Venezuelan equine encephalomyelitis virus: concentration, partial purification, inactivation and immunogenicity.

This study outlines the isolation and partial purification of Venezuelan equine encephalomyelitis (VEE) vaccinal virus, which was then inactivated with formalin but retained its ability to stimulate an immune response in horses and guinea pigs, protecting them from a subsequent exposure to the virulent VEE virus.

Methodology

• The researchers used large volumes of infected duck embryo fibroblast cell culture fluids, from which the Venezuelan equine encephalomyelitis (VEE) TC-84 vaccinal virus was isolated.
• The isolation was achieved through combined continuous-flow centrifugation with isopycnic banding in sucrose, a common technique in virology to separate and concentrate viruses.
• In this process, the team found that most of the recovered infectivity and hemagglutinating (the ability to cause red blood cells to clump together) activity were in a single band at a buoyant density (rho) of 1.2.
• Additionally, about 90% of the total input protein (450-520 mg) was removed with the effluent (liquid waste or sewage), whereas the majority of the remaining 10% also banded at a rho of 1.2.

Inactivation and Immunity

• The isolated VEE virus underwent inactivation with 0.05% of formalin at 37 degrees Celsius for 24 hours. Formalin, a solution of formaldehyde in water, is commonly used in virus inactivation.
• Even after inactivation, the virus retained its immunogenicity, or capability to trigger an immune response. The inactivated virus has been able to stimulate the production of VEE virus-specific antibodies in horses and guinea pigs.

Immunity Challenge

• The horses and guinea pigs that were previously immunized with the inactivated VEE virus were then subjected to a challenge to their immunity with the potent, or virulent, VEE virus.
• The animals that received equivalent doses of the vaccine were able to survive after this challenge, highlighting the efficacy of the inactivated vaccine against a live VEE virus invasion.