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Onchocerciasis

Onchocerciasis or river blindness is the world's second leading infectious cause of blindness. It is caused by Onchocerca volvulus, a parasitic worm that can live for up to fourteen years in the human body. more...

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Life cycle

The life cycle of O. volvulus begins when a parasitised female Black fly of the genus Simulium takes a blood meal. Saliva containing stage three O. volvulus larvae passes into the blood of the host. From here the larvae migrate to the subcutaneous tissue where they form nodules and then mature into adult worms over a period of one to three months. After the worms have matured they mate, the female worm producing between 1000 and 1900 eggs per day. The eggs mature internally to form stage one microfilariae, which are released from the female's body one at a time.

The microfilariae migrate from the location of the nodule to the skin where they wait to be taken up by a black fly. Once in the black fly they moult twice within seven days and then move to its mouthparts to be retransmitted.

Causes of morbidity

When the microfilariae migrate to the skin they are a target for the immune system. White blood cells release various cytokines that have the effect of damaging the surrounding tissue and causing inflammation. This kills the microfilariae but is the cause of the morbidity associated with this disease.

In the skin this can cause intense itching that leads to the skin becoming swollen and chronically thickened, a condition often called lizard skin. The skin may also become lax as a result of the loss of elastic fibres. Over time the skin may lose some of its pigment; on dark skin this gives rise to a condition known as leopard skin.

The symptom that gives the disease its common name river blindness is also caused by the immune system's reaction to the microfilariae. The surface of the cornea is another area to which the microfilariae migrate, where they are also attacked by the immune system. In the area that is damaged, punctate keratitis occurs, which clears up as the inflammation subsides. However, if the infection is chronic, sclerosing keratitis can occur, making the affected area become opaque. Over time the entire cornea may become opaque, thus leading to blindness.

Treatment and control

The treatment for onchocerciasis is ivermectin (mectizan); infected people can be treated once every twelve months. The drug paralyses the microfillariae and prevents them from causing itching. In addition, while the drug does not kill the adult worm, it does prevent them from producing additional offspring. The drug therefore prevents both morbidity and transmission.

Since 1988, ivermectin has been provided free of charge by Merck & Co. through the Mectizan Donation Program (MDP). The MDP works together with ministries of health and non-governmental development organsations such as the World Health Organisation to provide free mectizan to those who need it in endemic areas.

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Success in Africa : The Onchocerciasis control programme in West Africa, 1974-2002
From Indian Journal of Medical Research, 6/1/03 by Das, P K

Success in Africa : The onchocerciasis control programme in West Africa, 1974-2002 (World Health Organization, Geneva) 2002. 72 pages. Price : Sw.fr. 25.00/US $ 22.50; in developing countries: Sw.fr.12.50 ISBN 92 41562277

Onchocerciasis commonly known as river blindness, is a parasitic disease caused by filarial worm, Onchocerca volvulus and transmitted by a vector black (Ty Simuliuin damnosum. The symptoms include intensely itching rashes to wrinkling, thickening and degimentation of skin, lymphadenitis resulting in hanging groins, general debilitation including loss of weight.

River blindness is localized in communities living close to rocky rivers in which the Simulium breeds, in Onchoccrciasis Control Programme (OCP) areas vector consisted of six cytotaxonomically distinct forms of S. damnosum. Two members of the S. damnosum complex are noted for their exceptional flight activity and are capable of migrating to a distance of more than 300 km during the wet season. The most serious condition like visual impairment including blindness was the major impediment to socio-economic development. The prevalence of eye lesions in the three important bioclimatic zones namely forest, Guinea savannah, and Sudan savannah is now attributed to strain differences within the parasitic population.

In 1974 OCP was launched by the World Health Organization (WHO) covering seven West African countries and later extended to 11 countries. The programme was vertical m nature to control single disease. This generated some degree of skepticism as most of the countries were embracing the concept of integrated primary health care. Since then almost 30 years have passed and it is learnt that the control of parasitic diseases require sustained efforts from all partners.

To summarize more than 25 years of control efforts of a complex disease, operational complexity and inter country partnership in only sixty five pages is a Herculean task done by the WHO and OCP. This report provides invaluable information on the history, legacies and success of the Programme. The report is organized in eight section namely Imagine; Onchocerciasis and Africa, before the OCP; Knowing the enemy; Sickness, flies and worms; Science becomes practice: Planning control on a large scale; Concentric circles: How the OCP worked; Meeting the challenges: Conceptualising OCP's history; Looking back: Success in Africa; and The future. Besides these eight sections, a foreword written By Dr Ebrahim A. Samba, Regional Director of WHO Regional Office for Africa and a preface by Dr Boakye A. Boatin, Director, OCP set the background in which OCP was launched and highlighted the benefits of partnership approach.

The salient features of the OCP have been highlighted in this report. This is the first disease control programme where socio-economic development was one of the objectives. This concept has also been used for lymphatic filariasis elimination. It was one of the largest inter-country field operations protecting ultimately 30 million people in 11 countries. The section Onchoccrciasis in Africa, before the OCP raised an important issue of disrupting environmental harmony due to so called developmental activity and its implication on the disease. The number infected in stable ecosystem and sparse human population increased in epidemic proportion due to sustained contact with Europeans and demands of colonialism on the local people forced population movements and unfamiliar agricultural pursuits caused rapid changes in the balance between pathogens and humans. This is a lesson every one should learn that globalization and innovative agricultural practices have some price to pay in terms of public health problems it creates.

This is an excellent report which should be read by all public health specialists and students of preventive and social medicine. This report is an essential reading for planners and policy makers. Since risk of transmission still exists, one has to continue mass treatment with ivermectin. Hope this project will continue until the risk is eliminated.

Dr P.K. Das

Director

Vector Control Research Centre

Indira Nagar

Pondicherry 605006

Copyright Indian Council of Medical Research Jun 2003
Provided by ProQuest Information and Learning Company. All rights Reserved

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