Metabolic hormones and tissue concentrations of mRNA for IGF-I in lines of sheep that differ in their protein synthesis response to feed intake.

The rate of protein synthesis in the skin and muscle of sheep that have been genetically selected for high wool staple strength (SS) is less dependent on the level of dietary intake than that of low SS sheep. This study examined potential hormonal mediators of this difference in responsiveness. Sheep from SS+ and SS- genotypes were fed at 0.4, 1.1 or 1.8 times maintenance. Circulating concentrations of metabolic hormones and tissue concentrations of the mRNA for IGF-I were measured and compared with rates of protein synthesis measured previously. Plasma concentrations of GH, insulin, cortisol, thyroxine and IGF-I responded similarly to dietary intake in both genotypes, but SS+ sheep had higher plasma concentrations of IGF-I at all levels of nutrition (P<0.05). There were no interactions between diet and genotype. The concentration of mRNA for IGF-I was higher in the liver of SS+ sheep (P<0.05), and tended to increase (P=0.06) with nutrient intake, but there were no significant effects of genotype or nutrition in skin, muscle or gut. Concentrations of mRNA for IGF-I were not related to the rate of protein synthesis in any tissue examined. It was concluded that IGF-I did not drive the rate of protein synthesis directly, but it may mediate the responsiveness of protein synthesis rate, or protein degradation rate, to nutrient supply.

The severity of murray valley encephalitis in mice is linked to neutrophil infiltration and inducible nitric oxide synthase activity in the central nervous system.

A study of immunopathology in the central nervous system (CNS) during infection with a virulent strain of Murray Valley encephalitis virus (MVE) in weanling Swiss mice following peripheral inoculation is presented. It has previously been shown that virus enters the murine CNS 4 days after peripheral inoculation, spreads to the anterior olfactory nucleus, the pyriform cortex, and the hippocampal formation at 5 days postinfection (p.i.), and then spreads throughout the cerebral cortex, caudate putamen, thalamus, and brain stem between 6 and 9 days p.i. (P. C. McMinn, L. Dalgarno, and R. C. Weir, Virology 220:414-423, 1996). Here we show that the encephalitis which develops in MVE-infected mice from 5 days p.i. is associated with the development of a neutrophil inflammatory response in perivascular regions and in the CNS parenchyma. Infiltration of neutrophils into the CNS was preceded by increased expression of tumor necrosis factor alpha and the neutrophil-attracting chemokine N51/KC within the CNS. Depletion of neutrophils with a cytotoxic monoclonal antibody (RB6-8C5) resulted in prolonged survival and decreased mortality in MVE-infected mice. In addition, neutrophil infiltration and disease onset correlated with expression of the enzyme-inducible nitric oxide synthase (iNOS) within the CNS. Inhibition of iNOS by aminoguanidine resulted in prolonged survival and decreased mortality in MVE-infected mice. This study provides strong support for the hypothesis that Murray Valley encephalitis is primarily an immunopathological disease.

Geographic distribution and evolution of Sindbis virus in Australia.

The molecular epidemiology and evolution of Sindbis (SIN) virus in Australia was examined. Several SIN virus strains isolated from other countries were also included in the analysis. Two regions of the virus genome were sequenced including a 418 bp region of the E2 gene and a 484 bp region containing part of the junction region and the 5' end of the C gene. Analysis of the nucleotide and deduced amino acid sequence data from 40 SIN virus isolates clearly separated the Paleoarctic/Ethiopian and Oriental/Australian genetic types of SIN virus. Examination of the Australian strains showed a temporal rather than geographic relationship. This is consistent with the virus having migratory birds as the major vertebrate host, as it allows for movement of virus over vast areas of the continent over a relatively short period of time. The results suggest that the virus is being periodically redistributed over the continent from an enzootic focus of evolving SIN virus. However, SIN virus strains isolated from mosquitoes collected in the south-west of Australia appear to represent a new SIN virus lineage, which is distinct from the Paleoarctic/Ethiopian and Oriental/Australian lineages. Given the widespread geographic dispersal of the Paleoarctic/Ethiopian and Oriental/Australian lineages, it is surprising that the South-west genetic type is so restricted in its area of circulation. Nucleotide sequence data from the C gene of the prototype strain of the alphavirus Whataroa were also determined. This virus was found to be genetically distinct from the SIN virus isolates included in the present study; however, it is clearly SIN-like and appears to have evolved from a SIN-like ancestral virus.

Geographic distribution and evolution of Ross River virus in Australia and the Pacific Islands.

