant genotypes infecting humans. The infection ranges from asymptomatic to chronic diarrhea, but whether disease severity depends on parasite strain or host factors remains unclear. This study analyzed Giardia isolates from non-Inflammatory Bowel Disease (non-IBD) and Inflammatory Bowel Disease (IBD) patients at PGIMER, Chandigarh, to explore link between assemblage type and symptom severity. A total of 180 non-IBD and 80 IBD patients were enrolled categorized into mild, moderate, and severe groups based on symptom severity scores. Detection was done by microscopy and nested PCR, followed by assemblage specific conventional and real-time PCR. The present study revealed that among non-IBD patients, 20 cases were identified as assemblage A, 25 as assemblage B, and 2 as mixed assemblages. Among IBD patients, 4 cases each were classified as assemblage A and assemblage B. Assemblage B predominated in the severe symptom group among non-IBD patients. In IBD patients, a possible association of assemblage A with severe symptoms was observed, although this finding remains preliminary due to the limited sample size. In non-IBD cases, assemblage A was frequent in females and B in males, while in IBD cases, assemblage A dominated in males and B showed equal distribution. This study reveals novel association between Giardia assemblages and symptom severity, highlighting the value of assemblage-level detection for better diagnosis and treatment, and the role of host factors in disease outcome.

Giardiasis has been classified as a neglected disease by the World Health Organization since 2004. Despite ongoing efforts, challenges such as drug resistance and treatment failures continue to hinder effective management. In recent years, the exploration of plant-derived compounds as antiparasitic agents has emerged as a promising strategy. This is supported by the discovery of plant-derived compounds such as quinine and artemisinin in antiparasitic pharmacology. The identification of specific molecular targets in Giardia lamblia, a protozoan with unique cytoskeletal and metabolic features, has further advanced drug discovery efforts. In this study, we evaluated the in vitro and in silico effects of a polyphenol-enriched extract from Annona muricata (soursop) leaves against G. lamblia trophozoites. The extract had a noticeable impact on parasite growth, cell adhesion, and morphology. Ultrastructural analyses revealed elongation, flagellar abnormalities, and damage to the ventral disk. Western blot and immunofluorescence assays demonstrated reduced α-tubulin expression and altered localization, indicating cytoskeletal alterations in treated trophozoites. Molecular docking analyses predicted favorable interactions between soursop polyphenols and Giardia aldose reductase, particularly involving the catalytic residues Y40 and K71. Collectively, these findings suggest that A. muricata polyphenols exert antigiardial effects through multiple cellular alterations and support the hypothesis that metabolic and cytoskeletal processes may both contribute to the observed biological effects. Further studies are required to experimentally validate the role of aldose reductase and its relationship with cytoskeletal disruption.

X-linked agammaglobulinemia (XLA) is a rare immunodeficiency caused by a mutation in Bruton's tyrosine kinase, resulting in profoundly low immunoglobulin levels and susceptibility to recurrent infections. We report a 14-year-old patient with XLA who presented with persistent fever, bloody diarrhea, and headache suggestive of pachymeningitis. The patient had chronic giardiasis. His clinical condition deteriorated with worsening thrombocytopenia, hepatitis, and minimal diffuse dural thickening on brain magnetic resonance imaging, interpreted as pachymeningitis. Empirical immunosuppressive therapy was initiated, but the patient ultimately succumbed to illness. Although Giardia has been linked to various extra-intestinal manifestations, its association with meningitis or pachymeningitis is not reported. This case highlights the complexity of managing immunocompromised patients with unexplained fever and neurological symptoms, emphasizing the need for further research into the potential neurological effects of Giardia infection.