A meta-analysis of changes in schistosomiasis prevalence in Zambia: implications on the 2020 elimination target

Prevalence of schistosomiasis and its association with anemia in Ethiopia, 2024: a systematic review and meta‑analysis

BACKGROUND

Schistosomiasis is a neglected tropical disease that affects over 250 million people, predominantly in impoverished communities, including those in Ethiopia. However, there is currently no available national data regarding its prevalence in Ethiopia or its potential association with anemia.

METHODS

The Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA-2020) guideline was followed in our study. A comprehensive search strategy was conducted using international databases (PUB Med, Embase, Scopus, and Science Direct) and websites (Google Scholar and Google) from their date of inception to April 22, 2024. The quality of the retrieved studies was assessed using an adapted version of the Newcastle-Ottawa Scale. Publication bias and statistical heterogeneity were statistically assessed. A random effects model was applied, and all analysis was performed with STATA 17 statistical software.

RESULT

The prevalence of schistosomiasis was assessed in twelve studies with 5747 participants. S. mansoni was studied in 11 research papers, while S. hematobium was assessed in one study. Using a random effect model due to high heterogeneity (I2 = 98.46%; P < 0.001), the overall pooled prevalence of schistosomiasis in Ethiopia was 22% (95% CI: 14.3, 29.6). The prevalence of schistosomiasis was about two and a half times higher in rural settings (23%) (95% CI: 15, 31) than in urban areas (10%) (95% CI: 3, 17). The burden of schistosomiasis was 23% between 2020 and 2024, compared to 16% from 2015-2019, with a higher prevalence among pediatric age groups (22%) versus 14% in mixed pediatric and adult age groups. The magnitude of schistosomiasis for good and very good-quality papers was 22% and 17%, respectively. In all the subgroup analyses, there was considerable statistically significant heterogeneity. No study was found to evaluate the association of schistosomiasis with anemia.

CONCLUSION

The study reveals Ethiopia's higher schistosomiasis prevalence. Rural areas have a high burden of schistosomiasis. No eligible study was found to evaluate the association of schistosomiasis with anemia. Therefore, prevention and control measures should focus on rural settings.

TRIAL REGISTRATION

The registration number at PROSPERO is CRD42024538522.

Genetic diversity and population genetics of Schistosoma haematobium isolated from children in Lusaka and Siavonga districts, Zambia

Urogenital schistosomiasis remains a pervasive health challenge in rural Zambian communities. This study explores the molecular epidemiology and genetic diversity of Schistosoma haematobium using mitochondrial genes (cox1 and nadh1). Urine samples from 421 children in Siavonga and Lusaka districts, Zambia, were collected between December 2020 and February 2022. Microscopy and DNA extraction facilitated the identification of S. haematobium, followed by amplification, sequencing, and phylogenetic analysis of cox1 and nadh1 genes. Phylogenetic analysis revealed clustering with samples from mainland African countries, emphasizing shared haplotypes. Both mitochondrial genes exhibited substantial diversity, with 5 haplotypes from 37 cox1 sequences and 12 haplotypes from 23 nadh1 sequences. High haplotype diversity (0.621-0.808) and low nucleotide diversity (0.00181-0.03288) were observed. Siavonga and Lusaka districts shared the majority of S. haematobium haplotypes. Molecular variance and genetic differentiation analysis indicated variations within populations rather than between populations (cox1: -0.025, nadh1: 0.01646). These findings suggest a limited differentiation between S. haematobium populations in Siavonga and Lusaka, potentially indicating gene flow. Tajima's test revealed negative values, indicating a departure from neutrality, introduction of rare alleles, and recent population expansion. This study contributes essential insights into S. haematobium population genetics, crucial for effective urogenital schistosomiasis control in Zambia.

