'Catch-up' growth velocities after treatment for Trichuris dysentery syndrome

Systematic review to evaluate a potential association between helminth infection and physical stunting in children

BACKGROUND

Despite considerable public health efforts over the past 20 years, childhood stunting (physical and/or cognitive) levels globally remain unacceptably high-at 22% amongst children under 5 years old in 2020. The aetiology of stunting is complex and still largely unknown. Helminths can cause significant mortality and morbidity and have often been cited as major causative agents for stunting, although their actual role in childhood stunting remains unclear. Our aim was to systematically review the current evidence to help support or refute the hypothesis that helminths cause physical stunting in children.

METHODS

Inclusion criteria were as follows: infected with (and/or exposed to) helminths (soil-transmitted helminths, schistosomes or food-borne trematodes), children, pregnant or breastfeeding women as study participants (children included infants 0-1 year old, preschool-age children 1-5 years and school-age children > 5 years old), anthelmintic treatment intervention, stunting-related variables reported (e.g. height, height-for-age z-score, birth weight), helminth infection reported in relation to stunting, any geographic location, any date, peer-reviewed literature only. Exclusion criteria were: non-primary research, study protocols, studies with no new data, non-English language papers and animal (non-human) helminth studies. Seven databases were searched on 28 May 2021. Risk of bias was assessed for included studies and GRADE was used for studies included in RCT subgroup meta-analyses (in preschool-age children and pregnant women). This systematic review was registered with PROSPERO (CRD42021256201).

RESULTS

Eighty studies were included in the analyses. No significant overall evidence was found in support of the hypothesis that helminths cause physical stunting in children, although there was some association with wasting.

CONCLUSIONS

Whilst analyses of the available literature to date failed to support a direct association between helminth infection and childhood stunting, there was significant heterogeneity between studies, and many had follow-up periods which may have been too short to detect impacts on growth. Most apparent was a lack of available data from key demographic groups wherein one may predict the greatest association of helminth infection with stunting-notably that of infants, preschool-age children, and pregnant or nursing women. Thus this review highlights the urgent need for further targeted empirical research amongst these potentially most vulnerable demographic groups.

Un-‘Egg’-Plored: Characterisation of Embryonation in the Whipworm Model Organism Trichuris muris

Trichuris muris, is the murine parasite and widely deployed model for the human whipworm Trichuris trichiura, a parasite that infects around 500 million people globally. Trichuriasis is a classical disease of poverty with a cycle of re-infection due to the continual exposure of humans, particularly children, to infective eggs, which contaminate the soil in endemic areas. Indeed, modelling studies of trichuriasis have demonstrated that the low efficacy rate of current anthelmintics combined with the high possibility of re-infection from the reservoir of infective eggs within the environment, mean that the elimination of morbidity due to trichuriasis is unlikely to occur. Despite the importance of the infective egg stage in the perpetuation of infections, understanding the biology of the Trichuris ova has been neglected for decades. Here we perform experiments to assess the impact of temperature on the embryonation process of T. muris eggs and describe in detail the stages of larval development within these eggs. In keeping with the early works performed in the early 1900s, we show that the embryonation of T. muris is accelerated by an elevation in temperature, up to 37°C above which eggs do not fully develop and become degenerate. We extend these data to provide a detailed description of T. muris egg development with clear images depicting the various stages of development. To the best of our knowledge we have, for the first time, described the presence of birefringent granules within egg-stage larvae, as well as providing a qualitative and quantitative description of a motile larval stage prior to quiescence within the egg. These experiments are the first step towards a better understanding of the basic biology which underlies the process of egg embryonation. With the threat of elevation in global temperatures, the accelerated embryonation rate we observe at higher temperatures may have important consequences for parasite transmission rates and prospective modelling studies. In addition, a deeper understanding of the Trichuris ova may allow the development of novel control strategies targeting the egg stage of Trichuris in the environment as an adjunct to MDA.

