Detection of serum antibodies to ovine progressive pneumonia virus in sheep by using a caprine arthritis-encephalitis virus competitive-inhibition enzyme-linked immunosorbent assay

Serological, Molecular and Culture-Based Diagnosis of Lentiviral Infections in Small Ruminants

Small ruminant lentiviruses (SRLVs) infections lead to chronic diseases and remarkable economic losses undermining health and welfare of animals and the sustainability of farms. Early and definite diagnosis of SRLVs infections is the cornerstone for any control and eradication efforts; however, a "gold standard" test and/or diagnostic protocols with extensive applicability have yet to be developed. The main challenges preventing the development of a universally accepted diagnostic tool with sufficient sensitivity, specificity, and accuracy to be integrated in SRLVs control programs are the genetic variability of SRLVs associated with mutations, recombination, and cross-species transmission and the peculiarities of small ruminants' humoral immune response regarding late seroconversion, as well as intermittent and epitope-specific antibody production. The objectives of this review paper were to summarize the available serological and molecular assays for the diagnosis of SRLVs, to highlight their diagnostic performance emphasizing on advantages and drawbacks of their application, and to discuss current and future perspectives, challenges, limitations and impacts regarding the development of reliable and efficient tools for the diagnosis of SRLVs infections.

Diagnostic accuracy of three commercial immunoenzymatic assays for small ruminant lentivirus infection in goats performed on individual milk samples

Caprine arthritis-encephalitis (CAE) caused by small ruminant lentivirus (SRLV) infection is one of the most widespread and devastating diseases of goats. Serological methods, mainly immunoenzymatic assays (ELISA), are the mainstay of CAE diagnostics. Even though blood is still the most commonly tested material, animal welfare issues and increasing costs of veterinary service prompt the development of serological methods based on milk testing. Several different types of ELISAs for CAE are available on the market. All of them perform well on serum, however their diagnostic accuracy for testing milk has not been so far compared. Therefore, we carried out the study in 5 dairy goat herds in Poland whose previous epidemiological situation regarding CAE was known. Paired serum and milk samples were collected from all adult females (n = 420) and tested with 3 commercial ELISAs - indirect ELISA based on the whole-virus antigen (wELISA), indirect ELISA based on the recombined transmembrane and capsid protein (TM/CA-ELISA), and competitive ELISA based on the surface glycoprotein (SU-ELISA). Milk was tested as lactoserum at dilution of 1/2 in wELISA and TM/CA-ELISA, and undiluted in SU-ELISA. The true status of goats was based on the composite reference standard comprising the results of all three ELISAs done on serum and the true prevalence of SRLV infection in the herd of origin. 243 (57.9 %) goats were classified as truly positive and 177 (42.1 %) goats as truly negative. Diagnostic accuracy was evaluated using the area under the ROC curve (AUROC) as well as sensitivity (Se) and specificity (Sp) for a range of cut-off values. AUROC was 98.8 % (CI 95 %: 97.5 %, 100 %) for wELISA, 97.9 % (CI 95 %: 96.5 %, 99.2 %) for TM/CA-ELISA, and 91.7 % (CI 95 %: 88.9 %, 94.5 %) for SU-ELISA. At the cut-off values recommended by the manufacturers both indirect ELISAs were highly sensitive (89.3 % and 91.4 %, respectively) and highly specific (98.3 % and 95.5 %, respectively), whereas SU-ELISA had only moderate Se (71.2 %) at comparably high Sp (96.6 %). Nevertheless, the optimal cut-off values were lower than those recommended by manufacturers for serum - sample-to-positive control serum ratio (S/P%) of 10 % for wELISA, S/P% of 80 % for TM/CA-ELISA, and percentage inhibition of 23 % for SU-ELISA. Concluding, the study shows that wELISA and TM/CA-ELISA may be interchangeably used for testing individual goat milk samples for SRLV infection. Diagnostic sensitivity and specificity of these ELISAs appear not to be lower on milk than on serum. SU-ELISA is considerably less sensitive on milk samples than indirect ELISAs.