Re-assessing thermal response of schistosomiasis transmission risk: Evidence for a higher thermal optimum than previously predicted

The geographical range of schistosomiasis is affected by the ecology of schistosome parasites and their obligate host snails, including their response to temperature. Previous models predicted schistosomiasis' thermal optimum at 21.7°C, which is not compatible with the temperature in sub-Saharan Africa (SSA) regions where schistosomiasis is hyperendemic. We performed an extensive literature search for empirical data on the effect of temperature on physiological and epidemiological parameters regulating the free-living stages of S. mansoni and S. haematobium and their obligate host snails, i.e., Biomphalaria spp. and Bulinus spp., respectively. We derived nonlinear thermal responses fitted on these data to parameterize a mechanistic, process-based model of schistosomiasis. We then re-cast the basic reproduction number and the prevalence of schistosome infection as functions of temperature. We found that the thermal optima for transmission of S. mansoni and S. haematobium range between 23.1-27.3°C and 23.6-27.9°C (95% CI) respectively. We also found that the thermal optimum shifts toward higher temperatures as the human water contact rate increases with temperature. Our findings align with an extensive dataset of schistosomiasis prevalence in SSA. The refined nonlinear thermal-response model developed here suggests a more suitable current climate and a greater risk of increased transmission with future warming for more than half of the schistosomiasis suitable regions with mean annual temperature below the thermal optimum.

Re-assessing thermal response of schistosomiasis transmission risk: evidence for a higher thermal optimum than previously predicted

The geographical range of schistosomiasis is affected by the ecology of schistosome parasites and their obligate host snails, including their response to temperature. Previous models predicted schistosomiasis' thermal optimum at 21.7 °C, which is not compatible with the temperature in sub-Saharan Africa (SSA) regions where schistosomiasis is hyperendemic. We performed an extensive literature search for empirical data on the effect of temperature on physiological and epidemiological parameters regulating the free-living stages of S. mansoni and S. haematobium and their obligate host snails, i.e., Biomphalaria spp. and Bulinus spp., respectively. We derived nonlinear thermal responses fitted on these data to parameterize a mechanistic, process-based model of schistosomiasis. We then re-cast the basic reproduction number and the prevalence of schistosome infection as functions of temperature. We found that the thermal optima for transmission of S. mansoni and S. haematobium range between 23.1-27.3 °C and 23.6-27.9 °C (95 % CI) respectively. We also found that the thermal optimum shifts toward higher temperatures as the human water contact rate increases with temperature. Our findings align with an extensive dataset of schistosomiasis prevalence in SSA. The refined nonlinear thermal-response model developed here suggests a more suitable current climate and a greater risk of increased transmission with future warming for more than half of the schistosomiasis suitable regions with mean annual temperature below the thermal optimum.

Epidemiology of intestinal helminthiasis with an emphasis on taeniasis in Chipata district of the Eastern province of Zambia

BACKGROUND

Intestinal helminth infections are among the most common infections worldwide and have a negative impact on the health, education, nutrition and economic development of affected populations. This study aimed to estimate the prevalence of intestinal helminthiasis, including T. solium taeniasis, using a large-scale community-based study in Chiparamba area of Chipata District in the Eastern province of Zambia.

METHODS/PRINCIPAL FINDINGS

A cross-sectional study was conducted between June 2019 and December 2022 in a rural community of 25 randomly selected villages known to be at risk for T. solium infection. Stool samples were examined for intestinal helminths using the formol-ether concentration technique and further tested for taeniasis by copro antigen-ELISA (copro Ag-ELISA). Descriptive statistical analyses were conducted, and associations between the disease prevalence of active infections and individual- and village-level variables were determined using the chi-square or Fisher's exact test. Predictors of an individual being positive for either taeniasis or other soil-transmitted helminths were determined using binary logistic regression. A total of 2762 stool samples were examined. One hundred ninety-five (7.1%) tested positive for at least one helminthic parasite on microscopy, with hookworm being the most frequent 84 (3.0%), followed by S. mansoni, 66 (2.4%). For taeniasis, 11 (0.4%) participants were positive for Taenia spp. microscopically, while 241 (8.7%) tested positive via copro Ag-ELISA. On bivariate analysis, male sex was significantly associated with the prevalence of intestinal parasites (p = 0.012) but not with that of taeniasis based on copro Ag-ELISA results. Village level differences were significant for infection with intestinal helminths as well as for taeniasis positivity on copro Ag-ELISA (p <0.001).

CONCLUSION

Intestinal helminths, including T. solium taeniasis, are prevalent in Chiparamba area of Chipata district in the eastern province of Zambia, supporting the clear need for further targeted public health interventions for surveillance and control.

