Revision of Clone of The life cycle of schistosomes from Mon, 2015-09-07 12:40

About schistosomiasis
Schistosomiasis, a trematode parasite, is an agent of significant human and veterinary disease. It infects over 207 million people globally, with 700 million at risk of infection, mostly in Sub-Saharan Africa and is endemic in 74 countries. Classified as a Neglected Tropical Disease (NTD), it results in chronic health problems, and causes 200,000 deaths a year. NTD’s are usually found in developing countries and are most prevalent in the poorest communities; in wealthier regions they have been contained so are less visible than other diseases such as HIV AIDS, tuberculosis and malaria (‘the big three’). Schistosomiasis requires water contact for transmission and therefore thrives in areas where there is poor sanitation and unsafe (or contaminated) water. While schistosomiasis has lower mortality rates than the big three it causes high levels of morbidity, pain and disability.

Schistosomes
Schistosomes belong to the Schistosoma genus (Phylum: Platyhelminthes, Class: Trematoda, Order: Strigeiformes, Family: Schistosomatidae). Many Schistosoma species have a specific relationship with their definitive vertebrate host and there are over 20 species infecting mammals, birds and crocodiles. Six main species infect humans, Schistosoma haematobium, S. mansoni, S. japonicum, S mekongi S. guiniensis, and S. intercalatum. belong to the Schistosoma genus (Phylum: Platyhelminthes, Class: Trematoda, Order: Strigeiformes, Family: Schistosomatidae). Many Schistosoma species have a specific relationship with their definitive vertebrate host and there are over 20 species infecting mammals, birds and crocodiles. Unusual among flatworms, which are mainly hermaphroditic, schistosomes are dioecious, and the adult worms pair together.

Schistososma species_snails_hosts_continent.jpg

Transmission
Transmission requires contact with freshwater together with the presence of a suitable intermediate snail host in the water body. Children generally have higher rates of infection, as they generally have more frequent exposure by swimming and playing in infected water, also the immune response to schistosomiasis tends to increase with age.

Intermediate host snail species
The intermediate hosts of schistosoma species all belong to the class Gastropoda mainly to the Planorbidae, Lymnaedae and Pomatiopsidae families . The relationship between schistosomes and their snail host is very specific.

Planorbidae: Bulinus (hosts of S. haematobium group)
Biomphalaria (hosts of S. mansoni)
Lymnaeidae: Lymnaea and Radix (hosts of certain animal schistosomes)
Pomatiopsidae: Oncomelania (hosts of S. japonicum) and Neotricula (hosts of S.mekongi) species

Taxonomic name:

Schistosoma (Parasite taxonomy), Planorbidae (Taxonomy of Hosts), Pomatiopsidae (Taxonomy of Hosts), Bulinus (Taxonomy of Hosts), Biomphalaria (Taxonomy of Hosts), Radix (Taxonomy of Hosts), Oncomelania (Taxonomy of Hosts), Neotricula (Taxonomy of Hosts), Schistosomatidae (Parasite taxonomy), Schistosoma haematobium (Parasite taxonomy)

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