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Serum samples collected from feral swine (Sus scrofa) throughout Florida (USA) from 1980 to 1989 were tested for antibodies to pseudorabies virus (PRV) by the serum neutralization test, the latex agglutination test, or by the enzyme-linked immunosorbent assay. Seropositive swine were detected at 11 of 13 sites with a composite seroprevalence of 34.8% (579 of 1,662 samples; range = 5.9% to 58.2%) for sites with seropositive swine. Data on age and sex of the swine were available from three sites. Seroprevalence in males and females did not differ significantly (P = 0.62 for the combined data). Seroprevalence in adult (> or = 8 mo) and juvenile swine (< 8 mo) was significantly different at all sites (P < 0.05 for the combined data). From these data, PRV infections appear to occur widely in populations of Florida feral swine and may seriously undermine efforts to eradicate this virus from the domestic swine population of the USA.

Serum samples collected from feral swine (Sus scrofa) throughout Florida (USA) from 1974 to 1989 were tested for antibodies to Brucella sp. by the card test, the standard tube test, the rivanol test or the complement fixation test. Seropositive swine were detected at six of 18 sites with a composite prevalence of 23.4% (238 of 1,015 samples; range = 5.5% to 33.3%) for sites with seropositive swine. At one site for which age and sex data were available there was no significant difference (P = 0.50) in seroprevalence between males and females. Antibody prevalence in adult (> or = 8 mo) and juvenile swine (< 8 mo), however, was significantly different (P < 0.05). Based on these data, Brucella sp. infections are limited only to certain populations of feral swine. To avoid the spread of Brucella sp. organisms, however, relocation of feral swine is not recommended.

After confirming that long-term serum storage (frozen at -20 C for greater than 3 mo) causes optical density to drift upward, several modifications of an enzyme-linked immunosorbent assay (ELISA) protocol were evaluated to identify a protocol that would reduce background in porcine sera tested for trichinellosis. Modifications evaluated included blocking the antigen-coated ELISA plate with sample diluent containing 10% bovine serum albumin (BSA) or 10% nonfat milk powder (bovine lacto transfer optimizer or BLOTTO), diluting sera in sample diluent containing 10% BSA or 10% BLOTTO, and preincubating samples in sample diluent containing 10% BSA or 10% BLOTTO. Overnight preincubation (approximately 12 hr at 2 C) of fresh sera diluted (1:10) in sample diluent containing 10% BLOTTO significantly reduced background and improved the detection of experimentally infected pigs by enhancing positive-negative discrimination. When testing stored sera, the modified protocol effectively reduced the effect of storage and the kit revealed specificity of 98.4%; there was no loss in sensitivity. The effect of long-term storage at -20 C must therefore be considered when testing swine sera for trichinellosis by ELISA and possibly also when conducting other immunoglobulin assays. The modification described here may prove useful if there is no alternative to using serum stored for greater than 3 mo at -20 C.

Experimental and field trials were conducted to evaluate an ELISA for its ability to detect Trichinella-infected domestic swine and to compare ELISA results with muscle-digestion test results. The ELISA used was a commercial double-antibody kit, containing an excretory-secretory antigen, and was evaluated principally for epidemiologic use. Experimentally induced infection in swine (4 groups of 3 pigs each; inoculated with 0, 50, 500 or 5,000 larvae) was detected as early as postinoculation week 4, with seroconversion of all inoculated swine by postinoculation week 8. The rate of seroconversion appeared to be affected by initial larval dose, time after inoculation, and immunocompetence of the individual host. Determination of antibody kinetics generally revealed rapidly increasing antibody titer, followed by its steady decrease in most pigs. Once seropositive, however, all pigs remained seropositive for the duration of the 10-week study. Presence of muscle larvae was confirmed in all infected pigs at termination of the study. We recognize that the experimental conditions may not be truly representative of those under which natural infection develops in pigs; however, the ELISA detected an infected pig with muscle larval density of 0.87 larvae/g of tissue. Results of a field trial (n = 310) indicated no muscle digestion test-positive pigs (35 g of diaphragm muscle digested/pig), but 3 samples tested positive by ELISA for specificity of 99.0%.