Lymphocystis Disease Virus Infection in Cultured Three-Spot Gourami (Trichogaster trichopterus) in Brazil

Lymphocystis disease virus (LCDV) infection induces massive hypertrophy of dermal cells with intracellular accumulation of virions, resulting in skin nodules that are observed to the naked eye. In September 2022, an ornamental fish producer noted white spots and nodules on the skin and fins of a three-spot gourami (Trichogaster trichopterus) population, which compromised the aesthetic of the fish. The disease only affected this fish species in the farm and was intermittent. Ten diseased and four apparently healthy fish were collected during the first sampling, and 20 diseased fish were collected approximately 1 year after for a follow-up examination. Macroscopically, the fish presented isolated or small clusters of white to grey nodules, measuring 0.1-0.5 mm, concentrated on the fins and caudal peduncle. Histologically, nodules in the skin and internal viscera were composed of numerous hypertrophied cells with nucleolar components and karyomegaly and thick hyaline cell walls. Virions, with a diameter of approximately 180 nm, were visualised in infected interstitial cells in the skin through transmission electron microscopy. The presence of LCDV in the skin, spleen, and kidney was confirmed by specific PCR. Phylogenetic analysis of the MCP gene revealed that the isolates from Brazilian gouramis belonged to the cluster of LCDV genogroup VI, similar to an unclassified virus identified in a population of gouramis in Korea. This report describes the pathological and molecular findings of LCDV infection in cultured three-spot gourami in Brazil.