Mixed-genotype white spot syndrome virus infections of shrimp are inversely correlated with disease outbreaks in ponds

Abstract

Outbreaks of white spot syndrome virus (WSSV) in shrimp culture and the relationship between the virus and virulence are not well understood. Here, we provide evidence showing that WSSV mixed-genotype infections correlate with lower outbreak incidence and that disease outbreaks correlate with single-genotype infections. We tested 573 shrimp samples from 81 shrimp ponds in the Mekong delta with outbreak or non-outbreak status. The variable number tandem repeat (VNTR) loci of WSSV were used as molecular markers for the characterization of single-and mixed-genotype infections. The overall prevalence of mixed-genotype WSSV infections was 25.7 %. Non-outbreak ponds had a significantly higher frequency of mixed-genotype infections than outbreak ponds for all VNTR loci, both at the individual shrimp as well as at the pond level. The genetic composition of WSSV populations appears to correlate with the health status of shrimp culture in ponds. The causal relationship between genotypic diversity and disease outbreaks can now be experimentally approached.

Genetic variations among white spot syndrome virus (WSSV) isolates from shrimp farms in Gujarat, north-west coast of India

“…Similar to previous observations, mixed infection with two RU types, 4 and 11 was noticed in the present study (Hoa et al, 2005(Hoa et al, , 2011(Hoa et al, , 2012Musthaq et al, 2006;Pradeep et al, 2008). In contrast to the earlier observation which correlated mixed infection with lower virulence (Hoa et al, 2012), in this case the farm with mixed WSSV infection had suffered the similar severity as that of single genotype infection.…”

White spot syndrome virus (WSSV) genome stability maintained over six passages through three different penaeid shrimp species

“…Factors responsible for virulence are difficult to conclude from confounding reports of difficulties in correlating specific genotypes to shrimp mortality (John et al (Walker et al 2011a,b) or the presence of mixed WSSV genotypes being related inversely to shrimp mortality at farms (Hoa et al 2011). In another study examining WSSV strains from the same geographic region, a WSSV strain containing a 19 kb genome deletion was found to be more virulent, possibly as a result of the smaller genome providing the strain with some advantage in replication (Marks et al 2005).…”

“…1B−E, Table 1). ORF94 and ORF125 VNTR types have been used widely to distinguish WSSV strains (Wongteerasupaya et al 2003, Hoa et al 2005, 2011, and many WSSV strains have been associated with disease at shrimp farms in India (Syed Musthaq et al 2006, Pradeep et al 2008, John et al 2010, Walker et al 2011a. The VNTR variations detected were thus not unexpected considering the different species examined and the fact that the diseased shrimp had been sourced from different farms in different regions of South India.…”

“…While it has been re ported that a single passage of various WSSV strains in a different crustacean host can promote a shift in VNTR type (Waikhom et al 2006), a very recent study found the ORF94 VNTR to be unaltered following several serial passages through 3 diverse crustacean host species (Gudkovs et al 2014). As stable VNTR types have been identified among susceptible crustaceans sampled from aquaculture ponds containing WSSVinfected shrimp (Hoa et al 2011), it appears likely that the rapid shifts in VNTR type reported by Waikhom et al (2006) were due to host selection of a WSSV genetic variant present in low levels and not de tected in the parental tissue used for challenge, or to the detection of a WSSV type pre-existing at low levels and/or prevalence in the less-susceptible host species challenged. Thus, to examine more closely what potential impacts host and passage number might impart upon VNTR stability, and to reaffirm how VNTR marker data can be interpreted in epidemiological studies, 2 WSSV strains with different VNTR genotypes were passaged sequentially through 3 different penaeid shrimp species.…”

Genotyping WSSV isolates from northwestern Mexican shrimp farms affected by white spot disease outbreaks in 2010-2012

“…Nevertheless, if we consider the diversity for the entire study area and over the 3 years analyzed, the conclusion is that this molecular marker has high variability (0.902), which again means either a high rate of mutation of the viral genome in this region, or the constant introduction or mobility of new WSSV varieties ( Guasave Sur 7-2 and 10-10 Angostura 11-9 and 13-3 Elota 7-7 and 9-10 Elota 7-7 and 10-5 As in other works that have reported double infections with isolates of WSSV and different sizes of the ORF 94 region (Wongteerasupaya et al 2003, Pradeep et al 2008, we found 2 cases, indicating a frequency of only 1.9% during the study period (Table 8). Some research groups have sought to associate this finding with virulence, but results are contradictory (Hoa et al 2011, Walker et al 2011, so its biological role is still unknown. A haplotype lacking the ORF 94 region has been described for Saudi Arabia (Tang et al 2012).…”