Genomic heterogeneity of small ruminant lentiviruses detected by PCR

Genetic Characterization of Small Ruminant Lentiviruses Isolated from Dairy Sheep in Greece

The high genetic heterogeneity of small ruminant lentiviruses (SRLV) renders the genetic characterization of the circulating strains crucial for the epidemiological investigation and the designation of effective diagnostic tools. In Greece, research data regarding the genetic diversity of the circulating SRLV strains is scarce, hindering the implementation of efficient surveillance and control programs. The objective of the study was to genetically characterize SRLV strains isolated from intensive dairy sheep farms in Greece and evaluate the variability of the immunodominant regions of the capsid protein. For this reason, a total of 12 SRLV-infected animals from four intensive dairy sheep farms with purebred Chios and Lacaune ewes were used for the amplification and sequencing of an 800 bp gag-pol fragment. The phylogenetic analyses revealed a breed-related circulation of strains; Chios ewes were infected with strains belonging exclusively to a separate group of genotype A, whereas strains belonging to subtype B2 were isolated from Lacaune ewes. Immunodominant epitopes of capsid protein were quite conserved among the strains of the same genotype, except for the Major Homology Region which showed some unique mutations with potential effects on viral evolution. The present study contributes to the extension of the current knowledge regarding the genetic diversity of SRLV strains circulating in sheep in Greece. However, broader genetic characterization studies are warranted for the exploration of possible recombinant events and the more comprehensive classification of the circulating strains.

First molecular detection of Maedi-Visna virus in Awassi sheep of Middle Iraq regions

Respiratory viral infections cause significant economic losses in sheep production. This preliminary molecular study aimed to detect the Maedi-Visna virus infection in Awassi sheep in three governorates in the middle region of Iraq. The presence of one or more of the specific four genes (gag, pol, env and LTR) were considered as positive result. A total of 210 blood samples of Awassi sheep were collected for the purpose of the project. The molecular prevalence of Maedi-Visna virus in sheep was 12.85% (27/210). As a result, Maedi-Visna virus was observed in sheep with chronic respiratory system disease with non-significant difference between governorates and between primers percentage (P>0.05). Sequencing studies strongly suggested that Maedi-Visna virus originated in Iraq. This is the first study describing Iraqi Maedi-Visna virus sequences with molecular characterisation of gag, pol, env and LTR genes, suggesting that Maedi-Visna virus originated in Iraq.

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.

Replication of Small Ruminant Lentiviruses in Aluminum Hydroxide-Induced Granulomas in Sheep: a Potential New Factor for Viral Dissemination

Aluminum (Al)-based salts are widely used adjuvants in ruminants and other species to strengthen the immune response elicited against vaccine antigen(s). However, they can lead to the formation of long-lasting granulomas composed of abundant activated macrophages. Small ruminant lentiviruses (SRLV) are widely distributed macrophage-tropic retroviruses that cause persistent infections in sheep and goats. Infected monocytes/macrophages and dendritic cells establish an inflammatory microenvironment that eventually leads to clinical manifestations. The aim of this work was to study the effect of Al-induced granulomas in the replication and pathogenesis of SRLV. Eleven adult, naturally SRLV-infected sheep showing clinical arthritis were distributed in vaccine (n = 6), adjuvant-only (n = 3), and control (n = 2) groups and inoculated with commercial Al-based vaccines, Al hydroxide adjuvant alone, or phosphate-buffered saline, respectively. In vitro studies demonstrated viral replication in Al-induced granulomas in 5 out of 10 sheep. Immunohistochemistry (IHC) evinced granular, intracytoplasmic SRLV presence in macrophages within granulomas. Viral sequences obtained from granulomas, blood monocytes, and other tissues were highly similar in most animals, suggesting virus circulation among body compartments. However, notable differences between isolated strains in granulomas and other tissues in specific animals were also noted. Interestingly, the B2 subtype was the most commonly found SRLV genotype, reaching a wider body distribution than previously described. Recombination events between genotypes B2 and A3 along the gag region were identified in two sheep. Our results indicate that Al-hydroxide-derived granulomas may represent an ideal compartment for SRLV replication, perhaps altering natural SRLV infection by providing a new, suitable target tissue.IMPORTANCE Granulomas are inflammation-derived structures elicited by foreign bodies or certain infections. Aluminum adjuvants included in vaccines induce granulomas in many species. In sheep, these are persistent and consist of activated macrophages. Small ruminant lentiviruses (SRLV), which are macrophage-tropic lentiviruses, cause a chronic wasting disease affecting animal welfare and production. Here, we studied the occurrence of SRLV in postvaccination granulomas retrieved from naturally infected ewes after vaccination or inoculation with aluminum only. SRLV infection was confirmed in granulomas by identification of viral proteins, genomic fragments, and enzymatic activity. The infecting SRLV strain, previously found exclusively in carpal joints, reached the central nervous system, suggesting that occurrence of SRLV in postvaccination granulomas may broaden tissue tropism. SRLV recombination was detected in inoculated animals, a rare event in sheep lentiviruses. Potentially, virus-host interactions within granulomas may modify viral pathogenesis and lead to more widespread infection.

