Onchocerciasis – or river blindness – is a parasitic disease caused by the worm filariae Onchocerca volvulus. River blindness is one of the most common infectious causes of blindness worldwide.
What is river blindness?
A massive health problem, river blindness occurs in over 99% of all cases in sub-Saharan Africa, but it is also known to occur in Yemen and Latin America. In the past, fear of river blindness led many people to leave the fertile river valleys of the African savannah. An estimated 18 million people are infected by river blindness, and about half a million people are blind or visually impaired by the disease. River blindness also causes skin lesions with depigmentation and severe, unrelenting itching. Untreated infection with river blindness reduces the host’s immunity and resistance to other diseases, consequently shortening lifespan by about 13 years.
Causes
The nematode that causes river blindness is transmitted by the bite of infected female Simulium black flies that habitat in fast-flowing streams and rivers. The parasite is initially ingested via an infected human host and matures to larvae in the blackfly for about 7 days. When bitten again, the larva is transferred into the blood of the next host. There, the larvae penetrate the subcutaneous tissue, mature for six to twelve months, and can live as worms in the human body for up to 15 years. In the adult stage, the worms mate and produce more microfilariae, which form nodules under the skin. Dying microfilariae release the Wolbachia bacterium. This causes intense inflammatory reactions that trigger an immune system response (river blindness).
Symptoms, complaints, and signs
River blindness (onchocerciasis) is characterized by a variety of symptoms, which are mainly determined by the strength of the immune system‘s response to the microfilariae. Typical symptoms include itching of the skin, skin inflammation, eczema formation, lymph node swelling in the groin region, changes in skin pigmentation, skin thickening due to fibrous damage to the skin, skin abscesses, vascular inflammation, development of palpable skin nodules, and eye problems. Especially the eye problems give the disease its name, because in severe cases they can lead to complete blindness. When the nematodes migrate into the eyes, damage to the entire visual organ occurs. The eye symptoms range from conjunctivitis to glaucoma. These include eye inflammation, eye itching, tearing and burning. Sufferers have the feeling that there is sand in the eyes. Similar symptoms are also described in choroiditis. However, the intraocular pressure may increase and glaucoma may develop. Since the high intraocular pressure damages the optic nerve, glaucoma can lead to complete blindness. Furthermore, damage to the cornea also occurs. Initially, punctiform corneal defects occur, which can later develop into a corneal opacity with a loss of vision. Here, too, pain, eye redness, increased lacrimation and sensitivity to light occur initially. More rarely, optic neuritis is also observed. Without treatment of river blindness, susceptibility to infection generally increases with reduction in life expectancy.
Diagnosis and course
Skin patch tests are used to confirm the diagnosis because river blindness causes different types of skin lesions. The severity of the disease is directly proportional to the number of infected microfilariae and the resulting immune response. In the most common cases, river blindness is accompanied by skin inflammation accompanied by hyperpigmentation (microfilariae shed through the skin) and severe itching. Other characteristic skin manifestations of river blindness include “leopard skin” (depigmentation on the lower legs), “elephant skin” (thickening of the skin), or “lizard skin” (thickened, wrinkled skin). People with river blindness may have several hundred nodules on the skin ranging in size from one to five centimeters in diameter, which are usually not painful.River blindness can also affect any part of the eye from the conjunctiva to the cornea, including the retina, as well as the optic nerve, causing visual disturbances and even blindness.
Complications
Complications occur with river blindness primarily because the disease does not become apparent and lead to symptoms until about six months after infection. There is usually swelling of the lymph nodes and a skin rash. The rash is often associated with severe itching and feels very uncomfortable. The patient’s daily life is restricted as a result. The affected person also suffers from lumps, which settle in different parts of the body. The affected areas dry out and itch. As a rule, the nodes cause a strong feeling of shame. Complications can also occur if the worms enter the eye and inflame the optic nerve. This results in severe pain and clouding of the lens. In the worst case, the patient can go completely blind or suffer from glaucoma. If river blindness is not treated, there is also serious damage to the immune system and the patient becomes more susceptible to various immune diseases. Treatment of river blindness is usually done with the help of medications and in most cases leads to a positive course of the disease. If the worms are located near the eyes, surgical intervention is necessary.
When to go to the doctor?
