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. 2017 Oct 13;8:2004. doi: 10.3389/fmicb.2017.02004

Giardia duodenalis Infections in Humans and Other Animals in China

Junqiang Li 1,†, Haiyan Wang 1,†, Rongjun Wang 1, Longxian Zhang 1,*
PMCID: PMC5645521  PMID: 29081771

Abstract

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.

Keywords: G. duodenalis, humans, animals, prevalence, assemblage, multilocus sequence typing, China, zoonotic

Introduction

Giardia is one of the most common intestinal parasites of both humans and a diverse range of other animals (Feng and Xiao, 2011). The parasite was first discovered by Antonie van Leeuwenhoek over 300 years ago (Dobell, 1920), and since then, six Giardia species have been described. Among them, Giardia agilis, Giardia ardeae, Giardia psittaci, Giardia muris, and Giardia microti infect animals ranging from amphibians to rodents and birds, whereas the broad range of hosts for Giardia duodenalis (syn. Giardia intestinalis and Giardia lamblia) includes humans and domestic, farmed, and wild animals (Monis et al., 2009; Feng and Xiao, 2011; Ryan and Cacciò, 2013). Giardiasis, which is caused by Giardia duodenalis, is an important zoonotic disease for both public and veterinary health (Ryan and Cacciò, 2013).

The G. duodenalis life cycle is simple in that it comprises rapidly multiplying trophozoites (attached to intestinal epithelial cells) and cysts that are resistant to environmental degradation, which are excreted with feces and transmitted onwards via the fecal-oral route (Lv et al., 2013; Einarsson et al., 2016). G. duodenalis has long been considered to reproduce asexually by simple binary fission, but there is increasing evidence from epidemiological, molecular genetics, and whole genome sequencing studies that Giardia is capable of sexual reproduction (Cooper et al., 2007; Morrison et al., 2007; Poxleitner et al., 2008; Nolan et al., 2010; Gabín-García et al., 2017).

Molecular biological analysis of G. duodenalis has benefited from understanding the taxonomy, population genetics, and epidemiology of this pathogen, and such studies are essential to the effective control of giardiasis in clinical practice (Cacciò and Ryan, 2008). In terms of its genetic variation, G. duodenalis isolates genotypically fall into one of at least eight assemblages (A–H), each of which have a distinct host range (Cacciò and Ryan, 2008; Sprong et al., 2009; Feng and Xiao, 2011; Ryan and Cacciò, 2013). There is also genetic diversity within these assemblages. For example, sub-assemblages AI, AII, and AIII fall within assemblage A (Feng and Xiao, 2011) and BIII and BIV form assemblage B (Monis et al., 2003), while various sub-assemblages form assemblage E (Zhang et al., 2012c).

Multilocus genotyping (MLG) analysis using both conserved (e.g., ssrDNA, ef, h2b, h4) and variable (e.g., tpi, gdh, bg) genes was originally used to assess the G. duodenalis assemblages (Wielinga et al., 2011). Nowadays, variable genes such as tpi, gdh, and bg are used to characterize G. duodenalis isolates from humans and other animals and determine the genotype or subtype. These analyses provide sufficient resolution to assess the disease burden arising from zoonotic transmission of the parasite (Cacciò et al., 2008; Sprong et al., 2009; Wang et al., 2014b; Wang H. et al., 2016). To date, four genetically distinct G. duodenalis isolates (WB, AI; AS175, AII; P15, E, and GS, B) have been studied genomically (Franzén et al., 2009; Jerlström-Hultqvist et al., 2010; Adam et al., 2013) and transcriptomically (Franzén et al., 2013). Differences between the genomic and transcriptomic profiling results may explain the differences observed in host preferences and clinical presentation of G. duodenalis infection (Franzén et al., 2009, 2013; Jerlström-Hultqvist et al., 2010; Adam et al., 2013).

Annually, 280 million people worldwide are estimated to have clinically diagnosable giardiasis (Feng and Xiao, 2011; Ryan and Cacciò, 2013; Einarsson et al., 2016; Squire and Ryan, 2017), and infection rates are higher in developing countries (Feng and Xiao, 2011; Ryan and Cacciò, 2013). Giardiasis is generally a self-limiting clinical illness characterized by watery diarrhea, abdominal cramps, bloating, weight loss, and malabsorption (Feng and Xiao, 2011; Einarsson et al., 2016). However, asymptomatic infections occur more frequently than symptomatic ones (Himsworth et al., 2010; Feng and Xiao, 2011; Ryan and Cacciò, 2013; Wegayehu et al., 2016). In China, approximately 28.5 million giardiasis cases are estimated to occur in humans per year (Feng and Xiao, 2011), although the true incidence is likely underestimated as there are many undetected and/or unreported cases. In recent years, G. duodenalis has been identified in humans, non-human primates (NHPs), ruminants, companion animals, domestic animals, wildlife, and even in the environment in China (Liu et al., 2011; Wang et al., 2011, 2014b; Li N. et al., 2012; Zhang et al., 2012c; Liu A. et al., 2014; Liu H. et al., 2014; Li J. et al., 2015; Qi et al., 2016a,b; Wang H. et al., 2016). Here, the epidemiology, genotyping, and subtyping of G. duodenalis in humans and various other animals in China are summarized and reviewed.

