Giardia and giardiasis

Remediation of multifarious metal ions and molecular docking assessment for pathogenic microbe disinfection in aqueous solution by waste-derived Ca-MOF

The present study demonstrates an eco-friendly and cost-effective synthesis of calcium terephthalate metal-organic frameworks (Ca-MOF). The Ca-MOF were composed of metal ions (Ca2+) and organic ligands (terephthalic acid; TPA); the former was obtained from egg shells, and the latter was obtained from processing waste plastic bottles. Detailed characterization using standard techniques confirmed the synthesis of Ca-MOF with an average particle size of 461.9 ± 15 nm. The synthesized Ca-MOF was screened for its ability to remove multiple metal ions from an aqueous solution. Based on the maximum sorption capacity, Pb2+, Cd2+, and Cu2+ ions were selected for individual parametric batch studies. The obtained results were interpreted using standard isotherms and kinetic models. The maximum sorption capacity (qm) obtained from the Langmuir model was found to be 644.07 ± 47, 391.4 ± 26, and 260.5 ± 14 mg g-1 for Pb2+, Cd2+, and Cu2+, respectively. Moreover, Ca-MOF also showed an excellent ability to remove all three metal ions simultaneously from a mixed solution. The metal nodes and bonded TPA from Ca-MOF were dissociated by the acid dissolution method, which protonated and isolated TPA for reuse. Further, the crystal structure of Ca-MOF was prepared and docked with protein targets of selected pathogenic water-borne microbes, which showed its disinfection potential. Overall, multiple metal sorption capability, regeneration studies, and broad-spectrum antimicrobial activity confirmed the versatility of synthesized Ca-MOF for industrial wastewater treatment.

[Feline and canine giardiosis: An Update]

Giardia duodenalis is a facultative pathogenic intestinal parasite. Giardiosis in dogs and cats may appear with or without clinical signs. Typical signs include diarrhea with or without vomiting. The prevalence in young animals is high and may amount to up to 50%. There are 8 different genotypes (A - H), which are called assemblages. Assemblages C and D are most common in dogs and assemblage F most frequent in cats. However, animals may also be infected with the zoonotically effective assemblages A and B or exhibit mixed infections. The immunofluorescence test (IFA), the enzyme-linked immunosorbent assay (ELISA) and fecal centrifugation using zinc sulphate solution are currently recommended as diagnostic methods. Polymerase chain reaction (PCR) may be used to determine the corresponding assemblage. Approved treatments for giardiosis include fenbendazole and metronidazole. In addition, undertaking specific hygiene measures is warranted. Only animals showing clinical signs or those living in the same household with high-risk patients (e. g. immunosuppressed humans) are recommended to receive medication. The aim of treatment is clinical improvement of the diseased dogs and cats. Frequently, complete elimination of Giardia is not attained.

Molecular Epidemiology and Assemblage Typing of Giardia duodenalis in School-Age Children Situated along the Southern Shoreline of Lake Malawi, Malawi

Almost all human giardiasis infections are caused by Giardia duodenalis assemblages A and B. Differentiation between human infections with these assemblages, as well as between single-assemblage (A or B) and mixed-assemblage (A and B) infections, is therefore needed to better understand the pathological impact of infection with either, or both, assemblages. We assessed the prevalence of G. duodenalis assemblages A and B using 305 fecal samples provided by school-age children situated along the southern shoreline of Lake Malawi. Concurrently, intestinal pathology data were also collected to test for association(s) between assemblage infection status and intestinal health. Prevalence of G. duodenalis infection was 39.3% by real-time polymerase chain reaction. Of all identified infections, 32% were single G. duodenalis assemblage A and 32% were single G. duodenalis assemblage B, whereas 33% were mixed-assemblage infections. Fifteen unique G. duodenalis assemblage A and 13 unique G. duodenalis assemblage B β-giardin haplotypes were identified. There was a positive association between single infection with G. duodenalis assemblage B and both self-reporting of abdominal pain (odds ratio [OR]: 3.05, P = 0.004) and self-reporting of diarrhea (OR: 3.1, P = 0.003). No association between single infection with assemblage A and any form of intestinal pathology was found. Additionally, there was a positive association between mixed-assemblage infections and self-reporting of abdominal pain (OR: 3.1, P = 0.002). Our study highlights the importance G. duodenalis assemblage typing and reaffirms the need for improved access to water, sanitation and hygiene infrastructure in rural areas of low- and middle-income countries.

Medicinal plants as a source of antiparasitics: an overview of experimental studies

Despite advances in modern human and veterinary medicine, gastrointestinal (GI) parasitic infections remain a significant health issue worldwide, mainly in developing countries. Increasing evidence of the multi-drug resistance of these parasites and the side effects of currently available synthetic drugs have led to increased research on alternative medicines to treat parasitic infections. The exploration of potential botanical antiparasitics, which are inexpensive and abundant, may be a promising alternative in this context. This study summarizes the in vitro/in vivo antiparasitic efficacy of different medicinal plants and their components against GI parasites. Published literature from 1990-2020 was retrieved from Google Scholar, Web of Science, PubMed and Scopus. A total of 68 plant species belonging to 32 families have been evaluated as antiparasitic agents against GI parasites worldwide. The majority of studies (70%) were conducted in vitro. Most plants were from the Fabaceae family (53%, n = 18). Methanol (37%, n = 35) was the most used solvent. Leaf (22%, n = 16) was the most used plant part, followed by seed and rhizome (each 12%, n = 9). These studies suggest that herbal medicines hold a great scope for new drug discoveries against parasitic diseases and that the derivatives of these plants are useful structures for drug synthesis and bioactivity optimization.

Occurrence of Giardia duodenalis in Cats from Queretaro and the Risk to Public Health

Giardia is a protozoan that affects humans as well as a wide range of domestic species. It is distributed worldwide, and the highest frequency is seen in developing countries. Due to the potential for domestic cats to be carriers of this parasite and subsequently transmit the infection to humans, it is important to know the risk of transmission. For this reason, the objective of this study was to determine the frequency of this parasite in the cat population of the city of Santiago de Queretaro, Mexico, and identify the assemblages present to determine the role this host plays in public health, this being the first study of its type to be performed in the country. This was a cross-sectional study during which 200 fecal samples were collected from cats of both sexes and varying ages and strata of origin. The samples were analyzed by microscopy following the flotation technique, having obtained a general frequency of 25%. Giardia cysts were found at higher frequency in pasty stools. The assemblages found were zoonotic, specifically assemblage A, which suggests that the cat poses an important risk for the dissemination of the parasite to humans, making it an important public health problem.

