Under-reporting giardiasis: time to consider the public health implications

Microbial Matryoshka: Addressing the Relationship between Pathogenic Flagellated Protozoans and Their RNA Viral Endosymbionts (Family Totiviridae)

Three genera of viruses of the family Totiviridae establish endosymbiotic associations with flagellated protozoa responsible for parasitic diseases of great impact in the context of One Health. Giardiavirus, Trichomonasvirus, and Leishmaniavirus infect the protozoa Giardia sp., Trichomonas vaginalis, and Leishmania sp., respectively. In the present work, we review the characteristics of the endosymbiotic relationships established, the advantages, and the consequences caused in mammalian hosts. Among the common characteristics of these double-stranded RNA viruses are that they do not integrate into the host genome, do not follow a lytic cycle, and do not cause cytopathic effects. However, in cases of endosymbiosis between Leishmaniavirus and Leishmania species from the Americas, and between Trichomonasvirus and Trichomonas vaginalis, it seems that it can alter their virulence (degree of pathogenicity). In a mammalian host, due to TLR3 activation of immune cells upon the recognition of viral RNA, uncontrolled inflammatory signaling responses are triggered, increasing pathological damage and the risk of failure of conventional standard treatment. Endosymbiosis with Giardiavirus can cause the loss of intestinal adherence of the protozoan, resulting in a benign disease. The current knowledge about viruses infecting flagellated protozoans is still fragmentary, and more research is required to unravel the intricacies of this three-way relationship. We need to develop early and effective diagnostic methods for further development in the field of translational medicine. Taking advantage of promising biotechnological advances, the aim is to develop ad hoc therapeutic strategies that focus not only on the disease-causing protozoan but also on the virus.

Assessment of Drug Activities against Giardia Using Hyperspectral Raman Microscopy

This study demonstrates the capability of Raman microscopy for detecting structural differences in Giardia cells exposed to different drugs and incubation times. While metronidazole (MTZ) visibly affects the cells by inducing extracellular vesicle releases of toxic iron intermediates and modified triple-bond moieties, oseltamivir (OSM) alters the phenylalanine and lipid structures. Modifications in the heme protein environment and the transformation of iron from ferric to ferrous observed for both drug treatments are more notable for MTZ. Different contents and amounts of vesicle excretion are detected for 24 h or 48 h with MTZ incubation. At a shorter drug exposure, releases of altered proteins, glycogen, and phospholipids dominate. Agglomerates of transformed iron complexes from heme proteins and multiple-bond moieties prevail at 48 h of treatment. No such vesicle releases are present in the case of OSM usage. Drug incorporations into the cells and their impact on the plasma membrane and the dynamics of lipid raft confirmed by confocal fluorescence microscopy reveal a more destructive extent by OSM, corroborating the Raman results. Raman microscopy provides a broader understanding of the multifaceted factors and mechanisms responsible for giardiasis treatment or drug resistance by enabling a label-free, simultaneous monitoring of structural changes at the cellular and molecular levels.

Molecular characterisation of Giardia duodenalis from human and companion animal sources in the United Kingdom using an improved triosephosphate isomerase molecular marker

Giardia duodenalis is a protozoan parasite known for its ability to cause gastrointestinal disease in human and non-human mammals. In the UK, the full impact of this parasite has yet to be fully explored, due to the limited testing which has been undertaken in humans and the low-resolution assemblage-typing methods currently available. Rather than being primarily a travel-associated condition, a recent study has highlighted that an endemic Giardia cycle is present in the UK, although the source of human disease is unclear in the majority of cases. This study focussed on the improvement of one of the commonly used assemblage-typing assays, a nested topoisomerase phosphate (tpi) PCR, to increase the amplification success rate across both human and companion animal samples. After comparing published primers to full Giardia reference genomes, this marker protocol was optimised and then deployed to test a substantial number of human (n ​= ​79) and companion animal (n ​= ​174) samples to gain an insight into the molecular epidemiology of Giardia in the UK. One assemblage A1 and eleven assemblage A2 genotypes were detected in humans, along with and 25 assemblage B genotypes. Assemblage A1 genotypes, known to be human-infective, were found in three feline and one canine sample, while one feline sample contained assemblage A2. Additionally, four feline samples contained assemblage B, which is recognised as potentially human-infective. This study demonstrates the presence of potentially human-infective Giardia genotypes circulating in the companion animal population, notably with 17.4% (8/46) of feline-derived Giardia strains being potentially zoonotic. Using a modified tpi-based genotyping assay, this work highlights the potential for domestic pets to be involved in the endemic transmission of giardiasis in the UK and underlines the need for appropriate hygiene measures to be observed when interacting with both symptomatic and asymptomatic animals. It also serves to underline the requirement for further studies to assess the zoonotic risk of Giardia associated with companion animals in high-income countries.

