Schitosoma Mekongi Essay

3. REVIEW OF LITERATURE
Schistosomiasis is a chronic parasitic disease caused by the three main species: Schistosoma mansoni, Schistosoma haematobium and Schistosoma japonicum. In addition, Schistosoma mekongi has been considered as a pathogen in some areas of South East Asia while, Schistosoma intercalatum is identified as a pathogen in West Africa (Despommier et al., 1995).
3.1. Historical Background
In 1852, Theodor Bilharz (figure 1) a German physician working at Medical School of Cairo, noticed a flat worm in the porto-mesenteric veins of post-mortem Egyptian boy . He named the parasite “Distomum haematobium”. Figure 1: Theodor Maximillian Bilharz (1825-1862)
In 1856, Meckel Von Helmsback named it Bilharzia rather than Distomum, as the

Activities such as swimming, bathing, washing laundry, fetching water and fishing were placing people at risk of acquiring schistosomiasis (Keiser et al,. 2011).
The life cycle of schistosomiasis is illustrated in Figure (2). Briefly, the cercariae emerge from the snails at daylight and they move in water with the aid of their bifurcated tails, seeking for their final host (Beltran and Boissier, 2008). When they recognize human skin, they penetrate it, transforming into the larval stage (Schistosomules) that migrate to the lungs (5–7 days post-penetration) and then move via circulation through the left side of the heart to the hepato-portal circulation (Loverde and Chen,1991).
In the hepato-portal circulation, Schistosomules develop into adult worms; mate and female Schistosomes begin to lay eggs. Some of the eggs are passed out of the body in the feces to continue the parasite’s life cycle, while others become trapped in body tissues of the infected host, causing immune reactions and progressive damage to organs (Adel,

Morphology of Shistosoma mansoni
3.4.1. Adult worms:
Schistosomes are not like other trematodes as they are long and slim worms with separate sexes (figure 3). They live in couples (male and female). The thinner female is located in the male’s gynaecophoric canal, in the porto-mesenteric veins (Webbe, 1982).
All species possess an oral and ventral sucker but the female suckers are very small and weak. A strong oral sucker surrounds the mouth of the worm. The digestive tube is composed of an oesophagus, which divides into two branches (right and left). The paired intestinal caeca fuse together and continue as a single gut till the posterior end of the worm with no anus. There is no pharynx (Schmidt and Roberts, 2000).
The male of S. mansoni is white and about (0.5-1.2 cm) long and (0.1-0.2 cm) wide. It has a funnel-shaped oral sucker at its anterior end followed by another pediculated ventral sucker. The male genital system is composed of 6 to 9 testicular masses that lied in one or 2 rows, postro-lateral to the ventral sucker; they are linked to a seminal vesicle opening through a vas deferens to the gonopore. The 2 lateral borders of its body are bent to form the gynaecophoric canal in which the female is held (Luíz, 1991). Inside the gynaecophoric canal nutrients and hormones are transferred from the male to the female and vice versa (Basch,