Friday, 1 February 2013

Predatory Prawns


Schistosomiasis is a parasitic disease which affects mostly rural communities in tropical areas of Africa, the source of which is contaminated river water(1). The parasite burrows through the skin and infect the host, migrating to the lungs and liver, leading to sever chronic illness, and in some cases death. The parasites life cycle is rather special; it uses a special snail as an intermediate host, which is vital for its life cycle. The parasite infects the snail and transforms, exiting the snail in a form which can then infect humans who are in the water(2).  
 
 
Schistosomiasis, also known as Bliharzia disease, is the second most damaging parasitic disease in terms of both social and economic terms, beaten only by malaria(3). It is a devastating disease, infecting more than 200 million people, 20 million become chronically infected, and 0.02 million die(4, 5). deemed Schistosomiasis is deemed a Neglected Tropical Disease by the CDC(6) because it is largely a disease of developing countries like Africa, due to the lack of financial incentives research has been slow in finding effective treatments and cures.  


One of the first inventions developed to address the problem was snail traps, because the snails are vital for the life cycle of the parasite, which were built across the river to capture the snails and remove them from the river(7). However, these traps have been mostly unsuccessful(8). A new method is currently being trialled, involving the introducing or reintroducing a species of prawn which predates the snail(9). This eradication or dramatic reduction of the amount of parasite in the water will reduce the risk of infection, and eventually eliminating it. This method if far more effective, because it encompasses the biology of the parasite. Rather than relying solely on drugs to treat those infected, which would be a never ending battle as it doesn't prevent reinfection, as the source of infection is never addressed. Instead this uses nature to effectively remove the parasite population from the water, while at the same time all those living in the community can take a short term dose of medication to clear any parasites currently in their system. While the trial is currently only in its early stages, it is already showing favourable results, and is unlikely to dramatically damage the environment through the prawns introduction, as the prawns were previously present but due to changes in the river they died out(9).

(1)http://en.wikipedia.org/wiki/Schistosomiasis
(2)http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0002298/
(3)http://www.cdc.gov/parasites/schistosomiasis/
(4)http://www.ingentaconnect.com/content/nrc/cjz/2004/00000082/00000002/art00012
(5)http://www.ncbi.nlm.nih.gov/pubmed/10072156
(6)http://www.cdc.gov/parasites/schistosomiasis/
(7)http://www.merckmanuals.com/vet/circulatory_system/blood_parasites/schistosomiasis.html
(8)http://www.lifesci.ucsb.edu/eemb/labs/kuris/pubs/SenegalReportFieldMissi.pdf
(9)http://www.guardian.co.uk/global-development/video/2012/dec/30/scientists-prawns-schistosomiasis-video

E Markham (2013). Predatory Prawns Blogspot

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