Whipworm and roundworm infections

Trichuriasis and ascariasis are neglected tropical diseases caused by the gastrointestinal dwelling nematodes Trichuris trichiura (a whipworm) and Ascaris lumbricoides (a roundworm), respectively. Both parasites are staggeringly prevalent, particularly in tropical and subtropical areas, and are associated with substantial morbidity. Infection is initiated by ingestion of infective eggs, which hatch in the intestine. Thereafter, T. trichiura larvae moult within intestinal epithelial cells, with adult worms embedded in a partially intracellular niche in the large intestine, whereas A. lumbricoides larvae penetrate the gut mucosa and migrate through the liver and lungs before returning to the lumen of the small intestine, where adult worms dwell. Both species elicit type 2 anti-parasite immunity. Diagnosis is typically based on clinical presentation (gastrointestinal symptoms and inflammation) and the detection of eggs or parasite DNA in the faeces. Prevention and treatment strategies rely on periodic mass drug administration (generally with albendazole or mebendazole) to at-risk populations and improvements in water, sanitation and hygiene. The effectiveness of drug treatment is very high for A. lumbricoides infections, whereas cure rates for T. trichiura infections are low. Novel anthelminthic drugs are needed, together with vaccine development and tools for diagnosis and assessment of parasite control in the field.

100 Years of Mass Deworming Programmes: A Policy Perspective From the World Bank's Disease Control Priorities Analyses

For more than 100 years, countries have used mass drug administration as a public health response to soil-transmitted helminth infection. The series of analyses published as Disease Control Priorities is the World Bank's vehicle for exploring the cost-effectiveness and value for money of public health interventions. The first edition was published in 1993 as a technical supplement to the World Bank's World Development Report Investing in Health where deworming was used as an illustrative example of value for money in treating diseases with relatively low morbidity but high prevalence. Over the second (2006) and now third (2017) editions deworming has been an increasingly persuasive example to use for this argument. The latest analyses recognize the negative impact of intestinal worm infection on human capital in poor communities and document a continuing decline in worm infection as a result of the combination of high levels of mass treatment and ongoing economic development trends in poor communities.

The Hygiene Hypothesis and Its Inconvenient Truths about Helminth Infections

Current iterations of the hygiene hypothesis suggest an adaptive role for helminth parasites in shaping the proper maturation of the immune system. However, aspects of this hypothesis are based on assumptions that may not fully account for realities about human helminth infections. Such realities include evidence of causal associations between helminth infections and asthma or inflammatory bowel disease as well as the fact that helminth infections remain widespread in the United States, especially among populations at greatest risk for inflammatory and autoimmune diseases.

The role of nutrition in integrated programs to control neglected tropical diseases

There are strong and direct relationships between undernutrition and the disease caused by infectious organisms, including the diverse pathogens labeled as neglected tropical diseases (NTDs). Undernutrition increases the risk of infection, the severity of disease and the risk that children will die, while the physical damage, loss of appetite, and host responses during chronic infection can contribute substantially to undernutrition. These relationships are often synergistic. This opinion article examines the role of nutrition in controlling NTDs and makes the point that mass drug treatment--the major strategy currently proposed to control several diseases--is crucial to controlling disease and transmission, but is only the start of the process of physical recovery. Without adequate energy and nutrients to repair damaged tissues or recover lost growth and development, the benefits of treatment may not be evident quickly; the effects of control programs may be not appreciated by beneficiaries; while vulnerability to reinfection and disease may not be reduced. There is substantial potential for nutritional interventions to be added to large-scale programs to deliver drug treatments and thereby contribute, within a broad strategy of public health interventions and behavior change activities, to controlling and preventing NTDs in populations, and to restoring their health.

