Annette Olsen

Strongyloidiasis - the most neglected of the neglected tropical diseases?

Soil-transmitted helminths of the genus Strongyloides (S. fuelleborni and the more prevalent S. stercoralis) are currently believed to infect an estimated 30-100 million people worldwide. The health consequences of S. stercoralis infections range from asymptomatic light infections to chronic symptomatic strongyloidiasis. Uncontrolled multiplication of the parasite (hyperinfection) and potentially life-threatening dissemination of larvae to all internal organs is found among individuals with compromised immune system functions. This paper provides an overview of the current state of the art in relation to diagnostic methods for detecting the infection, the morbidity caused by the infection and the recommended treatment. It further discusses some of the reasons why this infection is so neglected and the consequence of this for the estimated global prevalence. The paper finally points to the gaps in our knowledge and future research needs related to this infection. As Strongyloides infections have the potential to develop into severe disease in certain population subgroups, untreated infections could cause serious problems in the community. Therefore, we need to carefully investigate this parasite in order to develop and implement effective control programmes.

Low technology water purification by bentonite clay and Moringa oleifera seed flocculation as performed in sudanese villages: effects on Schistosoma mansoni cercariae

Schistosoma mansoni cercariae were removed from clear and turbid water by flocculation with Sudanese bentonite clays, with Moringa oleifera seeds as well as with pure bentonite. The flocculation technique employed corresponds to that used to clarify Nile water in Sudanese villages. Moringa seeds, pure bentonite and one type of bentonite clay were able to reduce the number of cercariae by more than 90%.

The contribution of hookworm and other parasitic infections to haemoglobin and iron status among children and adults in western Kenya

A cross-sectional study of 729 children and adults in western Kenya investigated the impact of infection with hookworm, Ascaris lumbricoides, Trichuris trichiura, Schistosoma mansoni and malaria on iron status. In bivariate analyses, hookworm intensities as low as 300 eggs/g of faeces were negatively related to levels of haemoglobin (Hb) and serum ferritin (SF). Malaria parasitaemia was negatively related to Hb and positively related to SF, while S. mansoni intensities were negatively related to SF. Multivariate regression analysis was done to identify predictors of Hb and SF levels. In children, age (in years) was the only predictor for Hb (B = 1.7 g/L) and only malaria parasitaemia (negative, light, moderate, heavy) was retained in the model for log10 SF (B = 0.097 microgram/L). In adults, hookworm infection and malaria parasitaemia together with age, sex, pregnancy, SF levels < 12 micrograms/L and elevated body temperature were significant predictors of low Hb. The regression coefficient for hookworm egg count (for increments of 100 eggs/g) was -1.3 g/L. Significant interactions between sex and age and between sex and malaria parasitaemia were revealed. Age and malaria parasitaemia were significant predictors only among females, with a regression coefficient for malaria parasitaemia of -6.9 g/L. The regression coefficient for hookworm did not change when SF < 12 micrograms/L was taken out of the model, indicating that the effect of hookworm cannot be explained by low iron stores alone. Using SF as the dependent variable, hookworm and S. mansoni intensities together with age and sex were retained in the model. The regression coefficients for hookworm egg count (increments of 100 eggs/g) and S. mansoni egg count (increments of 10 eggs/g) were -0.011 microgram/L and -0.012 microgram/L, respectively. Iron deficiency was a problem in this population and hookworm infections contributed significantly to this situation.

Remote sensing, geographical information system and spatial analysis for schistosomiasis epidemiology and ecology in Africa

Beginning in 1970, the potential of remote sensing (RS) techniques, coupled with geographical information systems (GIS), to improve our understanding of the epidemiology and control of schistosomiasis in Africa, has steadily grown. In our current review, working definitions of RS, GIS and spatial analysis are given, and applications made to date with RS and GIS for the epidemiology and ecology of schistosomiasis in Africa are summarised. Progress has been made in mapping the prevalence of infection in humans and the distribution of intermediate host snails. More recently, Bayesian geostatistical modelling approaches have been utilized for predicting the prevalence and intensity of infection at different scales. However, a number of challenges remain; hence new research is needed to overcome these limitations. First, greater spatial and temporal resolution seems important to improve risk mapping and understanding of transmission dynamics at the local scale. Second, more realistic risk profiling can be achieved by taking into account information on peoples socio-economic status; furthermore, future efforts should incorporate data on domestic access to clean water and adequate sanitation, as well as behavioural and educational issues. Third, high-quality data on intermediate host snail distribution should facilitate validation of infection risk maps and modelling transmission dynamics. Finally, more emphasis should be placed on risk mapping and prediction of multiple species parasitic infections in an effort to integrate disease risk mapping and to enhance the cost-effectiveness of their control.