Multi-Platform Detection of Small Ruminant Lentivirus Antibodies and Provirus as Biomarkers of Production Losses

Small ruminant lentiviruses (SRLVs) are endemic in most areas of Europe, causing a chronic infection and a multisystemic disease affecting the udder, carpal joints, lungs, and central nervous system. Due to the lack of treatments and protective vaccination strategies, infection control is focused on the identification of infected animals through serological or molecular techniques. However, antigenic and genetic heterogeneity of SRLVs represent a clear drawback for diagnosis. Infected animals may present lower animal production parameters such as birth weight or milk production and quality, depending on productive systems considered and, likely, to the diagnostic method applied. In this study, four sheep flocks dedicated to dairy or meat production were evaluated using three different ELISA and two PCR strategies to classify animal population according to SRLV infection status. Productive parameters were recorded along one whole lactation or reproductive period and compared between positive and negative animals. SRLV was present in 19% of the total population, being unequally distributed in the different flocks. Less than half of the infected animals were detected by a single diagnostic method, highlighting the importance of combining different diagnostic techniques. Statistical analysis employing animal classification using all the diagnostic methods associated lambing size, lamb weight at birth, and daily weight gain with SRLV infection status in meat flocks. Milk production, somatic cell count, fat, and protein content in the milk were associated with SRLV infection in dairy flocks, to a greater extent in the flock showing higher seroprevalence. A multi-platform SRLV diagnostic strategy was useful for ensuring correct animal classification, thus validating downstream studies investigating production traits.

A highly sensitive semi-nested real-time PCR utilizing oligospermine-conjugated degenerate primers for the detection of diverse strains of small ruminant lentiviruses

Small ruminant lentiviruses (SRLVs) are highly diverse retroviruses infecting sheep and goats. Although PCR-based testing is being utilized for diagnostics, its application is hampered by various factors. These include, among others, the exceptionally high genetic variability of SRLVs, as well as the low number of infected blood monocytes. For this reason, a highly sensitive and specific semi-nested real-time PCR for proviral DNA detection and quantification was developed. The method is innovative in that a) its design is based on selecting the preferred codon usage in the targeted conserved genomic regions and b) oligospermine-conjugated degenerate primers with increased Tm were utilized. Modifications permitted primer/template duplex formation in the cases of mismatches due to sporadic nucleotide polymorphisms in a number of variant SRLV strains and consequently, the detection of highly diverse SRLV strains. The potential loss of analytical sensitivity and specificity was counterbalanced by including a semi-nested step in combination with LNA probes. An in silico procedure for the evaluation of hybridization efficiency of the designed oligonucleotides to all known targeted variants was also implemented. The method presents a linear range of quantification over a 3-log₁₀ range and a limit of detection of 3.9 proviral dsDNA copies per reaction. Its diagnostic performance was evaluated by testing field samples from seropositive and seronegative animals, followed by phylogenetic analysis of the strains detected. To further increase the diagnostic sensitivity, a DNA extraction protocol for blood leukocytes was developed and evaluated. A minimum of 500 ng input DNA is recommended for PCR-based detection of SRLV proviral DNA, given the low numbers of infected blood monocytes. The developed methodology may serve as a useful tool, which can be adjusted for the quantitative detection of viruses exhibiting high genetic variability.

Duplex nested-PCR for detection of small ruminant lentiviruses

Small ruminant lentiviruses (SRLV) have high genetic variability which results in different viral strains around the world. This create a challenge to design sensible primers for molecular diagnosis in different regions. This work proposes a protocol of duplex nested-PCR for the precise diagnosis of SRLV. The technique was designed and tested with the control strains CAEV Co and MVV 1514. Then, field strains were submitted to the same protocol of duplex nested-PCR. Blood samples of sheep and goats were tested with AGID and nested PCR with specific primers for pol, gag and LTR. The AGID results showed low detection capacity of positive animals, while the nested PCR demonstrated a greater capacity of virus detection. Results demonstrated that LTR-PCR was more efficient in detecting positive sheep samples, whereas gag-PCR allowed a good detection of samples of positive goats and positive sheep. In addition, pol-PCR was more efficient with goat samples than for sheep. Duplex nested PCR performed with standard virus samples and field strains demonstrated that the technique is more efficient for the detection of multiple pro-viral DNA sequences. This study demonstrated a successful duplex nested PCR assay allowing a more accurate diagnosis of SRLV.

Pathology and polymerase chain reaction detection of ovine progressive pneumonia (maedi) cases in slaughtered sheep in India

Aim

The small ruminant lentiviruses are known to cause maedi-visna (MV) and caprine arthritis - encephalitis in sheep and goats, typically affecting joints, udder, lungs, and the central nervous system. The diagnosis usually involves serology, clinical signs, immunohistochemistry, and polymerase chain reaction (PCR). In the present study, the histopathologically positive pneumonia cases of MV were confirmed by PCR in lung tissue probably for the first time in India.

Materials and Methods

A total of 888 lungs of adult sheep, aged between 2 and 5 years, were screened during slaughter, of which 121 were found to have pneumonic lesions. The tissues from each pneumonic lung including associated lymph nodes were collected in 10% neutral buffered formalin for histopathology. The frozen tissues of the same were also collected and stored at -20°C for PCR confirmation.

Results

Three of 121 cases of pneumonic lungs of sheep revealed gross and histopathological lesions suggestive of maedi or ovine progressive pneumonia infection. These 3 cases were further confirmed by PCR technique that amplified 291-base pair DNA in the long terminal repeat sequence of MV provirus.

