Optimizing protocols for monitoring replication of a novel chimeric Marek's disease vaccine with an insertion of the long terminal repeat of reticuloendotheliosis virus in the CVI988 strain genome (CVI-LTR).

Monitoring Marek's disease (MD) vaccination is routinely done by evaluating the load of MD vaccine in the feather pulp (FP) between 7 and 10 days of age. However, attempts in our laboratory to detect a novel CVI-LTR vaccine in the FP samples from commercial flocks failed. The objective of this study was to evaluate the most suitable tissue and age to monitor CVI-LTR vaccination.

Evaluation of Adjuvant Effect of Cytosine-Guanosine-Oligodeoxynucleotide in Meat-Type Chickens Coadministered with Herpesvirus of Turkey Vaccine.

Herpesvirus of turkey (HVT) increases activation of T cells in 1-day-old chickens when administered . This study evaluated whether adding cytosine-guanosine oligodeoxynucleotides (CpG ODNs) to the HVT vaccine could enhance the adjuvant effect of HVT. We used a CpG ODN dose of 10 g per egg.

In ovo HVT vaccination enhances cellular responses at hatch and addition of poly I:C offers minimal adjuvant effects.

In ovo vaccination with herpesvirus of turkey (HVT) hastens immunocompetence in chickens and the recommended dose (RD) of 6080 plaque-forming-units (PFU) offers the most optimal effects. In previous studies conducted in egg-type chickens, in ovo vaccination with HVT enhanced lymphoproliferation, wing-web thickness with phytohemagglutinin-L (PHA-L), and increased spleen and lung interferon-gamma(IFN-γ) andToll-like receptor 3 (TLR3) transcripts. Here, we evaluated the cellular mechanisms by which HVT-RD can hasten immunocompetence in one-day-old meat-type chickens, and also determined if HVT adjuvantation with a TLR3 agonist, polyinosinic-polycytidylic acid (poly(I:C)), could enhance vaccine-induced responses and provide dose-sparing effects.

Effect of CpG-Oligonucleotide in Enhancing Recombinant Herpes Virus of Turkey-Laryngotracheitis Vaccine-Induced Immune Responses in One-Day-Old Broiler Chickens.

Infectious laryngotracheitis (ILT) is an economically important disease of chickens. While the recombinant vaccines can reduce clinical disease severity, the associated drawbacks are poor immunogenicity and delayed onset of immunity. Here, we used CpG-oligonucleotides (ODN) as an adjuvant in boosting recombinant herpesvirus of turkey-laryngotracheitis (rHVT-LT) vaccine-induced responses in one-day-old broiler chickens.

Cytokine expression in the eye and brain of chickens following infection with a very virulent plus Marek's disease virus strain.

Cytokine transcripts were evaluated chronologically in the brain and in the eye of chickens infected with the very virulent plus Marek's disease virus (vv + MDV) strain 648A. Brain and eye samples were collected from chickens that were either suffering from transient paralysis (TP) (11 days post inoculation, dpi) or had completely recovered from TP but started developing clinical signs of persistent neurological disease (PND) (18-31 dpi). Results obtained from samples collected at 11 dpi are referred as EL (early lesions) and results obtained from samples collected at later times (18-31 dpi) are referred as LL (late lesions).

In ovo vaccination with herpesvirus of turkey enhances innate and cellular responses in meat-type chickens: Effect of vaccine dose and strain.

In ovo vaccination with herpesvirus of turkey (HVT) or recombinant HVT (rHVT) is commonly used in meat-type chickens. Previous studies showed that in ovo vaccination with HVT enhances innate, cellular, and humoral immune responses in egg-type chicken embryos. This study evaluated if in ovo vaccination with HVT hastens immunocompetence of commercial meat-type chickens and optimized vaccination variables (dose and strain of HVT) to accelerate immunocompetence.

Effect of Marek's disease vaccines on interferon and toll like receptors when administered in ovo.

The effect of two Marek's disease (MD) vaccines on the chicken embryo immune responses were evaluated. Transcription of interferon (IFN-α, IFN-β, IFN-λ, and IFN-γ) and interferon-I receptors (IFN-AR1 and IFN-AR2), as well as transcription of toll like receptors (TLR-3, TLR-7, and TLR-21) were evaluated in the bursa, thymus, spleen and lung of 1-day-old chickens that had been vaccinated with HVT, CVI988, or sham inoculated at embryonic day 18 (ED18). Each vaccine had a unique effect on the transcription of the evaluated genes and it differs among tissues.

Differential attenuation of Marek's disease virus-induced tumours and late-Marek's disease virus-induced immunosuppression.