Role of anti-Giardia recombinant cyst wall protein IgG polyclonal antibodies in diagnosis and protection

Giardia duodenalis (G. duodenalis) is an infectious protozoan that has a global distribution especially in the hot climate. Around 200 million people are infected worldwide annually by Giardia, but infection is not always accompanied by symptoms, especially in endemic countries. Using traditional microscopy techniques in diagnosis, both in stool and water samples were less sensitive when compared to immunological methods; and the need for new diagnostic methods was necessary. Also, protection from infection is required in endemic areas. Therefore, the study aimed to produce anti- G. duodenalis IgG polyclonal antibodies (pAbs) by immunizing rabbit by G. duodenalis cyst recombinant protein. The produced antibodies were evaluated in the detection of G. duodenalis antigens in patients' stool and water samples from endemic areas across River Nile; where pAbs were used as a coating and a peroxidase conjugate antibody in sandwich ELISA. Moreover, pAbs were tested for the protection of mice from giardiasis. Sandwich ELISA using pAb has succeeded in the detection of G. duodenalis coproantigens in stool samples by a sensitivity of 97% and a specificity of 92.72%. Moreover, G. duodenalis cyst was detected in only seven water samples by ordinary microscopy; while sandwich ELISA revealed nineteen positive results. IgG pAb (1/200 µg/ml) protected mice from giardiasis; which was evident from the reduction in cysts and trophozoites numbers. We recommended the use of sandwich ELISA to monitor water quality, investigate environmental contamination and diagnosis in patients' stools. The pAbs can be prepared in large amount and used in field diagnosis and protection. This will help in the early diagnosis of G. duodenalis in water, which in turn can control outbreaks in rural areas.

Natural marine products as antiprotozoal agents against amitochondrial parasites

The goal of this work is to compile and discuss molecules of marine origin reported in the scientific literature with anti-parasitic activity against Trichomonas, Giardia, and Entamoeba, parasites responsible for diseases that are major global health problems, and Microsporidial parasites as an emerging problem. The presented data correspond to metabolites with anti-parasitic activity in human beings that have been isolated by chromatographic techniques from marine sources and structurally elucidated by spectroscopic and spectrometric procedures. We also highlight some semi-synthetic derivatives that have been successful in enhancing the activity of original compounds. The biological oceanic reservoir offers the possibility to discover new biologically active molecules as lead compounds to develop new drug candidates. The molecular variety is extensive and must be correctly explored and managed. Also, it will be necessary to take some actions to preserve the source species from extinction or overharvest (e.g., by cryopreservation of coral spermatozoa, oocytes, embryos, and larvae) and coordinate appropriate exploitation to increase the chemical knowledge of the natural products generated in the oceans. Additional initiatives such as the total synthesis of complex natural products and their derivatives can help to prevent overharvest of the marine ecosystems and at the same time contribute to the discovery of new molecules.

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Natural active components of marine organisms have specific biological properties.

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The marine compounds have multiple anti-parasitic activity.

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The semi-synthetic derivatives of natural active components of marine organism are candidates for new drugs.

Linearolactone Induces Necrotic-like Death in Giardia intestinalis Trophozoites: Prediction of a Likely Target

Linearolactone (LL) is a neo-clerodane type diterpene that has been shown to exert giardicidal effects; however, its mechanism of action is unknown. This work analyzes the cytotoxic effect of LL on Giardia intestinalis trophozoites and identifies proteins that could be targeted by this active natural product. Increasing concentrations of LL and albendazole (ABZ) were used as test and reference drugs, respectively. Cell cycle progression, determination of reactive oxygen species (ROS) and apoptosis/necrosis events were evaluated by flow cytometry (FCM). Ultrastructural alterations were analyzed by transmission electron microscopy (TEM). Ligand–protein docking analyses were carried out using the LL structure raised from a drug library and the crystal structure of an aldose reductase homologue (GdAldRed) from G. intestinalis. LL induced partial arrest at the S phase of trophozoite cell cycle without evidence of ROS production. LL induced pronecrotic death in addition to inducing ultrastructural alterations as changes in vacuole abundances, appearance of perinuclear and periplasmic spaces, and deposition of glycogen granules. On the other hand, the in silico study predicted that GdAldRed is a likely target of LL because it showed a favored change in Gibbs free energy for this complex.

Bile Salt Hydrolases: At the Crossroads of Microbiota and Human Health

The gut microbiota has been increasingly linked to metabolic health and disease over the last few decades. Several factors have been suggested to be involved in lipid metabolism and metabolic responses. One mediator that has gained great interest as a clinically important enzyme is bile salt hydrolase (BSH). BSH enzymes are widely distributed in human gastrointestinal microbial communities and are believed to play key roles in both microbial and host physiology. In this review, we discuss the current evidence related to the role of BSHs in health and provide useful insights that may pave the way for new therapeutic targets in human diseases.

Observation of Giardia sp. in the termite gut of Heterotermes tenuis

Giardia comprises one genus with several morphologically distinct species described in mammals (including humans, marsupials, rodents), birds, and amphibians. This group of protists provokes diarrhoea diseases in humans and animals worldwide. Transmission of the parasite occurs through the faecal-oral route. Regarding the presence of Giardia in invertebrates, some works have shown that flies can transmit Giardia cysts by contact and transport between contaminated faeces and food. In this way, flies would eventually transmit this parasite. To date, Giardia's presence in the gut of other invertebrates has not been described in the literature. Here we show by first time, using scanning electron microscopy, the presence of Giardia-like trophozoites in the gut of termite Heterotermes tenuis. Two groups of Giardia were found based exclusively on the size and the flange shape of the protozoa: one presented eight flagella, a ventral disc, size, and shape very similar to Giardia intestinalis. In contrast, other cells were smaller and showed some differences in the external morphology. We cannot exclude the possibility that they correspond to the same species and that these differences result from protozoan heterogeneity.

Epidemiology of Giardia duodenalis assemblages in Brazil: there is still a long way to go

Giardia duodenalis infection is distributed worldwide and can achieve prevalence around 60%, especially in developing countries. This protozoan is divided into eight assemblages, in which A and B have high zoonotic potential, whereas C to H are host-specific. This scenario is changing as molecular studies progress, highlighting that knowledge on host-specificity still has a long way to go. Understanding the players involved in transmission routes enables rational designs of control strategies. Considering the high prevalence of giardiasis, this review aims to gather together the data on available studies on the distribution of G. duodenalis assemblages in Brazil until September 2020.