Conclusion

This study suggests the low occurrence of MV virus (MVV) infection in India in naturally affected sheep based on pathomorphological lesions and using the molecular tool of PCR detection of the virus in tissues. Further, a combination of pathomorphology or/and PCR testing might be optimal for detecting the animals infected with MVV.

Post-entry blockade of small ruminant lentiviruses by wild ruminants

Small ruminant lentivirus (SRLV) infection causes losses in the small ruminant industry due to reduced animal production and increased replacement rates. Infection of wild ruminants in close contact with infected domestic animals has been proposed to play a role in SRLV epidemiology, but studies are limited and mostly involve hybrids between wild and domestic animals. In this study, SRLV seropositive red deer, roe deer and mouflon were detected through modified ELISA tests, but virus was not successfully amplified using a set of different PCRs. Apparent restriction of SRLV infection in cervids was not related to the presence of neutralizing antibodies. In vitro cultured skin fibroblastic cells from red deer and fallow deer were permissive to the SRLV entry and integration, but produced low quantities of virus. SRLV got rapidly adapted in vitro to blood-derived macrophages and skin fibroblastic cells from red deer but not from fallow deer. Thus, although direct detection of virus was not successfully achieved in vivo, these findings show the potential susceptibility of wild ruminants to SRLV infection in the case of red deer and, on the other hand, an in vivo SRLV restriction in fallow deer. Altogether these results may highlight the importance of surveilling and controlling SRLV infection in domestic as well as in wild ruminants sharing pasture areas, and may provide new natural tools to control SRLV spread in sheep and goats.

Identification and characterization of an emerging small ruminant lentivirus circulating recombinant form (CRF)

The molecular epidemiology of small ruminant lentiviruses (SRLVs) is constantly changing due to animal movements, cross species transmission and because of their rapid evolutionary rate. This study reports a comprehensive genetic and phylogenetic analysis based on consensus gag and pol sequences covering 3kb of the SRLV genome from small ruminants in Québec, Canada. A group of strains obtained from goats originating from different flocks, segregated in a unique clade distinct from currently known SRLV groups. Genetic dissection of the gag gene from these strains revealed that it originated as a result of a recombination event between parental strains currently circulating in small ruminants of the country. Following HIV nomenclature, we propose to call this group of strains, circulating recombinant form 1 SRLV, or CRF01_AB SRLV. In addition, the study confirms the existence of genetically distinct and homogeneous populations of SRLVs infecting sheep and goats housed in single species flocks.

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.

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.

Maedi in slaughtered sheep: a pathology and polymerase chain reaction study in southwestern Iran

Maedi-visna (MV) is an important slow viral disease of sheep leading to a progressive lymphoproliferative disease. It affects multiple organs primarily the lungs, where it causes interstitial pneumonia (maedi). In this study, the lungs of 1,000 sheep carcasses were grossly inspected and those suspected to have maedi were studied at histopathological and molecular levels. A polymerase chain reaction (PCR) technique that amplified a 291-base pair DNA in the long terminal repeat (LTR) sequence of MV provirus was conducted on all the 50 suspected lungs together with 10 normal appearing lungs as controls. Amplicons of the expected size were detected in 11 (n=11/50) suspected sheep, and one of the 10 control sheep. Histopathologic study of the pulmonary lesions of all 11 (n=11/11) positive sheep showed MV lesions, including hyperplasia of the perivascular and peribronchiolar lymphoid cells, interstitial lymphoplasmacytic infiltration and smooth muscle hyperplasia and the histopathologic findings were correlated with PCR results. In contrast, the tissue sections of control animals were almost normal at histopathological level; however, PCR technique demonstrated that one of them was affected by maedi. This study showed that the LTR-PCR had high specificity and sensitivity in diagnosis of this viral infection. This study is the first to evaluate the prevalence of MV virus infection in sheep in Iran.

Molecular characterization and phylogenetic analysis of small ruminant lentiviruses isolated from Canadian sheep and goats

Background

Small Ruminant Lentiviruses (SRLV) are widespread in Canadian sheep and goats and represent an important health issue in these animals. There is however no data about the genetic diversity of Caprine Arthritis Encephalitis Virus (CAEV) or Maedi Visna Virus (MVV) in this country.

Findings

We performed a molecular and phylogenetic analysis of sheep and goat lentiviruses from a small geographic area in Canada using long sequences from the gag region of 30 infected sheep and 36 infected goats originating from 14 different flocks. Pairwise DNA distance and phylogenetic analyses revealed that all SRLV sequences obtained from sheep clustered tightly with prototypical Maedi visna sequences from America. Similarly, all SRLV strains obtained from goats clustered tightly with prototypical US CAEV-Cork strain.

Conclusions

The data reported in this study suggests that Canadian and US SRLV strains share common origins. In addition, the molecular data failed to bring to light any evidence of past cross species transmission between sheep and goats, which is consistent with the type of farming practiced in this part of the country where single species flocks predominate and where opportunities of cross species transmissions are proportionately low.

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.

