Onchocerca volvulus

By Mark R. Beatty

            How would you feel if you suffered from a disease that was neglected by the majority of the world, making it difficult to receive proper care?  The purpose of this is to educate you about a certain type of NTD (Neglected Tropical Disease) named Onchocerciasis, commonly called “River Blindness”.  There are approximately 37 million individuals that suffer from Onchocerciasis, all in Sub-Saharan Africa, Yemen, and isolated areas in Central and South America.  The diseases’ cause is the parasite Onchocerca volvulus, which is transmitted by the blackfly (Simulium damnosum).

            The parasite is transmitted near rivers and fast flowing streams, because this is where the blackflies live and breed.  The parasite itself is classified as a nematode (roundworm), and it inhabits the sub-cutaneous tissues of the human host.  Once the blackfly takes a blood-meal from an individual, the parasitic larvae enter the bite wound and begin to mature toward adulthood and will form nodules under the skin, sometimes called an onchocercoma.  Here the adult worms will live for the remainder of their lives, mating and releasing larvae into the infected individuals sub-cutaneous tissue so that they can migrate throughout the body.  The adult worms can survive within these nodules for up to 15 years and produce microfilariae (larvae) for up to 9 years.  These larvae can be found in the peripheral blood, urine, and sputum (mucus that is coughed up from the lower airways), but is most commonly found in the skin and lymphatics of connective tissue.  So, once another blackfly comes around to take a bloodmeal, it becomes infected with the parasitic larvae allowing it to develop further and become infective for another person.

            There are several symptoms to the disease caused by O. volvulus.  Most of the body’s responses to the parasite are due to the dead/dying larvae.  It can cause inflammation of the skin, along with itching and long-term damage to the person’s skin.  This can cause changes in the color of the skin which results in a “leopard skin” appearance, and can also cause thinning of the skin with loss of elastic tissue that gives the skin a “cigarette-paper” appearance.  “Hanging groin” is a possible symptom relating to losing the elasticity of the skin, the skin in the groin area will begin to sag severely.  The inflammation caused by larvae that die in the eye results initially in reversible lesions on the cornea that without treatment progress to permanent clouding of the cornea, resulting in blindness.  There can also be inflammation of the optic nerve causing vision loss, particularly peripheral vision, and eventual blindness.

            The most common method for diagnosing the  disease is to take about 5-6 shavings or biopsy of the skin in different areas to detect the larvae.  If the larvae are detectable, a PCR (Polymerase Chain Reaction) test may be administered. Infections in the eye can be diagnosed with a slit-lamp examination on the anterior part of the eye, where the larvae or lesions they cause are visible.  Ivermectin is the drug treatment for Onchocerciasis, it kills the larvae and prevents any of the damage from occurring.  This would need to be administered to a patient once every 6 months for the lifetime of the adult worm.

            This debilitating disease could be eradicated fairly easily with enough directed effort towards the matter.  It can simply be transmitted while an individual is simply fishing for food, or gathering water for a family but yet can have such serious effects on that person’s life.  Hopefully, with heightened awareness on the problem, we can begin to try and disrupt the transmission cycle of this parasite and save millions from losing their eyesight.

1.      The Filarial Genome Network. (2000) http://www.science.smith.edu/departments/Biology/SWILLIAM/fgn/pnb/oncvol.html

2.      University of Michigan Museum of Zoology:  Animal Diversity Web. (2001) http://animaldiversity.ummz.umich.edu/site/accounts/information/Onchocerca_volvulus.html

3.      CDC 24/7:  Saving Lives. Protecting People.  (2010)  http://www.cdc.gov/parasites/onchocerciasis/

4.      The Carter Center: Waging Peace. Fighting Disease. Building Hope. (2012)  http://www.cartercenter.org/health/river_blindness/index.html