We examined the molecular epidemiology and evolution of Ross River (RR) virus in Australia and the Pacific Islands. Nucleotide sequences of the E2 and E3 genes of five RR virus strains revealed remarkable conservation between 1959 and 1989 with a maximum divergence of only 3.3%. Sequence data from a 505-base pair fragment of the E2 gene from 51 additional strains showed that RR virus has diverged genetically into three separate groups although at least 95% sequence homology was still maintained between all 56 strains. Each genetic type predominates in a particular geographic region of Australia and can be broadly defined as occurring in the western, northeastern, and southeastern regions of Australia. However, some RR virus strains did not follow this pattern of geographic distribution indicating movement of virus by the travel of viremic humans or livestock across the continent. The Pacific Islands isolates all belong to the southeastern genotype. These findings suggest genetic divergence and independent evolution of RR virus within geographically isolated enzootic foci; however, selective pressures maintain high nucleotide conservation in nature.

Nucleotide sequence analysis of Jembrana disease virus: a bovine lentivirus associated with an acute disease syndrome.

The complete nucleotide sequence of the RNA genome of Jembrana disease virus (JDV), a lentivirus that causes an acute disease syndrome in Bali cattle (Bos javanicus), is reported. In addition to the gag, pol and env genes and flanking long terminal repeats (LTRs) that characterize all retroviruses, a number of accessory genes represented by small multiply spliced ORFs in the central and 3'-terminal regions of the genome, including tat and rev that are typical of lentiviruses, were identified. The genome of JDV was 7732 bp in length, 750 bp smaller than the genome of bovine immunodeficiency virus (BIV) strain BIV127. A striking feature of the genome was the many deletions relative to BIV127, the largest of which were 471 bp from the env gene and 157 bp from the U3 (promoter) region in the LTR. There were also several insertions of up to 33 bp in the JDV genome relative to BIV127 found in the env gene and small ORFs that overlap env. Other significant genomic differences between JDV and BIV127 included changes to cis-acting sequences throughout the genome such as promoter and enhancer sequences in the LTR, the trans-activation response region, splice sites and frameshift sequences; alterations to the gag precursor protein cleavage sites and thus the processed products; loss of the vpw and vpy ORFs; and amino acid changes in all coding regions. The significance of these changes is discussed in relation to the differences in pathogenicity between JDV and BIV.

Molecular epidemiology and evolution of mosquito-borne flaviviruses and alphaviruses enzootic in Australia.

Three distinct patterns in the molecular epidemiology and evolution are evident among the alphaviruses and flaviviruses enzootic in Australia. One pattern, exemplified by MVE and KUN viruses, is of a single genetic type evolving slowly and uniformly in geographically widely separated regions of Australia with no evidence of independent divergence. The second pattern, exemplified by RR virus, is of separate genotypes evolving in different geographic regions with significant nucleotide divergence between genotypes. The third pattern, exemplified by SIN virus, is of a succession of temporally related genotypes that extend over most of the Australian continent, with relatively low levels of nucleotide divergence within a genotype, and which are each replaced by the subsequent genotype. These patterns are associated in part due to the nature and dispersal of their vertebrate hosts. Nucleotide divergence rates for Australian alphaviruses are similar to those reported elsewhere. Genomic relationships between Australian flavivirus members of the JE virus serological complex and between Australian alphaviruses are discussed, and evidence is presented for a possible new genomic lineage of SIN virus.

Glycosylation and antigenic variation among Kunjin virus isolates.

Previous studies have found Kunjin (KUN) virus isolates from within Australia to be genetically homogenous and that the envelope protein of the type strain (MRM61C) was unglycosylated and lacked a potential glycosylation site. We investigated the extent of antigenic variation between KUN virus isolates from Australia and Sarawak using an immunoperoxidase assay and a panel of six monoclonal antibodies. The glycosylation status of the E protein of each virus was also determined by N glycosidase F (PNGase F) digestion and limited sequence analysis. The results showed that KUN viruses isolated within Australia oscillated between three antigenic types defined by two epitopes whose expression was influenced by passage history and host cell type. In contrast an isolate from Sarawak formed a stable antigenic type that was not influenced by passage history and was distinct from all Australian isolates. PNGase F digestions of KUN isolates indicated that 19 of the 33 viruses possessed a glycosylated E protein. Nucleotide sequence of the 5' third of the E gene of selected KUN isolates revealed that a single base change in PNGase F sensitive strains changed the tripeptide N-Y-F (amino acids 154-156 of the published sequence) to the potential glycosylation site N-Y-S. Further analysis revealed that passage history also had a significant influence on glycosylation.

Genomic sequence analysis identifies Jembrana disease virus as a new bovine lentivirus.

Jembrana disease virus, the cause of an acute, severe disease in Bali (Bos javanicus) cattle in Indonesia was recently identified as a retrovirus, and possibly a lentivirus. We have produced sequence data representing 598 bp of the pol gene, amplified by PCR from viral cDNA using broadly reactive universal primers for retroviruses and more specific genus-reactive primers for lentiviruses. When the sequence data were compared with that of known lentiviruses and other bovine retroviruses, the closest alignment was with bovine immunodeficiency-like lentivirus (BIV), showing 74% nucleotide sequence identity. This confirmed that JDV is a lentivirus and that it is distinguishable from BIV. The pathogenesis of Jembrana disease is most unusual for a lentivirus infection and differs markedly from that reported for BIV infection.