What is Onchocerciasis?
Onchocerciasis is a parasitic infection also called river blindness or Robles disease.
It affects people in the tropical regions of Africa and some South American countries. It causes skin and eye disease, and can even result in blindness.
Onchocerciasis is caused by the filarial parasite, Onchocerca volvulus and spreads through the bite of the blackfly. The blackfly breeds in areas of fast-flowing rivers and streams, especially in agricultural regions.
Onchocerciasis/River blindness is caused when the larvae of the parasite are introduced into the skin by bites of the blackfly. Unlike mosquito-borne diseases like malaria where a single bite is enough to cause the infection, repeated bites of the blackfly are required to transmit onchocerciasis to the person. The larvae settle just below the skin in the subcutaneous tissue and grow into adults in about a year. The adults live for 10-15 years in small swellings in the subcutaneous tissue called nodules. The female adult lays eggs, which develop into microfilariae. The microfilariae pass on to the blackfly when it bites the same person again. They undergo some development in the blackfly for around 2 weeks and infect the next person bitten by the blackfly.
Onchocerciasis mainly affects the skin and the eyes. A patient with severe infection may appear thin and has no fat (wasting).
- Skin: Skin-related symptoms and signs of onchocerciasis include the following:
- Severe itching with red itchy bumps on the affected skin
- Nodules in the subcutaneous tissue, which are formed around the adult worm. They can be felt on touching the skin, or can sometimes be seen with the naked eye. They are not painful and can occur anywhere in the body, especially over bony prominences.
- Early appearance of wrinkled and loose skin
- Dark or light patches on the skin, commonly referred to as leopard-skin pattern
- Thickening or scaling of the skin
- Eye: Symptoms and signs of onchocerciasis in the eye include the following:
- Inflammation of the conjunctiva, resulting in increased sensitivity to light.
- Damage to the cornea: Mild damage may recover on its own, but extensive damage may result in scarring and blindness.
- Damage to the inner choroid and retinal layers of the eye
- Damage to the optic nerve resulting in blindness
- Lymph nodes: The lymph nodes in the groin region may be enlarged. They may hang loose and result in hernia.
Onchocerciasis is diagnosed based on the following tests:
- Skin biopsy, which is used to demonstrate the larvae. A technique called skin snip biopsy is used. The biopsy sample is put into a solution for around 24 hours, so that any microfilariae present move into the solution.
- Surgical excision and examination of the nodules, which may demonstrate the adult worms
- Slit-lamp examination of the eye, which may demonstrate the larvae as well as changes in the eye
- Blood test, which shows an increase in eosinophil count and an increase in IgE antibody levels, both of which are indicative of an allergic reaction or parasitic infection.
Treatment of onchocerciasis is with the following medications:
- Ivermectin is an oral drug that is effective against microfilariae. It is given orally once in 6 months or once a year. It should not be given to patients also suffering from another parasitic infection called Loa loa infection, since it can cause brain-related complications.
- Doxycycline antibiotic is given for a duration of 6 weeks. It kills certain bacteria which are necessary for the adult worms, thereby resulting in the death of the adult worms or making them sterile.
Several steps have brought down cases of onchocerciasis in endemic areas. These include:
- Control of blackflies with insecticides. Insecticides have been sprayed from helicopters in endemic areas to reduce the population of blackflies
- Ivermectin is given once every 6 to 12 months in endemic areas.
Here are some useful health tips if you stay or plan to stay in areas endemic for onchocerciasis:
- Cover the body well leaving minimal exposed areas. Wear long-sleeved shirts and long pants. Cover your feet well with socks and shoes
- Use approved insecticides or repellents on the exposed parts of the skin
- Wear clothes that are pre-treated with permethrin to keep the blackflies away
- Since the blackfly bites during the day, make sure you take adequate precautions during the day
- Harrison’s Principles of Internal Medicine 19th edition
- Parasites - Onchocerciasis (also known as River Blindness) - (http://www.cdc.gov/parasites/onchocerciasis/)
Latest Publications and Research on Onchocerciasis / River BlindnessPost-elimination surveillance in formerly onchocerciasis endemic focus in Southern Mexico. - Published by PubMed
Genomic Epidemiology in Filarial Nematodes: Transforming the Basis for Elimination Program Decisions. - Published by PubMed
In vivo efficacy of the boron-pleuromutilin AN11251 against Wolbachia of the rodent filarial nematode Litomosoides sigmodontis. - Published by PubMed
Safety of high-dose ivermectin: a systematic review and meta-analysis. - Published by PubMed
Update on parasitic dermatoses. - Published by PubMed