Zoonotic genotype of Giardia intestinalis detected in a ferret

Examining the molecular epidemiology of Giardia and Eimeria species in Japan: a comprehensive review

Globally, animals and humans suffer from diarrheal illnesses due to protozoan parasites such as Giardia and Eimeria species. The molecular epidemiology of these parasites in Japan is summarized in this review. In humans, researchers found only one main species of Giardia, which is most referred to as G. lamblia, but it's also known by different names like G. duodenalis or G. intestinalis. However, within this species, six assemblages (A, B, C, D, E, and F) were found in animals, and assemblage B was frequently recorded in human and monkey populations, whereas assemblages A and E were predominant in calves. Assemblage A was found in sika deer and assemblages A, C, D, and F were predominant in dogs, cats, and ferret. Eimeria bovis, E. zuernii, and other species found in animals made up the group of species known as Eimeria spp., with E. bovis and E. zuernii being the most common in cattle. Our review highlighted a notable lack of data investigations regarding these two pathogens in water and environmental sources. Giardia cysts were found in the few studies that have been done on water sources, suggesting that water may play a significant role in the transmission of Giardia species. Our review suggests that further research is necessary to fully comprehend the molecular diversity and dynamics of transmission of Giardia spp. and Eimeria spp. in humans, animals, and environmental sources in Japan.

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.

Giardia duodenalis in the UK: current knowledge of risk factors and public health implications

Giardia duodenalis is a ubiquitous flagellated protozoan parasite known to cause giardiasis throughout the world. Potential transmission vehicles for this zoonotic parasite are both water and food sources. As such consumption of water contaminated by feces, or food sources washed in contaminated water containing parasite cysts, may result in outbreaks. This creates local public health risks which can potentially cause widespread infection and long-term post-infection sequelae. This paper provides an up-to-date overview of G. duodenalis assemblages, sub-assemblages, hosts and locations identified. It also summarizes knowledge of potential infection/transmission routes covering water, food, person-to-person infection and zoonotic transmission from livestock and companion animals. Public health implications focused within the UK, based on epidemiological data, are discussed and recommendations for essential Giardia developments are highlighted.

Molecular epidemiology of Cryptosporidium spp. and Giardia spp. in mussels (Mytilus californianus) and California sea lions (Zalophus californianus) from Central California

Cryptosporidium and Giardia are of public health importance, with recognized transmission through recreational waters. Therefore, both can contaminate marine waters and shellfish, with potential to infect marine mammals in nearshore ecosystems. A 2-year study was conducted to evaluate the presence of Cryptosporidium and Giardia in mussels located at two distinct coastal areas in California, namely, (i) land runoff plume sites and (ii) locations near sea lion haul-out sites, as well as in feces of California sea lions (CSL) (Zalophus californianus) by the use of direct fluorescent antibody (DFA) detection methods and PCR with sequence analysis. In this study, 961 individual mussel hemolymph samples, 54 aliquots of pooled mussel tissue, and 303 CSL fecal samples were screened. Giardia duodenalis assemblages B and D were detected in hemolymph from mussels collected near two land runoff plume sites (Santa Rosa Creek and Carmel River), and assemblages C and D were detected in hemolymph from mussels collected near a sea lion haul-out site (White Rock). These results suggest that mussels are being contaminated by protozoa carried in terrestrial runoff and/or shed in the feces of CSL. Furthermore, low numbers of oocysts and cysts morphologically similar to Cryptosporidium and Giardia, respectively, were detected in CSL fecal samples, suggesting that CSL could be a source and a host of protozoan parasites in coastal environments. The results of this study showed that Cryptosporidium and Giardia spp. from the feces of terrestrial animals and CSL can contaminate mussels and coastal environments.

