Ovine Echinococcus granulosus transmission dynamics in the province of RioNegro, Argentina, 1980-1999

In this work, the impact of a hydatidosis control programme for dogs on the intermediate ovine host was specifically analysed to determine the levels of prevalence achieved and the dynamics of parasite transmission, as well a s to evaluate the quality of diagnostic systems in slaughterhouses. A field study was conducted in four slaughterhouses (Valcheta, Los Menucos, Jacoba cci, Bariloche) that process animals coming from all the departments within the work area. The control programme for dogs entailed treating dogs with 5 mg/kg praziquantel at 2-month intervals for 20 years. Sample size was determined with a 10% error margin and a 95% significance l evel. Harvested viscera (liver, lungs, kidneys) were preserved in 5% formal dehyde and sent to the laboratory for diagnostic confirmation of both posit ive and negative specimens. The 61% initial prevalence dropped to 18.3% at the end of the 10-year period, observed differences proving significant (Ch i-square = 15.454, P = 0.00). There were statistically significant increase s in infection prevalence with age (Pearson's Chi-square = 133.61, P = 0,00 ), Overall, 37.2% of hydatidosis cases diagnosed in slaughterhouses were co nsidered non-hydatid by histological study. On the other hand, 1.1% of thos e diagnosed as healthy were found to be infected with hydatidosis. The numb er of hydatid cysts per animal increased with age: 0.04 in lambs and 1,22 i n adults (linear regression equation, -0.0539 + 0.0127 x age), whereas the average for the whole period was 3.7% in lambs and 20.5% in adults. Viabili ty studies indicated that 63.8% of parasitised animals had viable cysts, ou t of which 53.3% were fertile. Diagnosis of infection in sheep made by mean s of an adjusted statistical design and with histological confirmation of t he presumptive diagnosis made in slaughterhouses demonstrated the flaws of the official systems for epidemic surveillance of hydatidosis. However, the re was no overall significant difference in slaughterhouse and laboratory d ata. Ro was 0.53 and could imply a decrease in reproductive capacity of the para site and steady state extinction. (C) 2001 Elsevier Science B.V. All rights reserved.