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

• Published in: Journal of aquatic animal health Vol. 19; no. 1; pp. 27 - 34
• Main Authors: Mauel, M. J., Soto, E., Moralis, J. A., Hawke, J.
• Format: Journal Article
• Language: English
• Published: United States Taylor & Francis Group 01-03-2007
• Subjects: Animals; Aquaculture; Brackish; Disease Outbreaks - veterinary; Fish Diseases - epidemiology; Fish Diseases - mortality; Fish Diseases - pathology; Francisella; Francisella - isolation & purification; Francisella - pathogenicity; Freshwater; Gadus morhua; Gills - microbiology; Gills - pathology; Gram-Negative Bacterial Infections - epidemiology; Gram-Negative Bacterial Infections - mortality; Gram-Negative Bacterial Infections - pathology; Gram-Negative Bacterial Infections - veterinary; Latin America - epidemiology; Marine; Oreochromis niloticus; Parapristipoma trilineatum; Piscirickettsiaceae - isolation & purification; Piscirickettsiaceae - pathogenicity; Piscirickettsiaceae Infections - epidemiology; Piscirickettsiaceae Infections - mortality; Piscirickettsiaceae Infections - pathology; Piscirickettsiaceae Infections - veterinary; Spleen - microbiology; Spleen - pathology; Tilapia - microbiology; Latin America
• ISSN: 0899-7659; 1548-8667
• DOI: 10.1577/H06-025.1

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