Cestode infections in animals : immunological diagnosis and vaccination

Abstract

Cestode infections in animals are important because several species are zoonotic, causing cysticercosis and hydatidosis in man, and because of the economic losses incurred due to infections in livestock. Information on immunological diagnosis of and vaccination against cestode infection is restricted almost exclusively to the taeniid cestodes in which two groups of mammalian hosts are concerned: the intermediate host infected with the larval parasite and the definitive host infected with the adult tapeworm parasite. Research towards developing serological tests for the diagnosis of larval cestode infection in animals has been largely unsuccessful. Substantial problems remain, due to the frequent existence of multiple infections with different taeniid species and antigenic crossreactivity between these related parasites, and the low level of specific antibody response to infection. Problems with poor specificity and sensitivity of traditional serological tests for cysticercosis and hydatidosis have prevented the development of any practical test for ante-mortem diagnosis of infection. A recent new approach to the diagnosis of Taenia saginata infection by detecting circulating parasite antigen offers some prospect for the development of a practical diagnostic test for cysticercosis in cattle. The effectiveness of the arecoline purge for detection of Echinococcus granulosus in dogs has been reduced by the widespread availability of praziquantel. A serological method for diagnosis of E. granulosus in dogs has been developed which offers equivalent or superior diagnostic sensitivity compared with arecoline purge. This test should provide a valuable tool in hydatid control campaigns for the diagnosis of existing or recent past infections in dogs. Substantial progress has been made towards developing a practical vaccine for the prevention of T. ovis infection in sheep. An antigen derived from the parasite egg has been identified and produced in Escherichia coli using recombinant DNA techniques. The vaccine, which protects sheep against challenge infection with T. ovis, is the first highly effective defined antigen vaccine against any parasite infection of man or animals. Commercial development of this vaccine is in progress. The success achieved with the T. ovis vaccine augurs well for the rapid development of other recombinant vaccines against cysticercosis caused by other taeniid species and against hydatidosis in animals.