Soil transmitted helminth infections in Ghana: a ten year review

For more than a decade, intervention programs have been instituted in Ghana to combat soil transmitted helminth (STHs) infections. Knowledge of the trend of the infection in the country is needed for evaluation and modification of existing control programs to achieve national targets. The objective of this review is to examine the pattern of soil transmitted infections in Ghana between 2009-2018. We searched and reviewed published literature on soil transmitted helminths in Ghana in PubMed, Medline, Google Scholar and Institutional Repositories of Kwame Nkrumah University of Science and Technology, University of Ghana, University of Cape Coast, and University for Development Studies-Tamale. We observed paucity of research work on STHs in Ghana over the period of this review. Twenty-nine studies consisting of 24 published works in peer reviewed journals and five graduate theses were included in the study. Hookworm was the most prevalent of STHs recorded followed by roundworm, threadworm, and whipworm. Pinworm was very rarely reported. These infections were reported from different regions and ecological zones of the country and among children, pregnant women, farmers, food vendors, children in orphanage home and psychiatric institution. Although there is some downward trend over the period, soil transmitted helminths are still prevalent in Ghana. This is an indication of some hope of eventual control and elimination of these diseases in the country if control measures are optimised. Further research particularly population studies into soil transmitted helminths in Ghana is needed.


Introduction
Soil transmitted helminths (STHs) are parasitic worms that live in the intestine of humans and other animals. The infections are associated with inadequate water supply, poor personal hygiene and environmental sanitation practices. Despite advancement in science and technology, these infections continue to be prevalent in less developed countries of sub-Saharan Africa, Latin America and Asia, where sanitation and hygiene remain major challenges [1,2].
Worldwide, approximately 2 billion people are infected by STHs with the highest prevalence occurring in sub-Saharan Africa [3]. These infections are associated with high morbidity and mortality. Thus, the World Health Organization targets their elimination. Progressive socio-economic development with adoption of effective control measures offers hope to people living in deprived communities of eventual freedom from STHs [4]. The three most common species of STHs worldwide are roundworm (Ascaris lumbricoides), whipworm (Trichuris trichiura) and hookworms (Necator americanus or Ancylostoma duodenale) [5]. Worldwide, roundworm and hookworms infect about 1.2 billion and 740 million people respectively [1,6].
Threadworm (Strongyloides stercoralis), another STH often associated with major morbidity in some settings has caught little research attention [7]. person or through contact with freshly passed faeces. Usually, the eggs and larvae become mature and infective three weeks after they are passed in faeces into the soil [8]. Populations mostly at risk of acquiring STHs are children, pregnant women and farmers who frequently come in contact with the soil [9]. The worms usually cause asymptomatic chronic infections [10]. Heavy infection is associated with intestinal damage with loss of nutrients resulting in impaired mental and physical growth, anaemia, low resistance to other infections of children and poor birth outcomes of pregnant women [11]. Children and pregnant women are most vulnerable to developing complications because they are in physiological state of high demand for nutrients for growth and development.
World Health Organization targeted STHs for control and prevention to reduce maternal and child morbidity and mortality associated with the infections. The recommended effective and easily available strategies include education on safe and hygienic handling of human faeces, wearing footwear in areas designated for defecation and improving quality of water supply, sanitation, and hygiene (WASH).
Other measures have been periodic mass administration of antihelminthic drugs through school-based treatment programs [12,13]. By adopting these measures, WHO globally target eliminating morbidity due to STHs in children by 2020. In Ghana [20].
Ghana has ten administrative regions. The population in 2017 was estimated to be 28.96 million with an estimated gross domestic product (GDP) per capita of 1,632 dollars [21]. Approximately, 23.4% of the population live in poverty [22]. About 85% of children are enrolled in primary, 53% in secondary school and 16% in tertiary.
Ghana has 71% adult literacy rate [23]. Whiles about 89% of the country´s population has access to safe water, 23% do not have access to adequate sanitation facilities. Only 15% has improved unshared sanitation facilities [24].

Current status of knowledge
Studies under review: we retrieved a total of 43 full-text articles from peer-reviewed journals and six (6) theses from university repositories within the ten-year period under review. Of this, 29 consisting of 24 published works in peer reviewed journals and four (4) graduate theses from Ghanaian university repositories and one (1) from Yale university scholarly publishing digital platform satisfied the eligibility criteria. Nineteen journal papers were excluded; 15 of the studies were conducted before 2009, two were on parasitic infections other than STHs, one did not state the prevalent records and one was hospital morbidity reports ( Figure 1).  Table 2 show five theses that were included in the review. All were descriptive cross-sectional studies with minimum sample size of 83 among pregnant women and highest sample size of 2400 among school children.
We found studies that were conducted in eight out of the ten administrative regions of the country. Most of the studies were conducted in Ashanti (6), Greater Accra (5) and Brong-Ahafo (5)

regions. No research work was reported from the Western and Upper
West regions of the country. Nine (9) of the studies were conducted in Coastal savanna, eight (8) in Decidual forest, seven (7) in Forestsavanna transitional and five (5) in Guinea savanna ecological zones.
No work was done in the wet Evergreen (part of Western region) and Sudan savanna (part of Upper West region) ecological zones ( Table 1,  Table 2). Sixteen, nine (9) and four (4) studies were carried out in rural, urban and peri-urban populations respectively. Majority of the studies were conducted among children (16) and pregnant women (5).
Types of soil transmitted helminths: as indicated in Table 1,   Table 1 (suite 3), Table 2). Roundworm and threadworm were also wide spread in the country.      (Table 1 (suite 1)). The observed STHs prevalence record among these populations with special need could be linked to overcrowding nature mostly seen in these institutions that can easily cause the spread of these infections.
The need to include these populations in surveillance programs should strongly be considered.

Conclusion
We • Patterns of STHs prevalence record from theses presented at university repositories are similar to those published in peer review journals.

Competing interests
The authors declare no competing interests.

Authors' contributions
Both authors contributed equally in writing, correcting and approving the final version of the manuscript.