Anti-Giardia Drug Discovery: Current Status and Gut Feelings

Giardia parasites are ubiquitous protozoans of global importance that impact a wide range of animals including humans. They are the most common enteric pathogen of cats and dogs in developed countries and infect ∼1 billion people worldwide. While Giardia infections can be asymptomatic, they often result in severe and chronic diseases. There is also mounting evidence that they are linked to postinfection disorders. Despite growing evidence of the widespread morbidity associated with Giardia infections, current treatment options are limited to compound classes with broad antimicrobial activity. Frontline anti-Giardia drugs are also associated with increasing drug resistance and treatment failures. To improve the health and well-being of millions, new selective anti-Giardia drugs are needed alongside improved health education initiatives. Here we discuss current treatment options together with recent advances and gaps in drug discovery. We also propose criteria to guide the discovery of new anti-Giardia compounds.

Intestinal Schistosomiasis and Giardiasis Co-Infection in Sub-Saharan Africa: Can a One Health Approach Improve Control of Each Waterborne Parasite Simultaneously?

Both intestinal schistosomiasis and giardiasis are co-endemic throughout many areas of sub-Saharan Africa, significantly impacting the health of millions of children in endemic areas. While giardiasis is not considered a neglected tropical disease (NTD), intestinal schistosomiasis is formally grouped under the NTD umbrella and receives significant advocacy and financial support for large-scale control. Although there are differences in the epidemiology between these two diseases, there are also key similarities that might be exploited within potential integrated control strategies permitting tandem interventions. In this review, we highlight these similarities and discuss opportunities for integrated control of giardiasis in low and middle-income countries where intestinal schistosomiasis is co-endemic. By applying new, advanced methods of disease surveillance, and by improving the provision of water, sanitation and hygiene (WASH) initiatives, (co)infection with intestinal schistosomiasis and/or giardiasis could not only be more effectively controlled but also better understood. In this light, we appraise the suitability of a One Health approach targeting both intestinal schistosomiasis and giardiasis, for if adopted more broadly, transmission of both diseases could be reduced to gain improvements in health and wellbeing.

An image-based Pathogen Box screen identifies new compounds with anti-Giardia activity and highlights the importance of assay choice in phenotypic drug discovery

Giardia duodenalis, the most prevalent human intestinal parasite causes the disease, giardiasis. On an annual basis G. duodenalis infects ~1 billion people, of which ~280 million develop symptomatic disease. Giardiasis can be severe and chronic, causing malnutrition, stunted growth and poor cognitive development in children. Current treatment options rely on drugs with declining efficacy and side-effects. To improve the health and well-being of millions of people world-wide, new anti-Giardia drugs with different modes of action to currently used drugs are required. The Medicines for Malaria Venture's Pathogen Box, a collection of bio-active compounds specifically chosen to stimulate infectious disease drug discovery, represents an opportunity for the discovery of new anti-Giardia agents. While the anti-Giardia activity of Pathogen Box compounds has been reported, this work failed to identify known anti-Giardia controls within the compound set. It also reported the activity of compounds previously screened and shown to be inactive by others, suggesting data may be inaccurate. Given these concerns the anti-Giardia activity of Pathogen Box compounds was re-assessed in the current study. Data from this work identified thirteen compounds with anti-Giardia IC₅₀ values ≤2 μM. Five of these compounds were reference compounds (marketed drugs with known anti-microbial activity), or analogues of compounds with previously described anti-Giardia activity. However, eight, including MMV676358 and MMV028694, which demonstrated potent sub-μM IC₅₀s against assemblage A, B and metronidazole resistant parasites (0.3 μM and 0.9 μM respectively), may represent new leads for future drug development. Interestingly, only four of these compounds were identified in the previously reported Pathogen Box screen highlighting the importance of assay selection and design when assessing compounds for activity against infectious agents.

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13 compounds with anti-Giardia IC₅₀ values < 2 μM were identified.

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8 compounds represent new leads for drug development.

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MMV676358 and MMV028694 demonstrated the most promising acting.

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Data highlight the importance of assay selection and design in drug discovery.

Giardia Infection and Trypanosoma Cruzi Exposure in Dogs in the Bosawás Biosphere Reserve, Nicaragua

Indigenous Mayangna and Miskitu inhabit Nicaragua's remote Bosawás Biosphere Reserve, located in the North Caribbean Coast Autonomous Region. They are sedentary horticulturists who supplement their diet with wild game, hunting with the assistance of dogs. To test whether hunting dogs increased the risk of human exposure to protozoal zoonotic neglected tropical diseases (NTDs), we sampled dogs from three communities varying in population size and level of contact with other communities. We screened dog feces (n = 58) for Giardia and Cryptosporidium DNA and sera (n = 78) for Trypanosoma cruzi antibodies and DNA. Giardia DNA was detected in 22% (13/58) of samples; sequencing revealed the presence of both zoonotic genotypes (assemblages A and B) and dog-specific genotypes (assemblages C and D). Giardia shedding was associated with community and age. Older dogs and those in the two, more accessible communities had greater odds of shedding parasites. Seroprevalence of T. cruzi antibodies, indicating prior exposure, was 9% (7/78). These results contribute to the limited literature on NTDs in indigenous populations, and suggest hunting dogs can both serve as sentinels of environmental NTDs and pose zoonotic risk for their owners and communities.

First report of Giardia duodenalis infection in bamboo rats

Background

The zoonotic parasite, Giardia duodenalis (syns. G. lamblia and G. intestinalis), has been widely reported in humans and animals, including rodents. The bamboo rat, a rodent species belonged to the subfamily Rhizomyinae, is farmed in China because of its medicinal and edible values. However, no information of G. duodenalis infection was available in bamboo rats prior to the present study. Here, the prevalence and genetic diversity of G. duodenalis in bamboo rats from Hunan Province of China were investigated.

Results

Of 480 faecal samples collected from six farms located in four cities (Wugang, Chenzhou, Huaihua and Jishou) of Hunan Province, 52 (10.8%) were positive for G. duodenalis infection by using a nested PCR approach targeting the beta giardin (bg) gene. Significant differences (P < 0.01) in prevalence were found among different age groups and geographical localities, and among different farms in Wugang city. Sequence analysis revealed existence of the zoonotic assemblage B and genetic diversity of G. duodenalis in these animals. Multilocus genotyping analysis also indicated broad genetic diversity of assemblage B isolates in these bamboo rats.

