The key gene mutation of the novel Varicellovirus suidalpha1 variant strain DML-5 may alter its nerve conduction and virulence.

Varicellovirus suidalpha1 has brought huge economic losses to the global pig industry. However, existing vaccines do not provide sufficient protection against circulating strains. In this study, the molecular characteristics of Varicellovirus suidalpha1 isolates were tracked to provide a basis for the prevention and treatment of Varicellovirus suidalpha1. In this study, samples were collected from a pig farm suspected of Varicellovirus suidalpha1 infection in China, and a Varicellovirus suidalpha1 strain DML-5 was successfully isolated. Phylogenetic analysis showed that DML-5 belonged to genotype II variant strain, which was genetically distinct from the known genotype I classic strain. Unique amino acid mutations was identified for the first time at the highly conserved gL, UL6, UL21, UL26.5, and gE. Including gE and UL21, which are involved in axon transport, these mutations may affect the nerve conduction and virulence of Varicellovirus suidalpha1. By constructing three-dimensional protein models, it was found that the unique amino acid mutations of UL6 and UL21 caused the tertiary structure changes of the corresponding proteins. In addition, the amino acid sequences of gL, UL6, UL21, UL26.5 and gE proteins of Varicellovirus suidalpha1 were found to be conserved among different groups, which is the basis of Varicellovirus suidalpha1 group identification. Possible recombination events were detected in DML-5 by gene recombination prediction, which indicated that DML-5 may be a recombinant strain of Ea and PRV-GD. Varicellovirus suidalpha1 are becoming more complex, so enhanced surveillance of Varicellovirus suidalpha1, as well as improved mutant vaccines, are necessary.