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.     

Molecular characterisation of species and genotypes of Cryptosporidium and Giardia and assessment of zoonotic transmission

The molecular characterisation of species and genotypes of Cryptosporidium and Giardia is essential for accurately identifying organisms and assessing zoonotic transmission. Results of recent molecular epidemiological studies strongly suggest that zoonotic transmission plays an important role in cryptosporidiosis epidemiology. In such cases the most prevalent zoonotic species is Cryptosporidium parvum. Genotyping and subtyping data suggest that zoonotic transmission is not as prevalent in the epidemiology of giardiasis. Molecular characterisation of Cryptosporidium and Giardia is a relatively recent application that is evolving as new genes are found that increase the accuracy of identification while discovering a greater diversity of species and yet unnamed taxa within these two important genera. As molecular data accumulate, our understanding of the role of zoonotic transmission in epidemiology and clinical manifestations is becoming clearer.     

Unravelling Cryptosporidium and Giardia epidemiology

Molecular biology has provided insights into the taxonomy and epidemiology of Cryptosporidium and Giardia, which are major causes of protozoal diarrhoea in humans worldwide. For both genera, previously unrecognized differences in disease, symptomatology, zoonotic potential, risk factors and environmental contamination have been identified using molecular tools that are appropriate for species, genotype and subtype analysis. In this article, to improve understanding of the epidemiology of cryptosporidiosis and giardiasis, we consider specific requirements for the development of more-effective molecular identification and genotyping systems that should be applicable to both clinical and environmental samples.     

Human giardiasis in Serbia: asymptomatic vs symptomatic infection

Despite the public health importance of giardiasis in all of Europe, reliable data on the incidence and prevalence in Western Balkan Countries (Serbia, Bosnia and Herzegovina, Croatia, Montenegro and FYR Macedonia) are scarce, and the relative contribution of waterborne and food-borne, or person-to-person and/or animal-to-person, transmission of human giardiasis is not yet clear. To provide baseline data for the estimation of the public health risk caused by Giardia, we here review the information available on the epidemiological characteristics of asymptomatic and symptomatic human infection in Serbia. Although asymptomatic cases of Giardia represent a major proportion of the total cases of infection, high rates of Giardia infection were found in both asymptomatic and symptomatic populations. No waterborne outbreaks of giardiasis have been reported, and it thus seems that giardiasis mostly occurs sporadically in our milieu. Under such circumstances, control measures to reduce the high prevalence of giardiasis in Serbia have focused on person-to-person transmission, encouraging proper hygiene, but for more targeted intervention measures, studies to identify other risk factors for asymptomatic and symptomatic infections are needed.     

A natural zoonotic giardiasis: Infection of a child via Giardia cysts in pet chinchilla droppings

Here, we report a case of direct zoonotic transmission of giardiasis between a pet chinchilla and a human. Microscopic and molecular examinations of stool samples from a child and samples of chinchilla droppings revealed cysts/DNA of Giardia intestinalis. The transmission from the chinchilla to the child has been confirmed as coprophagous after the 1-year-old toddler ingested pet chinchilla droppings. Molecular analysis of the gdh gene from both hosts classified the G. intestinalis cysts into the assemblage B genetic group, which has been previously shown to be characteristic of both human and chinchilla giardiasis. Both Giardia sub-assemblages BIII and BIV were present in the chinchilla droppings, whereas only the sub-assemblage BIV was isolated from the child's stool sample. To the best of our knowledge, this is the first report of a true zoonotic transmission of giardiasis, supporting the zoonotic potential of assemblage B.     

Giardia infection in farm animals

Giardia infection is prevalent in farm animals from an early age. Despite the wide occurrence of the infection and recent understanding of its epidemiology, many aspects of giardiasis of farm animals remain unclear. In this article, Lihua Xiao discusses the prevalence, patterns, sources and clinical importance of Giardia infection in a variety of farm animals.     

Zoonotic genotype of Giardia intestinalis detected in a ferret

Giardia intestinalis has been found in a variety of mammals, including humans, and consists of host-specific and zoonotic genotypes. There has been only 1 study of G. intestinalis infection in weasels, but the genotype of its isolate remains unclear. In this study, we report the isolation of Giardia in a ferret exhibited at a pet shop. The isolate was analyzed genetically to validate the possibility of zoonotic transmission. Giardia diagnostic fragments of the small subunit ribosomal RNA, beta-giardin, and glutamate dehydrogenase genes were amplified from the ferret isolate and sequenced to reveal the phylogenetic relationships between it and other Giardia species or genotypes of G. intestinalis reported previously. The results showed that the ferret isolate represented the genetic group A-I in assemblage A, which could be a causative agent of human giardiasis.     

