A school-based soil-transmitted helminths survey in the Guadalcanal Province,the Solomon Islands

Abstract

Infections by soil-transmitted helminths are a major public health problem worldwide, especially among schoolchildren in low-income countries. Little information is described about their prevalence in the Solomon Islands. From 2017 to 2018, a school-based soil-transmitted helminths survey in the Guadalcanal Province was conducted. A total of 454 schoolchildren were selected; the Merthiolate–iodine–formaldehyde concentration and stain was used. The prevalence was 17% of one or more parasites, including hookworm (8.8%), Strongyloides stercoralis (5.7%), Ascaris lumbricoides (4.2%) and Trichuris trichiura (3.5%). STH infection was significantly correlated with parents' occupations, hand washing, shoe wearing as well as gastrointestinal symptoms. To prevent STH transmission for schoolchildren in the Solomon Islands completely, combined preventive strategies seem necessary.

Keywords

Soil-transmitted helminths intestinal parasites schoolchildren the Solomon Islands

Introduction

Intestinal parasitic infections, and in particular those caused by soil-transmitted helminths (STH), are a major public health problem worldwide. Globally, approximately over 1 billion people are infected with at least one type of STH, including three main nematodes: Ascaris lumbricoides, hookworm (Ancylostoma duodenale/Necator americanus) and Trichuris trichiura. STH infections are among the most widespread human infections in low-income countries, with children being the most susceptible and vulnerable population,¹ even in richer countries.² STH infections can lead to malabsorption and chronic blood loss, together with long-term effects on childhood physical and cognitive development.³ Therefore, schools in low-income countries have been a focus for both surveillance and control of STH infection.⁴ STH school surveillance has been investigated in many Asian^5–7 and African countries.^8,9 However, there are still few childhood STH survey studies in the Solomon Islands, a tropical country located in the Pacific islands.

Methods

Our study was conducted in Visale, a rural district of Honiara, located in north-west Guadalcanal Province, the Solomon Islands. Visale district covers a total of 9 km² area, with a population of approximately 1500, about 40 km from the city centre of Honiara. Nearly 35% of the total population in this district are school aged children. Assessment of STH infection prevalence was undertaken as part of a partially World Health Organization (WHO) funded multi-country evaluation and control in STH treatment. From October 2017 to May 2018, children aged 6–14, studying in Visale primary school, were selected for the presence of STH in their faecal samples; in total, 454 schoolchildren had stool specimens collected.

Permission for the survey was obtained from the educational authorities of the school administration, following which STH infection health education about their morphology, life cycle, infection route, diseases, laboratory diagnosis and prevention methods was given to all teachers and schoolchildren. After the educational programme, a participant information sheet, including questionnaire and informed consent form, was provided to all eligible schoolchildren. A child was enrolled into the study only after at least one parent had provided written informed consent. The study protocol was approved by Kaohsiung Medical University (KMU) and KMU Hospital (KMUH), Kaohsiung, Taiwan.

After information sheets were received, S–Y faeces examination apparatus for parasite ova-only (CFEA-P, Shin-Yung Medical Instruments, Taiwan) stool containers were distributed to participant schoolchildren along with handling instructions to bring a morning stool sample. On the following days, CFEA-P were collected and transported to Taiwan Health Center (THC), National Referral Hospital (NRH), Honiara. In the THC laboratory, the samples were processed using the CFEA-P manual which is based on a Merthiolate–iodine–formaldehyde concentration (MIFC) technique,¹⁰ and the stained sediment was examined for STH.

The differences in the distribution of infection among schoolchildren along lines of gender, ethnicity, parent's occupation, hand washing, shoes wearing and gastrointestinal symptom complaints were analysed for significance using Chi-square test. A P-value of <0.05 was considered significant. All children found to have an intestinal parasitic infection were referred to THC for further medical treatment, advanced inquiry and follow-up.

Results

As shown in Table 1, the prevalence of STH infections among 454 schoolchildren in Visale primary school was 17%. These were infected with at least one or more STH; 55 harboured single, 22 double and 3 triple infections. A total of four species of nematode was found, whose incidence rate was hookworm 8.8%, Strongyloides stercoralis 5.7%, A. lumbricoides 4.2% and T. trichiura 3.5%.

Table 1.

Single and multiple soil-transmitted helminths infections among 454 schoolchildren in Visale primary school in Guadalcanal Province, the Solomon Islands.

