Evaluation of a serological test system for the diagnosis of natural Echinococcus granulosus infection in dogs using E. granulosus protoscolex and oncosphere antigens

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Abstract
SUMMARY: Serum antibody responses in feral or domesticated dogs naturally infected with Echinococcus granulosus orland other common helminths were examined in an enzyme-linked immunosorbent assay (ELISA) using antigens prepared from E. granulosus protoscoleces or oncospheres. The ELISA using the protoscolex antigen was optimised with serums from experimental dogs monospecifically infected with E. granulosus or other helminth parasites, and helminth-free dogs. Anti-protoscolex antibody was detected in 16 of 22 (72.7%) serums from feral dogs with E. granulosus burdens ranging from 300 to 302,600 worms per dog. Seven serums from feral dogs which did not harbour E. granulosus at autopsy but which originated from an endemic hydatid region were tested using protoscolex antigen, and 1 serum gave a positive reaction. One hundred and two serums from dogs known never to have been infected with E. granulosus all gave negative reactions to protoscolex antigen. The sensitivity of the ELISA test proved to be superior to that which has been achieved by arecoline purging as a method of diagnosis for E. granulosus infection in dogs. For use of the assay in hydatid control or eradication campaigns, its Sensitivity can be increased by choosing a lower absorbance discrimination value above which serums are regarded as having positive reactions. However, this does introduce positive reactions of some serums from dogs infected with helminths other than E. granulosus. In further development of the assay, use of defined recombinant antigens may improve both sensitivity and specificity. Anti-oncosphere antibody responses in dogs with experimental E. granulosus infection were apparently stage-specific, and anti-oncosphere antibody was detected in 11 of 21 (52.4%) E. granulosus-Infected feral dogs. There was no apparent correlation between level of antibody measured by ELSA of serums from E. granulosus-infected feral dogs and E. granulosus worm burdens using either antigen, but there was a marked difference in antibody levels in some serums to either the protoscolex or oncosphere antigen. This suggests that a discrimination between prepatent and patent natural E. granulosus infections in dogs may be possible.

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