Circannual incidence of Giardia lamblia in Mexico

Giardia lamblia, once considered a harmless commensal organism, has become one of the most common pathogenic intestinal parasites. Evidence for various methods of transmission has accumulated and serious physiological and nutritional disturbances as a result of infestation with this parasite have been clinically documented. Giardia lamblia has now been identified as a causative agent of waterborne, foodborne and sexually transmitted infectious diarrhea. Preventive interventions by health education (especially in personal hygiene) are indicated to reduce its spread in the community. The timing of such educational endeavours may be adjusted to the changes in the incidence of giardiasis if such should be predictable insofar as they are rhythmic. Accordingly, monthly totals of positive detected cases of giardiasis reported in Mexico between 1977 and 1985 were first fitted by linear least-squares with a 1-yr cosine curve. Results indicate a predictable circannual variability of Giardia incidence (P less than 0.001), with a crest time situated on the third week of July and monthly means of detected cases above the yearly average incidence between May and September. The validity of this circannual rhythm was further checked by nonlinear least-squares. Results show a presumably 1-yr synchronized estimated period of 8715.1 hr, with a total predictable change (double amplitude of 1788 cases per month) of 43% the average monthly incidence. Moreover, circannual rhythm parameters computed separately for each consecutive year are similar in terms of acrophase (P = 0.771). Awareness of the thus detected circannual predictable variability in the incidence of giardiasis may be important in the prevention, diagnosis and treatment of this infectious disorder. According to the results here found, the timing of prevention interventions by health education should be a readily exploitable factor.     

Split introns in the genome of Giardia intestinalis are excised by spliceosome-mediated trans-splicing

Spliceosomal introns are hallmarks of most eukaryotic genomes and are excised from premature mRNAs by a spliceosome that is among the largest, and most complex, molecular machine in cells. The divergent unicellular eukaryote Giardia intestinalis, the causative agent of giardiasis, also possesses spliceosomes, but only four canonical (cis-spliced) introns have been identified in its genome to date. We demonstrate that this organism has a novel form of spliceosome-mediated trans-splicing of split introns that is essential for generating mature mRNAs for at least two important genes: one encoding a heat shock protein 90 (HSP90), which controls the conformation of a suite of cellular proteins, and the other encoding a dynein molecular motor protein, involved in the motility of eukaryotic flagella. These split introns have properties that distinguish them from other trans-splicing systems known within eukaryotes, suggesting that Giardia independently evolved a unique system to splice split introns.     

Evaluation of ELISA for detection of Giardia lamblia-specific copro-antigen employing monospecific antibodies

An enzyme linked immunosorbent assay (ELISA) system, using monospecific antibodies for the detection of Giardia lamblia specific 66 kDa copro-antigen has been developed and evaluated. The assay detected the antigen in stool eluates of all the 24 microscopically confirmed cases of giardiasis and in 17 (68%) of the 25 microscopy-negative clinically suspected cases of giardiasis. None of stool eluates from 20 subjects infected with other protozoal/helminthic intestinal parasites or from 20 apparently healthy subjects had G. lamblia-specific copro-antigen. The ELISA employing monospecific antibodies is a sensitive and specific tool for the diagnosis of giardiasis and is especially useful for confirming microscopy-negative suspected cases of giardiasis.     

Circannual Incidence of Giardia Lamblia in Mexico

Giardia lamblia, once considered a harmless commensal organism, has become one of the most common pathogenic intestinal parasites. Evidence for various methods of transmission has accumulated and serious physiological and nutritional disturbances as a result of infestation with this parasite have been clinically documented. Giardia lamblia has now been identified as a causative agent of waterborne, foodborne and sexually transmitted infectious diarrhea. Preventive interventions by health education (especially in personal hygiene) are indicated to reduce its spread in the community. The timing of such educational endeavours may be adjusted to the changes in the incidence of giardiasis if such should be predictable insofar as they are rhythmic. Accordingly, monthly totals of positive detected cases of giardiasis reported in Mexico between1977 and1985 were first fitted by linear least-squares with a 1-yr cosine curve. Results indicate a predictable circannual variability of Giardia incidence (P < 0.001), with a crest time situated on the third week of July and monthly means of detected cases above the yearly average incidence between May and September. The validity of this circannual rhythm was further checked by nonlinear least-squares. Results show a presumably 1-yr synchronized estimated period of 871S.1 hr, with a total predictable change (double amplitude of 1788 cases per month) of 43% the average monthly incidence. Moreover, circannual rhythm parameters computed separately for each consecutive year are similar in terms of acrophase (P = 0.771). Awareness of the thus detected circannual predictable variability in the incidence of giardiasis may be important in the prevention, diagnosis and treatment of this infectious disorder. According to the results here found, the timing of prevention interventions by health education should be a readily exploitable factor.     