Serotyping versus genotyping in infected sheep and goats with small ruminant lentiviruses

Despite SRLV infection being endemic in Mexico, there is little information regarding which genotypes are present. We compared serotyping and PCR-sequencing results from sheep and goats infected with SRLV. We separated plasma and peripheral blood leukocytes (PBL) from 1940 blood samples from sheep and goats from 12 states across Mexico. To detect SRLV infection, we tested plasma samples using two commercial ELISA kits (VMRD and Eradikit SRLV Screening). Then, we serotyped the infecting virus (A/ B) using Eradikit SRLV Genotyping. PBL DNA was used to detect the proviral genome via PCR. Positive amplicons were sequenced to identify viral genotypes using a phylogenetic analysis. Also, we analysed for residues differences in the sequences of a capsid epitope between genotypes. The serological results indicated a higher detection of seropositive animals using the VMRD ELISA compared to Eradikit, with 21 % and 15.3 % more in sheep and goats respectively. Only 25.7 % of the ELISA serotyping results matched those from PCR-sequencing. PCR-sequencing was able to identify genotype A, B and coinfections in animals classified as indeterminate by the ELISA test. This lack of sensitivity may be related to the lack of epitopes from the matrix and transmembrane peptides used by ELISA screening. Sequences analysis revealed that SRLVs found in sheep cluster with genetic subtypes A2 and B1, while those in goats cluster with subtypes A1 and B1. Serotyping did not prove to be an adequate method for predicting the viral genotype (A and / or B) in infections caused by SRLV.

Prevalence of Maedi-visna in Saskatchewan sheep

A study was conducted to estimate flock and individual seroprevalence of Maedi-visna in Saskatchewan and evaluate risk factors for seropositive flocks. Thirty-five percent (24/68) of flocks and 4.6% (93/2010) of individual samples were positive. Within-flock prevalence ranged from 3.3% to 96.7%. Significant flock-level predictors of flock prevalence included large flock size, purchasing > 50 sheep and respiratory problems in the previous 5 years.

Incidence of infection in 39-month-old ewes with TMEM154 diplotypes "1 1," "1 3," and "3 3" after natural exposure to ovine progressive pneumonia virus

Production and well-being of sheep and goats in many countries are harmfully impacted by small ruminant lentiviruses (SRLV) that cause incurable, progressive diseases. Susceptibility to ovine progressive pneumonia virus (OPPV), the North American form of SRLV, is influenced by variants of the ovine transmembrane protein 154 gene (TMEM154). The experimental objective was to estimate additive and dominance effects of TMEM154 haplotypes 1 and 3 on susceptibility of breeding ewes to infection after natural exposure to OPPV from birth to 39 mo of age. Sires and dams were heterozygous for TMEM154 haplotypes 1 and 3, producing ewe lambs with diplotypes "1 1," "1 3," and "3 3." These lambs were raised by mature, infected dams to ensure natural, maternal exposure to OPPV. Ewe lambs (n = 108) were kept for breeding and joined an infected flock of ewes to guarantee natural, nonmaternal exposure to OPPV. Ewes were bred to lamb at 1, 2, and 3 yr of age. Serum samples were collected at breeding, 1 mo before lambing and shortly after weaning each year to monitor infection status to 39 mo of age. During the experiment, 9 of the 108 ewes died while uninfected and data collected on these ewes were not analyzed. Infection status of the remaining 99 ewes at 39 mo of age was analyzed using logistic regression procedures. Effects of ewe type of birth, ewe type of rearing, and breed type of dam were not detected (P > 0.10), and the estimated sire variance component was nil. Ewe diplotype affected infection status (P < 0.0001), as did additive (P < 0.0001) and dominance (P < 0.0022) effects. Predicted probabilities of infection for ewes with diplotypes "1 1," "1 3," and "3 3" were 0.10, 0.88, and 0.89, respectively, and confidence intervals for diplotypes "1 3" and "3 3" were distinct from "1 1." Haplotype 3 was completely dominant to haplotype 1 at 39 mo of age. The probability of infection for ewes with either diplotype "1 3" or "3 3" averaged 8.5 times that of ewes with diplotype "1 1." Diplotype "1 3" and "3 3" ewes were highly susceptible to nonmaternal transmission of OPPV, in contrast to diplotype "1 1" ewes. Therefore, the distribution of ewes with diplotypes "1 1," "1 3," and "3 3" within a flock will influence the number of infections caused by each route of transmission. Selection and mating strategies can be implemented to produce sheep that are genetically less susceptible to OPPV infection.