Reevaluation of health risk benchmark for sustainable water practice through risk analysis of rooftop-harvested rainwater

Health risk concerns associated with household use of rooftop-harvested rainwater (HRW) constitute one of the main impediments to exploit the benefits of rainwater harvesting in the United States. However, the benchmark based on the U.S. EPA acceptable annual infection risk level of ≤1 case per 10,000 persons per year (≤10(-4) pppy) developed to aid drinking water regulations may be unnecessarily stringent for sustainable water practice. In this study, we challenge the current risk benchmark by quantifying the potential microbial risk associated with consumption of HRW-irrigated home produce and comparing it against the current risk benchmark. Microbial pathogen data for HRW and exposure rates reported in literature are applied to assess the potential microbial risk posed to household consumers of their homegrown produce. A Quantitative Microbial Risk Assessment (QMRA) model based on worst-case scenario (e.g. overhead irrigation, no pathogen inactivation) is applied to three crops that are most popular among home gardeners (lettuce, cucumbers, and tomatoes) and commonly consumed raw. The infection risks of household consumers attributed to consumption of these home produce vary with the type of produce. The lettuce presents the highest risk, which is followed by tomato and cucumber, respectively. Results show that the 95th percentile values of infection risk per intake event of home produce are one to three orders of magnitude (10(-7) to 10(-5)) lower than U.S. EPA risk benchmark (≤10(-4) pppy). However, annual infection risks under the same scenario (multiple intake events in a year) are very likely to exceed the risk benchmark by one order of magnitude in some cases. Estimated 95th percentile values of the annual risk are in the 10(-4) to 10(-3) pppy range, which are still lower than the 10(-3) to 10(-1) pppy risk range of reclaimed water irrigated produce estimated in comparable studies. We further discuss the desirability of HRW for irrigating home produce based on the relative risk of HRW to reclaimed wastewater for irrigation of food crops. The appropriateness of the ≤10(-4) pppy risk benchmark for assessing safety level of HRW-irrigated fresh produce is questioned by considering the assumptions made for the QMRA model. Consequently, the need of an updated approach to assess appropriateness of sustainable water practice for making guidelines and policies is proposed.

Metagenomic analysis of the ferret fecal viral flora

Ferrets are widely used as a small animal model for a number of viral infections, including influenza A virus and SARS coronavirus. To further analyze the microbiological status of ferrets, their fecal viral flora was studied using a metagenomics approach. Novel viruses from the families Picorna-, Papilloma-, and Anelloviridae as well as known viruses from the families Astro-, Corona-, Parvo-, and Hepeviridae were identified in different ferret cohorts. Ferret kobu- and hepatitis E virus were mainly present in human household ferrets, whereas coronaviruses were found both in household as well as farm ferrets. Our studies illuminate the viral diversity found in ferrets and provide tools to prescreen for newly identified viruses that potentially could influence disease outcome of experimental virus infections in ferrets.

Zoonotic potential of Giardia

Giardia duodenalis (syn. Giardia lamblia and Giardia intestinalis) is a common intestinal parasite of humans and mammals worldwide. Assessing the zoonotic transmission of the infection requires molecular characterization as there is considerable genetic variation within G. duodenalis. To date eight major genetic groups (assemblages) have been identified, two of which (A and B) are found in both humans and animals, whereas the remaining six (C to H) are host-specific and do not infect humans. Sequence-based surveys of single loci have identified a number of genetic variants (genotypes) within assemblages A and B in animal species, some of which may have zoonotic potential. Multi-locus typing data, however, has shown that in most cases, animals do not share identical multi-locus types with humans. Furthermore, interpretation of genotyping data is complicated by the presence of multiple alleles that generate "double peaks" in sequencing files from PCR products, and by the potential exchange of genetic material among isolates, which may account for the non-concordance in the assignment of isolates to specific assemblages. Therefore, a better understanding of the genetics of this parasite is required to allow the design of more sensitive and variable subtyping tools, that in turn may help unravel the complex epidemiology of this infection.