Antibody-based diagnosis of small ruminant lentivirus infection in seminal fluid

Antibody-based diagnosis of small ruminant lentiviruses (SRLVs) has been efficiently achieved using serum and milk, but not semen, for which polymerase chain reaction (PCR) has been proposed as a confirmatory technique. This work, involving 296 ovine (Ovis aries) and caprine (Capra hircus) semen donors, investigates whether seminal fluid (SF) can be reliably used in antibody-based SRLV diagnosis. First, a gold standard was established to assess the infection status and determine the sensitivity and specificity of three commercial enzyme-linked immunosorbent assays (ELISAs) in serum testing using Western blot and PCR as confirmatory tests. For SF testing, both gold standard and serum testing results were used as reference. The performance of SF testing was affected not only by the ELISA assay sensitivity (related to antigen spectrum) compared with that of the gold standard (as it occurred in serum testing) but also by SF sample quality and SF working dilution. Nonturbid SF samples, commonly collected in artificial insemination centers (AICs), were required. Compared with serum, SF testing had a decreased sensitivity in two of the ELISA assays (with original serum working dilutions <or=1/20 in serum testing) but reached a similar sensitivity (and specificity) in the assay designed to work at the highest serum dilution (1/500). A SF concentration of about 1/2 (250-fold that used in serum testing) was found optimal in this assay, yielding highly repeatable results that were in almost perfect agreement with those of serum testing (kappa +/- SE, 0.91 +/- 0.81). Thus, SF ELISA can be reliably applied in antibody-based SRLV diagnosis. This information may be useful to control infection in AICs and animal and semen trade programs requiring health-certified quality of semen donors.

Phylogenetic analysis of SRLV sequences from an arthritic sheep outbreak demonstrates the introduction of CAEV-like viruses among Spanish sheep

Small ruminant lentiviruses (SRLVs) cause different clinical forms of disease in sheep and goats. So far in Spain, Maedi visna virus-like (MVV-like) sequences have been found in both species, and the arthritic SRLV disease has never been found in sheep until a recent outbreak. Knowing that arthritis is common in goats, it was of interest to determine if the genetic type of the virus involved in the sheep arthritis outbreak was caprine arthritis encephalitis virus-like (CAEV-like) rather than MVV-like. Alignment and phylogenetic analyses on nucleotide and deduced amino acid sequences from SRLV of this outbreak, allowed a B2 genetic subgroup assignment of these SRLV, compatible with a correspondence between the virus genetic type and the disease form. Furthermore, an isolate was obtained from the arthritic outbreak, its full genome was CAEV-like but the pol integrase region was MVV-like. Although its LTR lacked a U3 repeat sequence and had a deletion in the R region, which has been proposed to reduce viral replication rate, its phenotype in sheep skin fibroblast cultures was rapid/high, thus it appeared to have adapted to sheep cells. This outbreak study represents the first report on CAEV-like genetic findings and complete genome analysis among Spanish small ruminants.

Genome analysis of small-ruminant lentivirus genotype E: a caprine lentivirus with natural deletions of the dUTPase subunit, vpr-like accessory gene, and 70-base-pair repeat of the U3 region

The nucleotide sequence of the highly divergent small-ruminant lentivirus genotype E has been determined. The full genome consists of 8,418 nucleotides and lacks two large portions corresponding nearly to the entire dUTPase subunit of the pol and vpr-like accessory genes. Moreover, the 70-bp repeat of the U3 region of the long terminal repeat was observed to be deleted. Interestingly, this lentivirus genotype is able to persist in a local breed population, and retrospective analysis revealed its presence in milk samples collected in 1999. gag sequences obtained from a flock coinfected with the B1 and E genotypes revealed that the evolutionary rates of the two viruses were quite similar. Since a reduced viral load and/or disease progression was observed for viruses with artificially deleted dUTPase and vpr-like genes, it is proposed that this viral cluster be designated a low-pathogenicity caprine lentivirus.

Evaluation of five enzyme-linked immunosorbent assays and an agar gel immunodiffusion test for detection of antibodies to small ruminant lentiviruses

In the framework of the Dutch control program for small ruminant lentiviral (SRLV) infections, too many drawbacks were encountered with respect to serological testing. To improve the quality of testing, five enzyme-linked immunosorbent assays (ELISAs) and an agar gel immunodiffusion test (AGIDT) were evaluated. The focus was on the sensitivity, specificity, and variances of the commercially available tests. Clear differences were found among the tests in analytical and diagnostic sensitivity and overall diagnostic performance, whereas no significant differences in specificity were found. For serodiagnosis of sheep with clinical symptoms of maedi-visna virus (MVV) (histopathologically confirmed), one ELISA was significantly more sensitive than the other ELISAs and than the AGIDT, while for asymptomatic sheep originating from infected flocks, three ELISAs and the AGIDT demonstrated similar performance. The diagnostic performance appeared to be related to animal species and virus infection (MVV or caprine arthritis encephalitis virus [CAEV]) as well as the phase of infection/progression of disease. Receiver operating characteristic analysis, demonstrating the diagnostic potential of tests irrespective of defined cutoffs, again revealed clear differences between tests with respect to diagnostic performance for detection of antibodies against CAEV or MVV. An indirect ELISA, of which the solid phase is sensitized with a combination of the core protein p27 of MVV produced in Escherichia coli and a peptide derived from the transmembrane protein gp46, appeared to be the test of choice for serodiagnosis of SRLV infections in sheep and goats.

