Multiple zoonotic pathogens identified in canine feces collected from a remote Canadian indigenous community

Echinococcus species in wildlife

Transmission of Echinococcus spp. in life cycles that involve mainly wildlife is well recognized for those species with small mammals as intermediate hosts (e. g. E. multilocularis), as well as for E. felidis and the 'northern' genotypes of E. canadensis (G8 and G10). In contrast, the remaining taxa of E. granulosus sensu lato are best known for their domestic life cycles, and the numerous wild mammal species (mainly ungulates) that have been recorded with cystic echinococcosis in the past were mainly considered a result of spill-over from the dog-livestock transmission system. This view was challenged with the advent of molecular characterization, allowing discrimination of the metacestodes, although the contribution of wild mammals to various Echinococcus life cycles has remained uncertain for scarcity of wildlife studies. Numerous records of cysts in wild ungulates date back to the 20th century, but cannot with certainty be allocated to the Echinococcus species and genotypes that are recognized today. This means that our current knowledge is largely restricted to studies of the past two decades that kept adding gradually to our concepts of transmission in various geographic regions. In particular, new insights were gathered in the past years on E. granulosus s.l. in wildlife of sub-Saharan Africa, but also on transmission patterns of E. multilocularis in previously neglected regions, e. g. North America. Here, an update is provided on the current state of knowledge on wild mammals as hosts for all Echinococcus species, listing >150 species of wild hosts with references, as well as estimates on their epidemiological impact and our current gaps of knowledge.

Giardia and Cryptosporidium in resident wildlife species in Arctic Alaska

Giardia and Cryptosporidium are zoonotic protozoan parasites that can infect humans and other taxa, including wildlife, often causing gastrointestinal illness. Both have been identified as One Health priorities in the Arctic, where climate change is expected to influence the distribution of many wildlife and zoonotic diseases, but little is known about their prevalence in local wildlife. To help fill information gaps, we collected fecal samples from four wildlife species that occur seasonally on the northern Alaska coastline or in nearshore marine waters-Arctic fox (Vulpes lagopus), polar bear (Ursus maritimus), Pacific walrus (Odobenus rosmarus divergens), and caribou (Rangifer tarandus)-and used immunofluorescence assays to screen for Giardia cysts and Cryptosporidium oocysts. We detected Giardia cysts in 18.3% and Cryptosporidium oocysts in 16.5% of Arctic foxes (n = 109), suggesting that foxes may be potentially important hosts in this region. We also detected Giardia cysts in a single polar bear (12.5%; n = 8), which to our knowledge represents the first such report for this species. Neither parasite was detected in walruses or caribou.

Novel strains of Campylobacter cause diarrheal outbreak in Rhesus macaques (Macaca mulatta) of Kathmandu Valley

Campylobacter spp. is often underreported and underrated bacteria that present real health risks to both humans and animals, including non-human primates. It is a commensal microorganism of gastrointestinal tract known to cause gastroenteritis in humans. Commonly found in many wild animals including non-human primates (monkeys- Rhesus macaques) these pathogens are known to be a common cause of diarrhea in humans in many parts of developing and under developed countries. Rhesus macaques from the two holy sites in Kathmandu (Pashupati and Swoyambhu) were included in this cross-sectional study. Diarrheal samples of monkeys were analyzed to detect and characterize the pathogen using 16S rRNA-based PCR screening, followed by DNA sequencing and phylogenetic analysis. Out of a total 67 collected diarrheal samples, Campylobacter spp. were detected in the majority of the samples (n = 64; 96%). DNA sequences of the amplified PCR products were successfully obtained from 13 samples. Phylogenetic analysis identified Candidatus Campylobacter infans (n = 10, Kimura-2 parameter (K2P) pairwise distance values of 0.002287). Remaining three sequences might potentially belong to a novel Campylobacter species/sub-species- closely relating to known species of C. helviticus (K2P pairwise distance of 0.0267). Both Candidatus Campylobacter infans and C. helvitucus are known to infect humans and animals. Additionally, we also detected the bacteria in water and soil samples from the sites. Campylobacter spp. caused the 2018 diarrhea outbreak in Rhesus macaques in the Kathmandu valley. Campylobacter might be one of the important contributing pathogens in diarrheal outbreaks-both in humans and animals (monkeys) in Nepal. Due to close interactions of these animals with humans and other animals, One Health approach might be the most effective way to prevent and mitigate the threat posed by this pathogen.

Gastrointestinal helminths of stray dogs in Erzurum province: prevalence and risk to public health

Dogs have an important role in public health due to their close contact with humans and living in common areas. This study was aimed to investigate the presence and prevalence of gastrointestinal system helminths in stray dogs in Erzurum province. Gastrointestinal helminth eggs were detected in a total of 190 out of 446 (42.6%) in stray dogs in Erzurum province. In the study, taeniid eggs (17.71%, 79/446), T. canis (16.82%, 75/446), T. leonina (12.78%, 57/446), Linguatula spp. (4.48%, 20/446), spiny-headed worms (2.91%, 13/446), hookworms (2.69%, 12/446), Alaria spp. (1.12%, 5/446) and Trichuris spp. (0.22%, 1/446) eggs were observed. In addition, proglottid structures of Mesocestoides spp. (3.14%), Taenia spp. (2.69%), and D. caninum (1.12%), adults of Alaria spp. (0.22%), T. canis (0.22%), and T. leonina (0.22%) were detected. According to the results of the study, zoonotic parasites including taeniid cestodes, T. canis, Linguatula spp., spiny-headed worm, hookworm, Alaria spp., and Trichuris spp. were common in stray dogs in the province. Public health risks can be reduced by regular deworming of dogs, proper management of the process, prevention of environmental contamination with dog feces, and proper enforcement of sanitation protocols.

Climate Change and Enteric Infections in the Canadian Arctic: Do We Know What’s on the Horizon?

