CHAPTER IV
RESULTS AND DISCUSSION
Results
Methodological Quality
Studies included in the risk of bias assessment are shown in Figures 5 and 6 where unclear risk bias, low risk of bias and high risk of bias is indicated as yellow, green, and red, respectively. Four studies out of 21 did not describe their randomization methods (Sternberg et al. 1997; Jardim-Botelho et al. 2008;
Simarma et al. 2015). Performance and detection bias were present in two studies for their respective interventions not blinded to participants and personnel as well as of outcome assessment (Sari et al. 2012). Additionally, three studies had incomplete data (Jardim-Botelho et al. 2008; Sari et al. 2012; Edwina et al. 2016).
All studies reported details on allocation concealment.
Figure 5. Risk of bias summary
Figure 6. Risk of bias graph
Physiological Effects
The meta-analysis showed that infection with T. trichiura was not associated with a higher likelihood of malnutrition compared to uninfected groups in school age children (OR: 2.76, 95% CI: 0.35-21.79, Figure 7). Similar results were seen when analyzing A. lumbricoides (OR: 1.14, 95% CI: 0.81-1.59, Figure 8) and hookworm (OR: 1.02, 95% CI: 0.70-1.50, Figure 9), where infection of either species was not associated with a higher likelihood of malnutrition compared to uninfected groups in school children. The pooled effects showed that studies on T. trichiura and A. lumbricoides were highly heterogeneous, displaying a large variation in outcomes measuring for nutrition status. Variation may be attributed to the different age groups of school children observed in cross-sectional studies.
Figure 7. Meta-analysis examining the association of T. trichiura infection with malnutrition
Figure 8. Meta-analysis examining the association of A. lumbricoides infection with malnutrition
Figure 9. Meta-analysis examining the association of hookworm infection with malnutrition
No significant association was found between infection with A.
lumbricoides and a higher likelihood of anemia compared to uninfected groups in school age children (OR: 1.79, 95% CI: 0.40-7.90, Figure 10). Conversely, infection with hookworms was significantly associated with a higher likelihood of anemia compared to uninfected groups (OR: 1.62, 95% CI: 0.1.05-2.52, figure 11).
The pooled effects show that studies of A. lumbricoides were highly heterogeneous, indicating a large variation in the measured outcomes. Studies of hookworm infection in the meta-analysis showed no heterogeneity, indicating no variation in the measured outcomes. No variation was seen across all hookworm infection studies due to the association of younger age groups with a greater prevalence of anemia.
Figure 10. Meta-analysis examining the association of A. lumbricoides infection with anemic status
Figure 11. Meta-analysis examining the association of hookworm infection with anemic status
Cognitive function Memory
In the comparison of infected and uninfected groups for cognitive function, a total of three studies were included in the memory domain meta-analyses.
Heterogeneity was not found to be statistically significant for all three tests assessing memory: digit span forwards (I2 = 48%, Pheterogeneity = 0.11), digit span backwards (I2 = 0%, Pheterogeneity = 0.55), and corsi block (I2 = 0%, Pheterogeneity = 0.91), indicating no variability in the results of the studies. No variation was present as there was little spreading of data sets across studies. The T-test for the studies under each cognitive test was conducted using the fixed-effects model. The uninfected group scored higher than the infected group in the digit span forwards test (Figure 12) and pooled results found this to be statistically significant (Z = 4.20, P-value < 0.0001, mean difference = 0.51, 95% CI: 0.27 to 0.75). Similarly, pooled results for the digit span backwards test (Figure 13) showed that there is a significant difference between the infected and uninfected groups. (Z = 2.32, P- value = 0.02, mean difference = 0.30, 95% CI: 0.05 to 0.55). The uninfected group also scored higher than the infected group in the corsi block test (Figure 14) however pooled results showed that this did not reach statistical significance (Z = 0.28, P-value = 0.78, mean difference = 0.06, 95% CI: -0.35 to 0.47), indicating no significant difference in the scores between the two groups.
