Schistosoma transmission in a dynamic seasonal environment and its impact on the effectiveness of disease control

Efficacy of praziquantel drug against Schistosoma haematobium and performance of urine reagent strips among pre-and-school aged children during the high transmission season in North-Western Tanzania

The World Health Organization calls for schistosomiasis endemic countries to regularly monitor the efficacy of Praziquantel (PZQ) drug, the only antischistosomal drug used for four decades in Tanzania. In response to that call, the current study investigated the efficacy of single dose of PZQ against Schistosoma haematobium during the high transmission season and further assessed, the sensitivity and specificity of urine reagent strips before and after treatment. The study recruited a total of 2,498 -children aged (4 -17 years old) who provided a single urine sample that was visually examined for macro-haematuria, then using urine dipstick and urine filtration technique for microhaematuria and the presence of S. haematobium eggs. The baseline prevalence of S. haematobium eggs positive based on urine filtration test was 29.2 % (95 %CI:27.5-31.0) and that of microhaematuria was 43.1 % (95 %CI:41.1-45.0). Of the infected participants, 40.9 % (95 %CI:37.4-44.6) had a heavy intensity of infection and the geometrical mean intensity (GMI) of infection was 33.7 eggs/10mls of urine. A single dose of PZQ reduced the prevalence of infection to 16.2 %, the GMI of infection to 18.8eggs/10mls of urine and that of microhaematuria to 27.9 %. Cure rate and egg reduction rates (ERR) were 83.8 % and 44.3 % respectively. At baseline, the sensitivity and specificity of the urine reagent strips were 59.7 % and 93.8 %, whereas at post-treatment they were 16.7 % and 93.6 %. When PZQ drug is administered during the high transmission season, its efficacy in term of ERR is poor. The urine reagent strips had low sensitivity but high specificity at pre-and-post PZQ treatment.

Mechanisms of Arachidonic Acid In Vitro Schistosomicidal Potential

Arachidonic acid (ARA) was shown to possess safe and effective schistosomicidal impact on larval and adult Schistosoma mansoni and Schistosoma hematobium in vitro and in vivo in laboratory rodents and in children residing in low and high endemicity regions. We herein examine mechanisms underlying ARA schistosomicidal potential over two experiments, using in each pool a minimum of 50 adult male, female, or mixed-sex freshly recovered, ex vivo S. mansoni. Worms incubated in fetal calf serum-free medium were exposed to 0 or 10 mM ARA for 1 h at 37 °C and immediately processed for preparation of surface membrane and whole worm body homogenate extracts. Mixed-sex worms were additionally used for evaluating the impact of ARA exposure on the visualization of outer membrane cholesterol, sphingomyelin (SM), and ceramide in immunofluorescence assays. Following assessment of protein content, extracts of intact and ARA-treated worms were examined and compared for SM content, neutral sphingomyelinase activity, reactive oxygen species levels, and caspase 3/7 activity. Arachidonic acid principally led to perturbation of the organization, integrity, and SM content of the outer membrane of male and female worms and additionally impacted female parasites via stimulating neutral sphingomyelinase activity and oxidative stress. Arachidonic powerful action on female worms combined with its previously documented ovocidal activities supports its use as safe and effective therapy against schistosomiasis, provided implementation of the sorely needed and long waited-for chemical synthesis.

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.

The Impact of Targeted Treatment and Mass Drug Administration Delivery Strategies on the Prevalence and Intensity of Schistosomiasis in School Aged Children in Africa: A Systematic Review

