The immune response to Giardia

First report of Giardia duodenalis infection in bamboo rats

Background

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

Results

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

Conclusions

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

Electronic supplementary material

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

Barcoding of Giardia duodenalis isolates and derived lines from an established cryobank by a mutation scanning-based approach

We barcoded 25 in vitro isolates (representing 92 samples) of Giardia duodenalis from humans and other animals, which have been assembled by the Upcroft team at the Queensland Institute of Medical Research over a period of almost three decades. We used mutation scanning-coupled sequencing of loci in the triosephosphate isomerase, glutamate dehydrogenase and β-giardin genes, combined with phylogenetic analysis, to genetically characterise them. Specifically, the isolates (n514) of G. duodenalis from humans from Australia (AD113; BRIS/83/HEPU/106; BRIS/87/HEPU/713; BRIS/89/HEPU/1003; BRIS/92/HEPU/1541; BRIS/92/HEPU/1590; BRIS/92/HEPU/2443; BRIS/93/HEPU/1706), Malaysia (KL/92/IMR/1106) and Afghanistan (WB), a cat from Australia (BAC2), a sheep from Canada (OAS1) and a sulphur-crested cockatoo from Australia (BRIS/95/HEPU/2041) represented assemblage A (sub-assemblage AI-1, AI-2 or AII-2); isolates (n510) from humans from Australia (BRIS/91/HEPU/1279; BRIS/92/HEPU/2342; BRIS/92/HEPU/2348; BRIS/93/HEPU/1638; BRIS/93/HEPU/1653; BRIS/93/HEPU/1705; BRIS/93/HEPU/1718; BRIS/93/HEPU/1727), Papua New Guinea (BRIS/92/HEPU/1487) and Canada (H7) represented assemblage B (sub-assemblage BIV) and an isolate from cattle from Australia (BRIS/92/HEPU/1709) had a match to assemblage E. Isolate BRIS/90/HEPU/1229 from a human from Australia was shown to represent a mixed population of assemblages A and B. These barcoded isolates (including stocks and derived lines) now allow direct comparisons of experimental data among laboratories and represent a massive resource for transcriptomic, proteomic, metabolic and functional genomic studies using advanced molecular technologies.

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

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

Giardiasis--why do the symptoms sometimes never stop?

Although giardiasis is considered by most medical practitioners to be an easily treated infection, prolonged symptoms due to, or following, Giardia duodenalis infection can have a significant impact on quality of life. Symptom recurrence, including abdominal symptoms and fatigue, can result from re-infection, treatment failure, disturbances in the gut mucosa or post-infection syndromes. In developed countries, these sequelae can have an enormous impact on quality of life; in developing countries, particularly in children, they add yet another burden to populations that are already disadvantaged. Here, we outline current knowledge, based on individual case sequelae from sporadic infections, observations of population effects following outbreaks and studies of phenotypic and genotypic diversity between morphologically identical isolates of parasites. We also raise further questions, looking for clues as to why giardiasis sometimes becomes an intrusive, long-term problem.

Changes in beta-giardin sequence of Giardia intestinalis sensitive and resistant to albendazole strains

Giardia intestinalis can develop resistance to albendazole, although the molecular mechanism is not understood. The aim of this study was to investigate the differences and permanent mutation in the beta-giardin gene of G. intestinalis strains: sensitive, resistant, or recovered-resistance to albendazole. The beta-giardin gene was amplified by nested polymerase chain reaction. The IC(50) values varied from 0.29 to 0.38 microg/mL for strains sensitive to albendazole. For resistant strains, the IC(50) range was 1.31-2.12 microg/mL. Recovered-sensitivity albendazole strains' IC(50) values were 0.33-0.49 microg/mL, and for strains with recovered-resistance, the IC(50) was 1.42-2.74 microg/mL. beta-giardin amplicon (720 bp) was sequenced and analysis sequence revealed several amino acid mutations from resistant and recovered-sensitive strains of G. intestinalis. Most of the mutations were located in the ROD domain of beta-giardin with a change from the sequence "TIARERA" in sensitive strains instead "IDRPRE" in resistant strains. A comparative sequence analysis in resistant, recovered-sensitive, and resistant-recovered strains revealed permanent mutation. This is the first report of combinatorial serine-proline-arginine repeats in the ROD domain of beta-giardin, whereas such repeats have been reported previously in the HEAD domain of SF-assemblin proteins. This is the first time that the resistance to albendazole correlates with genetics but it is not necessarily caused by mutations in the beta-giardin gene of G. intestinalis.