Molecular characterization of lentiviruses from goats from Poland based on gag gene sequence analysis

Caprine arthritis-encephalitis virus (CAEV) infection in goats is worldwide but with higher prevalence in industrialized countries. While positive serology of CAEV in Polish goats was reported there was no genetic study of this virus. In this study, we described the molecular characterization of lentiviruses isolated from seropositive goats from Poland. We cloned and sequenced a fragment from the gag gene covering part of the coding sequences for the matrix (MA) p17 and for the capsid (CA) p25 proteins. Resulting nucleotide sequences were aligned with those from other ovine/caprine lentivirus isolates. We present data showing that the sequences of most goat lentivirus isolates are closer to the prototypic CAEV-Co isolate, nevertheless from one goat we isolated a virus that is closer to the sheep Maedi Visna virus (MVV) isolate. This might indicate a recent cross-species infection from sheep to goat.

Development of a semi-nested PCR using degenerate primers for the generic detection of small ruminant lentivirus proviral DNA

A PCR assay was developed for the reliable detection of small ruminant lentivirus (SRLV) proviral DNA. The method involved the use of degenerate deoxyinosine-substituted primers and a second semi-nested PCR step that increased the polyvalency and sensitivity of the detection, respectively. Primers were designed from the pol gene conserved motifs of 85 SRLV isolates and were evaluated using different SRLV isolates together with Maedi-Visna virus (MVV) and caprine arthritis-encephalitis virus (CAEV) reference strains. The method successfully detected SRLV proviral DNA in total DNA extracts originating from whole blood samples, separated peripheral blood mononuclear cells (PBMCs) and tissue cultures. The semi-nested PCR was compared with the agar gel immunodiffusion test and proved to be highly sensitive, specific and capable of detecting many SRLV variants in infected or suspect animals. Therefore, it would be useful in the diagnosis of natural SRLV infections, in eradication programs and epidemiological studies. Whole blood samples can be used directly, thus alleviating the need for PBMC separation, and thereby enables a simple, fast and cost-effective analysis of a large number of samples.

Phylogenetic analysis of the gag region encoding the matrix protein of small ruminant lentiviruses: Comparative analysis and molecular epidemiological applications

Little sequence information exists on the matrix-protein (MA) encoding region of small ruminant lentiviruses (SRLV). Fifty-two novel sequences were established and permitted a first phylogenetic analysis of this region of the SRLV genome. The variability of the MA encoding region is higher compared to the gag region encoding the capsid protein and surprisingly close to that reported for the env gene. In contrast to primate lentiviruses, the deduced amino acid sequences of the N- and C-terminal domains of MA are variable. This permitted to pinpoint a basic domain in the N-terminal domain that is conserved in all lentiviruses and likely to play an important functional role. Additionally, a seven amino acid insertion was detected in all MVV strains, which may be used to differentiate CAEV and MVV isolates. A molecular epidemiology analysis based on these sequences indicates that the Italian lentivirus strains are closely related to each other and to the CAEV-CO strain, a prototypic strain isolated three decades ago in the US. This suggests a common origin of the SRLV circulating in the monitored flocks, possibly related to the introduction of infected goats in a negative population. Finally, this study shows that the MA region is suitable for phylogenetic studies and may be applied to monitor SRLV eradication programs.

Genetic and antigenic characterization of the matrix protein of two genetically distinct ovine lentiviruses

Small Ruminant Lentiviruses (SRLV) are a group of non-oncogenic retroviruses including Maedi-Visna virus (MVV) and Caprine Arthritis-Encephalitis virus (CAEV), which cause a chronic, multisystemic disease in sheep and goats, respectively. Phylogenetic analyses of SRLV are based in most cases on partial pol sequences. Several reports indicate that the species specificity of these viruses is not as strict as previously thought; MVV-like viruses have been found in goat populations and vice versa. Recently, the sequencing of some Italian ovine isolates has shown the presence of a new cluster more similar to classical caprine isolates (CAEV-like). Few data are available on the variability of structural proteins involved in the antibody response of infected animals. In this study, the gag gene of two genetically distinct ovine isolates, namely the MVV-like It-561 and the CAEV-like It-Pi1, was sequenced and the epitopes of matrix protein (MA) were mapped. Recombinant MAs and their subunits from both ovine aforementioned strains were tested against a panel of sheep and goat sera. Reactive epitopes were found in all three subunits of MA, although the central subunit displayed a more consistent reactivity. Epitope mapping of this subunit demonstrated that the amino acid sequence of at least one immunodominant epitope was quite different in the two strains. This antigenic variability may affect the sensitivity of a single strain-based immunoassay and suggests that both SRLV genotypes should be used in the development of future diagnostic tests, to avoid viral strain selection during the eradication programmes.

Diagnostic tests for small ruminant lentiviruses

Maedi visna virus and caprine arthritis encephalitis virus are closely related retroviruses that cause chronic inflammatory disease in small ruminants. The infections are characterised by insidious onset and slow progression. Diagnosis of infection is usually by serological testing. A variety of assays are available for this purpose, though the relative sensitivity and specificity of these assays has not been compared systematically. Here we review recent developments in laboratory diagnostic methods and their use in field diagnosis. The results suggest that a combination of ELISA and PCR might afford optimal detection of SRLV infection.