The placenta shed from goats with classical scrapie is infectious to goat kids and lambs

The placenta of domestic sheep plays a key role in horizontal transmission of classical scrapie. Domestic goats are frequently raised with sheep and are susceptible to classical scrapie, yet potential routes of transmission from goats to sheep are not fully defined. Sparse accumulation of disease-associated prion protein in cotyledons casts doubt about the role of the goat's placenta. Thus, relevant to mixed-herd management and scrapie-eradication efforts worldwide, we determined if the goat's placenta contains prions orally infectious to goat kids and lambs. A pooled cotyledon homogenate, prepared from the shed placenta of a goat with naturally acquired classical scrapie disease, was used to orally inoculate scrapie-naïve prion genotype-matched goat kids and scrapie-susceptible lambs raised separately in a scrapie-free environment. Transmission was detected in all four goats and in two of four sheep, which importantly identifies the goat's placenta as a risk for horizontal transmission to sheep and other goats.

Epizootic pneumonia of bighorn sheep following experimental exposure to Mycoplasma ovipneumoniae

Background

Bronchopneumonia is a population limiting disease of bighorn sheep (Ovis canadensis). The cause of this disease has been a subject of debate. Leukotoxin expressing Mannheimia haemolytica and Bibersteinia trehalosi produce acute pneumonia after experimental challenge but are infrequently isolated from animals in natural outbreaks. Mycoplasma ovipneumoniae, epidemiologically implicated in naturally occurring outbreaks, has received little experimental evaluation as a primary agent of bighorn sheep pneumonia.

Methodology/Principal Findings

In two experiments, bighorn sheep housed in multiple pens 7.6 to 12 m apart were exposed to M. ovipneumoniae by introduction of a single infected or challenged animal to a single pen. Respiratory disease was monitored by observation of clinical signs and confirmed by necropsy. Bacterial involvement in the pneumonic lungs was evaluated by conventional aerobic bacteriology and by culture-independent methods. In both experiments the challenge strain of M. ovipneumoniae was transmitted to all animals both within and between pens and all infected bighorn sheep developed bronchopneumonia. In six bighorn sheep in which the disease was allowed to run its course, three died with bronchopneumonia 34, 65, and 109 days after M. ovipneumoniae introduction. Diverse bacterial populations, predominantly including multiple obligate anaerobic species, were present in pneumonic lung tissues at necropsy.

Conclusions/Significance

Exposure to a single M. ovipneumoniae infected animal resulted in transmission of infection to all bighorn sheep both within the pen and in adjacent pens, and all infected sheep developed bronchopneumonia. The epidemiologic, pathologic and microbiologic findings in these experimental animals resembled those seen in naturally occurring pneumonia outbreaks in free ranging bighorn sheep.

Advances in diagnosis of respiratory diseases of small ruminants

Irrespective of aetiology, infectious respiratory diseases of sheep and goats contribute to 5.6 percent of the total diseases of small ruminants. These infectious respiratory disorders are divided into two groups: the diseases of upper respiratory tract, namely, nasal myiasis and enzootic nasal tumors, and diseases of lower respiratory tract, namely, peste des petits ruminants (PPR), parainfluenza, Pasteurellosis, Ovine progressive pneumonia, mycoplasmosis, caprine arthritis encephalitis virus, caseous lymphadenitis, verminous pneumonia, and many others. Depending upon aetiology, many of them are acute and fatal in nature. Early, rapid, and specific diagnosis of such diseases holds great importance to reduce the losses. The advanced enzyme-linked immunosorbent assays (ELISAs) for the detection of antigen as well as antibodies directly from the samples and molecular diagnostic assays along with microsatellites comprehensively assist in diagnosis as well as treatment and epidemiological studies. The present review discusses the advancements made in the diagnosis of common infectious respiratory diseases of sheep and goats. It would update the knowledge and help in adapting and implementing appropriate, timely, and confirmatory diagnostic procedures. Moreover, it would assist in designing appropriate prevention protocols and devising suitable control strategies to overcome respiratory diseases and alleviate the economic losses.

