What is Onchocerciasis?
Onchocerciasis is a parasitic disease caused by Onchocerca volvulus, which is a parasite. This parasite gets transmitted to humans through the bite of the female black fly. Onchocerciasis is also known as River Blindness because the vector, which is the black fly, often breeds near rapidly flowing rivers and streams; Also the fatal manifestation of Onchocerciasis is blindness; hence this disease is also known by the name River Blindness. Majority of patients who suffer from Onchocerciasis live in sub-Saharan Africa, however, this disease is also found in Yemen and South and Central American countries, albeit less frequently. Onchocerciasis is the second-main cause of blindness caused by infection.
What are the Causes of Onchocerciasis?
The cause of onchocerciasis is the parasite Onchocerca volvulus whose larva gets through the humans by the bite of the female black fly. After which the larvae enters the subcutaneous tissues in humans, it grows into adult female and male worms and reproduce in the human tissue resulting in formation of microfilariae. These microfilariae then migrate to other regions of connective tissue and sometimes even to sputum, urine and blood. Additionally Wolbachia, a genus of bacteria, colonize with these adult worms and help with the survival of these parasites. The death of these worms triggers a host immune response, which damages the optical tissue in the patient’s eyes leading to blindness.
What are the Risk Factors for Onchocerciasis?
People who live or visit sub-Sahara Africa and those epidemic areas of black fly are at an increased risk for developing onchocerciasis. Onchocerciasis commonly develops after multiple exposures to black fly bites; so travelers who are visiting these places for a short while carry somewhat a lesser risk; however, volunteer health workers, missionaries and other individuals who are spending some months in these areas are at high risk for contracting Onchocerciasis.
Is Onchocerciasis Contagious?
No, Onchocerciasis is not a contagious disease, i.e. it does not transmit from one person to another. Onchocerciasis gets transmitted to humans only through the bite of female black fly and repeated bites are needed before the infection is transmitted to humans.
What are the Signs & Symptoms of Onchocerciasis?
Patients with Onchocerciasis experience the following signs and symptoms:
- Inflammation of the skin where there is itchiness of the skin and formation of papules on the skin.
- There are saggy, drooping and scarred areas of skin.
- There is development of subcutaneous nodules or bumps.
- Patient has lymphadenitis (lymph node inflammation).
- Patient has patchy de-pigmentation of the skin which gives the appearance of leopard skin.
- Patient develops eye problems or eye lesions, such as redness, itching or swelling of the eyes.
- Patient experiences visual problems, such as visual impairment, inability to differentiate certain colors and even partial or complete blindness.
- Eosinophilia is present, which is the presence of increased levels of eosinophils in the blood.
- Patient develops severe itching and skin darkening/ discoloration which is described by the term "Sowda." This is usually confined to one limb.
Who Treats Onchocerciasis?
Patient’s general physician and primary-care provider commonly treats onchocerciasis. Other than this, infectious-disease specialists, dermatologist, ophthalmologist and travel-medicine doctors are also consulted to treat patients with onchocerciasis.
What is the Incubation Period for Onchocerciasis?
The infection with larvae starts immediately; however, the disease may not be apparent in the patient for months to years. In many of the patients, Onchocerciasis progresses slowly in the skin. There are a few patients who suffer from eye problems initially.
How is the Diagnosis of Onchocerciasis Made?
Patient’s Travel History: Diagnosis of Onchocerciasis is made on the basis of the patient’s travel history; whether the patient has visited areas where Onchocerciasis is endemic.
Physical exam of the patient is done to look for characteristic eye and skin changes, which indicate Onchocerciasis.
Excision of Skin Nodules: Definitive diagnosis of Onchocerciasis is made after excising the skin nodules and seeing the adult worms in them and also in eye lesions.
Punch Biopsy of the Skin: Diagnosis is also made by finding microfilariae in punch biopsies of the skin and in shavings/scrapings of the skin.
Immunological Test: Other than this, an immunological test can be done for antibodies which are produced against the parasites in the initial stages of infection. This immunological test is beneficial in determining whether a person is infected before the detection of microfilariae.
Definitive diagnosis of Onchocerciasis is important to start appropriate treatment on time Onchocerciasis is a type of filariasis which does not respond well to certain medicines that are used to treat similar filarial diseases.
How is Onchocerciasis Treated?
Treatment of Onchocerciasis using Anti-Parasitic Drugs
Treatment of Onchocerciasis is done by giving the patient an anti-parasitic drug, Ivermectin, around once or twice in a year for around 10-15 years, which is the life span of adult worms. Anti-parasitic drugs are effective in killing the microfilariae; however, they do not destroy the adult worms due to which the adult mature worms can remain alive for about 10-15 years within the patient.
Treatment of Onchocerciasis by Excising Subcutaneous Nodules
It is recommended to excise the subcutaneous nodules which will remove the adult worms thus preventing reproduction of more microfilariae.
Treatment of Onchocerciasis by Doxycycline Antibiotic
Some physicians recommend that after the patient has been given Ivermectin, patient should also be given a six-week dose of doxycycline antibiotic which will benefit the patient by killing the Wolbachia bacteria present inside the adult worms and microfilariae and cause the death of microfilariae. This will help in halting or slowing the disease Onchocerciasis.
Future Treatment of Onchocerciasis by Moxidectin
Studies are going on moxidectin which is a new drug that is capable of killing the adult worms of onchocerciasis. However, it has not been approved yet for use in humans in treatment for onchocerciasis.
Contraindicated Treatment of Onchocerciasis
Diethylcarbamazine is a medication which was used for treating Onchocerciasis before Ivermectin was available; however, Diethylcarbamazine is contraindicated, as there is a chance of this medicine causing fatal or severe reactions in patients with onchocerciasis.
What is the Prognosis of Onchocerciasis? Are there any complications of Onchocerciasis?
The prognosis depends on how soon Onchocerciasis is diagnosed and treated. The prognosis is good if the disease is adequately and promptly treated and the patient follows up their treatment schedule regularly with their physician. The prognosis is fair to poor if the diagnosis and treatment of Onchocerciasis is delayed, as the patient develops significant complications including changes in the skin, visual problems and even complete blindness.
Can Onchocerciasis be Prevented?
As of now, there no drug or vaccine to prevent onchocerciasis. One can prevent onchocerciasis by warding off black fly bites by avoiding endemic areas. There are other measures which can be taken, such as using insect repellent, wearing long-sleeved shirts and pants, keeping pants tucked in boots to prevent the biting of black fly as well as other insects. There is an insect repellent, Permethrin, which can be impregnated into clothes and netting thus providing additional protection against the bite of black fly.
- Impairment and Disability
- Hemianopia: Types, Causes, Treatment
- Disorder of Refraction or Refractive Disorder: Symptoms, Types, Treatment, Epidemiology, Causes
- What Causes Blurred Vision in One Eye & How is it Treated
- Exophthalmos or Bulging Eyes: Causes, Symptoms, Treatment, Diagnosis
- What is Traumatic Iritis: Causes, Symptoms, Treatment, Pathophysiology, Prognosis, Complications
- Visual Impairment: Types, Causes, Symptoms, Treatment, Diagnosis