Passive immunity and serological immune response in dairy calves associated with natural Giardia duodenalis infections

In a previous study, Giardia infection patterns were studied in newborn dairy calves over a 4-month period. Chronic Giardia infections were observed in all calves with initial cyst excretion occurring at approximately 1 month of age. In the work presented here, the passive immunity and serological immune response associated with these Giardia infections were examined. Colostrum and milk samples were collected from the dams of these calves, and monthly serum samples were collected from each calf. The colostrum, milk and sera samples were analyzed by ELISA and Western blot for the presence of anti-Giardia IgG antibodies. In addition, the in vitro anti-Giardia activity of milk and colostrum was examined using a miniculture adherence assay. When examined by ELISA, mean anti-Giardia antibody titres were found to be significantly higher in colostrum compared to milk. The monthly mean serum antibody titres in the calves were not found to differ significantly at any time point during the study. Western blot analysis revealed that colostrum from the dams reacted strongly with many different Giardia antigens between 205 and 7.5kDa, while milk reacted with few antigens in the same size range. Sera collected from the calves when 30 and 60 days of age reacted with few Giardia antigens, but as the calves aged, IgG antibodies in their sera began to react with antigens of 21, 50, 65, 73 and 79kDa. The miniculture adherence assay demonstrated that colostrum had significantly more anti-Giardia activity in vitro compared to milk. These results suggest that the calves in this dairy did not mount a significant humoral immune response against Giardia following infection. However, colostrum contained a high level of anti-Giardia antibodies and exhibited anti-Giardia activity in vitro. Therefore, colostrum may have the potential to provide initial protection against Giardia infections in calves, but the lack of a strong, specific humoral immune response by these calves could account for the high prevalence and chronic duration of the infections.

Human secretory immune response to fatty acid-binding protein fraction from Giardia lamblia

The secretory immune response in humans infected with Giardia lamblia was studied by using saliva samples and an 8-kDa antigen capable of binding fatty acids. This antigen was not recognized by saliva samples from healthy individuals. The antigen may be useful in diagnostic studies of G. lamblia infection.

Advances and prospects for subunit vaccines against protozoa of veterinary importance

Protozoa are responsible for considerable morbidity and mortality in domestic and companion animals. Preventing infection may involve deliberate exposure to virulent or attenuated parasites so that immunity to natural infection is established early in life. This is the basis for vaccines against theilerosis and avian coccidiosis. Vaccination may not be effective or practical with diseases, such as cryptosporidiosis, that primarily afflict the immune-compromised or individuals with an incompletely developed immune system. Strategies for combating these diseases often rely on passive immunotherapy using serum or colostrums containing antibodies to parasite surface proteins. Subunit vaccines offer an attractive alternative to virulent or attenuated parasites for several reasons. These include the use of bacteria or lower eukaryotes to produce recombinant proteins in batch culture, the relative stability of recombinant proteins compared to live parasites, and the flexibility to incorporate only those antigens that elicit "protective" immune responses. Although subunit vaccines offer many theoretical advantages, our lack of understanding of immune mechanisms to primary and secondary infection and the capacity of many protozoa to evade host immunity remain obstacles to developing effective vaccines. This review examines the progress made on developing recombinant proteins of Eimeria, Giardia, Cryptosporidium, Toxoplasma, Neospora, Trypanosoma, Babesia, and Theileria and attempts to use these antigens for vaccinating animals against the associated diseases.

Giardiasis as a re-emerging infectious disease and its zoonotic potential

The reasons for considering giardiasis as a re-emerging infectious disease are presented, with emphasis on Giardia infections in child care centres, livestock and pets, and the role of zoonotic transmission. However, the aetiology and control of giardiasis is complicated by the genetic and phenotypic variability of Giardia species infective to mammals. Of particular significance has been the uncertainty about host specificity and the question of zoonotic transmission. The recent application of molecular characterisation procedures based on PCR has made an enormous contribution to an understanding of the genetic structure of Giardia populations, and this is reviewed in the context of the zoonotic transmission and molecular epidemiology of Giardia infections.

Giardia vaccination

Recently, a Giardia vaccine has become commercially available in the USA for prevention of clinical signs of giardiasis and reduction of cyst shedding in dogs and cats. The vaccine is based upon the current state of knowledge of Giardia antigenicity and immunology. Here, Merle Olson, Howard Ceri and Douglas Morck describe studies that led to the development of this vaccine and subsequent efficacy studies. Immunoprophylaxis and immunotherapeutic application of the vaccine are discussed.

