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A number of herpesviruses have now been shown to encode microRNAs (miRNAs) that have roles in control of both viral and cellular gene expression. Ovine herpesvirus 2 (OvHV-2) is the causative agent of sheep-associated malignant catarrhal fever, a fatal lymphoproliferative disease of cattle. Using massively parallel sequencing and Northern hybridization we have identified eight putative miRNAs encoded by OvHV-2 expressed in an OvHV-2-immortalized bovine lymphocyte cell line. These eight miRNAs are encoded in two areas of the OvHV-2 genome that contain no predicted protein coding regions and show no sequence similarity with other herpesvirus or cellular miRNAs. This represents the first report of the expression of virally encoded miRNAs in the genus Macavirus of herpesviruses.

Ovine herpesvirus 2 (OvHV-2) causes malignant catarrhal fever in cattle, pigs and deer. We have observed intact circular and linear OvHV-2 genomes in infected T cell lines derived from cows and rabbits. Bovine T cell lines were predominantly latently infected but rabbit T cell lines supported OvHV-2 productive cycle gene expression and virus capsids were demonstrated for the first time.

A domain, previously termed RE1, exists within the herpes simplex virus type 1 genome potentially influencing expression of immediate early genes and the latency associated transcripts. This domain consists of 10 tandem copies of a CT-rich sequence. We demonstrate that this domain binds multiple host-cell factors that may allow RE1 to act either as a transcriptional regulator and/or to affect nucleosomal and DNA structure in the latent genome.

Jaagsiekte retrovirus (JSRV) is an exogenous type D-related retrovirus specifically associated with a contagious lung cancer of sheep (sheep pulmonary adenomatosis; SPA). Recently, epithelial tumour cells in the lungs of SPA-affected sheep were identified as major sites of JSRV replication by immunological techniques and RT-PCR amplification of part of JSRV gag. JSRV was not detected outside the lungs and their draining lymph nodes. However, low levels of JSRV expression in non-respiratory tissues could have been masked by co-amplification of endogenous JSRV-related sequences, which were differentiated from JSRV by the lack of a Scal restriction site in the PCR product. To further investigate the pathogenesis of SPA, an exogenous virus-specific hemi-nested PCR was developed utilizing primers in the U3 region of JSRV LTR, where major differences between endogenous and exogenous sequences exist. This technique was shown to beor = 10(5)-fold more sensitive than the previous gag PCR/ScaI digestion method. Using this new assay the tissue distribution of JSRV in sheep with natural and experimentally induced SPA was analysed. Proviral DNA and JSRV transcripts were found in all tumours and lung secretions of SPA-affected sheep (n = 22) and in several lymphoid tissues. The mediastinal lymph nodes draining the lungs were consistently demonstrated to be infected by JSRV (10/10). JSRV transcripts were also detected in spleen (7/9), thymus (2/4), bone marrow (4/8) and peripheral blood mononuclear cells (3/7). Proviral DNA was also detected in these tissues although in a much lower proportion of cases. JSRV was not detected in 27 samples from unaffected control animals (n = 15).

Sheep pulmonary adenomatosis (SPA) is a naturally occurring contagious lung tumour of sheep which has been associated aetiologically with a type D- and B-related retrovirus (Jaagsiekte retrovirus; JSRV). To improve understanding of the aetio-pathogenesis of SPA, the distribution and the sites of JSRV replication in sheep with naturally or experimentally induced SPA or in unaffected controls were identified. New immunological reagents were produced and a blocking enzyme-linked immunosorbent assay (B-ELISA) and an immunohistochemical technique for the detection of JSRV major capsid protein at the tissue and cellular levels were developed. JSRV was detected only in the respiratory tract of sheep affected by pulmonary adenomatosis and specifically in the transformed epithelial cells of the alveoli of SPA-affected sheep.

We have isolated a maedi-visna-like virus from the peripheral blood mononuclear cells of a British sheep displaying symptoms of arthritis and pneumonia. After brief passage in fibroblasts this virus (designated EV1) was used to infect choroid plexus cells. cDNA clones of the virus were prepared from these cells and sequenced. Gaps between non-overlapping clones were filled using gene amplification by the polymerase chain reaction. The genome structure is similar to that described for visna virus strain 1514, and differs from that described for visna virus strain SA-OMVV in not having a W reading frame. Overall the genome differs by about 20% between each of these strains, but there is fivefold variation in the amount of divergence of derived amino acid sequences of different open reading frames. Two sequenced EV1 clones each contain only one copy of the 43 bp repeat, with paired AP-1 sites, which is a feature of other ruminant lentiviral long terminal repeats (LTRs). However, analysis of viral DNA in infected cells by gene amplification shows that LTRs with two repeats do occur, albeit at a relatively low frequency.