Coverage and predictors of the uptake of the mass drug administration of praziquantel chemotherapy for schistosomiasis in a selected urban setting in Zambia

The burden of schistosomiasis in Zambia has remained high over the years. The World Health Assembly recommended adequate mass drug administration coverage for schistosomiasis using Praziquantel chemotherapy for school-aged children and all at-risks adults. We aimed at investigating the coverage and the factors associated to the uptake for MDA for schistosomiasis in Ng'ombe township of Lusaka, Zambia. A cross-sectional survey was conducted in May and June 2021 via phone calls to the residents of Ng'ombe township. Commcare software was used in the conduct of the survey. Pearson's Chi-square test and multiple logistic regression were conducted using the STATA version 15.0. 769 study participants were randomly selected using systematic sampling, of which 76.3% were younger than 40 years, 64.9% were female, 64.4% were married, 56.3% had reached the secondary educational level and 51.9% were employed. Coverage for MDA for schistosomiasis in Ng'ombe township in 2018 was found to be 49.8% (95% CI: 46.2%-53.4%). Positive predictors of the MDA were prior knowledge of the occurrence of the MDA in 2018 (aOR: 2.892, p < 0.001) and believing that the provision of incentives like snacks was important during the MDA with PZQ in Ng'ombe township (aOR: 1.926, p = 0.001), whereas age (aOR:0.979, p = 0.009), marital status (aOR:0.620, p = 0.006), employment status (aOR:0.587, p = 0.001) were negative predictors of the MDA. Elimination of the burden of schistosomiasis in endemic settings needs the attainment of an optimum coverage and uptake during MDA with PZQ. Therefore, prior knowledge about an impending intervention and the provision of incentives like snacks during the intervention should be prioritized by MDA implementers, while background characteristics such as age, marital status, and employment status need to be taken into consideration when planning and promoting uptake in future MDAs.

Rationale and design of a screening study to detect schistosomiasis-associated pulmonary hypertension in Ethiopia and Zambia

Schistosomiasis is a major cause of pulmonary arterial hypertension (PAH) worldwide, but the prevalence and risk factors for schistosomiasis-associated PAH (SchPAH) development are not well understood. Schistosomiasis-associated hepatosplenic disease (SchHSD) is thought to be a major risk factor for PAH development. Herein, we describe our plans for prospectively screening SchHSD subjects for clinical evidence of PAH at two major academic medical centers and national referral hospitals in Addis Ababa, Ethiopia and Lusaka, Zambia. The screening study will primarily be conducted by echocardiography, in addition to clinical assessments. Plasma samples will be drawn and banked for subsequent analysis based on preclinical animal model rationale. If successful, this study will demonstrate feasibility of conducting prospective cohort studies of SchPAH screening in schistosomiasis-endemic regions of Africa, and provide initial data on clinic-based disease prevalence and potential mechanistic biomarkers underlying disease pathogenesis.

Prevalence of Schistosoma mansoni and Associated Risk Factors in Human and Biomphalaria Snails in Ethiopia: A Systematic Review and Meta-analysis

PURPOSE

Schistosomiasis is one of the leading chronic parasitic diseases in Ethiopia. We aimed to summarize the prevalence of S. mansoni in human and Biomphalaria snails as well as risk factors in Ethiopia.

METHODS

Literature search was carried out from Scopus, Google Scholar, Science Direct and PubMed which reported Schistosoma mansoni infection in human and Biomphalaria snails in Ethiopia. The overall prevalence was estimated by a random-effect model and heterogeneities among studies were assessed by I² test.

RESULTS

A total of 178,251 participants and 1,097 snails were tested for the presence of S. mansoni in the eligible studies. The pooled prevalence of S. mansoni was 32.5% (95% CI 28.0-37.0) and 15.9% (95% CI - 5.6-37.5) in human and Biomphalaria snails in Ethiopia, respectively. The highest pooled prevalence was 43.2% (95% CI 27.3-59.1) in South Nations and National Peoples region while the lowest pooled prevalence was 25% (95% CI 19.3-30.7) observed in the Afar region. Interestingly, the pooled prevalence of S. mansoni declined from 40.7% (95% CI 33-48.4) to 22.4% (95% CI 18.5-26.3) after the launching of mass drug administration (MDA). The analysis of risk factors showed that swimming habit (OR, 2.78; 95% CI 2.35-3.21) and participation in irrigation (OR, 2.69; 95% CI 1.45-3.73) were independent predictors for S. mansoni infection.