Effects of TMEM154 haplotypes 1 and 3 on susceptibility to ovine progressive pneumonia virus following natural exposure in sheep

Small ruminant lentiviruses (SRLV) adversely affect production and well-being of sheep and goats throughout much of the world. The SRLV, including ovine progressive pneumonia virus (OPPV) in North America, cause lifetime infections, and management procedures to eradicate or reduce disease prevalence are costly. Variants of ovine transmembrane protein 154 gene (TMEM154) affect susceptibility to OPPV. The primary experimental objective was to estimate additive and dominance effects of TMEM154 haplotypes 1 and 3 on susceptibility to OPPV infection following natural exposure. A group of 187 trial lambs was born and raised by mature, infected ewes to ensure natural exposure to OPPV. Parents of trial lambs were heterozygous for haplotypes 1 and 3, producing lambs with diplotypes "1 1," "1 3," and "3 3." A group of 20 sentinel lambs was born and raised by mature, uninfected ewes that were diplotype "1 1." Sentinel lambs had diplotypes "1 1" and "1 3," being sired by the same set of rams as trial lambs. Trial and sentinel lambs were comingled during the experiment. Lambs were weaned at 60 d of age, bled 1 wk after weaning, and thereafter at intervals of 4 or 5 wk until 9 mo of age when OPPV infection status was determined by use of a competitive enzyme-linked immunosorbent assay. Only 1 sentinel lamb became infected. Infection status of trial lambs was analyzed using logistic regression procedures to account for the binary nature of infection status and random effects of sires. Effects of sex, type of birth, type of rearing, age of dam, breed type of dam, and sires were not detected (P>0.20). Infection status was affected by diplotype of lamb (P=0.005), with additive (P=0.002) and dominance (P=0.052) effects identified. Predicted probabilities of infection for lambs with diplotypes "1 1," "1 3," and "3 3" were 0.094, 0.323, and 0.346, respectively. Confidence intervals for probabilities of infection for diplotypes "1 3" and "3 3" were similar, but distinct from diplotype "1 1." These results are consistent with complete dominance of haplotype 3 relative to haplotype 1. The probability of infection at 9 mo of age for lambs with either diplotype "1 3" or "3 3" averaged 3.56 times that of lambs with diplotype "1 1." Genetic susceptibility to OPPV infection can be reduced by selection to increase the frequency of haplotype 1, resulting in a greater proportion of lambs with diplotype "1 1."

A polytropic caprine arthritis encephalitis virus promoter isolated from multiple tissues from a sheep with multisystemic lentivirus-associated inflammatory disease

Caprine arthritis encephalitis virus (CAEV) is a lentivirus that infects both goats and sheep and is closely related to maedi-visna virus that infects sheep; collectively, these viruses are known as small ruminant lentiviruses (SRLV). Infection of goats and sheep with SRLV typically results in discrete inflammatory diseases which include arthritis, mastitis, pneumonia or encephalomyelitis. SRLV-infected animals concurrently demonstrating lentivirus-associated lesions in tissues of lung, mammary gland, joint synovium and the central nervous system are either very rare or have not been reported. Here we describe a novel CAEV promoter isolated from a sheep with multisystemic lentivirus-associated inflammatory disease including interstitial pneumonia, mastitis, polyarthritis and leukomyelitis. A single, novel SRLV promoter was cloned and sequenced from five different anatomical locations (brain stem, spinal cord, lung, mammary gland and carpal joint synovium), all of which demonstrated lesions characteristic of lentivirus associated inflammation. This SRLV promoter isolate was found to be closely related to CAEV promoters isolated from goats in northern California and other parts of the world. The promoter was denoted CAEV-ovine-MS (multisystemic disease); the stability of the transcription factor binding sites within the U3 promoter sequence are discussed.