Gastrointestinal Disease in Exotic Small Mammals

Exotic small mammal medicine is a relatively new specialty area within veterinary medicine. Ferrets, rabbits, and rodents have long been used as animal models in human medical research investigations, resulting in a body of basic anatomic and physiologic information that can be used by veterinarians treating these species. Unfortunately, there is a paucity of veterinary articles that describe clinical presentation, diagnosis, and treatment options of gastrointestinal (GI) disease as it affects exotic small mammals. Although there is little reference material relating to exotic small mammal GI disease, patients are commonly presented to veterinary hospitals with digestive tract disorders. This article provides the latest information available for GI disease in ferrets (Helicobacter mustelae gastritis, inflammatory bowel disease [IBD], GI lymphoma, systemic coronavirus, coccidiosis, and liver disease), rabbits (GI motility disorders, liver lobe torsion, astrovirus, and coccidiosis), guinea pigs (gastric dilatation volvulus [GDV]), rats (Taenia taeniaeformis), and hamsters (Clostridium difficile). Both noninfectious diseases and emerging infectious diseases are reviewed as well as the most up-to-date diagnostics and treatment options.

Zoonoses of ferrets, hedgehogs, and sugar gliders

With urbanization, people live in close proximity to their pets. People often share their living quarters and furniture, and this proximity carries a new potential for pathogen transmission. In addition to the change in lifestyle with our pets, new exotic pets are being introduced to the pet industry regularly. Often, we are unfamiliar with specific clinical signs of diseases in these new exotic pets or the routes of transmission of pathogens for the particular species. This article reviews zoonoses that occur naturally in ferrets, hedgehogs, and sugar gliders, discussing the occurrence and clinical symptoms of these diseases in humans.

Zoonotic potential and molecular epidemiology of Giardia species and giardiasis

Molecular diagnostic tools have been used recently in assessing the taxonomy, zoonotic potential, and transmission of Giardia species and giardiasis in humans and animals. The results of these studies have firmly established giardiasis as a zoonotic disease, although host adaptation at the genotype and subtype levels has reduced the likelihood of zoonotic transmission. These studies have also identified variations in the distribution of Giardia duodenalis genotypes among geographic areas and between domestic and wild ruminants and differences in clinical manifestations and outbreak potentials of assemblages A and B. Nevertheless, our efforts in characterizing the molecular epidemiology of giardiasis and the roles of various animals in the transmission of human giardiasis are compromised by the lack of case-control and longitudinal cohort studies and the sampling and testing of humans and animals living in the same community, the frequent occurrence of infections with mixed genotypes and subtypes, and the apparent heterozygosity at some genetic loci for some G. duodenalis genotypes. With the increased usage of multilocus genotyping tools, the development of next-generation subtyping tools, the integration of molecular analysis in epidemiological studies, and an improved understanding of the population genetics of G. duodenalis in humans and animals, we should soon have a better appreciation of the molecular epidemiology of giardiasis, the disease burden of zoonotic transmission, the taxonomy status and virulences of various G. duodenalis genotypes, and the ecology of environmental contamination.

An atypical proprotein convertase in Giardia lamblia differentiation

Proteolytic activity is important in the lifecycles of parasites and their interactions with hosts. Cysteine proteases have been best studied in Giardia, but other protease classes have been implicated in growth and/or differentiation. In this study, we employed bioinformatics to reveal the complete set of putative proteases in the Giardia genome. We identified 73 peptidase homologs distributed over 5 catalytic classes in the genome. Serial analysis of gene expression of the G. lamblia lifecycle found thirteen protease genes with significant transcriptional variation over the lifecycle, with only one serine protease transcript upregulated late in encystation. The translated gene sequence of this encystation-specific transcript was most similar to eukaryotic subtilisin-like proprotein convertases (SPC), although the typical catalytic triad was not identified. Epitope-tagged gSPC protein expressed in Giardia under its own promoter was upregulated during encystation with highest expression in cysts and it localized to encystation-specific secretory vesicles (ESV). Total gSPC from encysting cells produced proteolysis in gelatin gels that co-migrated with the epitope-tagged protease in immunoblots. Immuno-purified gSPC also had gelatinase activity. To test whether endogenous gSPC activity is involved in differentiation, trophozoites and cysts were exposed to the specific serine proteinase inhibitor 4-(2-aminoethyl)-benzenesulfonyl fluoride hydrochloride (AEBSF). After 21 h encystation, a significant decrease in ESV was observed with 1mM AEBSF and by 42 h the number of cysts was significantly reduced, but trophozoite growth was not inhibited. Concurrently, levels of cyst wall proteins 1 and 2, and AU1-tagged gSPC protein itself were decreased. Excystation of G. muris cysts was also significantly reduced in the presence of AEBSF. These results support the idea that serine protease activity is essential for Giardia encystation and excystation.

