ABSTRACT:Diphyllobothriosis in fish from freshwater ecosystems in southern Chile was first reported in 1949. Infection by plerocercoids of Diphyllobothrium latum and Diphyllobothrium dendriticum occurs in introduced trout (Oncorhynchus mykiss) and native fish. We determined the prevalence, mean intensity, and mean abundance of seasonal infection and tissue damage produced by Diphyllobothrium spp. in native fish (Percichthys trucha, Odontesthes mauleanum, and Basilichthys australis) and introduced trout (O. mykiss) from Lake Panguipulli, Chile. Prevalence, mean intensity, and mean abundance of D. latum infection were significantly greater in trout than they were in native fish. Prevalence and mean abundance were similar in O. mauleanum and P. trucha, but they were greater than those in B. australis. Prevalence and abundance were similar among seasons between sexes for the four hosts. For all host species, except P. trucha, there was a statistically significant positive correlation between host length and the abundance of plerocercoids. Infections in muscle tissue were present in 61% of trout compared with 23% in O. mauleanum and 12% in P. trucha, suggesting a greater risk for human infection when consuming trout. In general, prevalence of infection by D. dendriticum was lower than was D. latum prevalence. Encapsulation of plerocercoids was common and severe in 71% of the trout examined. Only slight encapsulation of plerocercoids was found in the native O. mauleanum, and no encapsulation was observed in P. trucha or B. australis. The greater concentration of plerocercoids in the walls of the digestive tract of trout suggests a more-rapid immune response in trout than in native fish. The low frequency of encapsulation of plerocercoids in native fish would mean greater tissue damage in the natives than that observed in the trout because they are free to migrate among the viscera, potentially endangering these native fish populations in regions where Diphyllobothrium spp. are endemic.

The objective of this study was to evaluate the effect of selenium (Se) supplementation on milk somatic cell count (SCC) in dairy cows. Twelve multiparous Holstein-Friesian cows were fed a diet containing a suboptimal Se concentration (<0.05 ppm, dry basis) starting 2 months before calving. Supplemented cows (n=6) received a single s.c. injection of barium selenate (1 ml/50 kg BW) 45 days prior to calving, whereas control group was kept unsupplemented. Twenty weeks after calving, two mammary quarters (right side) of each cow were challenged with 205,000 cfu/ml of Staphylococcus aureus (strain Newbould 305). Blood was collected bi-weekly until day 150 of lactation for the analysis of blood glutathione peroxidase (GPx1; EC 1.11.1.9) activity. To re-isolate the challenging pathogen and to evaluate SCC, aseptic milk samples were collected daily starting on the day of challenge, and finishing 7 days after inoculation. Unsupplemented cows had a lower activity of GPx1 through the experiment (P<0.001). Natural log SCC (lnSCC) was higher in unsupplemented than Se-supplemented cows (P=0.04), showing evidence of significance after 5 days. Selenium supplementation of dairy cows fed a diet containing a suboptimal Se concentration, resulted in higher blood activity of GPx1, and lower mean lnSCC after an intramammary challenge with Staph. aureus.

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Thymulin is a well-characterized thymic hormone that exists as a nonapeptide coupled to equimolar amounts of Zn 2+ . Thymulin is known to have multiple biological roles, including T cell differentiation, immune regulation, and analgesic functions. It has been shown that thymulin is produced by the reticulo-epithelial cells of the thymus, and it circulates in the blood from the moment of birth, maintain its serum level until puberty diminishing thereafter in life. To study the localization of this hormone, we prepared polyclonal and monoclonal antibodies against the commercial peptide and utilized immunocytochemical techniques for visualization. The results indicate that thymulin stains the thymic reticular cells, the outer layers of Hassall´s corpuscles and a large round cellular type, which is keratin-negative and does not show affinity for the common leukocyte antigen (CD-45). In mice, this thymulin-positive cell remains in the thymus throughout life and even appears in relatively increased numbers in old involuted thymi. It also appears in thymusdependent areas of the spleen and lymph nodes, demonstrating that at least one of the thymus cells containing this peptide can be found in peripheral lymphoid tissue.