Onchocerciasis (River Blindness)

River Blindness, a parasitic disease, is the second leading infectious cause of blindness.

River Blindness is caused by a round worm, onchocerca volvulus

It is one of the tropical diseases for research (TDR)

Reservoir: Humans

Vector: Simulium damnosum (Blackfly)

• Can breed at high altitudes (610m or more)
• Larvae and pupae are found attached to highly oxygenated waters. Infection occurs in proximity to fast moving water (river blindness)
• The period of greatest transmission is in the rainy season coinciding with the period of maximal Simulium breeding.

River blindness is transmitted to humans by the blackfly

The adult worms are found in subcutaneous nodules and tissue spaces.

The females, which are ovoviviparous, measure about 30-80cm in length while the males are only 3-5cm long.

Worms of both sexes are found coiled together in nodules and larvae are present in large numbers near the coiled gravid female.

The developed larvae (microfilariae) vary in size (250-300um) and are unsheathed

The lifespan is between 9-14years

Has a focal distribution in both Africa and Central America.

99 percent of River Blindness cases occur in Africa

36 countries

• 29 in sub-Saharan Africa
• 6 in Latin America
• Yemen

Endemic in West Africa, equatorial & east Africa & Sudan

One of the largest endemic areas occur in the Volta River Basin area, which incorporates parts of Benin, Ghana, Ivory coast, Mali, Niger, Togo and Burkina Faso. These are the areas of the onchocerciasis control program (OCP)

Males are more affected than females (? occupational hazards)

Incidence of infection increases with age (up to 75% of middle aged in endemic area might be infected)

• Rashes
• Lesions
• Intense itching
• Depigmentation of the skin
• Lymphadenitis
• General debilitation
• Serious visual impairment
• Blindness

• Rapid epidemiological assessment (REA)
• Rapid epidemiological mapping of onchocerciasis (REMO)

Rapid epidemiological assessment (REA)

REA refers to a broad collection of epidemiological, statistical and anthropological techniques which aim to provide accurate information quickly, at a low cost, in a simple format.

Historical aspects of REA

1981, ACHBRD was formed to identify areas of research to improve health of developing countries.

WHO developed novel epidemiological sampling and surveillance methods for smallpox eradication in EPI. The committee named them Rapid Epidemiological Assessment.

REA began as an amalgam of concepts and techniques borrowed from the fields of health services research and operations research, as well as traditional epidemiology.

It was largely inspired by the ‘quick and dirty’ methods of epidemiology.

Aspects of Rapid Methods

1. Sampling methods for rapid health assessment
• WHO-EPI cluster sampling
• LQAS
• Case control methodology
2. Collection, organization and analysis of data

Methods of data collection

• Focused group discussion
• Key-informant interviews
• Observations
• Case reports
• Personal diaries
• Conversations
• Participant observations
• Collection of data from secondary sources

Methods of organizing, analyzing and presenting data

• Geographical information systems
3. Rapid management in emergency situations

Rapid Epidemiological Mapping of Onchocerciasis (REMO)

REMO uses nodule palpation in combination with geographic information system mapping, and was used by African Programme for Onchocerciasis Control (APOC) to map prevalence in 20 countries from 1996 to 2012.

REMO revealed that the prevalence of Onchocerca volvulus nodules was patchy and heterogenous across Africa and identified areas for ivermectin intervention using a threshold for treatment set at a nodule prevalence of 20%. Onchocerciasis-endemic communities were divided into 3 based on nodule prevalence.

• Hypoendemic (nodule prevalence of < 20%)
• Mesoendemic (nodule prevalence of 20—45%)
• Hyperendemic (nodule prevalence >45%)

Laboratory

Examination of Skin or conjunctival snips

Excision of nodules for histological examination

Aspiration of fluid from nodules

Serology

Complement fixation

Immunofluorescence

ELISA

The vector

Attack the breeding site

The human reservoir

Chemotherapy: Ivermetin (Mectizan)

• Ivermectin is a broad-spectrum antiparasitic drug that can be used to treat river blindness
• Ivermectin does not kill adult worms, but prevents them from producing additional offspring
• Drug binds to and activates glutamate-gated chloride channels
• By activating channels, drug causes inhibitory postsynaptic potential
• Microfilaria experience paralysis and then death

Nodulectomy

Mectizan Donation Program (1987)

IDP: Ivermectin Distribution Program (1989-1994)

OCP: Onchocerciasis Control Programme (1988)

APOC: African Programme for Onchocerciasis Control (1995)

The Carter Center (1996)

Angola, Burundi, Cameroon, Central African Republic, Chad, Congo, Democratic Republic of Congo, Ethiopia, Equatorial Guinea, Gabon, Kenya, Liberia, Malawi, Mozambique, Nigeria, Rwanda, Sudan, Tanzania and Uganda.