The Canadian Arctic has a long history with diarrheal disease, including outbreaks of campylobacteriosis, giardiasis, and salmonellosis. Due to climate change, the Canadian Arctic is experiencing rapid environmental transformation, which not only threatens the livelihood of local Indigenous Peoples, but also supports the spread, frequency, and intensity of enteric pathogen outbreaks. Advances in diagnostic testing and detection have brought to attention the current burden of disease due to Cryptosporidium, Campylobacter, and Helicobacter pylori. As climate change is known to influence pathogen transmission (e.g., food and water), Arctic communities need support in developing prevention and surveillance strategies that are culturally appropriate. This review aims to provide an overview of how climate change is currently and is expected to impact enteric pathogens in the Canadian Arctic.

The Gut Viral Metagenome Analysis of Domestic Dogs Captures Snapshot of Viral Diversity and Potential Risk of Coronavirus

The close relations between dogs (Canis lupus familiaris) and humans lay a foundation for cross species transmissions of viruses. The co-existence of multiplex viruses in the host accelerate viral variations. For effective prediction and prevention of potential epidemic or even pandemic, the metagenomics method was used to investigate the gut virome status of 45 domestic healthy dogs which have extensive contact with human beings. A total of 248.6 GB data (505, 203, 006 valid reads, 150 bp in length) were generated and 325, 339 contigs, which were best matched with viral genes, were assembled from 46, 832, 838 reads. In the aggregate, 9,834 contigs (3.02%) were confirmed for viruses. The top 30 contigs with the most reads abundance were mapped to DNA virus families Circoviridae, Parvoviridae and Herpesviridae; and RNA virus families Astroviridae, Coronaviridae and Picornaviridae, respectively. Numerous sequences were assigned to animal virus families of Astroviridae, Coronaviridae, Circoviridae, etc.; and phage families of Microviridae, Siphoviridae, Ackermannviridae, Podoviridae, Myoviridae and the unclassified phages. Further, several sequences were homologous with the insect and plant viruses, which reflects the diet and habitation of dogs. Significantly, canine coronavirus was uniquely identified in all the samples with high abundance, and the phylogenetic analysis therefore showed close relationship with the human coronavirus strain 229E and NL63, indicating the potential risk of canine coronavirus to infect humans by obtaining the ability of cross-species transmission. This study emphasizes the high detection frequency of virus harbored in the enteric tract of healthy contacted animal, and expands the knowledge of the viral diversity and the spectrum for further disease-association studies, which is meaningful for elucidating the epidemiological and biological role of companion animals in public health.

Canine gastrointestinal parasites as a potential source of zoonotic infections in Nigeria: A nationwide survey

Dog feces may contain zoonotic parasites that contaminate the environment and serve as a potential source of infection to animals and humans. In this study, microscopic and molecular analyses were used to estimate the prevalence and intensity of gastrointestinal (GI) parasites and assess the risk factors for infection in 948 dogs in three climatically distinct zones of Nigeria. Zoonotic helminths including Strongyloides stercoralis, Ancylostoma braziliense, A. caninum and Toxocara canis were detected either as single or multiple infections in 377 (39.8 %) of dogs examined. At multiple logistic regression analyses, association was found between GI parasite infection and deworming practices and dog management. Regarding A. braziliense, A. caninum and T. canis infections, intensity of egg shedding was statistically associated with the age of the dogs and not with their sex or breed. The majority of GI parasite-positive dogs did not receive regular deworming treatment (59 %) and roamed freely (56 %) thereby constituting public health risk. This is the first nationwide survey and analyses of risk factors of GI parasites of dogs using molecular methods as confirmation of their identity. The zoonotic potential of these parasites is exacerbated by the lack of both operational national policies to control the population of free-roaming dogs and to promote responsible dog ownership, and veterinary public health programs for dogs.

Cryptosporidium and Giardia in locally harvested clams in Iqaluit, Nunavut

High prevalences of Cryptosporidium and Giardia were recently found in enteric illness patients in the Qikiqtaaluk region of Nunavut, Canada, with a foodborne, waterborne or animal source of parasites suspected. Clams (Mya truncata) are a commonly consumed, culturally important and nutritious country food in Iqaluit; however, shellfish may concentrate protozoan pathogens from contaminated waters. The goal of this work was to investigate clams as a potential source of Cryptosporidium and Giardia infections in residents in Iqaluit, Nunavut. The objectives were to estimate the prevalence and genetically characterize Cryptosporidium and Giardia in locally harvested clams. Clams (n = 404) were collected from Iqaluit harvesters in September 2016. Haemolymph (n = 328) and digestive gland (n = 390) samples were screened for Cryptosporidium and Giardia via PCR, and amplified products were further processed for sequence analyses for definitive confirmation. Giardia DNA was found in haemolymph from 2 clams, while Cryptosporidium was not detected. The two Giardia sequences were identified as zoonotic Giardia enterica assemblage B. The overall prevalence of Giardia in clams near Iqaluit was low (0.6%) compared with other studies in southern Canada and elsewhere. The presence of Giardia DNA in clams suggests human or animal faecal contamination of coastal habitat around Iqaluit in shellfish harvesting waters. Results from this study are intended to inform public health practice and planning in Inuit Nunangat.

