Newcastle disease virus-attenuated vaccine LaSota played a key role in the pathogenicity of contaminated exogenous virus

Fowl Adenovirus Infection – Potential Cause of a Suppressed Humoral Immune Response of Broilers to Newcastle Disease Vaccination

Fowl adenovirus infections have a significant economic impact, especially in the production of broilers. It is considered the leading cause of three syndromes: adenoviral gizzard erosions and ulcerations, inclusion body hepatitis, and hepatitis-hydropericardium syndrome. A critical feature of this virus is its immunosuppressive effect, via suppressing humoral and cellular immunity.

In this study, we examined the humoral immune response after administration of the Newcastle disease vaccine in broiler flocks with previously confirmed seroconversion against Fowl adenovirus. The study was conducted on 5 farms. A total of 220 chickens, five weeks of age, showing no clinical signs of the disease, were included in this study. The control group consisted of 20 chickens from a negative farm. Chickens were vaccinated with commercially available live NDV vaccines between 11 and 13 days of life. ELISA determined the presence of specific antibodies against FAdV in a total of 130/200 (65%) blood sera. Depending on the farm, seroprevalence ranged from 30-100%. The presence of specific antibodies against NDV was determined three weeks after vaccination using the hemagglutination inhibition assay. A positive hemagglutination inhibition (HI) titer (≥ 16) was found in 41/200 (20.5%) sera, which was significantly less compared to the control farm, where a positive HI titer was found in 20/20 (100%) sera.

The results of our study indicate the immunosuppressive effect of FAdV in subclinically infected birds and highlight the need for its diagnosis, prevention, and control.

Genomic Characteristics of a Chicken Infectious Anemia Virus in Contaminated Attenuated Vaccine

Chicken infectious anemia virus (CIAV) can be transmitted by contaminated live vaccines, and causes huge economic losses. This study evaluated the contamination status of CIAV in 24 batches of vaccines by recombinase-aided amplification assay (RAA), fluorescence quantitative PCR and dot blot assay, and then found a contaminated attenuated vaccine. The whole genome of the CIAV contaminant was then sequenced and named JS2020-PFV (Genbank accession number: MW234428, 2296bp). It showed 94.5 to 99.9% identities with reference strains and shared the closest evolution relationship with AB1K strain which was isolated from a chicken farm in Turkey. All of these suggested that the use of CIAV contaminated live vaccine may be one of the reason for its epidemic in poultry.

Vaccination as a Strategy to Prevent Bluetongue Virus Vertical Transmission

Bluetongue virus (BTV) produces an economically important disease in ruminants of compulsory notification to the OIE. BTV is typically transmitted by the bite of Culicoides spp., however, some BTV strains can be transmitted vertically, and this is associated with fetus malformations and abortions. The viral factors associated with the virus potency to cross the placental barrier are not well defined. The potency of vertical transmission is retained and sometimes even increased in live attenuated BTV vaccine strains. Because BTV possesses a segmented genome, the possibility of reassortment of vaccination strains with wild-type virus could even favor the transmission of this phenotype. In the present review, we will describe the non-vector-based BTV infection routes and discuss the experimental vaccination strategies that offer advantages over this drawback of some live attenuated BTV vaccines.

