Molecular Examination of the Sympatry and Distribution of Sheep and Camel Strains of Echinococcus granulosus in Kenya

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  • Molecular Helminthology Laboratory, Division of Tropical Health and Infectious Diseases, Queensland Institute of Medical Research, African Medical and Research Foundation, Brisbane, Queensland, Australia

Previous studies have shown that camel and sheep strains of the cystic hydatid parasite Echinococcus granulosus occur in Kenya. We examined 208 larval isolates and 40 worm samples of E. granulosus from various hosts in Kenya using restriction fragment length polymorphism analysis of a segment of ribosomal DNA amplified by the polymerase chain reaction. This was in an effort to determine whether additional strains of E. granulosus occur in Kenya, to examine the level of genetic heterogeneity within the sheep/dog and camel/dog strains previously identified, and to map out their intermediate host range and geographic distribution in Kenya. We confirmed the existence of the two strains in Kenya and showed that the distribution of the camel strain appears restricted to the Turkana region, where camels are kept as livestock. The intermediate host range for both strains seems to be similar except that humans appear refractory to infection with the camel strain. We have also shown that although the life-cycle patterns of the two strains overlap both geographically and in intermediate and definitive hosts, the strains maintain their homogeneous genetic identity.