Trichuris sp. and Strongyloides sp. infections in a free-ranging baboon colony

We conducted cross-sectional surveys of parasites infecting a large free-living colony of baboons at the Southwest National Primate Research Center in San Antonio in October 2003 and April 2004, immediately before, and 6 mo after, treatment with ivermectin. Trichuris sp. was the predominant species present, infecting 79 and 69% of individual animals in the 2 surveys, with fecal egg counts (FEC) of up to 60,200 eggs per g (epg) (mean = 1,235 in October 2003 and 1,256 in April 2004). Prevalence remained fairly stable across age groups, and intensity was highest in animals <1 or >15 yr old, in contrast to patterns observed in humans, where school-age children show the heaviest infections. Strongyloides sp. was also identified, but the species identity remains uncertain. Small subunit ribosomal DNA sequences differed from published sequences of Strongyloides fuelleborni at multiple sites, but resided in a monophyletic group with other Strongyloides species with 92% bootstrap support. This may reflect a recent acquisition from a local host, or that the published sequence of S. fuelleborni is incorrect. Widespread infections with 2 nematode genera in a free-ranging baboon colony that are an important source of morbidity in human populations provide a useful model system for work on the epidemiology, control, pathology, and genetics of these parasites in a host species that is physiologically, immunologically, and genetically similar to humans.

Early exposure of infants to GI nematodes induces Th2 dominant immune responses which are unaffected by periodic anthelminthic treatment

We have previously shown a reduction in anaemia and wasting malnutrition in infants <3 years old in Pemba Island, Zanzibar, following repeated anthelminthic treatment for the endemic gastrointestinal (GI) nematodes Ascaris lumbricoides, hookworm and Trichuris trichiura. In view of the low intensity of worm infections in this age group, this was unexpected, and it was proposed that immune responses to the worms rather than their direct effects may play a significant role in morbidity in infants and that anthelminthic treatment may alleviate such effects. Therefore, the primary aims of this study were to characterise the immune response to initial/early GI nematode infections in infants and the effects of anthelminthic treatment on such immune responses. The frequency and levels of Th1/Th2 cytokines (IL-5, IL-13, IFN-γ and IL-10) induced by the worms were evaluated in 666 infants aged 6–24 months using the Whole Blood Assay. Ascaris and hookworm antigens induced predominantly Th2 cytokine responses, and levels of IL-5 and IL-13 were significantly correlated. The frequencies and levels of responses were higher for both Ascaris positive and hookworm positive infants compared with worm negative individuals, but very few infants made Trichuris-specific cytokine responses. Infants treated every 3 months with mebendazole showed a significantly lower prevalence of infection compared with placebo-treated controls at one year following baseline. At follow-up, cytokine responses to Ascaris and hookworm antigens, which remained Th2 biased, were increased compared with baseline but were not significantly affected by treatment. However, blood eosinophil levels, which were elevated in worm-infected children, were significantly lower in treated children. Thus the effect of deworming in this age group on anaemia and wasting malnutrition, which were replicated in this study, could not be explained by modification of cytokine responses but may be related to eosinophil function.

Infants and very young children commonly become infected with intestinal nematode infections. However, the worm burdens are generally very light, so a beneficial effect of deworming on wasting malnutrition and anaemia in this age group which we have demonstrated was unexpected and the mechanism unclear. To investigate this, we have, for the first time, determined whether such worm infections in infants induce significant immune reactions which might be detrimental to nutrition and growth e.g. by inducing inflammation in the gut or by cytokine effects on erythropoiesis. We also determined if such responses are modulated by regular deworming over a 9 month period. Peripheral blood cells from infants infected with Ascaris and hookworms in particular responded to stimulation with worm antigens, producing predominantly Th2 cytokines. Although the Th2 cytokine responses in the periphery were not significantly altered by deworming, the levels of eosinophils, which are regulated by the Th2 cytokine, IL-5, were lower after treatment. It is possible that eosinophils play a role in gut pathology leading to wasting malnutrition and anaemia in the very young and that this effect is reduced by deworming.

A review and meta-analysis of the impact of intestinal worms on child growth and nutrition

More than a half of the world's population are infected with one or more species of intestinal worms of which the nematodes Ascaris lumbricoides, Trichuris trichiura and the hookworms are the most common and important in terms of child health. This paper: (1) introduces the main species of intestinal worms with particular attention to intestinal nematodes; (2) examines how such worms may affect child growth and nutrition; (3) reviews the biological and epidemiological factors that influence the effects that worms can have on the growth and nutrition of children; (4) considers the many factors that can affect the impact of treatment with anthelmintic drugs; (5) presents the results of a meta-analysis of studies of the effect of treating worm infections on child growth and nutrition; (6) discusses the results in terms of what is reasonable to expect that deworming alone can achieve; (7) describes some important characteristics of an ideal study of the effects of deworming; and (8) comments on the implications for programmes of recommendations concerning mass deworming.