G. duodenalis in humans

Investigations and case reports on G. duodenalis infections in humans are common in China (Table 1). Sporadic reports of human giardiasis have been documented since 1962, although a number of giardiasis cases were recoded in 1983 in Xi'an (Zhang and Li, 1983). The large number of epidemiological investigations conducted at the start of this century suggested that the average infection rate was 0.85% (197/23,098), with the highest infection rate (9.46%, 7/74) reported by one study carried out in Shanghai (Wang L. et al., 2013). Differences in the observed rates of infection may be due, in part, to the age of the patients. In China, children <15 years of age were the most affected, with the peak infection rate occurring in those aged 5–10 years (Yu et al., 1994; Lv et al., 2013). A similar observation was made in Malaysia, where children under 15 years old were more likely to be infected with G. duodenalis (Mohammed Mahdy et al., 2009; Anuar et al., 2014).

Table 1.

Giardia duodenalis infection rates and genotypes in humans in China.

Locations Patient group Specimens Positive (%) Assemblage (no.) Subassemblage (no.) References
Shaanxi:Xi'an Patients 19a Case reports Zhang and Li, 1983
Anhui 10a Genotypes identified A (4) AII (4) Yong et al., 2000
B (4)
Sichuan Diarrhea patients 2a Case reports Chen, 2001
Henan Inpatients 18a Genotypes identified A (12) AI(8); AII (4) Wang et al., 2011
B (6)
Hebei: Chengde Resident 216 3 (1.39%) A (3) AII (3) Chen et al., 2000
Anhui: Huainan School pupils 1,332 81 (6.08%) Fu et al., 2004
Hainan: Haikou Elementary school students 535 8 (1.50%) Gan et al., 2006
Henan: Kaifeng Patients 6,093 10 (0.16%) Wang et al., 2009
Henan: Zhengzhou Patients 4,836 11 (0.23%) Sun et al., 2010
Henan: Zhengzhou Children patients 1,996 12 (0.60%) Xu et al., 2011
Anhui: Fuyang HIV positive patients 302 4 (1.32%) Tian et al., 2012
Anhui: Fuyang HIV negative individuals 303 2 (0.66%) Tian et al., 2012
Shanghai Children with various congenital or inherited diseases 74b 7 (9.46%) A (6) AII (6) Wang L. et al., 2013
Shanghai Children attending the endocrinology 283 4 (1.41%) A (2) AII (2) Wang L. et al., 2013
B (2)
Shanghai children attending general surgeries 216 0 Wang L. et al., 2013
Shanghai Children 3,472 25 (0.72%) A (17) AII (17) Wang L. et al., 2013
B (9)
Shanghai Diarrhea outpatients 252 17 (6.75%) B (1) Liu H. et al., 2014
C (16)
Hubei: Chibi Kindergarten children 20 1 (5.00%) Yuan et al., 2015
Shanghai Diarrhea patients 95 1 (1.05%) B (1) Liu H. et al., 2015
Tibet: Lhasa Resident 1,015 4 (0.39%) Liu et al., 2016
Guangdong: Shenzhen Diarrhea children 126 0 Shen et al., 2016
Guangdong: Shenzhen Diarrhea adults patients 286 0 Shen et al., 2016
Guangdong: Shenzhen Diarrhea patients <18 126 0 Shen et al., 2016
Yunnan: Kunming Diarrhea children 850 0 Zhang S. X. et al., 2016
Yunnan: Kunming Diarrhea children 170 0 Zhang S. X. et al., 2016
Wuhan Diarrhea children 500 7 (1.40%) A (7) AII (7) Wang T. et al., 2017
Total 23,098 197 (0.85%) A (51); B (23); C (16) AI (8); AII (43)
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a

Not included in the G. duodenalis infection rate calculation.

b

Specimens from a cryptosporidiosis outbreak.

Despite its widespread occurrence, molecular epidemiological data for G. duodenalis infections in humans from China is limited. According to the few available genotyping studies, both assemblage A (subtypes AI and AII) and B isolates have been found in China, with subtype AII and assemblage B being the dominant genotypes (Yong et al., 2000; Wang et al., 2011; Wang L. et al., 2013; Wang T. et al., 2017). Interestingly, a canid-specific assemblage C strain, which was first identified in Egypt (Soliman et al., 2011), was found in 16 Giardia-positive diarrheal outpatients in Shanghai (Liu H. et al., 2014). MLG analysis of assemblage AII and B isolates from Shanghai identified six and 11 sequence types, respectively (Wang L. et al., 2013). No significant gender-specific association for G. duodenalis infections or assemblage distribution has been reported in China (Liu H. et al., 2014; Wang T. et al., 2017).

G. duodenalis in NHPs

The prevalence of G. duodenalis infections in NHPs varies markedly between different studies (Table 2). The average rate of infection for NHPs was 4.49% (172/3,827), with the highest rate recorded by a study conducted in Hunan Province (44.00%, 33/75). However, variability in the feeding habitats, health status, and age of the subjects, as well as differences in the geographic location and diagnostic techniques used in the studies probably contribute to the discrepant infection rates (Li J. et al., 2017).

