Malaria and Helminthic Co-Infection during Pregnancy in Sub-Saharan Africa: A Systematic Review and Meta-Analysis

Malaria and helminthic co-infection during pregnancy causes fetomaternal haemorrhage and foetal growth retardation. This study determined the pooled burden of pregnancy malaria and helminthic co-infection in sub-Saharan Africa. CINAHL, EMBASE, Google Scholar, Scopus, PubMed, and Web of Science databases were used to retrieve data from the literature, without restricting language and publication year. The Joanna Briggs Institute’s critical appraisal tool for prevalence studies was used for quality assessment. STATA Version 14.0 was used to conduct the meta-analysis. The I2 statistics and Egger’s test were used to test heterogeneity and publication bias. The random-effects model was used to estimate the pooled prevalence at a 95% confidence interval (CI). The review protocol has been registered in PROSPERO, with the number CRD42019144812. In total, 24 studies (n = 14,087 participants) were identified in this study. The pooled analysis revealed that 20% of pregnant women were co-infected by malaria and helminths in sub-Saharan Africa. The pooled prevalence of malaria and helminths were 33% and 35%, respectively. The most prevalent helminths were Hookworm (48%), Ascaris lumbricoides (37%), and Trichuris trichiura (15%). Significantly higher malaria and helminthic co-infection during pregnancy were observed. Health systems in sub-Saharan Africa must implement home-grown innovative solutions to underpin context-specific policies for the early initiation of effective intermittent preventive therapy.


Introduction
Globally, approximately 1.5 billion cases of infection from malaria and helminths pose a significant risk of mortality and morbidity to the population at risk including pregnant women and the foetus [1,2]. Recently, a total of 12 million incidences of gestational malaria were reported out of 33 million pregnancies in sub-Saharan Africa (SSA) [2].
Ten countries in SSA-Burkina Faso, Cameroon, The Democratic Republic of the Congo, Ghana, Mali, Mozambique, Niger, Nigeria, Uganda, and The United Republic of Tanzania-that were hard hit by malaria endorsed the "High Burden to High Impact Approach (HBHI)" [3]; this sets out four response mechanisms to malaria elimination-namely, a political will to reduce death associated with malaria, strategic information to deliver impact, better guidance and policies, and a coordinated national malaria response strategy [4][5][6][7][8]. However, the already fragile healthcare delivery in SSA has faced the doubled burden of malaria and the novel coronavirus (nCoV-2) pandemic, which has stalled the hard-won gains in the fight against malaria [9][10][11].
The World Health Organisation (WHO) 2030 road map aims to establish an efficient helminths control program specifically for women of reproductive age. Nevertheless, helminths continue to constitute major public health problems for pregnant women in SSA [19][20][21]. Co-infection from malaria and helminths is a major indicator of global health inequality, and failure to tackle this health disparity slows down the race to realising universal health coverage and attainment of the Sustainable Development Goal (SDG)-3 [22][23][24][25][26][27][28][29].

