Infantile hookworm disease in China. A review

Effect of incorporation of bead-beating during DNA extraction for quantitative polymerase chain reaction-based detection of Trichuris trichiura in stool samples in community settings: a systematic review

This meta-analysis was designed to assess the effect of the addition of a bead-beating (BB) step during DNA extraction to effectively isolate Trichuris trichiura DNA from stool samples for quantitative polymerase chain reaction (qPCR)-based diagnosis. qPCR-based molecular studies comparing the inclusion of a bead-beating step during the DNA extraction from stool samples with extraction without the step were included in the analysis. Studies using real patient samples in community settings were included. The PubMed database and Google search engine were searched in December 2019. Risk of bias and applicability were assessed using the Quality Assessment of Diagnostic Accuracy Studies-2 checklist. Odds ratios (ORs) for individual studies were combined to estimate the random effects model OR. A total of six independent sub-studies were gathered from two published original articles. The division of the two major studies into six sub-studies was indispensable due to the nature of the study carried out. 128 of the total 192 samples (in all studies) were positive for T. trichiura when BB was used during DNA extraction compared to 108/192 when BB was excluded. The combined OR was 1.66 (95% confidence interval: 1.059 to 2.602). Though only two articles were included in the study, six exclusive individual sub-studies were analyzed. Inherent differences in the background prevalence of helminths in the study population could impact the sensitivity of qPCR. It was found that the inclusion of the BB step during DNA extraction significantly increased the sensitivity of the test. This study was not registered in any database.

Hookworm infection in infants: a case report and review of literature

BACKGROUND

Hookworm infections (Necator americanus, Ancylostoma duodenale) are common in rural areas of tropical and subtropical countries. Human acquisition results from direct percutaneous invasion of infective larvae from contaminated soil. Overall, almost 472 million people in developing rural countries are infected. According to simulation models, hookworm disease has a global financial impact of over US$100 billion a year. Hookworm infection in newborn or infancy is rare, and most of the cases reported in literature are from endemic countries. Here, we describe the case of an infant with an Ancylostoma duodenale infection and review the literature currently available on this topic.

CASE PRESENTATION

An Italian 2-month-old infant presented with vomit and weight loss. Her blood exams showed anemia and eosinophilia and stool analysis resulted positive for hookworms' eggs, identified as Ancylostoma duodenale with real time-PCR. Parasite research on parents' stools resulted negative, and since the mother travelled to Vietnam and Thailand during pregnancy, we assumed a transplacental transmission of the infection. The patient was treated successfully with oral Mebendazole and discharged in good conditions.

DISCUSSION

Hookworm helminthiasis is a major cause of morbidity in children in the tropics and subtropics, but rare in developed countries. Despite most of the patients is usually asymptomatic, children are highly exposed to negative sequelae such as malnutrition, retarded growth and impaired cognitive development. In infants and newborns, the mechanism of infection remains unclear. Although infrequent, vertical transmission of larvae can occur through breastfeeding and transplacentally. Hookworm infection should be taken into account in children with abdominal symptoms and unexplained persistent eosinophilia. The treatment of infants infected by hookworm has potential benefit, but further studies are needed to define the best clinical management of these cases.

Of dogs and hookworms: man's best friend and his parasites as a model for translational biomedical research

We present evidence that the dog hookworm (Ancylostoma caninum) is underutilised in the study of host-parasite interactions, particularly as a proxy for the human-hookworm relationship. The inability to passage hookworms through all life stages in vitro means that adult stage hookworms have to be harvested from the gut of their definitive hosts for ex vivo research. This makes study of the human-hookworm interface difficult for technical and ethical reasons. The historical association of humans, dogs and hookworms presents a unique triad of positive evolutionary pressure to drive the A. caninum-canine interaction to reflect that of the human-hookworm relationship. Here we discuss A. caninum as a proxy for human hookworm infection and situate this hookworm model within the current research agenda, including the various 'omics' applications and the search for next generation biologics to treat a plethora of human diseases. Historically, the dog hookworm has been well described on a physiological and biochemical level, with an increasing understanding of its role as a human zoonosis. With its similarity to human hookworm, the recent publications of hookworm genomes and other omics databases, as well as the ready availability of these parasites for ex vivo culture, the dog hookworm presents itself as a valuable tool for discovery and translational research.

