Soil-transmitted helminth (STH) infection remains a major public health problem among the Malaysian Orang Asli population, thereby possibly contributing to their overall backwardness and low productivity. The adherence of these people to be confined within the rainforest away from other people possibly contributes to their limited integration into Malay society, poor public enlightenment and low level of education. The findings of the present study showed high prevalence of STH infections with 78% of the children was infected with at least one STH species. The predominant parasite was T. trichiura, followed by A. lumbricoides, while hookworm was the least prevalent. Although, Strongyloides stercoralis larvae were detected in 7.1% of soil samples in the study area (Lipis district), S. stercoralis infection is not endemic in Malaysia and it usually occurs as sporadic cases [26, 27]. These findings are consistent with the reports from previous studies among Orang Asli people in Malaysia [5, 16, 17, 28]. However, our findings were contrary to some recent reports from neighbouring countries such as Thailand (mainly southern region) where hookworms were reported as the most prevalent species [29, 30] and China where ascariasis was most prevalent .
The high prevalence rates of T. trichiura infection reported in this study could be attributed to the low efficacy of the benzimidazole anthelminthics drugs against this worm as reported previously [32, 33]. The adult worm usually live embedded in the walls of the lumen of their host, hence it is difficult to be killed and expelled by a single dose of anthelminthics. Researchers therefore fear that anthelminthics resistance might be emerging in T. trichiura[34, 35]. On the other hand, the low prevalence rate of hookworm reported in our study might be connected to the nature of the soil in several parts of Malaysia which is the heavy clayey-loam type. This type of soil was found to be unsuitable for hookworm larval development [36, 37].
The findings of the current study also revealed that almost all, three quarters and one fifth of the total infections by T. trichiura, A. lumbricoides and hookworm, respectively, were of moderate-to-heavy intensities. This is higher than the prevalence reported by previous studies conducted among the Orang Asli [5, 16, 17]. This prevalence is alarming especially considering the fact that clinical manifestations and other consequences of these infections tend to be positively correlated with the burden of infection [5, 6, 31]. Besides the continuous exposure to the infections in these communities, the majority of the children did not receive any anthelmintic drugs in the last 12 months. In the absence of effective control and preventive measures, it is more likely that STH infections will continue to have devastating consequences and public health implications in these communities.
The World Health Organization is aware that the elimination of STH infections in endemic communities around the world may not be a feasible proposition; hence effort is geared towards the reduction of prevalence and intensity of infection to a low level. Endemic communities for STH are classified into 3 transmission categories for the adoption of treatment strategy in preventive chemotherapy; category I (high), category II (medium), and category III (low) . Based on this classification, our study area and most probably all Orang Asli areas in Peninsular Malaysia fall within the first category (high risk communities), with STH prevalence of more than 50% and more than 10% of the infections being of heavy intensity. Hence, this high prevalence calls for urgent interventions particularly considering the fact that these infections lead to malnutrition and growth retardation [7, 31], poor school performance , high school absenteeism rate , IDA and VAD [40, 41], and overall poor productivity .
The present study investigated the possible factors associated with STH infections (trichuriasis, ascariasis and hookworm infection) among the studied children and revealed that age (school-age), absence of toilet and piped water supply in the household, large family size (≥ 7 members), and not washing hands before eating and after defecation are the key factors that found to be associated with the three STH species. Many previous studies, including our previous published reports, have investigated and presented the risk factors of STH in different ways; either for overall intestinal parasitic infections (protozoa & helminth) or for only one species of STH or for the heavy burden of overall STH infections. In order to develop an integrated control programme, the current study attempted to provide a complete picture and identified the significant associated key factors of the three STH species within the same community. However, our findings are in agreement with previous studies conducted in Malaysia [5, 16, 28] and abroad [30, 43–46]. School-age children may have more exposure to the sources of infections due to their excessive mobility as compared to the pre-school children who usually receive more parental care. Moreover, if school environment is unhygienic this may also contribute to the transmission of these parasites.
In addition, poor personal hygiene including not washing hands before eating and after defecation is well documented as a significant risk factor of intestinal parasitic/bacterial/viral infections [45, 47]. Given the fact that the infective stages of these helminths are found in soil, washing hands before eating will help significantly in preventing these infections especially among children who love to play with soil.
In Malaysia, all Orang Asli communities are located close to rivers which are considered essential for Orang Asli life as they use water from streams for most of their daily activities (swimming, cooking, drinking, bathing and washing). However, rivers are also their preferred site for defecation and the practice of defecating near the streams by the residents (especially children) in these communities has been noted by other workers [5, 28]. Thus, the untreated water is always likely to be contaminated with parasites eggs and/or cysts and its usage for household activities enhances the likelihood of infections. Moreover, the lack of functioning toilet facilities in the house contributes to the spread of intestinal parasitic infections. Overall, our findings showed that school-age, using unsafe sources for drinking water and lack of toilets in the house increases the odds of Trichuris, Ascaris and hookworm infections by about 2 to 3 times among these children.
Our findings also showed that children who belong to large families (≥ 7 members) were at higher odds of Ascaris infection compared to children from smaller families. This finding is consistent with previous studies [16, 48]. The horizontal spread or the focal transmission of infection among family members in the vicinity of the home may explain this finding. Moreover, a significant association between intestinal parasitic infections and the presence of other infected family members was reported .
The associated key factors identified by the present study are the main focus of effective STH control programmes . In Malaysia, the national mass de-worming programme using a single dose of pyrantel pamoate once or twice a year was discontinued in 1983 due to the low effectiveness of the drug against Trichuris and hookworm. However, children in some rural areas are still receiving albendazole tablets. This is an intermittent distribution, without any monitoring system, of anthelmintics by researchers and community health campaigns by the Ministry of Health. This practice is not recommended as it may contribute to the emergence of anthelmintics drug resistance. Moreover, the re-infection rates of STH were reported to be high and by 6 months after complete de-worming the prevalence and intensity of infections were similar to pre-treatment levels [50, 51].
Orang Asli communities in Peninsular Malaysia share similar socioeconomic, environmental and health profiles. Our study provides a community-based picture of STH status among children with a poor socioeconomic, environmental and personal hygiene background. Thus, we may speculate that the findings of the present study can be generalised to rural Orang Asli children in other states. On the other hand, these results may not be generalisable to the entire Malaysian rural population as ethnic groups other than Orang Asli have a better socioeconomic and environmental situation. However, further investigations are required to confirm these conjectures.