Small ruminant lentiviruses: genetic variability, tropism and diagnosis

Small ruminant lentiviruses (SRLV) cause a multisystemic chronic disease affecting animal production and welfare. SRLV infections are spread across the world with the exception of Iceland. Success in controlling SRLV spread depends largely on the use of appropriate diagnostic tools, but the existence of a high genetic/antigenic variability among these viruses, the fluctuant levels of antibody against them and the low viral loads found in infected individuals hamper the diagnostic efficacy. SRLV have a marked in vivo tropism towards the monocyte/macrophage lineage and attempts have been made to identify the genome regions involved in tropism, with two main candidates, the LTR and env gene, since LTR contains primer binding sites for viral replication and the env-encoded protein (SU ENV), which mediates the binding of the virus to the host’s cell and has hypervariable regions to escape the humoral immune response. Once inside the host cell, innate immunity may interfere with SRLV replication, but the virus develops counteraction mechanisms to escape, multiply and survive, creating a quasi-species and undergoing compartmentalization events. So far, the mechanisms of organ tropism involved in the development of different disease forms (neurological, arthritic, pulmonary and mammary) are unknown, but different alternatives are proposed. This is an overview of the current state of knowledge on SRLV genetic variability and its implications in tropism as well as in the development of alternative diagnostic assays.

Genome-wide association identifies multiple genomic regions associated with susceptibility to and control of ovine lentivirus

BACKGROUND

Like human immunodeficiency virus (HIV), ovine lentivirus (OvLV) is macrophage-tropic and causes lifelong infection. OvLV infects one quarter of U.S. sheep and induces pneumonia and body condition wasting. There is no vaccine to prevent OvLV infection and no cost-effective treatment for infected animals. However, breed differences in prevalence and proviral concentration have indicated a genetic basis for susceptibility to OvLV. A recent study identified TMEM154 variants in OvLV susceptibility. The objective here was to identify additional loci associated with odds and/or control of OvLV infection.

METHODOLOGY/PRINCIPAL FINDINGS

This genome-wide association study (GWAS) included 964 sheep from Rambouillet, Polypay, and Columbia breeds with serological status and proviral concentration phenotypes. Analytic models accounted for breed and age, as well as genotype. This approach identified TMEM154 (nominal P=9.2×10(-7); empirical P=0.13), provided 12 additional genomic regions associated with odds of infection, and provided 13 regions associated with control of infection (all nominal P<1 × 10(-5)). Rapid decline of linkage disequilibrium with distance suggested many regions included few genes each. Genes in regions associated with odds of infection included DPPA2/DPPA4 (empirical P=0.006), and SYTL3 (P=0.051). Genes in regions associated with control of infection included a zinc finger cluster (ZNF192, ZSCAN16, ZNF389, and ZNF165; P=0.001), C19orf42/TMEM38A (P=0.047), and DLGAP1 (P=0.092).

CONCLUSIONS/SIGNIFICANCE

These associations provide targets for mutation discovery in sheep susceptibility to OvLV. Aside from TMEM154, these genes have not been associated previously with lentiviral infection in any species, to our knowledge. Further, data from other species suggest functional hypotheses for future testing of these genes in OvLV and other lentiviral infections. Specifically, SYTL3 binds and may regulate RAB27A, which is required for enveloped virus assembly of human cytomegalovirus. Zinc finger transcription factors have been associated with positive selection for repression of retroviral replication. DLGAP1 binds and may regulate DLG1, a known regulator of HIV infectivity.