Marek's disease virus (MDV) is a herpesvirus that induces lymphoma and a variety of non-neoplastic syndromes in chickens. Furthermore, very virulent plus (vv+) MDVs induce a form of immunosuppression (late-MDV-IS) that might involve both neoplastic and non-neoplastic mechanisms. The objective of this study was to evaluate whether the attenuation of MDV-induced tumours and late-MDV-IS occurs simultaneously or can be dissociated.

Use of real-time PCR to rule out Marek's disease in the diagnosis of peripheral neuropathy.

This article reports nine cases of neurological disease in brown layer pullets that occured in various European countries between 2015 and 2018. In all cases, the onset of neurological clinical signs was at 4-8 weeks of age and they lasted up to 22 weeks of age. Enlargement of peripheral nerves was the main lesion observed in all cases.

Evaluation of factors influencing the development of late Marek's disease virus-induced immunosuppression: virus pathotype and host sex.

Marek's disease virus (MDV) is a herpesvirus that induces lymphoma and immunosuppression in chickens. MDV-induced immunosuppression (MDV-IS) is complex and can be divided into two phases: early-MDV-IS associated with cytolytic infection in the lymphoid organs in chickens lacking maternal antibodies against MDV (MAbs) and late-MDV-IS that appears later in the pathogenesis and occurs even in chickens bearing MAbs. We have recently developed a model to reproduce late-MDV-IS under laboratory conditions.

Early infection with Marek's disease virus can jeopardize protection conferred by laryngotracheitis vaccines: a method to study MDV-induced immunosuppression.

Marek's disease virus (MDV) is a herpesvirus that induces lymphomas and immunosuppression in chickens. MDV-induced immunosuppression (MDV-IS) is divided into two phases: early-MDV-IS occurring mainly in chickens lacking maternal antibodies (MAb) against MDV and associated with lymphoid organ atrophy; and late-MDV-IS occurring once MDV enters latency and during tumour development. Our objectives were to document the impact of late-MDV-IS on commercial poultry (meat-type chickens bearing MAb against MDV and that were vaccinated or unvaccinated against MD) and to optimize a model to study late-MDV-IS under laboratory conditions.

Efficacy of various Marek's disease vaccines protocols for prevention of Marek's disease virus-induced immunosuppression.

Marek's disease virus (MDV) induces tumors and severe immunosuppression in chickens. MDV-induced immunosuppression (MDV-IS) is very complex and difficult to study. In particular, the late MDV-IS (late-MDV-IS) is of great concern since it can occur in the absence of lymphoid organ atrophy or gross tumors.

Evaluation of Factors Influencing Efficacy of Vaccine Strain CVI988 Against Marek's Disease in Meat-Type Chickens.

Marek's disease (MD) strain CVI988 is the most-protective commercially available vaccine against very virulent plus (vv+) Marek's disease virus (MDV). However, its use in meat-type chickens has been controversial. While several countries have been using CVI988 for more than 40 yr, others do not authorize its use or it is restricted mainly to layers.

In Ovo Vaccination with Turkey Herpesvirus Hastens Maturation of Chicken Embryo Immune Responses in Specific-Pathogen-Free Chickens.

Administration of Marek's disease (MD) vaccines in ovo has become a common practice for the poultry industry. Efficacy of MD vaccines is very high, even though they are administered to chicken embryos that are immunologically immature. We have recently demonstrated that in ovo vaccination with turkey herpesvirus (HVT) results in increased activation of T cells at hatch.

Evaluation of the Protection Efficacy of a Serotype 1 Marek's Disease Virus-Vectored Bivalent Vaccine Against Infectious Laryngotracheitis and Marek's Disease.

Laryngotracheitis (LT) is a highly contagious respiratory disease of chickens that produces significant economic losses to the poultry industry. Traditionally, LT has been controlled by administration of modified live vaccines. In recent years, the use of recombinant DNA-derived vaccines using turkey herpesvirus (HVT) and fowlpox virus has expanded, as they protect not only against the vector used but also against LT.

Detection and differentiation of CVI988 (Rispens vaccine) from other serotype 1 Marek's disease viruses.

The serotype 1 Marek's disease virus (MDV) is the causative agent for Marek's disease (MD), a lymphoproliferative disease of chickens of great concern to the poultry industry. CVI988 (Rispens vaccine), an attenuated serotype 1 MDV, is currently the most efficacious commercially available vaccine for preventing MD. However, it is difficult to detect and differentiate CVI988 when other serotype 1 MDVs are present.

Optimization of the protocols for double vaccination against Marek's disease by using commercially available vaccines: evaluation of protection, vaccine replication, and activation of T cells.

