B73 Onchocerciasis

(River blindness)

RATIONALE FOR SURVEILLANCE

Onchocerciasis is endemic in 34 countries of Africa, the Arabian peninsula and the Americas. Success at controlling the disease in West Africa was achieved through the strategy of larviciding for vector control in order to interrupt transmission; since 1988 this has been combined with treatment by ivermectin, a safe, effective drug. The global strategy for controlling onchocerciasis is based on the yearly administration of ivermectin to affected populations. The first step is to map the endemicity of onchocerciasis in known or potentially endemic areas. The second is to implement cost-effective and sustainable ivermectin delivery, focusing on methods involving community treatment.

Once onchocerciasis is under control (as is currently the case in 11 West African countries), the risk of recrudescence must be kept to a minimum. The participating countries, during the phasing-out period 1998-2002 in West Africa, will ensure that detection and control of onchocerciasis recrudescence are routinely integrated within, and become a routine function of, national disease surveillance and control services.

RECOMMENDED CASE DEFINITION

Clinical case definition

In an endemic area, a person with fibrous nodules in subcutaneous tissues.

Laboratory criteria for confirmation

One or more of the following

· Presence of microfilariae in skin snips taken from the iliac crest

· Presence of adult worms in excised nodules

· Presence of typical ocular manifestations, such as slit-lamp observations of microfilariae in the cornea, the anterior chamber, or the vitreous body

Case classification

Suspected: A case that meets the clinical case definition.

Probable: Not applicable.

Confirmed: A suspected case that is laboratory-confirmed.

RECOMMENDED TYPES OF SURVEILLANCE

In zones where onchocerciasis is endemic:

Active case finding (skin snips, ophthalmological examination, diethylcarbamazine patch test) through surveys. Distribution of the disease can be assessed through rapid epidemiological mapping of onchocerciasis (REMO), a technique developed recently.

In the onchocerciasis-freed zones of West Africa:

Surveillance in sentinel villages:

To detect recrudescence of infection, a minimum of 260 sentinel villages in onchocerciasis-freed zones of West Africa have been kept under periodic surveillance (once every 3 years). They are located near former productive larval breeding sites and had high prevalence rates prior to beginning of control activities.

Routine surveillance:

All suspected cases must be investigated locally, with routine reporting of aggregated data from peripheral level to intermediate and central level. This is not yet fully effective in all of the countries because of insufficient training of health workers.

Migration investigation:

In the event that a positive case is detected in the course of epidemiological surveillance, a migration investigation is systematically carried out in order to identify the origin of infection and take appropriate action.

RECOMMENDED MINIMUM DATA ELEMENTS

Individual patient record at peripheral level

· Age, sex, place of infection, treatment (Y/N), date treatment with Ivermectin started, reason for non-treatment (non-compliance)

· Prevalence and incidence by age, sex and geographical area
· Community microfilarial load (CMFL)
· Number of cases treated
· Number of cases not treated and reason for non-treatment (pregnancy, breast-feeding, other defaulting)

RECOMMENDED DATA ANALYSES, PRESENTATION, REPORTS

Graphs: Number of cases by year, geographical area, age group.

Tables: Number of cases by year, geographical area, age group.

Maps: Number of cases by geographical area, using geographical information system (GIS).

PRINCIPAL USES OF DATA FOR DECISION-MAKING

· Eliminate onchocerciasis as a disease of public health and socioeconomic importance
· Prevent recrudescence of infection in the onchocerciasis-freed zones
· Assess effectiveness of intervention
· (In West Africa), decide on the cessation of larviciding activities

SPECIAL ASPECTS

New diagnostic tests, such as patch test with DEC (diethylcarbamazine citrate), may become suitable for use in the field.

CONTACT

Regional Offices

See Regional Communicable Disease contacts on section "Communicable disease contacts in Regional Offices".

Headquarters: 20 Avenue Appia, CH-1211 Geneva 27, Switzerland

Onchocerciasis Control Programme/African Programme of Onchocerciasis Control

Control Liaison Office (ACP/APOC)

E-mail: daribia@who.ch / Surveillancekit@who.ch
Tel: (41 22) 791 3883/2111
Fax: (4122) 791 4190