Geophagy and its association with geohelminth infection in rural schoolchildren from northern KwaZulu-Natal, South Africa

The social pattern of geophagy (soil-eating) and its possible role in the transmission of Ascaris lumbricoides, Trichuris trichiura and hookworm were investigated in a rural area of South Africa between March 1998 and July 1999. Schoolchildren (median age = 10.7 years; interquartile range 8.3-14.8 years) were examined for geohelminth infection at baseline and re-examined 3 and 29 weeks after treatment with albendazole. Interviews were conducted with the pupils in order to find out about their socio-economic background and their behaviour regarding geophagy. Soil-eating was less frequent in boys (39%), where it decreased with age, than in girls (53%), where no such age trend was apparent. The habit was more common in children from families of higher socio-economic status. The baseline prevalence of A. lumbricoides infection was higher in pupils who regularly ate soil from termite mounds (28%) when compared with non-geophageous pupils (19%; prevalence ratio (PR) = 1.46; 95% confidence interval (95% CI) 1.04-2.03). In contrast it was markedly lower in the groups who preferred eating tree termite soil (13%; PR = 0.67; 95% CI 0.43-1.04) or soil from other sources (8%; PR = 0.40; 95% CI 0.15-1.04). This pattern was still apparent after adjusting for possible confounders and was also found when analysing A. lumbricoides reinfection. In contrast, differences in prevalence of T. trichiura and hookworm infection between groups with different soil preference were small.

Effects of iron and multimicronutrient supplementation on geophagy: a two-by-two factorial study among Zambian schoolchildren in Lusaka

Geophagy has been associated with iron deficiency and anaemia, but no causal relationship has been established. To clarify this, we conducted a two-by-two factorial randomised, controlled trial on the effect of iron and multimicronutrient supplementation on geophagy in Zambian schoolchildren in Lusaka, from February to December 2001. Of the 406 children, 212 (52.2%) were girls and the mean (range) age was 10.2 (7-15) years. Geophagy was reported by 302 (74.4%) and more often in girls than in boys (80.2 vs. 67.7%, P = 0.007). The mean (range) daily earth intake was 25.2 (1-200) g. Geophageous children had more often geophageous relatives than non-geophageous children (79.5 vs. 1.9%, P < 0.001). Geophageous children had lower serum ferritin (20.5 vs. 25.0 microg/l, P = 0.032) but not haemoglobin (Hb) (129.2 vs. 130.4 g/l, P = 0.59), than non-geophageous. Among those with Hb < 130 g/l, geophageous children had significantly higher prevalence (53.7 vs. 30.6%, P = 0.024) of Ascaris lumbricoides infection than non-geophageous. The prevalence of geophagy (74.4 to 51.6%) and the intake of earth (25.3 to 15.0 g/day) declined (P = 0.001 and P < 0.001, respectively) among the 220 (54.2%) children followed-up. In bivariate analysis, non-iron supplementation reduced the prevalence of geophagy more than iron supplementation did, but this was not confirmed in the multiple logistic regression analysis. Multimicronutrients had no effect on either geophagy prevalence or earth intake. Geophagy was prevalent and associated with iron deficiency, but iron supplementation had no effects on geophageous behaviour. Geophagy could be a copied behaviour and the association between geophagy and iron deficiency due to impaired iron absorption following earth eating.

Prevalence of fishborne zoonotic parasites in important cultured fish species in the Mekong Delta, Vietnam

A seasonal investigation on the occurrence of fishborne zoonotic trematodes (FZT) in economically important mono-cultured hybrid catfish and giant gouramy was conducted in the Mekong Delta of Vietnam. Fish from carp poly-culture and intensive small-scale integrated vegetable–aquaculture–animal husbandry farming (VAC) systems were also examined. No FZT metacercariae were found in any mono-cultured hybrid catfish. FZT metacercariae were common, however, in fish from the other three systems: All metacercariae belonged to the Heterophyidae family of trematodes, Haplorchis pumilio, H. taichui, Centrocestus formosanus and Stellantchasmus falcatus. The FZT prevalence was 1.7% in mono-cultured giant gouramy, 6.6% in carp from the poly-culture and 3.0% in fish raised in the VAC system. H. pumilio was the most common FZT species constituting more than 58.0% of all metacercariae recovered. The prevalence of infection was significantly higher in the flooding season compared to the non-flooding season for both giant gouramy and fish reared in the VAC system. FZT intensity was greatest in fish from carp poly-culture, particularly in the flooding season. The results indicate that certain fish production systems are at risk for FZT, and control approaches will benefit from understanding these risk factors.