Toxocara spp. in dogs and cats in Canada

Toxocara spp. (T. canis and T. cati) are the dominant ascarids of domestic dogs and cats, respectively, in populated regions of southern Canada, where they pose animal and public health concerns. A review of the published literature indicated that prevalence of both parasites is declining in more recent studies (post 2000), likely due to changes in animal husbandry as well as use of anthelmintics. Geographically, prevalence was higher in the east (Atlantic), and in more southerly locations, possibly due to more favourable climate conditions for egg survival and development. At northern latitudes and in wild felids and canids in general, the non-zoonotic ascarid Toxascaris leonina appears to outcompete Toxocara spp.; however, T. leonina is rare in domestic cats in Canada. Prevalence of Toxocara spp. was higher in cats than dogs, shelter/rural/remote/feral/stray vs owned animals, and young vs adult animals, as has been observed in many other studies and regions of the world. While the regional prevalences in this review should be interpreted carefully in light of variation in diagnostic methods and study populations, they generally follow the same trends observed in a recent national study of shelter animals. This review is a timely summary of the state of the published knowledge on prevalence of Toxocara spp. in Canada, and highlights knowledge gaps to be addressed, including the northern distributional limits of these species in Canada, the potential for transmission to and from wildlife hosts, and the public health significance of the parasite in the mainstream Canadian population.

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.

Prevalence and genetic characterization of Giardia spp. and Cryptosporidium spp. in dogs in Iqaluit, Nunavut, Canada

There are few epidemiologic studies on the role of dogs in zoonotic parasitic transmission in the Circumpolar North. The objectives of this study were to: (a) estimate the faecal prevalence of Giardia spp. and Cryptosporidium spp. in dogs; (b) investigate potential associations between the type of dog population and the faecal presence of Giardia spp. and Cryptosporidium spp.; and (c) describe the molecular characteristics of Giardia spp. and Cryptosporidium spp. in dogs in Iqaluit, Nunavut. We conducted two cross-sectional studies in July and September 2016. In July, the team collected daily faecal samples for 3 days from each of 20 sled dogs. In September, the team collected three faecal samples from each of 59 sled dogs, 111 samples from shelter dogs and 104 from community dogs. We analysed faecal samples for the presence of Giardia spp. and Cryptosporidium spp. using rapid immunoassay and flotation techniques. Polymerase chain reaction (PCR) and sequencing of target genes were performed on positive faecal samples. Overall, the faecal prevalence of at least one of the target parasites, when one faecal sample was chosen at random for all dogs, was 8.16% (CI: 5.52-11.92), and for Giardia spp. and Cryptosporidium spp., prevalence was 4.42% (CI: 2.58-7.49) and 6.12% (CI: 3.88-9.53), respectively. The odds of faecal Giardia spp. in sled dogs were significantly higher than those in shelter and community dogs (OR 10.19 [CI: 1.16-89.35]). Sequence analysis revealed that 6 faecal samples were Giardia intestinalis, zoonotic assemblage B (n = 2) and species-specific assemblages D (n = 3) and E (n = 1), and five faecal samples were Cryptosporidium canis. Giardia intestinalis is zoonotic; however, Cryptosporidium canis is rare in humans and, when present, usually occurs in immunosuppressed individuals. Dogs may be a potential source of zoonotic Giardia intestinalis assemblage B infections in residents in Iqaluit, Nunavut, Canada; however, the direction of transmission is unclear.

Prevalence of potentially zoonotic gastrointestinal parasites in canine faeces in Ibadan, Nigeria

BACKGROUND

Humans can get infected through direct or indirect contact with infective stages of zoonotic parasites shed to the environment through dog faeces.

OBJECTIVES

This study was designed to investigate the presence of gastrointestinal parasites present in dog faeces shed on the street of Ibadan metropolis, one of the largest cities in Africa.

METHODS

Twenty-three locations were randomly selected using grid-sampling method. A total of 203 faecal samples collected from the streets of selected areas were processed for detection of helminth eggs and protozoan oocysts using flotation technique. Eggs/oocysts per gram of faeces was counted using modified McMaster technique.

RESULTS

The prevalence of gastrointestinal parasites was 43.3% (88/203). Single and multiple infections were 69 (78.4%) and 19 (21.6%) respectively. The parasites detected were Ancylostoma sp. 24.6% (50/88) Isospora sp. 14.2% (29/88), Toxocara sp. 9.8% (20/88), Uncinaria sp. 2.5% (5/88) and Strongyloides sp, 3.9% (8/88). Ancylostoma sp. (320 × 10² epg) and Uncinaria sp. (5 × 10² epg) had the highest and least intensity respectively. Streets within residential areas having markets had the highest number of positive samples. All the genera of parasites detected in this study have zoonotic potential.

CONCLUSION

The high prevalence of zoonotic parasites detected in dog faeces from Ibadan metropolis showed that infected stray dogs roam the streets and constitute potential risk to human health. This study suggests the need for enforcement of laws restraining roaming or straying dogs and proper veterinary care of dogs.

FUNDING

None declared.

Giardia duodenalis Infections in Humans and Other Animals in China

Giardia duodenalis is an important zoonotic pathogen in both public and veterinary health, and has been genotyped into at least eight assemblages (A-H), each with a distinct host range. In recent years, this intestinal protozoan parasite has been identified widely in humans and various other animals, and has even been recorded in environmental contaminants. Along with whole genome sequencing of G. duodenalis, multilocus sequence typing is increasingly being used to characterize G. duodenalis isolates. Here, we review the epidemiology, genotyping, and subtyping of G. duodenalis from humans and a wide range of other animals, as well as from wastewater, in China.

A Comparative Exposure Assessment of Campylobacter in Ontario, Canada

To inform source attribution efforts, a comparative exposure assessment was developed to estimate the relative exposure to Campylobacter, the leading bacterial gastrointestinal disease in Canada, for 13 different transmission routes within Ontario, Canada, during the summer. Exposure was quantified with stochastic models at the population level, which incorporated measures of frequency, quantity ingested, prevalence, and concentration, using data from FoodNet Canada surveillance, the peer-reviewed and gray literature, other Ontario data, and data that were specifically collected for this study. Models were run with @Risk software using Monte Carlo simulations. The mean number of cells of Campylobacter ingested per Ontarian per day during the summer, ranked from highest to lowest is as follows: household pets, chicken, living on a farm, raw milk, visiting a farm, recreational water, beef, drinking water, pork, vegetables, seafood, petting zoos, and fruits. The study results identify knowledge gaps for some transmission routes, and indicate that some transmission routes for Campylobacter are underestimated in the current literature, such as household pets and raw milk. Many data gaps were identified for future data collection consideration, especially for the concentration of Campylobacter in all transmission routes.

