The location of Taenia pisiformis, Taenia ovis and Taenia hydatigena in the gut of the dog and its effect on net environmental contamination with ova.

Autopsy of dogs 56 days after infection with either T. pisiformis, T. ovis or T. hydatigena showed that these worms could be found attached at any point along the length of the small intestine, but were most commonly in the anterior half. The mean relaxed lengths of T. pisiformis, T. ovis and T. hydatigena were 107 cm, 156 cm and 177 cm respectively. Attached gravid proglottides contained a mean of 41 000 eggs each in T. pisiformis, 31 000 eggs in T. hydatigena and 95000 eggs in T. ovis, whereas proglottides free in the gut contained means of only 1370, 500 and 1400 eggs respectively; therefore, the majority of eggs were released into the gut before segments passed out into the faeces. It was shown that eggs of all 3 species of worms hatched and activated in the small intestine of the dog, especially in the anterior half. Eggs of T. pisiformis which had been passaged through the intestine of the dog and stored in the faeces for 5 days were poorly infective for rabbits compared with eggs only stored in faeces. It was concluded, therefore, that during taeniid infections of dogs the point of apolysis in the gut plays a significant role in determining environmental contamination with eggs. Puppies which had been fed 10000 T. ovis eggs daily for 6 weeks prior to infection with T. ovis cysticerci showed no difference in susceptibility to the infection when compared with untreated puppies.