In case of river blindness, it is always necessary to see a doctor immediately. In the worst case, this disease can lead to complete blindness of the affected person and for this reason should always be treated immediately. Sufferers must then see a doctor if they have been bitten by a mosquito in a tropical region and feel the symptoms of river blindness. These include a very itchy rash on the skin and also swelling of the lymph nodes. General fatigue and exhaustion may also indicate the disease. Furthermore, river blindness causes unusual pigmentation on the skin and also nodules that form near joints. In the further course of the disease, the eyes are also damaged, resulting in visual complaints or conjunctivitis. Immediate treatment is necessary for these symptoms. Treatment can usually be carried out by a general practitioner or in a hospital. The earlier the disease is diagnosed, the better the prospects for a positive course of the disease. Good hygiene can also prevent river blindness.
Treatment and therapy
Ivermectin (e.g., Mectizan) is the main drug used to treat river blindness. It paralyzes and kills the microfilariae, reduces intense itching, and stops the progression of river blindness to prevent blindness. At the same time, it stops further production of microfilariae for several months by paralyzing the parasitic reproductive organs, thus reducing the transmission rate of river blindness. Infected humans can be treated with two doses of ivermectin given 6 months apart. Thereafter, a single dose of ivermectin must be taken annually for 3 years to maintain efficacy. For best efficacy, WHO recommends treating entire communities at the same time. Since the final hosts of river blindness are humans, animals do not need to be treated. Other drugs used to treat river blindness are used to kill the bacterium Wolbachia, which lives in symbiosis with the worms, and to sterilize the female nematodes. These include the tetracycline antibiotic doxycycline in addition to the antiparasitic moxidectin. However, this adjunct therapy for river blindness requires daily dosing for at least four to six weeks, which is difficult to implement in crisis areas.
Outlook and prognosis
The prognosis of river blindness depends on the number of pathogens present in the organism and the disorders that have already occurred. A particular difficulty is the timing of diagnosis. By the time impairments are consciously perceived, the causative parasite of the disease has already been in the body of the affected person for approximately six months to three years.Since the nematode occurs mainly in Africa or Latin America, residents and travelers from these areas are particularly at risk. Due to the long incubation period, tourists or guests of the regions often lack the connection and correlation of the occurring symptoms with the stay in the tropical region. This makes early diagnosis difficult and often delays the start of treatment. If medical therapy is not started, the patient is threatened with complete blindness. With good and efficient medical care, onchocerciasis is easily treatable and curable. The existing symptoms regress and there is a gradual improvement in the general state of health. Patients can be discharged as symptom-free after completion of drug treatment. As the disease is being intensively and systematically combated by the WHO worldwide, a decrease in the incidence of river blindness and faster and better treatment can be expected in the coming years.
Prevention
Through the vector-organized use of environmentally friendly insecticides on rivers to control blackfly populations, WHO has been implementing prevention measures to control river blindness for more than 40 years. For the treatment of river blindness, the manufacturer of ivermectin – Merck and Co. Inc – has provided the drug free of charge since 1987.
Follow-up
As a rule, the measures and possibilities of aftercare for onchocerciasis prove to be very difficult or are only barely possible in the process. First and foremost, of course, the contact with the infected water should be interrupted, so that it does not come to a new infection or transmission. In general, a high standard of hygiene should be maintained to prevent infection and to treat onchocerciasis properly. In most cases, onchocerciasis is treated with the help of medications that can completely alleviate the symptoms. There are rarely any particular complications. The affected person is dependent on regular and correct use of the medication in order to completely alleviate the symptoms. Attention should also be paid to the correct dosage. If there are any questions or uncertainties, a doctor should always be consulted. In most cases, the medication must continue to be taken for some time after the symptoms have subsided. Self-cure cannot occur with this disease. If onchocerciasis is detected and treated early, there is usually no reduced life expectancy of the affected person.
This is what you can do yourself
In any case, river blindness must be treated by a physician. Possibilities for self-help are very limited in this disease, so that the affected person is primarily dependent on drug treatment. As a rule, the medication must be taken for almost three years. Care should be taken to avoid interactions with other medications so as not to reduce the effect of the substance. However, river blindness can be well prevented by using insecticides in rivers. Good hygiene can also prevent infection. If river blindness is not treated, the patient may go completely blind. In this case, the affected person is then dependent on support in his or her everyday life. This should be provided primarily by family or friends. In severe cases, the affected person is also dependent on psychological treatment. Conversations with other affected patients are often very helpful in mastering everyday life. In order to guarantee a positive course of the disease in river blindness, an immediate treatment should be guided. In doing so, further complications can be avoided, which in the worst case can lead to blindness.