Ecology and Life Cycle Patterns of Echinococcus Species

The genus Echinococcus is composed of eight generally recognized species and one genotypic cluster (Echinococcus canadensis cluster) that may in future be resolved into one to three species. For each species, we review existing information on transmission routes and life cycles in different geographical contexts and - where available - include basic biological information of parasites and hosts (e.g., susceptibility of host species). While some Echinococcus spp. are transmitted in life cycles that involve predominantly domestic animals (e.g., dog - livestock cycles), others are wildlife parasites that do or do not interact with domestic transmission. In many cases, life cycle patterns of the same parasite species differ according to geography. Simple life cycles contrast with transmission patterns that are highly complex, involving multihost systems that may include both domestic and wild mammals. Wildlife transmission may be primary or secondary, i.e., resulting from spillovers from domestic animals. For most of the species and regions, existing information does not yet permit a conclusive description of transmission systems. Such data, however, would be highly relevant, e.g., for anticipation of geographical changes of the presence and frequency of these parasites in a warming world, or for initiating evidence-based control strategies.

Intestinal parasites of gray wolves (Canis lupus) in northern and western Canada

Gray wolves (Canis lupus L., 1758) are mobile opportunistic predators that can be infected by a wide range of parasites, with many acquired via predator–prey relationships. Historically, many of these parasites were identified only to genus or family, but genetic tools now enable identification of parasite fauna to species and beyond. We examined 191 intestines from wolves harvested for other purposes from regions in the Northwest Territories, British Columbia, Saskatchewan, and Manitoba. Adult helminths were collected from intestinal contents for morphological and molecular identification, and for a subset of wolves, fecal samples were also analyzed to detect helminth eggs and protozoan (oo)cysts. Using both detection methods, we found that 83% of 191 intestines contained one or more parasite species, including cestodes (Taenia spp., Echinococcus spp., and Diphyllobothrium sp.), nematodes (Uncinaria stenocephala Railliet, 1884, Trichuris spp., Physaloptera spp., and Toxascaris leonina (von Linstow, 1902)), a trematode (Alaria sp.), and protozoa (Sarcocystis spp., Giardia sp., and Cryptosporidium spp.). Molecular characterization identified one species of Diphyllobothrium (Diphyllobothrium latum (L., 1758) Cobbold, 1858), three species of Taenia (Taenia krabbei Moniez, 1879, Taenia hydatigena Pallas, 1766, and Taenia multiceps Leske, 1786), and two Giardia duodenalis (Davaine) Deschiens, 1921 assemblages (B and C). These results demonstrate the diverse diet of wolves and illustrate the possibility of parasite spillover among wildlife, domestic animals, and people.

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.

Cryptosporidium hominis Is a Newly Recognized Pathogen in the Arctic Region of Nunavik, Canada: Molecular Characterization of an Outbreak

Background

Cryptosporidium is a leading cause of childhood diarrhea in low-resource settings, and has been repeatedly associated with impaired physical and cognitive development. In May 2013, an outbreak of diarrhea caused by Cryptosporidium hominis was identified in the Arctic region of Nunavik, Quebec. Human cryptosporidiosis transmission was previously unknown in this region, and very few previous studies have reported it elsewhere in the Arctic. We report clinical, molecular, and epidemiologic details of a multi-village Cryptosporidium outbreak in the Canadian Arctic.

Methodology/Principal Findings

We investigated the occurrence of cryptosporidiosis using a descriptive study of cases with onset between April 2013 and April 2014. Cases were defined as Nunavik inhabitants of any age presenting with diarrhea of any duration, in whom Cryptosporidium oocysts were detected by stool microscopy in a specialised reference laboratory. Cryptosporidium was identified in stool from 51 of 283 individuals. The overall annual incidence rate (IR) was 420 / 100,000 inhabitants. The IR was highest among children aged less than 5 years (1290 /100,000 persons). Genetic subtyping for stool specimens from 14/51 cases was determined by DNA sequence analysis of the 60 kDa glycoprotein (gp60) gene. Sequences aligned with C. hominis subtype Id in all cases. No common food or water source of infection was identified.

Conclusions/Significance

In this first observed outbreak of human cryptosporidiosis in this Arctic region, the high IR seen is cause for concern about the possible long-term effects on growth and development of children in Inuit communities, who face myriad other challenges such as overcrowding and food-insecurity. The temporal and geographic distribution of cases, as well as the identification of C. hominis subtype Id, suggest anthroponotic rather than zoonotic transmission. Barriers to timely diagnosis delayed the recognition of human cryptosporidiosis in this remote setting.

In mid-2013, an outbreak of moderate-to-severe diarrhea caused by Cryptosporidium was identified in the Arctic region of Nunavik, Quebec, and it predominantly affected young children. Cryptosporidium is a leading cause of childhood diarrhea in low-resource settings, but was previously unknown in this region. This is important because cryptosporidiosis has been repeatedly associated with impaired growth and development, and may interact with other challenges currently faced by children in remote Arctic communities, such as overcrowding and food-insecurity. Although animals in the Arctic have previously been found to harbour Cryptosporidium parvum, which can infect both animals and humans, we found that the Cryptosporidium identified in the stool of affected people all belonged to the species C. hominis, which is only known to infect humans. Together with the temporal and geographic distribution of cases, this suggests that cryptosporidiosis in this outbreak was transmitted person-to-person, rather than acquired from contact with animals. The emergence of Cryptosporidium infections in Arctic communities may have public health impacts beyond the occurrence of diarrhea.