Clinical Implications of Concurrent Malaria and Helminthic Infection in Pregnancy
Malaria during pregnancy increases the risk of miscarriage and stillbirth by 3 to 4 times, compared with pregnant women with no clinically confirmed malaria [30]. Helminths cause alterations in immune response and physiological changes that affect fecundity, due to induced immunological states, with resultant adverse effects on conception and pregnancy [31]. Anemia during pregnancy is the most common adverse health outcome caused by Ascaris lumbricoides [32,33], and Hookworm [34]. In addition, Schistosoma mansoni is also associated with anemia and undernutrition during pregnancy [34], while A. lumbricoides is implicated with gallbladder perforation [35]. Pregnancy malaria co-infection with A. lumbricoides and Hookworm has been associated with increased odds of P. falciparum infection [36,37], and the pathophysiology of pregnant women simultaneously infected with Plasmodium species and helminths revealed negative pregnancy outcomes such as anemia, fetomaternal haemorrhage, antepartum stillbirth syndrome, and low birth weight [38][39][40]. Malaria and helminths co-infection causes elevated and unregulated inflammatory biomarkers such as C-reactive protein and serum level Hepcidin, which results in reduced iron absorption during pregnancy [41][42][43][44][45][46][47][48][49][50][51]. In addition, comorbidity of Plasmodium falciparum and helminthiasis elucidates the incidence of cervical cancer among pregnant women [52][53][54]. Moreover, during pregnancy, malaria co-infection with A. lumbricoides has been associated with an increased odds of P. falciparum infection [55,56], and malaria-Hookworm co-infection is associated with risks of increased Plasmodium parasitaemia [57,58].
Currently, evidence on the burden of intestinal helminths and malaria co-infection, the nature of their interaction, and their impact on pregnancy is not well established in endemic countries [59][60][61]. Most of the studies conducted in SSA emphasized the negative health outcomes of infection from malaria and helminths among pre-and schoolchildren [62][63][64][65][66], while very limited attention has been given to the dire impact of concurrent maternal gestational nematode and Plasmodium species infection [67][68][69][70]. Therefore, this systematic review and metaanalysis synthesised the available data on the burden of malaria and helminthic co-infections and their interaction among pregnant women living in SSA. It will further highlight evidenceinformed planning and implementation for the comprehensive elimination of co-endemic malaria and helminthic infections during pregnancy in SSA [71,72].

Search Strategy and Information Sources
A robust search was performed on CINAHL, EMBASE, Google Scholar, Scopus, Pub-Med, and Web of Science databases to retrieve published and unpublished data from the

Search Strategy and Information Sources
A robust search was performed on CINAHL, EMBASE, Google Scholar, Scopus, PubMed, and Web of Science databases to retrieve published and unpublished data from the literature. (Supplementary File S1). No restrictions were made regarding the language and years of all publications. The Boolean operators "AND" and "OR" were used to combine the MeSH terms ""Hookworm Infections" [ Potentially relevant studies were fully retrieved, including their citation details, and additional data were obtained from the reference lists of some of the articles selected for critical appraisal.

Study Selection
All the identified citations were exported into the EndNote version 15.0 reference manager. Two independent reviewers (M.T.B. and E.H.) rigorously screened the titles, abstracts, and the full text of selected literature against the inclusion criteria. The doublecheck of the included studies was performed by a third reviewer (H.T.A.). Discussions were made among the reviewers to resolve disagreements that arose at each stage of the study selection process.

Eligibility Criteria
Inclusion Criteria: Observational studies published in SSA, which reported the coinfection of malaria in pregnancy with helminths as their main outcome were eligible for inclusion. Studies published in all languages of SSA until 20 January 2022 were included.
Exclusion Criteria: Systematic reviews, studies with poor methodological quality after, and reports of studies conducted outside SSA were excluded. Studies that employed inappropriate sampling frames, inadequate sample sizes, and poor data analysis were excluded. Studies that reported malaria or helminthic infection alone during pregnancy were also excluded.

Quality Assessment
The Joanna Briggs Institute's (JBI) standardised critical appraisal instrument for prevalence studies was used to assess the methodological quality of included studies [88]. The JBI checklist contains nine quality measurement items (Supplementary File S2). Studies scoring 6 and above out of the 9 criteria were considered to have high quality to be included in the meta-analysis (Table 1). Two reviewers (M.T.B. and H.T.A.) independently screened the eligible studies, and a third reviewer (E.H.) was involved to resolve the disagreement. The observed risk of bias in this study is low (93%) ( Table 1). Studies that employed appropriate way of sampling procedures, had a clear description of settings and target population, appropriateness and adequacy of subject recruitment, reliability, and validity of methods used for the identification of outcomes of interest that included no co-infected cases (numerator), and a clear description of the study population (denominator) were deemed quality articles for final meta-analysis (Table 2).

Data Extraction
Data extraction was principally carried out by two reviewers (M.T.B. and E.H.). The validity and eligibility of the extracted data for the meta-analysis were cross-checked by a third reviewer (H.T.A.). Variables such as the name of the corresponding author and publication year, study design and data collection period, sample size and study setting, the test approaches for the diagnosis of malaria, and helminths were extracted ( Table 2). In addition, data extraction tools were used to extract the percentage of infection from Plasmodium falciparum, Hookworm, Ascaris lumbricoides, Trichuris trichiura, Schistosomiasis, the burden of helminths, prevalence of malaria, and malaria-helminthic co-infections, respectively.

