Virus Espionage Replicates Inside the Grouper’s Eggs: Red Alert for New Treatment Method!

Viral infection is not a new threat to fish industries. Since 1979, grouper fish farms in Taiwan have been decimated by the widespread virus infection (nodavirus and iridovirus) that resulted in economic loss to aquaculture companies. There are two common viruses that can be found in farmed groupers; the Nervous Necrosis Virus (NNV), which is a two-single-stranded RNA nodavirus that damages the central nervous system of juvenile or larvae fish; and the iridoviruses, which is a double stranded DNA that affects most poikilothermic vertebrates. These viruses can cause vibriosis which leads to high mortality rates.

Kuo H-C .et al (2012) address the issue of vertical transmission of the viruses through egg membrane development or sperm gene transfer. They believe that the NNV and iriodoviruses also replicate inside the egg and, following the embryonic development, these viruses are found inside the egg shell. This discovery of viruses multiplying inside the eggs makes the ozone treatment to remove the viruses almost impossible and thus scientists need to find new treatments for this viral infection.

The high mortality of the test subjects that were infected by these viruses makes the transmission pathway of this virus a missing puzzle piece on how it interacts with its host. As a result, Kuo H-C.et al (2012) focused on developing a microfluidic-based RT-PCR to detect and understand the infection status of different pathogens that leads to predicting the transmission pathway of the two viruses. Microfluidic chip system enables us to perform multiplex assay, which identifies the virus’ presence in situ or in the lab, easier than the previous method of Target RNA 2.

The microfluidic chip Multiplex RT-PCR assay was able to detect multiple infecting agents in a sample, but before applying the microfluidic chip for field use, a test run was necessary. The test run required a juvenile to be exposed to multiple infections of bacteria and viruses in the lab to see if the microfluidic chip RNA detection works in controlled lab conditions, then field sample from different fish farm can be examined for the presence of NNV.

Three experiments were monitored for 27 days and the presence of two viruses differed over this period. The results showed that NVV was localized inside the embryo and even after hatching, the number of viruses during development was increasing.

NNV replicates inside the embryo alongside its development caused 80-90% of the mortality rate of juvenile grouper post hatching which is a fatal. Understanding the transmission pathway of the viruses gives the researcher and aquaculture company the edge to fight against these NNV and iridoviruses. Studying the interaction between viruses and juveniles can be applied to find future treatments for NNV, and the method of identifying RNA through microfluidic chips is also applicable to any other type of infections.

This paper had a detailed result diagram, however more details about the application of the microfluidic chip would have been interesting to read and also a separate link to a detailed methods section would be beneficial for repeating this experiment. The paper is excellent for discussing findings and raising attention for new approaches to identify viruses and diseases. Overall, I really like the paper because it opens up a new perspective and understanding of the NNV transmission pathway that can lead to a new field of virology and also better life quality for farmed fish.

Reviewed Paper

Kuo H-C, Wang T-Y, Hsu H-H, Chen P-P, Lee S-H, Chen Y-M, et al. (2012) Nervous Necrosis Virus Replicates Following the Embryo Development and Dual Infection with Iridovirus at Juvenile Stage in Grouper. PLoS ONE 7(4): e36183. https://doi.org/10.1371/journal.pone.0036183