Table 2.

Giardia duodenalis infection rates and genotypes in non-human primates in China.

Locations Specimens Positive (%) Host species (no.) Assemblage (no.) Subassemblage (no.) References
Henan 74 1 (1.35%) Rhesus macaque (1) Zhao et al., 2011
Guangxi 232 0 Zhao et al., 2011
Sichuan 40 0 Zhao et al., 2011
Guizhou 411 35 (8.52%) Rhesus macaque (10) A (10) AII (10) Ye et al., 2012
Rhesus macaque (24) B (24)
Guangxi 784 4 (0.51%) Rhesus macaque / Cynomolgus monkey Li J. et al., 2013
Guangxi 205 5 (2.44%) Rhesus macaque (2) A (2) AII (2) Ye et al., 2014
Rhesus macaque (3) B (3)
Beijing 72 16 (22.22%) Cynomolgus monkey (1) A (1) AIII (1) Karim et al., 2014, 2015
Ring-tailed lemur (6); Squirrel monkey (5); Golden monkey (3); Cynomolgus monkey (1) B (15) BIV (15)
Hebei 89 10 (11.24%) Ring-tailed lemur (5); Rhesus macaque (4); Mona monkey (1) B (10) BIV (10) Karim et al., 2014, 2015
Henan 518 20 (3.86%) Rhesus macaque (14); Japanese macaque (3); Olive baboon (2); Assam macaque (1) B (20) BIV (20) Karim et al., 2014, 2015
Shanxi 66 9 (13.64%) Rhesus macaque (5); Yellow baboon (2); Northern white-cheeked gibbon (2) B (9) BIV (9) Karim et al., 2014, 2015
Shaanxi 197 4 (2.03%) Rhesus macaque (3); Saimiri sciureus (1) E (4) Du et al., 2015
Shanghai 128 19 (14.84%) Green monkey (1) A (1) AI (1) Karim et al., 2014, 2015
Ring-tailed lemur (10); Golden monkey (2); Squirrel monkey (2); Cynomolgus monkey (2) King colobus (1); Mandrill (1) B (18) BIV (18)
Hubei 66 5 (7.58%) Pig-tailed macaque (4); Hamadryas baboon (1) B (5) BIV (5) Karim et al., 2014, 2015
Hunan 75 33 (44.00%) Ring-tailed lemur (2) A (2) AI (1); AII (1) Karim et al., 2014, 2015
Pig-tailed macaque (8); Bornean orangutan (5); Hussar monkey (5); Ring-tailed lemur (3); Squirrel monkey (3); Cynomolgus monkey (3); Green monkey (2); Roloway monkey (1); Francois' leaf monkey (1) B (31) BIV (31)
Guangdong 57 1 (1.75%) Cynomolgus monkey (1) B (1) BIV (1) Karim et al., 2014, 2015
Guangxi 363 9 (2.48%) Rhesus macaque (8); White-headed (1) B (9) BIV (9) Karim et al., 2014, 2015
Sichuan 304 0 Karim et al., 2014, 2015
Yunnan 144 0 Karim et al., 2014, 2015
Henan 2 1 (50.00%) Nomascus leucogenys (1) B (1) Li J. et al., 2015
Total 3,827 172 (4.49%) A (16); B (146); E (4) AI (2); AII (13); AIII (1); BIV (118)
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Thus far, assemblage A, B, and E strains have been identified in NHPs, with assemblage B dominant in China (Karim et al., 2014, 2015). Only one study, from Shaanxi Province, identified an assemblage E isolate in NHPs in China (Du et al., 2015), although an assemblage E isolate has also been found in a red colobus monkey in western Uganda (Johnston et al., 2010). MLG has also been used for genotyping G. duodenalis in NHPs. Like humans, several assemblage A (subtypes AI and AII) and B (subtype BIV) subtypes have been identified in NHPs, with subtype BIV identified as the dominant subtype (Karim et al., 2014, 2015). A total of 15 MLG genotypes (two known and 13 novel) were reported in one study, although the two known MLG genotypes were not significant from a public health perspective (Karim et al., 2015).

Phylogenetic analysis has suggested the possibility of geographical segregation and host-adaptation amongst assemblage B strains in NHPs in China. The role of NHPs in the transmission of G. duodenalis to humans is not clear. It is believed that the frequent occurrence of assemblage B strains in captive NHPs may be associated with transmission from human sources, or an indication of adaptation to primate host (Sprong et al., 2009; Karim et al., 2015).

G. duodenalis in cattle

In cattle, G. duodenalis infections vary in their prevalence and genotypic distribution according to region and cattle species (Table 3). The first documentation of G. duodenalis infection in dairy cattle occurred in 2006 in Guangdong Province (Xiao et al., 2006). The average infection rate in cattle (including dairy cattle, beef cattle, and yaks) is 5.43% (693/12,753), with the highest rate observed in Shaanxi Province (18.87%, 70/371). However, use of different detection methods may contribute to the observed differences in prevalence.

