—from Epidemiological Bulletin, Vol. 24 No. 3, September 2003—

Case Definition
African trypanosomiasis (Sleeping sickness)

Rationale for surveillance
The leading principle for sleeping sickness control is the reduction of human reservoir through treatment of infected individuals and the reduction of man-fly contact through adapted vector control. An intercountry approach for surveillance / control activities is essential and supported by WHO. The objective of surveillance is the precise identification and proper epidemiological assessment of all endemic foci.

Recommended case definition
Clinical description
In the early stages, a painful chancre*, which originates as a papule and evolves into a nodule may be found at the primary site of tsetse fly bite. There may be fever, intense headache, insomnia, painless lymphadenopathy, anemia, local edema and rash. In the later stage, there is cachexia, somnolence and signs of central nervous system involvement. The disease may run a protracted course of several years in the case of Trypanosoma brucei gambiense. In case of T. b. rhodesiense, the disease has a rapid and acute evolution. Both diseases are always fatal without treatment.

Laboratory criteria for diagnosis
Presumptive: serological: card agglutination trypanosomiasis test (CATT) for T. b. gambiense only or immunofluorescent assay (IFA) for T. b. rhodesiense mainly and possibly for T. b. gambiense
Confirmative: parasitological: detection (microscopy) of trypanosomes in blood, lymph nodes aspirates or CSF.

Case classification
Suspected: A case that is compatible with the clinical description and/or a history of exposure.**
Probable: A case with a positive serology with or without clinical symptoms in persons without previous history of trypanosomiasis diagnosis or treatment.
Confirmed: A case with positive parasitology, with or without clinical symptoms.***

Recommended types of surveillance
The surveillance system will use a village-based definition using 4 classes:
– Village of unknown epidemiological status
– Suspected village
– Endemic village
– Disease-free village
– In the context of control programs, surveillance provides valuable village-based data, with the precise geographic location of each village using global positioning system (GPS). Data are analysed using geographical information systems (GIS).

In areas not covered by control activities, surveillance provides valuable case-based information. Results of serological surveys based on micro-card agglutination trypanosomiasis tests (micro-CATT) will be indicators of endemicity.

Information collected at village level is aggregated at intermediate / central level and reported to WHO.

Recommended minimum data elements
Village-based data:
In addition to the number of parasitologically confirmed cases (presence of trypanosomes shown), and to the number of probable cases (suspected cases with positive serology), the system should include information on:
– strategy used
– village geographic coordinates (latitude, longitude)
– name
– administrative levels
– village type
– population at last census / date of last census, estimated population
– school (levels)
– health infrastructures (type, activities)
– protected sources of water

Recommended data analyses, presentation, reports
Mapping: at intermediate and central level: map of villages and their endemic status.

Principal uses of data for decision-making
– Knowledge of endemic and suspected areas to direct control activities
– Epidemiological monitoring of endemic foci
– Assessing impact of control programs

Special aspects
– Use of Global Positioning System (GPS) to define village geographic coordinates
– Sensitivity of parasitological techniques is low and depends on lab facilities and personnel skills

* The painful chancre is very rare in T. b. gambiense infection
** In the early stage or even early in the late stage of the disease there are often no clinical signs or symptoms which can be associated with the disease. Suspicion is then based on local risk of contracting the disease and local disease historical background.
*** Confirmed positive healthy carriers are a major public health risk. As a reservoir of parasites, they disseminate the disease, and must be treated as soon as possible.

Source: “WHO Recommended Surveillance Standards, Second Edition, October 1999”, WHO/CDS/CSR/ISR/99.2

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Epidemiological Bulletin, Vol. 24 No. 3, September 2003