CONCLUSION

This study revealed that about one-third of human and nearly 16% of Biomphalaria snails were infected with S. mansoni in Ethiopia. This review indicated that the prevalence of S. mansoni declined after the implementation of MDA. This study highlights the importance of further integrated approaches for better control of schistosomiasis in Ethiopia.

Prevalence of soil-transmitted helminth infections, schistosomiasis, and lymphatic filariasis before and after preventive chemotherapy initiation in the Philippines: A systematic review and meta-analysis

Objective

To estimate the impact of preventive chemotherapy on the prevalence and intensity of soil-transmitted helminth (STH) infections, schistosomiasis, and lymphatic filariasis in the Philippines, using systematic review and meta-analysis.

Methods

We included reports reporting prevalence of STH infections, schistosomiasis, or lymphatic filariasis in the Philippines published until 31 March 2021. Peer-reviewed studies were identified in electronic databases. Grey literature reports by the University of the Philippines and the Department of Health were also included. Pooled infection prevalence, before and after the initiation of preventive chemotherapy, stratified by age group, was calculated using the inverse variance heterogeneity model.

Findings

A total of 109 reports were included in the review and meta-analysis. Overall prevalence of moderate-heavy intensity Ascaris lumbricoides (6.6%) and Trichuris trichiura (2.7%) infection after initiation of preventive chemotherapy were significantly lower than the prevalence prior to initiation (23.6% for A. lumbricoides and 12.2% for T. trichiura). Prevalence reductions were also found in school and preschool-age children for A. lumbricoides and T. trichiura. Studies conducted after preventive chemotherapy initiation had significantly lower overall prevalence of moderate-heavy intensity schistosomiasis (3.1% vs 0.2%) and of schistosomiasis in school-age children (30.5% vs 1%). Pooled prevalence of lymphatic filariasis prior to preventive chemotherapy initiation was 3.2% across 12 provinces, while currently only two provinces still have prevalence of more than 1%. There were no published studies reporting prevalence of lymphatic filariasis after initiation of preventive chemotherapy. Heterogeneity was high with I² mostly above 90%.

Conclusion

The burden of STH infections and schistosomiasis in children were significantly lower in studies conducted following the initiation of preventive chemotherapy. Eliminating morbidity and interrupting transmission, however, may require expanded control initiatives including community-wide treatment, and improved water, sanitation, and hygiene. Lymphatic filariasis burden has decreased since the implementation of preventive chemotherapy, with all but two provinces having reached the elimination of lymphatic filariasis as a public health problem.

Mass treatment with anti-parasitic medications is a key control and elimination strategy for several helminth infections, namely intestinal worm infections, schistosomiasis, and lymphatic filariasis, which are common in the Philippines and other endemic countries. To gain insight into the impact of such a strategy that has been in place for more than 14 years, we used systematic review and meta-analysis to compare the prevalence of each of these helminth infections in the Philippines before and after the initiation of mass treatment. The review included 109 reports, composed of peer-reviewed studies and grey literature. The pooled overall prevalence of heavy intensity and the prevalence in children of intestinal worm infection and schistosomiasis were significantly lower in studies conducted after initiation of mass treatment. The studies included are highly heterogenous reflecting variability in sampling procedures, diagnostic tests, study sites, and years of data collection. Eliminating morbidity and interrupting transmission may require expanded control initiatives including community-wide treatment, and improved water, sanitation, and hygiene. The same significantly lower prevalence after initiation of mass treatment was observed for lymphatic filariasis where only two out of the initial 12 endemic provinces still require mass treatment due to prevalence above 1%.

