Onchocerciasis (African River Blindness)

What is Onchocerciasis (African River Blindness)?

Onchocerciasis, also called African river blindness, ranks as the second leading cause of blindness from infection around the world, after a disease known as trachoma.

This disease is caused by a type of worm known as the filarial nematode, specifically the Onchocerca volvulus. It’s spread through the repeated bites of a female black fly, a species called Simulium damnosum. These flies tend to breed in areas around rivers that have fast, oxygen-rich currents. This is why the disease often spreads along these river areas, hence the name “river blindness”.

In addition to causing blindness, onchocerciasis can also lead to a long-lasting and very uncomfortable skin irritation known as chronic dermatitis.

What Causes Onchocerciasis (African River Blindness)?

Onchocerca volvulus, the parasite that causes a disease known as river blindness, needs two hosts to complete its life cycle: humans and a type of black fly known as Simulium. The black fly helps the parasite grow by providing the environment for its larval stages (the stages the parasite goes through before becoming an adult). There are different types of black flies, which are classified based on how they fly and their genetic patterns.

Black flies live in various environments such as savannas, rainforests, and transitional zones. They have different biting habits and some are more likely to spread the disease that leads to blindness.

When a female black fly bites a human, it injects tiny larvae of the parasite into the person’s bloodstream. These larvae then grow into adult worms over six to 12 months. The worms live in lumps under the skin, often around the waist, head and torso. Each lump may contain a couple of female worms and a smaller male worm. These worms mate and produce between 1000 to 1500 tiny baby worms every day and can live for 10 to 15 years.

These baby worms are extremely small – about the width of a human hair – and live for up to two years. There could be millions of them moving around under the skin and, to a lesser extent, in the lymphatic system, which is part of the body’s immune system.

When a black fly bites an infected person, it can suck up these baby worms, which then grow and develop within the fly over one to three weeks. Once they’re mature, they move into the fly’s salivary gland, ready to be injected into the next person the fly bites. Once inside a human, these larvae take about a year to mature into adult worms.

Risk Factors and Frequency for Onchocerciasis (African River Blindness)

This disease is found mostly in 31 sub-Saharan African countries, the Arabian peninsula, and a small area in Latin America, spanning Venezuela and Brazil. The vast majority of occurrences are in Sub-Saharan Africa, with about 90% of cases happening there.

According to the World Health Organization (WHO), around 25 million people worldwide have this disease, and a further 90 million people are at risk, almost all of whom are in Africa. It’s estimated that over a million people have lost their vision as a result of this disease.

Treatments using a mass supply of the drug ivermectin have helped to significantly reduce the disease and related eye conditions. However, a recent study in 2018 from Togo has raised concerns. Despite the mass treatment, young adults and children were found with eye illnesses due to the disease, and the rates of small worm-like parasites were not declining as expected.

The disease is more commonly found in people who work in agriculture and live near rivers. These rivers are where the Simulium black fly, which spreads the disease, breeds. A study in Ethiopia discovered that men, people living less than 2km from a river, those who didn’t take ivermectin, and people over 35 years old were all more likely to have the disease.

• The disease is prevalent in 31 sub-Saharan African countries, the Arabian peninsula, and a small area in Latin America covering parts of Venezuela and Brazil, with 90% of cases occurring in Sub-Saharan Africa.
• The WHO estimates that at least 25 million people have the disease worldwide, and another 90 million are at risk, the vast majority of whom are in Africa.
• Onchocerciasis causes vision loss in about 1.15 million people.
• Mass administration of the drug ivermectin has greatly reduced disease levels, but concerns have arisen due to a study from Togo.
• Increased risk of the disease has been observed in individuals engaged in the agricultural industry, living near rivers, not taking ivermectin therapy, males, and those over 35 years old.

Signs and Symptoms of Onchocerciasis (African River Blindness)

The most common symptoms of this particular skin condition include persistent severe itching, skin sores, thick inflamed patches of skin, and areas of lightened skin. This usually affects the lower part of the legs and can often result in a pattern similar to a leopard’s skin. The skin patches become lighter due to the constant scratching to relieve itching caused by the body’s immune response to tiny dead or dying worms (microfilariae). These skin symptoms usually show up years before eye problems do.

• Severe persistent itching
• Skin sores
• Thick and inflamed patches of skin
• Lightened skin patches, especially on the lower legs

Eyes can be affected too, and symptoms may include recurrent eye inflammation (conjunctivitis), small painful inflamed spots on the cornea (punctate keratitis), sensitivity to light (photophobia), and an increasing loss of vision due to scarring of the cornea (anterior damage) or damage to the optic nerve and the part of the eye responsible for detailed central vision (posterior damage). Dead microfilariae can cause specific focal corneal reactions that resemble stage 3 adenoviral keratitis (a viral infection of the eye).