Figure 12. Meta-analysis examining the association between STH infection and digit span forwards test for memory in infected and uninfected groups
Figure 13. Meta-analysis examining the association between STH infection and digit span backwards test for memory in infected and uninfected groups
Figure 14. Meta-analysis examining the association between soil-transmitted helminth infection and corsi block test for memory in infected and uninfected groups
A total of five studies were included in the meta-analyses for comparison between groups that received anthelmintic treatment and groups that received identical placebo. Heterogeneity was found to be statistically significant for both digit span forwards (I2 = 92%, Pheterogeneity = < 0.00001) and digit span backwards (I2 = 96%, Pheterogeneity = < 0.00001) tests, indicating variability in the results of the studies. Variation was present due to greater spreading of data sets across studies.
The T-test for the studies under each cognitive test was conducted using the random effects model. The treatment group scored higher than the placebo group in three
of the five studies under the digit span forwards test (Figure 15), however pooled results showed that there is no significant difference between the treatment and placebo group (Z = 1.19, P-value = 0.24, mean difference = 0.38, 95% CI: -0.25 to 1.00). Only one of the three studies under digit span backwards showed a treatment group that scored higher than the placebo group (Figure 16); pooled results also found no significant difference between the treatment and placebo group (Z = 0.14, P-value = 0.89, mean difference = 0.06, 95% CI: -0.77 to 0.88).
Figure 15. Meta-analysis examining the association between STH infection and digit span forwards test for memory in treatment and placebo groups
Figure 16. Meta-analysis examining the association between STH infection and digit span backwards test for memory in treatment and placebo groups
Learning
Two studies were included in the learning domain meta-analysis for the comparison between infected and uninfected groups (Figure 17). Heterogeneity was found to be statistically significant (I2 = 89%, Pheterogeneity < 0.0001), indicating variability in the results of the studies. Variation was present as there is greater spreading of data sets across studies. The T-test for studies assessing learning ability through the Raven’s test was conducted using the random effects model. The pooled results showed that there is no significant difference in the scores for the Raven’s test between the infected and uninfected groups (Z= 1.33, P-value = 0.18, mean difference = 5.52, 95% CI: -2.64, 13.68).
Figure 17. Meta-analysis examining the association between STH infection and Raven’s test for learning in infected and uninfected groups
In the comparison of anthelmintic treatment and placebo groups, a total of four studies were included for the meta-analyses (Figures 18, 19, and 20).
Heterogeneity was not found to be statistically significant for immediate French test (I2 = 0%, Pheterogeneity = 0.33), delayed French test (I2 = 40%, Pheterogeneity = 0.20), and for reading (I2 = 0%, Pheterogeneity = 0.39), indicating no variability in the results of the studies. No variation was present as there is less spreading of data sets across
studies. A fixed-effects model was used to conduct the T-test for each cognitive test. One study under each test showed a treatment group that scored higher than the placebo group. Pooled results showed no significant difference for immediate French test (Z = 0.91, P-value = 0.37, mean difference = 0.60, 95% CI: -0.70 to 1.91), delayed French test (Z = 0.12, P-value = 0.90, mean difference = -0.02, 95%
CI: -0.36 to 0.32), and reading scores (Z = 0.23, P-value = 0.82, mean difference = 0.15, 95% CI: -1.17 to 1.48) between the treatment and placebo groups.
Figure 18. Meta-analysis examining the association between STH infection and immediate French test for learning in treatment and placebo groups
Figure 19. Meta-analysis examining the association between STH infection and delayed French test for learning for treatment and placebo groups
Figure 20. Meta-analysis examining the association between STH infection and reading for learning in treatment and placebo groups
Reaction Time
Two studies were included in the reaction time domain meta-analysis for the comparison between anthelmintic treatment and placebo groups (Figure 19).
Heterogeneity was not found to be statistically significant (I2 = 0%, Pheterogeneity = 0.67), indicating no variability in the results of the studies. No variation was seen as there is little spreading of data sets across studies. A fixed effects model was used for T-test for studies assessing reaction time through the silly sentences test.
Pooled results showed that there is a statistically significant difference in the silly sentences scores between the treatment and placebo groups (Z = 2.32, P-value = 0.02, mean difference = 0.40, 95% CI: 0.06 to 0.74).
