Elsevier

Vaccine

Volume 35, Issue 5, 1 February 2017, Pages 789-795
Vaccine

Newcastle disease virus vectored infectious laryngotracheitis vaccines protect commercial broiler chickens in the presence of maternally derived antibodies

https://doi.org/10.1016/j.vaccine.2016.12.038Get rights and content

Abstract

Newcastle disease virus (NDV) recombinants expressing the infectious laryngotracheitis virus (ILTV) glycoproteins B and D have previously been demonstrated to confer complete clinical protection against virulent ILTV and NDV challenges in naive chickens. We extended this study to assess whether maternally derived antibody (MDA) against NDV and ILTV would interfere with protection in vaccinated broiler chickens. Chickens with a mean NDV MDA hemagglutination inhibition (HI) titer of 6.4 (log2) and detectable ILTV neutralization (VN) antibodies at hatch were vaccinated with rLS/ILTV-gB or rLS/ILTV-gD at 1 or 10 day of age (DOA) or on both days. Groups of birds vaccinated with the commercial ILT vaccines (FP-LT and CEO) or sham inoculated were also included in this study. All vaccinated birds were challenged with virulent ILTV strain at 21 DOA. By that time, NDV HI titers declined to 2.6 (log2) in unvaccinated birds, whereas the HI titers in NDV vectored vaccine groups increased to 3.5–6.3 (log2). At standard dosages, both vaccine candidates conferred significant clinical protection; however, the protection elicited by the rLS/ILTV-gD was superior to that of rLS/ILTV-gB. Recombinant rLS/ILTV-gD reduced ILTV shedding from tracheal and ocular tissues by approximately 3 log10 TCID50. Notably, there was no improvement in protection after booster vaccination at 10 DOA. Overall results indicate that the presence of maternal antibodies to NDV and ILTV did not significantly interfere with the ability of the NDV LaSota strain-vectored ILTV gB and gD vaccine candidates to elicit protective immunity against infectious laryngotracheitis.

Introduction

Infectious laryngotracheitis (ILT) is an acute upper respiratory tract disease of chickens caused by the alphaherpesvirus infectious laryngotracheitis virus (ILTV) or gallid herpesvirus type 1 (GaHV-1). Despite the extensive use of attenuated, and more recently recombinant vaccines, ILT continues to affect poultry on a worldwide basis [1]. Historically, the commonly used live ILT vaccines were first attenuated in the 1950s by either multiple passages in embryonated eggs (chicken embryo origin [CEO]) or in tissue culture (tissue culture origin [TCO]) [2], [3]. Although these vaccines protect against clinical disease, they have residual virulence, which is exacerbated by continued infections of naïve birds from productively infected animals and latent carriers [4], [5], [6]. In high-density poultry rearing facilities there is a continuous reservoir of ILT viruses, both virulent and vaccinal. It has been reported that CEO vaccinal “revertants” can become the dominant field strains in poultry populations and cause outbreaks [7], [8]. Although the recombinant vaccines, turkey herpesvirus (HVT) and fowlpox virus (FPV) expressing ILTV antigens are safe [9], [10], [11], [12], [13], [14], they only induce partial protection when compared with that induced by live-attenuated vaccines [15]. Thus, a significant need exists to revise the ILT control strategies particularly regarding the development of next generation vaccines that are safe, protective and incapable of vaccinal reversion.

Recently, we developed Newcastle disease virus (NDV) recombinants expressing the ILTV glycoproteins B and D as bivalent vaccines [16]. Vaccination of one-day-old specific pathogen free (SPF) and 3-week-old commercial boiler chickens conferred complete clinical protection against virulent ILTV and NDV challenges [16]. However, there was a general concern that the maternally derived antibodies (MDA) may interfere with the immunoresponses of the chicks to the corresponding vaccines [17], [18], [19]. It has been reported that the NDV MDA confers protection to young chicks against ND, but it can also interfere with NDV vaccine efficacy at 1 day of age (DOA) [17], [19]. This interference is dependent on the titer of maternal antibodies and the strain of the NDV vaccine administered [20], [21]. The LaSota vaccine strain has been demonstrated to overcome MDA interference better than the Hitchner, B1 or V4 strains [21]. Higher levels of circulating maternal antibodies to the LaSota strain were required to depress the immunoresponse than that required to do the same for the other three strains [21]. In contrast, maternal antibodies to ILTV do not confer protection against disease nor interfere with the immune response following vaccination [22].

