Seven new ovine progressive pneumonia virus (OPPV) field isolates from Dubois Idaho sheep comprise part of OPPV clade II based on surface envelope glycoprotein (SU) sequences

Genome-Wide Search for Host Association Factors during Ovine Progressive Pneumonia Virus Infection

Ovine progressive pneumonia virus (OPPV) is an important virus that causes serious diseases in sheep and goats with a prevalence of 36% in the USA. Although OPPV was discovered more than half of a century ago, little is known about the infection and pathogenesis of this virus. In this report, we used RNA-seq technology to conduct a genome-wide probe for cellular factors that are associated with OPPV infection. A total of approximately 22,000 goat host genes were detected of which 657 were found to have been significantly up-regulated and 889 down-regulated at 12 hours post-infection. In addition to previously known restriction factors from other viral infections, a number of factors which may be specific for OPPV infection were uncovered. The data from this RNA-seq study will be helpful in our understanding of OPPV infection, and also for further study in the prevention and intervention of this viral disease.

Small ruminant lentivirus genetic subgroups associate with sheep TMEM154 genotypes

Small ruminant lentiviruses (SRLVs) are prevalent in North American sheep and a major cause of production losses for the U.S. sheep industry. Sheep susceptibility to SRLV infection is influenced by genetic variation within the ovine transmembrane 154 gene (TMEM154). Animals with either of two distinct TMEM154 haplotypes that both encode glutamate at position 35 of the protein (E35) are at greater risk of SRLV infection than those homozygous with a lysine (K35) haplotype. Prior to this study, it was unknown if TMEM154 associations with infection are influenced by SRLV genetic subgroups. Accordingly, our goals were to characterize SRLVs naturally infecting sheep from a diverse U.S. Midwestern flock and test them for associations with TMEM154 E35K genotypes. Two regions of the SRLV genome were targeted for proviral amplification, cloning, sequence analysis, and association testing with TMEM154 E35K genotypes: gag and the transmembrane region of env. Independent analyses of gag and env sequences showed that they clustered in two subgroups (1 and 2), they were distinct from SRLV subtypes originating from Europe, and that subgroup 1 associated with hemizygous and homozygous TMEM154 K35 genotypes and subgroup 2 with hemi- and homozygous E35 genotypes (gag p < 0.001, env p = 0.01). These results indicate that SRLVs in the U.S. have adapted to infect sheep with specific TMEM154 E35K genotypes. Consequently, both host and SRLV genotypes affect the relative risk of SRLV infection in sheep.

Phylogenetic analysis of small ruminant lentiviruses in mixed flocks: multiple evidence of dual infection and natural transmission of types A2 and B1 between sheep and goats

Previous molecular analyses of small ruminant lentivirus (SRLV) populations in single species herds in Quebec, Canada, have revealed a relatively simple structure where goats and sheep appeared exclusively infected with B1 and A2 subtypes respectively. The present work aimed at extending these earlier findings with the analysis of SRLVs in mixed flocks. Molecular analyses revealed a more complex picture of SRLV population structure in mixed herds compared to single species herds. Notably, phylogenetic analyses of long gag sequences strongly support transmission of A2 subtype from sheep to goats as well as transmission of B1 subtype from goats to sheep. Hence, this work uncovered for the first time natural transmission between sheep and goats of North American subtype A2. In addition, multiple evidences of mixed infection of sheep and goats with A2 and B1 subtypes were found. The data reported in this study reinforces the concept of a genetic continuum of SRLVs where strains are exchanged between sheep and goats under favourable conditions and in the absence of specific species barriers. Most interestingly, this study suggests that dual infection, which is a hallmark of the lentivirus paradigm HIV, may not be such rare events in small ruminants but may simply be understudied and underreported. Overall, the present data shows that sheep and goats in Canada can be infected with both SRLV A and B types, sometimes simultaneously, and that mixed flocks may represent a breeding ground for their evolution.

Phylogenetic analysis of small ruminant lentiviruses detected in Slovenia

Small ruminant lentiviruses (SRLV), which belong to the Retroviridae family, infect goats and sheep worldwide. The aim of this study was to characterize the SRLV strains circulating in Slovenia, by phylogenetic analysis of two genomic regions, 1.8 kb gag-pol fragment and 1.2kb pol fragment. The results of our study revealed that Slovenian SRLV strains are highly heterogeneous, with ovine strains belonging to genotype A and caprine strains to genotypes A and B. The closest relatives of sheep virus sequences from two flocks that clustered together (SLO 35, 36) were found to be in subtype A5. A cluster composed of four sheep virus sequences (SLO 31) was clearly divergent from all other subtypes in group A and could not be assigned to any of them. The virus sequences from one goat flock belonged solely to subtype B1, whereas virus sequences from more than one genotype were found to circulate within the other two goat flocks, belonging to subtype B1 (SLO 1 and SLO 37) and to genotype A (SLO 2 and 78-88 g). Two goat virus sequences (SLO 2) were found to belong to genotype A and could not be assigned to existing subtypes. One goat virus sequence (37-88 g) from flock 37 was clearly different from other sequences of this flock and was more closely related to genotype A sequences. We propose two new subtypes within genotype A, subtype A14 (SLO 2) and A15 (SLO 31).

