Use of reverse transcriptase polymerase chain reaction for detection of vaccine contamination by avian leukosis virus

Chronological analysis of gross and histological lesions induced by field strains of fowl adenovirus serotypes 1, 8b and 11 in one-day-old chickens

Fowl adenoviruses (FAdVs) cause diseases in domestic chickens, including inclusion body hepatitis (IBH), with immunosuppression believed to play a role in their pathogenesis. To gain a better understanding of the pathogenesis and chronology of disease caused by FAdVs, the gross pathology, histopathology and dissemination of virus were examined at several different time points, after inoculation of one-day-old specific pathogen-free chickens with FAdV-1, FAdV-8b or FAdV-11 via the ocular route. FAdV-8b had a slightly greater virulence than FAdV-11, but both were primary pathogens. The presence and severity of hepatic lesions were used to define the three stages of the disease: incubation (1-3 days post-inoculation, PI), degeneration (4-7 days PI) and convalescence (14 days PI). Both viruses were detected in the liver, kidney, bursa, thymus and gizzard of most birds during the degenerative stage, and persisted in the gizzard into convalescence. The FAdV-1 isolate was found to be apathogenic, but virus was detected in the bursa and/or gizzard of several birds between 2 and 7 days PI. This is the first study examining the chronology of gross and microscopic lesions of pathogenic and apathogenic FAdVs in association with viral presence in multiple tissues. It was concluded that both FAdV-8b and FAdV-11 are primary pathogens, and that these strains may play a role in immunosuppression.

Identification of a novel B-cell epitope specific for avian leukosis virus subgroup J gp85 protein

Avian leukosis virus subgroup J (ALV-J) is an avian oncogenic retrovirus that has caused severe economic losses in China. Gp85 protein is the main envelope protein and the most variable structural protein of ALV-J. It is also involved in virus neutralization. In this study, a specific monoclonal antibody, 4A3, was produced against the ALV-J gp85 protein. Immunofluorescence assays showed that 4A3 could react with different strains of ALV-J, including the British prototype isolate HPRS103, the American strains, an early Chinese broiler isolate, and layer isolates. A linear epitope on the gp85 protein was identified using a series of partially overlapping fragments spanning the gp85-encoding gene and subjecting them to western blot analysis. The results indicated that (134)AEAELRDFI(142) was the minimal linear epitope that could be recognized by mAb 4A3. Enzyme-linked immunosorbent assay (ELISA) revealed that chicken anti-ALV-J sera and mouse anti-ALV-J gp85 sera could also recognize the minimal linear epitope. Alignment analysis of amino acid sequences indicated that the epitope was highly conserved among 34 ALV-J strains. Furthermore, the epitope was not conserved among subgroup A and B of avian leukosis virus (ALV). Taken together, the mAb and the identified epitope may provide valuable tools for the development of new diagnostic methods for ALV-J.

Use of PCR-based assays for the detection of the adventitious agent porcine circovirus type 1 (PCV1) in vaccines, and for confirming the identity of cell substrates and viruses used in vaccine production

Safety and quality are important issues for vaccines. Whereas reversion to virulence poses a safety risk with live attenuated vaccines, the potential for the presence of adventitious agents is also an issue of vaccine quality. The recent detection or porcine circovirus type 1 (PCV1) in human vaccines has further highlighted the importance of quality control in vaccine production. The purpose of this study was to use a novel conventional PCR to detect PCV1, and subsequently screen materials used in the manufacture of vaccines at Bharat Biotech International Limited, India. The genome or gene fragments of PCV1 were not detected in any of the vaccines and materials tested, including the live attenuated rotavirus vaccine candidate ROTAVAC(®). Further, the identity of the cells and the viruses used as starting materials in the manufacture of these vaccines was confirmed by species-specific PCR or virus-specific RT-PCR, and no cross-contamination was detected in any case. The methods can be applied for regular in-house quality control screening of raw materials and seeds/banks, as well as formulated vaccines.

