Abstract
Vaccination against Newcastle disease (ND), a devastating viral disease of chickens, is often hampered by thermal inactivation of the live vaccines, in particular in tropical and hot climate conditions. In the past, “thermostable” vaccine strains (I-2) were proposed to overcome this problem but previous comparative studies did not include formulation-specific factors of commercial vaccines. In the current study, we aimed to verify the superior thermal stability of commercially formulated I-2 strains by comparing six commercially available ND vaccines. Subjected to 37 °C as lyophilized preparations, two vaccines containing I-2 strains were more sensitive to inactivation than a third I-2 vaccine or compared to three other vaccines based on different ND strains. However, reconstitution strains proved to have a comparable tenacity. Interestingly, all vaccines still retained a sufficient virus dose for protection (106 EID50) after 1 day at 37 °C. These results suggest that there are specific factors that influence thermal stability beyond the strain-specific characteristics. Exposing ND vaccines to elevated temperatures of 51 and 61 °C demonstrated that inactivation of all dissolved vaccines including I-2 vaccine strains occurred within 2 to 4 h. The results revealed important differences among the vaccines and emphasize the importance of the quality of a certain vaccine preparation rather than the strain it contains. These data highlight that regardless of the ND strain used for vaccine preparation, the appropriate cold chain is mandatory for keeping live ND vaccines efficiency in hot climates.
Highlights
Newcastle disease (ND) is one of the most devastating endemic viral diseases of poultry in many countries worldwide [1,2]
Investigation of vaccines stored at 4 ◦ C over a period of 21 days resulted in virus titers well above 106 Egg infectious dose 50 (EID50) per dose at any time (Figure 1A)
Virus titers measured by cell culture were lower, but clearly support the notion of stability of lyophilized ND vaccines at 4 ◦ C (Figure 1B)
Summary
Newcastle disease (ND) is one of the most devastating endemic viral diseases of poultry in many countries worldwide [1,2]. The disease is caused by avian orthoavulavirus 1(AOAV-1, ND virus (NDV)) within the subfamily. Depending on the virulence of the ND virus (NDV), infections can cause a wide spectrum of clinical signs ranging from asymptomatic (apathogenic, lentogenic pathotype) or mild clinical respiratory signs or a drop of egg production (mesogenic pathotype) to up to 100% mortality (velogenic pathotype) [7]. The subsequent development of the vaccine strains La Sota and B1 with derivatives such asclone are the basis for most ND vaccines. Some strains of NDV isolated in Australia between 1967 and 1978 were found to be avirulent [10], and the V4 strain, which was claimed to have enhanced thermostability, was used to develop live ND vaccines with the
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