The specific effect of STHs on human nutritional status

STHs cause undernutrition by different mechanisms depending on where the organisms live and how they feed. In a review and meta-analysis, these mechanisms are: an increased metabolic rate (fever) as a result of inflammatory responses so that energy and nutrients are used at a greater rate than usual, for example in gut inflammation due to trichuriasis; increased nutrient requirements to meet the needs for immune and pathological responses to worms, larvae, or eggs, for example in schistosomiasis; loss of nutrients due to tissue damage, for example due to hookworm; malabsorption or maldigestion of nutrients, for example due to intestinal nematode worms and anorexia mediated by inflammatory cytokines released as a response to all infections.²⁶⁵ Loss of appetite may make an important contribution to the development of undernutrition and may be exacerbated if the caregiver's response, is to withhold food or, for reasons of culture or poverty, give a nutritionally poor diet ²⁶⁶, and although it may be an important protective response in acute infection, the effects during repeated infection or chronic disease may eventually be harmful.²⁶⁷ Stunted growth and underweight in children are probably among the most important consequences of STHs.²⁷

72 The relationship between intestinal parasitic infections and nutritional status in 400 Mexican schoolchildren was investigated and was found that more than half of the children in the study showed intestinal parasites and polyparasitism.⁶⁶ A significantly higher Z score for weight-for-height (WH), WA, and HA were found in non-infected versus infected children (P < 0.05).

Higher prevalence of intestinal infections were found in children with lower HA and WA than in normally nourished children (P < 0.05). Negative and significant associations were found between Hymenolepis nana and T. trichiura infection (eggs per gram) and nutritional status and it was concluded that intestinal parasitic infections may be regarded as main risk factors associated with poor nutritional status in Mexican schoolchildren.⁶⁶A survey conducted in 1074 grade 5 children (mean age 10 years) from 17 schools in Belen, Peru, a community of extreme poverty reported that hookworm infection (OR=1.74; 95% CI: 1.05, 2.86) was among the significant independent risk factors for stunting and underweight while anaemia (OR=1.98;

95% CI: 1.26, 3.11) and moderate and heavy Trichuris and Ascaris co-infection (OR=1.95;

95% CI: 1.35, 2.82) were among the significant independent risk factors for stunting only.¹⁷⁹ Parasitic worms contribute to anaemia, especially iron-deficiency anaemia, among children in Sub-Saharan Africa, the predominant species being the hookworms (which inhabit the gut) and Schistosoma species (which inhabit the blood vessels surrounding the gut and bladder).²⁶⁸ Hookworm adhere to gut mucosa, feed on blood, and leave areas of intraluminal microhaemor-rhage when they detach. Daily blood loss due to A. duodenale is estimated at 0.2 ml per worm, equivalent to 100 ml in heavy infections. This is about 10 times greater than with N.

americanus infection, and surveys in Africa confirm that anaemia is more common with A.

duodenale infection.²⁶⁹ Blood loss during whipworm infection comes mainly from the inflamed gut mucosa, and at 8.6 ml/day is less than with hookworm. Blood loss is not typical of roundworm infection, and it is unclear whether the low serum retinol and serum ferritin concentrations associated with fat malabsorption result in anaemia.²⁵⁷ There is no constant

73 linear relationship between worm load and the haemoglobin concentration as the amount of iron in the diet and its absorption efficiency, which typically ranges from 5% to 25%

depending on its dietary quality can serve to counterbalance blood loss up to a point, although other micronutrients are required as well for haemopoiesis.²⁷⁰

School-aged children are particularly vulnerable to iron deficiency anaemia exacerbated by parasitic infection because they typically harbour the heaviest worm loads in communities.²⁶⁸ An intervention survey of school children in rural Malaysia reported that baseline haemoglobin level was significantly lower among the moderate-to-heavy infected children compared to the negative-to-light infected children. Less than 10 years old and moderate-to-heavy ascariasis were the predictors of anaemia. Stunting was also associated with moderate-to-heavy ascariasis and trichuriasis. Three months post-treatment assessment showed that the moderate-to-heavy infected children gained significant increment in their mean Hb level compared to the negative-to-light infected children (0.44 g/dl compared to 0.08 g/dl).⁶⁷

Among school children in Zanzibar, analysis of the association between hookworm and anaemia suggested that 25% of all anaemia cases, 35% of iron deficiency anaemia cases and 73% of severe anaemia cases could be attributed to hookworm infection and hookworm has been shown to contribute more than schistosomiasis or even malaria to iron deficiency anaemia in school-aged children.²⁶⁸ In areas of high prevalence of infection in East Africa, 15-25% of anaemia in schoolchildren was due to hookworm infection.⁹⁹ In Brazil, it was shown that haemoglobin and serum ferritin were both significantly negatively associated with hookworm intensity among both school-aged children and adults. Multivariate analysis showed that, after controlling for socio-economic status, iron indicators were significantly associated with heavy hookworm infection indicating that even in areas where there is a low overall prevalence of

74 anaemia; hookworm can still have an important impact on host iron status, especially in school-aged children and the elderly.²⁷¹

Several studies done in Nigeria amongst school children have reported the association between helminthic infestation and anaemia and have found significant association between them, for example, that of Plateau State in which it was reported that prevalence rate of hookworm infection is inversely related to blood level in the children³⁸,and that carried out among 316 children aged 1-15 year in Edo State where they reported that there was a statistically significant association between hookworm and Ascaris lumbricoides infection and anaemia (P

< .001).⁶²

Recent studies on relationship between STH, anaemia and nutritional status showed that STH infections, anaemia and malnutrition are still prevalent and a matter of public health concern and reported that helminthic infections are significantly associated with nutritional status and anaemia.^65-68