A Systematic Review and Meta-Analysis of the Campylobacter spp. Prevalence and Concentration in Household Pets and Petting Zoo Animals for Use in Exposure Assessments

Animal contact is a potential transmission route for campylobacteriosis, and both domestic household pet and petting zoo exposures have been identified as potential sources of exposure. Research has typically focussed on the prevalence, concentration, and transmission of zoonoses from farm animals to humans, yet there are gaps in our understanding of these factors among animals in contact with the public who don't live on or visit farms. This study aims to quantify, through a systematic review and meta-analysis, the prevalence and concentration of Campylobacter carriage in household pets and petting zoo animals. Four databases were accessed for the systematic review (PubMed, CAB direct, ProQuest, and Web of Science) for papers published in English from 1992-2012, and studies were included if they examined the animal population of interest, assessed prevalence or concentration with fecal, hair coat, oral, or urine exposure routes (although only articles that examined fecal routes were found), and if the research was based in Canada, USA, Europe, Australia, and New Zealand. Studies were reviewed for qualitative synthesis and meta-analysis by two reviewers, compiled into a database, and relevant studies were used to create a weighted mean prevalence value. There were insufficient data to run a meta-analysis of concentration values, a noted study limitation. The mean prevalence of Campylobacter in petting zoo animals is 6.5% based on 7 studies, and in household pets the mean is 24.7% based on 34 studies. Our estimated concentration values were: 7.65x103cfu/g for petting zoo animals, and 2.9x105cfu/g for household pets. These results indicate that Campylobacter prevalence and concentration are lower in petting zoo animals compared with household pets and that both of these animal sources have a lower prevalence compared with farm animals that do not come into contact with the public. There is a lack of studies on Campylobacter in petting zoos and/or fair animals in Canada and abroad. Within this literature, knowledge gaps were identified, and include: a lack of concentration data reported in the literature for Campylobacter spp. in animal feces, a distinction between ill and diarrheic pets in the reported studies, noted differences in shedding and concentrations for various subtypes of Campylobacter, and consistent reporting between studies.

Campylobacter species in animal, food, and environmental sources, and relevant testing programs in Canada

Campylobacter species, particularly thermophilic campylobacters, have emerged as a leading cause of human foodborne gastroenteritis worldwide, with Campylobacter jejuni, Campylobacter coli, and Campylobacter lari responsible for the majority of human infections. Although most cases of campylobacteriosis are self-limiting, campylobacteriosis represents a significant public health burden. Human illness caused by infection with campylobacters has been reported across Canada since the early 1970s. Many studies have shown that dietary sources, including food, particularly raw poultry and other meat products, raw milk, and contaminated water, have contributed to outbreaks of campylobacteriosis in Canada. Campylobacter spp. have also been detected in a wide range of animal and environmental sources, including water, in Canada. The purpose of this article is to review (i) the prevalence of Campylobacter spp. in animals, food, and the environment, and (ii) the relevant testing programs in Canada with a focus on the potential links between campylobacters and human health in Canada.

Parasite prevalence in fecal samples from shelter dogs and cats across the Canadian provinces

BACKGROUND

In Canada, surveys of enteric parasites in dogs and cats have been reported sporadically over the past 40 years, mostly focusing on a specific region. The present work was performed to determine the current prevalence of various parasites in fecal samples from shelter dogs and cats across the Canadian provinces.

METHODS

A total of 1086 dog and 636 cat fecal samples from 26 shelters were analysed using a sugar solution double centrifugal flotation technique. Prevalences (national, regional, provincial, age and parasite-specific), were calculated and compared using the Fisher-Exact test. A multiplex PCR was performed to distinguish Taenia spp, Echinococcus granulosus and E. multilocularis on samples positive for taeniid eggs.

RESULTS

Overall, 33.9% of dogs and 31.8% of cats were positive for at least one parasite. Toxocara canis and T. cati were the most prevalent parasite present in fecal samples followed by Cystoisospora spp. Prevalence in dogs was similar across the Atlantic, East, West and Pacific regions, while prevalence in cats varied regionally. Eggs of E. granulosus/E. canadensis were detected in samples from dogs from BC, AB, and ON.

CONCLUSIONS

Data from this study will help in the development of strategies, based on the level of risk per geographic location for the prevention and response to these parasites in pets and free-roaming and shelter animals in Canada.

The prevalence of Giardia infection in dogs and cats, a systematic review and meta-analysis of prevalence studies from stool samples

Giardia has a wide range of host species and is a common cause of diarrhoeal disease in humans and animals. Companion animals are able to transmit a range of zoonotic diseases to their owners including giardiasis, but the size of this risk is not well known. The aim of this study was to analyse giardiasis prevalence rates in dogs and cats worldwide using a systematic search approach. Meta-analysis enabled to describe associations between Giardia prevalence and various confounding factors. Pooled prevalence rates were 15.2% (95% CI 13.8-16.7%) for dogs and 12% (95% CI 9.2-15.3%) for cats. However, there was very high heterogeneity between studies. Meta-regression showed that the diagnostic method used had a major impact on reported prevalence with studies using ELISA, IFA and PCR reporting prevalence rates between 2.6 and 3.7 times greater than studies using microscopy. Conditional negative binomial regression found that symptomatic animals had higher prevalence rates ratios (PRR) than asymptomatic animals 1.61 (95% CI 1.33-1.94) in dogs and 1.94 (95% CI 1.47-2.56) in cats. Giardia was much more prevalent in young animals. For cats >6 months, PRR=0.47 (0.42-0.53) and in dogs of the same age group PRR=0.36 (0.32-0.41). Additionally, dogs kept as pets were less likely to be positive (PRR=0.56 (0.41-0.77)) but any difference in cats was not significant. Faecal excretion of Giardia is common in dogs and slightly less so in cats. However, the exact rates depend on the diagnostic method used, the age and origin of the animal. What risk such endemic colonisation poses to human health is still unclear as it will depend not only on prevalence rates but also on what assemblages are excreted and how people interact with their pets.

