Short‐ and long‐term stability studies on four lyophilised and one cell‐associated turkey herpesvirus vaccines against marek's disease of chickens1

Abstract

One cell-associated and four lyophilised turkey herpesvirus (HVT) vaccines of different manufacturers were investigated comparatively in respect of the stability of their infectivity. All titrations were performed in primary chicken embryo fibroblast cell cultures and repeated seven times. The obtained data were computerised and statistically analysed. The long term stability study employed vaccine ampoules containing only lyophilised HVT. After appropriate storage in a refrigerator (4 degrees C) of all tested vaccine ampoules for 1 year no drop of titre was found. In contrast, storage at room temperature (24 degrees C) resulted in a loss of about 50% of the infectious units of HVT by 4 months. Marked differences between the products of different manufacturers were noted after 4 weeks of storage at 37 degrees or 45 degrees C. The infectivity dropped to values between 1/10 to 1/100 and 1/100 to 1/300, respectively. In the short term stability study cell-associated and lyophilised vaccine virus was resuspended in the manufacturer's diluent and maintained at temperatures of 4 degrees , 24 degrees , 37 degrees and 45 degrees C. The infectious units were titrated at 0, 2, 4, 6, 8 and 24 hours for estimation of the half life of the infectivity of HVT. The half life of infectivity of HVT at 4 degrees C was for three vaccines approximately 5 hours and for two vaccines between 1 and 3 hours. With increase of temperature the loss of infectivity increased resulting in half life times close to 1 hour at 45 degrees C.