Susceptibility of ornamental African cichlids Aulonocara spp. to experimental infection with Tilapia lake virus

Tilapia lake virus (TiLV) is a single-stranded negative-sense RNA virus associated with high morbidity and mortality in tilapia. Although the susceptibility of different fish species against TiLV has been investigated, there is limited information of the infectivity of this emerging virus in ornamental African cichlids, which share a genetic background with tilapia. Here, our results revealed that TiLV could cause disease in ornamental Malawi cichlid, Aulonocara spp. Severe morbidity and mortality occurred 5-11 days post-coelomic injection of 1 x 105 TCID50/mL, with a cumulative mortality of 56.25%, 11 days post-challenge. The moribund fish exhibit clinical signs of infection, including coelomic distension, abnormal swimming, exophthalmos, fin rot, and lethargy. Most affected fish also present gross changes, including hyperemic and sometimes ulcerative skin lesions, particularly in the head. Histopathological examination revealed syncytial cells formation, necrosis and lymphocytic inflammation in the liver, with eosinophilic inclusion body in hepatocytes, and necrosis and lymphocytic inflammation in spleen and anterior kidneys. Further, myocardial and intestinal necrosis with infiltration of lymphocytes in the cardiac muscle and intestinal lamina propria were observed in TiLV challenged fish. The infectivity of TiLV in ornamental African cichlids was confirmed by virus isolation in E-11 cells. Cytopathic effect (CPE) developed within three days of inoculation of TiLV challenged fish brain homogenates. The presence of TiLV nucleic acid was further demonstrated in liver, anterior kidney, and heart of the challenged fish by in situ hybridization and reverse transcription-quantitative polymerase chain reaction assay. Altogether, these findings suggest that ornamental African cichlids could be a potential carrier for TiLV and highlight the need for additional assessment to determine the role of other fish species in the transmission of TiLV.

Automated summary

The results indicate that ornamental Malawi cichlid can be infected with Tilapia lake virus (TiLV), leading to severe symptoms and mortality. The infected fish show various clinical signs and histopathological changes, suggesting that ornamental African cichlids could be potential carriers for TiLV.