Echinococcus granulosus of camel origin: development in dogs and parasite morphology

The developmental characteristics of Echinococcus granulosus of camel origin were studied in four dogs artificially infected with protoscolices originating from hydatid cysts isolated from the lung of a camel (Camelus dromedarius). Two dogs each were necropsied 34/35 and 41 days post-infection (p.i.); one dog had a low worm burden and the others were heavily infected (27,625-41,150 worms). At day 35 p.i., 20% of the parasites had developed three segments and the uterus of the vast majority of the total population was full of developing eggs in the terminal segment. At day 41, up to 58% of the parasites contained mature eggs (embryonated eggs with fully developed, "thick-shelled" embryophores). Morphological studies revealed the following major characteristics for 35 day-old worms: the mean length of the terminal segment accounted for 54% of the total worm length; the position of the sexually mature segment was always terminal; the female reproductive system possessed an elongated ovary with compact lobules; the female ducts were also compact; the Mehlis' gland was covered by the vitelline gland and the testes were distributed throughout the segment, with 1 row posterior to the vitelline gland. The camel isolate can readily be distinguished from the horse and sheep strains, but it is similar to the cattle strain in some respects, particularly in its precocious development. However, the camel isolate differs from the cattle strain in the position of the sexually mature segment, arrangement of the testes and structure of the female reproductive system. As in the cattle strain, the metacestodes in the principal intermediate host are mostly localised in the lung and have a high fertility rate.