Schistosomiasis with a Focus on Africa

Schistosomiasis is a common neglected tropical disease of impoverished people and livestock in many developing countries in tropical Africa, the Middle East, Asia, and Latin America. Substantial progress has been made in controlling schistosomiasis in some African countries, but the disease still prevails in most parts of sub-Saharan Africa with an estimated 800 million people at risk of infection. Current control strategies rely primarily on treatment with praziquantel, as no vaccine is available; however, treatment alone does not prevent reinfection. There has been emphasis on the use of integrated approaches in the control and elimination of the disease in recent years with the development of health infrastructure and health education. However, there is a need to evaluate the present status of African schistosomiasis, primarily caused by Schistosoma mansoni and S. haematobium, and the factors affecting the disease as the basis for developing more effective control and elimination strategies in the future. This review provides an historical perspective of schistosomiasis in Africa and discusses the current status of control efforts in those countries where the disease is endemic.

An Update on the Knowledge of Parasite-Vector Interactions of Chagas Disease

This review focusses on the interactions between the etiologic agent of Chagas disease, Trypanosoma cruzi, and its triatomine vector. The flagellate mainly colonizes the intestinal tract of the insect. The effect of triatomines on trypanosomes is indicated by susceptibility and refractoriness phenomena that vary according to the combination of the strains. Other effects are apparent in the different regions of the gut. In the stomach, the majority of ingested blood trypomastigotes are killed while the remaining transform to round stages. In the small intestine, these develop into epimastigotes, the main replicative stage. In the rectum, the population density is the highest and is where the infectious stage develops, the metacyclic trypomastigote. In all regions of the gut, starvation and feeding of the triatomine affect T. cruzi. In the small intestine and rectum, starvation reduces the population density and more spheromastigotes develop. In the rectum, feeding after short-term starvation induces metacyclogenesis and after long-term starvation the development of specific cells, containing several nuclei, kinetoplasts and flagella. When considering the effects of T. cruzi on triatomines, the flagellate seems to be of low pathogenicity. However, during stressful periods, which are normal in natural populations, effects occur often on the behaviour, eg, in readiness to approach the host, the period of time before defecation, dispersal and aggregation. In nymphs, the duration of the different instars and the mortality rates increase, but this seems to be induced by repeated infections or blood quality by the feeding on infected hosts. Starvation resistance is often reduced by infection. Longevity and reproduction of adults is reduced, but only after infection with some strains of T. cruzi. Only components of the surface coat of blood trypomastigotes induce an immune reaction. However, this seems to act against gut bacteria and favours the development of T. cruzi.

Prevalence of Schistosoma mansoni infection in Ethiopia: a systematic review and meta-analysis

Background

Schistosomiasis is a common helminthic infection in the tropics and subtropics, particularly in sub-Saharan African countries including Ethiopia. In these counties, Schistosoma mansoni infection is a significant public health problem due to the risk of reinfection and recurrent disease despite implementing several rounds preventive chemotherapy. This systematic review and meta-analysis aimed at assessing the pooled prevalence of schistosomiasis in Ethiopia.

Methods

The PRISMA guidelines were followed to perform the systematic review and meta-analysis. Published studies from January 1999 to June 2020 were searched in Medline, PubMed, Google Scholar, EMBASE, HINARI, and Cochrane Library using key words including: “prevalence”, “incidence”, “schistosomiasis” “Bilharziasis”, “Bilharzia”, “S. mansoni “, “Ethiopia”. Heterogeneity of included studies was assessed using Cochran’s Q test and I² test statistics while publication bias was assessed using Egger’s test.

Results

Ninety-four studies were included in the systematic review and meta-analysis. The pooled prevalence of S. mansoni in Ethiopia was 18.0% (95%CI: 14.0–23.0). The southern region of Ethiopia had a higher S. mansoni prevalence of 25.9% (995% CI, 14.9–41.1) than the national prevalence. The burden of S. mansoni infection was also higher than the national average in rural areas and among men with pooled prevalence of 20.2% (95% CI, 13.2–28.5) and 28.5% (95%CI, 22.7,35.1), respectively. The trend analysis showed that the prevalence of S. mansoni infection in Ethiopia decreased over the past 15 years, potentially because of the repeated preventive chemotherapy.

Conclusion

The review unveiled a moderate prevalence of S. mansoni infection in Ethiopia. Targeted treatment of at-risk population groups ad high burden areas coupled with implementation of integrated vector control strategies are critical to address the burden of Schistosomiasis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40794-020-00127-x.