Cystic echinococcosis (CE or hydatid disease) is a zoonotic infection caused by the larval stage of the taeniid tapeworm Echinocaccus granulasus. The parasite's life cycle is maintained through dogs (which harbour the adult worm in their small intestine) and a range of domestic livestock that serve as intermediate hosts. E. granulasus eggs are excreted in the faeces of infected dogs and may thus contaminate soil, grass and water. Ungulates (hoofed animals) can become infected by grazing on pasture contaminated with dog faeces. Ingested eggs hatch inside the intestine, penetrate the gut wall and are carried by the bloodstream to different organs and tissues (mainly the liver and lungs) where they develop into cysts (metacestodes) that can eventually cause severe pathological damage. Humans can become infected by ingesting eggs through consuming contaminated food or water or from handling the faeces of infected dogs.
As in other countries of the Mediterranean basin, CE is endemic in Spain. (1,2) Most affected regions are the central, north-eastern and western regions of the country, where extensive or semi-extensive farming of livestock (mostly sheep) is common: Since the mid-1980s, a number of prevention and control programmes to reduce E. granulasus infection have been implemented in these regions. These programmes have led to a considerable decrease in human and animal CE infection rates. (3-5) However, the disease remains a serious health concern in many of the affected regions. A recent survey showed human CE annual incidence rates in the range of 1.1 to 3.4 cases per [10.sup.5] person-years, in combination with ovine or bovine CE prevalence proportions of up to 23%.6
Spain is a developed country with a population of more than 43 million (77% of whom live in urban areas) and a high average income; in 2005, the gross domestic product per head was [euro]18 677. (7) The national public health system provides health services for an estimated 90% of the population; the remaining 10% (mainly from the autonomous regions of Madrid and Catalonia) have both public and private coverage. (8) The national epidemiological surveillance network is based on three interdependent systems--compulsory notifiable diseases, outbreaks alerts and microbiological information. The autonomous regions where CE infection is considered endemic (Aragon, Cantabria, Castile-La Mancha, CastileLeon, Catalonia, Ceuta and Melilla, Comunidad Valenciana, Extremadura, La Rioja and Navarre) report human CE to the compulsory notifiable diseases system. (9) The proportion of symptomatic CE cases that are detected and reported to the system has been estimated at 47-57%. (10) However, the completeness of case detection increases to more than 95% when the microbiological information system and computerized hospital discharge records are also considered, and the specificity is 100% (LP Sanchez-Serrano, unpublished data, 2009). Surveillance of CE in livestock is carried out through routine postmortem examination in all national slaughterhouses, with detected cases reported to the Spanish Food Safety Agency. (11) Official figures on human and animal CE are subsequently submitted to the European Commission as part of the Spanish Report on Trends and Sources of Zoonoses. (12)
CE affects both human and animal health and has important economic consequences. (13) Human-associated economic losses arise through diagnostic procedures, surgical or chemotherapeutic treatment, hospitalization, convalescence, life impairment and fatalities. Animal-associated economic losses arise from decreases in carcass weight, milk production and fertility rates, and from increased condemnation of viscera. Estimation of the economic burden in humans and livestock is important and should be part of any cost--benefit programme for the control of parasitic zoonoses. (14,15) Early surveys attempting to quantify human and animal CE losses were hampered by the scarcity of reliable epidemiological and economic data. …