Conclusions

This is the first report of the infection and genetic variations of G. duodenalis in bamboo rats. These findings will provide basic data for implementing effective strategies to control giardiasis in bamboo rats.

Electronic supplementary material

The online version of this article (10.1186/s13071-018-3111-2) contains supplementary material, which is available to authorized users.

The course of experimental giardiasis in Mongolian gerbil

Fifteen Mongolian gerbils were inoculated with 10 × 10⁶ viable trophozoites of Giardia intestinalis. Their faeces were examined daily by flotation method and the number of shed cysts was counted. Two animals (male and female) were euthanised at 4- to 5-day intervals (9, 14, 18 days post-infection (DPI)). The remaining nine gerbils were sacrificed and dissected at the end of the experiment (23 DPI). Their small intestinal tissues were processed for examination using histological sectioning and scanning electron microscopy and their complete blood count (CBC) was examined. The highest number of trophozoites at the total was observed in the duodenum in gerbils sacrificed on 14 DPI. Number of shed cysts was positively correlated with number of trophozoites rinsed from the intestine. Infected gerbils had lower body weight gain in comparison with control group and in three male gerbils; diarrhoea occurred during infection. Cyst shedding was negatively correlated with values of mean corpuscular haemoglobin concentration. Females showed another pattern in cyst shedding than males. This information needs to be taken into account while planning the experiments.

Bile Salt Hydrolase Activities: A Novel Target to Screen Anti-Giardia Lactobacilli?

Giardia duodenalis is a protozoan parasite responsible for giardiasis, a disease characterized by intestinal malabsorption, diarrhea and abdominal pain in a large number of mammal species. Giardiasis is one of the most common intestinal parasitic diseases in the world and thus a high veterinary, and public health concern. It is well-established that some probiotic bacteria may confer protection against this parasite in vitro and in vivo and we recently documented the implication of bile-salt hydrolase (BSH)-like activities from strain La1 of Lactobacillus johnsonii as mediators of these effects in vitro. We showed that these activities were able to generate deconjugated bile salts that were toxic to the parasite. In the present study, a wide collection of lactobacilli strains from different ecological origins was screened to assay their anti-giardial effects. Our results revealed that the anti-parasitic effects of some of the strains tested were well-correlated with the expression of BSH-like activities. The two most active strains in vitro, La1 and Lactobacillus gasseri CNCM I-4884, were then tested for their capacity to influence G. duodenalis infection in a suckling mice model. Strikingly, only L. gasseri CNCM I-4884 strain was able to significantly antagonize parasite growth with a dramatic reduction of the trophozoites load in the small intestine. Moreover, this strain also significantly reduced the fecal excretion of Giardia cysts after 5 days of treatment, which could contribute to blocking the transmission of the parasite, in contrast of La1 where no effect was observed. This study represents a step toward the development of new prophylactic strategies to combat G. duodenalis infection in both humans and animals.

Effect of Piper betle on Giardia intestinalis infection in vivo

Piper betle has been used as a medicinal plant in traditional medical systems throughout South and South East Asia. Experimental studies have revealed its wide and diverse biological and pharmacological effects. In this study, antigiardial activity of Piper betle was tested using experimental infections of Giardia intestinalis, the most common cause of protozoal diarrhoea worldwide, in Mongolian gerbils. Plants were extracted in water, methanol and methanol:tetrahydrofuran. Gerbils were treated for ten days intragastrically twice a day, with the dose of 40 mg of the extract per 100 g of body weight. Drug metronidazole was used as a negative control. Gerbils' faeces were taken every day and examined by flotation method, the number of shed cysts were counted using a haemocytometer. After gerbils' sacrifice and dissection, their duodena were then processed for examination using histological sectioning and scanning electron microscopy. The antigiardial activity was evaluated by the course of cyst shedding throughout the entire experiment. A significant decline in cyst shedding, evaluated by linear regression was found in gerbils treated with the aqueous extract. Our results indicate that the aqueous extract of P. betle shows giardicidal effects.

TLR2-/- Mice Display Decreased Severity of Giardiasis via Enhanced Proinflammatory Cytokines Production Dependent on AKT Signal Pathway

Giardia infection is one of the most common causes of waterborne diarrheal disease in a wide array of mammalian hosts, including humans globally. Although numerous studies have indicated that adaptive immune responses are important for Giardia defense, however, whether the host innate immune system such as TLRs recognizes Giardia remains poorly understood. TLR2 plays a crucial role in pathogen recognition, innate immunity activation, and the eventual pathogen elimination. In this study, we investigated the role of TLR2 as a non-protective inflammatory response on controlling the severity of giardiasis. RT-PCR analysis suggested that TLR2 expression was increased in vitro. We demonstrated that Giardia lamblia-induced cytokines expression by the activation of p38 and ERK pathways via TLR2. Interestingly, the expression of IL-12 p40, TNF-α, and IL-6, but not IFN-γ, was enhanced in TLR2-blocked and TLR2^−/− mouse macrophages exposed to G. lamblia trophozoites compared with wild-type (WT) mouse macrophages. Further analysis demonstrated that G. lamblia trophozoites reduced cytokines secretion by activating AKT pathway in WT mouse macrophages. Immunohistochemical staining in G. lamblia cysts infected TLR2^−/− and WT mice showed that TLR2 was highly expressed in duodenum in infected WT mice. Also, infected TLR2^−/− and AKT-blocked mice showed an increased production of IL-12 p40 and IFN-γ compared with infected WT mice at the early stage during infection. Interestingly, infected TLR2^−/− and AKT-blocked mice displayed a decreased parasite burden, an increased weight gain rate, and short parasite persistence. Histological morphometry showed shortened villus length, hyperplastic crypt and decreased ratio of villus height/crypt depth in infected WT mice compared with in infected TLR2^−/− and AKT-blocked mice. Together, our results suggested that TLR2 deficiency leads to alleviation of giardiasis and reduction of parasite burden through the promotion of proinflammatory cytokines production. For the first time, our results demonstrated that TLR2 played a negative role in host defense against Giardia.

