Avian leukosis virus subgroup - J as a contaminant in live commercially available poultry vaccines distributed in Nigeria

Current Status of Poultry Recombinant Virus Vector Vaccine Development

Inactivated and live attenuated vaccines are the mainstays of preventing viral poultry diseases. However, the development of recombinant DNA technology in recent years has enabled the generation of recombinant virus vector vaccines, which have the advantages of preventing multiple diseases simultaneously and simplifying the vaccination schedule. More importantly, some can induce a protective immune response in the presence of maternal antibodies and offer long-term immune protection. These advantages compensate for the shortcomings of traditional vaccines. This review describes the construction and characterization of primarily poultry vaccine vectors, including fowl poxvirus (FPV), fowl adenovirus (FAdV), Newcastle disease virus (NDV), Marek's disease virus (MDV), and herpesvirus of turkey (HVT). In addition, the pathogens targeted and the immunoprotective effect of different poultry recombinant virus vector vaccines are also presented. Finally, this review discusses the challenges in developing vector vaccines and proposes strategies for improving immune efficacy.

Transcriptome-wide N6-methyladenosine modification and microRNA jointly regulate the infection of avian leukosis virus subgroup J in vitro

N6-methyladenosine (m6A) methylation in transcripts has been suggested to influence tumorigenesis in liver tumors caused by the avian leukosis virus subgroup J (ALV-J). However, m6A modifications during ALV-J infection in vitro remain unclear. Herein, we performed m6A and RNA sequencing in ALV-J-infected chicken fibroblasts (DF-1). A total of 51 differentially expressed genes containing differentially methylated peaks were identified, which were markedly enriched in microRNAs (miRNAs) in cancer cells as well as apoptosis, mitophagy and autophagy, RNA degradation, and Hippo and MAPK signaling pathways. Correlation analysis indicated that YTHDC1 (m6A-reader gene) plays a key role in m6A modulation during ALV-J infection. The env gene of ALV-J harbored the strongest peak, and untranslated regions and long terminal repeats also contained peaks of different degrees. To the best of our knowledge, this is the first thorough analysis of m6A patterns in ALV-J-infected DF-1 cells. Combined with miRNA profiles, this study provides a useful basis for future research into the key pathways of ALV-J infection associated with m6A alteration.

First report of co-infections of Marek's disease virus and chicken infectious anaemia virus in poultry flocks in Nigeria

Marek's disease (MD) and chicken infectious anaemia (CIA) are viral immunosuppressive diseases of poultry caused by the MD virus (MDV) and CIA virus (CIAV) respectively. Despite vaccination against MD, the incidence of the disease in vaccinated poultry flocks in Nigeria persists. However, underlying factors like co-infection with CIAV have not been investigated in the country. This study was designed to investigate possible co-infections of MDV and CIAV in poultry flocks in Nigeria. In 2016, tumorous tissue samples were collected from suspected cases of MD at necropsy in Jos, Plateau State, Nigeria. The samples collected were fixed in formalin for histopathological examination, genomic DNA was extracted from a second part and analysed by polymerase chain reaction (PCR), targeting the meq and VP1 genes of the MDV and CIAV, respectively. The histology results revealed that the cutaneous and proventricular lymphomas were characterized by large numbers of mononuclear cellular infiltrates admixed with heterophils. The PCR results revealed that MDV was detected in 66.7% (16/24), CIAV in 45.8% (11/24), and co-infections of MDV and CIAV were detected in 45.8% (11/24) of the samples analysed. In addition, co-infections of MD and CIA were recorded in 100% (6/6) and 27.7% (5/18) of broilers and layer/pullet' samples respectively. Phylogenetic analysis of the meq gene sequences revealed that the Nigerian MDV clusters with very virulent MDV from Egypt and Italy. While, CIAV sequences were genotype II and genotype III and clustered with CIAVs from Cameroon and China. This is the first report of co-infections of MD and CIA in Nigeria.

Global Maps of Avian Leukosis Viruses: Research Trends and Themes Based on Networking

Avian leukosis virus (ALV) has a tremendous adverse impact on the poultry industry. Since its discovery, research on different aspects of ALV have been published. Due to the vast academic emphasis and economic importance of the ALV infection in poultry worldwide, this bibliometric analysis explored the scientific output associated with ALV utilizing the Web of Science (Core Collection) database. The relevant data were collected using the search query "AVIAN LEUKOSIS VIRUS", further refined by document types (article, book chapter, and proceedings paper). Finally, 1060 items with full records were imported in Plaintext and tab-delimited formats. The data analysis was carried out using MS Excel, VOS viewer, and R (Biblioshiny) software. Chinese and American research institutions produced the majority of papers during study time period. The Journal of Virology and Avian Diseases appeared as the favorite journal/source for publications. Apart from the avian leukosis virus and the ALV-J, the important keywords mentioned included avian leukosis virus subgroup j, chicken, and retrovirus. The analysis revealed substantial findings on ALV research, with a strong research response from the USA and China.