Recent insights into the mucosal reactions associated with Giardia lamblia infections

Giardia lamblia is an intestinal protozoan parasite infecting humans and various other mammalian hosts. The most important clinical signs of giardiasis are diarrhoea and malabsorption. Giardia lamblia is able to undergo continuous antigenic variation of its major surface antigen, named VSP (variant surface protein). While intestinal antibodies, and more specifically anti-VSP IgA antibodies, were proven to be involved in modulating antigenic variation of the parasite the participation of the local antibody response in control of the parasite infection is still controversial. Conversely, previous studies based on experimental infections in mice showed that cellular immune mechanisms are essential for elimination of the parasite from its intestinal habitat. Furthermore, recent data indicated that inflammatory mast cells have a potential to directly, or indirectly, interfere in duodenal growth of G. lamblia trophozoites. However, this finding was challenged by other reports, which did not find a correlation between intestinal inflammation and resistance to infection. Since intestinal infiltration of inflammatory cells and/or CD8+T-cells were demonstrated to coincide with villus-shortening and crypt hyperplasia immunological reactions were considered to be a potential factor of pathogenesis in giardiasis. The contribution of physiological factors to pathogenesis was essentially assessed in vitro by co-cultivation of G. lamblia trophozoites with epithelial cell lines. By using this in vitro model, molecular (through surface lectins) and mechanical (through ventral disk) adhesion of trophozoites to the epithelium was shown to be crucial for increased epithelial permeability. This phenomenon as well as other Giardia-induced intestinal abnormalities such as loss of intestinal brush border surface area, villus flattening, inhibition of disaccharidase activities, and eventually also overgrowth of the enteric bacterial flora seem to be involved in the pathophysiology of giardiasis. However, it remains to be elucidated whether at least part of these pathological effects are causatively linked to the clinical manifestation of the disease.     

Giardia intestinalis: electrophoretic evidence for a species complex

The technique of allozyme electrophoresis was applied to 29 Australasian stocks and 48 clones of Giardia intestinalis from humans as a means of increasing the number of genetic markers currently available for identification and classification. Fifty different enzymes were examined and of these 26 loci were found to be suitable for use as genetic markers. The data indicate the presence of four discrete genetic groups within the sample of G. intestinalis examined. The groups had fixed genetic differences at 23-69% of loci established. The evidence suggests that G. intestinalis is a species complex. The results have important implications for the systematics of human isolates of Giardia, as well as for studies on the epidemiology and demography of giardiasis in Australia and elsewhere.     

Is Giardia a significant pathogen in production animals?

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

Waterborne Giardia cysts and Cryptosporidium oocysts in the Yukon, Canada.

Several outbreaks of waterborne giardiasis have occurred in southern Canada, but nothing has been reported from the Canadian North. The objective of this study was to collect information relevant to waterborne giardiasis and cryptosporidiosis in the Yukon including epidemiological data and analyses of water, sewage, and animal fecal samples. Remote, pristine water samples were found to be contaminated with Giardia cysts (7 of 22 or 32%) but not with Cryptosporidium oocysts. Giardia cysts were found in 21% (13 of 61) of animal scats, but no Cryptosporidium oocysts were observed (small sample size). Whitehorse's drinking water was episodically contaminated with Giardia cysts (7 of 42 or 17%) and Cryptosporidium oocysts (2 of 42 or 5%). Neither were found in Dawson City's water supply. The only water treatment in the Yukon is chlorination, but contact times and free chlorine residuals are often too low to provide adequate protection by disinfection. Raw sewage samples from the five largest population centers in the Yukon contained 26 to 3,022 Giardia cysts and 0 to 74 Cryptosporidium oocysts per liter. Treated sewage from Whitehorse contained fewer Giardia cysts but more Cryptosporidium oocysts on average. Both were detected in Lake Laberge, downstream of Whitehorse, which has a history of fecal coliform contamination. Daily monitoring of raw sewage from the suburbs of Whitehorse showed a summertime peak of Giardia cysts and occasional Cryptosporidium oocysts after springtime contamination of drinking water. Despite this evidence, epidemiological data for the Yukon showed an endemic infection rate of only 0.1% for giardiasis (cryptosporidiosis is not notifiable).(ABSTRACT TRUNCATED AT 250 WORDS)     