More bark than bite: Comparative studies are needed to determine the importance of canine zoonoses in Aboriginal communities. A critical review of published research

The objective of this review was to identify and critique over forty years of peer‐reviewed literature concerned with the transmission of canine zoonoses to Aboriginal people and determine the zoonotic organisms documented in dogs in Australian Aboriginal communities. A systematic literature search of public health, medical and veterinary databases identified 19 articles suitable for critical appraisal. Thirteen articles documented the occurrence of recognized zoonotic organisms in dogs in Aboriginal communities, including Toxocara canis, Dirofilaria immitis, Streptococcus dysgalactiae, Rickettsia felis, Sarcoptes scabiei and Giardia. Currently, there is definitive evidence indicating that dogs act as a reservoir for human scabies in Aboriginal communities. However, there is a need for large‐scale, high‐quality, comparative studies of dogs and humans from the same household to assess the occurrence and importance of transmission of S. scabiei and other diseases between dogs and humans. These studies should use current genetic and molecular techniques along with traditional techniques to identify and type organisms in order to better understand their epidemiology. This review has revealed that there is a lack of high‐quality comparative studies to determine whether dogs are contributing to human disease by transmitting zoonoses. Our recommendations differ significantly from current public health policy and may have substantial implications for human and dog health.

Vaccination of domestic animals with a novel oral vaccine prevents Giardia infections, alleviates signs of giardiasis and reduces transmission to humans

Giardia lamblia is a human intestinal parasite and one of the most frequent enteric pathogen of companion animals. Clinical manifestations of giardiasis, such as diarrhoea, anorexia, weight loss and lethargy, have been associated with Giardia infections in both domestic and farm animals. A few anti-parasitic drugs are routinely used to treat giardiasis, but re-infections are common and drug-resistant strains have already been reported. Unfortunately, efficient vaccines against Giardia are not available. Giardia undergoes antigenic variation; through this mechanism, parasites can avoid the host’s immune defenses, causing chronic infections and/or re-infections. Antigenic variation is characterised by a continuous switch in the expression of members of a homologous family of genes encoding surface antigens. In a previous report, we indicated that in Giardia, the mechanism responsible for the exchange of variant-specific surface proteins (VSPs) involves the RNA interference (RNAi) pathway. From a repertoire of ~200 VSP genes, only one is expressed on the surface of single trophozoites; however, RNAi machinery disruption generates trophozoites that express the complete VSP repertoire. We also demonstrated that gerbils orally immunised with VSPs isolated from these altered parasites showed high levels of protection. Here we tested this vaccine in cats and dogs, and found that it is highly efficient in preventing new infections and reducing chronic giardiasis in domestic animals both in experimental and natural infections. Remarkably, immunisation of dogs in a highly endemic area strongly decreased the percentage of infected children in the community, suggesting that this vaccine would block the zoonotic transmission of the disease.

Adaptive immune response in symptomatic and asymptomatic enteric protozoal infection: evidence for a determining role of parasite genetic heterogeneity in host immunity to human giardiasis

The genetic basis of the ultimate clinical outcomes of human giardiasis has been the subject of numerous investigations. We previously demonstrated roles for both host and parasite factors in determining the outcome of enteric infection in a murine model of Giardia duodenalis infection. In the current study, fecal and serum specimens from healthy controls and human subjects infected with the intestinal parasite G. duodenalis were assessed. Using a semi-nested PCR method, clinical isolates were genetically characterized based on the gdh and tpi loci, and the phylogenetic trees were constructed. Using a sandwich ELISA method, the serum levels of representative T_H1 and T_H2 cytokines were measured in infected human subjects and healthy controls. Here we showed that symptomatic human giardiasis was characterized by significantly elevated serum levels of the T_H1 cytokine IFN-γ compared to healthy controls, whereas asymptomatic human subjects and healthy controls had comparable levels of serum IFN-γ. Further analyses showed that human subjects infected with G. duodenalis genotype AI had significantly elevated levels of serum IFN-γ and IL-10, but not IL-5, whereas human subjects infected with AII had similar levels of those cytokines compared to healthy controls. These data demonstrate roles for both host and parasite factors in the determination of the outcome of enteric infections and may further broaden our understanding of host-parasite interaction during enteric protozoal infections.

Anti-giardial therapeutic potential of dichloromethane extracts of Zingiber officinale and Curcuma longa in vitro and in vivo

Giardiosis is one of the common parasitic diarrhoea in humans, especially in children, worldwide. Many drugs are used for its treatment, but there is evidence of drug resistance, insufficient efficacy and unpleasant side effects. Natural products are good candidates for discovering more effective anti-giardial compounds. This study evaluated the activity of extracts of Zingiber officinale (ginger) and Curcuma longa (curcumin) against Giardia lamblia in vitro and in vivo. Giardia cyst suspension was prepared from children faecal specimens. For the in vitro experiment, 1, 10 and 50 mg⁄mL dichloromethane extracts of ginger and curcumin separately were incubated with Giardia cysts for 5, 10, 30 and 60 min. The viability was distinguished by 0.1 % eosin and a haemocytometer. For the in vivo experiments, Balb/c mice were infected with Giardia cyst suspension containing 10,000 cysts/mL. Infected mice were administered 10 and 20 mg kg(-1) day(-1) ginger and curcumin extracts separately for 7 days post-infection. The effectiveness of the extracts was evaluated by faecal cyst and intestinal trophozoite counts and histopathological examination of the small intestine. In vitro ginger extract had a higher significant effect on cyst viability than curcumin, in a dose- and time-dependent manner. In vivo ginger (more effective) and curcumin extracts significantly treated infected mice, and this was evidenced by the faecal cyst and intestinal trophozoite counts reduction, in addition to evident improvement of intestinal mucosal damages induced by Giardia infection. Z. officinale and C. longa extracts may represent effective and natural therapeutic alternatives with low side effects and without drug resistance in the treatment of giardiosis.

Predominance of Giardia duodenalis Assemblage AII in Fresh Leafy Vegetables from a Market in Southern Brazil

We investigated the presence of Giardia duodenalis cysts and its genotypes in raw leafy vegetables sold in a Brazilian market. These products are different from those sold in most street markets because the producers themselves display and sell their products and rely on specialized technical and sanitary assistance. Vegetable and water samples were collected from 14 (80%) producers who cultivated vegetables that are typically consumed raw for sale at the market, obtained at the market and farms, respectively. A total of 128 samples of leafy greens (chives, parsley, cabbage, arugula, watercress, and chicory) and 14 water samples were analyzed by direct immunofluorescence and PCR techniques. The positive samples were genotyped (GHD gene) using PCR and restriction fragment length polymorphism. The analyses indicated that 16 (12.5%) of 128 samples were positive by PCR, while 1 (0.8%) of 128 samples were positive by immunofluorescence. Giardia cysts were not detected in the water samples obtained at the farms. The molecular technique revealed a genotype with zoonotic potential, which underscores the challenge in the control of giardiasis dissemination via the consumption of raw vegetables.

