A multiple bioassay technique (FSIS-USDA) has been evaluated with standard solutions of 38 antibiotics and sulphonamides. Activity patterns at five levels were obtained when antibiotic solutions were assayed on seven plates prepared with different media and microorganisms. A different activity pattern was obtained for the main antibiotic groups: tetracyclines, beta-lactam antibiotics, macrolides and aminoglycosides. Sulphonamides were not detected at levels at under 100 micrograms/ml. This technique, as a post-screening test for antibiotic residues, can be used after a screening test to identify antibiotic groups to which more specific techniques can be applied for full identification and quantification.
This study establishes the seroprevalence of Hypoderma spp in cattle and the influence of some internal and environmental factors in the distribution of this myiasis in Galicia (northwest of Spain). Humoral antibody levels were measured by means of an indirect enzyme-linked immunosorbet assay, using as the antigen hypodermin C obtained from 1st-instar Hypoderma lineatum (De Villers). The percentage of positive sera in the total sample of 1,473 animals was 78.4%. Considering the different climatic areas in Galicia, the seroprevalence was lower in coastal areas; whereas, in the inland the percentages of positive sera were higher. The study revealed significant differences in seroprevalence between breeds; the autochthonous Rubia Gallega breed was the most prevalent, followed by the crossbreeds Brown Swiss and Friesian. The breeding system was an important factor affecting the occurrence of hypodermosis.
Twelve batches of the mollusc Cernuella (Cernuella) virgata (Mollusca: Helicidae) were deposited monthly directly on faeces containing first-stage larvae of Neostrongylus linearis, so that they were naturally infected. Every two weeks the molluscs were examined to study the larval development of N. linearis. No correlation was found between the number of first-stage larvae of N. linearis on the faeces and the number of total larvae and third-stage larvae which developed in the snails. However, a negative correlation was found between temperature and the days needed to reach the different larval stages. Thus, the molluscs harboured third-stage larvae from mid-spring to mid-autumn, the period of time which carries the greatest risk of infection for the definitive hosts.
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