Many species of ornamental freshwater fishes are imported into Japan from all over the world. We found African lampeye Aplocheilichthys normani and dwarf gourami Colisa lalia suffering from an iridovirus infection just after being imported by tropical fish wholesalers from Singapore. African lampeye were cultured on the Indonesian Island of Sumatra and dwarf gourami were cultured in Malaysia before export. Diseased fishes displayed distinct histopathological signs of iridovirus infection: systemic appearance of inclusion body-bearing cells, and necrosis of splenocytes and hematopoietic cells. Electron microscopy revealed viral particles (African lampeye:180 to 200 nm in edge to edge diameter; dwarf gourami: 140 to 150 nm in diameter) in an inclusion body within the cytoplasm of inclusion body-bearing cells as well as in the cytoplasm of necrotized cells. Experimental infection with an iridovirus isolate from African lampeye (ALIV) revealed pathogenicity of ALIV to African lampeye and pearl gourami Trichogaster leeri. Polymerase chain reaction (PCR) products from ALIV and an iridovirus isolate from dwarf gourami (DGIV) using iridovirus-specific primers were indistinguishable. The nucleotide sequence of PCR products derived from ALIV (696 base pairs) and DGIV (701 base pairs) had 95.3% identity. These results indicate that ALIV and DGIV have a single origin. KEY WORDS: Tropical iridovirus · African lampeye · Dwarf gourami · Inclusion body-bearing cells · Polymerase chain reaction assay · DNA sequence Resale or republication not permitted without written consent of the publisherDis Aquat Org 48: [163][164][165][166][167][168][169][170][171][172][173] 2002 brown-spotted groupers Epinephelus tauvina (Chua et al. 1994) and E. malabaricus (Danayadol et al. 1996), farmed in Singapore and Thailand, respectively; sea bass, Lateolabrax sp., captured in the South China Sea ; mandarin fish Siniperca chuatsi, reared in offshore pens in the South China Sea in China (He et al. 2000); red sea bream Chrisophylus major (= Pagrus major, Inouye et al. 1992), yellowtail Seriola quinqueradiata, and striped jack Caranx delicatissimus, etc., farmed in Japan (Miyazaki unpubl.); and striped beakperch Oplegnathus fasciatus, cultured in Korea (Jung & Oh 2000).Here we present the results of histopathological and electron microscopic (EM) examinations of the diseased African lampeye and dwarf gourami. We report the results of artificial infections with an isolate from African lampeye to African lampeye and pearl gourami. We also describe a polymerase chain reaction (PCR) assay and DNA sequence analysis of the PCR products for identification of iridovirus isolates from African lampeye (ALIV) and dwarf gourami (DGIV). MATERIALS AND METHODSHistopathological and EM examinations, virus culture in natural outbreaks. Diseased African lampeye and dwarf gourami were found just after being imported to Japan from Singapore by tropical fish wholesalers. The African lampeye had been cultured in freshwater ponds on Sumatra Island, Indonesia, a...

Tropical iridovirus infection causes severe epizootic resulting in mass mortalities and large economic losses in freshwater ornamental fishes cultured in Southeast Asian countries, in wild fish seedlings captured in South China Sea, and in marine fishes farmed in Japan, Singapore, and Thailand. All of tropical iridovirus-infected fishes histopathologically showed the systemic formation of inclusion body-bearing cells and necrosis of virus-infected splenocytes and hematopoietic cells. We designed primer sets for the ATPase gene and the major capsid protein (MCP) gene and sequenced the PCR products derived from 5 iridovirus isolates from sea bass in South China Sea, red sea bream in Japan, brown-spotted grouper with a grouper sleepy disease in Thailand, dwarf gourami from Malaysia and African lampeye from Sumatra Island, Indonesia. The ATPase gene and the MCP gene of these 5 viral isolates were highly homologous (> 95.8%, > 94.9% identity, respectively) and the deduced amino acid sequences of the ATPase and the MCP were also highly identical (> 98.1%, > 97.2% identity, respectively). Based on the high homology, these 5 isolates of tropical iridovirus from various fishes in geographically different regions were determined to have a single origin and to be native to Southeast Asian regions. However, these sequences were far different from those of members of the genera Ranavirus, Lymphocystivirus and Iridovirus in the Family Iridoviridae. We propose a new genus "Tropivirus" for tropical iridovirus in the Family Iridoviridae.