Control Strategies

There has been a resurgence of research on the epidemiology, biology, and control of Trichinella spiralis during the recent decade. A major ingredient in this renewed attention has been the biotechnological revolution and the new tools it has provided. Especially important has been the application of hybridoma technology to the development of better immunodiagnostic tests. The techniques of recombinant DNA have also been instrumental for providing a potential means to produce antigens and to develop probes for use in epidemiological research and systematics.

Because human infections derive mainly from the ingestion of infected pork, an immunodiagnostic test suitable for the abattoir has had high priority for both the Agricultural Research Service and the Food Safety and Inspection Service, USDA. The efforts of these agencies have been successful, and a commercial ELISA-type test is now available. The critical step in producing this test was the discovery of a simple parasite-cultivation procedure for obtaining the diagnostic antigen (16). The antigens have been purified using a monoclonal antibody in combination with immunoaffinity techniques. In field tests, the antigens proved to be highly specific and sensitive (17,18). Currently, research is underway to produce the antigens by recombinant methods, and preliminary results indicate these efforts will also be successful. This will enhance the commercial viability of the test.

This serological test has been valuable not only for national epidemiologic studies but also for the development of effective control strategies. An important aspect of the epidemiologic investigations has been the assessment of the role of the sylvatic trichinellosis in domestic pig infections. Considerable concern exists over the threat of wild-animal Trichinella infections as a source of infection for humans and domestic swine. Although many wild-animal isolates of Trichinella are poorly infective for swine, the highly infective pig-type strain has been isolated from wild animals (12). The high genetic variability among morphologically indistinguishable isolates of the Trichinella presents problems in interpreting epidemiologic data. However, these questions are being resolved through the application of such techniques as DNA restriction-enzyme fragment-length polymorphism analysis (RFLP) and the development of hybridization probes by cloning unique DNA sequences (12,19). It is clear that human encroachment on the habitat of wild animals has facilitated the introduction of the domestic pig type (Trichinella spiralis sensu stricto) into wild-animal populations and, hence, a sylvatic reservoir of parasites capable of infecting domestic swine has been established (20). Effective control strategies must take this potential threat into account.

Vaccines

A vaccine has been developed for swine trichinellosis (21). It will soon be subjected to field trials. However, the vaccine is based on whole, inactivated newborne larvae and can only be produced on a limited scale. If, however, the field trials are successful, efforts to produce the protective antigens by recombinant DNA methods can be anticipated.

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