Figure 20. Meta-analysis examining the association between STH infection and silly sentences test for reaction time in treatment and placebo groups
Table 2. Summary of findings from the meta-analyses
Variables Findings
Physiologic Effects
Malnutrition No significant association between helminth infection and likelihood of malnutrition Anemic Status Hookworm infection is a significant predictor
of anemia Cognitive Domains
Memory Uninfected children scored significantly higher in two out of three tests. Deworming does not have any significant effect on improving performance for tests assessing memory
Learning No significant association between helminth infection and learning ability and between deworming and learning ability
Reaction time Deworming is significantly associated with improving speed of comprehension
A proposed agenda for control solidifies the links between disease transmission, the sequelae induced by the infection and its overall influence on the cognition of school children. Five aspects of intervention were identified: poverty reduction initiatives, health education, water-related intervention, hookworm infection control and drug therapy. The first four intervention approaches and their rationale focused on prevention and the fifth approach evaluated current anthelmintic drug therapies.
Table 3. Control measures to mitigate incidence of helminthiasis and treat current infection
Control Measures Rationale
Poverty Reduction Initiatives Upward social mobility to improve quality of life for impoverished families
Health Education
Hygienic Practices Proper hygiene behavior to mitigate infection
Micronutrient intervention Feeding programs to sustain nutritional needs
Water-related Intervention Sewerage and septage management for access to clean water
Hookworm Infection Control
Footwear campaign Increased awareness of physical barriers to disrupt cutaneous transmission of hookworm parasites
Drug Therapy Other public health control measures must accompany the administration of anthelmintic treatment such as community water source decontamination and improving health education
Discussion
In the current study, none of the parasitic species of interest showed a significant association with a higher likelihood of malnutrition in children who were afflicted with helminthiasis in comparison to those who had an absence of infection. These results are consistent with a study in 2005 by Al-Mekhlafi et al. on children in Malaysia where the presence of T. trichiura and A. lumbricoides even at severe infection levels were not associated with the status of being underweight in children and instead found that a younger age group (2-6 years old) was greater predictors of malnutrition. Conversely, the present meta-analysis is inconsistent with the findings of Degarege et al. (2014), where the examination showed a
significant association between T. trichiura and A. lumbricoides with the likelihood of being underweight but only with children below the age of 5. Despite the variation in findings, previous literature indicates that other mediating factors may play a role in nutritional health and may be a combination of other demographic variables such as socioeconomic factors, childhood illnesses originally present in individuals and immunization status (Al-Mekhlafi et al. 2005). Other research has confirmed the sequelae induced by helminth infection as stomach aches, sleep disorders and malaise which may suppress a child’s appetite, invariably leading to malnutrition and impaired concentration at school. Helminths in the gastrointestinal tract compete and consume nutrients and blood, resulting in malabsorption and eventual anorexia (Sari et al. 2012). Nonetheless, the analysis suggests that initiatives to improve nutrition and socioeconomic status should be considered when implementing parasitic control strategies.
The meta-analysis found that only the presence of hookworm infection showed a significant association with a higher likelihood of anemia in children in a comparison between infected and uninfected groups. This is consistent with a cross- sectional study by Jardim-Botelho et al. in 2008 on the analysis of hookworm and A. lumbricoides infection regarding anemic status and cognitive performance.
Intestinal blood loss caused by adult hookworms and the disruption of oxygen to the brain via hemoglobin in red blood cells may be the underlying mechanism between the presence of hookworm infection and cognition (Jardim-Botelho et al.
2008). Results from a study observing the age-related changes in hookworm infection by Brooker et al. (2007) indicate that children above the age of 5 and hookworm infection are predictors for anemia, reinforcing the vulnerability of school children. Conversely, this study may contrast the findings of Grimes et al.
(2017) where there was no significant association between hookworm infection and anemia or any other parameters for nutritional status such as stunting or wasting.
The findings of the meta-analysis are also not consistent with the results determined by Le et al. (2007) where infection of A. lumbricoides and hookworm and children were not associated with anemia prevalence. Variables other than helminthiasis such as poor living conditions, deficiency in vitamins B6, B12, riboflavin and folic acid and an existing endemic disease in children may also mediate the occurrence of anemia (Le et al. 2007; Grimes et al. 2017). Anemia is shown to be a regulator of academic performance in a study by Olson et al. in 2009 where Filipino children with anemia performed worse on tests assessing verbal memory and learning. These findings were similar to a cross-sectional survey on anemia and cognitive performance by Perignon et al. in 2014 on Cambodian children where both nutrition and low iron status influenced cognitive performance. Results of the study implies a greater need to target the prevention and control of hookworm infection which may be initiated by disrupting its life cycle and reinforcing the nutritional needs of school children.
