Strategic Control of Schistosome Intermediate Host

Status Quo and Future Perspectives of Molecular and Genomic Studies on the Genus Biomphalaria-The Intermediate Snail Host of Schistosoma mansoni

Schistosomiasis, or also generally known as bilharzia or snail fever, is a parasitic disease that is caused by trematode flatworms of the genus Schistosoma. It is considered by the World Health Organisation as the second most prevalent parasitic disease after malaria and affects more than 230 million people in over 70 countries. People are infected via a variety of activities ranging from agricultural, domestic, occupational to recreational activities, where the freshwater snails Biomphalaria release Schistosoma cercariae larvae that penetrate the skin of humans when exposed in water. Understanding the biology of the intermediate host snail Biomphalaria is thus important to reveal the potential spread of schistosomiasis. In this article, we present an overview of the latest molecular studies focused on the snail Biomphalaria, including its ecology, evolution, and immune response; and propose using genomics as a foundation to further understand and control this disease vector and thus the transmission of schistosomiasis.

The Effect of Climate Change and the Snail-Schistosome Cycle in Transmission and Bio-Control of Schistosomiasis in Sub-Saharan Africa

In the next century, global warming, due to changes in climatic factors, is expected to have an enormous influence on the interactions between pathogens and their hosts. Over the years, the rate at which vector-borne diseases and their transmission dynamics modify and develop has been shown to be highly dependent to a certain extent on changes in temperature and geographical distribution. Schistosomiasis has been recognized as a tropical and neglected vector-borne disease whose rate of infection has been predicted to be elevated worldwide, especially in sub-Saharan Africa; the region currently with the highest proportion of people at risk, due to changes in climate. This review not only suggests the need to develop an efficient and effective model that will predict Schistosoma spp. population dynamics but seeks to evaluate the effectiveness of several current control strategies. The design of a framework model to predict and accommodate the future incidence of schistosomiasis in human population dynamics in sub-Saharan Africa is proposed. The impact of climate change on schistosomiasis transmission as well as the distribution of several freshwater snails responsible for the transmission of Schistosoma parasites in the region is also reviewed. Lastly, this article advocates for modelling several control mechanisms for schistosomiasis in sub-Saharan Africa so as to tackle the re-infection of the disease, even after treating infected people with praziquantel, the first-line treatment drug for schistosomiasis.

Phytochemical Molluscicides and Schistosomiasis: What We Know and What We Still Need to Learn

Worldwide schistosomiasis remains a serious public health problem with approximately 67 million people infected and 200 million at risk of infection from inhabiting or transiting endemically active regions. Africa, South America, the Caribbean, and the Middle East are the main transmission regions of Schistosoma mansoni. The fight against transmission through the use of molluscicides is not recent and has been advocated as the only activity with the possibility of interruption of transmission in small, epidemiologically active outbreaks. Euphorbia milii var. hislopii (syn. splendens) (Des Moulins, 1826) is the most promising for use in official schistosomiasis control programs according to the WHO. In this review, we show that an understanding of some how E. milii latex affects the snail vector and their parasites from a molecular level to field conditions is lacking. On the other hand, this type of treatment could also provide a rationale for the control of schistosomiasis and other parasitosis. Several publications contribute to enforcing the use of E. milii latex in endemic countries as a cheap alternative or complement to mass drug treatment with praziquantel, the only available drug to cure the patients (without preventing re-infection).

Molecular context of Schistosoma mansoni transmission in the molluscan environments: A mini-review

Schistosoma mansoni, being transmitted by some freshwater Biomphalaria snails, is a major causative agent of human schistosomiasis. In the absence of effective vaccine and alternative drug designs to fight against the disease, and with the limitations of molluscicide application, developing more efficient strategies to interrupt the snail-mediated parasite transmission is being emphasized as potentially instrumental in the efforts toward schistosomiasis elimination, hence, necessitating thorough and comprehensive understanding of the fundamental mechanisms involved in the transmission process. Based on the current advances, this paper presents a concise exposition of the cellular, biochemical, genetic and immunological dynamics of the complex and statge-by-stage interactions between the parasite and its vector in their aquatic environment. It also highlights the possible crosstalk between the parasite's intracellular cyclic adenosine monophosphate (cAMP) and p38 mitogen-activated protein kinase (p38 MAPK) during the intramolluscan stage. Undoubtedly, decades of intensive investigation have untangled many S. mansoni-B. glabrata complexities, yet many aspects of the parasite-vector cycle which can help define potential control clues await further elucidation.