Complement Activation by Giardia duodenalis Parasites through the Lectin Pathway Contributes to Mast Cell Responses and Parasite Control

Infection with Giardia duodenalis is one of the most common causes of diarrheal disease in the world. While numerous studies have identified important contributions of adaptive immune responses to parasite control, much less work has examined innate immunity and its connections to the adaptive response during this infection. We explored the role of complement in immunity to Giardia using mice deficient in mannose-binding lectin (Mbl2) or complement factor 3a receptor (C3aR). Both strains exhibited delayed clearance of parasites and a reduced ability to recruit mast cells in the intestinal submucosa. C3aR-deficient mice had normal production of antiparasite IgA, butex vivo T cell recall responses were impaired. These data suggest that complement is a key factor in the innate recognition of Giardia and that recruitment of mast cells and activation of T cell immunity through C3a are important for parasite control.

Phenotypic variation in Blastocystis sp. ST3

Background

Blastocystis, is one of the most common human intestinal protozoan, which has many conflicting reports on its pathogenic role. Gut conditions which obviously varies in asymptomatic individuals, symptomatic and irritable bowel syndrome (IBS) patients in terms of gut flora, pH, osmotic pressure and water potentials could play an important role in its pathogenicity. The present study is the first study to investigate phenotypic characteristics of Blastocystis sp. ST3 isolated from asymptomatic, symptomatic and IBS isolates.

Methods

A total of 8 Blastocystis isolates were obtained from four IBS patients (IBS1-4) and four symptomatic patients (S1-4) at a local gastroenterology clinic. Asymptomatic isolates (A1-4) were obtained from a field survey at a local village.

Results

All 12 isolates were determined as subtype 3 (ST3). A1-4 isolates showed the highest peak growth followed by IBS1-4 isolates and S1-4 isolates for the growth profile. Parasites from IBS isolates (IBS1-4) showed the largest diameter with a mean 18.43 ± 2.22 μm compared to parasites of symptomatic isolates (isolates S1-4) 15.54 ± 3.02 μm and asymptomatic isolates (isolates A1-4) 11.76 ± 0.82 μm. The symptomatic isolates (average generation time: 9.87 ± 2.97 h) grew faster than the IBS isolates (average generation time: 7.56 ± 1.06 h) and asymptomatic isolates (average generation time: 5.97 ± 1.52 h). The parasites isolated from IBS isolates showed strong aggregation and clumping, which had seen reduced in parasites of isolates S1-4. No clumping was seen in parasites from A1-4. The outer surface of parasites in IBS isolates showed greater binding affinities towards FITC-labelled Concanavalin A (Con A) than symptomatic isolates and asymptomatic isolates. Scanning electron microscopy showed that in IBS isolates, the surface of Blastocystis showed a very coarse and intensely folded surface. The IBS isolates also exhibited a dense material and a thicker layer of surface coat can be seen compared to asymptomatic and symptomatic isolates.

Conclusion

There have been no studies thus far providing evidence for phenotypic variation within a particular subtype. The present study is the first to demonstrate the phenomenon of gut environment facilitating adaptation of parasites possibly for survival leading to phenotypic differences for Blastocystis.

In vitro antigiardial activity of the cysteine protease inhibitor E-64

The quest for new antiparasitic alternatives has led researchers to base their studies on insights into biology, host-parasite interactions and pathogenesis. In this context, proteases and their inhibitors are focused, respectively, as druggable targets and new therapy alternatives. Herein, we proposed to evaluate the in vitro effect of the cysteine protease inhibitor E-64 on Giardia trophozoites growth, adherence and viability. Trophozoites (10⁵) were exposed to E-64 at different final concentrations, for 24, 48 and 72 h at 37 °C. In the growth and adherence assays, the number of trophozoites was estimated microscopically in a haemocytometer, whereas cell viability was evaluated by a dye-reduction assay using MTT. The E-64 inhibitor showed effect on growth, adherence and viability of trophozoites, however, its better performance was detected in the 100 µM-treated cultures. Although metronidazole was more effective, the E-64 was shown to be able to inhibit growth, adherence and viability rates by ≥ 50%. These results reveal that E-64 can interfere in some crucial processes to the parasite survival and they open perspectives for future investigations in order to confirm the real antigiardial potential of the protease inhibitors.

Transcriptomic analysis of the host response to Giardia duodenalis infection reveals redundant mechanisms for parasite control

The immune system has numerous mechanisms that it can use to combat pathogens and eliminate infections. Nevertheless, studies of immune responses often focus on single pathways required for protective responses. We applied microarray analysis of RNA in order to investigate the types of immune responses produced against infection with the intestinal pathogen Giardia duodenalis. Infection with G. duodenalis is one of the most common causes of diarrheal disease in the world. While several potential antiparasitic effector mechanisms, including complement lysis, nitric oxide (NO), and α-defensin peptides, have been shown to inhibit parasite growth or kill Giardia in vitro, studies in vivo have thus far shown clear roles only for antibody and mast cell responses in parasite control. A total of 96 transcripts were identified as being upregulated or repressed more than 2-fold in the small intestine 10 days following infection. Microarray data were validated using quantitative PCR. The most abundant category of transcripts was antibody genes, while the most highly induced transcripts were all mast cell proteases. Among the other induced transcripts was matrix metalloprotease 7 (Mmp7), the protease responsible for production of mature α-defensins in mice. While infections in Mmp7-deficient mice showed only a small increase in parasite numbers, combined genetic deletion of Mmp7 and inducible nitric oxide synthase (iNOS, Nos2) or pharmacological blockade of iNOS in Mmp7-deficient mice resulted in significant increases in parasite loads following infection. Thus, α-defensins and NO are redundant mechanisms for control of Giardia infections in vivo.

The immune system has multiple weapons which it uses to help control infections. Many infections result in activation of several of these response mechanisms, but it is not always clear which responses actually contribute to control of the pathogen and which are bystander effects. This study used the intestinal parasite Giardia duodenalis to examine the redundancy in immune responses during infections in mice. Our results showed that at least four distinct mechanisms are activated following infections. Furthermore, by blocking two pathways at the same time, we showed that both mechanisms contribute to control of the infection, whereas blocking single responses showed no or minimal effect in these cases.

