The size of the Epstein-Barr virus (EBV) nuclear antigen (EBNA) in cells infected with different EBV isolates varies directly with the size of the EBV triplet repeat array, IR3. The isolate with the largest IR3 fragment has approximately 170 more codons than the isolates with the smallest IR3 fragment; it encodes an EBNA which is approximately 17,000 daltons larger than the smallest EBNA. The EBV IR3 encodes part of a 2-kilobase exon of a latently infected cell messenger RNA which must be translated into a repetitive amino acid domain of EBNA.

At least three separate regions of the Epstein-Barr virus (EBV) genome encode RNA in a cell line that is growth transformed and nonpermissively infected with EBV. Six polyadenylylated cytoplasmic RNAs have been identified from these three regions. An abundant RNA 3.0-3.1 kilobases (kb) long is encoded by DNA of the internal reiteration, IR, and DNA that maps at 25.7-30 megadaltons. A second, abundant, 2.9-kb RNA is primarily encoded by DNA at 110-03 megadaltons but probably has a 3' end to the left of 110 megadaltons. A third, abundant, 3.7-kb RNA is largely encoded by DNA at 63-66 megadaltons and has a 5' end to the left of 63 megadaltons. A less-abundant 1.5-kb RNA is also encoded by IR. The least-abundant polyadenylylated RNAs identified are 2.3 and 2.0 kb. These RNAs have 3' ends mapping of 5-7 megadaltons and 5' ends mapping to the right of 7 megadaltons. The data suggest that there may be two additional polyadenylylated cytoplasmic RNAs, a 3-kb RNA mapping at 26.2-30 megadaltons and a minor RNA mapping at 102-110 megadaltons. An abundant 0.16-kb nonpolyadenylylated RNA is also present in the cytoplasm of IB-4 cells. This RNA precipitates from the cytoplasm in the presence of high concentrations of magnesium, indicating that it is complexed with protein or polyribosomes.

Epstein-Barr virus (EBV) is the human prototype of a family of closely related herpesviruses of Old World primates. These agents probably evolved and spread among the Old World primates since the divergence of apes from monkeys about 30 million years ago. Although the DNAs of the EBV family have no sequence homology to other herpesviruses, there are some features in common with other herpesviral genomes. EBV DNA is unusual in having five tandem direct repeat elements which divide the genome into five unique sequence domains. The tandem direct repeats at the ends of the linear virion DNA probably mediate circularization of the viral DNA to form the circular episomal viral DNA which is characteristic of EBV-infected cells. In latent transforming infection, messenger RNAs are encoded by three widely separate regions of the EBV genome. The remainder of the viral genome encodes many RNAs and proteins which are expressed in productive infection. Early and late viral genes are intermixed along the full length of EBV DNA.

