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A serological survey was conducted in the Patagonia region of Argentina to estimate the prevalence of nine disease agents within the populations of free-ranging culpeo (Dusicyon culpaeus) and grey (Dusicyon griseus) foxes. The disease agents were Aujeszky's disease virus (ADV), Brucella, canine adenovirus (CAV), canine distemper virus (CDV), canine parvovirus (CPV), Encephalitozoon cuniculi, Leptospira, Neospora caninum, and Toxoplasma gondii. A total of 84 foxes were sampled (28 culpeo and 56 grey), and 73% of the sera had antibodies against one or more pathogens. Among these seropositive sera, 47% of them reacted to only one antigen, while the other 53% reacted to multiple antigens. The presence of antibodies to Toxoplasma (20%), Neospora (44%), Leptospira (30%) and Brucella (18%) suggests that these organisms actively circulate in the area. Antibodies against CDV, CAV and CPV were detected in 2%, 5% and 5% of foxes, respectively. Regarding Encephalitozoon cuniculi and ADV, no evidence of either was found.

Sarcocystis speeri Dubey and Lindsay, 1999 from the South American opossum Didelphis albiventris was successfully transmitted to the North American opossum Didelphis virginiana. Sporocysts from a naturally infected D. albiventris from Argentina were fed to 2 gamma-interferon knockout (KO) mice. The mice were killed 64 and 71 days after sporocyst feeding (DAF). Muscles containing sarcocysts from the KO mouse killed 71 DAF were fed to a captive D. virginiana; this opossum shed sporocysts 11 days after ingesting sarcocysts. Sporocysts from D. virginiana were fed to 9 KO mice and 4 budgerigars (Melopsittacus undulatus). Schizonts, sarcocysts, or both of S. speeri were found in tissues of all 7 KO mice killed 29-85 DAF; 2 mice died 39 and 48 DAF were not necropsied. Sarcocystis stages were not found in tissues of the 4 budgerigars fed S. speeri sporocysts and killed 35 DAE These results indicate that S. speeri is distinct from Sarcocystis falcatula and Sarcocystis neurona, and that S. speeri is present in both D. albiventris and D. virginiana.

Two isolates of Sarcocystis falcatula were obtained from the lungs of budgerigars (Melopsittacus undulatus) fed sporocysts from two naturally-infected South American opossums (Didelphis albiventris). The two isolates were designated SF-1A and SF-2A. Both isolates induced fatal infections in budgerigars. Both isolates underwent schizogony in African green monkey kidney cells. The structure of schizonts in the lungs of budgerigars was more variable than that observed in cell culture. The two isolates were identified as S. falcatula by the two species-specific Hinf 1 restriction fragments dervied from digestion of a PCR amplification using primers JNB33/JNB54. Thus, the South American opossum, D. albiventris, is a definitive host for S. falcatula.

Sarcocystis sporocysts from the intestines of four opossums (Didelphis albiventris) from Argentina were identified as Sarcocystis falcatula based on schizogonic stages and pathogenicity to budgerigars (Melopsittacus undulatus). Seven budgerigars fed sporocysts from the opossum feces died of acute sarcocystosis 8, 9, 11, 12, and 14 days after inoculation. Schizonts and merozoites found in the lungs and other organs of the budgerigars were identified as S. falcatula based on structure and immunoreactivity with S. falcatula-specific antibody. Sarcocystis falcatula was also isolated in bovine monocyte cell cultures inoculated with lung tissue from a budgerigar that died nine days after ingesting sporocysts. Two budgerigars inoculated subcutaneously with 1,000,000 culture-derived S. falcatula died 11 and 12 days post-inoculation. This is the first report of S. falcatula infection in South America.

Sera and diaphragm muscle tissues were obtained from 109 commercial pigs between September 1991 and May 1992 from the slaughterhouse at La Plata, Provincia Buenos Aires, Argentina. Anti-Toxoplasma gondii IgG antibody reactivity to T. gondii antigens were assayed using sera by indirect immunofluorescence assay and immunoblotting technique. Anti-T. gondii IgG titers at serum dilutions of 1:1024 and higher were noted in 11.0% of the tested sera, and at dilutions of 1:16 and lower in 36.7% of the serum samples. Using mouse inoculation test, T. gondii was isolated from 14 pig diaphragm samples. Of five samples derived from pigs with antibodies at dilutions of 1:1024 and higher, four contained trophozoites which, when inoculated into mice intraperitoneally, killed all recipient hosts within 15 days post inoculation. Parasites detected in seven out of eight samples from pigs with antibodies at serum dilutions of 1:64 and lower formed cysts in the brain, and mice survived longer than 13 days post inoculation. Immunoblotting demonstrated antibody reactivity in pig sera samples with relatively high titers for parasite antigens. Results of the present study suggest that antibody production in infected pigs is apparently dependent on the pathogenicity of the parasite strain.