Non-maternal transmission is the major mode of ovine lentivirus transmission in a ewe flock: a molecular epidemiology study

Transmission of ovine progressive pneumonia virus (OPPV), a lentivirus of sheep, occurs through both maternal and non-maternal means. Currently, the contribution of each route to the overall flock OPPV prevalence is poorly understood since previous serological epidemiologic studies lacked the ability to accurately track routes of transmission within an infected flock. In this study, the amount of maternal OPP transmission was assessed in a naturally infected ewe flock by applying molecular analyses to proviral sequences derived from peripheral blood leukocytes of OPP positive dam-daughter pairs (N=40). Both proviral envelope (env) and long terminal repeat (LTR) sequences, separately and combined, were utilized in the following 2 sequence analysis methods: phylogenetic analysis and pairwise distance calculations. True maternal transmission events were defined as agreement in 2 out of the 2 sequence analysis methods. Using this criterion, proviral env sequences resulted in a 14.3% maternal transmission frequency, and proviral LTR sequences resulted in a 10% maternal transmission frequency. Both proportions of maternal transmission varied significantly from equality (P<0.0001). This indicates that the remaining 85.7-90% of daughters are infected via non-maternal transmission. This is also the first study to calculate the OPP proviral rate of change for the env gene and LTR promoter. Accurately defining the routes of OPPV transmission provides critical epidemiological data supporting management intended to reduce flock transmission and viral dose.

Ovine progressive pneumonia virus capsid antigen as found in CD163- and CD172a-positive alveolar macrophages of persistently infected sheep

In situ detection of ovine progressive pneumonia virus (OPPV) and the phenotypic identification of the cells that harbor OPPV have not been described for the OPPV-affected tissues, which include lung, mammary gland, synovial membranes of the carpal joint, and choroid plexus of the brain. In this study, the authors first developed a single enzyme-based automated immunohistochemical (IHC) analysis for detection of OPPV capsid antigen (CA) on OPPV-affected tissues, using 2 anti-CAEV CA monoclonal antibodies, 5A1 and 10A1, and 2 enzyme-based IHC systems. Out of 10 naturally and persistently OPPV-infected ewes, OPPV CA was detected in intercellular regions of the carpal synovial membrane of 1 ewe, in cells resembling alveolar macrophages and pulmonary interstitial macrophages in lung tissue of 3 ewes, and in mammary alveolar cells of 1 ewe. Furthermore, dual enzyme-based automated IHC analyses revealed that OPPV CA was predominantly detected in CD172a- or CD163-positive alveolar macrophages of the lungs and mammary gland. That anti-inflammatory (CD163) and downregulatory (CD172a) types of alveolar macrophage harbor OPPV CA leads to the possibility that during persistent infection with OPPV, the host alveolar macrophage might serve to limit inflammation while OPPV persists undetected by the host adaptive immune response in the lung and mammary gland.

Evaluation of a caprine arthritis-encephalitis virus/maedi-visna virus indirect enzyme-linked immunosorbent assay in the serological diagnosis of ovine progressive pneumonia virus in U.S. sheep

A caprine arthritis-encephalitis virus (CAEV)/maedi-visna virus (MVV) indirect enzyme-linked immunosorbent assay (iELISA) was validated with samples from U.S. sheep and by the use of radioimmunoprecipitation as the standard for comparison. The sensitivity and the specificity were 86.0% (+ or - 5.8%) and 95.9% (+ or - 2.9%), respectively. The iELISA format and phylogenetic differences based on the MVV gag sequence contribute to the reduced sensitivity.

Minimum intravenous infectious dose of ovine progressive pneumonia virus (OPPV)

The minimum intravenous infectious dose for ovine progressive pneumonia virus (OPPV) WLC1 was determined using twenty-four 6month-old lambs. Twelve groups of two 6month-old lambs were inoculated intravenously (i.v.) with tissue culture fluid containing ovine progressive pneumonia virus (OPPV) WLC1 titers ranging from 10(7.6) TCID(50)/lamb down to 10(-3.4) TCID(50)/lamb and were monitored for seroconversion using the OPPV agar gel immunodiffusion assay (AGID). Fifteen of the 16 lambs given equal or greater than 10(0.6) TCID(50) seroconverted, and virus could be isolated from peripheral blood leukocytes in 13 out of the 15 of these lambs. None of the eight lambs receiving less than 10(0.6) TCID(50) seroconverted during the 12months. The results of this study indicated that 10(0.6) or 4 TCID(50)/lamb given i.v. was capable of establishing infection.