Enhanced Antiviral Ability by a Combination of Zidovudine and Short Hairpin RNA Targeting Avian Leukosis Virus

Avian leukosis virus (ALV) causes tumor diseases in poultry and is circulating all over the world, leading to significant economic losses. In addition, mixed infection of ALV with other viruses is very common and is often reported to contaminate live vaccines. At present, there is no effective method to suppress the replication of ALV in vitro, so it is very difficult to remove it in mixed infection. As a retrovirus, the replication of ALV can be limited by reverse transcriptase (RT) inhibitors like zidovudine (AZT), but it also causes nontargeted cytotoxicity. To find the optimal solution in cytotoxicity and inhibition efficiency in vitro culture system, we firstly designed a combination therapy of AZT and short hairpin RNA (shRNA) targeting ALV and then verified its efficiency by multiple biological methods. Results showed that shRNA can effectively inhibit the expression of RT and then limit the replication of ALV. The combination of AZT and shRNA can significantly improve the antiviral efficiency in viral replication, shedding, and provirus assembly under the condition of low cytotoxicity. Overall, in this study, the combination therapy of AZT and shRNA targeting ALV showed excellent antiviral performance against ALV in vitro culture system. This method can be applied to multiple scenarios, such as the removal of ALV in mixed infection or the purification of contaminated vaccine strains.

Antibody profiles of avian leukosis virus subgroups A/B and J In layer flocks suspected to have Marek’s disease in Nigeria

Previous reports indicate high seroprevalence of avian leukosis virus (ALV) p72 antigen in layer flocks suspected to have Marek’s disease (MD) in Kaduna and Plateau States. However, the specific subgroups responsible for ALV infection in layers in the States are still unknown, hence the need for this study. Therefore, the objective of this study was to determine the antibody profiles of ALV subgroups A/B and J in layer flocks suspected to have MD in Kaduna and Plateau States. Sera from 7 and 16 layer flocks suspected to have MD in Kaduna and Plateau States respectively, were screened for the presence of antibodies to ALV subgroups A/B and J using IDEXX enzyme linked immunosorbent assay (ELISA) kits. Out of the seven layer flocks screened in Kaduna State, antibodies to ALV subgroup A/B was detected in six of the flocks (85.7%), while antibodies to ALV subgroup J was detected in only one flock (14.3%). Antibodies to both ALV subgroups A/B and J were detected in one flock (14.3%), which suggests co-infection of the two ALV subgroups. Out of the 16 flocks screened in Plateau State, antibodies to ALV subgroup A/B were detected in 15 flocks (93.8%), while antibodies to ALV subgroup J were detected in six flocks (37.5%). Antibodies to both ALV subgroups A/B and J were detected in five flocks (31.3%). The high detection of antibodies to ALV A/B suggests that ALV infection in layers is mostly due to ALV subgroup A or B in the study areas.

ALV-J-contaminated commercial live vaccines induced pathogenicity in Three-Yellow chickens: one of the transmission routes of ALV-J to commercial chickens

One avian leukosis virus of subgroup J (ALV-J) strain GX14YYA1 was isolated from a commercial bivalent Newcastle disease (ND)–infectious bronchitis (IB) vaccine in our previous study. To evaluate the pathogenicity of the ALV-J-contaminated vaccine on commercial chickens, day-old Three-Yellow chicks in group I were vaccinated with ALV-J-contaminated bivalent ND-IB live vaccine by intranasal and eye drop at 1-day-old for the primary vaccination and at 7-day-old for the secondary vaccination. Groups II and III were kept as the normal vaccination group with the noncontaminated ND-IB vaccine and blank control groups, respectively. The birds of different groups were maintained separately in isolators for 175 d. The first viremia was detected at 4 wk of age and 20% (2/10) of the birds maintained viremia during 11 to 25 wk of age. At the same time, the birds in group I experienced a significant suppression of body weight gain when compared with those of groups II and III (P < 0.05). In addition, the birds in group I showed obvious ALV-J hemangioma-type anatomical lesions in the liver and tumors were observed in the abdominal cavity. The results demonstrated that the ALV-J contaminated commercial live vaccines can induce pathogenicity in commercial Three-Yellow chickens and indicate that ALV-J-contaminated commercial live vaccines could be one of the transmission routes of ALV-J to commercial chickens.