Emergence of fowl aviadenovirus C-4 in a backyard chicken flock in California

Fowl aviadenovirus (FAdV) species D and E are associated with inclusion body hepatitis (IBH); species C, serotype 4 (hereafter, FAdV4) is associated with hepatitis-hydropericardium syndrome (HHS) in young chickens. Outbreaks of HHS have led to significant losses in the poultry industry in several countries, predominantly in China. In April 2020, FAdV4 was detected in a remote backyard flock in California. In a mixed flock of chickens of various breeds and ages (6 mo to 2 y old), 7 of 30 were found dead within a week without premonitory signs. One additional bird died after the flock was relocated to fresh pasture, bringing the total mortality to 8 of 30 (27%). Postmortem examination of 3 birds revealed good body condition scores and active laying. One chicken had subtle hemorrhages throughout the liver, and the other 2 had diffusely dark mahogany livers. On histopathology, 2 chickens had hepatic necrosis with hepatocytes containing large, mostly basophilic, intranuclear inclusion bodies, identified by electron microscopy as 82.2-nm diameter adenoviral particles. Virus isolation and genomic sequencing performed on a liver sample revealed strains with 99.9% homology to FAdV4 isolates reported from China. To our knowledge, FAdV4 has not been reported in the United States to date. Furthermore, the chickens affected here were all adults and exhibited a variation of serotype 4 disease in which IBH was present but not hydropericardium.

Molecular characterisation of Newcastle disease virus exotic isolate in East Java, Indonesia

Newcastle disease virus (NDV) is ssRNA paramyxovirus causing clinical signs, varying from subclinical infections to 100% mortality in infected chickens. Haemagglutinin-neuraminidase (HN) protein has an important role related to infection and pathogenesis, therefore, the protein was characterised in this study. Samples were collected from 45 cloacal swabs of native chickens. They were isolated by inoculating in specific pathogen-free embryonated eggs. Molecular detection of NDV was done by reverse transcriptase polymerase chain reaction (RT-PCR) encoding HN protein. RT-PCR for HN gene of NDV generated DNA fragments sized 503 bp, which were then sequenced using ABI Prism. The results have shown that virus isolates were mostly lentogenic and might contribute to outbreak in East Java, Indonesia. Based on this fact, NDV infected native chickens can act as reservoir and contribute to outbreak in the poultry. Our study provides baseline information on genetic characteristics of NDV circulating in East Java and serves as a basic work for further research.

Research Note: Molecular relationship of the fowl adenovirus serotype 4 isolated from the contaminated live vaccine and wild strains isolated in China, 2013-2018

Since June 2013, hydropericardium-hepatitis syndrome caused by putative novel fowl adenovirus 4 (FAdV-4) infection has spread all over China, leading to great economic losses. Previous study found that the use of attenuated vaccines contaminated with FAdV-4 is likely to be an important cause of such large-scale transmission. Here, we sequenced the whole genome of this strain through the next-generation sequencing and carried out a retrospective analysis of the FAdV-4 strains that have been determined in China recently. Results show the vaccine strain was almost 100% identical with wild virus strains, especially with 4 strains considering the difference of the GA repeat region, further linking the relationship between vaccine contamination and FAdV-4 prevalence in China. Meanwhile, there is no time and regional preference for the emergence of FAdV-4 strains with different molecular characteristics in China, which indicates that there may be multiple routes of transmission of this virus, suggesting that we still need to pay more attention to and formulate correct prevention and control in the future.

Immune effect of a Newcastle disease virus DNA vaccine with IL-12 as a molecular adjuvant delivered by electroporation

Newcastle disease (ND), caused by virulent Newcastle disease virus (NDV) strains, has been one of the most problematic diseases affecting the poultry industry worldwide. Conventional vaccines provide effective protection for birds to survive ND outbreaks, but they may not completely suppress NDV shedding. NDV strains circulate on farms for a long time after the initial infection and cause potential risks. A new vaccine with fast clearance ability and low viral shedding is needed. In this study, we used interleukin-12 (IL-12) as an adjuvant and electroporation (EP) as an advanced delivery system to improve a DNA vaccine candidate. The fusion (F) protein gene from an NDV strain of the prevalent genotype VII.1.1 was cloned to prepare the vaccine. Chickens immunized with the F gene DNA vaccine co-delivered with an IL-12-expressing plasmid DNA showed higher neutralizing antibody levels and stronger concanavalin-A-induced lymphocyte proliferation than those treated with the F gene DNA vaccine alone. The co-delivered vaccine provided 100% protection, and less viral shedding and a shorter release time were observed in challenged chickens than when the F gene DNA vaccine was administered alone. The use of F gene DNA combined with IL-12 delivered by electroporation is a promising approach for vaccination against ND.

