Abstract
Avian metapneumovirus (aMPV) and Newcastle disease virus (NDV) are threatening avian pathogens that can cause serious respiratory diseases in poultry worldwide. Vaccination, combined with strict biosecurity practices, has been the recommendation for controlling these diseases in the field. In the present study, we generated NDV LaSota vaccine strain-based recombinant viruses expressing the glycoprotein (G) of aMPV, subtype A or B, using reverse genetics technology. These recombinant viruses, rLS/aMPV-A G and rLS/aMPV-B G, were characterized in cell cultures and evaluated in turkeys as bivalent, next-generation vaccines. The results showed that these recombinant vaccine candi-dates were slightly attenuated in vivo, yet maintained similar growth dynamics, cytopathic effects, and virus titers in vitro when compared to the parental LaSota virus. The expression of the aMPV G protein in recombinant virus-infected cells was detected by immunofluorescence. Vaccination of turkeys with rLS/aMPV-A G or rLS/aMPV-B G conferred complete protection against velogenic NDV, CA02 strain challenge and partial protection against homologous patho-genic aMPV challenge. These results suggest that the LaSota recombinant virus is a safe and effective vaccine vector and expression of the G protein alone is not sufficient to provide full protection against aMPV-A or -B infections. Ex-pression of other aMPV-A or -B virus immunogenic protein(s) individually or in conjunction with the G protein may be necessary to induce stronger and more protective immunity against aMPV diseases.
Highlights
Avian metapneumovirus is the causative agent for turkey rhinotracheitis (TRT) and is associated with “swollen head syndrome (SHS)” in chickens, resulting in substantial economic losses to the poultry industry worldwide [1,2]
The G deletion or truncation mutants of Avian metapneumovirus (aMPV) were viable in cell cultures, but attenuated in SPF turkeys and induced a weaker immune response than the wild-type virus [29,37], implying that the G protein may play a role in immunogenicity to the natural host
We selected the G protein to be expressed by the recombinant Newcastle disease virus (NDV) vector to investigate the role of the G protein in inducing protective immunity against aMPV challenge, as well as the protective efficacy conferred by the NDV vector against an NDV challenge in turkeys
Summary
Avian metapneumovirus (aMPV) is the causative agent for turkey rhinotracheitis (TRT) and is associated with “swollen head syndrome (SHS)” in chickens, resulting in substantial economic losses to the poultry industry worldwide [1,2]. Ture-attenuated or inactivated vaccines are currently being used to control the diseases caused by the subtypes A and B of aMPV [6,7,8]. These live, attenuated vaccines have been approved and appear to be effective in most countries where the disease is prevalent, several reports have suggested that the stability and safety of some of these live vaccines are of concern [9,10,11,12]. In Italy [12] and Brazil [13], field evidence has suggested that the existing vaccines may not fully protect against the circulating field strains of aMPV in these countries.
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