An Optimized Polymerase Chain Reaction Assay to Identify Avian Virus Vaccine Contamination with Chicken Anemia Virus

The use of embryonating chicken eggs in preparation of avian virus vaccines is the principle cause for contamination with Chicken anemia virus (CAV). Identification of CAV in contaminated vaccines relies on the expensive, tedious, and time-consuming practice of virus isolation in lymphoblastoid cell lines. The experience of the last 2 decades indicates that polymerase chain reaction is extending to replace most of the classic methods for detection of infectious agents. In the present report, a simple, rapid, and accurate polymerase chain reaction method for detection of CAV in poultry vaccines is described. Oligonucleotide primers homologous to highly conserved sequences of the VP1 gene were used to amplify a fragment of 676 bp. The developed assay was specific for detecting CAV from different sources, with no cross reactivity with many avian viruses. No inter- and intra-assay variations were observed. The analytical sensitivity of the test was high enough to detect 5 TCID50 (50% tissue culture infective dose) of the virus per reaction; however, different factors related to the vaccine matrix showed considerable effects on the detection limit. In conclusion, this method may represent a suitable alternative to virus isolation for identification of CAV contamination of poultry virus vaccines.

Development of a loop-mediated isothermal amplification assay for rapid detection of subgroup J avian leukosis virus

Infection of breeder flocks in China with subgroup J avian leukosis virus (ALV-J) has increased recently. In this study, we have developed a loop-mediated isothermal amplification (LAMP) assay for rapid detection of ALV-J from culture isolates and clinical samples. The ALV-J-specific LAMP assay efficiently amplified the target gene within 45 min at 63 degrees C using only a simple laboratory water bath. To determine the specificity of the LAMP assay, various subgroup ALVs and other related viruses were detected. A ladder pattern on gel electrophoresis was observed for ALV-J isolates but not for other viruses. To evaluate the sensitivities of the LAMP assay and conventional PCR, the NX0101 isolate plasmid DNA was amplified by them. The detection limit of the LAMP assay was 5 target gene copies/reaction, which was up to 20 times higher than that of conventional PCR. To evaluate the application of the LAMP assay for detection of ALV-J in clinical samples, 49 samples suspected of ALV infection from breeder flocks were tested by the LAMP assay and PCR. Moreover, virus isolation from these samples was also performed using cell culture. The positive-sample ratios were 21/49 (43%) by conventional PCR, 26/49 (53%) by the LAMP assay, and 19/46 (41%) by virus isolation. Additionally, a positive LAMP reaction can be visually ascertained by the observation of turbidity or a color change after addition of SYBR green I dye. Consequently, the LAMP assay is a simple, rapid, and sensitive diagnostic method and can potentially be developed for rapid detection of ALV-J infection in the field.

Marek's disease virus: lytic replication, oncogenesis and control

Marek's disease (MD) is caused by a ubiquitous, lymphotropic alphaherpesvirus, MD virus (MDV). MD has been a major concern in the poultry industry owing to the emergence of increasingly virulent strains over the last few decades that were isolated in the face of comprehensive vaccination. The disease is characterized by a variety of clinical signs; among them are neurological symptoms, chronic wasting and, most notably, the development of multiple lymphomas that manifest as solid tumors in the viscera and musculature. Much work has been devoted to study MD-induced oncogenesis and the genes involved in this process. Among the many genes encoded by MDV, a number have been shown recently to affect the development of tumors in chickens, one protein directly causing transformation of cells (Meq) and another being involved in maintaining transformed cells (vTR). Other MDV gene products modulate and are involved in early lytic in vivo replication, thereby increasing the chance of transformation occurring. In this review, we will summarize specific genes encoded by MDV that are involved in the initiation and/or maintenance of transformation and will focus mostly on current vaccination and control strategies against MD, particularly how modern molecular biological methods may be used to improve strategies to combat the disease in the future.