Schistosomiasis is a public health problem in more than 78 countries in the world. The disease is most prevalent among children than adults due to their high exposure to infectious water sources. Various interventions such as mass drug administration (MDA), snail control, safe water provision and health education have been implemented independently or jointly to control, reduce and ultimately eliminate Schistosomiasis. This scoping review focused on studies reporting the impact of different delivery strategies of targeted treatment and MDA on the prevalence and intensity of schistosomiasis infection in school aged children in Africa. The review focused on Schistosoma haematobium and Schistosoma mansoni species. A systematic search for eligible literature from peer-reviewed articles was done from Google Scholar, Medline, PubMed and EBSCO host databases. The search yielded twenty-seven peer-reviewed articles. All articles found reported a decrease in the prevalence of schistosomiasis infection. Five studies (18.5%) reported a prevalence change below 40%, eighteen studies (66.7%) reported a change between 40% and 80%, and four studies (14.8%) reported a change above 80%. The infection intensity post-treatment was varied: twenty-four studies reported a decrease, while two studies reported an increase. The review showed that the impact of targeted treatment on the prevalence and intensity of schistosomiasis depended on the frequency at which it was offered, complementary interventions, and its uptake by the target population. Targeted treatment can significantly control the infection burden, but cannot eliminate the disease. Constant MDA programs coupled with preventative and health promotional programs are required to reach the elimination stage.

A Human-Bovine Schistosomiasis Mathematical Model with Treatment and Mollusciciding

To mitigate the spread of schistosomiasis, a deterministic human-bovine mathematical model of its transmission dynamics accounting for contaminated water reservoirs, including treatment of bovines and humans and mollusciciding is formulated and theoretically analyzed. The disease-free equilibrium is locally and globally asymptotically stable whenever the basic reproduction number [Formula: see text], while global stability of the endemic equilibrium is investigated by constructing a suitable Lyapunov function. To support the analytical results, parameter values from published literature are used for numerical simulations and where applicable, uncertainty analysis on the non-dimensional system parameters is performed using the Latin Hypercube Sampling and Partial Rank Correlation Coefficient techniques. Sensitivity analysis to determine the relative importance of model parameters to disease transmission shows that the environment-related parameters namely, [Formula: see text] (snails shedding rate of cercariae), [Formula: see text] (probability that cercariae shed by snails survive), c (fraction of the contaminated environment sprayed by molluscicides) and [Formula: see text] (mortality rate of cercariae) are the most significant to mitigate the spread of schistosomiasis. Mollusciciding, which directly impacts the contaminated environment as a single control strategy is more effective compared to treatment. However, concurrently applying mollusciciding and treatment will yield a better outcome.

Effectiveness of Four Different Interventions against Schistosoma haematobium in a Seasonal Transmission Setting of Côte d'Ivoire: A Cluster Randomized Trial

BACKGROUND

Annual mass drug administration (MDA) using praziquantel is the cornerstone of schistosomiasis morbidity control, but is not sufficient to interrupt transmission. We implemented a cluster-randomized trial to compare the effectiveness of four different intervention packages to interrupt transmission of Schistosoma haematobium in a seasonal transmission setting of Côte d'Ivoire.

METHODS

Sixty-four localities with a S. haematobium prevalence in school children aged 13-14 years above 4% were randomly assigned to one of four intervention arms over a 3-year period: (1) the current standard strategy consisting of annual MDA before peak of transmission; (2) annual MDA after peak of transmission; (3) biannual MDA; and (4) standard MDA combined with snail control. The primary outcome was prevalence and intensity of S. haematobium infection in children aged 9-12 years 1 year after the final intervention, using urine filtration performed by experienced microscopists.

RESULTS

By study end, we observed the lowest S. haematobium prevalence in the biannual MDA, compared to the standard treatment arm (0.6% vs. 7.5%; odds ratio [OR] = 0.07, 95% confidence interval [CI] = 0.02 to 0.24). The prevalence in arms 2 and 4 was about 3.5%, which was not statistically significantly different from the standard strategy (both ORs 0.4, 95% CI = 0.1 to ~1.8). New cases of infection were still observed in all arms at study end.

CONCLUSIONS

Biannual MDA was the only regimen that outperformed the standard treatment. All strategies resulted in decreased prevalence of infection, however none of them was able to interrupt transmission of S. haematobium within a 3-year period.