Continual injury and healing of the cornea results in more and more scarring, which is typically noticed initially at the border between the cornea and the white part of the eye (limbal area) and eventually leads to blindness. The diseases related to the back of the eye (posterior segment) have to do with the optic nerve and the death of the cells that line the back of the eye (atrophy).

Testing for Onchocerciasis (African River Blindness)

A slit-lamp examination could show the presence of small spots or flake-like patterns (punctate and snow-flake keratitis) on your eyes. This usually happens as a reaction to dead or dying tiny worms (microfilariae). In some rare cases, it could also cause swollen areas around the edges of your cornea (limbal global infiltrates), especially if medication has been started. Continuous flares of these corneal reactions could lead to lasting scars on your cornea. Other signs may be related to conditions like uveitis, cataract, and glaucoma.

At times, we may be able to see these microfilariae in the cornea (transparent, front part of your eye) and more often, in the front part of your eye (anterior chamber). Here, they can be seen swimming actively, which can even be filmed. In order to increase the chance of spotting them, you may be asked to lean forward with your head between your knees for at least 3 minutes.

There could also be non-specific features that can be seen in the back of your eye (posterior segment), like inflammation of the tissues between your retina and sclera (chorioretinitis), gradual damage to the retinal pigment epithelium (RPE) layer, and loss of nerve tissue in your eye (optic nerve atrophy). For a more comprehensive assessment, we may need additional imaging and tests such as detailed pictures of your retina (fundus photo), a test that uses light to create detailed images of the retina and optic disc (optical coherence tomography), autofluorescence imaging of your eyes, angiography, or a visual field test.

We can diagnose the disease onchocerciasis based on clinical signs and symptoms. By using a high-magnification instrument (slit lamp biomicroscope), it is possible to see microfilariae in the anterior chamber. “Skin snips” are considered the best method for diagnosing onchocerciasis. For this, small samples of skin from various areas like your shoulder blade, hip bone area, or calf muscle are taken. These samples are soaked in salt water (saline) 24 hours and then checked under a microscope. Microfilariae have specific characteristics that help to differentiate them from other worms like Wuchereria bancrofti, Brugia malayi, and Brugia timori.

There are also other tests that check for antibodies for Onchocerca volvulus (the worm responsible for onchocerciasis) in your skin, tears, or urine samples. Tests such as ELISA (enzyme-linked immunosorbent assay) and Western Blot are currently used for this. There are also techniques like PCR (polymerase chain reaction) and ultrasound scanning that can help identify the disease, but these are rarely used in managing onchocerciasis.

Performing a skin snip involves taking a small biopsy (skin sample) to check for microfilariae. First, an area of skin is cleaned with alcohol, then a tiny piece is raised with a needle and cut (about 3mm in diameter). This piece of skin is placed on a microscope slide, covered, and soaked in saline at room temperature for 24 hours. This allows any microfilariae present to come out of the skin and can be seen under a microscope.

Treatment Options for Onchocerciasis (African River Blindness)

In the past, a medication known as diethylcarbamazine was often used to treat onchocerciasis, a parasitic disease that can cause blindness and skin disorders. However, this medication was known to cause serious side effects, especially in patients with high levels of parasites in their body.

Currently, the preferred treatment for onchocerciasis is a drug called ivermectin. This medication is usually taken orally once or twice a year for a period of 10 to 15 years. This drug is designed to interfere with the function of the parasites, specifically targeting the younger ones and reducing the reproductive ability of the adult parasites. It should be noted that ivermectin does not kill adult worms, it only paralyzes or kills the younger ones. As such, the drug has to be taken for as long as the patient displays symptoms of infection such as skin itching or presence of parasites on the skin.

Ivermectin is effective in reducing severity of the skin disease and the occurrence of blindness due to onchocerciasis. It has been found that increased frequency of ivermectin administration can reduce the duration of the disease and the infectivity of the adult worms, particularly for people who no longer live in areas where the disease is common

Despite the effectiveness of ivermectin, a major hurdle in the treatment of onchocerciasis is the absence of medications that can safely and effectively kill the adult parasites. Currently, a drug known as doxycycline holds promise as it can potentially kill the adult worms by targeting bacteria called Wolbachia, which are crucial for the survival and reproduction of the worms. However, this medication does not kill the younger parasites, so it often has to be used in combination with ivermectin.

Older treatments such as suramin and diethylcarbamazine, are generally avoided today because they are less effective and can pose greater risk of harmful side effects. Diethylcarbamazine may even accelerate the progression of blindness. Special care should also be taken for patients who are co-infected with Loa loa, also known as African eye worm, because ivermectin can cause serious reactions in these cases. It’s crucial to consult with specialists before starting therapy in these circumstances.