Detection and characterization of avian leukosis virus in Marek's disease vaccines

Avian leukosis virus (ALV) infection in chickens is known to induce increased mortality, tumors, delayed growth, and suboptimal egg production. Countries importing specified pathogen-free eggs, vaccines, and poultry breeding stock require freedom of infection or contamination with ALV in such products among other avian pathogens. Recently, ALV was found as a contaminant in a limited number of commercial poultry vaccines, even after routine quality assurance procedures cleared the vaccines for commercialization. The contaminated vaccines were promptly withdrawn from the market, and no direct detrimental effects were reported in poultry vaccinated with such vaccines. We describe herein the characterization in vitro of the contaminant viruses. All exogenous viruses detected in four vaccine lots belong to subgroup A of ALV based on cell receptor interaction, subgroup-specific polymerase chain reaction (PCR), envelope gene sequencing, and virus neutralization. A combination of thermal treatment and serial dilutions of the contaminated vaccines facilitated detection of contaminating ALVs in cell culture coupled with antigen-capture enzyme-linked immunosorbent assay. Subgroup-specific PCR readily detected ALV-A directly in the contaminated vaccines but not in naive vaccines or cell controls. Our methods are proposed as complementary procedures to the currently required complement fixation for avian leukosis test for detection of ALV in commercial poultry vaccines.

Application of RT-PCR for the detection of avian reovirus contamination in avian viral vaccines

An efficient procedure for the detection of avian reovirus (ARV)-specific RNA sequences in veterinary immunological medicinal products using reverse transcriptase polymerase chain reaction (RT-PCR) is described. Four ARV vaccine strains (1133, 1733, 2408 and Olson WVU2937), two ATCC strains (VR826 and VR856) as well as several ARV field isolates obtained from domestic, wild and pet birds could be easily detected with S2- and S4-specific primers. The identity of the amplified fragments was confirmed by restriction endonuclease analysis and sequence analysis. Furthermore, not only the starting substrates used for the production of a vaccine, but also additives and the manufacturing process (matrix effects) can influence the results. These RT-PCRs have been useful for screening poultry vaccines for extraneous ARV in the quality control of biologicals used in veterinary medicine.

Primer on medical genomics part II: Background principles and methods in molecular genetics

The nucleus of every human cell contains the full complement of the human genome, which consists of approximately 30,000 to 70,000 named and unnamed genes and many intergenic DNA sequences. The double-helical DNA molecule in a human cell, associated with special proteins, is highly compacted into 22 pairs of autosomal chromosomes and an additional pair of sex chromosomes. The entire cellular DNA consists of approximately 3 billion base pairs, of which only 1% is thought to encode a functional protein or a polypeptide. Genetic information is expressed and regulated through a complex system of DNA transcription, RNA processing, RNA translation, and posttranslational and cotranslational modification of proteins. Advances in molecular biology techniques have allowed accurate and rapid characterization of DNA sequences as well as identification and quantification of cellular RNA and protein. Global analytic methods and human genetic mapping are expected to accelerate the process of identification and localization of disease genes. In this second part of an educational series in medical genomics, selected principles and methods in molecular biology are recapped, with the intent to prepare the reader for forthcoming articles with a more direct focus on aspects of the subject matter.

Reduction of animal use in human vaccine quality control: opportunities and problems

In vivo assays play a crucial role in the assessment of the potency and safety of human vaccines. Robust vaccine production procedures, improved characterisation methods and development of well-characterised vaccines create possibilities to reduce animal use. In this paper the current status in this field is reviewed. Achievements with regard to in vivo and in vitro potency and safety testing are discussed as well as new developments and possibilities in the field of in vitro characterisation of vaccine components. Finally, validation and implementation issues will be dealt with. Although replacement of in vivo tests for batch release of existing vaccines is difficult, emerging technologies allow well-considered reduction of in vivo experiments during product and process development and improvement. Inextricably bound up with this approach is good manufacturing practice (GMP), resulting in robust, validated production processes.