Avian leukosis virus contamination in live vaccines: A retrospective investigation in China

Avian leukosis (AL) is one of the most pandemic immunosuppressive diseases and has been widely spread between 2006 and 2009 in China. The contamination of avian leukosis virus (ALV) in attenuated vaccine is considered as one of the possible transmission routes of this disease. Based on a retrospective survey of 918 batches of attenuated vaccine produced before 2010, three of them were identified as ALV-positive and corresponding ALV strains were successfully isolated from a live Fowlpox virus vaccine, a live Newcastle disease virus vaccine and a live Infectious Bursal Disease virus vaccine, respectively, and whole-genome sequencing showed that these three isolates shared the highest homology with ALV-A wild strains isolated in China (97.7%) over the same period, and the phylogenetic analysis based on their gp85 genes further confirmed that they belong to subgroup A. Meanwhile, although these three ALV-A strains isolated from contaminated vaccines shared a close genetic relationship, their U3 region of genome have a relatively low identity, suggesting that these three strains may have different sources. This study reminds us once again that the possibility of ALV infecting chickens through contaminated live vaccines, requiring us to carry out stricter exogenous virus monitoring in vaccines.

Genetic characterization of fowl adenovirus serotype 4 isolates in Southern China reveals potential cross-species transmission

Increasing numbers of hepatitis-hydropericardium syndrome (HHS) outbreaks associated with Fowl adenovirus 4 (FAdV-4) have been confirmed in several provinces of China since 2015, mainly affecting 3-5-week-old broiler chicks, resulting in significant losses to the poultry industry. However, little is currently known regarding the molecular epidemiology and host specificity of FAdV-4 associated with HHS in Southern China. In the present study, we isolated 37 FAdV-4 strains from 52 suspected cases of HHS (33 from broilers, one from a layer, two from ducks, and one from a mandarin duck) from Guangdong province during 2016 to 2017. All 37 FAdV-4 strains obtained showed 100% identity of hexon genes at the nucleotide level, and also showed 100% nucleotide sequence identities with strains obtained from other provinces such as Shandong, Zhejiang, and Anhui, which grouped into a FAdV-C cluster. To our knowledge, this represents the first report of an FAdV-4 strain (GZ1) from a mandarin duck with HHS. Experimental infection of the GZ1 strain via intramuscular injection led to a 100% mortality rate in 21-day-old specific pathogen-free chickens. These data indicate the possibility of the cross-species transmission of FAdV-4, highlighting the need for implementing strict biosecurity measures to avoid the mixing of different bird species.

A genotype VII Newcastle disease virus-like particles confer full protection with reduced virus load and decreased virus shedding

Newcastle disease (ND) is one of the most severe avian infectious disease inflicting a great loss on poultry industry worldwide. The control of ND relies on proper vaccination strategies. The vaccine strains of Newcastle disease virus (NDV) mainly belong to genotype I, II or III, which cannot fully prohibit virus shedding against the prevalent genotype VII virulent strain attack. To develop a safe, genotype matched vaccine candidate, we employed a bac-to-bac expression system and constructed a genotype VII NDV strain based virus-like particles (NDV VLPs). It was constructed with NDV M protein as the skeleton, and protective antigen F and HN proteins displayed on the surface. The NDV VLPs exhibited a similar appearance to the live NDV particles, but with denser F and HN proteins displayed on the surface. The immunization assay indicated that NDV VLPs stimulated a longer protection period, less tissue virus loading and shorter virus shedding period than the commercialized LaSota-formulated vaccine when challenged with genotype VII NDV strain. These results proposed the potential role of NDV VLPs as an alternative to current live genotype unmatched vaccine for the control and eliminate NDV in the avian flocks.