Outcome Measurement
Malaria and helminthic co-infection during the gestation period were considered to occur when a laboratory-confirmed case of at least one Plasmodium and helminth species identified from blood and faecal bio-specimens was obtained from pregnant women [63].

Statistical Analysis
A quantitative meta-analysis of eligible studies was performed to estimate the event rate (prevalence of malaria-helminthic co-infection during pregnancy) [89]. Based on the random distribution assumption, the prevalence of each disease condition was obtained from the individual study estimate (ES), which includes a standard error (seES) and lower and upper confidence intervals. The pooled estimates were calculated and reported with respect to the relative weight given for each study [90,91]. Egger's regression test analyses were used to check the publication bias [92]. The standard chi-squared I2 test was used to test heterogeneity [93]. A random-effects model using the double arcsine transformation approach was applied [94]. Decisions made regarding the included studies were checked by sensitivity analyses test. Funnel plot asymmetry visual examination and Egger's regression tests were used to check for publication bias [95]. The pooled magnitude of co-infection of pregnancy malaria and helminths in SSA were estimated by computing a forest plot with 95%CI. Microsoft Excel 2019 workbook was used for data collection. The meta-analysis was performed using STATA version 14.0.3.

Literature Search
A total of 1525 publications ( Figure 1) were obtained from PubMed, CINAHL, EM-BASE, Google Scholar, Scopus, and Web of Science databases, after removing 167 duplicates (Supplementary File S1). Following title and abstract screening, a total of 1367 articles were excluded. Furthermore, 27 studies were eligible for quality assessment, out of which 24 studies were included in the meta-analysis (Figure 1).

Characteristics of Included Studies
A total of 14,087 pregnant women from 24 eligible studies from SSA participated in this systematic review. Studies with the highest (n = 2,507) and lowest (n = 87) sample sizes were reported from Uganda and Nigeria, respectively ( Table 2). Only six studies reported data on parity rate with primigravida (n = 1159) and multigravida (n = 1803). Ten studies were reported from Nigeria [96][97][98][99][100][101][102][103][104][105][106], and three studies were from Kenya [69,107,108] and Uganda [109][110][111]. Two studies were reported from Ethiopia [112,113], Gabon [114,115], and Ghana [116,117], respectively. The remaining studies were reported from Malawi [118] and Cameroon [119]. All of the studies included in the review were conducted using cross-sectional study designs ( Table 2). The majority of the studies employed the Kato-Katz thick smear, followed by formalin-ether and MacMaster concentration techniques for the detection of helminthic infection from faecal specimens, while the conventional microscopic method was used for the detection of malaria parasites (Table 2). Funnel plot asymmetry visual examination indicated no publication bias ( Figure 2 conventional microscopic method was used for the detection of malaria parasites ( Table  2). Funnel plot asymmetry visual examination indicated no publication bias ( Figure 2).

Figure 2.
Funnel plot with pseudo 95% confidence limit of individual study estimates attributed with prevalence of malaria and helminthic co-infection among pregnant women in sub-Saharan Africa.

The Burden of Malaria and Helminthic Co-Infection
The lowest and the highest prevalence rates of comorbidity with malaria and helminths were 3% and 69% ( Table 2). The pooled prevalence of malaria and helminthic coinfection was 20% (95%CI: 15%, 26%) ( Figure 8).

The Burden of Malaria and Helminthic Co-Infection
The lowest and the highest prevalence rates of comorbidity with malaria and helminths were 3% and 69% ( Table 2). The pooled prevalence of malaria and helminthic co-infection was 20% (95%CI: 15%, 26%) ( Figure 8).