The controversies surrounding Giardia intestinalis assemblages A and B

Giardia intestinalis continues to be one of the most encountered parasitic diseases around the world. Although more frequently detected in developing countries, Giardia infections nonetheless pose significant public health problems in developed countries as well. Molecular characterisation of Giardia isolates from humans and animals reveals that there are two genetically different assemblages (known as assemblage A and B) that cause human infections. However, the current molecular assays used to genotype G. intestinalis isolates are quite controversial. This is in part due to a complex phenomenon where assemblages are incorrectly typed and underreported depending on which targeted locus is sequenced. In this review, we outline current knowledge based on molecular epidemiological studies and raise questions as to the reliability of current genotyping assays and a lack of a globally accepted method. Additionally, we discuss the clinical symptoms caused by G. intestinalis infection and how these symptoms vary depending on the assemblage infecting an individual. We also introduce the host-parasite factors that play a role in the subsequent clinical presentation of an infected person, and explore which assemblages are most seen globally.

First case of community acquired giardiasis in Nuuk, Greenland

We report a case of community acquired giardiasis, in Nuuk, Greenland. Likely source of infection being consumption of untreated water from a local reservoir, alternatively through contact with sewage. Giardia is widespread worldwide but has not commonly been considered a cause of gastrointestinal distress in patients in Greenland, without relevant travel history. This may be due to under diagnosis, or historically low prevalence of Giardia in the region. Climate change with increasing temperatures, growing tourism and pet travel may influence the presence of Giardia in the region. This case highlights the need to include giardiasis as a differential diagnosis in patients presenting with suspected infectious gastroenteritis in Greenland.

Giardiavirus: an update

Giardiavirus is the only virus that infects Giardia duodenalis, a highly prevalent parasite worldwide, especially in low-income and developing countries. This virus belongs to the Totiviridae family, being a relative of other viruses that infect fungi and protozoa. It has a simple structure with only two proteins encoded in its genome and it appears that it can leave the cell without lysis. All these characteristics make it an interesting study model; however, its research has unfortunately made little progress in recent years. Thus, in this review, we summarize the currently available data on Giardiavirus, from their structure, genome and main proteins, to the uses that have been given to them and the possible health applications for the future.

Molecular Epidemiology of Giardia Infections in the Genomic Era

Giardia duodenalis is a major gastrointestinal parasite of humans and animals across the globe. It is also of interest from an evolutionary perspective as it possesses many features that are unique among the eukaryotes, including its distinctive binucleate cell structure. While genomic analysis of a small number of isolates has provided valuable insights, efforts to understand the epidemiology of the disease and the population biology of the parasite have been limited by the molecular tools currently available. We review these tools and assess the impact of affordable and rapid genome sequencing systems increasingly being deployed in diagnostic settings. While these technologies have direct implications for public and veterinary health, they will also improve our understanding of the unique biology of this fascinating parasite.

An update on the incidence of human giardiasis in Scotland, 2011-2018

BACKGROUND

Giardia duodenalis is one of the most common parasites in the UK to cause diarrhoeal illness. Giardiasis is likely to be significantly under-reported in the UK as laboratory testing is largely based on examining stool samples from individuals with a recent travel history. This results in the majority of locally-acquired cases going undetected. To increase awareness of giardiasis, we describe data gathered from cases reported within Scotland during 2011-2018.

METHODS

All of the 21 Scottish National Health Service (NHS) diagnostic microbiology laboratories performed microscopy examination to detect Giardia cysts in stools, from mostly travel-related cases. The exception was one laboratory that implemented an antigen-based enzyme immunoassay in 2015. This resulted in every submitted stool being tested for Giardia. Laboratory-confirmed cases of giardiasis were reported to Health Protection Scotland (HPS) via the Electronic Communication of Surveillance in Scotland (ECOSS) during the eight-year period. Data for calculating the incidence per 100,000 of the population were obtained from the National Records of Scotland mid-2018 population estimates in Scotland.