Risk of human infection with Giardia duodenalis from cats in Japan and genotyping of the isolates to assess the route of infection in cats

The number of facilities in which customers make contact with cats before eating and drinking, called 'cat cafés', has recently increased in Tokyo, Japan. In a survey to clarify the possibility of zoonotic transmission in Giardia duodenalis, the infection rates of G. duodenalis in 321 stool samples of cats from 16 cat cafés, 31 pet shops, and the Animal Care and Consultation Center of Tokyo were 19·1% (22/115), 1·2% (1/85), and 2·5% (3/121), respectively. In the molecular analysis of 26 G. duodenalis isolates, 6 samples from 2 cat cafés belonged to the zoonotic genotype assemblage A I, and 20 other samples were of assemblage F. Moreover, phylogenetic analysis of glutamate dehydrogenase (GDH) and triosephosphate isomerase (TPI) genes of the 20 assemblage F isolates revealed 2 major lineages. The 6 assemblage A isolates belonged to the same cluster with regard to the GDH gene; however, 2 of the 6 isolates belonged to a different cluster from the other 4 isolates with regard to the TPI gene. Therefore, a risk of transmission from cats to humans is suggested because of the detection of zoonotic Giardia genotypes in cat cafés.

Molecular characterization of Giardia duodenalis isolates from domestic ferrets

Giardia duodenalis is a pathogen that has been found in a variety of mammals, including humans, and consists of host-specific (assemblages C, D, E, F, and G) and zoonotic (assemblages A, B) genetic groups. Ferrets are popular pets, and they, like humans, are hosts to this pathogen. The genetic characteristics of the Giardia population in ferrets are unclear because only one ferret isolate has been genotyped. To develop a more complete picture of the genetic characteristics of the Giardia population in domestic ferrets two additional Giardia isolates, recovered independently from two ferrets suffering from intestinal or hepatic giardiasis, were analyzed genetically. The sequences of both isolates at three loci, small subunit ribosomal RNA (SSUrDNA, 292 bp), beta-giardin (734 bp), and glutamate dehydrogenase (GDH, 713 bp) were identical to each other, but the sequences of triosephosphate isomerase locus (TPI, 512 bp) had five substitutions between isolates. Sequence homology and phylogenetic analyses at four loci identified both isolates as members of the assemblage A. Moreover, the sequences of SSUrDNA, beta-giardin, and GDH from both isolates were identical to those of the previous ferret isolate genotyped as assemblage A within the regions of overlap. The result obtained in the present study indicates that at least two genetically different types in assemblage A exist in domestic ferrets. In addition, there have been no reported human and animal isolates with the same sequence as those from ferret isolates at all four loci examined, suggesting that the present ferret isolates might be host-specific.

From mouse to moose: multilocus genotyping of Giardia isolates from various animal species

