Onchocerciasis (River Blindness)

Introduction

The causative agent of this disease is the parasite Onchocerca volvulus which can lead to skin rashes, itching, and visual disturbances. It transmits through the bites of black flies. This disease is also called river blindness because the blackfly that causes the infection presents near the river. Frequent bites from the fly can lead to blindness. Antiparasitic and antibiotics are usually recommended to treat this disease.

What Is Onchocerciasis or River Blindness?

This disease is caused by the parasite Onchocerca volvulus and spreads in humans from the bite of a blackfly called Simulium. This black fly is most commonly found near rivers, and the more severe form of this disease can lead to blindness. Onchocerciasis is the second cause of blindness after trachoma. It is also classified in the neglected tropical diseases list, and it is not a contagious disease.

What Is the Cause of River Blindness or Onchocerciasis?

The cause of river blindness is the transmission of larvae of the Onchocerca volvulus parasite when the female blackfly bites the person. This larva penetrates the skin's subcutaneous tissue and grows into an adult male and female parasite. After reproduction in the subcutaneous tissue, they produce microfilariae and move to the other connective tissue regions and sometimes to the blood, sputum, and urine. The adult parasites and microfilariae established colonies with bacteria that help in the survival of these parasites. When the parasite dies, a host immune response develops, which destroys the optical tissues of the eye. This life cycle continues when the blackfly bites a person and removes microfilariae.

What Are the Sign and Symptoms if a Person Gets Infected With River Blindness or Onchocerciasis?

The sign and symptoms in an infected person include:

• A skin inflammation that results in itchy and blisters on the skin.

• Subcutaneous nodules or bumps in the skin.

• Scarring and drooping of the skin.

• Vitiligo (skin loses its pigment cells), also called leopard skin.

• Inflammation of the lymph nodes.

• Eye inflammation (swelling, redness, and itching in the eyes).

• Visual disturbances, color blindness (inability to see the difference between colors), and incomplete or complete blindness.

• Increased levels of eosinophils in the blood (eosinophilia).

• Intense itching and darkening of the skin of one limb (sowda).

• Infection with the larvae starts as soon as the fly bites a person, but the symptoms may appear for months to years. In most people, visual disturbances occur initially.

What Are the Risk Factors for River Blindness or Onchocerciasis?

Individuals are at high risk if they live near rivers in intertropical areas because blackflies live and reproduce there. Travelers might not get this disease because this fly needs multiple bites to get the infection. The volunteers, missionaries, and the people living in Africa are at a higher risk.

How to Diagnose River Blindness or Onchocerciasis?

A primary diagnosis is made if the patient lives or travels to these areas and has skin and eye inflammation. The doctor will perform a skin biopsy called a snip test. In this procedure, the doctor will remove two to five milligrams of skin and put it in a saline solution, which causes microfilariae to appear in the solution.

Another test used for diagnosis is called the Mizzotti test, in which the skin sample is tested with the drug Diethylcartbamazepine. Diethylcartbamazepine causes the death of the microfilariae and produces symptoms like itching within two hours of giving the medicine. The doctor may provide this drug in the form of oral medication or put this medication on the skin. If the infection persists, severe itching develops within two hours of taking this medication orally, and itching with rash develops after putting it on a skin sample. A nodulectomy test is also done in which the doctor removes the nodule surgically and checks for microfilariae.

Polymerase chain reaction (PCR) is also a very highly effective test, and it requires a small skin sample and works by boosting the deoxyribonucleic acid of the microfilariae. Even minute infections are detected by this test, and it is a costly procedure. Another practical test is called a rapid format antibody card test, in which a drop of blood is put on the card. Suppose the card changes its color; that means that infection is present. This test requires less equipment and is highly effective.

How Is River Blindness or Onchocerciasis Treated?

Previously this disease is treated with Diethylcarbamazine, which kills the microfilariae, but the death of microfilariae produces certain side effects in the body like fever, rash, anaphylaxis, body pain, and inflammation in the eyes. So, nowadays, it is being treated with the drug Ivermectin. Ivermectin kills the microfilariae and disinfects it in the body for approximately six months, thereby preventing the production of microfilariae in the body. Ivermectin is prescribed once daily for six to twelve months, but treatment may be of longer course depending upon the severity of the infection. Treatment with this drug in the initial stages can improve inflammation as well as visual disturbances.

How to Prevent Getting River Blindness or Onchocerciasis?

No vaccines or medications are available to prevent infection with O. volvulus. Prevention can lower the risk. The various methods of prevention of this disease as follows:

• Diethyltoluamide (DEET) spray on the skin per the manufacturer’s directions.

• Apply sunscreen 20 minutes before applying the DEET spray.

• Apply permethrin on the clothes and shoes, but not on the skin. It kills the insect that comes in contact.

• Cover the body adequately with clothes while going outside, and wear a hat with a mesh net that covers the neck and face.

• Close windows and doors properly so the fly will not come inside the house.

Conclusion

Doxycycline is the new drug that kills and disinfects the parasite and produces long-lasting results. The daily dose of Ivermectin and Doxycycline is the most effective treatment for onchocerciasis. If this disease causes serious infections in the eyes, then surgery may be required, like a corneal transplant to replace the inflamed cornea with the healthy one, glaucoma and retinal surgeries, and cataract removal are required.