Quantitative real-time PCR reveals viral interference between white spot syndrome virus (WSSV) and infectious myonecrosis virus (IMNV) in Penaeus vannamei

The phenomenon of viral interference during co-infections has already been reported for several aquatic species. Understanding the relationship established between different viruses and the host's immune system is necessary to understand the forms of progression and/or remediation of a disease. In the present study, we investigated viral interference in healthy shrimp naturally co-infected by the two main viruses that affect Brazilian shrimp farming, IMNV and WSSV. Through quantitative real-time PCR we have observed a reduction in IMNV viral load after overexposure to WSSV, reaching the lowest point four days post infection (dpi). That trend was similar among all tissues analyzed (gills, muscle, intestine, pleopods, hepatopancreas and hemolymph). At 13 dpi, viral loads reset to baseline levels of natural co-infection. We hypothesize that WSSV and IMNV compete for cellular receptors to promote the initiation of infection. Viral competition would explain the lower load of IMNV after challenge with WSSV, which was evident from the viral load results obtained by qPCR. The re-establishment of viral loads at 13 dpi is likely due to the shrimp's immune responses mainly to WSSV, reaching what appears to be a double viral accommodation point for these shrimp.