A phosphonoacetate-resistant mutant of herpesvirus of turkeys

Area of Science:

• Virology
• Molecular Biology
• Immunology

Background:

• Herpesvirus of turkeys (HVT) is a gallid herpesvirus type 1.
• Marek's disease virus (MDV) causes significant economic losses in the poultry industry.
• Antiviral agents are crucial for controlling viral infections in poultry.

Purpose of the Study:

• To isolate and characterize a phosphonoacetate (PA)-resistant mutant of HVT (HVTpa).
• To evaluate the biological and biochemical properties of HVTpa.
• To assess the potential of HVTpa as a vaccine candidate against MDV.

Main Methods:

• Isolation and characterization of PA-resistant HVT mutant in duck embryo fibroblast (DEF) culture.
• Plaque morphology, antigenic analysis, and in vitro temperature sensitivity assays.
• Replication studies in chickens and challenge experiments with MDV.
• Biochemical analysis of HVTpa-induced DNA polymerase activity and kinetics.

Main Results:

• HVTpa replicated in DEF culture with 300 µg/ml PA, while wild-type HVT (HVTwt) replication was inhibited at 100 µg/ml.
• HVTpa exhibited distinct plaque morphology but was antigenically similar to HVTwt.
• HVTpa showed in vitro temperature sensitivity at 41°C and poor replication in chickens.
• HVTpa failed to provide complete protection against MDV challenge.
• HVTpa-induced DNA polymerase showed altered kinetic constants for PA, pyrophosphate, and dCTP, and increased thermolability compared to HVTwt.

Conclusions:

• A PA-resistant HVT mutant (HVTpa) was successfully isolated and characterized.
• HVTpa possesses altered biological and biochemical properties, including reduced virulence and immunogenicity.
• HVTpa is not a suitable candidate for protecting chickens against MDV due to its poor efficacy.