Cystic echinococcosis : analysis of the serological profile related to the risk factors in individuals without ultrasound liver changes living in an endemic area of Tacuarembo ´, Uruguay A. HERNA ´ NDEZ 1 *#, G. CARDOZO 1 #, S. DEMATTEIS 1 , A. BAZ 1 , N. TRIAS 1 , H. NUN ˜ EZ 2 , A. BARRAGUE ´ 2 , L. LO ´ PEZ 2 , J. FUENTES 3 , O. LO ´ PEZ 2 and C. FERREIRA 2 1 Ca ´ tedra de Inmunologı ´a, Facultad de Quı ´mica-Facultad de Ciencias, Instituto de Higiene, Avda. A. Navarro 3051, Montevideo 11600, Uruguay 2 Hospital Regional, deTacuarembo ´ , Treinta y Tres 444, Tacuarembo ´ , Uruguay 3 Ca ´tedra de Matema ´ticas, Facultad de Quı ´mica, Avda. General Flores 2124, Montevideo 11800, Uruguay (Received 5 May 2004; revised 6 September 2004; accepted 8 September 2004) SUMMARY 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 develop- ment 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. Key words : cystic echinococcosis (CE), Echinococcus granulosus, risk of exposure, serological tests, abdominal ultrasound. INTRODUCTION Cystic echinococcosis (CE) is the zoonosis caused by the larval stage of the dog tapeworm Echinococcus granulosus. In view of the life-cycle characteristics of this helminth, transmission of CE to humans is highly associated with rural environments. Eggs are disseminated from dog faeces and contaminate food, water and hands. Ingestion of eggs by intermediate hosts (sheep, man) results in the development of the larval stage (hydatid cyst), which is located mainly in the liver. The influence of habits contributing to transmission has been analysed by several authors in different geographical areas; consumption of home- grown vegetables, the use of rural water and home slaughter of sheep were reported to be major risk factors (Carmona et al. 1998). Ultrasound is a reliable method for screening for cysts, while serology is used as a complementary tool, since small cysts and/or non-hepatic localizations cannot be detected by sonography alone (Craig, Rogan & Allan, 1996). Based on these methods, several studies have shown E. granulosus to be en- demic in various regions of Uruguay (Perdomo et al. 1990 ; Bonifacino et al. 1991; Carmona et al. 1998; Cohen et al. 1998). Present work was carried out in Caraguata ´ (Tacuarembo ´), a region with ultrasound CE prevalence of 1% (on the basis of 13 000 sono- graphies) according to previous surveys carried out between 1995 and 1997 by the Regional Hospital (data not published). The first survey included several rural communi- ties. The sonographic prevalence was examined in conjunction with the incidence of specific risk factors and the serological data. A group of individuals who were positive in specific serological tests but showed no presumptive cyst images was defined (‘ ultrasound normal group ’) and further studied using purified antigen B from E. granulosus and antigens obtained from other parasites exhibiting cross-reactivity with E. granulosus (Taenia hydatigena and Toxocara canis), similar transmission patterns (Lightowlers & Gottstein, 1995) and a high rate of infection in dogs (Cabrera et al. 1996). * Corresponding author : Ca ´tedra de Inmunologı ´a, Facultad de Quı ´mica-Facultad de Ciencias, Instituto de Higiene, Avda Alfredo Navarro 3051, Montevideo 11600, Uruguay. Tel : +598 2 480 11 96. Fax : +598 2 487 43 20. E-mail : aherna@fq.edu.uy # The first two authors contributed equally to this work. 455 Parasitology (2005), 130, 455–460. f 2004 Cambridge University Press DOI: 10.1017/S0031182004006717 Printed in the United Kingdom