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staining method is routinely used because it is rapid and inexpensive. This method measures the effects of compounds on cell growth through the colorimetric evaluation of fixed cells stained with crystal violet. Briefly, cells maintained in culture medium are seeded into 96-well culture microplates in the presence of different concentrations of extracts, fractions or isolated compounds. After different timepoints of incubation (e.g., 2, 24, 48, 72, and 96 h), the supernatants are removed and the remaining live cells are assessed by xing and staining them with crystal violet (0.2% in 20% methanol). Viable cells attach to the bottom of the well plate, and the absorbance is measured by reading each well at 595 nm in

Neutral red is another cell viability assay often used to determine cytotoxicity following exposure to toxic substances (Borenfreund & Puerner, 1985). It has been used as an indicator of cytotoxicity in cultures of primary hepatocytes and other cell lines (Fautz et al., 1991; (Fotakis & Timbrell, 2006; Morgan et al., 1991). Living cells take up the neutral red, which is

The MTT assay is also used to measure cell viability. MTT is a water-soluble tetrazolium salt, which is converted to an insoluble purple formazan upon the cleavage of the tetrazolium ring by succinate dehydrogenase within the mitochondria. The formazan product is impermeable to the cell membranes, and therefore, it accumulates in healthy cells. The MTT assay has been tested for its validity in various cell lines (Fotakis & Timbrell,

Alternatively, the lactate dehydrogenase (LDH) leakage assay and protein assay are also used to detect cytotoxicity, despite the fact that they have low sensitivity when compared to the methods already described. The LDH leakage assay is based on the measurement of LDH activity in the extracellular medium. The loss of intracellular LDH and its release into the culture medium is an indicator of irreversible cell death due to cell membrane damage (Decker & Lohmann-Matthes, 1988; Fotakis & Timbrell, 2006). The protein assay is an indirect measurement of cell viability because it measures the protein content of viable cells. Despite the existence of several protocols to establish total protein concentration (e.g., biuret, bicinchoninic acid, Lowry and Bradford protocols), the two most commonly used methods for protein quantification are the Lowry and Bradford assays (Bradford et al., 1976; Lowry et

Finally, tritiated thymidine-based methods, which act through the incorporation of tritium into the DNA of cells, have also been used currently to detect cytotoxicity, especially in

Schistosomiasis is a neglected disease that is one of the most common chronic infections among the poorest people in the world. Most chemotherapeutic-based programs attempting to eradicate schistosomiasis in the developing world rely on the effectiveness of a single drug, praziquantel; therefore, there is an urgent need to identify new parasite targets and effective antischistosomal compounds. Secondary plant metabolites have attracted the attention of many researchers over the years as a result of the variety of their chemical structures and their broad range of biological activities that may provide lead structures for the development of new drugs. Recently, marine organisms have also been recognised as an attractive source of antiparasitic compounds, and it can be expected that other living organisms, such as insects and amphibians, will emerge as additional sources in the future.

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**21** 

*Cameroon* 

**Control of Schistosomiasis and Soil-**

**Africa: Challenges and Prospects** 

*University of Yaoundé I, Laboratory of Parasitology and Ecology,* 

*Centre for Schistosomiasis and Parasitology, Yaoundé* 

Louis-Albert Tchuem Tchuenté

**Transmitted Helminthiasis in Sub-Saharan** 

Schistosomiasis and soil-transmitted helminthiasis (STH) are the most common types of parasitic infections in the world. These diseases have major health and socio-economic repercussions, and constitute an important public health problem in developing countries. Human schistosomiasis is caused by six species of schistosomes, i.e. *Schistosoma haematobium*, *Schistosoma mansoni*, *Schistosoma japonicum*, *Schistosoma mekongi*, *Schistosoma intercalatum* and *Schistosoma guineensis*; and is endemic in 78 countries, where 779 million people are at risk of infection. *S. haematobium* is responsible for urogenital schistosomiasis, and the other species cause intestinal schistosomiasis. It is estimated that 207 million people are infected (WHO, 2002; Steinmann et al. 2006). STH, also known as intestinal worm infection, is caused by four main species of worms commonly known as roundworms (*Ascaris lumbricoides*), whipworms (*Trichuris trichiura*) and hookworms (*Ancylostoma duodenale* and *Necator americanus*). It is estimated that STH affects more than 2 billion people worldwide, and the greatest numbers of infections occur in sub-Saharan Africa, the Americas, China and east Asia (WHO, 2006; Hotez

These diseases affect the poorest of the poor and infections are particularly abundant among people living in rural or deprived urban settings with low socio-economic status, lack of clean water and poor sanitation (Hotez et al., 2006). The morbidity caused by these worms is commonly associated with heavy infection intensities. Compared with any other age group, school-aged children and pre-school children are the most vulnerable group and they harbor the greatest numbers of intestinal worms. As a result, they experience growth stunting and diminished physical fitness as well as impaired memory and cognition (Crompton and Nesheim, 2002; Stephenson et al., 2000; Bethony et al., 2006). These adverse health consequences combine to impair childhood educational performance and reduce school attendance (Miguel & Kremer, 2004; Hotez et al., 2008). Studies have demonstrated that children may acquire helminth infections early in life (Sousa-Figueiredo et al., 2008; Stothard et al., 2008); which causes initial organ damage that can remain subclinical for years and manifest overtly only later, in adulthood (WHO, 2006; Odogwu et al., 2006). Despite the existence of tools in the 1970s and 1980s, control was sustained for a prolonged period only in few countries and almost no progress was made in sub-Saharan African

**1. Introduction** 

et al., 2006; Brooker et al., 2006; Awasthi et al., 2003).