Multiple zoonotic parasites identified in dog feces collected in Ponte de Lima, Portugal-a potential threat to human health

Dogs play many roles and their presence within people’s houses has increased. In rural settings dog faeces are not removed from the streets, representing an environmental pollution factor. Our aim was to evaluate the occurrence of environmental contamination with zoonotic intestinal parasites of three groups of dogs in Ponte de Lima, Portugal, with a particular emphasis on Echinococcus granulosus. We collected 592 dog faecal samples from the environment, farm and hunting dogs. Qualitative flotation coprological analysis was performed and the frequency in the positive samples ranged between 57.44% and 81.19% in different groups. We isolated up to four different parasites in one sample and detected seven intestinal parasitic species, genera or families overall. Ancylostomatidae was the most prevalent parasite, followed by Trichuris spp., Toxocara spp., Isospora spp., Dipylidium caninum, Taeniidae and Toxascaris leonina. Taeniidae eggs were analyzed with the PCR technique and revealed not to be from Echinococcus. The parasite prevalence and the diversity of zoonotic parasites found were high, which calls for a greater awareness of the problem among the population, especially hunters. Promoting research at the local level is important to plan control strategies. Health education should be developed with regard to farmers and hunters, and a closer collaboration between researchers, practitioners and public health authorities is needed.

Occurrence and molecular characterization of Cryptosporidium in dogs in Henan Province, China

Background

Cryptosporidiosis in dogs has been reported worldwide, involving both asymptomatic and diarrheic dogs. Large-scale surveys of Cryptosporidium infection in dogs have been performed in some countries using differents diagnostic methods. But, few data are available on the infection rate and molecular characteristics of Cryptosporidium spp. in dogs in China.

Result

In this study, 770 fecal samples from 66 locations in Henan Province were examined. The average Cryptosporidium infection rate was 3.8%, with dogs in kennels having the highest rate of 7.0% (χ² = 14.82, P < 0.01). The infection rate was 8.0% in dogs younger than 90 days, which was significantly higher than that in the other age groups (1.1–3.8%;χ² = 18.82, P < 0.01). No association was noted between the infection rate and the sex of the dogs. Twenty-nine Cryptosporidium-positive samples were amplified at the small subunit rRNA (SSU rRNA), 70-kDa heat shock protein (HSP70), and actin loci using PCR. Sequence analysis of these amplicons identified only Cryptosporidium canis, which showed 100% identity with the published sequences of the SSU rRNA, HSP70, and actin genes.

Conclusions

Our results confirm that C. canis is popular in the dog population in China, considering the large number of dogs in China and the close contact between dogs and humans, the role of C. canis in the transmission of human cryptosporidiosis warrants attention.

Canine echinococcosis: global epidemiology and genotypic diversity

Canine echinococcosis is a potential zoonotic infection caused by the adult form of several cestode species belonging to the genus Echinococcus, of which E. granulosus sensu lato and E. multilocularis are the most epidemiologically relevant. Dogs infected with E. granulosus and E. multilocularis are widely regarded as the main source of infection for human cystic and alveolar echinococcosis, diseases that cause substantial morbidity and socio-economic burden in several regions of the world. Following our previous review on the global situation of cystic echinococcosis in livestock species (Cardona and Carmena. Vet. Parasitol. 2013;192:10-32), we summarize here current knowledge on the global epidemiology, geographical distribution and molecular diversity of Echinococcus spp. infection in dogs. We address relevant topics including the implications of the increasing urbanization of wildlife species such as foxes, coyotes, and dingoes in the establishment of urban cycles of Echinococcus spp., or the rising concerns regarding the role of unsupervised translocation of infected dogs in spreading the infection to Echinococcus-free areas. The involvement of wildlife species as natural reservoirs of disease to domestic animals and humans and the epidemiological significance of the sympatric occurrence of different Echinococcus species in the same geographical region are also debated. Data presented are expected to be useful for policy makers, educational and health authorities responsible for designing and implementing effective measures for disease control and prevention.

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.

Nanolitre real-time PCR detection of bacterial, parasitic, and viral agents from patients with diarrhoea in Nunavut, Canada

Background

Little is known about the microbiology of diarrhoeal disease in Canada's Arctic regions. There are a number of limitations of conventional microbiology testing techniques for diarrhoeal pathogens, and these may be further compromised in the Arctic, given the often long distances for specimen transport.

Objective

To develop a novel multiple-target nanolitre real-time reverse transcriptase (RT)-PCR platform to simultaneously test diarrhoeal specimens collected from residents of the Qikiqtani (Baffin Island) Region of Nunavut, Canada, for a wide range of bacterial, parasitic and viral agents.

Study design/methods

Diarrhoeal stool samples submitted for bacterial culture to Qikiqtani General Hospital in Nunavut over an 18-month period were tested with a multiple-target nanolitre real-time PCR panel for major diarrhoeal pathogens including 8 bacterial, 6 viral and 2 parasitic targets.

Results

Among 86 stool specimens tested by PCR, a total of 50 pathogens were detected with 1 or more pathogens found in 40 (46.5%) stool specimens. The organisms detected comprised 17 Cryptosporidium spp., 5 Clostridium difficile with toxin B, 6 Campylobacter spp., 6 Salmonella spp., 4 astroviruses, 3 noroviruses, 1 rotavirus, 1 Shigella spp. and 1 Giardia spp. The frequency of detection by PCR and bacterial culture was similar for Salmonella spp., but discrepant for Campylobacter spp., as Campylobacter was detected by culture from only 1/86 specimens. Similarly, Cryptosporidium spp. was detected in multiple samples by PCR but was not detected by microscopy or enzyme immunoassay.

