Stability of viability and immunizing potency of lyophilized, modified equine arteritis live-virus vaccine.

This research investigates the stability and immunizing potency of a specially modified live-virus vaccine for equine arteritis. The findings suggest that when stored at colder temperatures, the vaccine retains its viability and ability to protect against the disease for a longer period.

Background of the Research

• The vaccine in this study is made from the Bucyrus strain of equine arteritis virus. It was modified into a non-threatening, vaccinal virus through 131 serial passages in primary cell cultures of horse kidney, and then 111 passages in primary cell cultures of rabbit kidney. A passage is a round of growing the virus in cell cultures and then transferring it to a new set of fresh cells – a process that often modifies the virus into a form that is no longer harmful.
• For this research, the researchers further passaged the virus in cultures of the E. Derm (NBL-6) cell line. This is a continuous diploid cell line – a line of cells that divide and reproduce indefinitely and retain the exact same genetic material.

Stability of the Vaccine

• Following the additional passages in the E. Derm (NBL-6) cell line, vaccines from the 16th and 25th passages were lyophilized – a method for freeze-drying. This makes the vaccine easier to store and transport.
• The dry vaccines were then stored at different temperatures: 37 C, 23 to 28 C, 4 C, and -20 C. The goal was to see how well the vaccine survived in different conditions over time.
• Results revealed that the vaccine’s viability deteriorated rapidly at higher temperatures (37 C and 23 to 28 C). However, when stored at colder temperatures (4 C and -20 C), it remained relatively stable for at least 1 year.

Efficacy of the Vaccine

• The researchers also tested the vaccine on horses to ensure it was still effective after storage. The vaccine stored at 4 C for 9 months was used to inoculate 2 horses, while two other non-vaccinated horses served as controls.
• The vaccinated horses were then exposed to the avirulent virus of equine arteritis. The two vaccinated horses were protected from the disease. However, the control horses developed severe symptoms of arteritis and died from acute arteritis.
• This result indicates that the vaccine, when stored properly at low temperatures, not only retains its viability but also continues to provide a strong immune response against equine arteritis.