EFFECT OF HOST SEX AND LITTER ON THE POPULATION-DYNAMICS OF ECHINOCOCCUS-GRANULOSUS IN DOGS

Twenty-one Beagle dogs consisting of 10 males and 11 females and belonging to 3 litters were infected with 60,000 E. granulosus protoscolices each. They were killed on day 40, the parasites from their intestines recovered, and the number of worms, average number of proglottides per worm, average length per worm, percentage of worms with a uterine cavity, and percentage of egg-bearing worms were determined for each dog and analyzed per sex and litter. On average, the dogs had 1,253 +/- 339 worms (means +/- standard error) with 2.42 +/- 0.1 proglottides, were 1.59 +/- 0.07 mm long, and 25.6 +/- 4.8% of the worms presented a uterine cavity and 1.2 +/- 0.6% bore eggs. The number of worms exhibited a bimodal distribution with 19 dogs having less-than-or-equal-to 2,565 worms and 2 greater-than-or-equal-to 5,520 worms. Average number of proglottides also showed a bimodal distribution with 7 dogs having less-than-or-equal-to 2.1 proglottides per worm and 14 dogs having greater-than-or-equal-to 2.4 proglottides per worm. The parasites were significantly more numerous in females than in the males (1,964 +/- 573 vs. 681 +/- 202), had more proglottides (2.6 7 +/- 0.08 vs. 2.15 +/- 0.16), and were longer (1.72 +/- 0.07 vs. 1.44 +/- 0.11 mm). The percentages of parasites with a uterine cavity (27.8 +/- 5.9 vs. 23.2 +/- 8.1) or bearing eggs (1.0 +/- 0.5 vs. 1.5 +/- 1.8) were comparable in females and males. Litter A had significantly more (2,509 +/- 840 vs. 732 +/- 226) and longer (2.71 +/- 0.18 vs. 2.35 +/- 0.11 mm) parasites than litter B. Litter C had significantly fewer parasites with a uterine cavity than litters A or B (9.0 +/- 3.0 vs. 38.3 +/- 11.0 or 27.0 +/- 5.5). The interaction sex-litter influenced significantly only the number of worms; females of litter A had more parasites than any other sex-litter combination. Correlation between average number of worms and average number of proglottides was moderate (r = 0.48), but correlation between average number of worms and the other characteristics was low (r less-than-or-equal-to 0.23). These results indicate that the host genetic composition influences the establishment and development of the worms. They also suggest that parasite developmental arrest occurs but that a crowding effect is absent in E. granulosus infections of dogs.