What else can Onchocerciasis (African River Blindness) be?

Onchocerciasis, a type of parasitic disease, is often challenging to diagnose because it can cause both skin and eye symptoms. These symptoms can resemble those from other sources or diseases which may sometimes make it difficult to accurately diagnose.

For example, skin itchiness can be a result of allergic reactions, while bumps under the skin may be due to various other conditions. Some of these conditions include:

• Inflammatory conditions like rheumatoid arthritis or skin inflammation complications
• Metabolic disorders such as gout, or conditions that cause a build-up of certain substances in the body
• Conditions caused by bacterial, fungal, or viral infections
• Parasitic diseases like Chagas disease
• Tumors, whether harmless (benign) or cancerous (malignant).

Eye symptoms seen in onchocerciasis are also not unique to the disease, as they can be caused by several eye conditions like uveitis (eye inflammation), cataracts, glaucoma, and may also be due to certain changes at the back of the eye.

It’s also worth considering other types of parasitic infestations when diagnosing onchocerciasis. These could include infestations with hookworms, schistosomiasis (a condition caused by a different type of parasite), sparganosis (another type of parasitic infection), and cestodes.

What to expect with Onchocerciasis (African River Blindness)

Onchocerciasis, also known as river blindness, can cause issues with the eyes and skin. These problems often get better when treated with a medication called ivermectin, particularly if the disease hasn’t progressed too far. However, if the disease is advanced, the damage caused to the eyes, such as blindness due to damage to the optic nerve (optic atrophy) or scarring and blood vessel growth in the cornea, cannot be reversed. Similarly, advanced skin changes, like loss of skin color (depigmentation) and thinning of the skin (atrophy), are also irreversible.

Possible Complications When Diagnosed with Onchocerciasis (African River Blindness)

Onchocerciasis, also known as river blindness, can cause various eye complications which can lead to blindness. These issues often include inflammation of the cornea (keratitis), overgrowth of fine blood vessels on the corneal surface (pannus), and scarring of the cornea. Blindness can also happen due to other reasons such as decay of the optic nerve (optic atrophy), a type of eye condition that damages the eye’s optic nerve called open-angle glaucoma, and inflammation of the middle layer of the eye and retina (chorioretinitis).

Half of the blindness cases from onchocerciasis are caused by complications related to the back part of the eye. These complications might include changes in the choroid and retina that result in the clumping of pigments inside the retina, wastage of the epithelial tissue in the retina, inflammation of the retina, fibrosis beneath the retina, and inflammation of the optic nerve.

Additionally, other eye complications might include the presence of live and dead tiny worms in the front chamber of the eye and the cornea, tiny areas of opacity in the cornea, hardening of the cornea (sclerosis keratitis), formation of pannus, and eye inflammation, specifically in the iris and the ciliary body (uveitis).

Eye Complications of Onchocerciasis:

• Blindness
• Inflammation of the cornea (Keratitis)
• Overgrowth of fine blood vessels on the corneal surface (Pannus)
• Corneal scarring
• Decay of the optic nerve (Optic Atrophy)
• Open-angle glaucoma
• Inflammation of the middle layer of the eye and retina (Chorioretinitis)
• Changes in the choroid and retina, resulting in the clumping of pigments inside the retina
• Wastage of the epithelial tissue in the retina
• Inflammation of the retina
• Fibrosis beneath the retina
• Inflammation of the optic nerve
• Presence of live and dead tiny worms in front chamber of the eye and the cornea
• Tiny areas of opacity in the cornea
• Hardening of the cornea (Sclerosis Keratitis)
• Formation of Pannus
• Eye inflammation, specifically in the iris and the ciliary body (Uveitis)

Preventing Onchocerciasis (African River Blindness)

You can avoid getting Onchocerciasis, a type of parasitic infection, by preventing bites from the bugs that spread it. This involves using bug repellent on your skin or wearing protective clothing. People travelling to areas where this infection is common should be well-informed about these preventive measures.

Efforts to control the spread of this infection also include getting rid of the environments where these bugs thrive. This approaches, known as “vector habitat control programs”, are being actively promoted.

In some areas where the disease is common, strategies include the elimination of these bugs and providing a drug called ivermectin to everyone, every year.

If you have a high number of microfilariae, tiny worms involved in this infection, you should know that treating this can lead to a severe reaction, especially if you also have Loa loa (another parasitic infection). This reaction can be quite serious and even life-threatening. If you have a lot of microfilariae and your eyes are involved, you should also be aware of possible complications from using ivermectin.