Micronutrient supplements for children after deworming

The availability of a few inexpensive, single-dose drugs to treat soil-transmitted helminths and schistosomiasis offers the potential to reduce a considerable burden of acute disease, especially among children in sub-Saharan Africa. These treatments are being promoted as "rapid impact interventions". However, if helminth infections cause underweight, stunting, anaemia, and impaired mental development in children, how will removing worms alone lead to recovery without treating the underlying deficits that have been caused or made worse by helminth disease? Energy, protein, and micronutrients are required by children who are underweight or who have stunted growth; children who are anaemic will require iron and other micronutrients for haemopoiesis; and children who have lost education will need remedial teaching. Treating neglected worm diseases is an essential first step to good health, but anthelmintic drugs need to be integrated with simple and inexpensive nutritional interventions such as micronutrient supplements to promote recovery and have a rapid effect.

Global anthelmintic chemotherapy programs: learning from history

May 2001 was a landmark in the control of helminth infections. For the first time, the global community recognized that tools existed to deal with some of the commonest infections on the planet. Yet, many of the concepts had been identified nearly a century before, and subsequently largely forgotten. The lessons of the past have much to impart, and recent work has strengthened the evidence and identified the tools to make global control programs feasible. The challenge will now be to make it happen, and some of the problems ahead are truly massive.

Nutritional impact of intestinal helminthiasis during the human life cycle

Poor people in developing countries endure the burden of disease caused by four common species of soil-transmitted nematode that inhabit the gastrointestinal tract. Disease accompanying these infections is manifested mainly as nutritional disturbance, with the differing infections having their deleterious effects at different phases during the human life cycle. Reduced food intake, impaired digestion, malabsorption, and poor growth rate are frequently observed in children suffering from ascariasis and trichuriasis. Poor iron status and iron deficiency anemia are the hallmarks of hookworm disease. The course and outcome of pregnancy, growth, and development during childhood and the extent of worker productivity are diminished during hookworm disease. Less is known about the impact of these infections in children under 2 years of age. The severity of disease caused by soil-transmitted nematodes has consistently been found to depend on the number of worms present per person. Cost-effective measures based on highly efficacious anthelminthic drugs are now available to reduce and control disease caused by these infections.

Evaluation of the Integrated Management of Childhood Illness guidelines for treatment of intestinal helminth infections among sick children aged 2-4 years in western Kenya

Anthelmintic treatment of sick preschool-age children at health facilities is a potentially effective strategy for intestinal helminth control in this age-group. We conducted a study from July 1998 to February 1999 in western Kenya to determine whether the Integrated Management of Childhood Illness (IMCI) guidelines' clinical assessment can be used to identify helminth-infected children, and to evaluate the nutritional benefit of treating sick children without pallor with an anthelmintic (mebendazole is already part of IMCI treatment for sick children aged 2-4 years with palmar pallor in areas where hookworm and Trichuris trichiura infections are endemic). Sick children aged 2-4 years seen at 3 rural health facilities were clinically evaluated and tested for haemoglobin concentration, malaria parasites, and intestinal helminths. Children without pallor were randomly assigned to receive a single dose of 500 mg of mebendazole or a placebo and re-examined 6 months later. Among the 574 children enrolled, 11% had one or more intestinal helminths. Most infections were of light intensity. Selected clinical signs and symptoms available from the IMCI assessment, including palmar pallor and low weight-for-age, were not associated with helminth infection. Six months after enrollment, no differences in growth of children without pallor were observed between the mebendazole (n = 166) and placebo (n = 181) groups. However, there was a significantly greater mean increase in weight, height, and weight-for-age Z score among the helminth-infected children in the mebendazole group (n = 22) as compared with helminth-infected children in the placebo group (n = 20). We conclude that even lightly infected preschool-age children without palmar pallor benefit from anthelmintic treatment; however, in this study setting of low helminth prevalence and intensity, helminth-infected children could not be identified using the IMCI guidelines. Cost-effectiveness studies are needed to help define helminth prevalence thresholds for routine anthelmintic treatment of sick preschool-age children seen at first-level health facilities.