Worm Infections in Children

• On the basis of research evidence, worm infections are important global child health conditions causing chronic disability that lasts from childhood into adulthood (Table 1). (2)(3) Evidence Quality: B • On the basis of research evidence, the major worm infections found in developing countries include ascariasis, trichuriasis, hookworm infection, and schistosomiasis; toxocariasis, enterobiasis, and cysticercosis are also found in poor regions of North America and Europe. (4)(9)(13) Evidence Quality: B • On the basis of expert consensus, children and adolescents are often vulnerable to acquiring large numbers of worms, ie, high-intensity infections (Fig 1)(21)(22)(23) Evidence Quality: D • On the basis of expert consensus and research evidence, moderate and heavy worm burdens cause increased morbidity because of growth and intellectual stunting in children and adolescents. Many of these effects may result from helminth-induced malnutrition. (21)(22)(23) Evidence Quality: C • On the basis of expert consensus and research evidence, worm infections are also commonly associated with eosinophilia. (48) (49) Evidence Quality: B • On the basis of research evidence as well as consensus, helminthes can cause inflammation in the lung (asthma), gastrointestinal tract (enteritis and colitis), liver (hepatitis and fibrosis), and urogenital tract. (7)(21)(22)(23)(27)(28)(40)(41)(43) Evidence Quality: B • On the basis of research evidence, microscopy techniques for diagnosis of worm infections in children often exhibit suboptimal sensitivities and specificities, necessitating new or improved diagnostic modalities such as polymerase chain reaction. (54)(55) Evidence Quality: A • On the basis of research evidence and expert consensus, mass drug administration (“preventive chemotherapy”) has becomea standard practice for ministries of health in low- and middle-income countries to control intestinal helminth infections and schistosomiasis. (67)(68) Evidence Quality: B.

The microbiota and helminths: sharing the same niche in the human host

Human gastrointestinal bacteria often share their environment with parasitic worms, allowing physical and physiological interaction between the two groups. Such associations have the potential to affect host health as well as the bacterial and helminth populations. Although still in its early stages, research on the interaction between the microbiome and parasitic helminths in humans offers the potential to improve health by manipulating the microbiome. Previously, supplementation with various nutritional compounds has been found to increase the abundance of potentially beneficial gut commensal bacteria. Thus, nutritional microbiome manipulation to produce an environment which may decrease malnutrition associated with helminth infection and/or aid host recovery from disease is conceivable. This review discusses the influence of the gut microbiota and helminths on host nutrition and immunity and the subsequent effects on the human host's overall health. It also discusses changes occurring in the microbiota upon helminth infections and the underlying mechanisms leading to these changes. There are still significant knowledge gaps which need to be filled before meaningful progress can be made in translating knowledge from studying the human gut microbiome into therapeutic strategies. Ultimately this review aims to discuss our current knowledge as well as highlight areas requiring further investigation.

In vivo endoscopic imaging of ancylostomiasis-induced gastrointestinal bleeding: clinical and biological profiles

Little data are available regarding the association of ancylostomiasis with overt gastrointestinal bleeding. This 6-year retrospective study describes the clinical and biological profiles of unexpectedly identified ancylostomiasis in a 4-month-old baby and four adults; they presented with melena and were referred for urgent diagnostic gastrointestinal endoscopy, which confirmed numerous small intestine injuries with surrounding blood pools caused by Ancylostoma duodenale worms. Gastric erosions were also encountered in one patient. Uniquely, worm biological activities were recorded live in vivo, including mucosal invasion through a vigorous, rapid piercing process, repeated bloodsucking habits, and gut appearance during the stages of feeding, digestion, and excretion in male and female worms. In conclusion, ancylostomiasis-induced melena may occur in all ages from infants to the elderly. Worm bloodfeeding occurs after quick mucosal piercing, with blood loss being aggravated by a repeated feeding behavior. After treatment is started, bleeding stops rapidly in response to anthelmintic therapy.