Giardia intestinalis is a protozoan parasite that consists of seven genetically distinct assemblages (A to G). Assemblage A and B parasites have been detected in a wide range of animals including humans, while the other assemblages (C to G) appear to have a narrower host range. However, the knowledge about zoonotic transmission of G. intestinalis is limited. To address this question, 114 Giardia isolates from various animals in Sweden including pets, livestock, wildlife and captive non-human primates were investigated by a sequence-based analysis of three genes (beta-giardin, glutamate dehydrogenase and triose phosphate isomerase). Assemblage A infections were detected in nine ruminants, five cats and one dog, while three sheep were infected with both assemblages A and E. Multilocus genotypes (MLGs) were defined for assemblage A, and three of these MLGs have previously been detected in Giardia isolates from humans. The newly described sub-assemblage AIII, until now reported mainly in wild hoofed animals, was found in one cat isolate. Assemblage B occurred in three monkeys, one guinea pig and one rabbit. The rabbit isolate exhibited sequences at all three loci previously detected in human isolates. The non-zoonotic assemblages C, D, E, F or G were found in the remaining 83 G. intestinalis isolates, which were successfully amplified and genotyped, generating a wide variety of both novel and known sub-genotypes. Double peaks in chromatograms were seen in assemblage B, C, D and E isolates but were never observed in assemblage A, F and G isolates, which can reflect differences in allelic sequence divergence. No evidence of genetic exchange between assemblages was detected. The study shows that multilocus genotyping of G. intestinalis is a highly discriminatory and useful tool in the determination of zoonotic sub-groups within assemblage A, but less valuable for subtyping assemblages B, C, D and E due to the high frequency of double peaks in the chromatograms. The obtained data also suggest that zoonotic transmission of assemblages A and B might occur to a limited extent in Sweden.

Bacterial and parasitic diseases of ferrets

The domestic ferret, Mustela putorius furo, is a popular companion animal and is used in biomedical research. When compared with other companion mammals, primary bacterial and parasitic infections are less common in domestic ferrets. In countries such as the United States, pet ferrets are generally kept indoors, and the risk for exposure to primary bacterial and parasitic infectious agents is low. Companion, breeding, and working ferrets are commonly kept outdoors in other parts of the world, placing them at comparatively greater risk for exposure to infectious diseases. This article discusses clinical signs, diagnosis, and treatment of bacterial and parasitic diseases of ferrets.

Bacterial and parasitic zoonoses of exotic pets

Zoonoses are estimated to make up to 75% of today's emerging infectious diseases. Many of these diseases are carried and transmitted by exotic pets and wildlife. Exotic animal practitioners must be aware of these risks not only to protect their health but also to safeguard the health of staff and clients. This article reviews selected bacterial and parasitic zoonoses associated with exotic animals.

Molecular evidence of Enterocytozoon bieneusi in Japan

Enterocytozoon bieneusi is an emerging and clinically significant enteric pathogen in humans associated mainly with chronic diarrhea. It has been found in a variety of wild, domestic and companion mammals and birds. To date, epidemiological surveys of E. bieneusi infection in humans, other mammals and birds have been performed in more than 21 countries in Africa, the Americas, Australasia and Europe. In Asia E. bieneusi has been found in India, Thailand, Vietnam and Korea, but it has been quite unclear whether this pathogen is present in Japan. In the present study, we examined 149 DNAs extracted from 45 human (9 of them HIV-positive) and 104 animal fecal samples by PCR. Two dogs and a cat were positive and their genotypes were found to be dog specific and zoonotic (genotype K) types, respectively. Present study is the first record of E. bieneusi in Japan.

Classification of Giardia intestinalis isolates by multiple polymerase chain reaction (multiplex)

Agarose gel electrophoresis of gdh gene fragments, amplified by Multiplex, was used to classify the assemblage of 24 Giardia isolates obtained from axenic cultures, children's stools, and feces of puppies from different dog breeds. Isolates were compared with seven reference strains of Giardia intestinalis. The results showed that 22/24 isolates (91%) belonged to assemblage A and could be further subclassified as assemblage A1 (18/22, 81%) and assemblage A2 (4/22, 19%). One sample revealed a mixture of A1/A2 genotypes, and another was assemblage G, indicating mixed infections by different strains in the same host, and an association with the assemblage reported in animals. The procedure described is useful to determine the Giardia genotype that parasitizes each host to conduct epidemiological studies assessing the close association between human- and animal-infecting strains and to monitor the adaptability of animal strains to humans.

