Onchocerciasis

• Rarely life-threatening, the disease causes chronic suffering and severe disability.
• In Africa, it constitutes a serious obstacle to socio-economic development.
• It is often called river blindness because of its most extreme manifestation and because the blackflies that transmit the disease abound in riverside areas, where they breed in fast-flowing waters.
• Fertile riverine areas are frequently abandoned for fear of the disease.
• 78 millon people are estimated to be at risk
• 300 000 people are blind 

The blackfly, Simulium damnosum, the vector of Onchocerca volvulus, the parasite which causes onchocerciasis (river blindness).	A patient infected suffering from river blindness. This elderly man shows nodules, skin changes and blindness, all manifestations of the disease.	Fast-flowing water, a typical breeding site for larvae of the blackfly

35 countries in total.

• 28 in tropical Africa, where 99% of infected people live.
• Isolated foci in Latin America (6 countries) and
• Yemen.

A parasitic worm, Onchocerca volvulus, of the family filariidae, which lives in the human body for up to 14 years.

	Onchocerca volvolus is a helminthic worm male: 2-3 cm long female: 60 cm long Adults occur in the subcutaneous tissues and in nodules microfilariae: 300 x 8 micrometer, 1000-3000 produced per day per adult female worm Adult worms have a longevity of 10-15 years
Onchocerca volvulus (adult worms)

The vector is Simulium damnosum or blackfly.

• Blackflies deposit their eggs in the highly oxygenated water of rivers where also larvae develop.
• The young flies feed on the blood of humans and pick up the microfilariae from infected people.
• The development in the fly takes about 7 days and occurs in the fly's proboscis.
• When the fly feeds again the larvae are transmitted.
• Man is the only definitive host of this parasite.

Fast-flowing water, a typical breeding site for larvae of the blackfly, Simulium damnosum, the vector of Onchocerca volvulus, the parasite which causes onchocerciasis (river blindness).	Via the bite of infected blackflies (Simulium spp.) that carry immature larval forms of the parasitic worms from human to human.

Each adult female worm produces millions of microscopic larvae (microfilariae) (1000-3000 per day), that migrate throughout the body to cause a variety of symptoms.

Symptoms

Adult worms lodge in nodules under the skin, releasing large numbers of microfilariae into surrounding tissues. Immature worms move through the body and after dying, cause a variety of conditions including:

• serious visual impairment and blindness,
• skin rashes,
• lesions,
• intense itching and depigmentation of the skin,
• lymphadenitis (resulting in hanging groins and elephantiasis of the genitals) and
• general debilitation.

Nodules caused by the adult worms

A patient infected with onchocerca volvulus, the parasite which causes onchocerciasis (river blindness). This elderly man shows nodules, skin changes and blindness, all manifestations of the disease.	Onchocerca volvulus: nodules (removed from under the skin of infected people) contain the adult worms.

Eye infections by the microfilaria larvae

Ocular lesions in an onchocerciasis (river blindness) victim blinded from sclerosing Keratitis.
This woman has leopard skin and onchocercal skin lesions on both legs.

• Search for the presence of microfilaria in blood urine and eyes
• Search for adult worms (macrofilaria)

  Yanomami mother and her children waiting at the clinic for medical attention, especially for diagnosis and treatment of onchocerciasis	examination of a young Yanomami indian child

Catching adult Simulium blackflies, the vectors of the parasites which cause onchocerciasis, using a man as bait.	Medical doctor using an ultrasound machine to examine a male patient for signs of nodules and worms.

Drug treatment: the development of ivermectin in the 1980s provided a safe, effective drug for killing microfilariae in infected people. A single dose of the drug (being supplied free by the manufacturer, Merck & Co. Inc.) needs to be taken annually.

	Drugs: Diethylcarbamazine (DEC) only kills microfilaria Ivermectine (150 microgram/kg single dose) only kills microfilaria Suramin only kills macrofilaria
Masindi district: A Community-directed distributor (CDD) dispensing ivermectin tablets to a young girl during a central point distribution in her village

Vector control: insecticide spraying to control blackflies has proved successful in certain areas.Temephos as larvicide is effective but resistance develops

Helicopters and fixed wing aircraft are used to spray insecticides (chemical and biological) on rivers and fast-flowing water

OCP, a major control initiative

• Launched in 1974 in an area encompassing originally 7 countries in West Africa.
• In 1986, the programme was extended to include a further 4 countries,
• A total operational area of 1.23 million sq. km,
• A combined human population of 30 million.
• Jointly sponsored by the
  • WHO,
  • World Bank,
  • UNDP and
  • FAO,
  • plus a coalition of 20 donor countries and agencies,
• the OCP is scheduled to come to an end by 2002.

OCP's principal method for controlling onchocerciasis involved interrupting transmission by eliminating the blackfly vector. Simulium larvae are killed by applying insecticides via aerial spraying over breeding sites in fast-flowing rivers. Following interruption of transmission, the reservoir of adult worms dies out in humans after 14 years. To complement vector control activities, OCP also distributes ivermectin.

Following the success of the OCP, the same co-sponsors and donors created APOC in 1995.

• The objective is to create, by 2007,
• sustainable community-directed distribution systems using ivermectin.
• Coverage of 59 million people in 17 non-OCP countries, where the disease remains a serious public health problem and some 15 million people are infected.
• In a few isolated foci elimination of the blackfly through insecticide spraying.

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