Infectivity of Echinococcus granulosus protoscolices under different conditions of temperature and humidity

The aim of this study was to examine the effect of different temperatures and humidities on the infectivity of Echinococcus granulosus protoscolices. Eighteen dogs (6 groups, n = 3 each) were fed with offal mince harbouring approximately 20,000 protoscolices of E. granulosus of different viabilities. Dogs were infected with E. granulosus protoscolices of: (1) 5% viability at -10 degrees C and 50% relative humidity (RH); (2) 30% viability at 0 degrees C and 60% RH; (3) 20% viability at +10 degrees C and 65% RH; (4) 15% viability at +30 degrees C and 75% RH; (5) 11% viability at +40 degrees C and 80% RH; (6) 68% viability (control group). Dogs in each group were necropsied at 29-49 days post-infection. Mean intensities of E. granulosus recovered from dogs were 256.7 +/- 60.3 in the second group; 32.7 +/- 7.1 in the third group; 40.3 +/- 15.5 in the fourth group and 1533 +/- 513 in the control group. However, no parasites were recovered from the first and fifth groups. Results obtained in the present study show that larval stages could be infective for 1 to 4 weeks during spring, autumn or winter months when maximal temperatures are approximately 0-10 degrees C. In conclusion, cold-storage depots in slaughterhouses and abattoirs where sheep carcasses might be discarded should be kept at -20 degrees C for 2-3 days, dogs should be properly controlled and adequate control programmes must be established in areas where the disease is endemic.