Giardia lamblia: a new target for miltefosine

Giardia lamblia, the causative agent of giardiasis, is an intestinal infection with worldwide distribution and high rates of prevalence. Increased resistance of the parasite and the side effects of the reference drugs employed in the treatment of giardiasis make it necessary to seek new therapeutic agents. Therefore,the aim of this study was to examine the activity of hexadecylphosphocholine (miltefosine), a membrane active alkylphospholipid, that is licensed as an antileishmanial agent against giardiasis. The efficacy of miltefosine was evaluated both in vitro and in vivo in Swiss albino mice. Results of the in vitro testing revealed susceptibility of G. lamblia trophozoites to miltefosine with the following effective concentrations:EC50s of between 20 and 40 lM, and EC90s of between 20 and 80 lM. Immediate total lysis of the organisms was achieved by 100 lM. In vivo testing showed that oral administration of miltefosine,in a daily dose regimen course of 20 mg/kg for three successive days, to infected mice resulted in total elimination of the parasite from the intestine and amelioration of intestinal pathology. Scanning and transmission electron microscopy studies revealed that miltefosine induced severe morphological alterations to G. lamblia trophozoites, mainly at the level of cell membrane and adhesive disc. In conclusion,we believe that this is the first study highlighting G. lamblia as a possible new target for miltefosine.     

Tools for investigating the environmental transmission of Cryptosporidium and Giardia infections in humans

Cryptosporidiosis and giardiasis are major public health concerns. The role of water and food in the epidemiology of these diseases is now well recognized. Molecular techniques are available to determine the species and genotypes of Cryptosporidium and Giardia and to distinguish human from non-human pathogens. Validated methods to determine the species, genotype and subgenotype that are present in heterologous mixtures should be applied to environmental samples to enable the monitoring and characterization of infection sources, disease tracking and the establishment of causative links to both waterborne and foodborne outbreaks. Meaningful interpretation of population structures and occurrence-prevalence baselines can be performed only by analysing a well-planned set of samples from all possible sources taken regularly over time, rather than focusing on outbreak investigations. For food, this includes such analyses in the country of origin.     

Human giardiasis: genotype linked differences in clinical symptomatology

Giardia duodenalis infection in humans can cause a variety of clinical symptoms. The relation between clinical symptomatology and the Giardia isolate genotype was studied in 18 Dutch patients infected with G. duodenalis who visited their general practitioner. Contrary to earlier studies, a 100% correlation between severity of diarrhoeal complaints and genotype was found: assemblage A isolates were solely detected in patients with intermittent diarrhoeal complaints, while assemblage B isolates were present in patients with persistent diarrhoeal complaints. These results are significant because they show for the first time that genetically linked features of G. duodenalis are major determinants in the severity of infection in human giardiasis.     

Cryptosporidium and Giardia: Treatment options and prospects for new drugs

Cryptosporidium species and Giardia intestinalis are the most common enteric protozoan pathogens affecting humans worldwide. In recent years, nitazoxanide has been licensed in the United States for the treatment of cryptosporidiosis in non-immunodeficient children and adults, becoming the first drug approved for treating this disease. There is a need for a highly effective treatment for cryptosporidiosis in immunodeficient patients, but the quest for such a drug has proven to be elusive. While not effective against Cryptosporidium, nitroimidazoles such as metronidazole or tinidazole are effective treatments for giardiasis and can be administered as a single dose. Albendazole and nitazoxanide are effective against giardiasis but require multiple doses. Nitazoxanide is the first new drug developed for treating giardiasis in more than 20 years. New potentially promising drug targets in Cryptosporidium and Giardia have been identified, but there appears to be little activity toward clinical development of new drugs.     

The zoonotic transmission of Giardia and Cryptosporidium

The molecular characterisation of Giardia and Cryptosporidium has given rise to a more epidemiological meaningful and robust taxonomy. Importantly, molecular tools are now available for 'typing' isolates of the parasites directly from clinical and environmental samples. As a consequence, information on zoonotic potential has been obtained although the frequency of zoonotic transmission is still poorly understood. Analysis of outbreaks and case-control studies, especially when coupled with genotyping data, is slowly providing information on the public health significance of zoonotic transmission. Such studies support the hypothesis that Cryptosporidium hominis is spread only between humans but that the major reservoir for Cryptosporidium parvum is domestic livestock, predominantly cattle, and that direct contact with infected cattle is a major transmission pathway along with indirect transmission through drinking water. The situation is less clearcut for Giardia duodenalis but the evidence does not, in general, support zoonotic transmission as a major risk for human infections. However, for both parasites there is a need for molecular epidemiological studies to be undertaken in well-defined foci of transmission in order to fully determine the frequency and importance of zoonotic transmission.