Schistosomiasis, also known as Bilharzia, is a chronic debilitating disease, whose public health importance is second to malaria as the most common parasitic condition in Africa (National Institute of Communicable Diseases (NICD), 2018). Two main species of schistosomes infect human beings in Africa - Schistosoma haematobium and Schistosoma mansoni with each species determined by presence of a suitable snail host and its distribution. About 4 million people, mostly children, are infected with schistosomiasis in South Africa (NICD, 2018). Schistosomiasis is transmitted to humans through contact with contaminated water during bathing, swimming, fishing and domestic chores. Thus, the disease is more prevalent in coastal and rural areas of South Africa where there is no running or tap water (Global Atlas of Helminth Infections, 2017). Incidentally, the prevalence of schistosomiasis overlaps with that of soil-transmitted helminths (Global Atlas of Helminths Infections, 2017). The prevalence of soil-transmitted helminths (STH) in KwaZulu Natal is estimated at 38.8% in school aged children (Molvick et al., 2017).
Parasitic worms affect human nutrition and growth through a number of routes depending on the species, the mixture of species, the duration of infection and number of worms (Munŏz-Antoli, Parỏn, Pérez, Toledo, & Estenban, 2017). For instance, intestinal worms feed on the contents of the host’s gut and tissues including blood and serum resulting in loss of iron and protein. They can cause maldigestion or malabsorption of the nutrients or induce inflammatory responses that may affect appetite and food intake thereby modifying metabolism and storage of key nutrients. Additionally, contingent responses to infection such as fever and hypertrophy of the muscles also affect behaviour, concentration levels and changes anthropometric status (Munŏz-Antoli, Parỏn, Pérez, Toledo, & Estenban, 2017). The effect of schistosomiasis and STH on cognitive function could occur as a result of one or a combination of symptoms associated with parasitic infection including iron deficiency anaemia. Since early childhood is a period of rapid growth and development of all organ sytems, particularly the brain, early life iron deficiency results in abnormal neuronal structure. Hence, schistosomiasis has been associated with negative effects on school attendance, scholastic achievement, learning and memory (Ezeamama, Bustinduy, Nkwata, Martinez, Pabalan, Boivin & King, 2018).
Studies investigating effects of STH infections (Stoltzfus, Kvalsvig, Chwaya, Montressor, Albonico et al., 2001) as well as malaria and anaemia(Dellis, 2010) on neurological development have reported delayed motor and speech development. Neurological consequences are reported even in non-anaemic deficiencies where the potential for learning is reduced due to poor recognition memory and executive functions of infected learners (Luwoski, Koss, Burden, Jonides, Nelson et al., 2010). Early treatment of children with parasitic infections could potentially mitigate the memory and learning deficits in preschool children (Ezeamama, et al., 2018). There is also empirical evidence indicating cognitive and educational benefits of STH treatment (Pabalan, Singian, Tabangay et al., 2018).
Since infection with STH and schistosomiasis are confounding factors to cognitive impairment and developmental delays in communities with poor water and sanitation, there is a knowledge gap on whether STH and schistosomiasis have the same effect on expressive language skills as much as they may have on other cognitive skills. Our study aimed at determining the effect of schistosomiasis and STH on expressive language skills among isiZulu speaking pre-schoolers. We determined the profile of expressive language skills of isiZulu speaking preschool children in terms of age, gender, school, stunting and parasitic infection; and compared expressive language skills for children with and without schistosomiasis and STH.
The knowledge we have on isiZulu grammatical pattern is limited, achronological and has not yet produced developmental language norms for receptive and expressive language (Van der Merwe & Le Roux, 2014). We know that isiZulu, like Turkish and Finnish, has characteristically agglutinating morphology and in many ways isiZulu is different from English (Keet & Khumalo, 2016). Data collected from similar Nguni languages such as isiXhosa showed that trilingual and monolingual children had similar lexical development in the languages the children were exposed to (Potgieter, 2016). Expressive language builds up from nouns to verbs, adjectives, adverbs, prepositions, conjunctions and auxiliary verbs (Gonasilan, Bornman & Harty, 2013). Typical emergent skills for expressive language are memory, time-based relations, cause and effect reasoning, social script, sense of self and vocabulary which lead to learning colours, questions and narrative skills can all be achieved as early as 36 months (Phillips, 2008).
Expressive language development is usually described using the standards set in English according to the Brown’s stages of syntactic and morphological development where children begin to express their thoughts in single words around 12 months and achieve full sentences and narrative skills by 5 years (Bowen, 1998). By the age of 5 years children are usually enrolled in a preschool where early identification of at-risk children and the provision of appropriate interventions and support can substantially affect future scholastic progress (Wildschut, Moodley & Aronstam, 2016). Since attendance of grade R has been found to influence literacy development, we decided to determine expressive language skills in children attending a preschool (Daws, Biersteker, Girdwood, Snelling & Tredaux, 2018).
The main risks associated with expressive language development in English speaking children has been shown to include a variety of factors such as family dynamics, interaction with parents, immediate social environment, organic hazards such as brain injury, persistent otitis media, types of food (Gurger, Vidor, Joly & Reppold, 2014), a reactive temperament and being male (Harrison & McLeod, 2010). Hence, we examined the effect of age, gender, school and status of infection with schistosomiasis and STH on expressive language skills in our sample.