What is River Blindness and What are the Causes

is a disease also known as Onchocerciasis. It is an infectious disease that is caused by a parasitic worm known as Onchocerca volvulus. This worm is a parasitic nematode belonging to phylum nematoda. It is more commonly known as African river blindness. This disease affects skin and eyes of its victim. The carrier of this disease is Simulium blackfly. The parasite lives in the antennae of its host. This disease is caused by the repeated bites of infected female blackflies of the genus Simulium when they get a blood meal from its human host. 

River Blindness is called so because of the blackflies that transmit their infectious strains on the banks of fast flowing rivers and streams. It is a .

Statistics

The percentage of people with river blindness is surprisingly high. According to a report of The World Health Organization (WHO) on onchocerciasis, it is estimated that at least 25 million people are infected with river blindness and 123 million people live in those places which put them at danger of acquiring this infection. Nearly three lac people are blind because of the infection by the parasite and another 0.8 million people have different types of visual deficiencies. About 99% of the people infected with the parasite live in Africa, others live in Yemen and six countries in the united states of America. The number of people infected with Onchocerca volvulus is highest in tropical regions.

 Symptoms

This disease is common in remote rural areas. The person is affected by repeated infectious bites.  River blindness has different symptoms depending upon the severity of infection. People suffering from heavy infections will generally have one or more of three complex symptoms.

  1. Rashes on skin which are usually itchy
  2. Eye disease leading to blindness
  3. Redness of eyes
  4. Saggy and scarred skin
  5. Lumps under the skin.
  6. Leopard skin
  7. High level of eosinophils in blood
  8. Darkening of skin
  9. Severe itching on skin
  10. And swelling of lymph nodes

The symptoms might not appear from months to even many years. However, the infection with larvae starts immediately, but the disease is not apparent for months to years. These bumps under the skin causes intense itching, inflammation and swelling.

Causes

It is caused by the bite of infected blackfly. The parasitic nematode Onchocerca volvulus lives in the antenna of infected blackfly. They are small in size. Adult female is larger than adult male. Adult male Onchocerca volvulus is 15 to 45 mm in length while adult female worm is 20 to 50 mm in length. Adults reside in bumps of subcutaneous tissues. Usually, a single bite does not result in the dissemination of disease. Repeated bites of the blackfly cause infection. Female blackfly is the carrier of this parasite. During breeding season, the female blackflies feed on human blood to lay eggs. This disease is more common in tropical regions. This infection is transmitted to a normal female blackfly when it takes a blood meal from an infected human host. This fly ingests microfilaria with the blood of an infected person. This microfilaria enters into the thoracic flight muscles and gut of the female black fly which ultimately progress into the first larval stage. These infectious larvae mature into the second larval stage. Maturation of larvae takes place in about seven-eight days. Now, the female black fly feeds on another blood meal, hence passing the infectious larvae into another human host. In the blood of host, the larvae move into the subcutaneous tissue, stay there for some time and undertake two more molts. Finally, they form bumps when they mature into adult worms in the period of 6 to 12 months. After maturation, adult female worms mate with adult male worms in the subcutaneous tissue of their hosts to produce between 700 and 1,500 microfilariae per day. Their reproduction rate is rapid. The microfilariae move to the skin during the day time because the black flies feed only during the day. In this way, parasites are in an appropriate position for the female blackfly to ingest them. These parasites can also move to other areas of body like connective tissues, sputum, urine and blood. Black flies take blood meals to continue their reproductive cycle in tropical regions. People living near flowing rivers and streams are mostly the victims of this disease.

Prevention

At present, there is no known drug, medicine, treatment or vaccine existing that averts onchocerciasis. Therefore, protection is better as there is no cure available. African river blindness can be prevented by avoiding blackfly bites. This can be done by evading those places where they are pandemic. This can stop infections. Other precautionary measures such as covering your body completely by wearing full sleeved shirts and pants tucked in long boots, insect repellent, insecticide spray, personal defense against blackfly bites also decreases the chances of infection. Permethrin is an insect repellent this can also be infused into clothes for extra fortification against blackflies.

Treatment

As it is stated above, there is no specific treatment or vaccine available; however, some medicines are used to relieve its symptoms. Two medicines are mostly used for this purpose. These are ‘’Doxycycline and Ivermectin’’. Treatment is started by giving the patient an anti-parasitic drug, ivermectin. This drug is given once or twice per year for about 10 to 15 years. This is because 10 to 15 years is the life span of the adult Onchocerca volvulus worms. This anti-parasite drug can paralyze and kill the microfilariae of worms, but it is not effective for adult worms. The mature parasitic worms can stay alive for about 10 to 15 years in the body of their host. Most of the doctors recommend that subcutaneous nodules should be removed by surgery. This is the only possibility to remove adult parasitic worms from the body of host. Otherwise, they can reproduce at a rapid rate to produce a large number of microfilariae over time. Others believe that after ivermectin treatment, patients may take advantage from a dose of an antibiotic, doxycycline. Doxycycline works by killing and damaging Wolbachia bacteria, these bacteria live inside the microfilariae and adult worms. This drug works by sterilizing the female worms, hence gradually decreasing their number.  This results in the death microfilariae and inefficient microfilariae are produced by the adult parasitic worms which survived. This process may slow down or stop further infection. Therefore, no complete treatment is known. Researches are being done to invent or discover new drugs that can treat this river blindness. At present, a new drug is under study for use in humans. This drug is effective for killing the adult Onchocerca volvulus worms. This drug has been named ‘’Moxidectin’’ but this drug has not yet been permitted by the scientists for use in human beings for the treatment of African river blindness. This drug is being administered in human beings for experimental purposes.

This disease is not contagious. It is transmitted only by the bite of infected female blackfly. It is one of the leading causes of blindness after trachoma. At present, it is not curable hence needs to be prevented.

 

Image courtesy of [radnattr] at FreeDigitalPhotos.net

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