Ovine progressive pneumonia provirus levels are unaffected by the prion 171R allele in an Idaho sheep flock

Selective breeding of sheep for arginine (R) at prion gene (PRNP) codon 171 confers resistance to classical scrapie. However, other effects of 171R selection are uncertain. Ovine progressive pneumonia/Maedi-Visna virus (OPPV) may infect up to 66% of a flock thus any affect of 171R selection on OPPV susceptibility or disease progression could have major impact on the sheep industry. Hypotheses that the PRNP 171R allele is 1) associated with the presence of OPPV provirus and 2) associated with higher provirus levels were tested in an Idaho ewe flock. OPPV provirus was found in 226 of 358 ewes by quantitative PCR. The frequency of ewes with detectable provirus did not differ significantly among the 171QQ, 171QR, and 171RR genotypes (p > 0.05). Also, OPPV provirus levels in infected ewes were not significantly different among codon 171 genotypes (p > 0.05). These results show that, in the flock examined, the presence of OPPV provirus and provirus levels are not related to the PRNP 171R allele. Therefore, a genetic approach to scrapie control is not expected to increase or decrease the number of OPPV infected sheep or the progression of disease. This study provides further support to the adoption of PRNP 171R selection as a scrapie control measure.

Field evaluation of a gag/env heteroduplex mobility assay for genetic subtyping of small-ruminant lentiviruses

Small-ruminant lentiviruses (SRLVs) display a high genetic diversity and are currently classified into five genotypes and an increasing number of subtypes. The co-circulation of subtypes in restricted geographical regions, combined with the occurrence of cross-species infection, suggests the need for development of a large-scale screening methodology for rapid monitoring of the prevalence of the various genetic subtypes and their genetic evolution. Here, a heteroduplex mobility assay (HMA) was developed for the rapid identification of group B subtypes. The assay was validated for both the p14 nucleocapsid-coding region of the gag gene and the V1-V2 region of the env gene using a panel of reference standards and was applied to the genetic subtyping of SRLV field isolates from five mixed flocks in France. Subtyping of 75 blood samples using the env HMA revealed a preferential distribution of subtypes B1 and B2 in sheep and goats, despite direct evidence for interspecies transmission of both subtypes. Adding the gag HMA to the env HMA provided evidence for dual infection and putative recombination between subtypes B1 and B2 in five goats, and between groups A and B in one sheep. Phylogenetic analysis revealed that 100 % (23/23) and 96.7 % (30/31) of samples were correctly classified using the gag and env HMAs, respectively. These results indicate that dual infection and recombination may be a significant source of new variation in SRLV and provide a useful tool for the rapid genetic subtyping of SRLV isolates, which could be relevant for the development of more accurate diagnosis of prevalent SRLV strains in different countries.

Development and validation of an ovine progressive pneumonia virus quantitative PCR

Ovine progressive pneumonia virus (OPPV) infects at least one sheep in 81% of U.S. sheep flocks, as determined by serology, and can cause viral mastitis, arthritis, dyspnea, and cachexia. Diagnostic tests that quantify OPPV proviral load in peripheral blood leukocytes (PBL) provide an additional method for identification of infected sheep and may help to further understanding of the pathogenesis of OPPV-induced disease. In this study, we compared a new OPPV real-time quantitative PCR (qPCR) assay specific for the transmembrane region of the envelope gene (tm) with a competitive inhibition enzyme-linked immunosorbent assay (cELISA) using 396 PBL samples and sera from Idaho sheep. The OPPV qPCR had a positive concordance of 96.2% +/- 2.3% and a negative concordance of 97.7% +/- 2.5% compared to the cELISA, with a kappa value of 0.93, indicating excellent agreement between the two tests. In addition, the presence of tm in the three OPPV qPCR-positive and cELISA-negative sheep and in 15 sheep with different OPPV proviral loads was confirmed by cloning and sequencing. These data indicate that the OPPV qPCR may be used as a supplemental diagnostic tool for OPPV infection and for measurement of viral load in PBLs of infected sheep.