Effects of metronidazole analogues on Giardia lamblia: experimental infection and cell organization

The chemotherapeutic agents used for the treatment of giardiasis are often associated with adverse side effects and are refractory cases, due to the development of resistant parasites. Therefore the search for new drugs is required. We have previously reported the giardicidal effects of metronidazole (MTZ) and its analogues (MTZ-Ms, MTZ-Br, MTZ-N(3), and MTZ-I) on the trophozoites of Giardia lamblia. Now we evaluated the activity of some giardicidal MTZ analogues in experimental infections in gerbils and its effects on the morphology and ultrastructural organization of Giardia. The giardicidal activity in experimental infections showed ED(50) values significantly lower for MTZ-I and MTZ-Br when compared to MTZ. Transmission electron microscopy was employed to approach the mechanism(s) of action of MTZ analogues upon the protozoan. MTZ analogues were more active than MTZ in changing significantly the morphology and ultrastructure of the parasite. The analogues affected parasite cell vesicle trafficking, autophagy, and triggered differentiation into cysts. These results coupled with the excellent giardicidal activity and lower toxicity demonstrate that these nitroimidazole derivates may be important therapeutic alternatives for combating giardiasis. In addition, our results suggest a therapeutic advantage in obtaining synthetic metronidazole analogues for screening of activities against other infectious agents.

Prevalence and risk factors for Giardia duodenalis infection among children: a case study in Portugal

Background

Giardia duodenalis is a widespread parasite of mammalian species, including humans. The prevalence of this parasite in children residing in Portugal is currently unknown. This study intended to estimate G. duodenalis infection prevalence and identify possible associated risk factors in a healthy paediatric population living in the District of the Portuguese capital, Lisbon.

Methods

Between February 2002 and October 2008, 844 children were randomly selected at healthcare centres while attending the national vaccination program. A stool sample and a questionnaire with socio-demographic data were collected from each child. Giardia infection was diagnosed by direct examination of stools and antigen detection by ELISA.

Results

The population studied revealed a gender distribution of 52.8% male and 47.2% female. Age distribution was 47.4% between 0-5 years and 52.6% between 6-15 years.

The prevalence of Giardia infection was 1.9% (16/844) when estimated by direct examination and increased to 6.8% (57/844) when ELISA results were added. The prevalence was higher among children aged 0-5 years (7.8%), than among older children (5.8%), and was similar among genders (6.9% in boys and 6.5% in girls). The following population-variables were shown to be associated risk factors for G. duodenalis infection: mother's educational level (odds ratio (OR)= 4.49; confidence interval (CI): 1.20-16.84), father's educational level (OR = 12.26; CI: 4.08-36.82), presence of Helicobacter pylori infection (OR = 1.82; CI: 1.05-3.15), living in houses with own drainage system (OR = 0.10; CI: 0.02-0.64) and reported household pet contact, especially with dogs (OR = 0.53; CI: 0.31-0.93).

Conclusion

The prevalence of giardiasis in asymptomatic children residing in the region of Lisbon is high. Several risk factors were associated with Giardia prevalence and highlight the importance of parents' education and sanitation conditions in the children's well being. The association between G. duodenalis and H. pylori seems an important issue deserving further investigation in order to promote prevention or treatment strategies.

Seasonal prevalence and incidence of Cryptosporidium spp. and Giardia duodenalis and associated diarrhoea in children attending pre-school in Kafue, Zambia

Prevalence, incidence and seasonal variation of Cryptosporidium and Giardia duodenalis were studied over a 12-month period in 100 children from four pre-schools in Kafue, Zambia. Questionnaire data and a single stool sample were collected monthly from each child. Samples were processed using a commercial kit (Meridian Diagnostics Inc., USA) and oo(cysts) visualised by immunofluorescence microscopy. Cryptosporidium was detected in 30.7% (241/786; 95% CI = 27.5-33.9) while G. duodenalis was detected in 29.0% (228/786; 95% CI = 25.8-32.2). A total of 86% experienced one or more episodes of cryptosporidiosis while 75% had giardiasis. Cumulative incidence per 100 children was 75.4 for Cryptosporidium and 49.0 for G. duodenalis. Both infections were significantly more common in the wet compared to the dry season (34.8%, 162/466 vs. 24.7%, 79/320, P = 0.003 and 35.2%, 164/466 vs. 20.0%, 64/320, P < 0.001, respectively). Thus, risk ratios (RR) were 1.41 (95% CI = 1.13-1.77) and 1.76 (95% CI = 1.38-2.27) for Cryptosporidium and Giardia, respectively. Diarrhoea was significantly associated with cryptosporidiosis (RR = 1.23, 95% CI = 1.03-1.47; P = 0.029) but not with giardiasis (RR = 1.12, 95% CI = 0.91-1.53; P = 0.26). We conclude that gastro-intestinal protozoal infections are highly prevalent among children attending pre-school in peri-urban Zambia highlighting the need for further studies of risk factors.

Giardia duodenalis: the double-edged sword of immune responses in giardiasis

Giardiasis is one of the most common intestinal protozoan infections worldwide. The etiological agent, Giardia duodenalis (syn. Giardia lamblia, Giardia intestinalis), is a flagellated, binucleated protozoan parasite which infects a wide array of mammalian hosts (Adam, 2001). The symptoms of giardiasis include abdominal cramps, nausea, and acute or chronic diarrhea, with malabsorption and failure of children to thrive occurring in both sub-clinical and symptomatic disease (Thompson et al., 1993). Infections are transmitted by cysts which are excreted in the feces of infected humans and animals. Human giardiasis is distributed worldwide, with rates of detection between 2-5% in the developed world and 20-30% in the developing nations (Farthing, 1994). There is significant variation in the outcome of Giardia infections. Most infections are self-limiting, although re-infection is common in endemic areas and chronic infections also occur. Moreover, some individuals suffer from severe cramps, nausea and diarrhea while others escape these overt symptoms. This review will describe recent advances in parasite genetics and host immunity that are helping to shed light on this variability.

Risk factors for the initial symptomatic giardia infection in a cohort of young Arab-Bedouin children

BACKGROUND

Giardiasis is a common protozoan infection with clinical manifestations in children ranging from asymptomatic carriage to persistent diarrhoea with malabsorption. It can lead to growth and developmental retardation.

AIM

The study evaluated risk factors for the initial symptomatic giardiasis (SG) episode among Arab-Bedouin children in Israel.