Molecular approach for detecting early prepatent Schistosoma mansoni infection in Biomphalaria alexandrina snail host

The present study aimed to evaluate a polymerase chain reaction (PCR) assay used for detection of Schistosoma mansoni infection in Biomphalaria alexandrina snails in early prepatent period and to compare between it and the ordinary detection methods (shedding and crushing). Biomphalaria alexandrina snails are best known for their role as intermediate hosts of S. mansoni. DNA was extracted from infected snails in addition to non-infected "negative control" (to optimized the efficiency of PCR reaction) and subjected to PCR using primers specific to a partial sequence of S. mansoni fructose-1,6-bus phosphate aldolase (SMALDO). SMALDO gene was detected in the infected laboratory snails with 70, 85, and 100 % positivity at the 1st, 3rd, and 7th day of infection, respectively. In contrast, the ordinary method was not sensitive enough in detection of early prepatent infection even after 7 days of infection which showed only 25 % positivity. By comparing the sensitivity of the three methods, it was found that the average sensitivity of shedding method compared to PCR was 23.8 % and the average sensitivity of crushing method compared to PCR was 46.4 % while the sensitivity of PCR was 100 %. We conclude that PCR is superior to the conventional methods and can detect positive cases that were negative when examined by shedding or crushing methods. This can help in detection of the areas and times of high transmission which in turn will be very beneficial in planning of the exact timing of the proper control strategy.

Biomphalaria alexandrina in Egypt: past, present and future

The African species of Biomphalaria appeared as a result of the relatively recent west-to-east trans-Atlantic dispersal of the Biomphalaria glabrata-like taxon. In Egypt, Biomphalaria alexandrina is the intermediate host for Schistosoma mansoni. Biomphalaria alexandrina originated in the area between Alexandria and Rosetta and has historically been confined to the Nile Delta. Schistosoma mansoni reached Egypt via infected slaves and baboons from the Land of Punt through migrations that occurred as early as the Vth Dynasty. The suggestion of the presence of Schistosoma mansoni infection in Lower Egypt during Pharaonic times is discussed despite the fact that that there is no evidence of such infection in Egyptian mummies. It is only recently that Biomphalaria alexandrina colonized the Egyptian Nile from the Delta to Lake Nasser. This change was likely due to the construction of huge water projects, the development of new water resources essential for land reclamation projects and the movement of refugees from the Suez Canal zone to the Delta and vice versa. The situation with respect to Biomphalaria in Egypt has become complicated in recent years by the detection of Biomphalaria glabrata and a hybrid between both species; however, follow-up studies have demonstrated the disappearance of such species within Egypt. The National Schistosoma Control Program has made great strides with respect to the eradication of schistosoma; however, there has unfortunately been a reemergence of Schistosoma mansoni resistant to praziquantel. There are numerous factors that may influence the prevalence of snails in Egypt, including the construction of water projects, the increase in reclaimed areas, global climate change and pollution. Thus, continued field studies in addition to the cooperation of several scientists are needed to obtain an accurate representation of the status of this species. In addition, the determination of the genome sequence for Biomphalaria alexandrina and the use of modern technology will allow for the study of the host-parasite relationship at a molecular level.

Evidence-based treatment of schistosomiasis in pregnancy

Schistosomiasis is a parasitic infection that causes significant morbidity and mortality, especially in pregnant women originating from developing countries. Prompt diagnosis and treatment can improve pregnancy and infant outcomes. Currently, there are no formal guidelines for treatment in this population, which makes schistosomiasis in pregnancy a challenge to treat.