Discussion
This study estimated the pooled prevalence of co-infection of malaria and helminths during pregnancy from a total of 24 eligible studies and 14,087 pregnant women in SSA. The pooled prevalence of comorbidity of malaria and helminths among pregnant women in SSA was 20%, ranging from 9% in Ethiopia to 40% in Ghana. The burden of simultaneous infection from Plasmodium and helminthic species among pregnant mothers living in Uganda and Kenya was similar (16%). This could be attributed to the poor implementation of the intermittent preventive treatment of malaria during pregnancy, barriers to access to clean water, and inadequate sanitation in these three countries [120][121][122][123]. To tackle the impact of malaria and helminthic comorbidity on pregnant mothers, the WHO Africa region must establish a malaria data-sharing hub that can serve as a shared evidence-informing centre [124]. This will be a game changer by enabling the health systems

Discussion
This study estimated the pooled prevalence of co-infection of malaria and helminths during pregnancy from a total of 24 eligible studies and 14,087 pregnant women in SSA. The pooled prevalence of comorbidity of malaria and helminths among pregnant women in SSA was 20%, ranging from 9% in Ethiopia to 40% in Ghana. The burden of simultaneous infection from Plasmodium and helminthic species among pregnant mothers living in Uganda and Kenya was similar (16%). This could be attributed to the poor implementation of the intermittent preventive treatment of malaria during pregnancy, barriers to access to clean water, and inadequate sanitation in these three countries [120][121][122][123]. To tackle the impact of malaria and helminthic comorbidity on pregnant mothers, the WHO Africa region must establish a malaria data-sharing hub that can serve as a shared evidenceinforming centre [124]. This will be a game changer by enabling the health systems in SSA to allocate scarce resources by applying a combination of updated tools for intervention and elimination strategies [125][126][127].
The burden of malaria in the gestational period among women immune-compromised by helminthic infection in SSA was 33%. This finding was higher than those of studies in Colombia (3.4%) [128] and Ethiopia (12.72%) [129]. This implicates the challenges to global malaria elimination efforts and calls for a collective concerted effort from countries in SSA to implement context-specific and tailored, evidence-based malaria elimination interventions [128,129]. Pregnant women's poor adherence to the use of prescribed prophylactic antimalarial drugs and preventive measures puts strain on the malaria elimination goal [130][131][132][133][134][135][136].
This implies a concerted need to intensify malaria vaccine coverage in SSA to save the lives of pregnant mothers, in addition to having preventive, therapeutic, and control strategies in place to end malaria during pregnancy . Countries in SSA must make changes in their malaria elimination strategies by adopting context-specific, home-grown innovative solutions, learning from grassroots experience, and strengthening public-private partnerships [142][143][144][145][146][147][148][149][150][151].
Our review revealed that the pooled prevalence of helminthiasis among pregnant mothers in SSA whose immunity is weakened by malaria was 35%. Uganda had a burden of helminthic infection in pregnancy (70%), which was higher than Cameron and Malawi combined (22%). Hookworm (48%), Ascaris lumbricoides (37%), and Trichuris trichiura (15%), respectively, were the pooled estimates of the most prevalent helminths associated with unintended pregnancy complications in SSA. The findings of our study were higher than those reported as global burden of helminthic infection during pregnancy in terms of the aggregate (3.6%) and species-specific Hookworm (19%), Ascaris lumbricoides (17%), and Trichuris trichiura (11%) [152]. This could be attributed to the inadequate availability of water, sanitation, and hygiene services in SSA, which remains below the global target of 80 % [153][154][155][156]. The prevalence of Schistosoma mansoni and malaria was determined by narrative synthesis because only 6 studies from the eligible 24 articles were reported with (n = 692) pregnant women from five countries in SSA who were co-infected by malaria and Schistosoma mansoni. Only five countries in SSA have (n = 1159) and (n = 1803) pregnant women in primigravid and multigravida who were co-infected by malaria and helminths.

Optimisation of Anti-Malarial and Anti-Helminthic Infections in Endemic Areas
Although there are universal malaria interventions such as bed nets and access to prompt diagnosis and treatment for pregnant women in malaria-endemic settings, universal access to sanitation and hygiene should be implemented to prevent malaria and helminths co-infection in women of reproductive age and schoolchildren in endemic settings [157]. Moreover, improved diagnostic tools are required to better quantify the burden of malariahelminth co-infection, as this might help understand the burden of these infections for evidence-based planning and implementation of integrated control and elimination of both malaria and helminthic infections in co-endemic areas [158]. Future malaria vaccine development efforts might also need to understand the immune modulation in malariahelminth co-infection for better consideration of the effect of the helminth-malaria infection in vaccine immunogenicity [159].