The results of the meta-analyses performed for each of the three cognitive domains showed that between infected and uninfected groups, only memory measured by the digit span forwards and digit span backwards tests is associated with the presence of STH infection, the association being that uninfected children appeared to score higher compared to infected children. This association between STH infection and lower performance in tests that measure memory was consistent with the findings of a meta-analysis performed by Pabalan et al. (2018), where memory was one of the two cognitive domains found to be associated with infection in their study. Conversely, this was not in line with the analysis done between the treatment and placebo groups where, with the same tests used to assess memory, it was found that deworming STH-infected children did not cause significant differences in scores compared to children that were given identical placebo.
Previous meta-analyses have arrived at similar conclusions (Welch et al. 2016;
Welch et al. 2019), stating that deworming either had no clinically meaningful or little to no effect on this area of cognition. The results between infected and uninfected groups and between treatment and placebo groups are conflicting, however do suggest that the administration of anthelmintic treatment alone to infected children inadequately addresses low achievement in tests of memory.
For the meta-analyses performed for the learning domain under infected and uninfected groups and under treatment and placebo groups, there was no
association found between learning and STH infection, implying that learning ability in children is neither affected nor unaffected by the presence of infection.
The lack of association in this study is conflicting with the results of the studies used for analysis but are consistent with prior meta-analyses examining this subject.
Welch et al. (2019) has stated in two studies that deworming has little to no effect on cognition and Pabalan et al. (2018) similarly did not find results consistent with their hypothesis of STH infection and lower performance in learning amongst other cognitive domains. This suggests that implementing remedial education may be more necessary than administering anthelmintic treatment or should be given alongside treatment to improve academic performance. On the other hand, the meta-analysis for the reaction time domain was performed only between treatment and placebo groups due to scarcity of articles with suitable data. Results showed that deworming infected children caused a significant difference in test scores with children under the treatment group scoring higher than the children that received identical placebo. Previous meta-analyses have not looked into the relationship between STH infection and the reaction time domain, however this finding is consistent with the results of a meta-analysis by Pabalan et al. (2018) where they found that STH infection was associated with slower cognitive speediness or reaction time.
Overall, results for the cognitive domains from the current study present both contradictory and consistent with meta-analyses done by previous researchers.
Results from the current meta-analysis majorly implies that the presence of infection and its relationship with effects on cognitive function, as well as the administration of anthelmintic treatment and its relationship with effects on cognitive function, remains unclear. Inconsistent findings may be due to difficulty in measuring or controlling confounding factors in each analyzed study (Grigorenko et al. 2006) or the differing educational quality of the schools that the children attend. Justifying low cognitive function due to STH infection or lack of deworming may be misleading (Taylor-Robinson et al. 2012) and lends credence to the belief that other public health measures must be supplemented.
National control of helminthiasis is essential to alleviate the burden placed on vulnerable communities. Current remedies have emphasized the development and use of anthelmintic drugs but there has been little importance given to the values of upward social mobility, hygiene education, sanitation, nutrition, and the impact of targeted health campaigns that may prevent the incidence of disease. Neglected tropical diseases are able to proliferate in areas of inadequate water and sanitation (Engels & Zho 2020). Incidence of parasitic infection in school children is known to increase due to lower socioeconomic conditions. Factors such as an uneducated and unemployed mother, lower social status of father and living in crowded housing
have been found to significantly increase the incidence of intestinal parasites in school children (Ostan et al. 2007). This association recognizes the need for greater socioeconomic improvement for Filipino families. Projects such as Pantawid Pamilyang Pilipino Program through grant cash transfer to qualified poor households, AmBisyon 2040 and Philippine Development Plan 2017-2022 as the long-term anchors for development planning in the country are reinforcements of approaches that can eradicate poverty in the Philippines. As of 2021, the Pantawid Pamilyang Pilipino Program shows positive impacts on income and food security and community participation but inconsistencies in use of maternal health care services and a negative impact on nutrition outcomes have also been observed (Orbeta et al. 2021). Focusing on maternal health may be a key mediator in a child’s susceptibility to disease. In a study examining parasitic infection and pregnancy in 2014, Tsoka-Gwegweni & Ntombela demonstrated the link between intestinal helminthiasis and reduced quality of life during and after pregnancy. Presence of infection interferes with nutrient absorption of the mother and anemia which lead to adverse birth outcomes such as retardation, prematurity, and low-birth weight newborns. Infants with low birthweight are at a greater risk of intestinal and respiratory infections which may influence cognitive development and language (Tsoka-Gwegweni & Ntombela 2014).