Table 3.

Giardia duodenalis infection rates and genotypes in cattle in China.

Animals Locations Specimens Positive (%) Assemblage (no.) Subassemblage (no.) References
Dairy cattle Guangdong 1a Case report E (1) Xiao et al., 2006
Dairy cattle Heilongjiang 26a Genotypes identified B (10) Liu A. et al., 2014
E (16)
Dairy cattle Jilin 249 19 (7.63%) E (19) Zhang J. et al., 2012
Dairy cattle Heilongjiang 52 4 (7.69%) A (1) AI (1) Zhang J. et al., 2012
E (3)
Dairy cattle Heilongjiang 814 42 (5.16%) B (18) BI (6); BII (1); BIII (2); BIV (2); BV (1); BVI (1); BVII (1); BVIII (3); BIX (1) Liu et al., 2012
E (24)
A/E (1)
Dairy cattle Heilongjiang 52 8 (15.38%) E (8) Liu G. et al., 2015
Dairy cattle Jilin 377 25 (6.63%) A (1) AI (1) Liu G. et al., 2015
E (24)
Dairy cattle Liaoning 226 19 (8.41%) E (18) Liu G. et al., 2015
A/E (1)
Dairy cattle Beijing 822 14 (1.70%) E (14) Li F. et al., 2016
Dairy cattle Henan 1,777 128 (7.20%) A (21) AI (4); AII (3); AIII (1) Wang et al., 2014b
E (58)
A/E (2)
Dairy cattle Henan 622 21 (3.38%) Wang et al., 2014a
Dairy cattle Henan 507 48 (9.47%) E (48) Wang C. et al., 2016
Dairy cattle Henan 622 21 (3.38%) E (21) Zhao et al., 2016
Dairy cattle Xinjiang 514 69 (13.42%) A (5) AI (3); AII (2) Qi et al., 2016b
E (64)
Dairy cattle Gansu 1,224 32 (2.61%) E (32) Zhang et al., 2016a
Dairy cattle Ningxia 1,366 29 (2.12%) B (4) BI (1); BII (3) Huang et al., 2014
E (25)
Dairy cattle Ningxia 1,614 74 (4.58%) A (1) Zhang et al., 2016a
E (73)
Cattle Qinghai 47 3 (6.38%) Ma et al., 2014
Beef/dairy cattle Shaanxi 371 70 (18.87%) A (8) AI (8) Wang X. T. et al., 2016
E (62)
Yak Qinghai 57 7 (12.28%) Ma et al., 2014
Yak Henan 34 2 (5.88%) E (2) Qi et al., 2015a
Yak Gansu 117 4 (3.42%) E (4) Qi et al., 2015a
Yak Sichuan 146 4 (2.74%) E (4) Qi et al., 2015a
Yak Tibet 96 1 (1.04%) E (1) Qi et al., 2015a
Yak Qinghai 152 5 (3.29%) E (5) Qi et al., 2015a
Yak Qinghai 93 8 (8.60%) E (9) Wang et al., 2016a
Yak Qinghai 297 22 (7.41%) E (22) Wang et al., 2016b
Yak Gansu 208 4 (1.92%) E (4) Song et al., 2016
Yak Qinghai 297 10 (3.37%) E (10) Wang G. et al., 2017
Total 12,753 693 (5.43%) E (571); A (37); B (32); A/E (4) AI (17); AII (5); AIII (1); BI (7); BII (4); BIII (2); BIV (2); BV (1); BVI (1); BVII (1); BVIII (3); BIX (1)
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a

Not included in the G. duodenalis infection rate calculation.

There is a significant association between G. duodenalis infection and age in cattle. Most studies have reported that G. duodenalis infection rates are inversely associated with animal age in China (Liu et al., 2012; Huang et al., 2014; Wang et al., 2014b; Liu G. et al., 2015; Qi et al., 2015a; Li F. et al., 2016; Zhang et al., 2016b; Wang G. et al., 2017), except for a recent study from Xinjiang, which identified a higher prevalence in post-weaned calves (16.6%) compared with pre-weaned calves (9.7%; Qi et al., 2016b).

Cattle are dominantly infected with livestock-specific G. duodenalis assemblage E strains (Liu G. et al., 2015; Qi et al., 2015a; Li F. et al., 2016; Wang G. et al., 2017), with only a few reports of infection caused by assemblage A and/or B strains (Liu et al., 2012; Huang et al., 2014; Wang et al., 2014b; Zhang et al., 2016a). Moreover, sub-assemblages AI, AII, and AIII were identified by most studies conducted in China, with sub-assemblage AI found to be dominant (Wang et al., 2014b; Qi et al., 2016b; Wang X. T. et al., 2016). Mixed infections also appear to be common in cattle, especially those involving isolates belonging to assemblages A and E (Wang et al., 2014b; Liu G. et al., 2015).

