Infectious d iseases present one of the main threats to the expansion and productivity of the shrimp industry. In recent years, Enterocytozoon hepatopenaei (EHP), a microsporidian pathogen, and White Feces Syndrome (WFD), an emergent disease of unknown etiology, have caused severe losses for producers in Asia and Ame rica. Although the exact cause of WFD is still unknown, the disease has been reproduced by co-infection of P vannamei with EHP followed by vibrio parahemolyticus or vibrio algynolyticus. This approach mimics what happens in commercial ponds, where the animals first show the presence of EHP, and later, during the grow-out cycle, they develop the white discoloration of the gastrointestinal (GI) tract, and floating white fecal strings characteristic of WFD appear in the pond.
As management of EHP and WFD has proved difficult, selection for resistance to the diseases could be a useful tool, and the use of genomic selection can increase the accuracy of selection, accelerating genetic gain. This study aimed to quantify and characterize the genetic variation in resistance to EHP and WFD in P vannamei juveniles. A challenge test was developed at Dr Loc’s Tran laboratory in Vietnam, combining cohabitation with EHP-infected animals followed by infection with a vibrio algynolyticus strain. This challenge model was initially tested on different lines derived from the Benchmark Genetics Colombia breeding program in 2022 showing significant differences in the survival curves of the lines . In 2023, full siblings of the families from the breeding nucleus were also challenged with EHP+WFD . Animals from all families were challenged at an average weight of 0.6g with both pathogens and followed up for 40 days after infection. The dead animals during the test and all harvested survivors were tissue sampled and genotyped with a ~40K SNP array . Family assignment was performed using the genotype data, and t he final survival of the families in the challenge test ranged from 0 to 77% with an average of 32% , based on animals successfully genotyped and with assigned parents. Final survival in the co-infection of EHP and WFD had a moderate and highly significant heritability of 0.41± 0.003.
Furthermore, a low positive genetic correlation between body weight in the growth test in Colombia and survival of the families in the EHP +WFD combined challenge test was observed , implying that genetic improvement of resistance to EHP can be achieved without compromising on growth performance. Additionally , cross- validation analysis showed 0.81 ± 0.003 accuracy of genomic prediction, indicating the major potential of a genomic selection strategy for achieving genetic improvement for resistance to EHP + WFD in P vannamei .