Patterns of Schistosoma haematobium infection, impact of praziquantel treatment and re-infection after treatment in a cohort of schoolchildren from rural KwaZulu-Natal/South Africa

BackgroundSchistosomiasis is one of the major health problems in tropical and sub-tropical countries, with school age children usually being the most affected group. In 1998 the Department of Health of the province of KwaZulu-Natal established a pilot programme for helminth control that aimed at regularly treating primary school children for schistosome and intestinal helminth infections. This article describes the baseline situation and the impact of treatment on S. haematobium infection in a cohort of schoolchildren attending grade 3 in a rural part of the province.MethodsPrimary schoolchildren from Maputaland in northern KwaZulu-Natal were examined for Schistosoma haematobium infection, treated with praziquantel and re-examined four times over one year after treatment in order to assess the impact of treatment and patterns of infection and re-infection.ResultsPraziquantel treatment was highly efficacious at three weeks after treatment when judged by egg reduction rate (95.3%) and cure rate of heavy infections (94.1%). The apparent overall cure rate three weeks after treatment (57.9%) was much lower but improved to 80.7% at 41 weeks after treatment. Re-infection with S. haematobium was low and appeared to be limited to the hot and rainy summer. Analysis of only one urine specimen per child considerably underestimated prevalence when compared to the analysis of two specimens, but both approaches provided similar estimates of the proportion of heavy infections and of average infection intensity in the population.ConclusionAccording to WHO guidelines the high prevalence and intensity of S. haematobium infection necessitate regular treatment of schoolchildren in the area. The seasonal transmission pattern together with the slow pace of re-infection suggest that one treatment per year, applied after the end of summer, is sufficient to keep S. haematobium infection in the area at low levels.

Patterns of geohelminth infection, impact of albendazole treatment and re-infection after treatment in schoolchildren from rural KwaZulu-Natal/South-Africa.

BackgroundGeohelminth infection is a major health problem of children from rural areas of developing countries. In an attempt to reduce this burden, the Department of Health of the province of KwaZulu-Natal (KZN) established in 1998 a programme for helminth control that aimed at regularly treating primary school children for schistosomiasis and intestinal helminths. This article describes the baseline situation and the effect of treatment on geohelminth infection in a rural part of the province.MethodsGrade 3 schoolchildren from Maputaland in northern KZN were examined for infections with hookworm, Ascaris lumbricoides, and Trichuris trichiura, treated twice with 400 mg albendazole and re-examined several times over one year after the first treatment in order to assess the impact of treatment and patterns of infection and re-infection.ResultsThe hookworm prevalence in the study population (83.2%) was considerably higher than in other parts of the province whereas T. trichiura and especially A. lumbricoides prevalences (57.2 and 19.4%, respectively) were much lower than elsewhere on the KZN coastal plain. Single dose treatment with albendazole was very effective against hookworm and A. lumbricoides with cure rates (CR) of 78.8 and 96.4% and egg reduction rates (ERR) of 93.2 and 97.7%, respectively. It was exceptionally ineffective against T. trichiura (CR = 12.7%, ERR = 24.8%). Re-infection with hookworm and A. lumbricoides over 29 weeks after treatment was considerable but still well below pre-treatment levels.ConclusionHigh geohelminth prevalences and re-infection rates in the study population confirm the need for regular treatment of primary school children in the area. The low effectiveness of single course albendazole treatment against T. trichiura infection however demands consideration of alternative treatment approaches.

The impact of iron supplementation on reinfection with intestinal helminths and Schistosoma mansoni in western Kenya

A randomized, placebo-controlled, double-blind trial was carried out in 1994-96 among 231 children and 181 adults in order to determine the effects of iron on reinfection rates and intensities of hookworm, Ascaris lumbricoides, Trichuris trichiura and Schistosoma mansoni. Adults given 60 mg elemental iron twice-weekly for 12 months had significantly lower reinfection rates of A. lumbricoides (16.7% vs 31.9%, P = 0.046), T. trichiura (6.9% vs 20.6%, P = 0.03) and S. mansoni (38.3% vs 61.8%, P = 0.008) compared to adults given placebo. In contrast, adults allocated to iron had a significantly higher reinfection rate of hookworm at the 4-month examination (11.1% vs 0%, P = 0.009), but the difference was not significant at 8- and 12-month follow-up examinations. Iron supplementation had no effect on reinfection intensities in adults. Surprisingly, iron supplementation had no effect on either reinfection rates or intensities in children. Multiple logistic regression analyses controlling for baseline infection status confirmed the effect in adults of iron on A. lumbricoides, T. trichiura and S. mansoni reinfection rates. The effect is suggested to be due to reduced risk behaviour, to improved immune function or to unfavourable host gut conditions caused by an increased oxidative stress. In each case, the lack of effect in children remains to be explained. In contrast, iron supplementation apparently was short-lived in favour of hookworm infection, an effect that needs further clarification. The findings suggest that iron supplementation has a role to play in helminth control programmes and that intraluminal factors may contribute to the regulation of some helminth infections.