Several studies using MLG have suggested the possibility of geographical distribution differentiation among assemblage E isolates in cattle (Wang et al., 2014b; Qi et al., 2016b; Wang X. T. et al., 2016; Zhang et al., 2016a). A MLG subtype AII isolate identical to human-derived isolates from Italy, Sweden, and China was identified in dairy cattle from Henan Province, raising the possibility of it being an important zoonotic multilocus genotype (Wang et al., 2014b).

Limited information is available on the prevalence and assemblage distribution of G. duodenalis in yaks, despite confirmed cases of infection in Qinghai, Gansu, Sichuan, and Henan Provinces, as well as in Tibet (Ma et al., 2014; Qi et al., 2015a; Song et al., 2016; Wang et al., 2016a,b; Wang G. et al., 2017). Thus far, only assemblage E isolates have been identified in yaks in China.

G. duodenalis in sheep and goats

Reports of G. duodenalis infections in sheep and goats in recent years have presented variable results (Table 4). The average infection rate in sheep and goats is 6.07% (418/6,890), with the highest infection rate recorded in goats from Chongqing city (27.78%, 5/18). Except for one study that identified two assemblage B-type isolates in sheep in Heilongjiang (Zhang et al., 2012c), all reports of G. duodenalis infections in sheep and goats in China were caused by assemblage E and A strains, with assemblage E being significantly dominant (Gu et al., 2014; Peng et al., 2016; Wang H. et al., 2016). Mixed infections of assemblage A and E strains in sheep are commonly reported (Ye et al., 2015; Wang H. et al., 2016), while sub-assemblage AI was generally the dominant sub-genotype (Zhang et al., 2012c; Ma et al., 2014; Peng et al., 2016; Wang H. et al., 2016). A recent study from Henan Province using MLG yielded one new AI sub-assemblage with zoonotic potential, and six assemblage E MLGs (Wang H. et al., 2016).

Table 4.

Giardia duodenalis infection rates and genotypes in sheep and goats in China.

Animals Locations Specimens Positive (%) Assemblage (no.) Subassemblage (no.) References
Sheep Heilongjiang 21a Genotypes identified A (4) Liu A. et al., 2014
E (17)
Sheep/Goat Henan 880 16 (1.82%) Sui et al., 2015
Sheep Heilongjiang 539 25 (4.64%) A (4) AI(3), AIV(1) Zhang et al., 2012c
B (2)
E (19)
Sheep Henan 162 3 (1.85%) Zhu et al., 2012
Sheep Henan 1,028 58 (5.64%) Li M. et al., 2013
Sheep Henan 716 39 (5.45%) A (5) AI (9) Wang H. et al., 2016
E (31)
A/E (3)
Sheep Jilin 48 0 Li M. et al., 2013
Sheep Liaoning 16 0 Li M. et al., 2013
Sheep Shandong 17 0 Li M. et al., 2013
Sheep Inner Mongolia 375 16 (4.27%) A (13) AI (4); AII (1); AIV (8) Ye et al., 2015
A/E (3)
Sheep Qinghai 61 8 (13.11%) Ma et al., 2014
Goat Heilongjiang 139 4 (2.88%) E (4) Zhang et al., 2012c
Goat Henan 301 71 (23.59%) Chen et al., 2015
Goat Henan 63 1 (1.59%) Li M. et al., 2012
Goat Henan 844 48 (5.69%) Zhu et al., 2013
Goat Anhui 80 7 (8.75%) Zhu et al., 2013
Goat Chongqing 18 5 (27.78%) Zhu et al., 2013
Goat Qinghai 50 0 Zhu et al., 2013
Goat Inner Mongolia 51 0 Zhu et al., 2013
Goat Anhui 506 32 (6.32%) E (32) Gu et al., 2014
Goat Qinghai 51 2 (3.92%) Ma et al., 2014
Dairy goat Henan 316 3 (0.95%) Cao et al., 2015
Dairy goat Shaanxi 170 11 (6.47%) E (11) Peng et al., 2016
Meat goat Henan 144 35 (24.31%) E (35) Peng et al., 2016
Cashmere goat Shaanxi 315 34 (10.79%) A (4) AIV (4) Peng et al., 2016
E (30)
Total 6,890 418 (6.07%) E (179); A (30); B (2); A/E (6) AI (16); AIV (13); AII (1);
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a

Not included in the G. duodenalis infection rate calculation.

G. duodenalis in dogs and cats

In recent decades, a large number of cases of G. duodenalis infection in dogs, and some in cats, have been documented in different regions of China (Table 5). The first report of G. duodenalis infection in dogs occurred in 2000 in Jilin Province (He et al., 2000). The average infection rate in dogs is 13.64% (757/5,549), with the highest rate in Shanghai City (26.19%, 127/485) (Xu et al., 2016), whereas the average rate in cats is 10.19% (32/314), with the highest rate of infection also observed in Shanghai (13.13%, 21/160) (Xu et al., 2016).

Table 5.

Giardia duodenalis infection rates and genotypes in dogs and cats in China.

