CHAPTER I
INTRODUCTION
Helminthiasis in the Philippines is caused by infection of Ascaris lumbricoides, Trichuris trichiura, and hookworms, such as Necator americanus and Ancylostoma duodenale. Its impact on host health results in morbidity, malnutrition, abdominal pain, blood loss, and impaired cognitive ability (Parija et al. 2017). These sources of discomfort may result in poor health outcomes, hindering proper neurodevelopment and cognitive function in school children.
School children remain the most vulnerable due to their nutritional needs and may be prone to absenteeism and lower performance in academics if afflicted with parasitic infections (Belizario et al. 2013). Poor achievement in school may impede an individual’s productivity, increasing the risk of poverty and narrowing the opportunities to participate in civic life (Javed et al. 2016).
According to a nationwide survey in 2003, 16 out of 17 regions in the Philippines have a prevalence rate of at least 50 percent for soil-transmitted helminth infection in children between the ages of 1-6 years old, reflecting the need to continue mass deworming in children (Department of Health 2005). Efforts to mitigate the detrimental effect of the parasitic infection relies on the improvement
of sanitation infrastructure, access to clean water, and awareness of proper hygienic practices (Belizario et al. 2013). The adverse features of soil-transmitted helminth (STH) infection on the mental function of children are not clearly understood (Pabalan et al. 2018). Symptoms such as malnutrition, anemia, abdominal pain and diarrhea may cause discomfort and impair a child’s ability to concentrate, resulting in poor cognitive performance. Evaluating the association between STH infection and cognition provides the foundations to develop a strategy that can reduce disease transmission.
Previous research demonstrates that the presence of STH infection may be associated with lower cognitive test performance. Literature reveals that infection with A. lumbricoides in Brazilian children yields poorer cognitive outcomes than children without infection. This is due to its debilitating effects on host health, causing reduced food consumption, malabsorption of essential nutrients and intestinal tract damage. An individual’s ability to analyze complex situations and recall acquired information is reduced by the burden of infection (Jardim-Botelho et al. 2008). Similarly, Filipino children who were infected with A. lumbricoides and hookworms were found to have lower scores in cognitive assessments that measured memory compared to those who were uninfected. Results suggest that abdominal discomfort may be a contributing factor as this impact is sufficient to distract children from cognitive tasks (Ezeamama et al. 2006). In studies examining T. trichiura infection in children, clinical trials suggest that helminthiasis with this
species may also result in lower cognitive performance in measures of memory, visual processing, and learning (Simeon et al. 1995). It also suggests that while performance is hindered, the consequences of helminthiasis may not be significant if children receive adequate nutrition or have low levels of infection. These trials indicate that presence of infection should be accompanied by measures of infection intensity and nutritional status to observe significant impairment and assess the effectiveness of anti-parasitic treatments (Nokes et al. 1992; Simeon et al. 1995).
Literature in Southeast Asia and Brazil that investigated the link between hookworm infection and cognitive impairment in school children reinforces the importance of physiology to identify host-parasite relationships. Indonesian children infected with hookworm were found to perform worse than uninfected children in visual and auditory memory as well as attention and decision making.
A decrease in mental ability may be due to anemia and malnutrition where both conditions are associated with poorer performance on cognitive tests (Sakti et al.
2002). Iron-deficiency anemia, as a result of hookworm infection, was examined further in Brazilian school children. It proposed the mechanism that governs the link between anemia status and cognition as lower levels of hemoglobin may reduce an individual’s ability to work and concentrate (Jardim-Botelho et al. 2008). While previous studies were able to determine associations between helminthiasis and cognition, research examining the role of helminth infection and academic
performance yielded inconclusive results or found weak relationships (Pabalan et al. 2018).
This study provides an analysis of the relationship between STH infections and cognitive functions of school children. It examines the presence of STH infection and investigates the influence of each helminth species on academic performance defined through three domains: memory, learning, and reaction time.
The impact of helminthiasis on the cognitive domains is not assessed according to species and assumes that effects exerted by each species on cognition are equal.
The results obtained were used to develop suggestions that will enhance current health education and deworming programs that exist in the Philippines. The foundation for these proposed measures synthesizes the health and cognitive outcomes of helminthiasis to modify initiatives that can improve the wellbeing and academic performance of school children. Despite the existing literature used to investigate the associations between cognition and helminth infection, previous data have produced mixed and inconclusive results (Dickson et al. 2000; Taylor- Robinson et al. 2012). Lack of consensus requires further investigation on whether helminthiasis contributes to cognitive impairment.
Objectives
Exploring the presence of STH infection in school children between the ages of 3-15 years old and its influence on cognitive function provides the most efficient method to mitigate its impact on human health. This study aimed to:
1. to assess the physiological effects of helminth infection in school children;
2. to evaluate the presence of infection by investigating the influence of STH species on academic performance;
3. to identify control initiatives applicable in the Philippine setting that can alleviate the influence of helminthiasis on the health and cognition of children.
Scope and Limitations
This is a meta-analysis that seeks to understand the mechanisms that govern parasitic infections in individuals that result in cognitive impairment.
1. Domains such as verbal fluency and non-verbal intelligence that are used to assess cognitive function are not included in quantifying infection effects.
2. Hookworm species are not differentiated into Necator americanus and Ancylostoma duodenale and are considered as a single species.
3. Polyparasitism with other parasitic species and co-infection with other diseases that could occur in school children are not included.
4. Academic performance is defined as three variables: memory, learning, and reaction time.