Chapter 2: Introduction
Life Cycle Diagrams
This diagram shows a generalized disease cycle, including information on how the disease is
transmitted and ways in which the disease cycle could potentially be broken. Read the
information given below about the disease dracunculiasis (guinea worm) and compile a similar
diagram illustrating the disease cycle of dracunculiasis and how to break it.
Anthamatten and Hazen (2011), An Introduction to the Geography of Health
Dracunculiasis
Originally found across parts of Asia and Africa, by the end of the nineteenth century the life
cycle of the dracunculiasis pathogen had been elucidated and preventative measures were well
understood. The disease has now been eradicated from all but a few pockets of sub-Saharan
Africa. The disease is caused by the parasitic worm, Dracunculus medinensis, which lives in
water fleas (Cyclops) (Hopkins et al. 2005). Once a person drinks contaminated water, the fleas
are rapidly dissolved by stomach acids, releasing the parasites into the human host where they
breed. About a year after infection, the female worms emerge from the human body, typically
through the feet or lower leg, and release their eggs into water. At the point of emergence of the
female worm, a painful blister develops on the host’s skin. To soothe the pain, people are driven
to soak the affected limb in water, stimulating the adult worm to release her eggs (WHO 2009).
Although rarely fatal, the disease causes significant disability, incapacitating people for an
average of two to three months when the worm emerges (Hopkins et al. 2005). Migration of the
worm around the body through subcutaneous tissues can also cause severe pain (WHO 2009).
Individual infections last only one year, but people never develop immunity and there is no
vaccine or drug treatment for the disease (Hopkins et al. 2005). Tackling the disease therefore
relies on behavioral changes to prevent infection. Specifically, if drinking water can be filtered or
treated with a larvacide to kill the vector before drinking, infection can be prevented.
Alternatively, if people can be prevented from putting affected limbs in open water when the
worm emerges, the disease cycle can be broken. These measures are low-tech and inexpensive,
but require the education and cooperation of affected communities.
References
Hopkins, D., Ruiz-Tiben, E., Downs, P., Withers, Jr., P., and Maguire, J. (2005) “Dracunculiasis
eradication: the final inch,” American Journal or Tropical Medicine and Hygiene 74 (4):
669–75.
[WHO] World Health Organization. (2009) About Dracunculiasis. Available HTTP:
<http://www.who.int/dracunculiasis/disease/en/> (accessed 1 January 2009).
Anthamatten and Hazen (2011), An Introduction to the Geography of Health