paracitos

Valor diagnostico de la inmunofluorescencia indirecta
con anti-IgM para Enfermedad de Chagas,
en adultos y recien nacidos
Myriam Lorca y Erica Thiermann

Diagnostic value of the IgM Immunofluorescence test for chagas' disease in infants and
adults.
The IFAT-IgM with Trypanosoma cruzi antigen was applied in a double blind study of 242 serum samples
previously examined by the IFAT-IgG forChagas' disease. The sensitivity of the test was enhanced by prolonged
incubation at 4°C. The specificity of the IgM reaction in normal sera, was checked repeting the test in alliquots,
absorbed with IgG. The results were tabulated according to the origin of the samples and the presence, or
absence, of IgG antibodies for Chagas' disease. 84 of die samples belonged to infants and 158 toadults,131 had
IgG antibodies against T. cruzi and the remaining 111 served as negative controls in both groups.
In was demonstrated that a high proportion of positive IgM-results obtained in normal sera, of infants (15,5%)
and adults (28,5%), were due to otfier factors: Elimination of nonspecific IgM antibodies, by absorbtion, reduced
the reactions of IgM, at liters of 1/10 and 1/20, to three samplesin the infant's group. However, in the sera of adults,
positive IgM results remained after absorbtion, at titers up to 1/20, in the infected individuals as well as in
controls. Only one serum gaveatiterof 1/40, suggesting specificity.
The three samples of the infant's group, in which IgM antibodies to T. cruzi were demonstrated, belonged to a
child with Chagas' disease demonstrated byxeno-diagnosis. The specimen oi the adult in which a positive
IFAT-IgM-Chagas was obtained at a titer of 1/40, corresponded to a women with recently acquired infection, as
jugdedbyaseroconversion(from(-)to( + ) 1/40) in the IFAT-IgG for Chagas' disease.
The results indicate that the test yields specific results, if it is applied in sera previously absorbed with IgG and
confirm that low titers are ofdiagnostic value in sera of infants. However, in sera of adults, only titers from 1/40
onward are considered to be specific for Chagas's disease.

El empleo de la reacci6n de inmunofluorescencia Indirecta (RIFI), ha permitido ampliar el
estudio serologico en diferentes enfermedades
inlecciosas. Dicha tecnica, de ejecuci6n relativamente simple y rapida, ofrece la doble ventaja de
ser aplicabletanto en la pesquisa de diferentes
agentes infecciosos, lo que depende del microorganismo que se emplee como antigeno, conio en
la demostraci6n de diferentes tipos de anticuerpos, de acuerdo con la antigammaglobulina que se
utilice como reactivo.1'2
La RIFI practicada con antigammaglobulina de
tipo IgG y antigeno de Trypanosoma cruzi {RIFIIgG- Chagas), ha tenido gran aceptacion en elestudio de la enfermedad de Chagas, recomendandose su empleo para el diagnostico del caso
individual y para los estudios epidemiol6gicos.3
La demostraci6n de anticuerpos IgG, de aparici6n relativamente tardia y de persistencia proTrabajo financiado en parte por el Proyecto M-919-8122. U. de
Chile Serv. de Desarrollo Cientifico y de Cooperaci6n Internacional.
l
Unidad de Parasitologfa. Div. deCiencias Medicas Occidente,
Facultad de Medicina. Universidad de Chile.

longada, incluso indefinida, diagnostica la infecci6n y permite establecer su prevalencia. Sin embargo, esta informaci6n puede ampliarse, si en los
sueros positives se practica ademas, una RIFIIgM. Los anticuerpos de este tipo, debido a su
aparicion precoz y duracion limitada, caracterizan
la fase aguda de la infecci6n; demodo que la
demostracion de IgM especifica indica que la infeccion detectada se encuentra en una etapa reciente o activa y, con respecto a la epidemiologia,
se agrega al estudio de prevalencia, el de incidencia.
Si bien la RIFI-IgM es uril para el diagndstico
de las infecciones agudas adquiridas, se le atribuye aiin mayor importancia en la pesquisa precoz de las infecciosas congenitas del...