Onchocerciasis is caused by a parasitic worm that can lives up to 14 years inside the human body. This neglected tropical disease is caused by the worm Onchocerca volvulus. Humans get this disease through the bite of Simulium blackflies. The blackfly breeds and lives around flowing water especially rivers and the disease can cause blindness that is why it is sometimes called river blindness. People severely affected by Onchocerciasis develop severe itching of the skin or eye lesions. Symptoms of the disease show up three years after the infectious larvae enters the body. The disease is predominant in Africa and a single dose of ivermectin once a year is all that is needed to improve symptoms and prevent transmission. Onchocerciasis is the second leading cause of blindness in the world.
CAUSES AND RISK FACTORS
Onchocerciasis is caused by the worm Onchocerca volvulus and transmitted by blackfly of the genus Simulium. The blackfly bites during daylight hours. When an individual gets bitten by the infected blackfly, the female larvae produces millions of worms that migrate throughout the whole body. The victims then starts to show symptoms of the disease such as itchy skin and eye lesion when larvae (microfilariae ) develops into adult worm called the filariae.
People living in Africa and around fast-moving water like rivers are at high risk of contracting Onchocerciasis.
Symptoms appear between nine months and 2 years of initial biting infection. Symptoms include the following :
- itchy skin rashes
- nodules under the skin
- vision changes
Untreated Onchocerciasis may progress to chronic dermatitis and hyperpigmentation (black skin). Patchy depigmentation on the legs leads to a condition known as leopard skin. Eye lesions only occur after several years of severe infection.
TEST AND DIAGNOSIS
A physical exam may be used to detect localized dermatitis. A skin biopsy known as skin snip may also be done to identify the microfilariae. When skin snip is placed in saline solution, microfilariae emerge. Polymerase chain reaction, a sensitive but highly expensive procedure may also be used to diagnose patients with low levels of infections. Nodules may be removed surgically to identify the adult worm.
The recommended treatment for Onchocerciasis is ivermectin (Mectizan®). It targets and kills circulating microfilariae as well as those that are still in the adult worm. The drug prevents the disease from progressing. Standard treatment for Onchocerciasis is once a year but individuals may be treated up to three times in one year.