Cystic echinococcosis : analysis of the serological profile related to the risk factors in individuals without ultrasound liver changes living in an endemic area of Tacuarembó, Uruguay

Cystic echinococcosis (CE) is a high prevalence zoonosis among the rural population of Tacuarembo (Uruguay). The correlation between serological data and the incidence of risk factors was studied in a survey carried out in 1998 among rural communities where 480 individuals were examined by means of abdominal sonography (local prevalence=0.8%). Serum samples (305) were analysed by ELISA to determine specific IgG against crude antigens from Echinococcus granulosus. A total of 27 individuals exhibiting no detectable changes in abdominal sonographic examination were found to be sero-positive ('ultrasound normal group'). Of these individuals 9 were seroreactive against purified antigen B. A significant degree of correlation was found between seroreactivity and the incidence of some risk factors (CE antecedent in the family, P<0.005 and use of rural water, P<0.0001) among this group. Follow-up of individuals of the 'ultrasound normal group' was carried out after 2 years to evaluate the implications of this serological reactivity. No predictive value for cyst development was assessed with complementary image study; in contrast transient antibodies were observed with both crude and purified antigen as approximately 60% of individuals became negative when re-sampled.