Reproductive Potential of Echinococcus Multilocularis in Definitive Hosts

Data on the reproduction of E. multilocularis in the definitive host are essential for the understanding of parasite transmission. To date several approaches to model parasite transmission have made assumptions on important parameters with little available data (for example, 200 eggs per gravid proglottid, a patency of 3-6 months, or rate of proglottisation of 0.08-0.14). To provide better data, egg excretion was modelled logistically following experimental infection with 20,000 E. multilocularis protoscoleces. This resulted in a total mean biotic potential per infected fox of 405,109 eggs and per infected dog of 289,917 eggs. The mean worm counts observed at 35 dpi of 5 dogs and 5 foxes (16,792 and 2,466, respectively) were used to estimate the mean numbers of eggs produced per worm during patency. This suggested that approximately 117 and 24 eggs per worm were excreted in the faeces of dogs and foxes, respectively. During the first month of patency, worm burdens in foxes were reduced significantly compared to dogs (98% compared with 64%). In addition, the time taken from the beginning of patency to excrete 75% of total eggs was approximately 17 days in the fox. This period was significantly shorter than the 28 days taken by the dog. The estimated numbers of eggs excreted per worm in faeces is low in comparison to the expected numbers. This may be attributed to a large number of eggs that disintegrate or hatch in the intestine of the definitive hosts. Furthermore, the McMaster egg quantification system used underestimates the faecal eggs count by approximately 30%. However, the relative short life span of the worms in foxes supports the hypothesis that sequential proglottisation did not contribute significantly to the total egg production.