Vírus da artrite encefalite caprina: isolamento e caracterização de parte do gene gag

Amostras de sangue de 12 animais soropositivos pelo teste de imunodifusão em gel de agarose e que não apresentavam sinais clínicos sugestivos de infecção pelo vírus da artrite-encefalite caprina (CAEV) foram coletadas para isolamento viral. Mácrofagos derivados de monócitos foram co-cultivados com células de membrana sinovial caprina (MSC), resultando em cinco amostras que apresentaram efeito citopático característico do tipo persistente, semelhante ao observado para o CAEV. Uma técnica de reação em cadeia de polimerase (PCR) foi padronizada para amplificar parte do gene gag do genoma pró-viral, codificante para a proteína do capsídeo viral (p25). As cinco amostras foram amplificadas pela PCR e três delas, BR-UFMG/PL1, BR-UFMG/PL2 e BR-UFMG/PL3, foram seqüenciadas diretamente dos seus produtos de PCR. O alinhamento múltiplo das seqüências obtidas com outras de lentivírus de pequenos ruminantes (LVPR), obtidas no GenBank, e o dendrograma revelaram que as novas amostras de CAEV são únicas e distintas das demais amostras de LVPR, possuindo maior identidade de nucleotídeos e aminoácidos entre si e com as amostras de CAEV do que com a do vírus maedi-visna.

Phylogenetic analysis and reclassification of caprine and ovine lentiviruses based on 104 new isolates: evidence for regular sheep-to-goat transmission and worldwide propagation through livestock trade

We performed a phylogenetic analysis of caprine and ovine lentiviruses using long sequences in gag and pol of 104 new Swiss isolates and six available corresponding database sequences. Forty-five isolates, forming five sequence clusters, were unclassifiable by the present classification. Pairwise DNA distance analysis indicated different categories of relatedness, requiring a new classification system. We propose four principal sequence groups, A-D, which differ by 25-37%. Groups A and B are further divided into subtypes which differ by 15-27%. Group D and four of the seven group A subtypes, A3, A4, A5 and A7, are formed by new Swiss isolates. Molecular epidemiology revealed that Swiss B1 strains differed no more from French, Brazilian or US strains than from each other, suggesting virus propagation through international livestock trade. Furthermore, infection of goats by subtypes A3 or A4 was significantly associated with documented contact with sheep, which also harbor these subtypes, thus indicating regularly occurring sheep-to-goat transmission.

Detecção da infecção pelo vírus da artrite-encefalite caprina: imunodifusão em ágar e reação em cadeia da polimerase com "primers" degenerados

O objetivo deste trabalho foi analisar amostras de soro e de células sangüíneas de caprinos para detecção de anticorpos e DNA proviral do vírus da artrite-encefalite caprina (CAEV), respectivamente. Utilizou-se a técnica de imunodifusão em ágar (AGID) e a reação em cadeia da polimerase (PCR) com "primers" degenerados. Foram analisadas amostras de diferentes procedências: 39 de Mato Grosso do Sul (MS), 19 de São Paulo (SP) e 22 do Ceará (CE), dessas últimas, 12 oriundas de animais importados do Canadá. Os resultados de AGID e PCR foram discordantes, pois o primeiro permitiu a detecção de 25 animais soropositivos, enquanto a PCR detectou DNA proviral de CAEV em 16 amostras. Pela PCR foi possível identificar animais infectados cujos testes sorológicos foram negativos pelo AGID: oito amostras do MS e um do CE. São discutidos diferentes aspectos que poderiam estar envolvidos na discordância dos resultados.

Lentivírus de pequenos ruminantes (CAEV e Maedi-Visna): revisão e perspectivas

Os lentivírus de pequenos ruminantes (SRLV), cujos protótipos são os vírus da Artrite-Encefalite Caprina (CAEV) e Maedi-Visna, são patógenos amplamente distribuidos, os quais causam doenças degenerativas progressivas lentas em caprinos e ovinos, determinando importantes perdas econômicas. Estes vírus causam infecções persistentes com período de incubação longo e causam inflamatórias e degenerativas. As lesões são induzidas em tecidos específicos do hospedeiro como articulações, pulmões, CNS e glandulas mamárias devido à replicação viral em células da linhagem monocítico-fagocitária que são as principais células-alvo. A infecção ocorre principalmente durante os primeiros meses de vida, através da ingestão de vírus no leite ou colostro de cabras ou ovelhas infectadas. A indução da resposta imunológica é variável e não protege contra a infecção. O diagnóstico é baseado primariamente na detecção de anticorpos para SRLV, geralmente por imunodifusão em gel de agar (AGID) e enzyme linked immunosorbent assay (ELISA). O diagnóstico e separação ou descarte dos animais soropositivos associado ao uso de certas práticas de manejo, especialmente das crias, são os principais meios implementados para prevenir a disseminação de SRLV, uma vez que ainda não existe vacina contra o vírus. As estratégias adotadas pelos SRLV para enfrentar o sistema imune dificultam o diagnóstico da infecção, controle ou prevenção da disseminação de SRLV. Esta revisão apresenta alguns aspectos das lentivíroses de pequenos ruminantes baseadas em estudos filogenéticos de amostras isoladas, aspectos clínicos e imunopatológicos.