RESULTS

A total of 1631 Scottish cases were reported during 2011-2018 (8-year mean: 204; range: 166-269). National Health Service Grampian, Borders and Lothian reported the highest incidence of Giardia (9.8, 7.5 and 6.7 per 100,000, respectively), all of which were above the Scottish mean incidence (3.8 per 100,000). Following the implementation of antigen testing in NHS Grampian during 2015, reports significantly increased 3.6-fold (P = 0.005). The highest incidence of giardiasis occurred in the 20-49 years age group (mean 5.4 per 100,000). Of interest, the mean incidence of giardiasis was significantly higher in males than in females (4.8 versus 3.1 per 100,000, respectively; P < 0.0001).

CONCLUSIONS

This report highlights the need to capture enhanced information on every laboratory-confirmed case of giardiasis to gain a better understanding of the local sources and transmission pathways occurring in Scotland. In addition, implementing sensitive, automated technologies across UK NHS diagnostic microbiology laboratories to permit the efficient, routine testing of every submitted stool for Giardia, should be encouraged to ensure all cases are identified and treated appropriately.

Treatment-refractory giardiasis: challenges and solutions

Giardia is the commonest parasitic diarrheal pathogen affecting humans and a frequent cause of waterborne/foodborne parasitic diseases worldwide. Prevalence of giardiasis is higher in children, living in poor, low hygiene settings in developing countries, and in travelers returning from highly endemic areas. The clinical picture of giardiasis is heterogeneous, with high variability in severity of clinical disease. It can become chronic or be followed by post-infectious sequelae. An alarming increase in cases refractory to the conventional treatment with nitroimidazoles (ie, metronidazole) has been reported in low prevalence settings, such as European Union countries, especially in patients returning from Asia. In view of its relevance, we aim in this review to recapitulate present clinical knowledge about Giardia, with a special focus on the challenge of treatment-refractory giardiasis. We propose a working definition of clinically drug-resistant giardiasis, summarize knowledge regarding resistance mechanisms, and discuss its clinical management according to research-based evidence and medical practice. Advances in development and identification of novel drugs and potential non-pharmacological alternatives are also reviewed with the overall aim to define knowledge gaps and suggest future directions for research.

Detection of potentially human infectious assemblages of Giardia duodenalis in fecal samples from beef and dairy cattle in Scotland

This study aimed to determine the prevalence and assemblages of Giardia duodenalis present in Scottish beef and dairy cattle at different ages, to try to ascertain if cattle could play a role in the spread of zoonotic assemblages of Giardia. A total of 388 fecal samples (128 beef and 253 dairy, seven of unknown breed) were collected from 19 farms in Scotland. Samples were sub-divided by host age, 1, 2, 3, 4, 5 and 6, 7-24 and ⩾25 weeks. DNA was extracted and tested by PCR to detect G. duodenalis DNA. Of the 388 samples, 126 tested positive, giving an overall prevalence of 32.5%, with positive samples being observed in all age groups tested. The prevalence in dairy cattle was 44.7% (113/235), which was significantly higher (P &lt; 0.001) than the prevalence in beef cattle 10.1% (13/128). Sequence analysis demonstrated the presence of assemblage E (77.2%, sequence types E-S1-E-S5), assemblage B (18.2%) and assemblage A (sub-assemblages AI-AII) (4.6%). These data demonstrate that G. duodenalis is found routinely in both dairy and beef cattle throughout Scotland; the presence of assemblages A and B also indicates that cattle may play a role in the spread of potentially zoonotic assemblages of Giardia.

Giardiasis: a diagnosis that should be considered regardless of the setting

Although Giardia, the aetiological agent of giardiasis, is one of the most prevalent intestinal parasitic infections world-wide, for industrialised countries, it is mainly appreciated as an imported disease with the minimal local transmission. However, the current evidence challenges this perception; Giardia has relevance beyond the high prevalence areas. This infection may be asymptomatic or cause gastrointestinal complains and long-term sequelae, including irritable bowel syndrome, chronic fatigue and impaired child growth and cognitive development. Its detection and diagnosis present a challenge to physicians who may not be familiar with this infection. To improve interventions to control this parasitosis, it is necessary to maintain a high index of suspicion and remain vigilant in finding cases at risk for infection. A better understanding of the characteristics of populations importing infections alongside improved methods to reliably classify infections as imported or acquired locally will help to ensure early and accurate diagnosis. The evidence shows that public health problems like giardiasis are global issues that need to be addressed collectively by both high and low prevalence countries.