Risk of Tilapia Lake Virus transmission via frozen tilapia fillets?

Recent outbreaks of a novel Tilapia Lake Virus have raised concerns regarding the international spread of Tilapia Lake Virus via frozen tilapia products. You see, in theory it is quite possible that a virus might survive in the deep frozen fish fillets and, if thawed, could infect you.

[Naive red hybrid tilapia]

Like me, some scientists were also growing a bit worried and investigated the potential risks of frozen tilapia fillet as a source of transmission[1]. The results were that genomic RNA of the Tilapia Lake Virus could be detected in tilapia fillet and the virus isolated from non-frozen and frozen fillets with clinical Tilapia Lake Virus infection stored up to 28 days caused a cytopathic effect formation in the susceptible cell line in vitro.

However, frozen fillets from clinical Tilapia Lake Virus infection stored for 90 and 120 days did not cause a cytopathic effect in the susceptible cell line. Similarly, a cytopathic effect was not observed in Tilapia Lake Virus isolated from subclinically Tilapia Lake Virus-infected fish fillets. In addition, in vivo bioassay revealed that despite the presence of Tilapia Lake Virus isolated from subclinically Tilapia Lake Virus-infected fillet stored at -20°C for 14 days, there was no evidence of Tilapia Lake Virus disease in naïve red hybrid tilapia (Oreochromis mosssambicusxniloticus) based on the absence of clinical signs and mortality and without the detection of Tilapia Lake Virus genomic RNA using reverse transcription-quantitative polymerase chain reaction assay.

Collectively, the scientists conclude, these findings suggested minimal risk of transmission of Tilapia Lake Virus via frozen tilapia fillets.

But is it? While the scientists wrote quite a lot about conditions that resulted in non-transmission, they glossed over the bit that proved that a transmission of Tilapia Lake Virus via frozen fish fillets was quite possible.

[1] Thammatorn et al: Minimal risk of tilapia lake virus transmission via frozen tilapia fillets in Journal of fish Diseases – 2019