This is a 3 year study of approximately 840 male and female subjects aged 5 years old and above to be conducted in a Peruvian Highland community in Lima, Peru in order to described the dynamic and associated risk factors to both human infection and Cystic Hydatid Disease (CHD). The purpose is to determine the prevalence and incidence of both infection and disease in human population, to assess the proportion of seroconversion (positive to negative) through follow-up of the same indiviuals every year and to identify risk factors related to human infection and disease by using baseline questionnaire (e.g. husbandry practices and education level). Echinococcal infection is prevalent in regions of the world where dogs are used to care for large herds (Lima, Peru). This study involves collection of 5 ml of blood every year for 3 years. In addition, CXR and abdominal US will also be performed. Signs and symptoms of hydatid disease depend on the organ involved (lungs and liver) and the size of the cyst. At this time, the best therapeutic approach is surgical intervention preceded by careful radiological evaluation plus adjuvant chemotherapy. The mortality rate post surgery is 1-4% and for those patients who refuse to have surgery, 60%. Despite the presence of current methods of control, the parasite prevalence appears to be increasing worldwide therefore this study will obtain data to implement a control program to eradicate this zoonosis.