Evidence of proviral clearance following postpartum transmission of an ovine lentivirus

Lentiviral transmission by transfer of infected colostrum and/or milk is considered to be highly efficient. In this study, postpartum transmission of ovine progressive pneumonia virus (OPPV) from 10 naturally infected ewes to their 23 lambs was followed from the perinatal period throughout a four-year period. The lambs were allowed to suckle from their dam from birth through 32 weeks of age. Virus was tracked by virus isolation, quantitative PCR (qPCR), and anti-OPPV antibody responses as measured by cELISA. Cell-associated OPPV was isolated from colostrum/milk cells in 7 out of 10 ewes and provirus envelope (env) loads ranged 8 to 10(5) copies/mug DNA in colostrum/milk cells from the 10 ewes using qPCR. Provirus env loads were also detected in the peripheral circulation of 21 lambs at 8 weeks and two lambs at 22 weeks. The qPCR product at 8 weeks was confirmed as the transmembrane (tm) gene of OPPV by cloning and sequencing. Both cELISA titers ranging from 325 to 3125 and cross-neutralizing antibody titers ranging from 6 to 162 to seven different OPPV strains were found in the colostrum of the 10 ewes. Furthermore, cELISA titers in serum from lambs remained detectable through 32 weeks following the clearance of provirus at 24 weeks. After 32 weeks, both provirus and anti-OPPV antibody responses have subsequently remained undetectable through 4 years of age. These data suggest the clearance of cell-associated lentiviruses from lamb circulation after passive transfer of antibody via colostrum.

Ovine progressive pneumonia virus capsid is B-cell immunodominant using Western blot analysis: A comparison of sensitivity between Western blot analysis and immunoprecipitation

A Western blot assay was developed and analyzed against the comparable standard, immunoprecipitation of (35)[S]-methionine/cysteine-labeled ovine progressive pneumonia virus (OPPV) proteins, for its ability to detect anti-OPPV antibodies using endpoint titers. Western blot analysis is 12-fold more sensitive in detecting endpoint anti-capsid antibody titers than IP, and the capsid is the B-cell immunodominant OPPV protein when utilizing Western blot analysis. Since the surface envelope glycoprotein is the B-cell immunodominant OPPV protein when utilizing immunoprecipitation, this suggests immunoprecipitation and Western blot analysis measure different types of antibody that are more specific for conformational and linear OPPV protein epitopes, respectively.

Distribution and heterogeneity of small ruminant lentivirus envelope subtypes in naturally infected French sheep

Small ruminants lentiviruses (SRLV) nucleotide sequences spanning the V1V2 variable regions of the env gene were amplified by nested-PCR from 38 blood samples collected from 16 naturally infected sheep flocks in France. For the rapid SRLV group determination of field isolates, the PCR-amplified fragments were subjected to a SRLV-adapted heteroduplex mobility assay (HMA). All viral sequences were clearly assignable to the SRLV group B by HMA analysis. Twenty-seven SRLV isolates were selected for DNA sequence analysis. In each case, nucleotide comparison and phylogenetic analyses confirmed the genetic relationships inferred by HMA. Six SRLV isolates belonged to subtype B1, and 21 pertained to subtype B2, one flock being infected with both subtypes. Subtypes B1 and B2 were found with different frequencies and geographic spread, but exhibited similar genetic diversities. These results give a more complete picture of the distribution and heterogeneity of SRLV env subtypes in sheep and confirmed that multiple interspecies transmission occurred in the past. Furthermore, HMA appeared to be a rapid and reliable method to differentiate caprine arthritis encephalitis virus from maedi-visna virus.

Molecular evolution analysis and geographic investigation of severe acute respiratory syndrome coronavirus-like virus in palm civets at an animal market and on farms

Massive numbers of palm civets were culled to remove sources for the reemergence of severe acute respiratory syndrome (SARS) in Guangdong Province, China, in January 2004, following SARS coronavirus detection in market animals. The virus was identified in all 91 palm civets and 15 raccoon dogs of animal market origin sampled prior to culling, but not in 1,107 palm civets later sampled at 25 farms, spread over 12 provinces, which were claimed to be the source of traded animals. Twenty-seven novel signature variation residues (SNVs) were identified on the spike gene and were analyzed for their phylogenetic relationships, based on 17 sequences obtained from animals in our study and from other published studies. Analysis indicated that the virus in palm civets at the live-animal market had evolved to infect humans. The evolutionary starting point was a prototype group consisting of three viral sequences of animal origin. Initially, seven SNV sites caused six amino acid changes, at positions 147, 228, 240, 479, 821, and 1080 of the spike protein, to generate low-pathogenicity viruses. One of these was linked to the first SARS patient in the 2003-2004 period. A further 14 SNVs caused 11 amino acid residue changes, at positions 360, 462, 472, 480, 487, 609, 613, 665, 743, 765, and 1163. The resulting high-pathogenicity groups were responsible for infections during the so-called early-phase epidemic of 2003. Finally, the remaining six SNVs caused four amino acid changes, at positions 227, 244, 344, and 778, which resulted in the group of viruses responsible for the global epidemic.