Human cystic echinococcosis: contributions to the natural history of the disease

In areas where human cystic echinococcosis (CE) is endemic, the results of ultrasonographic or X-ray examinations have revealed a surprisingly high pr evalence of abdominal cysts in asymptomatic individuals. The results of pre liminary studies indicate that the ratio of liver infection: lung infection (LI: LU) is much higher in the asymptomatic individuals (9:1 or 7:1) than is usual among symptomatic cases of liver CE (2:1). This difference may ind icate that, compared with lung cysts, liver cysts rarely cause morbidity, p erhaps because they grow at a slower rate than those in the lungs. In an at tempt to explore this possibility, the published results of ultrasonographi c and radiological surveys on general populations and the records of autops ies and hospital-based investigations of symptomatic cases of liver CE were reviewed. In general populations, the overall prevalence of cysts in the l iver (2.5%) was found to be much higher than that of cysts in the lungs (0. 3%), giving a LI: LU ratio of 8.3:1. In the symptomatic cases, however, LI: LU ratios were only 2.5:1 (based on hospital records) or 4.1:1 (based on a utopsy records). In addition, the estimated mean growth rate of the cysts in 53 surgical cas es of CE from the province of Rio Negro in Argentina was found to be signif icantly higher than that of the cysts in 89 asymptomatic cases detected dur ing ultrasonographic surveys in the same area.