Reduced lentivirus susceptibility in sheep with TMEM154 mutations

Visna/Maedi, or ovine progressive pneumonia (OPP) as it is known in the United States, is an incurable slow-acting disease of sheep caused by persistent lentivirus infection. This disease affects multiple tissues, including those of the respiratory and central nervous systems. Our aim was to identify ovine genetic risk factors for lentivirus infection. Sixty-nine matched pairs of infected cases and uninfected controls were identified among 736 naturally exposed sheep older than five years of age. These pairs were used in a genome-wide association study with 50,614 markers. A single SNP was identified in the ovine transmembrane protein (TMEM154) that exceeded genome-wide significance (unadjusted p-value 3×10⁻⁹). Sanger sequencing of the ovine TMEM154 coding region identified six missense and two frameshift deletion mutations in the predicted signal peptide and extracellular domain. Two TMEM154 haplotypes encoding glutamate (E) at position 35 were associated with infection while a third haplotype with lysine (K) at position 35 was not. Haplotypes encoding full-length E35 isoforms were analyzed together as genetic risk factors in a multi-breed, matched case-control design, with 61 pairs of 4-year-old ewes. The odds of infection for ewes with one copy of a full-length TMEM154 E35 allele were 28 times greater than the odds for those without (p-value<0.0001, 95% CI 5–1,100). In a combined analysis of nine cohorts with 2,705 sheep from Nebraska, Idaho, and Iowa, the relative risk of infection was 2.85 times greater for sheep with a full-length TMEM154 E35 allele (p-value<0.0001, 95% CI 2.36–3.43). Although rare, some sheep were homozygous for TMEM154 deletion mutations and remained uninfected despite a lifetime of significant exposure. Together, these findings indicate that TMEM154 may play a central role in ovine lentivirus infection and removing sheep with the most susceptible genotypes may help eradicate OPP and protect flocks from reinfection.

Ovine lentivirus targets the host immune system and causes persistent retroviral infections affecting millions of sheep worldwide. In primates, lentivirus resistance is attributed to mutant virus coreceptors that are not expressed. In sheep, some animals are resistant to lentivirus infection despite repeated exposure; however, the mechanism of resistance is unknown. We designed a genome-wide association study to test whether sheep might have genetic variation that protects against lentivirus infection. Our results showed that variation in an ovine gene (TMEM154) was associated with infection. Sheep with the ancestral type of this gene were nearly three times more likely to become infected than those with mutant forms. We also discovered two mutant forms predicted to abolish the protein's function. Although the biological function of TMEM154 is unknown, our results indicate that it plays an important role in lentivirus infection in sheep. Producing sheep with the least susceptible form of TMEM154 may help eradicate the ovine disease caused by lentivirus.

Diagnostic assays used to control small ruminant lentiviruses

The serologic diagnostic tests, such as the agar gel immunodiffusion assay and various types of enzyme-linked immunosorbent assays (ELISAs), have contributed to the reduction of small ruminant lentivirus (SRLV) infections worldwide. Because there are no treatments or efficacious vaccines, the serologic diagnostic tests have supported most of the eradication efforts by testing and removal or separation of adult animals that generate antibodies to SRLVs. With the advent of molecular diagnostics, standard and quantitative polymerase chain reaction (PCR)-based assays for the detection of provirus in peripheral blood cells are becoming more common and aid in the detection of infected goats and sheep before antibody detection by ELISA in some animals. Performance of the serologic and molecular diagnostic tests is dependent upon a number of factors, including the format of the assay, the percentage of identity between the viral nucleotide sequences in a flock or herd of a certain geographic region and the sequences used to generate SRLV test reagents, and the intrinsic pathogenesis or amount of provirus and SRLV antibody generated in a species or individual small ruminant. In addition, small ruminant genomics may help with establishing genetic markers of SRLV infection and disease, which could also aid eradication or reduction of SRLVs from herds and flocks throughout the world.

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.

Herd risk factors associated with sero-prevalence of Maedi-Visna in the Manitoba sheep population

Disease associated with Maedi-Visna infection results in substantial economic losses in affected sheep producing areas of the world. A survey was conducted to estimate herd and individual seroprevalence in the province of Manitoba and evaluate risk factors for seropositive herds. Of 2207 sheep sampled from 77 selected sheep flocks, the animal level seroprevalence was 2.47% and herd level seroprevalence was 25.10%. The herd-level factors of presence of clinical skin disease, herd size of > 70, history of musculoskeletal/lameness abnormalities, and the purchase of new stock (> 50) in the last 1 to 5 y, showed significant associations with seropositive herd status. The study documented a remarkable stability of low seroprevalence in the province over a 20-year period in the absence of a systematic disease control program.