Immune response to Giardia duodenalis

The intestinal protozoan Giardia duodenalis is a widespread opportunistic parasite of humans and animals. This parasite inhabits the upper part of the small intestine and has a direct life cycle. After ingestion of cysts, which are the infective stage, the trophozoites emerge from the cysts in the duodenum and attach to the small intestinal mucosa of the host. Since the migration of trophozoites from the lumen of the intestine into surrounding tissues is an unusual occurrence, the immune response to Giardia remains localized. The identification of antigens that play a role in acquired immunity has been difficult because of the occurrence of antigenic variation and because, Giardia being an ubiquitous organism, it is possible that the antigenic profiles of isolates from different geographic areas will vary. Innate-immunity mechanisms play a role in the control and/or severity of the infection. Both humoral and cell-mediated immune responses play a role in acquired immunity, but the mechanisms involved are unknown. A variety of serological assays have been used to detect circulating antibodies in serum. Because of the biological characteristics of the parasite and the lack of suitable antigens, the sensitivity of serological assays remains poor. On the other hand, detection of antigens in feces of infected patients has met with success. Commercial kits are available, and they are reported to be more sensitive than microscopic examination for the detection of giardiasis on a single specimen.

Immune response to Giardia duodenalis

The intestinal protozoan Giardia duodenalis is a widespread opportunistic parasite of humans and animals. This parasite inhabits the upper part of the small intestine and has a direct life cycle. After ingestion of cysts, which are the infective stage, the trophozoites emerge from the cysts in the duodenum and attach to the small intestinal mucosa of the host. Since the migration of trophozoites from the lumen of the intestine into surrounding tissues is an unusual occurrence, the immune response to Giardia remains localized. The identification of antigens that play a role in acquired immunity has been difficult because of the occurrence of antigenic variation and because, Giardia being an ubiquitous organism, it is possible that the antigenic profiles of isolates from different geographic areas will vary. Innate-immunity mechanisms play a role in the control and/or severity of the infection. Both humoral and cell-mediated immune responses play a role in acquired immunity, but the mechanisms involved are unknown. A variety of serological assays have been used to detect circulating antibodies in serum. Because of the biological characteristics of the parasite and the lack of suitable antigens, the sensitivity of serological assays remains poor. On the other hand, detection of antigens in feces of infected patients has met with success. Commercial kits are available, and they are reported to be more sensitive than microscopic examination for the detection of giardiasis on a single specimen.

Antigenic variation and the murine immune response to Giardia lamblia

The protozoan parasite Giardia lamblia is an important causative agent of acute or chronic diarrhoea in humans and various animals. During infection, the parasite survives the host's reactions by undergoing continuous antigenic variation of its major surface antigen, named VSP (variant surface protein). The VSPs form a unique family of cysteine-rich proteins that are extremely heterogeneous in size. The relevance of antigenic variation for the survival in the host has been most successfully studied by performing experimental infections in a combined mother/offspring mouse system and by using the G. lamblia clone GS/M-83-H7 (human isolate) as model parasite. In-vivo antigenic variation of G. lamblia clone GS/M-83-H7 is characterised by a diversification of the intestinal parasite population into a complex mixture of different variant antigen types. It could be shown that maternally transferred lactogenic anti-VSP IgA antibodies exhibit cytotoxic activity on the Giardia variant-specific trophozoites in suckling mice, and thus express a modulatory function on the proliferative parasite population characteristics. Complementarily, in-vitro as well as in-vivo experiments in adult animals indicated that non-immunological factors such as intestinal proteases may interfere into the process of antigen variation in that they favour proliferation of those variant antigen-type populations which resist the hostile physiological conditions within the intestine. These observations suggest that an interplay between immunological and physiological factors, rather than one of these two factor alone, modulates antigenic diversification of a G. lamblia population within an experimental murine host and thus influences the survival rate and strategy of the parasite.

Influence of antibodies in mother's milk on antigenic variation of Giardia lamblia in the murine mother-offspring model of infection

In the present study, neonatal ZU.ICR mice and their mothers were infected with trophozoites of Giardia lamblia clone GS/M-83-H7 expressing the variant surface protein (VSP) H7. The infection experiments included a detailed analysis of the specificities of anti-Giardia immunoglobulin A (IgA) antibodies in mother's milk and a determination of the effects of the milk antibodies on both the growth of the parasite during in vitro cultivation and colonization of the parasite within the intestine of suckling offspring. These investigations revealed that transiently emerging milk IgA antibodies against a variant-specific 314-amino-acid N-terminal region of VSP H7 exhibit a strong parasiticidal effect on VSP H7-type trophozoites both in vitro and in vivo. These findings indicated that parasiticidal effects of local IgA antibodies against the N-terminal part of VSP H7 select for new variant types within the intestinal parasite population of suckling mice. The selective influence of such antibodies promotes in vivo antigenic variation of G. lamblia clone GS/M-83-H7 and modulates the early course of parasite infection in these animals.