Ending Preventable Maternal Mortality due to Malarial and Helminthic Co-Infection
The global effort to end the preventable death of the mother caused by the comorbidity of Plasmodium parasitaemia and helminthiasis requires a concerted global health leadership and commitment [160,161]. Sustainable implementation of the water, sanitation, and hygiene (WASH) programs, combined with improving the practice of early initiation of effective intermittent preventive therapy, can avert unintended health consequences as a result of malaria in pregnancy [162][163][164][165][166][167]. Unavailability of a platform for sharing realtime data, poor financing, and inadequate political commitment, coupled with the lack of an enabling and empowering environment to use state-of-the-art technology for the development of anti-malarial and anti-helminthic vaccines in the clinical and biomedical research and innovations in SSA, continue to hinder efforts to bring context-based solutions to achieve SDG3 [168][169][170][171][172][173][174][175][176][177].

Implications for Practice, Policy, and Future Research and Innovation
Ensuring adequate access and enforcing adherence to safety and hygiene practices among pregnant women and safeguarding gestational mothers from economically disadvantaged households by creating sustainable access to economic opportunities will be essential to meet the global effort to control, prevent, and eliminate helminthic infections in sub-Saharan Africa [178][179][180][181][182][183][184][185][186]. To meet the 2030 target of successful elimination of helminthic infection, health systems in SSA and their international development partners must enhance the capacity and uptake of promising vaccine technology and innovation to improve maternal outcomes following gestational treatment of intestinal nematodes to help guide clinical decision making [187][188][189][190][191][192][193][194][195][196]. Sustainable and inclusive financing must be in place for the cutting-edge research and prudent innovation to deeply investigate the clinical outcomes of immunogenicity of comorbidity of malaria and helminths among gestational mothers in SSA [197][198][199][200][201][202][203][204][205][206]. Given the presence of sub-patent asymptomatic malaria burden that cannot be detected by microscopy [207], and P. falciparum parasites with histidine-rich protein 2 (pfhrp2)and histidine-rich protein 3 (pfhrp3) gene deletions that can escape the current HRP2 based-RDTs detection [208], the estimated burden of malaria-helminth co-infection might be underestimated in these 24 articles. Therefore, future studies that investigate the public health impact of asymptomatic malaria in pregnant women living in helminth co-endemic settings should be undertaken for better policy decision making.

Conclusions
Significantly higher levels of malaria and helminthic co-infection during pregnancy were observed. Existing interventions, such as deworming, prioritisation, and distribution of insecticide-treated bed nets and other control measures addressing pregnant women need to be highly encouraged. In addition, health systems strengthening gatekeepers and health policy framers in sub-Saharan Africa must implement home-grown, innovative solutions to underpin context-specific policies and practice for early initiation of effective intermittent preventive therapy for the prevention of malaria in pregnancy. Investments in reverse vaccinology to augment cutting-edge research and innovations in the comorbidity of gestational malaria and helminths through public-private partnerships must be implemented by sub-Saharan African countries and their international development partners. Tailored advocacy on focused antenatal care must be in place to inform and raise awareness among pregnant women regarding the health benefits of universal sanitation and hygiene coverage, together with the effective establishment of integrated community-level early detection and treatment of malaria and helminthic co-infection in sub-Saharan Africa. Data Availability Statement: The datasets during and/or analysed during the current study are available from the corresponding author on reasonable request.

Acknowledgments:
The Armauer Hansen Research Institute for enabling us and granting access to the databases and The Joanna Briggs Institute (JBI), for helping us with access to the databases and development of the review protocol. The Evidence-Based Healthcare Centre at Jimma University in Ethiopia provided us with a comprehensive systematic review training opportunity.

Conflicts of Interest:
The authors declare no conflict of interest.