B57 American trypanosomiasis

(Chagas' disease)

RATIONALE FOR SURVEILLANCE

Targeted by WHO for elimination by the year 2000 (Resolution WHA51.14), American trypanosomiasis affects 17 countries with 16-18 million infected and over 100 million individuals at risk of infection. The disease is prevalent in the northern part of South America (the Andean Region) and in Central America; almost 25 million people are at risk and there are 5 to 6 million infected. The disease is potentially fatal and non-treatable; one third of those infected become incapacitated due to cardiac damage. Infection can also be acquired through blood transfusion.

The infection can be effectively eliminated through interruption of vector transmission and systematic screening of blood donors. Elimination has been successful in some countries of the Southern Cone of South America (Argentina, Bolivia, Brazil, Chile, Paraguay and Uruguay); surveillance is necessary to monitor prevention and control measures.

RECOMMENDED CASE DEFINITION

ACUTE STAGE

Clinical description

The main clinical signs are mainly fever, malaise, hepatosplenomegaly and lymphadenopathy in the acute phase. Many patients present without clinical signs. An inflammatory response at the site of infection (chagoma) may last up to 8 weeks.

Laboratory criteria for diagnosis

· Positive parasitology (direct, xenodiagnosis, blood culture) and/or

· Positive serology for Trypanosoma cruzi antibodies (IgM) (indirect haemagglutination test (IHA), indirect immunoflourescent antibody test (IFAT), direct agglutination test (DA) and ELISA)

Case classification

Suspected: Not applicable.

Probable: (Endemic areas) a case with unexplained fever, hepatosplenomegaly and a chagoma (inflammation at site of infection).

Confirmed: A clinically compatible case that is laboratory-confirmed.

Congenital: A newborn with positive parasitology (direct, xenodiagnosis, culture).

Indeterminate: Positive serology for T. cruzi antibodies alone, no other clinical findings related to the disease (e.g in blood donors).

Chronic: Positive serology or parasitology with chronic cardiac lesions and/or enlargement of the digestive viscera and/or peripheral neuropathies.

RECOMMENDED TYPES OF SURVEILLANCE

In endemic areas, sentinel surveillance may be the only feasible method at present.

Where possible, routine surveillance should be integrated in primary health services. At peripheral level, individual patient records must be maintained. Routine monthly reporting of aggregated data from peripheral level to intermediate level. Routine biannual reporting of aggregated data to central level.

All blood donations must be screened locally. Serological surveys (standardized and periodical) for surveillance and control.

RECOMMENDED MINIMUM DATA ELEMENTS

CLINICAL SURVEILLANCE

Individual patient records

Unique identifier, name, age, sex, geographical information, laboratory results.

Aggregated data for reporting

· Number of cases identified from transfusion donors
· Number of cases by age/sex/means of diagnosis
· Number of cases with positive serology
(Number of houses or communities subject to annual vector control)

LABORATORY SURVEILLANCE

Isolate-based data for reporting*

Scientific name of organism, clinical form, organ or tissue, geographical information (patient location), date of isolation, name laboratory, laboratory number of isolate, identification methods used, results.

*(WHO Technical Report Series N° 811: Control of Chagas disease. Geneva: World Health Organization, 1991: 77-78)

RECOMMENDED DATA ANALYSES, PRESENTATION, REPORTS

Graphs: Number of cases by geographical area, month, and means of diagnosis.

Maps: Number of cases by geographical area Vector control activities/geographical area/prevalence of disease.

PRINCIPAL USES OF DATA FOR DECISION-MAKING

· Monitor disease prevalence and measure the impact of disease
· Monitor control and elimination programme
· Target resources for prevention

SPECIAL ASPECTS

· Control has until now depended on vertical programmes. Monitoring and surveillance have been conducted during specific surveys. To integrate the control programme into PHC requires a network of laboratory services with different facilities at different levels for diagnosis

· Because of variation in specificity of the tests, cut-off points should be defined locally using a standard serum panel, provided by the reference laboratories of the intercontinental network for standardized serology in Brazil and Argentina

· A national laboratory network should be established in each of the countries in which Chagas' disease is endemic

CONTACT

WHO Regional Office for the Americas (AMRO, PAHO)

Dr S. Corber, Division of Communicable Disease Prevention and Control (HCP)

Direct telephone 001 202 974-3850,
fax 001 202 974-3648 or 001 202 974-3643
E-mail: CORBERST@PAHO.ORG

Dr G. Schmunis, Coordinator, Communicable Diseases program (HCP/HCT)

Direct telephone 001 202 974 32 72
Fax 001 202 974 36 88
E-mail: SCHMUNIG@PAHO.ORG

Dr. M. Libel, Communicable Diseases Program (HCP/HCT)

Direct telephone 001 202 974 31 29
Fax 001 202 974 36 88
E-mail: LIBELAMAR@PAHO.ORG

Dr. R. Rodriguez, Communicable Diseases Program (HCP/HCT)

Direct Telephone 001 202 974 34 94
Fax 001 202 974 36 88
E-mail: RODRIGRO@PAHO.ORG

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

Communicable Diseases Prevention and Control (CDP)

E-mail: moncayoa@who.ch / Surveillancekit@who.ch
Tel: (41 22) 791 3865/3903/2111
Fax: (41 22) 791 4854/0746 attn CRD