Animals Locations Specimens Positive (%) Assemblage (no.) Subassemblage (no.) References
Dog Jilin 1a Case report He et al., 2000
Dog Jilin 1a Case report He et al., 2002
Dog Beijing 2a Case reports Gao et al., 2009
Dog Guangdong 1a Case report A (1) Zhu et al., 2011
Dog Guangdong 2a Case reports A (1) AI (1) Zhang et al., 2011
D (1)
Dog Guangdong 1a Case report D (1) Li et al., 2011
Dog Guangdong 1a Case report D (1) Li et al., 2012a
Dog Shaanxi 56a Case statistics Quan et al., 2016
Dog Jinlin 242 61 (25.21%) He et al., 2001
Dog Henan 404 15 (3.71%) Qi et al., 2010a
Dog Henan 531 72 (13.56%) Qi et al., 2011
Dog Sichuan 146 46 (31.51%) Hu et al., 2011
Dog Beijing 910 109 (11.98%) Bi et al., 2011
Dog Shaanxi 120 11 (9.17%) Wang et al., 2015
Dog Henan 358 71 (19. 83%) Dong et al., 2015
Dog Guangdong 209 23 (11.00%) A (5) AI (5) Li et al., 2012b
D (23)
Dog Liaoning 205 27 (13.17%) A (25) AI (25) Li W. et al., 2013
C (2)
Dog Guangdong 216 21 (9.72%) A (7) AI (7) Zheng et al., 2014
C (2)
D (1)
A/C (2);
A/D (7);
C/D (2)
Dog Heilongjiang 267 12 (4.49%) C (7) Li W. et al., 2015
E (5)
Dog Henan 940 134 (14.26%) C (37) Qi et al., 2016a
D (44)
Dog Shanghai 485 127 (26.19%) A (23) AII (23) Xu et al., 2016
B (1)
C (26)
D (58)
A/C (2)
A/D (1)
C/D (10)
Dog Qinghai 31 2 (6.45%) Ma et al., 2014
Dog Qinghai 10 1 (10.00%) A (1) Wang G. et al., 2013
Dog Taiwan 42 4 (9.52%) Liang et al., 2012
Dog Taiwan 118 11 (9.32%) C (7) Tseng et al., 2014
D (4)
Dog Anhui 215 10 (4.65%) B (6) Gu et al., 2015
D (4)
Dog Zhejiang 100 0 Gu et al., 2015
Subtotal 5,549 757 (13.64%) D (137); C (81); A (63); B (7); E (5); C/D (12); A/D (8); A/C (4) AI (38); AII (23)
Cat Hebei 1a Case report Cui et al., 2010
Cat Guangdong 1a Case report F (1) Zheng et al., 2013
Cat Guangdong 102 10 (9.80%) A (8) AI (8) Zheng et al., 2015
F (1)
A/C (1)
Cat Shanghai 160 21 (13.13%) A (2) AI (1); AII (1) Xu et al., 2016
B (6);
C (2)
D (1)
F (7)
Cat Heilongjiang 52 1 (1.92%) F (1) Li W. et al., 2015
Subtotal 314 32 (10.19%) A (10); F (10); B (6); C (2); D (1); A/C (1) AI (9); AII (1)
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a

Not included in the G. duodenalis infection rate calculation.

Scant information on the epidemiology or molecular characteristics of G. duodenalis in dogs and cats in China is currently available. G. duodenalis assemblages A, C, and D have been identified as the most common genotypes in dogs, with A and F most prevalent in cats. Occasionally, assemblage B and E isolates have been reported (e.g., in two studies on dogs; Gu et al., 2015; Li W. et al., 2015), while assemblage B, C, and D isolates have been reported in cats (Zheng et al., 2015; Xu et al., 2016).

In general, sub-assemblage AI appears to be the dominant sub-genotype amongst isolates derived from dogs and cats in China (Li et al., 2012b; Li W. et al., 2013; Zheng et al., 2014, 2015), which agrees with findings from the limited number of reports from dogs and cats in Europe, USA, Brazil, Australia, and Japan (Vasilopulos et al., 2007; Volotão et al., 2007; Sprong et al., 2009; Feng and Xiao, 2011). However, one study from Shanghai showed that amongst 25 assemblage A sequences obtained from dog and cat specimens, 23 canine sequences and one feline sequence were identified as subtype AII (Xu et al., 2016).

G. duodenalis in pigs

G. duodenalis infections in pigs have been reported in Australia, Africa, Asia, Europe, and North America (Feng and Xiao, 2011). However, there are limited reports on the prevalence and genotypes of this organism in pigs in China, except in Sichuan Province, where the average infection rate was 3.51% (24/683, Table 6). Although assemblage E was the predominant genotype amongst these isolates from China, assemblage A is also frequently identified (Li W. et al., 2016; Li J. et al., 2017). In contrast, isolates belonging to assemblages A–F have been found in domestic pigs in other countries, with assemblage B and E isolates found in Canada (Budu-Amoako et al., 2012), assemblage C and F isolates in the UK (Minetti et al., 2014), assemblage A, D, and E isolates in Denmark (Petersen et al., 2015), and isolates belonging to assemblages A, E, and F identified in Australia (Armson et al., 2009). Thus far, the majority of the assemblage A strains from pigs in China belong to sub-assemblage AI (Li W. et al., 2016, 2017).