Conclusions

Cryptosporidium spp., Campylobacter spp. and Clostridium difficile may be relatively common but possibly under-recognised pathogens in this region. Further study is needed to determine the regional epidemiology and clinical significance of these organisms. This method appears to be a useful tool for gastrointestinal pathogen research and may also be helpful for clinical diagnostics and outbreak investigation in remote regions where the yield of routine testing may be compromised.

Parasitic zoonoses: one health surveillance in northern Saskatchewan

We report the results of a joint human-animal health investigation in a Dene community in northern Saskatchewan, where residents harvest wildlife (including moose, bear, elk, and fish), live in close contact with free roaming dogs, and lack access to permanent veterinary services. Fecal analysis of owned and free-roaming dogs over two consecutive years (N = 92, 103) identified several parasites of public health concern, including Toxocara canis, Diphyllobothrium spp., Echinococcus/Taenia, Cryptosporidium spp. and Giardia spp. Administration of pyrantel pamoate to a subset of dogs (N = 122) in the community in the first year was followed by reduced shedding of T. canis and other roundworms in the second year, demonstrating the potential utility of canine de-worming as a public health intervention. Using direct agglutination tests with confirmatory indirect fluorescent antibody test, 21% of 47 dogs were sero-positive for exposure to Toxoplasma gondii. Using enzyme-linked immunosorbent assay (ELISA) sero-prevalence rates in 201 human volunteers were as follows: Toxoplasma gondii (14%), Echinococcus granulosus (48%), Toxocara canis (13%) and Trichinella spp. (16%). Overall 65% of participants were sero-positive for at least one parasite. A survey administered to volunteers indicated few associations between widely accepted risk factors for parasite exposure and serological status, emphasizing the importance of environmental transmission of these parasites through soil, food, and waterborne routes.

Parasites are ubiquitous, and while some parasitize only one host, others are capable of crossing species barriers. Zoonotic parasites move between animals and people, and in some cases cause significant veterinary, medical and/or public health problems. Such parasites may be more prevalent in areas where veterinary and medical services are scarce, and especially if sanitation infrastructure is suboptimal. Additional risk factors include reliance on country foods, proximity to pets that come in contact with wildlife, and eating undercooked or raw fish and game. We visited one northern Indigenous community over two consecutive years to determine the prevalence of internal parasites in dogs, as well as to demonstrate the effect of selective deworming on reducing environmental contamination by zoonotic parasites. In addition, we collected blood samples and administered surveys to human volunteers in order to explore the relationship between exposure to four zoonotic parasites and several widely accepted risk factors for exposure (e.g. pet ownership). Our findings indicate that levels of parasite exposure in this community were higher than similar studies conducted in other Canadian Indigenous communities. Public health interventions that utilize a one health strategy by integrating medical, veterinary and environmental expertise may be the most effective approach in reducing human and animal exposure to parasites in this community.

Endoparasites in the feces of arctic foxes in a terrestrial ecosystem in Canada

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Few studies report the endoparasites of North American arctic foxes.

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Conventional, immunological, and molecular techniques detected parasites in arctic foxes at Karrak Lake, Nunavut.

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Karrak Lake foxes are infected with common parasites of foxes with a terrestrial diet.

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This study provides a comparison for future studies from the central Canadian Arctic.

The parasites of arctic foxes in the central Canadian Arctic have not been well described. Canada’s central Arctic is undergoing dramatic environmental change, which is predicted to cause shifts in parasite and wildlife species distributions, and trophic interactions, requiring that baselines be established to monitor future alterations. This study used conventional, immunological, and molecular fecal analysis techniques to survey the current gastrointestinal endoparasite fauna currently present in arctic foxes in central Nunavut, Canada. Ninety-five arctic fox fecal samples were collected from the terrestrial Karrak Lake ecosystem within the Queen Maud Gulf Migratory Bird Sanctuary. Samples were examined by fecal flotation to detect helminths and protozoa, immunofluorescent assay (IFA) to detect Cryptosporidium and Giardia, and quantitative PCR with melt-curve analysis (qPCR-MCA) to detect coccidia. Positive qPCR-MCA products were sequenced and analyzed phylogenetically. Arctic foxes from Karrak Lake were routinely shedding eggs from Toxascaris leonina (63%). Taeniid (15%), Capillarid (1%), and hookworm eggs (2%), Sarcocystis sp. sporocysts 3%), and Eimeria sp. (6%), and Cystoisospora sp. (5%) oocysts were present at a lower prevalence on fecal flotation. Cryptosporidium sp. (9%) and Giardia sp. (16%) were detected by IFA. PCR analysis detected Sarcocystis (15%), Cystoisospora (5%), Eimeria sp., and either Neospora sp. or Hammondia sp. (1%). Through molecular techniques and phylogenetic analysis, we identified two distinct lineages of Sarcocystis sp. present in arctic foxes, which probably derived from cervid and avian intermediate hosts. Additionally, we detected previously undescribed genotypes of Cystoisospora. Our survey of gastrointestinal endoparasites in arctic foxes from the central Canadian Arctic provides a unique record against which future comparisons can be made.

