New weapon defeats the river worm

A medical programme to eradicate river blindness enters its second decade with great results, writes Anthony Gilbert

For centuries, a debilitating, disfiguring and often blinding disease called river blindness (onchocerciasis) has plagued people who live in tropical regions.

The disease is endemic in 35 countries, primarily in parts of Central and West Africa and limited areas in Central and South America. At present, 18-million people are infected and approximately one to two million have been blinded or visually impaired by the disease.

River blindness is transmitted by an insect: a female blackfly bites a human being and deposits the larvae of a parasitic worm. The larvae mature, mate and produce millions of microworms, or microfilariae, a year. A single victim can host as many as 200-million. Blindness sets in when these tiny worms migrate to the victim’s eyes.

In endemic areas people return repeatedly to the rivers to wade, fish, bathe or collect water, which places them at great risk of infection, as this is the blackfly’s habitat. The name “river blindness” reflects this geographic pattern of transmission.

Now two remarkable developments have loosened the stranglehold of the disease. The first is a co-operative international effort, carried out in the face of enormous logistical obstacles for 15 years, to suppress blackfly. The Onchocerciasis Control Programme, run by the World Health Organisation (WHO), has strategically applied insecticides to curb the insect that carries the disease in large areas of West Africa.

The fight against the disease itself has an unexpected weapon: a safe, effective drug called ivermectin (Mectizan). It provides an important advance over previous therapies for the treatment of river blindness.

Patients need only take one dose a year, which makes it very well-suited for mass treatment programmes. As a result, it can be administered in affected communities far away from health care facilities.

Most drugs for the treatment of tropical diseases have to be given in multiple doses over days, weeks or even years. The ability to treat and control a serious disease such as river blindness with a single dose each year is nothing short of spectacular.

The drug does not kill the worm, but blocks the release of microworms from the female worm’s uterus, effectively keeping the parasite at low enough levels that its human carrier can survive.

Mectizan was discovered by the research laboratories of Merck pharmaceuticals in 1975 and initially used as a veterinary product to treat parasites in cattle, pigs, horses and domestic animals.

After extensive research by Dr William Campbell, the first patient received a single oral dose of Mectizan in February 1981.

The current joint venture between the WHO, the World Bank, Merck and various non- governmental organisations and ministries of health enables more than 16-million people to receive treatment each year.

In an unusual move for a pharmaceutical company, Mectizan is donated by Merck. Funding for its distribution is secured through the World Bank, the Inter-American Bank and a consortium of non-governmental development organisations.

The programme has been a great success. The incidence of death and blindness from the disease has slowed and medical authorities anticipate that a second decade of treatment will eradicate the disease altogether.

The disease causes excruciating itching and severe skin disfigurement and is the leading cause of blindness in Central and West Africa. The socio-economic impact of the disease is widespread and problems include ostracism, personal anguish and low self-esteem.

In villages where the rate of blindness is high, young, able-bodied people — fearful of contracting river blindness — abandon their villages. Farm production is greatly diminished and in time fertile land, once cultivated, can become a virtual wasteland. This results in poverty and famine.

The success of this programme should have major human and economic ramifications, especially in non-industrial Third World countries. Millions of acres of rich farmland have already been liberated from the disease.

As it does not kill the adult worm (researchers hope to find a drug that does), Mectizan is not truly a cure. Nor can it restore sight in victims who are already blind. More work is also needed to reach the millions who have not received the drug.

However, for the first time in the ancient battle against onchocerciasis, the people of the tropics have a chance to win the fight.

The programme is a reflection of what can be achieved when governments, private industry and international organisations combine their resources in the interests of public health. It is, unfortunately, one of the few of its kind in the world.

— Anthony Gilbert is a medical student at the University of the Witwatersrand

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