Use of polymerase chain reaction (PCR) for the detection of vaccine contamination by infectious laryngotracheitis virus

Quality control of biologicals for veterinary use includes certification of freedom from extraneous agents. Contamination of vaccines may originate from various materials used for production and during manufacturing process. Requirements for avian virus vaccines to demonstrate freedom of adventitious agents are stated in the European Pharmacopoeia and include monitoring for infectious laryngotracheitis virus (ILTV). ILTV is an avian herpesvirus belonging to the alphaherpesvirus subfamily causing acute respiratory disease. To date the methods to detect ILTV contaminating biologicals consist of demonstration of antibody induction in chicken after immunization or virus cultivation in embryonated eggs. These methods are time consuming and laborious. Therefore, a specific, simple and sensitive in vitro polymerase chain reaction (PCR) for the detection of ILTV contamination in avian virus vaccines was developed. Primers were designed to amplify part of the p32 gene. Four different ILTV vaccine strains could be unequivocally detected. The identity of the amplified fragment was confirmed by restriction endonuclease analysis.

Detection of avian leukosis virus in albumen of chicken eggs using reverse transcription polymerase chain reaction

A reverse transcriptase polymerase chain (RT-PCR) assay was developed to detect avian leukosis retrovirus (ALV) in egg albumen. Eggs of Single Comb White Leghorns were from a commercial breeder (stock F) and from a pathogen-free flock (stock N). RT-PCR was undertaken on isolated RNA from 20 unfertilized egg samples using seven sets of primers that correspond to the ALV gp85 envelope glycoprotein which determines the ALV subgroup classification. An ELISA assay for ALV gs antigen of egg albumen was positive for all stock F birds tested and negative for all stock N birds. Virus isolation was undertaken by inoculating egg albumen, feather pulp, or blood from five stock F chickens onto cultures of chicken embryo fibroblasts (C/E). IFA analysis of the inoculated C/E cultures indicated that all stock F birds tested contained infectious ALV. For the virus-positive stock F chickens, RT-PCR analyses using primers designed to detect all ALV subgroups detected ALV in 15/15 (100%) egg albumen samples, while primers designed to detect subgroup A ALV were positive for 12/15 (80%) egg albumen samples. RT-PCR products were not detected from five egg albumen samples from five stock N chickens by any primer sets. Direct sequencing using primers specific for subgroup A ALV verified the viral subgroup in the RT-PCR amplification products. The combined use of RT-PCR and direct sequencing of the RT-PCR product provides a new approach for identifying ALV-infected poultry.

Comparative Evaluation of In Vitro and In Vivo Assays for the Detection of Avian Infectious Bronchitis Virus as a Contaminant of Live Poultry Vaccines

A reverse transcriptase polymerase chain reaction (RT-PCR) assay specific for identifying avian infectious bronchitis virus (IBV) in poultry vaccines, and the serological response to IBV induced by the inoculation of chicks with a Newcastle disease vaccine spiked with the Massachusetts strain of IBV, were compared for their ability to detect IBV as a contaminant of avian vaccines. The sensitivity of the IBV-RT-PCR assay provided results which were at least equivalent to the biological effect produced by the inoculation of chicks, allowing this assay to be considered a valid alternative to animal testing in the quality control of avian immunologicals. This procedure can easily be adapted to detect a number of contaminants for which the in vivo test still represents the only available method of detection.

Development and application of polymerase chain reaction (PCR) tests for the detection of subgroup J avian leukosis virus

Subgroup J avian leukosis virus (ALV) is a recently identified avian retrovirus associated with myeloid leukosis in meat-type chickens. The env gene of the HPRS-103 strain of ALV, the prototype of this subgroup, differs considerably from that of other subgroups, but shows close homology to the env-like sequences of members of the EAV family of endogenous retroviruses. Polymerase chain reaction (PCR) tests using two sets of primers were developed for the specific detection of the members of this new subgroup along with another pair of primers for detecting other subgroup viruses. The specificity and sensitivity of this detection system was compared with the conventional detection methods in experimentally and naturally infected samples. The use of PCR was found to be rapid, specific and more sensitive than the conventional diagnostic tests for the detection of ALV. Moreover, the two subgroup J ALV-specific PCR tests were found to be capable of differentiating between 'prototype-like' viruses and more recent isolates which show extensive antigenic and sequence variations. The use of this test as a rapid and sensitive method of detection of viruses in epidemiological studies and eradication programs is discussed.