Abstract. A prevalence and transmission study of human cystic echinococcosis (CE), due to infection with the dog tapeworm Echinococcus granulosus, was undertaken in the village of La Paloma in central Uruguay. The human population was registered and screened for CE by abdominal ultrasound scan as well as a number of serologic tests. Dogs were screened for E. granulosus infection by arecoline purgation as well as specific coproantigen testing. The total prevalence of human CE (new cases and those with a previous history) was 5.6% (64 of 1,149); 3.6% (40) of the cases were new ultrasound detected asymptomatic cases (mean age ϭ 45 years). Age prevalence increased from 1.1% in the 4-6-year-old group to Ͼ 11% in the Ͼ 60-year-old group; the 20-29-year-old group had a significantly higher CE rate of 7.4%, compared with younger and older age groups, and there was no difference between sexes. A CE rate of 3.9% (20 of 514) was also recorded by ultrasound for new cases in the population residing outside the village. Most of the hydatid cysts were located in the liver presenting as either univesicular cysts or a solid mass, and of those 71% and 63%, respectively, with such cyst presentations were seropositive against E. granulosus cyst fluid antigens. Two of eight individuals who were filter paper blood spot seropositive, but ultrasound scan negative, were subsequently diagnosed respectively with pulmonary hydatidosis after radiography, and hepatic hydatidosis after computed tomography scan. Of 36 households with a CE patient, 32 were single cases while four households each harbored two CE cases. This did not represent a clustered distribution within families (23 of 117). Almost 20% of the dogs from La Paloma were found infected with E. granulosus after purge examination, with a mean worm number of 67 (range ϭ 1-1,020). An additional eight dogs that were purge negative were Echinococcus coproantigen positive. The study showed that human CE is highly endemic in Uruguay, with one of the highest local prevalence rates in the world. Transmission appears to occur readily within well-developed towns, as well as on rural sheep ranches. Mass screening by ultrasound scanning with confirmatory serologic testing is an effective approach to case detection at the community level.Echinococcosis (CE) is a chronic zoonotic parasitic helminthic disease due to infection with the larval stage (hydatid) of the small dog tapeworm Echinococcus granulosus. The parasite has a global distribution but is particularly prevalent in rural areas where it is transmitted in a cycle between the dog, the definitive host, and the sheep, the intermediate host. 1 In South America, E. granulosus is endemic and a significant public health problem in several countries including Brazil, Peru, Bolivia, Chile, Argentina, and Uruguay. [2][3][4][5][6][7][8][9][10][11][12]

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Serological tests using hydatid cyst fluid (HCF) are useful as a primary screen for detecting asymptomatic infections due to Echinococcus granulosus in human populations. An enzyme-linked immunosorbent assay (ELISA) performed with whole sheep HCF was used to determine the prevalence of hydatid antibodies in a rural human population in Uruguay. In order to eliminate cross-reactions with sheep proteins in HCF, 1% normal sheep serum was added to each human serum before testing. ELISA seropositives were further tested using the double diffusion test (DD5) and confirmed where possible by ultrasound and X-ray examination. Serum samples were obtained from 420 individuals inhabiting rural areas in the Department of Paysandu (160), Rivera (21) and San José (239). An overall seroprevalence of 1.24% was obtained. Two of 17 seroreactors were subsequently proven to have hydatidosis. These results confirm and extend previous studies indicating an unusually high prevalence of E. granulosus infection in the Uruguayan population.

Thirty cystic echinococcosis (CE) patients in Uruguay with severe bone or secondary disseminated echinococcosis were immunologically assessed using cellular (lymphocyte transformation assay, LTA) and humoral (specific antibody and subclass responses, circulating antigen and circulating immune-complexes) immunological assays during the course of chemotherapy (albendazole and/or praziquantel). CE patients were divided into 4 groups, according to clinical treatment and outcome: (I) surgery and chemotherapy, (II) chemotherapy with outcome unchanged, (III) chemotherapy with outcome improved, and (IV) chemotherapy considered cured. Increased circulating antigen was of prognostic value in some severe CE cases where levels remained high and/or increased. The lymphoproliferative response in vitro to Echinococcus granulosus antigen was statistically greater in all patient groups compared to normal individuals but at lower levels in improved or cured CE patients. Levels of non-specific LTA response were significantly lower than controls for all groups during albendazole treatment (P < 0.001) but returned to normal levels in cured patients, a result consistent with parasite-induced suppression of cellular responses. This study suggests that, at least in severe osseous and secondary CE, immunosurveillance by specific antibodies, especially total specific immunoglobulin, was overall of more practical use than antigen-specific in-vitro lymphocyte transformation assays.