The diagnosis of onchocerciasis can be difficult in light infections, which are more common in persons who have travelled to but are not residents of affected areas. There are multiple ways that the diagnosis can be made:

• The most common method of diagnosis is the skin snip. A 1- to 2- mg shaving or biopsy of the skin is done to identify larvae, which emerge from the skin when it is put in physiologic solutions (e.g. normal saline). Typically 6 snips are taken from different areas of the body. Polymerase chain reaction (PCR) of the skin can allow for diagnosis if the larvae are not visualized.
• In patients with nodules in the skin, the nodule can be surgical removed and examined for adult worms.
• Infections in the eye can be diagnosed with a slit-lamp examination of the anterior part of the eye where the larvae or the lesions they cause are visible.
• Antibody tests have been developed to test for infection, though they are not widely available in the United States. These tests cannot distinguish between past and current infections, so they are not as useful in people who lived in areas where the parasite exists, but they are useful in visitors to these areas. Some of the tests are general tests for infection with any filarial parasite and some are more specific to onchocerciasis.

People who are found to be infected with O. volvulus should be treated in order to prevent the long-term skin damage and blindness. The recommended treatment is ivermectin, which will need to be given every 6 months for the life span of the adult worms or for as long as the infected person has evidence of skin or eye infection. Ivermectin kills the larvae and prevents them from causing damage but it does not kill the adults. There is a promising new treatment using doxycycline that kills the adult worms by killing the Wolbachia bacteria on which the adult worms depend in order to survive. If you are infected, it is possible that your doctor will want to treat you both with the ivermectin and the new treatment. Before any treatment is begun, however, you need to make sure that you are not also infected with Loa loa, another filarial parasite that is sometimes found in the same areas where O. volvulus is found, because Loa loa can be responsible for severe side effects to the medications used to treat onchocerciasis.

There are no vaccines or medications available to prevent becoming infected with O. volvulus. The best prevention efforts include personal protection measures against biting insects. This includes wearing insect repellant such as N,N-Diethyl-meta-toluamide (DEET) on exposed skin, wearing long sleeves and long pants during the day when blackflies bite, and wearing permethrin- treated clothing. For a description of the CDC’s information for preventing insect bites, refer to CDC's Yellow Book. Mass distribution of ivermectin, donated by Merck & Co., Inc., to all people living in many areas where O. volvulus is found is being given to control onchocerciasis.