Molecular epidemiology of giardiasis

Giardia duodenalis is a widespread parasite of mammalian species, including humans. Due to its invariant morphology, investigation on aspects such as host specificity and transmission patterns requires a direct genetic characterization of cysts/trophozoites from host samples. A number of molecular assays have been developed to help unravel the complex epidemiology of this infection. A coherent picture has emerged from those studies, indicating the existence of seven genetic groups (or assemblages), two of which (A and B) are found in both humans and animals, whereas the remaining five (C-G) are host-specific. Sequence-based surveys have identified a number of genotypes within assemblages A and B in animal species, some of which may have zoonotic potential. Recently, however, molecular approaches have been complicated by the recognition of intra-isolate sequence heterogeneity (i.e., "mixed templates", that affects identification of subtypes within each assemblage), and by the unreliable assignment of isolates to G. duodenalis assemblages generated by different genetic markers. This raises concerns about previous interpretation of genotyping data, especially when single genetic markers have been used. The mechanisms that may be responsible for these findings, including allelic sequence heterozygosity and meiotic recombination, are discussed.

Comparative evaluation ofGiardia duodenalissequence data

A review of theGiardia duodenalissequences currently available on the GenBank database was completed to compare the different genotyping loci (small subunit ribosomal DNA, glutamate dehydrogenase, triose-phosphate isomerase and beta giardin) for their ability to discern assemblage and subassemblage groups and infer phylogenetic relationships. In total, 405Giardia duodenalissequences were sorted and aligned to examine the substitutions within and between the assemblages – A and B (zoonotic), C and D (dogs), E (livestock), F (cats) and G (rodents). It was found that all of the genes could reproducibly group isolates into their assemblages and that the AI/AII subassemblage groups were robust and identifiable at all loci. However, the assemblage B subgroups were not reproducible at half of the loci (small subunit ribosomal DNA and beta giardin), not due to their conserved nature, but because there was insufficient sequence data of reference isolates available for comparison. It is anticipated that further investigation of these loci may reveal the core subgroups of this medically important and zoonotic assemblage and also those of others. The closer, more recent, phylogenetic relationships amongst the assemblages appear to be resolved; however, more sequence data from the current loci, and possibly new loci, will be required to establish the remaining relationships.

Molecular and phylogenetic characterization of Cryptosporidium and Giardia from pigs and cattle in Denmark

The genetic diversity of Cryptosporidium spp. and Giardia duodenalis from dairy cattle and pigs in Denmark was determined in the present study. Faecal samples from 1237 pigs and 1150 cattle originating from 50 sow herds and 50 dairy herds, respectively, were analysed for the presence of the two parasites by immunofluorescence microscopy. A large proportion of the (oo)cyst containing samples were selected for molecular characterization. Sequencing and phylogenetic analysis of the 18S rDNA locus and/or the HSP70 gene of 183 pig and 154 cattle isolates of Cryptosporidium revealed the presence of C. suis, pig genotype II, C. parvum (cattle genotype), C. bovis, Cryptosporidium deer-like genotype and a novel C. suis-like genotype. For both cattle and pigs, a host age-related change in distribution of species/genotypes was observed. The zoonotic C. parvum (cattle genotype) was most prevalent in young calves. For Giardia, 82 and 145 isolates from pigs and cattle, respectively, were analysed at the 18S rDNA locus and/or the gdh gene. Giardia isolates belonging to the zoonotic Assemblage A was found in both young and older calves, as well as in weaners and piglets, whereas cows seemed to be infected purely by isolates of the livestock group, Assemblage E.

Genotyping of Giardia in Dutch patients and animals: a phylogenetic analysis of human and animal isolates

