Title: Effects of Newcastle disease virus vaccine antibodies on the shedding and transmission of challenge viruses Authors
|El Attrache, John -|
|Dorsey, Kristi -|
|Guo, Zijing -|
Submitted to: Developmental and Comparative Immunology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 16, 2013
Publication Date: June 21, 2013
Citation: Miller, P.J., Afonso, C.L., El Attrache, J., Dorsey, K.M., Courtney, S.C., Guo, Z., Kapczynski, D.R. 2013. Effects of Newcastle disease virus vaccine antibodies on the shedding and transmission of challenge viruses. Developmental and Comparative Immunology. DOI:S0145-305X(13)00170-5. 10.1016/j.dci.2013.06.007. Interpretive Summary: Newcastle disease virus (NDV) vaccines commercially available are usually made with NDV strains that are no longer found in most areas of the world and are not genetically very similar to the NDV strain circulating today that cause outbreaks. However, if given correctly these vaccines can prevent birds from dying or getting sick with Newcastle disease. These vaccines cannot prevent vaccinated birds from becoming infected with NDV that cause outbreaks and subsequently shedding that virus in their saliva and feces. We demonstrate that by making the NDV in the vaccine more genetically similar to the challenge strain that circulates in the environment, that we can decrease the amount of virus shed in saliva and feces. This decrease of NDV in the environment helps prevent other birds from being infected. The amount of NDV shed is related to not just how genetically similar the vaccine and challenge virus are to each other, but also to the amount of time the bird has to develop antibodies to the challenge virus. Birds that have more time between vaccination and getting infected develop higher levels of humoral antibodies and shed less virus after infection compared to birds infected soon after vaccination.
Technical Abstract: Different genotypes of avian paramyxovirus serotype-1 virus (APMV-1) circulate in many parts of the world. Traditionally, Newcastle disease virus (NDV) is recognized as having two major divisions represented by class I and class II, with class II being further divided into sixteen genotypes. Although all NDV are members of APMV-1 and are of one serotype, antigenic and genetic diversity is observed between the different genotypes. Reports of vaccine failure from many countries and reports by our lab on the inability of classical vaccines to significantly decrease viral replication and shedding have created renewed interest in developing vaccines formulated with genotypes homologous to the virulent NDV (vNDV) circulating in the field. We assessed how the amount and specificity of humoral antibodies induced by inactivated vaccines affected viral replication, clinical protection and evaluated how non-homologous antibody levels induced by live NDV vaccines relate to transmission of vNDV. In an experimental setting, all inactivated NDV vaccines protected birds from morbidity and mortality, but higher and more specific levels of antibodies were required to significantly decrease viral replication. It was possible to significantly decrease viral replication and shedding with high levels of antibodies, and those levels could be more easily reached with vaccines formulated with NDV of the same genotype as the challenge viruses. However, when the levels of heterologous antibodies were sufficiently high, it was possible to prevent transmission. As the level of humoral antibodies increase in vaccinated birds, the number of infected birds and the amount of vNDV shed decreased. Thus, in an experimental setting the effective levels of humoral antibodies could be increased by 1) increasing the homology of the vaccine to the challenge virus or 2) allowing optimal time for the development of the immune response.