Surveillance for Echinococcus canadensis genotypes in Canadian ungulates

The geographic and host distribution, prevalence and genotypes of Echinococcus canadensis in wild ungulates in Canada are described to better understand the significance for wildlife and public health. We observed E. canadensis in 10.5% (11/105) of wild elk (wapiti; Cervus canadensis) in Riding Mountain National Park, Manitoba, examined at necropsy, over two consecutive years (2010–2011). Molecular characterization of hydatid cyst material from these elk, as well as three other intermediate wildlife host species, was based on sequence of a 470 bp region of the NADH dehydrogenase subunit 1 (NAD1) mitochondrial gene. In moose [Alces alces], elk, and caribou [Rangifer tarandus] from northwestern Canada, the G10 genotype was the only one present, and the G8 genotype was detected in a muskox (Ovibos moschatus) from northeastern Canada. On a search of the national wildlife health database (1992–2010), cervids with hydatid cysts were reported in all provinces and territories except the Atlantic provinces, from which wolves [Canis lupis] are historically absent. Of the 93 cervids with records of hydatid cysts, 42% were elk, 37% were moose, 14% were caribou, and 6% were white-tailed and mule deer [Odocoileus virginianus and Odocoileus hemonius]. In these animals, 83% of cysts were detected in lungs alone, 8% in both lungs and liver, 3% in liver alone, and 6% in other organs. These observations can help target surveillance programs and contribute to a better understanding of ecology, genetic diversity, and genotype pathogenicity in the Echinococcus granulosus species complex.

Tradition and transition: parasitic zoonoses of people and animals in Alaska, northern Canada, and Greenland

Zoonotic parasites are important causes of endemic and emerging human disease in northern North America and Greenland (the North), where prevalence of some parasites is higher than in the general North American population. The North today is in transition, facing increased resource extraction, globalisation of trade and travel, and rapid and accelerating environmental change. This comprehensive review addresses the diversity, distribution, ecology, epidemiology, and significance of nine zoonotic parasites in animal and human populations in the North. Based on a qualitative risk assessment with criteria heavily weighted for human health, these zoonotic parasites are ranked, in the order of decreasing importance, as follows: Echinococcus multilocularis, Toxoplasma gondii, Trichinella and Giardia, Echinococcus granulosus/canadensis and Cryptosporidium, Toxocara, anisakid nematodes, and diphyllobothriid cestodes. Recent and future trends in the importance of these parasites for human health in the North are explored. For example, the incidence of human exposure to endemic helminth zoonoses (e.g. Diphyllobothrium, Trichinella, and Echinococcus) appears to be declining, while water-borne protozoans such as Giardia, Cryptosporidium, and Toxoplasma may be emerging causes of human disease in a warming North. Parasites that undergo temperature-dependent development in the environment (such as Toxoplasma, ascarid and anisakid nematodes, and diphyllobothriid cestodes) will likely undergo accelerated development in endemic areas and temperate-adapted strains/species will move north, resulting in faunal shifts. Food-borne pathogens (e.g. Trichinella, Toxoplasma, anisakid nematodes, and diphyllobothriid cestodes) may be increasingly important as animal products are exported from the North and tourists, workers, and domestic animals enter the North. Finally, key needs are identified to better assess and mitigate risks associated with zoonotic parasites, including enhanced surveillance in animals and people, detection methods, and delivery and evaluation of veterinary and public health services.

Parasites in ungulates of Arctic North America and Greenland: a view of contemporary diversity, ecology, and impact in a world under change

Parasites play an important role in the structure and function of arctic ecosystems, systems that are currently experiencing an unprecedented rate of change due to various anthropogenic perturbations, including climate change. Ungulates such as muskoxen, caribou, moose and Dall's sheep are also important components of northern ecosystems and are a source of food and income, as well as a focus for maintenance of cultural traditions, for northerners. Parasites of ungulates can influence host health, population dynamics and the quality, quantity and safety of meat and other products of animal origin consumed by people. In this article, we provide a contemporary view of the diversity of nematode, cestode, trematode, protozoan and arthropod parasites of ungulates in arctic and subarctic North America and Greenland. We explore the intricate associations among host and parasite assemblages and identify key issues and gaps in knowledge that emerge in a regime of accelerating environmental transition.

Sentinel surveillance for zoonotic parasites in companion animals in indigenous communities of Saskatchewan

Indigenous communities may have increased risk of exposure to zoonotic parasites, including Echinococcus granulosus, Toxocara canis, Toxoplasma gondii, Diphyllobothrium spp., and Giardia duodenalis, for which dogs may serve as sentinels for or sources of human infection. Canid fecal samples were collected from dogs and the environment in five indigenous communities across Saskatchewan and Alberta (N = 58, 62, 43, 66, and 25). Parasites in individual fecal samples were quantified using fecal flotation and a commercial immunofluorescent antibody test for Giardia and Cryptosporidium. Overall, the prevalence of canine intestinal parasitic infection was 20-71%, which is 5-16 times higher in indigenous communities than a nearby urban center in Saskatchewan. The overall prevalences of T. canis, Diphyllobothrium, and taeniid eggs in dog feces were, respectively, 11.8%, 4.9%, and 1.2% in our study compared with 0-0.2% in urban dogs. Giardia cysts present in 21% of samples were identified as zoonotic genotype Assemblage A.

Evaluation of the zoonotic potential of Giardia duodenalis in fecal samples from dogs and cats in Ontario

This study determined the distribution and zoonotic potential of Giardia duodenalis assemblage types among canine and feline fecal samples from Ontario. The effectiveness of Giardia assemblage typing methods by sequencing the genes of small subunit ribosomal RNA (ssu-rRNA), β-giardin (bg), glutamate dehydrogenase (gdh), and triose phosphate isomerase (tpi) was evaluated simultaneously. From 2008 to 2010, 118 canine and 15 feline Giardia positive fecal samples were tested. The ssu-rRNA sequencing method typed 64% (75/118) and 87% (13/15) of the Giardia-positive canine and feline samples, respectively. Among the typeable samples, 68% (51/75) of canine samples contained G. duodenalis assemblage D and 31% (23/75) contained G. duodenalis assemblage C (both non-zoonotic assemblage types). Only 1% (1/75) of the typeable canine samples contained a potentially zoonotic assemblage B. In contrast, 100% (13/13) of the typeable feline samples contained potentially zoonotic assemblages A (n = 12) or B (n = 1).

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.