Table 6.

Giardia duodenalis infection rates and genotypes in pigs, rabbits, and rodents in China.

Animals Locations Specimens Positive (%) Assemblage (no.) Subassemblage (no.) References
Wild boars Sichuan 308 11 (3.57%) A (1) AI (1) Li W. et al., 2016
E (10)
Pig Sichuan 18 2 (11.11%) E (2) Li W. et al., 2016
Wild boars Sichuan 357 11 (3.08%) A (2) AI (2) Li J. et al., 2017
E (9)
Subtotal 683 24 (3.51%) E (21); A (3) AI (3)
Rabbits Heilongjiang 14a Genotypes identified B (14) Liu A. et al., 2014
Rabbits Henan 1,027 80 (7.79%) Xi et al., 2011b
Rabbits Henan 1,081 57 (5.27%) Shi et al., 2010
Rabbits Henan 305 12 (3.93%) Xi et al., 2011a
Rabbits Heilongjiang 378 28 (7.40%) B (28) BI (18);BII (4); BIII (3); BIV (1); BV (1); BVI (1) Zhang et al., 2012b
Rabbits Henan 955 80 (8.38%) B (26) BIV (26) Qi et al., 2015b
E (2)
B/E (4)
Subtotal 3,746 257 (6.86%) B (68); E (2); B/E (4) BI (18); BII (4); BIII (3); BIV (27); BV (1); BVI (1)
Rodent Henan 140 38 (27.14%) A (5) AI (5) Qi et al., 2015c
B (33) BIV (31)
Rodent Henan 232 14 (6.03%) G (14) Zhao Z. et al., 2015
Rodent Henan 96 36 (37.50%) Lv et al., 2009b
Rodent Henan 439 91 (20.72%) Qi et al., 2010b
Rodent Henan 153 34 (22.22%) Lv et al., 2009a
Subtotal 1,060 213 (20.09%) B (33); G (14); A (5) AI (5); BIV(31)
Open in a new tab
a

Not included in the G. duodenalis infection rate calculation.

G. duodenalis in rabbits

G. duodenalis infections occur in rabbits in China at an average rate of 6.86% (271/3,746), and have mainly been documented in Henan and Heilongjiang Provinces (Table 6). Although assemblage E isolates are occasionally found (Qi et al., 2015b), assemblage B strains appear dominant in rabbits in China (Zhang et al., 2012b; Liu A. et al., 2014; Qi et al., 2015b), which agrees with reports from Europe (Pantchev et al., 2014) and the USA (Sulaiman et al., 2003).

G. duodenalis in rodents

G. duodenalis infections have been reported in rodents in Norway (Robertson et al., 2007), Poland (Bajer, 2008), Latin America (Bueno et al., 2016), Europe (Pantchev et al., 2014), and Sweden (Lebbad et al., 2010). Currently, G. duodenalis infections in rodents in China have only been reported in Henan Province, where the average infection rate was 20.09% (213/1,060; Table 6). According to the limited number of genotyping studies on G. duodenalis in rodents in China, only assemblage A and B strains, which have zoonotic potential, and host-adapted assemblage G isolates have been identified (Qi et al., 2015c; Zhao Z. et al., 2015).

G. duodenalis in other mammals

G. duodenalis infections have also been reported in beavers, Chinese leopards, Siberian tigers, golden takins, raccoon dogs, horses, deer, and donkeys (Table 7). Some of these infections have high prevalence rates, such as in donkeys in Shandong Province (18.27%, 19/104) (Zhang et al., 2017), raccoon dogs in Liaoning Province (15.28%, 11/72) (Zhang et al., 2016b), golden takins in Shaanxi Province (8.90%, 17/191) (Zhao G. H. et al., 2015), and Pika (9.09%, 1/11) and donkeys (7.69%, 1/13) in Qinghai Province (Ma et al., 2014).

Table 7.

Giardia duodenalis infection rates and genotypes in other mammals in China.

Animals Locations Specimens Positive (%) Assemblage (no.) References
Pika Qinghai 11 1 (9.09%) Ma et al., 2014
Chinese leopard Henan 2 1 (50.00%) F (1) Li J. et al., 2015
Beaver Henan 1 1 (100.00%) B (1) Li J. et al., 2015
Siberian tiger Henan 6 2 (33.33%) F (2) Li J. et al., 2015
Golden takins Shaanxi 191 17 (8.90%) B (3) Zhao G. H. et al., 2015
E (14)
Grazing horses Xinjiang 262 4 (1.50%) A (2) Qi et al., 2015d
B (2)
Raccoon dog Jilin 110 7 (6.36%) C (6) Zhang et al., 2016b
C/D (1)
Raccoon dog Heilongjiang 40 3 (7.50%) C (3) Zhang et al., 2016b
Raccoon dog Shandong 29 0 Zhang et al., 2016b
Raccoon dog Hebei 54 1 (1.85%) C (1) Zhang et al., 2016b
Raccoon dog Liaoning 72 11 (15.28%) C (10) Zhang et al., 2016b
C/D (1)
Donkey Qinghai 13 1 (7.69%) Ma et al., 2014
Donkey Jilin 48 5 (10.42%) B (5) Zhang et al., 2017
Donkey Shandong 104 19 (18.27%) B (19) Zhang et al., 2017
Donkey Liaoningz 29 4 (13.79%) B (4) Zhang et al., 2017
Deer Henan 199 5 (2.51%) E (5) Unpublished
Total 1,171 82 (7.00%) A (2); B (34); C (20); E (19); F (3); C/D (2)
Open in a new tab

