A Piscirickettsiosis-like Syndrome in Cultured Nile Tilapia in Latin America with Francisella spp. as the Pathogenic Agent

摘要: In 2004, cultured Nile tilapia Oreochromis niloticus in several Latin America farms began to succumb a disease similar the piscirickettsiosis-like syndrome previously reported Taiwan and United States. Mortality increased during 2005; reductions biomass ranged from 5% 80% individual ponds averaged 50% overall. All ages of fish have been involved. Clinical signs include lethargy, loss appetite, petechia, exophthalmia, abnormal swimming behavior. Gross lesions included splenomegaly, renomegaly, numerous white nodules observed spleen, kidney, testes, heart, ovaries, occasionally liver. A unreported black granulomatous lesion was up 30% fillets. Histologically, infiltrates were liver, ovary, choroid gland, rarely brain heart. small pleomorphic bacterium Giemsa-stained blood smears spleen imprints. The did not grow on standard microbiological media has isolated cell culture. We obtained near-complete 16S ribosomal DNA sequence with high similarity Francisella spp. sequences identified tilapias (Taiwan), Atlantic cod Gadus morhua (Norway), three-line grunts Parapristipoma trilineatum (Japan).