Tryptophan 95, an amino acid residue of the Caprine arthritis encephalitis virus vif protein which is essential for virus replication

The Caprine arthritis encephalitis virus (CAEV) vif gene was demonstrated to be essential for efficient virus replication. CAEV Vif deletion mutants demonstrated an attenuated replication phenotype in primary goat cell cultures and resulted in abortive infection when inoculated into goats. In this study, we determined the in vitro replication phenotype of five CAEV Vif point mutant infectious molecular clones and the ability of the corresponding in vitro translated Vif proteins to interact with the CAEV Pr55(gag) in the glutathione S--transferase (GST) binding assay. Here we show that (i) three of the mutants (S170E, S170G, S197G) behaved as the wild-type CAEV according to virus replication and Vif--Gag interactions; (ii) one mutant (Vif 6mut) was replication incompetent and bound weakly to GST-Gag fusion proteins; and (iii) one mutant (Vif RG) was impaired for replication while retaining its interaction properties. This mutant points out the critical importance of the CAEV Vif tryptophan residue at position 95 for efficient virus replication, defining for this lentivirus a functional domain unrelated to the Gag binding region.

Variability and immunogenicity of caprine arthritis-encephalitis virus surface glycoprotein

The complete surface glycoprotein (SU) nucleotide sequences of three French isolates of caprine arthritis-encephalitis virus (CAEV) were determined and compared with those of previously described isolates: three American isolates and one French isolate. Phylogenetic analyses revealed the existence of four distinct and roughly equidistant evolutionary CAEV subtypes. Four conserved and five variable domains were identified in the SU. The fine specificities of antibodies produced against these domains during natural infection were examined using a pepscan analysis. Nine immunogenic segments were delineated throughout the conserved and variable domains of SU, two of them corresponding to conserved immunodominant epitopes. Antigenic determinants which may be involved in the immunopathogenic process induced by CAEV were identified. These results also provide sensitive and specific antigen peptides for the serological detection and differentiation of CAEV and visna/maedi virus infections.

The detection of proviral DNA by semi-nested polymerase chain reaction and phylogenetic analysis of Czech Maedi-Visna isolates based on gag gene sequences

A semi-nested polymerase chain reaction (snPCR) for detecting proviral DNA of ovine lentivirus (OvLV) in peripheral blood mononuclear cells was developed. Primers for snPCR were situated within the gag gene of the Maedi-Visna virus (MVV) genome. A comparison between the snPCR and serological tests (agar gel immunodiffusion test, immunoblot) were performed using 98 ovine blood samples. Thirty (30.6%) of the 98 sheep examined had antibodies specific for the MVV. PCR showed 21 of them to be positive and nine seropositive animals to be PCR negative. Six of the 68 serologically negative sheep were found to be PCR positive, probably due to delayed seroconversion. The PCR amplification products of these six sheep were sequenced and subjected to phylogenetic analysis. The resulting phylogenetic tree of partial gag gene sequences confirmed that the ovine lentivirus genotype in the Czech Republic is more closely related to the prototype MVV isolates than to the caprine arthritis encephalitis viruses.

Caracterização molecular parcial do gene gag de amostras do vírus da artrite-encefalite caprina (CAEV) isoladas de animais naturalmente infectados no Rio Grande do Sul, Brasil

Realizou-se a análise de parte do gene gag, que codifica para as proteínas do capsídeo viral, de 5 amostras de CAEV isolados de animais naturalmente infectados do Rio Grande do Sul, Brasil. As amostras foram analisadas por PCR e clivagem com enzimas de restrição (DdeI, HaeIII e NdeI). Fragmentos de aproximadamente 600 pb foram amplificados na PCR e submetidos à digestão enzimática. Os perfis obtidos foram comparados com as seqüências gag de 6 lentivírus de pequenos ruminantes.Os resultados obtidos permitiram separar as amostras em 3 grupos distintos. Os fragmentos observados foram diferentes dos descritos previamente.

North American and French caprine arthritis-encephalitis viruses emerge from ovine maedi-visna viruses

The full extent of genetic diversity among small ruminant lentiviruses (SRLVs), i.e., caprine arthritis encephalitis viruses (CAEVs) and maedi-visna viruses (MVVs), remains unknown. This is due in part to the fact that few sequences of CAEV are available. To contribute to this knowledge, gag, pol, and env nucleotide sequences from an SRLV named CA680 originating from a goat from western France were determined. This analysis revealed that this virus is closely related to the Cork and 63 CAEV American isolates. Mismatched amino acids between the CA680 virus and prototype CAEVs ranged from 6.7, 0. 7, and 17.5% for gag, pol, and SU sequences, respectively. The differences between the CA680 virus and MVV prototypes ranged from 16.5, 12.5, and 32.3% for the protein sequences, respectively. A screening using a heteroduplex mobility assay (HMA) adapted to SRLVs revealed that 6 of 10 caprine virus field isolates were closely related to CA680, indicating that this latter isolate was a prototype of CAEVs common in the west of France. Phylogenetic trees drawn using CA, RT, or SU sequences of numerous SRLVs and rooted with EIAV sequences revealed that CA680 and CAEV prototypes, all infectious for goat, clustered in one group. From these HMA and phylogenetic analyses, it appears that U.S. and French caprine SRLVs form a clade that had emerged from a much more diverse group containing all SRLVs infectious for sheep. These ovine SRLVs form a more ancient group in which the EIAV is rooted.