METHODS

A community-based, prospective cohort study was conducted in Rahat, a Bedouin township in southern Israel. Infants (n=238) were followed by weekly visits from birth to age 18 months. Giardia infection was identified by antigen detection in faecal specimens.

RESULTS

Approximately 26% of children experienced one or more SG episode. Mean (SD) age for first SG episode was 12.3 (3.3) months, with 95% of episodes occurring in children >6 months of age. Risk for the first SG in children >6 months of age was associated with it being spring or summer [odds ratio (OR) 6.16, p<0.001], exposure to livestock (OR 4.89, p=0.002) and prior infection with entero-aggregative Escherichia coli (EAEC) (OR 1.12 for each additional percentage in stool prevalence, p=0.02). Weight-for-age Z-scores at age 6 months were inversely related to SG risk (OR 0.62 for each unit increase in Z-score, p=0.029).

CONCLUSIONS

Giardiasis is an important cause of diarrhoea in Bedouin children. Increased risk of SG in spring/summer might be linked to environmental conditions or seasonal dietary practices which increase virulence or transmission. SG in those exposed to livestock suggests that there are zoonotic risk factors or that hygiene is a causal factor. The association between EAEC infection and SG warrants further investigation.

Giardia duodenalis infection and anthropometric status in preschoolers in Salvador, Bahia State, Brazil

The aim of this study was to estimate the association between Giardia duodenalis infection and anthropometric deficits, as measured by weight-for-age and height-for-age. This cross-sectional study included 629 children from 12 to 48 months of age, selected from 30 geographic areas in the city of Salvador, Bahia State, Brazil. Poisson regression and linear regression were used for the multivariate statistical analyses. G. duodenalis was diagnosed in 13.5% of the children. The children's breastfeeding duration and living conditions (garbage collection and paved streets or sidewalks) modified the effect of G. duodenalis infection on anthropometric status. Among infected children, there were statistically significant associations between weight deficit and shorter breastfeeding (PR=2.22; 95%CI: 1.56-3.14) and inadequate paving of streets and sidewalks (PR=2.00; 95%CI: 1.37-2.92), while height deficit was associated with deficient public garbage collection (PR=2.21; 95%CI: 1.31-2.51). In the linear regression, the association with the anthropometric indicators remained positive and statistically significant. The child's unhealthy living environment aggravated the negative effect of G. duodenalis infection on anthropometric status, and breastfeeding was a protective factor in the outcome.

Classic and molecular study of Giardia duodenalis in children from a daycare center in the region of Presidente Prudente, São Paulo, Brazil

Epidemiological studies on giardiasis by using molecular techniques such as RAPD (Randomly Amplified Polymorphic DNA) may give information on factors related to the transmission of Giardia duodenalis. The aim of this work was to assess the epidemiology of G. duodenalis in 101 children attended at a daycare center in Presidente Bernardes, SP, Brazil. After parasitological examinations in feces samples, 15 children presented cysts of G. duodenalis. Their respective parents, brothers and pets, besides the daycare center workers, also had their feces submitted to parasitological analysis. Seven mothers and nine brothers also presented G. duodenalis cysts, while fathers, daycare workers and pets (dogs) did not presented the parasite. Besides the 15 cases with G. duodenalis, other 23 children presented other enteroparasites (Entamoeba coli, Endolimax nana, Enterobius vermicularis, Ascaris lumbricoides and Trichuris trichiura). Samples of G. duodenalis cysts from children and their relatives were submitted to molecular typing by RAPD after genomic DNA extraction and amplification of a fragment of the 18S rDNA region by PCR. After examining 31 isolates of G. duodenalis (children and their respective mothers and brothers), it was concluded that the parasite transmission occurred in children, probably during daily cohabitation at the daycare center, but not at home among their relatives or pets.

Genetic variability in parasites and host—parasite interactions

We have examined genetic variability in parasites in the context of ecological interactions with the host. Recent research onEchinococcus, GiardiaandCryptosporidiumhas been used to illustrate: (i) the problems that parasite variability and species recognition pose for understanding the complex and often controversial relationship between parasite and host occurrence; (ii) the need for accurate parasite characterization and the application of appropriate molecular techniques to studies on parasite transmission if fundamental questions about zoonotic relationships and risk factors are to be answered; (iii) our lack of understanding about within-host interactions between genetically heterogeneous parasites at the inter-and intraspecific levels, and the significance of such interactions with respect to evolutionary considerations and the clinical outcome of parasite infections. If advances in molecular biology and mathematical ecology are to be realized, we need to give serious consideration to the development of appropriate species concepts and in vivo systems for testing the predictions and assumptions of theoretical models.

Is Giardia a significant pathogen in production animals?

Although Giardia duodenalis is recognised worldwide as the most important parasitic cause of gastro-intestinal disorder in human patients, the relevance of infection in production animals is prone to debate. Since the 1980s, clinical disease has been associated with giardiasis in production animals, both in natural conditions and in experimental studies. However, most Giardia research is focussed on the relevance of production animals as a reservoir for zoonotic transmission. In this study, the current knowledge on clinical relevance of giardiasis in production animals is reviewed, along with the diagnosis, treatment and control of infection. Furthermore, future research objectives are discussed.

Lack of an adverse effect of Giardia intestinalis infection on the health of Peruvian children

Giardia intestinalis is a common gastrointestinal protozoan worldwide, but its effects on childhood growth in developing countries are not clearly understood. The authors aimed to describe its effects on child growth. They followed 220 Peruvian children daily for diarrhea, weekly for stool samples, and monthly for anthropometry. The authors modeled the effect of nutritional status on the risk of Giardia infection and the risk of diarrhea attributable to Giardia using negative binomial regression. They modeled the effects of Giardia infection on growth using linear regression, with 85% of children becoming infected with Giardia and 87% of these becoming reinfected. In multivariable analysis, the risk of Giardia infection did not vary with weight for age (relative risk = 1.00, 95% confidence interval: 0.89, 1.12) or height for age (relative risk = 0.92, 95% confidence interval: 0.82, 1.04). Giardiasis did not affect growth at 1 or 2 months following the first infection at any age interval. The longitudinal prevalence of Giardia between 6 and 24 months of age was not associated with height gain in that interval (p = 0.981). Giardia was not associated with an increased risk of diarrhea at any age interval. Study results question the importance of Giardia as a childhood pathogen in developing countries where giardiasis is hyperendemic.