Cellular and molecular aspects of the experimental ranavirus infection in Nile tilapias (Oreochromis niloticus).

Author(s)

Marcelo Candido

• Document type: Doctoral Thesis
• Press: Pirassununga.
• Institution: Universidade de São Paulo (USP). Faculdade de Zootecnica e Engenharia de Alimentos (FZE/BT)
• Defense date: 2018-12-10

Examining board members

Ricardo Luiz Moro de Sousa; Adriano de Oliveira Torres Carrasco; Fabio Carvalho Dias; Luiz Tadeu Moraes Figueiredo; Hélio José Montassier; Cláudia Maris Ferreira Mostério

• Advisor: Ricardo Luiz Moro de Sousa

Abstract

Some diseases associated with tilapia fish farming cause enormous losses to breeders, resulting in significant morbidity and mortality rates among animals of all ages. In this sense, requirements for the improvement of the laboratory diagnosis of diseases of infectious-contagious nature, became constant, in view of the related losses. Ranaviruses are viruses that infect ectothermal vertebrates causing widespread necrosis, focal haemorrhages and cell apoptosis in infected animals. The present study aimed to perform experimental infections in Nile tilapia (Oreochromis niloticus) fry and larvae through 3 different infection models, using Ranavirus Frog virus 3-like strain recently detected and isolated in Brazil, to evaluate the associated pathologies, including sequencing and genome analysis of the viral strain. Several macroscopic and microscopic clinical signs were observed, hemolysis, red blood cells presenting anisocytosis and polychromasia, alterations related to the mean red blood cell volumes and hemoglobin present in the red blood cells, hepato-somatic and spleno-somatic indexes showing statistically significant interactions, reactive lymphocytes, alterations in the levels of the enzymes alanine aminotransferase and basophilic inclusion corpuscles in different tissues of animals tested with Ranavirus FV3-like were observed within the 60-day post-infection period. In addition, experimentally infected animals were positive to Ranavirus through qPCR. The genome of the Ranavirus FV3-like Brazilian strain presented 105 kilobases, containing 54.98% of guanine + cytosine, with 94 potential ORFs annotated. The phylogenetic reconstruction, based on nucleotide sequences, grouped the Brazilian sample of Ranavirus in the clade of Frog virus 3-like, the greater identities of the genome were with North American strains of FV3-like. Twelve potential recombination events, statistically significant (p <0.05), were identified between the Brazilian strain and reference samples of Ranavirus FV3-like. The present work contributes to a better understanding of the infection caused by the Brazilian strain of Ranavirus FV3-like in Nile tilapia (Oreochromis niloticus). In addition, it adds and reinforces the potential recombination between different strains of Ranavirus, contributing to a better understanding of the characteristics of viral agents associated with severe outbreaks in ectothermic vertebrates. (AU)

• FAPESP's process: 17/01718-3 - Cellular and molecular aspects of the experimental ranavirosis in Nile tilapias (Oreochromis niloticus)
• Grantee: Marcelo Candido
• Support Opportunities: Scholarships in Brazil - Doctorate