Soil-transmitted helminths	No. infected	Infection rate (%)
Single infection
Hookworm	28	6.2
Strongyloides stercoralis	16	3.5
Trichuris trichiura	6	1.3
Ascaris lumbricoides	5	1.1
Subtotal	55	12.1
Double infection
Hookworm + Ascaris lumbricoides	5	1.1
Trichuris trichiura + Ascaris lumbricoides	4	1.0
Hookworm + Trichuris trichiura	3	1.0
Hookworm + Strongyloides stercoralis	3	1.0
Strongyloides stercoralis + Trichuris trichiura	2	<1
Strongyloides stercoralis + Ascaris lumbricoides	2	<1
Subtotal	19	4.2
Triple infection
Hookworm + Strongyloides stercoralis + Ascaris lumbricoides	2	<1
Strongyloides stercoralis + Trichuris trichiura + Ascaris lumbricoides	1	<1
Subtotal	3	1.0
Total infection	77	17

Infection rates per grade are shown in Table 2. Of the STH examinations in schoolchildren by grade, Grades 1 and 6 had the highest infection rates (21%) and Grade 2 (18%) followed. Grades 4 and 3 had rates of 15% and 13%, respectively. Grade 5 had the lowest rate of 12%.

Table 2.

Infection rates of soil-transmitted helminths of 454 schoolchildren per grade in Visale primary school in Guadalcanal Province, the Solomon Islands.

Grade	No. of schoolchildren examined	No. of schoolchildren infected	Infection rate (%)
1	89	19	21
2	76	14	18
3	75	10	13
4	65	10	15
5	76	9	12
6	73	15	21
Total	454	77	17

As shown in Table 3, STH infection showed no significant association with gender or ethnicity, but was significantly correlated with parents' occupations, hand washing, not wearing shoes as well as with gastrointestinal complaints. In fact, by special enquiry, we found that 94% of schoolchildren infected with S. stercoralis or hookworm were not regular wearers of shoes.

Table 3.

Risk factors associated with soil-transmitted helminths infections among 454 schoolchildren in Visale primary school in Guadalcanal Province, the Solomon Islands.

	Soil-transmitted helminths
Risk factors	Found % (N = 77)	Not found % (N = 377)	P-value
Gender			0.410
Male	48.2	46.3
Female	51.8	53.7
Ethnicity
Melanesian	46.8	45.4	0.11
Micronesian	53.2	54.6
Parent's occupation
Farmers	93.8	76.0	0.018^a
Others	6.2	24.0
Hand washing
Yes	37.5	53.4	0.009^a
No	62.5	46.6
Shoes wearing
Yes	20.6	87.5	<0.001^a
No	79.4	12.5
Gastrointestinal symptom complaints
Yes	76.1	8.5	<0.001^a
No	23.9	91.5

^aStatistically significant.

Discussion

Parasitic diseases are major obstacles to health, growth and socio-economic development in low-income countries. Parasitic diseases such as STH and malaria may both be as severe in populations at risk. Few studies from the Solomon Islands have focused on STH, the most neglected disease worldwide.¹¹ Guadalcanal Province is the principal, largest island and has the second highest population (c. 100,000, less than Malaita Province) in the Solomon Islands. Besides, the nation's capital, Honiara, is situated on the northwestern coast of Guadalcanal Province, with a population of c. 70,000, and is the most advanced cosmopolitan centre in the Islands. Though WHO funded that STH treatment programmes have been conducted for many years in Honiara, a high-infection rate is still found based in rural districts, as confirmed by our study. It is reasonable therefore to assume that in other more remote provinces, where STH treatment programmes have never been conducted, even higher STH infection rates may be found.

Hookworms and S. stercoralis are more prevalent than the other parasites (T. trichiura and A. lumbricoides). There are principally two species of hookworm, responsible: A. duodenale and N. americanus. Their geographical distribution overlaps considerably, and both species are endemic in many areas. Their ova are morphologically indistinguishable, and more advanced methods are needed to identify one from the other.

Strongyloides is usually asymptomatic, but a severe and life-threatening hyper-infection syndrome may occur.¹² Strongyloides infection is endemic in areas where sanitary conditions are poor and where the climate is warm and humid, such as South America,¹³ sub-Saharan Africa¹⁴ and South-East Asia;¹⁵ the infection is also prevalent in some Pacific islands.¹⁶ Little information is available on its prevalence in the Solomon Islands. We used the MIFC technique to examine Stronglyloides larvae in the stools although this is not the most sensitive method. Thus, more advanced sensitive diagnostic tools and suitable progressive chemotherapy are needed here.

Failure to wear shoes is strongly correlated with STH infection, as demonstrated in our schoolchildren survey. The route of infection involves skin-penetration, and wearing shoes will probably be an effective way to avoid Strongyloides infection, which is likely to be more effective than mass treatment programmes, which inevitably fail to reach some remote districts and provide only temporary relief before re-infection.

Footnotes

Acknowledgements

The authors would like to thank Visale primary school of Guadalcanal Province, the Solomon Islands for participating in the survey. They would also like to thank THC and KMUH for conducting the survey which included NRH staff for providing assistance. The authors thank WHO for affording albendazole for STH medical treatment in schoolchildren.

Declaration of conflicting interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: The funds for the survey and laboratory examinations were provided by Ministry of Health and Welfare, Taiwan.

ORCID iD

June-Der Lee

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