Infantile hookworm disease

Hookworm infection is common but has rarely been reported in neonates or infants. Two cases of hookworm infestation in early infancy are described. The infants presented with malena, severe pallor, lethargy and failure to gain weight. Initial stool examination was non-contributory and diagnosis was made by upper gastrointestinal endoscopy.

Hookworm causing melaena and severe anaemia in early infancy

Hookworm infestation is usually acquired by transcutaneous penetration of larvae whilst walking barefoot on contaminated soil. We present a small infant who presented with melaena and severe anaemia requiring multiple blood transfusions where the cause of gastro-intestinal bleeding was found to be massive hookworm infestation.

The mitochondrial genomes of Ancylostoma caninum and Bunostomum phlebotomum--two hookworms of animal health and zoonotic importance

Background

Hookworms are blood-feeding nematodes that parasitize the small intestines of many mammals, including humans and cattle. These nematodes are of major socioeconomic importance and cause disease, mainly as a consequence of anaemia (particularly in children or young animals), resulting in impaired development and sometimes deaths. Studying genetic variability within and among hookworm populations is central to addressing epidemiological and ecological questions, thus assisting in the control of hookworm disease. Mitochondrial (mt) genes are known to provide useful population markers for hookworms, but mt genome sequence data are scant.

Results

The present study characterizes the complete mt genomes of two species of hookworm, Ancylostoma caninum (from dogs) and Bunostomum phlebotomum (from cattle), each sequenced (by 454 technology or primer-walking), following long-PCR amplification from genomic DNA (~20–40 ng) isolated from individual adult worms. These mt genomes were 13717 bp and 13790 bp in size, respectively, and each contained 12 protein coding, 22 transfer RNA and 2 ribosomal RNA genes, typical for other secernentean nematodes. In addition, phylogenetic analysis (by Bayesian inference and maximum likelihood) of concatenated mt protein sequence data sets for 12 nematodes (including Ancylostoma caninum and Bunostomum phlebotomum), representing the Ascaridida, Spirurida and Strongylida, was conducted. The analysis yielded maximum statistical support for the formation of monophyletic clades for each recognized nematode order assessed, except for the Rhabditida.

Conclusion

The mt genomes characterized herein represent a rich source of population genetic markers for epidemiological and ecological studies. The strong statistical support for the construction of phylogenetic clades and consistency between the two different tree-building methods employed indicate the value of using whole mt genome data sets for systematic studies of nematodes. The grouping of the Spirurida and Ascaridida to the exclusion of the Strongylida was not supported in the present analysis, a finding which conflicts with the current evolutionary hypothesis for the Nematoda based on nuclear ribosomal gene data.

Human hookworm infection in the 21st century

The scientific study of human hookworm infection began at the dawn of the twentieth century. In recent years, there have been dramatic improvements in our understanding of many aspects of this globally widespread parasite. This chapter reviews recent advances in our understanding in the biology, immunology, epidemiology, public health significance and control of hookworm, and to look forward to the study of this important parasite in the 21st century. Advances in molecular biology has lead to the identification of a variety of new molecules from hookworms, which have importance either in the molecular pathogenesis of hookworm infection or in the host-parasite relationship; some are also promising vaccine targets. At present, relatively little is known about the immune responses to hookworm infection, although it has recently been speculated that hookworm and other helminths may modulate specific immune responses to other pathogens and vaccines. Our epidemiological understanding of hookworm has improved through the development of mathematical models of transmission dynamics, which coupled with decades of field research across multiple epidemiological settings, have shown that certain population characteristics can now be recognised as common to the epidemiology, population biology and control of hookworm and other helminth species. Recent recognition of the subtle, but significant, impact of hookworm on health and education, together with the simplicity, safety, low cost and efficacy of chemotherapy has spurred international efforts to control the morbidity due to infection. Large-scale treatment programmes are currently underway, ideally supported by health education and integrated with the provision of improved water and sanitation. There are also on-going efforts to develop novel anthelmintic drugs and anti-hookworm vaccines.

