Control Strategies

Current control strategies for these parasitic diseases are dependent on detecting infections in livestock in order to remove them from the food chain. However, procedures for this task are at present inadequate. For example, in the United States, the mandatory inspection of beef for cysticerci is known to be highly insensitive (26). Most current research on cysticercosis is aimed at developing rapid, more reliable immunodiagnostic tests for both livestock and humans.

Until recently, the prospects for an immunodiagnostic test for bovine cysticercosis were poor because of the low specificity of crude worm extracts as antigen reagents. Recently, biochemical fractionation approaches have greatly improved the specificity of these antigens. A genus-specific antigen from T. hydatigena (ThFAS) with a high degree of sensitivity and specificity for both bovine and porcine cysticercosis has been recently recovered (27,28). With this antigen, low infection levels in cattle could be detected as early as 3 weeks after exposure. Currently, efforts are underway to clone the gene for this antigen so that sufficient amounts of antigen for field tests can be made available.

The immunodiagnosis of human neurocysticercosis has also greatly improved. One of the most specific and sensitive test procedures is that described by Tsang and coworkers (29). This test is an enzyme-linked immuno-electrotransfer blot assay using glycoprotein antigens prepared by fractionation of T. solium cysticerci. In an evaluation using a large number of sera and cerebrospinal fluids, the test was 98% sensitive and 100% specific.

Recombinant DNA methods have had, to date, their greatest impact in human cysticercosis research in the area of taxonomy (30). As pointed out earlier, the syste-matics of the taeniid cestode group requires clarification because of its importance to understanding the epidemiology of these foodborne parasites. As various host and geographic isolates receive closer scrutiny, it is apparent that at least some of the species exist as complexes of intraspe-cific variants, frequently with variation in host specificity. Recently, a variety of geographic isolates of T. solium, have been analyzed with the aid of DNA probes (31). Considerable intraspecific genetic variation has been detected. Using a similar approach, distinct DNA differences between a T. sagmaia-like cestode from Taiwan and various other isolates of T. saginata have been observed (32). The human Taenia from Taiwan (and Korea) is unique in that it is more infective for swine than for cattle and has a predilection for the swine liver. The difference in DNA characteristics supports the interpretation that the Taiwan Taenia is genetically and biologically unique although closely related to T. saginata. It can be anticipated that these powerful methods will prove to be decisive in developing a greater understanding of the genetic variation and epidemiology of these important human parasites.

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