Pro-poor policies that provide sufficient sanitary infrastructure through equitable and accessible approaches can disrupt the transmission cycle of Ascaris
and Trichuris parasites. Initiatives such as CLTS and the WinS program by the Department of Education integrate proper hygienic practices to empower young people. As of 2012, only 36 communities in the Philippines have been certified open defecation free through the introduction of CLTS (Batmunk et al 2019).
According to a status report in 2019, the implementation of the WinS pogam has resulted in greater access to safe drinking water and water for cleaning in more than half of public schools and around three-fourths of schools in the country continue to conduct semi-annual deworming (Department of Education, 2019). Due to the COVID-19 pandemic, the Department of Education has developed teacher and patient orientations to educate families on the prevention of the corona virus and hand washing as well as the Weekly Home Learning Plan to advocate for the continuance of Wins activities such as toothbrushing, handwashing and waste segregation that is supplemented by instructional videos from teachers (Department of Education, 2020). The National Sustainable Sanitation Plan from the Department of Health in the Philippines is a promotion program for local government units to develop a sustainable response to deliver the issues of open defecation, improper handwashing, the lack of sanitary toilets and unsafe water and food for consumption to Filipinos. It is a campaign where primary and secondary audiences such as households, communities, and stakeholders such as social and political leaders can cooperate to achieve zero open defecation (ZOD) status. Despite the launch of this project, it may be overshadowed by current events and lack of cohesion in
communities and institutions (Department of Health 2016). This suggests that greater emphasis must be made to prevent the displacement of treating and controlling neglected tropical diseases in society.
The development of coupled deworming and nutritional programs has been suggested by previous literature to address malnutrition in Philippine primary schools. Implementation of this initiative would combat the risk of low nutritional status and decrease the susceptibility to infection (Ross et al. 2017). Gulayan sa Paaralan is a current control and sustainability program by the Philippine government that promotes vegetable production in primary and secondary schools, the values of gardening, good health, and nutrition (Department of Education 2016). Some vegetables planted and grown in the program are cabbage, sweet potato and legumes which provide important sources of vitamin A and zinc (Inocian 2015; Polak et al. 2015; Aserese et al. 2020). While this program has been successfully launched, it has only covered one percent of schools and has not been evaluated in a clinical trial to assess its efficacy (Ross et al. 2017). Despite the low coverage and assessment of Gulayan sa Paaralan, it is a promising step forward to reduce the nutritional impairment caused by helminthiasis as previous literature has established this relationship (Gopaldas 2005; Silva et al. 2006).
Increasing access to clean water supply can directly reduce exposure to infective stages of soil-transmitted helminths. Underlying diseases may exacerbate the debilitating effects of helminthiasis on school children, increasing the need for
effective sewage and water management. Despite the existence of the National Sewerage and Septage Management Program (NSSMP) to improve sanitation and water treatment, the nation continues to invest little due to the lack of political will, high cost of constructing more efficient systems and lack of funding for feasibility studies (Orejas 2017).
In the current meta-analysis, the significant association between hookworm infection and the likelihood of anemia in school children emphasizes an opportunity for species-targeted control. Due to the cutaneous transmission of hookworm infection, it is essential to create barriers to reduce skin invasion of third-stage hookworm larva. A visual campaign that can influence the attitudes of cleanliness and the importance of protection against helminthiasis may instill the value of adopting proper hygiene behavior. Currently, there are no programs in the Philippines that have implemented footwear campaigns as a sole targeted measure for hookworm infection but are instead, included in the WinS program. Increasing attention to shoe-wearing through low-cost pictural education and development of shoe-giving programs can become positive sources of preventative intervention (Paige et al. 2017).