Serum immune response to Giardia duodenalis in experimentally infected lambs

Twenty-three protozoan-free lambs were experimentally infected with Giardia duodenalis trophozoites at 6 weeks of age, while 24 controls lambs were not challenged. Weekly blood samples were taken and faecal cyst counts monitored for 11 weeks following infection. All experimentally infected lambs remained infected throughout the 11 week study period and control animals remained free of the parasite. Giardia-specific serum IgM, IgG and IgA antibody titers were determined weekly in 10 infected and 10 control lambs by enzyme-linked-immunosorbent assay (ELISA). Western blot analysis of serum immunoglobulins to proteins derived from four different Giardia isolates (S2, WB, D3 and NF) was performed. Weekly mean control IgM, IgG and IgA titers did not change throughout the study. Infected lambs showed no difference in IgM titers between weeks 0 and 11, but IgG and IgA titers of infected lambs differed from the preimmune (week 0) serum titer at weeks 5, 7, 9, 11 and weeks 5, 9 and 11 respectively. SDS polyacrylamide gel electrophoresis analysis showed homogeneity in the proteins of the four Giardia isolates. Antigenic proteins were also similar for all four isolates; however, the proteins recognized by IgM, IgG and IgA antibodies differed. The weak immune response of lambs to Giardia may account for the chronic nature of this disease in sheep.

Secretory immune response to membrane antigens during Giardia lamblia infection in humans

The secretory immune response in humans infected with Giardia lamblia was studied by using saliva samples and a membrane-rich protein fraction. The membrane fraction, studied by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, showed 24 antigen bands, ranging from 170 to 14 kDa. Saliva samples from giardiasis patients showed a heterogeneous response against the membrane fraction when they were assayed by immunoblotting. Among the antigens recognized by patient saliva samples, those of 170, 105, 92, 66, 32, 29, and 14 kDa stood out. These antigens were not recognized by saliva samples from healthy individuals. They may be of importance in future studies of protection from or diagnosis of G. lamblia infections.

Exogenous cytokines released by spleen and Peyer's patch cells removed from mice infected with Giardia muris

The role that T and B lymphocytes play in the clearance of Giardia muris in the mouse model is well known, but the cytokines produced by CD4+ T cells in response to Giardia antigenic stimulation are unknown. In this study, we have determined how Giardia trophozoite antigenic crude extract and T cell mitogens can trigger the production of cytokines by Peyer's patch and spleen cells removed from infected animals. When Giardia trophozoite proteins were used to challenge the cells in vitro, IL-4, IL-5 and IFN-gamma were not detected in the culture supernatant. When the cells were challenged with Con-A, all three cytokines were released in vitro. However, the level of each cytokine released by the spleen or Peyer's patch cells varied with the latent, acute and elimination phases of the infection. The high levels of IL-4 and IL-5 released by Peyer's patch cells confirm the importance of IgA in the control of the infection. However, we propose that the relative success of G. muris in completing its life cycle in a primary infection might be due, in part, to the stimulation of a Th2-type response (IL-4, IL-5). A stronger Th1 response (IFN-gamma) may lead to a better control of the primary infection.

Giardia lamblia infections in B-cell-deficient transgenic mice

In the present study, we infected B-cell (and antibody-)-deficient transgenic mice with the Giardia lamblia clone GS/M-83-H7. These animals were inhibited in intestinal anti-Giardia immunoglobulin A (IgA) production and could not resolve the parasite infection, and antigenic diversification within the respective parasite populations occurred in an unusually slow manner. These findings indicate an important immunological function of local IgA antibodies which promotes antigenic variation of the parasite and is involved in control of the parasite infection.

Systemic and local antibody response in mice induced by a recombinant peptide fragment from Giardia lamblia variant surface protein (VSP) H7 produced by a Salmonella typhimurium vaccine strain

Previous experimental infections of mice with the intestinal protozoan Giardia lamblia had revealed that antigenic variation of the parasite was associated with the major surface antigen, named variant surface protein (VSP). In the present study, a gene segment of the VSP (VSPH7) from the well-characterized G. lamblia clone GS/M-83-H7 was expressed in the live-attenuated Salmonella typhimurium vaccine strain LT2M1C. The recombinant vaccine was assessed for its potential to induce both a systemic and a local antibody response in mice. Peroral administration of the vaccine stimulated synthesis of serum IgG and intestinal IgA antibodies directed against Salmonella antigens as well as against VSPH7. With respect to the anti-VSPH7 antibody concentrations, vaccination of animals resulted in systemic and local antibody responses similar to those induced by experimental or natural infections of mice with G. lamblia clone GS/M-83-H7. Subclass specification of serum anti-VSPH7 IgG demonstrated THelper 2-cell dependent IgG1- and/or IgG2b-type antibody production. No significant THelper 1-cell dependent IgG2a-type anti-VSPH7 antibody production was detected in infected or in vaccinated animals. Taken together, these data indicate a strong intrinsic antigenicity of VSPH7, which stimulates a THelper 2-cell pathway of the murine immune system, independent of the route of antigen administration. Furthermore, the high immunostimulatory potential of the recombinant Salmonella/VSPH7 model vaccine suggests application of LT2M1C as an enteric biocarrier for the identification of putative new target vaccines in giardiasis.