Above is a picture of the parasitic tapeworm Taenia crassiceps I thought i would post it becuase it is a neat picture. This parasite does look horrifying but there is some evidence to suggest that these and other parasites can be beneficial, manipulating the host immune response and preventing diseases such as asthma. Although a reduction in worm infection is probably not the only reason for the recent dramatic rise in asthma and other inflammatory diseases.
Microscopy and the helminth parasite http://dx.doi.org/10.1016/j.micron.2003.12.001 (source of image)
Parasite role reversal: worms on trial http://dx.doi.org/10.1016/j.pt.2005.02.002
Wheeze, allergic sensitization and geohelminth infection in Butajira, Ethiopia. doi:10.1111/j.1365-2222.2005.02181.x - evidence contra to the beneficial effect of worms?