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.

Peripheral ovine progressive pneumonia provirus levels correlate with and predict histological tissue lesion severity in naturally infected sheep

Studies were undertaken to determine whether anti-ovine progressive pneumonia virus (OPPV) antibody responses in serum or OPP provirus levels in peripheral blood associate with the degree of histologically measured tissue lesions in naturally OPPV-infected sheep. Sections of formalin-fixed, paraffin-embedded, and hematoxylin- and eosin-stained lung, mammary gland, carpal synovial membrane, and brain tissues from 11 OPPV-infected ewes (mean age of 8.6 years) and 5 OPPV-uninfected ewes (mean age of 6 years) were evaluated for lesion severity. Ovine progressive pneumonia (OPP) provirus levels and anti-OPPV antibody titers in peripheral blood and serum samples, respectively, were measured upon euthanasia and 3 years prior to euthanasia. Both mean peripheral OPP provirus levels and mean serum anti-surface envelope glycoprotein (anti-SU) antibody titers at the time of euthanasia were significantly higher in ewes with moderate to severe histological lesions than in ewes with no to mild histological lesions. However, although mean peripheral blood OPP provirus levels at euthanasia and 3 years prior to euthanasia significantly correlated with the highest histological lesion score for any affected tissue (two-tailed P values, 0.03 and 0.02), mean serum anti-SU antibody titers, anti-capsid antibody titers, and anti-transmembrane 90 antibody titers at euthanasia did not show a significant correlation with the highest histological lesion score for any tissue (two-tailed P values, 0.32, 0.97, and 0.18, respectively). These data are the first to show that OPP provirus levels predict and correlate with the extent of OPPV-related histological lesions in various OPPV-affected tissues. These findings suggest that peripheral OPP provirus levels quantitatively contribute more to the development of histological lesions than the systemic anti-SU antibody host immune response.

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.

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.

Analysis of the antibody response to an immunodominant epitope of the envelope glycoprotein of a lentivirus and its diagnostic potential

The envelope glycoprotein of small ruminant lentiviruses (SRLV) is a major target of the humoral immune response and contains several linear B-cell epitopes. We amplified and sequenced the genomic segment encoding the SU5 antigenic site of the envelope glycoprotein of several SRLV field isolates. With synthetic peptides based on the deduced amino acid sequences of SU5 in an enzyme-linked immunosorbent assay (ELISA), we have (i) proved the immunodominance of this region regardless of its high variability, (ii) defined the epitopes encompassed by SU5, (iii) illustrated the rapid and peculiar kinetics of seroconversion to this antigenic site, and (iv) shown the rapid and strong maturation of the avidity of the anti-SU5 antibody. Finally, we demonstrated the modular diagnostic potential of SU5 peptides. Under Swiss field conditions, the SU5 ELISA was shown to detect the majority of infected animals and, when applied in a molecular epidemiological context, to permit rapid phylogenetic classification of the infecting virus.

Surface envelope glycoprotein is B-lymphocyte immunodominant in sheep naturally infected with ovine progressive pneumonia virus

The B-lymphocyte-immunodominant antigen involved in naturally ovine progressive pneumonia virus (OPPV)-infected mature sheep remains unknown. Therefore, the amount of antibody in sera from 10 naturally OPPV-infected sheep was evaluated by immunoprecipitation (IP) of the major viral proteins in [(35)S]methionine/cysteine-labeled OPPV (whole virus) lysate. Using an excess of OPPV proteins in whole-virus lysate, 8 out of 10 sheep had the highest serum antibody IP endpoint titers to the gp135 surface envelope glycoprotein (SU). Also, 2 out of 10 sheep had equivalent serum antibody IP endpoint titers to the transmembrane glycoprotein oligomer (TM90) and SU. Since these data indicate that SU is the immunodominant protein in most mature sheep persistently infected with OPPV, SU-specific diagnostic serological assays can be utilized for OPPV diagnosis.