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. 2022 Apr;15(4):1097-1106.
doi: 10.14202/vetworld.2022.1097-1106. Epub 2022 Apr 27.

Persistent detection of Tilapia lake virus in wild tilapia and tinfoil barbs

Azila Abdullah  1 , Afzan Muntaziana Mohd Pazai  2 , Mohd Syafiq Mohammad Ridzuan  1 , Fahmi Sudirwan  1 , Shahidan Hashim  1 , Adnan Abas  3 , Munira Murni  1 , Zuraidah Roli  1 , Rimatulhana Ramly  1 , Mohd Firdaus-Nawi  4
Affiliations

Persistent detection of Tilapia lake virus in wild tilapia and tinfoil barbs

Azila Abdullah et al. Vet World. 2022 Apr.

Abstract

Background and aim: One of the emerging viral diseases in freshwater fish is Tilapia lake virus (TiLV), which infects all stages of fish and results in mass mortalities. Previously, a TiLV case was detected in the wild environment in Malaysia that involved tilapia and tinfoil barb. Hence, this study aimed to determine the presence of TiLV in wild tilapia (Oreochromis niloticus) as well as tinfoil barbs (Barbonymus schwanenfeldii) at the similar lake after the initial outbreak in year 2017.

Materials and methods: Both fish species were sampled from this lake at a month interval for two years and subjected to TiLV detection using reverse transcriptase-polymerase chain reaction and cell culture isolation. Concurrently, bacterial isolation and water quality measurements were performed to deduce their correlation with TiLV occurrence. Other wild fish species and mollusk were also occasionally sampled during the fish inventory activity at this lake. The fish's weight, length, and associated clinical signs were noted throughout the entire study period.

Results: Mortality was not observed throughout the whole study period, and results indicated a moderate to high prevalence of TiLV infection in both tilapia and tinfoil barbs. There was no correlation between TiLV infection with the isolation rate of opportunistic bacteria such as Aeromonas spp., Plesiomonas spp., and Edwardsiella spp. in the study site. At the same time, the Pearson correlation test revealed a moderate negative correlation between the water pH with the presence of TiLV (R=-0.4472; p<0.05) and a moderate positive correlation between the water iron content with the monthly detection of Aeromonas spp. in wild tilapia. This is contrary to tinfoil barbs, where there was a moderate negative correlation between the water iron content with the monthly isolation of Aeromonas spp. (R=-0.5190; p<0.05). Furthermore, isolation of TiLV on cell culture-induced viral invasion was resulted in the cytopathic effects.

Conclusions: Our results suggest that the wild fish may harbor TiLV for an extended period following a massive die-off event in 2017 without any obvious clinical signs and mortality. The persistency of viruses in the wild may need continuous and effective control as well as prevention strategies.

Keywords: Malaysia; Tilapia lake virus; tinfoil barbs; wild tilapia.

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Conflict of interest statement

The authors declare that they have no competing interests.

Figures

Figure-1
Figure-1
Some of the clinical signs observed in infected wild tilapia and tinfoil barbs showed body discoloration (bold arrow), scale drop (thin arrow), eye abnormalities or congested (black arrow), and pale and patchy liver (white arrow).
Figure-2
Figure-2
Monthly isolation of AE, PL, ED, and TiLV in wild (a) tilapia and (b) tinfoil barbs throughout the 2 years of sampling period. AE=Aeromonas spp., PL=Plesiomonas spp., ED=Edwardsiella spp., TiLV=Tilapia lake virus.
Figure-3
Figure-3
The range of weight and length of wild (a) tilapia and (b) tinfoil barbs that were infected with TiLV. TiLV=Tilapia lake virus.
Figure-4
Figure-4
Cytopathic effect of the E-11 cells following inoculation of samples from (a) tilapia, (b) tinfoil barbs, (c and d) E-11 control cell.
Figure-5
Figure-5
The phylogenetic tree shows the similarity of these isolates with the other countries.
See this image and copyright information in PMC

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