We evaluated the effects of viral immunodeficiency on the outcome of infectious bronchitis virus (IBV) infection in chickens as a hypothetical cause for failure of adequate protection in vaccinated chickens. Initially, we investigated IBV isolations from cases of respiratory disease in association with the presence of thymic and/or bursal atrophy in 322 submissions during 1997 to 2002. Arkansas (Ark)-type IBV was most frequently isolated in spite of extensive ArkDPI vaccination in the broiler industry. The number of IBV isolations was consistently higher in broilers aged 27 to 43 days, coinciding with lymphocytic depletion of the bursa and/or thymus, providing circumstantial evidence that immunodeficiency and IBV incidence may be linked. S1 gene sequence analyses, antigenic characterizations, and challenge of susceptible chickens demonstrated that the field IBV isolates tested were closely related to vaccine strains and had low pathogenicity for chickens. We experimentally evaluated the effects of immunodeficiency caused by co-infection with chicken anaemia virus and infectious bursal disease virus on the outcome of IBV infection. Clinical signs and histological lesions were more persistent in immunodeficient chickens. Local specific IgA production was delayed and lower levels were achieved in immunodeficient chickens. At the same time, IBV RNA concentrations in tracheas and lachrymal fluids were higher and more persistent in immunodeficient chickens. Collectively, these results indicate that viral immunodeficiency most probably plays a relevant role in the epidemiology and outcome of IBV infection. Nous avons évalué les effets de l'immunodéficience virale sur le résultat de l'infection par le virus de la bronchite infectieuse aviaire (IBV) chez des poulets comme une cause hypothétique d'échec de protection adéquate chez des poulets vaccinés. Initialement, nous avons investigué les isolements d'IBV de cas de maladie respiratoire en association avec la présence d'atrophie bursale et/ou thymique à partir de 322 soumissions durant les années 1997-2002. L'IBV de type Arkansas (Ark) a été le plus fréquemment isolé en dépit de la vaccination ArkDPI à grande échelle des poulets de chair en élevage industriel. Le nombre d'isolement d'IBV a été nettement supérieur chez les poulets de chair âgés de 27 à 43 jours, coïncidant avec la déplétion lymphocytaire de la bourse de Fabricius et/ou du thymus, fournissant une évidence circonstanciée que l'immunodéficience et l'incidence de l'IBV peuvent être liées. Les analyses de séquence du gène S1 les caractérisations antigéniques, et l'épreuve de poulets sensibles ont démontré que les souches d'IBV isolées sur le terrain étaient très poches des souches vaccinales et présentaient une pathogénicité faible pour les poulets. Nous avons expérimentalement évalué les effets de l'immunodéficience causée par la co-infection avec le virus de l'anémie du poulet et le virus de la bursite infectieuse aviaire (IBDV) sur le résultat de l'infection par l'IBV. Les symptômes et les lésions histologiques ont persisté plus longtemps chez les poulets immunodéficients. La production locale d'IgA spécifique a été retardée et des niveaux inférieurs ont été enregistrés chez les poulets immunodéficients. Au même moment, les concentrations en ARN IBV dans les trachées et les liquides lacrymaux ont été plus élevées et ont persisté plus longtemps chez les poulets immunodéficients. Dans l'ensemble, ces résultats indiquent que l'immunodéficience virale, joue vraisemblablement un rôle important dans l'épidémiologie et le résultat de l'infection par l'IBV. Wir untersuchten die Auswirkungen einer viral bedingten Immuninsuffizienz auf den Verlauf einer Infektion mit dem infektiösen Bronchitisvirus (IBV) in Hühnern als eine hypothetische Ursache für das Ausbleiben eines adäquaten Impfschutzes in Hühnern. Anfänglich untersuchten wir IBV-Isolate aus Feldfällen von Respirationserkrankungen in Verbindung mit Thymus- und/oder Bursaatrophie in 322 Einsendungen in den Jahren 1997-2002. Trotz umfangreicher Arkansas (Ark) DPI-Vakzinationen in der Broilerindustrie war der Ark-Typ das am häufigsten isolierte IBV. Die Zahl der IBV-Isolate war bei den 27 bis 43 Tage alten Broilern durchweg höher, wobei gleichzeitig in Bursa und/oder Thymus ein Verlust der Lymphozyten festgestellt wurde. Dies belegt, dass die Immuninsuffizienz und das Auftreten einer infektiösen Bronchitis wahrscheinlich im Zusammenhang stehen. Analysen der S1-Gensequenzen, antigenetische Charakterisierungen und Balastungsinfektionen empfänglicher Hühner zeigten, dass die getesteten IBV-Feldstämme mit den Impfstämmen eng verwandt waren und nur eine geringe Pathogenität für Hühner besaßen. Die Effekte einer durch Ko-Infektion mit Hühneranämievirus und dem Virus der infektiösen Bursitis (IBDV) induzierten Immuninsuffizienz auf den Verlauf einer IBV-Infektion untersuchten wir auch experimentell. Die klinischen Symptome und die histologischen Veränderungen waren bei den immunschwachen Tieren persistierender. Ebenso war bei diesen Tieren die lokale spezifische IgA-Produktion verzögert und verringert. Gleichzeitig wiesen die immuninsuffizienten Hühner in Trachea und Tränenflüssigkeit höhere und länger nachweisbare IBV-RNS-Gehalte auf. Insgesamt legen diese Ergebnisse nahe, dass die viral bedingte Immuninsuffizienz höchstwahrscheinlich eine relevante Rolle bei der Epidemiologie und dem Verlauf von...

We examined spike (S) gene sequences of the virus populations of four different commercial ArkDPI-derived infectious bronchitis coronavirus vaccines before and during a single passage in specific pathogen free chickens. We found different degrees of genetic heterogeneity among the four vaccines before passage in chickens, ranging from no apparent heterogeneity to heterogeneity in 20 positions in the S gene. In all except one position, nucleotide differences were non-synonymous. The majority of amino acid differences were in the S1 subunit of the protein. For three of the four ArkDPI-derived vaccines, a single subpopulation with an S gene sequence distinct from the vaccine majority consensus at 5 to 11 codons was selected in chickens within 3 days after ocular vaccination. In contrast, we obtained no evidence for selection of specific subpopulations of the fourth ArkDPI-derived vaccine or Massachusetts or DE072 serotype vaccines. The virus subpopulations within each vaccine selected by chickens are similar in their S1 gene sequences, but distinct in the 3′ portion of the S2 subunit gene for each of the three vaccines. In the S1 gene, the selected subpopulations are more similar to the virulent parental ArkDPI isolate than to the predominant vaccine population. The different proportions of distinct subpopulations in Ark vaccines apparently more fit for replication in the respiratory tract of chickens might cause different degrees of damage to respiratory epithelium and/or immune responses in vaccinated chickens. Sequence comparisons provided no evidence to support that ArkDPI-like field isolates were derived directly from host-selected vaccine virus subpopulations.