To evaluate whether maternal antibodies interfere with protection induced by the LaSota strain-vectored ILTV recombinants, rLS/ILTV-gB and rLS/ILTV-gD, we carried out vaccination/challenge experiments with one-day-old commercial broiler chickens that had a mean NDV MDA HI titer of 6.4 (log2) and detectable ILTV virus neutralization (VN) antibodies. The immunoresponses following vaccination and protection indices (e.g. clinical signs, body weight gain and virus shedding after ILTV challenge) suggest significant protection against ILTV challenge even in the presence of maternally derived antibodies specific for NDV and ILTV.

Section snippets

Vaccines, viruses and cells

The generation of NDV LaSota strain-vectored ILTV vaccine candidates, rLS/ILTV-gD and rLS/ILTV-gB, were previously described [16] and propagated in 9-day-old SPF chicken embryos at passage level 3. The titers of these vaccine stocks were determined by the 50% egg infective dose (EID50) assay in 9-day-old SPF chicken embryos [23]. The commercial ILTV vaccines, Vectormune (FP-LT) and Trachivax (CEO), were purchased from Ceva Biomune (Lenexa, KS) and Merck Animal Health (Summit, NJ), respectively.

Detection of MDA and immunoresponses following vaccination

To determine the titers of NDV- and ILTV-specific maternally derived antibodies in commercial broiler chickens and immunoresponses following vaccination, serum samples collected at 1 DOA (before vaccination) and at 10 and 21 DOA (before challenge) were subjected to the HI (for NDV antibodies) and VN (for ILTV antibodies) tests. These results (Table 1) showed that unvaccinated birds at 1 DOA possessed a mean NDV HI titer of 6.4 (log2) and a mean ILTV VN titer of 0.51 (log10). The NDV HI titer

Discussion

In this study, we evaluated the protective efficacies of two NDV LaSota strain-vectored ILTV vaccine candidates rLS/ILTV-gB or rLS/ILTV-gD in commercial maternal antibody positive broiler chickens. The results showed that both bivalent vaccine candidates conferred clinical protection, maintained body-weight gains, and significantly reduced ILTV load following challenge. The data suggest that the presence of maternally derived antibodies capable of neutralizing ILTV and high titers of NDV MDA

Conflict of interest

The authors declare that they have no conflicts of interest.

Acknowledgements

The authors wish to thank Xiuqin Xia, Teresa Ross, Fenglan Li, and Sylva Riblet for excellent technical assistance. This research was supported by United States Department of Agriculture, ARS CRIS project 6040-32000-067-00D. W. Zhao and Z. Zhang were sponsored by a scholarship from China Scholarship Council, China, Y. Li was sponsored by a scholarship from Shandong Academy of Agricultural Sciences, China, J. Yang was sponsored by a scholarship from Chongqing Academy of Agricultural Sciences,

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    1

    Present address: Shandong Poultry Research Institute, Jinan 250023, China.

    2

    Present address: Chongqing Academy of Animal Sciences, Chongqing 402460, China.

    3

    Present address: Beijing Centre for Disease Control and Prevention, Beijing 100013, China.

    4

    Present address: College of Life Sciences, Northeast Agricultural University, Harbin 150030, China.

    5

    Present address: Institute of Animal Husbandry and Veterinary Sciences, Hubei Academy of Agricultural Sciences, Wuhan 430070, China.

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