Consequences of polyparasitism on anaemia among primary school children in Zimbabwe

Abstract

The effect of concomitant infection with schistosomes, Plasmodium falciparum and soil transmitted helminths (STHs) on anaemia was determined in 609 Zimbabwean primary school children. P. falciparum, haemoglobin levels and serum ferritin were determined from venous blood. Kato Katz, formal ether concentration and urine filtration techniques were used to assess prevalence of Schistosoma mansoni, STHs and Schistosoma haematobium infections. The prevalence of S. haematobium, S. mansoni, P. falciparum, hookworm, Trichuris trichiura and Ascaris lumbricoides were 52.3%, 22.7%, 27.9%, 23.7%, 2.3% and 2.1%, respectively. The overall prevalence of anaemia and iron deficiency anaemia (IDA) were 48.4% (277/572) and 38.1% (181/475). Haemoglobin levels among children who had P. falciparum, S. haematobium and hookworm were lower than negative individuals, p < 0.001, p < 0.001 and p = 0.030, respectively. The prevalence of anaemia and IDA in co-infections was almost double that in single infection. Children with P. falciparum/STHs/schistosome and schistosomes/P. falciparum co-infections recorded higher prevalence of anaemia and IDA (80.8% and 57.4%, respectively) than other combinations, p < 0.001. Logistic regression revealed that, age group ≥ 14years, P. falciparum, S. haematobium light and heavy infections, and S. mansoni moderate and heavy infection, hookworm light infection were predictors of anaemia. This study suggests that integrated school based de-worming and malaria control have the potential to reduce the burden of anaemia.

Introduction

Concomitant infection with Plasmodium falciparum, STH and schistosomes is common in tropical and sub-tropical countries due to geographic overlap of climatic and socio-economic conditions that support survival of STHs, reproduction of malaria parasites’ vectors and schistosomiasis intermediate host snails (Tshikuka et al., 1996, Brooker et al., 2007, Midzi et al., 2008). In Africa alone, about a quarter of school children may be at risk of co-infection with P. falciparum and helminths (Brooker et al., 2006, Brooker et al., 2007). They are also at risk of anaemia that reduces their cognitive potential, retard growth and predisposes them to other diseases (WHO, 2001). Although the etiologic factors of anaemia are complex including dietary insufficiency of iron, haemoglobinopathies, other micronutrient deficiencies (vitamin A, B₁₂, folate and riboflavin), several studies have demonstrated the contribution of parasitic infections to anaemia. Results from meta-analysis and community based studies on malaria provide compelling evidence that malaria contributes substantially to anaemia (Geerligs et al., 2003, Korenromp et al., 2004, Ronald et al., 2006, Clarke et al., 2008). Hookworm has been shown to be an important risk factor for anaemia (Stoltzfus et al., 1997, Brooker et al., 1999). Olsen et al observed that hookworm egg intensity as low as 300 eggs/g stool was negatively related to levels of haemoglobin and serum ferritin (Olsen et al., 1998). The mechanisms by which schistosomiasis cause anaemia have been described by Freidman et al. (2005). Whilst some extensive field studies have failed to demonstrate any significant effect of schistosomiasis infection on haemoglobin (Hb) levels (Befidi-Mengue et al., 1993), several other studies have highlighted a significant effect of schistosomiasis on Hb levels and anaemia (Stephenson et al., 1985, Prual et al., 1992, Koukounari et al., 2007).

Although schistosomes, STHs and P. falciparum are separately known etiological factors of anaemia with distinct mechanisms which reduce haemoglobin levels in human hosts (Menendez et al., 2000, Hotez et al., 2004, Freidman et al., 2005), data are still lacking on the effect of their coincidental infection on the level and severity of anaemia (Hotez et al., 2006, Midzi et al., 2008). Several studies have only explored the effect of single parasitic infections (Flemming et al., 2006, Koukounari et al., 2006), mixed infections with schistosomiasis and STH (Guyatt et al., 2001), STHs and P. falciparum (Koukounari et al., 2006) or multiple STHs infection on anaemia (Ezeamama et al., 2005). Studies on the impact of schistosomes, STHs and P. falciparum co-infection on anaemia, particularly in primary school children are relevant for the design and implementation of integrated control programmes aimed at reducing anaemia and other associated morbidities.

Zimbabwe is endemic for schistosomiasis, soil transmitted helminthiasis and malaria that pose a public health problem (Taylor and Makura, 1985, Chandiwana et al., 1989, Mutapi et al., 2000). This study was therefore conducted to determine the effect of malaria, schistosomiasis and STHs co-infection on the level of anaemia and also to identify predictors of anaemia among primary school children living in an area where P. falciparum, schistosome and STHs are co-endemic (Brooker et al., 2007).