Could control of soil-transmitted helminthic infection influence the HIV/AIDS pandemic

In May 2001, the World Health Assembly (WHA) estimated that two billion people were infected by soil-transmitted helminths (S-THs) and schistosomiasis, worldwide. The WHA urged member states to recognise that there can be synergy between public health control programmes for S-THs, schistosomiasis and other diseases. This is particularly relevant to the new dimension created by the HIV/AIDS epidemics in the same impoverished communities and countries where helminthiasis is hyperendemic. Immunological adaptation between humans and parasitic helminths has developed during evolution. Review of 109 research papers, 76% (83/109) of which, were published between 1995 and February 2002, revealed increasing evidence that this relationship may have created an opportunity for more rapid infection by the human immunodeficiency virus (HIV), as well as quicker progression to AIDS. Moreover, the efficacy of some vaccines against HIV is likely to be impaired by chronic helminthiasis. For this, there is strong, indirect evidence. There is an urgent need for parasitologists, epidemiologists, immunologists and virologists to undertake comprehensive, transdisciplinary research. On the other hand, there is no current evidence that immunosuppression by HIV facilitates helminthic infection. The situation in regard to strongyloidiasis, however, is not yet clear.

Immune responses in hookworm infections

Hookworms infect perhaps one-fifth of the entire human population, yet little is known about their interaction with our immune system. The two major species are Necator americanus, which is adapted to tropical conditions, and Ancylostoma duodenale, which predominates in more temperate zones. While having many common features, they also differ in several key aspects of their biology. Host immune responses are triggered by larval invasion of the skin, larval migration through the circulation and lungs, and worm establishment in the intestine, where adult worms feed on blood and mucosa while injecting various molecules that facilitate feeding and modulate host protective responses. Despite repeated exposure, protective immunity does not seem to develop in humans, so that infections occur in all age groups (depending on exposure patterns) and tend to be prolonged. Responses to both larval and adult worms have a characteristic T-helper type 2 profile, with activated mast cells in the gut mucosa, elevated levels of circulating immunoglobulin E, and eosinophilia in the peripheral blood and local tissues, features also characteristic of type I hypersensitivity reactions. The longevity of adult hookworms is determined probably more by parasite genetics than by host immunity. However, many of the proteins released by the parasites seem to have immunomodulatory activity, presumably for self-protection. Advances in molecular biotechnology enable the identification and characterization of increasing numbers of these parasite molecules and should enhance our detailed understanding of the protective and pathogenetic mechanisms in hookworm infections.

Endoscopic diagnosis of hookworm disease of the duodenum

Hookworm is one of the most common parasites in the world, but can be missed on stool examination. We report a 31-year-old man who was complaining of epigastric discomfort, with laboratory findings of iron-deficiency anemia and eosinophilia. He was found to be infected with hookworm (Ancylostoma duodenale), which was directly detected and retrieved from the duodenum with biopsy forceps during upper gastrointestinal endoscopy. We eliminated his infection successfully by the Damaso de Rivas-Kihara modified method and oral administration of pyrantel pamoate. This report indicates that it is important to check carefully even in the distal duodenum at routine upper gastrointestinal endoscopy whenever parasitic disease is suspected but is hard to diagnose because of a limited number of eggs in feces.

Emerging and reemerging helminthiases and the public health of China

Despite great strides in their control throughout the People's Republic of China, helminth infections remain an important public health problem. The Institute of Parasitic Diseases of the Chinese Academy of Preventive Medicine, under the guidance of the Chinese Ministry of Health, completed a nationwide survey of more than 1 million people that showed the high prevalence and intensity of intestinal nematode infections; prevalence can sometimes exceed 50% in the Yangtze River valley provinces. Schistosoma japonicum is also a major cause of illness in this region. Attempts to control Chinese helminthic diseases with conventional anthelminthic drugs have been partially thwarted by high posttreatment rates of reinfection. Recently, several new human trematode pathogens have been identified. Novel approaches to chemoprophylaxis and vaccination may alleviate the public health problem caused by Chinese helminths. However, recombinant helminth vaccine development will depend on first cataloguing the extensive genetic diversity of Chinese helminths and candidate vaccine antigens. Evidence from biogeography, genetics, and systematics suggests that the genetic diversification of Chinese helminths and their vectors is an ongoing evolutionary process that began 12 million years ago near the convergence of major Asian river systems. Construction of the Three Gorges Super Dam on the Yangtze River may promote the emergence and reemergence of new helminths and their snail vectors