Methods for the Detection of Trichinellosis in Horses

Twelve horses were infected with various doses of Trichinella spiralis and then tested for infection using direct (artificial digestion) and indirect (enzyme immunoassay) methods. Horses became infected in a dose-dependent manner. Larvae accumulated preferentially in the tongue, followed by the masseter, neck, supraspinatus, trapezius, and diaphragm. At lower infection levels, the tongue harbored several times more parasites than were found in other tissues. The sensitivity of artificial digestion methods for detecting infections was directly related to sample size. One-gram samples were not reliable for detecting infection levels of <3 larvae per g (LPG). In sample sizes of 5 or 10 g the technique allowed infections as low as 1 LPG to be detected. The enzyme immunoassay (EIA) detected all infected horses; the times following infection at which horses became seropositive varied in a dose-dependent manner, but 11 of 12 horses were positive in the EIA by 4 weeks postinoculation. One horse, with a larval density in the tongue of 0.39 LPG, did not become seropositive until 7 weeks postinoculation. The results suggest that artificial digestion of horse carcasses for trichinae should concentrate on tissue samples from the tongue or masseter muscles. Sample sizes should be a minimum of 5 g using pooled-sample digestion methods to assure detection of all infections which might pose a human health risk. The EIA is a potential substitute for artificial digestion methods and could also be useful for antemortem testing and for epidemiological studies.