Multiple helminth infections in children: impact and control

Parasitic worm infections are amongst the most widespread of all chronic human infections. It is estimated that there are more than 3 billion infections in the world today. In many low income countries it is often more common to be infected than not to be. Indeed, a child growing up in an endemic community can expect be infected soon after weaning, and to be infected and constantly reinfected for the rest of her or his life. Infection is most common amongst the poorest and most disadvantaged communities, and is typically most intense in children of school going age. As the risk of morbidity is directly related to intensity of infection, it follows that children are the most at risk from the morbid effects of disease. Multiparasite infections are also common in such communities and there is evidence that individuals harbouring such infections may suffer exacerbated morbidity, making children even more vulnerable. Thus, these infections pose a serious threat to the health and development of children in low income countries. For many years, the need to control these infections has lain uncontested, and with the advent of broad-spectrum anthelminthic drugs that are cheap, safe and simple to deliver, control has at last become a viable option for many communities. Furthermore, there is now increased emphasis being placed on a multispecies approach as a cost-effective mechanism to control the morbidity of virtually all the major helminthic infections of humans.

Relationship of childhood protein-energy malnutrition and parasite infections in an urban African setting

A clear understanding of protein-energy malnutrition (PEM), parasite infection and their interactions is essential in formulating health and development policies. We studied the prevalence of PEM indicators and the prevalence and/or intensity of infection in 558 Zairian children aged 4 months to 10 years. Multivariate analyses were used to estimate relationships between PEM indicators and parasitic infection. Stunting was found in 40.3% of children, wasting in 4.9% and kwashiorkor in 5.1%. The risk of stunting was significantly higher in children with Ascaris lumbricoides. The risk of wasting was higher in children with A. lumbricoides or Trichuris trichiura, whereas the risk of kwashiorkor was high with T. trichiura but very reduced in those with A. lumbricoides. Plasmodium infection was not related to nutritional indicators. These relationships highlight important interactions, both synergistic and antagonistic, between nutrition and parasites in central Africa.

Plasma proteins in children with trichuris dysentery syndrome

AIMS

To determine whether in Trichuris trichiura dysentery there is (1) evidence of a systemic inflammatory response, (2) evidence that the plasma protein disturbance has special characteristics compared with uninfected children in the endemic environment.

METHODS

Three groups of children (age 1.6 to 11.4 years) were studied: 53 cases of trichuris dysentery syndrome (TDS), 16 cases of chronic non-secretory diarrhoea not infected with the parasite ("disease controls", DC), and 20 asymptomatic, parasite-free primary schoolchildren (normal controls, NC). C reactive protein, alpha 1 antitrypsin, caeruloplasmin, albumin, total globulin, fibrinogen, fibronectin, ferritin, and transferrin were measured on a single occasion for each. The study was thus a cross sectional descriptive survey for group comparison. Plasma viscosity was measured on admission for TDS and DC and repeated after six weeks and six months for TDS.

RESULTS

Plasma C reactive protein, alpha 1 antitrypsin, total globulin, fibronectin, and viscosity were significantly higher in TDS than in NC. DC children also had acute phase protein elevations (C reactive protein, caeruloplasmin, viscosity). However, the increase in caeruloplasmin was specific to the DC group while an increase in fibronectin was specific to the TDS group. Serial measurement of viscosity in TDS showed a modest but significant fall during the six months following treatment.

CONCLUSIONS

There is an acute phase response in intense trichuriasis and a specific elevation of plasma fibronectin. Plasma viscosity remains abnormally high six months after treatment, although lower than at diagnosis.