Revaccination against Marek's disease is a widespread practice in some countries. The rationale of this practice is unknown, and there is no consensus in the protocols. Recently, we have demonstrated that administration of the first vaccine at 18 days of embryonation followed by a more protective second vaccine at hatch (18ED/1d) reproduced systematically the benefits of revaccination under laboratory conditions.

Standardization of a model to study revaccination against Marek's disease under laboratory conditions.

Revaccination, the practice of administering Marek's disease (MD) vaccine a second time, has been used in commercial poultry flocks for many years. The rationale is largely anecdotal as the few published reports have failed to provide support for the value of the practice. In the present work, we have standardized a model to study MD revaccination under laboratory conditions.

Replication ability of three highly protective Marek's disease vaccines: implications in lymphoid organ atrophy and protection.

The present work is a chronological study of the pathogenesis of three attenuated serotype 1 Marek's disease (MD) virus strains (RM1, CVI988 and 648A80) that provide high protection against MD but have been attenuated by different procedures and induce different degrees of lymphoid organ atrophy. All studied strains replicated in the lymphoid organs (bursa,x thymus and spleen) and a peak of replication was detected at 6 days post inoculation (d.p.

Replication of recombinant herpesvirus of turkey expressing genes of infectious laryngotracheitis virus in specific pathogen free and broiler chickens following in ovo and subcutaneous vaccination.

Replication of a recombinant herpesvirus of turkey vaccine expressing infectious laryngotracheitis virus genes (rHVT-LT) was evaluated in specific pathogen free (SPF) and commercial broiler chickens after various vaccination protocols (amniotic route at embryonation day [ED] 18; intra-embryonic route at ED 19; and subcutaneous at 1 day of age [s.c.]).

Comparison of blood and feather pulp samples for the diagnosis of Marek's disease and for monitoring Marek's disease vaccination by real time-PCR.

Comparison of blood and feather pulp (FP) samples for the diagnosis of Marek's disease (MD) and for monitoring Marek's diseases vaccination in chickens (serotypes 2 and 3 vaccines) by real time-PCR was evaluated. For diagnosis of MD, quantification of serotype 1 Marek's disease virus (MDV) DNA load was evaluated in 21 chickens suffering from MD. For each chicken, samples of blood and FP were collected and MDV DNA load was quantified.

Effect of diluting Marek's disease vaccines on the outcomes of Marek's disease virus infection when challenged with highly virulent Marek's disease viruses.

Dilution of Marek's disease (MD) vaccines is a common practice in the field to reduce the cost associated with vaccination. In this study we have evaluated the effect of diluting MD vaccines on the protection against MD, vaccine and challenge MD virus (MDV) kinetics, and body weight when challenged with strains Md5 (very virulent MDV) and 648A (very virulent plus MDV) by contact at day of age. The following four vaccination protocols were evaluated in meat-type chickens: turkey herpesvirus (HVT) at manufacturer-recommended full dose; HVT diluted 1:10; HVT + SB-1 at the manufacturer-recommended full dose; and HVT + SB-1 diluted 1:10 for HVT and 1:5 for SB-1.

Chronological study of cytokine transcription in the spleen and lung of chickens after vaccination with serotype 1 Marek's disease vaccines.

Transcription of cytokine genes was evaluated in the lung and spleen of chickens vaccinated with various serotype 1 Marek's disease (MD) vaccines. Three vaccine pairs/series, each consisting of one or two high protective (HP) and one low protective (LP) vaccine, were used. Vaccinated chickens had increased transcripts of IFN-γ in the lung and spleen at 3, 5, and 10 days post vaccination (dpv) compared to unvaccinated control chickens.

Evaluation of factors influencing replication of serotype 1 Marek's disease vaccines in the chicken lung.

Factors influencing replication of serotype 1 Marek's disease vaccines in the lung of chickens within the first 10 days of age (doa) were evaluated. In particular, the effect of vaccine efficacy, age/route of vaccination, and vaccine dose were examined in three experiments. In the first experiment, three vaccine pairs, each pair consisting of a high protective (HP) and a low protective (LP) vaccine (CVI988/BP5 and CVI988-Clone C, 648A80 and 648A100, R2 and R2/23) were used to inoculate chickens subcutaneously (s.

Validation of Marek's disease diagnosis and monitoring of Marek's disease vaccines from samples collected in FTA cards.

The use of Flinders Technology Associates (FTA) filter cards to quantify Marek's disease virus (MDV) DNA for the diagnosis of Marek's disease (MD) and to monitor MD vaccines was evaluated. Samples of blood (43), solid tumors (14), and feather pulp (FP; 36) collected fresh and in FTA cards were analyzed. MDV DNA load was quantified by real-time PCR.