Giardia duodenalis (syn. Giardia lamblia, Giardia intestinalis) is a protozoan organism that can infect the intestinal tract of many animal species including mammals. Genetic heterogeneity of G. duodenalis is well described but the zoonotic potential is still not clear. In this study, we analysed 100 Giardia DNA samples directly isolated from human stool specimens, to get more insight in the different G. duodenalis assemblages present in the Dutch human population. Results showed that these human isolates could be divided into two main Assemblages A and B within the G. duodenalis group on the basis of PCR assays specific for the Assemblages A and B and the DNA sequences of 18S ribosomal RNA and the glutamate dehydrogenase (gdh) genes. Genotyping results showed that G. duodenalis isolates originating from Dutch human patients belonged in 35% of the cases to Assemblage A (34/98) and in 65% of the cases to Assemblage B (64/98) whereas two human cases remained negative in all assays tested. In addition, we compared these human samples with animal samples from the Netherlands and human and animal samples from other countries. A phylogenetic analysis was carried out on the DNA sequences obtained from these Giardia and those available in GenBank. Using gdh DNA sequence analysis, human and animal Assemblage A and B Giardia isolates could be identified. However, phylogenetic analysis revealed different sub-clustering for human and animal isolates where host-species-specific assemblages (C, D, E, F and G) could be identified. The geographic origin of the human and animal samples was not a discriminating factor.

Evaluation of silymarin in the treatment on asymptomatic Giardia infections in dogs

We have reported previously the efficacy of antiprotozoal drugs against canine giardiasis (In press, Journal of Veterinary Clinic, the Korean Society of Veterinary Clinics). Fenbendazole was found to be the most efficacious for the treatment of canine giardiasis. There were no significant differences between the efficacy of albendazole and fenbendazole against canine giardiasis. On the other hand, the efficacy of metronidazole for the treatment of canine giardiasis, the efficacy was lower when compared to that of albendazole and fenbendazole. On the basis of these results, to evaluate clinical effect of silymarin, we evaluated the therapeutic efficacy of metronidazole alone, or combined with silymarin for 2 weeks for canine giardiasis. In addition, to observe effects on nutrition, we investigated the changes of body weight, the serum biochemical indicators for liver inflammation (GOT, GPT, NH3), the liver cell regeneration indicators (total protein, albumin) and the hematological changes during treatment (WBC, RBC, MCV, MCH and MCHC). The dogs were allocated to four groups; one group was treated with silymarin (3.5 mg/kg once a day, oral), another with metronidazole (50 mg/kg once a day, oral), and the other group with silymarin (3.5 mg/kg once a day, oral) plus metronidazole (50 mg/kg once a day, oral), while control group remained nontreated. The fecal samples from all the dogs were examined, using the ZSCT and giardia antigen test kit (SNAP(*) Giardia, IDEXX Laboratories), from each dog of each group for three times a week for 2 weeks. Dogs were considered to have giardiasis when one or more of the fecal samples had positive results for Giardia cysts. Seven days after treatment, the efficacy of silymarin plus metronidazole was found 79%, whereas that of metronidazole was 72%. Ten days post-treatment the efficacy of metronidazole plus silymarin (91%) was significantly different in comparison with that of metronidazole (75%). Two weeks post-treatment no cysts were detected in the fecal samples in the dogs of metronidazole or silymarin plus metronidazole-treated groups. Whereas, the fecal samples of all the dogs of the control and only silymarin-treated groups were giardia positive. Signs of side effects were not observed in silymarin plus metronidazole-treated dogs. But poor appetite and intermittent vomiting signs were observed in two dogs of the metronidazole-treated group that resolved when metronidazole administration was discontinued. The body weight of those treated with metronidazole was significantly decreased in comparison with those treated with silymarin and metronidazole plus silymarin. There were significant differences of body weight between the dogs treated with silymarin and metronidazole. Two weeks after metronidazole treatment, serum concentration of GOT, GPT and NH3 were significantly increased in comparison with those treated with silymarin. On the other hand, the serum concentration of GOT, GPT and NH3 were not significantly increased when treated with silymarin plus metronidazole compared to those treated with metronidazole. Serum total protein and albumin concentrations were decreased after metronidazole treatment as compared to those treated with silymarin and silymarin plus metronidazole. The concentrations of serum total protein and albumin decreased significantly in metronidazole-treated group as compared to that of treated with silymarin. The numbers of WBC and RBC did show significant differences in the dogs treated with metronidazole, while MCV, MCH were significant by different between silymarin and metronidazole-treated dogs. On the other hand, there were no significant differences in MCHC in any groups. These data suggest that silymarin, in supplement with antiprotozoal drugs, can influence the therapy of canine giardiasis.