Certain G. duodenalis assemblages have been associated with host adaptation in specific animals, such as, assemblages C and D in raccoon dogs (Zhang et al., 2016b), assemblage E in golden takins (Zhao G. H. et al., 2015) and deer (unpublished data), and assemblage F in a Chinese leopard and Siberian tigers (Li J. et al., 2015). Zoonotic G. duodenalis isolates belonging to assemblages A and B were also identified in beavers (Li J. et al., 2015), golden takins (Zhao G. H. et al., 2015), and horses (Qi et al., 2015d). The number of zoonotic isolates found in wild animals is quite limited, an observation supported by a large survey of G. duodenalis in wild mammals from Croatia that revealed a low prevalence and limited zoonotic potential for the parasite (Beck et al., 2011). This suggests that wild animals are probably not a major reservoir for human infections.

G. duodenalis in wastewater

Cases of giardiasis associated with polluted recreational and potable waters have been documented for more than a century worldwide (Guy et al., 2003; Karanis et al., 2007; Moss, 2016). Although there have been no G. duodenalis outbreaks documented in China, a high prevalence of oocysts was identified amongst samples from numerous municipal and domestic raw water sources in Shanghai (Zhang et al., 2010; Li N. et al., 2012), Guangzhou (Zhong et al., 2010; Sun et al., 2014), Wuhan (Li N. et al., 2012; Sun et al., 2014), Jiangsu (Sun et al., 2014), Harbin (Liu et al., 2011; Zhang et al., 2012a), Guiyang (Chen et al., 2009), Nanjing (Li N. et al., 2012), Qingdao (Li N. et al., 2012), Taiwan (Liang et al., 2012), and Qinghai (Ma et al., 2014), among others.

Assemblage A and B isolates, which have zoonotic potential, were identified in urban waste in China (Liu et al., 2011; Liang et al., 2012; Li N. et al., 2012), suggesting that this pathogen could be maintained and transmitted by water sources, with the attendant risk of disease outbreaks occurring. Similarly, zoonotic isolates were also identified in Iran (Mahmoudi et al., 2015), Australia (Nolan et al., 2013; Koehler et al., 2016), Malaysia (Lim et al., 2009a,b, and Portugal (Lobo et al., 2009), among others. Isolates belonging to other assemblages, such as assemblage E, were also documented in wastewater in France (Bertrand and Schwartzbrod, 2007).

Conclusions and perspectives

In conclusion, G. duodenalis is widely distributed in humans and various other animals in China. Among the G. duodenalis assemblages, A and B are considered to have the broadest host specificities, and strains belonging to these assemblage types have zoonotic potential. Generally speaking, assemblage A isolates are more frequently found in humans, livestock, and companion animals, while assemblage B isolates are commonly isolated from humans, NHPs, and rabbits, with only a few reports of infections in sheep, goats, dogs, and cats in China. Cattle, sheep, goats, and pigs are predominantly infected with host-specific assemblage E isolates, while assemblage C and D isolates have been found in dogs, assemblage F is associated with cats, and rodents tend to be infected with assemblage G isolates. Within assemblage A, humans and NHPs are more commonly infected with subgroup AII isolates, while in other animals, sub-assemblage AI is predominant.

Most molecular investigations of G. duodenalis in China have only examined one or two loci, which cannot provide sufficient information on the transmission profile of this pathogen. However, the availability of the whole genome sequence of G. duodenalis has enhanced population genetics-based studies, and multi-locus sequence typing (MLST) tools are increasingly being used for characterizing G. duodenalis infections in humans and animals. Access to these methods is especially important for gaining a better understanding of some host-adapted assemblages (e.g., C, D, E, and F) that are pathogenic in humans, and for assessing the zoonotic assemblages (A and B) with infective potential. Therefore, a comprehensive and systematic study based on MLST analysis should be carried out to allow a full assessment of the burden of giardiasis of animal origin in humans.

Author contributions

LZ conceived the idea for the review and revised the manuscript. JL and HW wrote the manuscript, and JL, HW, and RW reviewed and abstracted the data from each selected article.

Conflict of interest statement

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Acknowledgments

We thank Tamsin Sheen, Ph. D, from Liwen Bianji, Edanz Editing China (www.liwenbianji.cn/ac), for editing the English text of a draft of this manuscript.

Footnotes

Funding. This study was supported in part by the Key Program of the National Natural Science Foundation of China (31330079), the Natural Science Foundation of Henan Province (162300410129), the Key National Science and Technology Specific Projects (2012ZX10004220-001), and the National Natural Science Foundation of China (U1404327).

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