VP28, encoded by open reading frame (ORF) 421 (wsv421), is the major envelope protein and several studies suggest that VP28 may play a crucial role in the initial steps of systemic WSSV infection in shrimp. Furthermore, there is evidence that WSSV VP28 plays an important role in the infection process as an attachment protein, binding the virus to shrimp cells, and helping it to enter into the cytoplasm.