Implementation and analysis of diagnostic techniques for Mycobacterium spp. and Francisella spp. in granulomatous disease of fish in breeding and wild aquaculture of São Paulo/Brazil

Abstract— Mycobacterium spp. and Francisella spp. bacteria have serious implications for Animal Health, Public Health and Agribusiness and yet, in Brazil, there is little knowledge about the best diagnostic techniques to detect and characterize them. Therefore, the occurrence of these bacteria was verified in 519 fish from fish farms (active collection), wild freshwater animals from the State of São Paulo (active collection), and in materials filed in our laboratory (passive collection), using the techniques in situ hybridization (IHS), immunohistochemistry (IHC), optical microscopy (MO) (H&E and (ZN) Ziehl Neelsen or Fite-Faraco), and negative staining for transmission electron microscopy (TEM). Histologically, granulomas were observed in 135 fish. By the ZN Faraco technique, Mycobacterium spp was found in 54 animals. By Immunohistochemistry and in situ Hybridization, 46 fish were found infected with Mycobacterium spp, 40 with Francisella spp and 30 with both bacteria. In one of the animals the presence of granulomas was found, although not caused by Mycobaterium spp or Francisella spp. TEM also showed the presence of other bacteria, protozoa, and viruses. The aim of this study was to evaluate the best diagnostic techniques for Mycobaterium spp or Francisella spp in fish fragments.