Detection of animal pathogens by using the polymerase chain reaction (PCR)

The polymerase chain reaction (PCR) is a nucleic acid-based technique that enables the rapid and sensitive detection of specific micro-organisms. Although this technique is widely used in veterinary research, it has not yet found applications in routine microbiological analysis of veterinary clinical samples. However, advances in sample preparation together with the increasing availability of specific gene sequences will probably lead to the more widespread diagnostic use of PCR in the future. PCR is likely to have a strong impact in the epidemiology, treatment and prevention of animal infectious diseases.

Immunohistochemical identification of caprine arthritis-encephalitis virus in paraffin-embedded specimens from naturally infected goats

The expression of caprine arthritis-encephalitis virus capsid protein was studied in seropositive naturally infected asymptomatic goals (10< seropositive naturally infected encephalitic kids (12) and goats (4), and noninfected control goats (3). Rabbit antiserum to recombinant viral capsid and matrix proteins were used in a biotin-streptavidin-alkaline phosphatase complex immunohistochemical method on sections of formalin- and ethanol-fixed tissue specimens. Macrophages in inflamed areas of the lung (8/12), in the brain (5/16), and in the spinal cord (4/16) from encephalitic animals harbored viral antigens, as revealed by immunohistochemistry and use of a capsid protein-specific antiserum. Altogether 12/16 encephalitic animals tested positive for viral antigen. Viral antigens were found in 5/10 seropositive asymptomatic goals in macrophages located in the lung (3), the udder (1), and the medulla of lymph nodes (4). None of the control animals tested positive for viral antigen. Ethanol fixation showed highest sensitivity, and the lowest antigen concentration that revealed a positive signal discernible from background was twofold higher in ethanol-fixed specimens than in formalin-fixed specimens. The evaluation was performed on artificial antigen substrates embedded with defined concentrations of recombinant viral capsid protein. Immunohistochemistry is a valuable supplement to the methods presently available for diagnosis in cases suspicious of caprine arthritis-encephalitis.

Genome analysis of North American small ruminant lentiviruses by polymerase chain reaction and restriction enzyme analysis

The polymerase chain reaction (PCR) was used to amplify portions of the gag and env structural genes of 8 ovine and 1 caprine lentivirus isolates of North American origin. Three sets of primers were used to amplify p16, p25, and N'-gp40 gene fragments, and 1 set, annealing highly conserved portions of long terminal repeat (LTR) among small ruminant lentiviruses, was used as a positive control. Variable PCR amplification efficiency was observed. Different stringency conditions of hybridization with specific DNA probes were used to maximize detection of the PCR product. The p25 primers detected all strains, the gp40 primers detected 1 ovine and the caprine strain, and the p16 primers detected only 1 ovine isolate. All strains were detected by LTR primers. Restriction endonuclease analysis of 5 amplified p25 and 2 N'-gp40 gene fragments revealed extensive heterogeneity among these North American small ruminant lentiviruses.

Double-nested polymerase chain reaction for detection of caprine arthritis-encephalitis virus proviral DNA in blood, milk, and tissues of infected goats

A nested polymerase chain reaction (PCR) for detecting proviral DNA of caprine arthritis-encephalitis virus (CAEV) in biological samples was developed. Primers for both gag and pol sequences of the CAEV genome were included in a single tube for simultaneous amplification ('double' PCR), and the resulting bands were resolved visually in ethidium bromide-stained agarose gels. Internal gag and pol probes were used to verify the identity of the amplified products by non-radioactive Southern hybridization. Final confirmation of the identity of representative PCR bands was provided by DNA sequence analysis. A comparison between the PCR and an antibody ELISA (with recombinant CAEV p28 as target) using 141 caprine blood samples indicated very strong agreement between the two assays (kappa = 0.912). Four of 7 goats with indeterminate ELISA results were PCR-positive as were 5 of 40 (12.5%) seronegative goats, most probably indicating delayed seroconversion. Eleven of 27 goats (41%) PCR-positive on blood had detectable CAEV proviral DNA in milk. Proviral DNA was also detected in lung, mesenteric lymph node, bone marrow, synovial membrane, and mammary gland of a seropositive, clinically affected goat, but not in equivalent tissues of a healthy seronegative goat.

An ELISA based on whole virus for the detection of antibodies to small-ruminant lentiviruses

A new ELISA kit was developed, based on highly purified whole-virus antigen derived from the Swiss maedi-visna virus strain OLV. The sensitivity, specificity and accuracy of this assay were compared with that of an established ELISA based on recombinant GAG (group-specific antigens)-GST (glutathione S-transferase) fusion protein expressed in E. coli (GAG-GST ELISA). The whole-virus ELISA exhibits at least comparable specificity (99.3%) but higher sensitivity (98.6 versus 86.3%) and agreement with the 'true' status beyond chance in the detection of antiviral antibodies in serum from goats. Antibodies in milk samples are detected with higher specificity (98.9 versus 97.8%) but lower sensitivity (91.4 versus 98.2%) than in GAG-GST ELISA. The specificity of the new ELISA in the detection of antibodies in serum might be superior, since a set of 40 samples falsely rated positive in GAG-GST ELISA in routine diagnostic work was negative in the new ELISA. In both assays, milk samples can be tested instead of serum, although with slightly reduced sensitivity in the new ELISA. The major advantage of the new test kit is the low number of equivocal samples needing confirmation in a supplementary test. Results obtained with sheep sera indicate that the new ELISA kit is also suitable for the detection of antibodies to maedi-visna virus.