Transmission of small ruminant lentiviruses

Detection of small ruminant Lentivirus proviral DNA in red deer from Poland

Small ruminant lentiviruses (SRLVs) are widespread and infect goats and sheep. Several reports also suggest that SRLVs can infect wild ruminants. The presence of specific antibodies against SRLVs has been identified in wild ruminants from Poland, but no studies have been conducted to detect proviral DNA of SRLVs in these animals. Therefore, the purpose of this study was to examine samples from Polish wild ruminants to determine whether these animals can serve as reservoirs of SRLVs under natural conditions. A total of 314 samples were tested from red deer (n = 255), roe deer (n = 52) and fallow deer (n = 7) using nested real-time PCR. DNA from positive real-time PCR samples was subsequently used to amplify a CA fragment (625 bp) of the gag gene, a 1.2 kb fragment of the pol gene and an LTR-gag fragment. Three samples (0.95%) were positive according to nested real-time PCR using primers and probe specific for CAEV (SRLV group B). All the samples were negative for the primers and probe specific for MVV (SRLV A group). Only SRLV LTR-gag sequences were obtained from two red deer. Phylogenetic analysis revealed that these sequences were more closely related to CAEV than to MVV. Our results revealed that deer can carry SRLV proviral sequences and therefore may play a role in the epidemiology of SRLVs. To our knowledge, this is the first study describing SRLV sequences from red deer.

In vivo evaluation of the antiretroviral activity of Melia azedarach against small ruminant lentiviruses in goat colostrum and milk

This study aimed to evaluate in vivo the use of the extract from the leaves of Melia azedarach in the ethyl acetate fraction at a concentration of 150 µg/mL as an antiretroviral treatment against small ruminant lentiviruses (SRLV) in goat colostrum, and milk with a 90-min action. Two groups of six kids were treated with the extract. One group received three supplies of colostrum from does naturally positive for SRLV, treated with the ethyl acetate fraction of M. azedarach (EAF-MA) for three days, while the other group consumed milk from does also carrying the virus with the respective extract twice a day for five days. After undergoing treatment, all animals began to receive thermized milk until weaning (60 days) and were monitored for six months using nested polymerase chain reaction (nPCR) and western blot (WB) tests. The study revealed cumulative percentages of positive animals in WB or nPCR in the milk group of 66.66% on the seventh day, 83.33% in the following week, and 100% at 120 days, while the colostrum group showed values of 66.66% at 14 days, 83.33% at 90 days, and 100% at 120 days. Variation and intermittency were observed in viral detection, but all animals tested positive in WB or nPCR at some point. A potential delay in infection was observed, which was more significant in the colostrum group. The need for the combination of serological and molecular tests for a more efficient detection of the disease is also emphasized.

Development of in-house ELISA based on recombinant gag proteins of small ruminant lentiviruses isolated from goats in Thailand

Small ruminant lentiviruses (SRLVs), are grouped in Retroviridae family, remain a significant loss in the small ruminant husbandry. As a result of unavailability of vaccine and effective treatment, the diagnosis plays a crucial role for the control of SRLV infection. However, the major challenge of diagnosis of SRLV infection is the genetic and antigenic variability of the viruses that can lead to a failure in serological detection. This study investigated the circulating strains of the viruses in goats in Thailand and an in-house ELISA was developed. The coding sequences for gag protein were optimized, synthesized, and expressed in Escherichia coli for increasing the sensitivity of ELISA test. A total of 365 serum samples were examined against the recombinant protein in an in-house ELISA. The results showed that the recombinant gag achieves 96.67% sensitivity and 93.18% specificity as compared with the commercially available ELISA test kit.

Isolation and Identification of Caprine Arthritis Encephalitis Virus from Animals in the Republic of Mordovia

This article presents the results of virological and genetic studies of an isolate of caprine arthritis encephalitis (CAE) virus from the republic of Mordovia, Russian Federation. The isolate was found during monitoring studies of goat blood samples for the viral genome, and the presence of antibodies to lentiviruses was detected. According to the recommendation of the OIE, the positive result of PCR was confirmed with nucleotide sequencing. It was found that the obtained nucleotide sequence is identical to the genome of small ruminant lentiviruses presented in the GenBank database. Phylogenetic analysis showed that the isolate "Mordovia-2018" was included in the same cluster with an isolate from the Tver region of the Russian Federation detected in 2008. The sequence of the fragment of the env-gene of the isolate from the republic of Mordovia is available in GenBank under the number MN186380.1. To isolate the virus, a fraction of peripheral blood monocyte cells from the animal's blood was added to a monolayer of lamb synovial membrane cell culture, and ten passages were carried out. The first manifestations of the cytopathic effect were observed after the third passage on the eighth day of cultivation in the form of single large cells of irregular shape with 5-7 nuclei. At the seventh passage, multiple syncytium with 7-12 nuclei were observed. At subsequent passage levels, the formation of syncytium containing more than 10-14 nuclei was observed.

Small Ruminant Lentivirus Infection in Sheep and Goats in North Portugal: Seroprevalence and Risk Factors

Small ruminant lentiviruses (SRLVs) are transmitted among ovine and caprine species. This disease is a severe problem for small ruminant production, not only for animals' well-being but also for flocks' efficiency. The main aim of this research was to quantify the seroprevalence and associated risk factors for SRLV infection in the northern region of Portugal. Samples were collected from a total of 150 flocks, of which 129 (86.0%; 95% CI: 80.67%-91.33%) had at least one seropositive animal. Out of 2607 individual blood samples, 1074 (41.2%) were positive for SRLVs. Risk factors associated with SRLV infection were species (caprine), age (>2 years old), flock size (>100 animals), production system (intensive), food production system (milk), type of activity (professional), participation in livestock competitions (yes), replacement young ewe bought (yes), and natural feeding management (yes). This knowledge empowers the implementation of effective preventive measures. Overall, biosecurity measures should be promoted and implemented with the main aim of reducing viral transmission and reducing the prevalence of this disease. We recognise that government authorities should promote and audit voluntary control and eradication programs in small ruminant flocks in the region studied.

Associations between small ruminant lentivirus infection and total milk yield and somatic cell count in a dairy sheep flock

BACKGROUND

Small ruminant lentiviruses (SRLVs) are lentiviruses of sheep and goats, formerly known as maedi-visna (MV) in sheep and caprine encephalitis and arthritis in goats. In sheep, SRLVs commonly cause progressive pneumonia, wasting and indurative mastitis. SRLVs have a long latent period, and chronic production losses are often not recognised until very late. Few studies quantifying the production losses in ewes have been published, and none have been published under UK flock husbandry conditions.

METHODS

Production records of milk yield and somatic cell count (SCC) from a dairy flock of 319 milking East Friesian × Lacaune ewes identified as MV infected via routine serological screening for SRLV antibodies were used in multivariable linear regression modelling to estimate the impact of SRLV status on total milk yield and SCC.

RESULTS

Milk yield was reduced in seropositive ewes by 8.1%-9.2% over an entire lactation. SCC counts were not significantly different in SRLV-infected and unifected animals.

LIMITATIONS

Further parameters, such as body condition score or clinical mastitis, that were not available may have clarified the underlying cause of milk yield drop.

CONCLUSIONS

The study demonstrates substantial production losses in an SRLV-affected flock and highlights the impact of the virus on a farm's economic viability.

A large-scale study on the seroprevalence of small ruminant lentiviral infection in the Polish goat population

A large-scale study was carried out in a Polish goat population in 2014-2022 to determine the herd-level (between-herd) and within-herd seroprevalence of small ruminant lentivirus (SRLV) infection. A total of 8354 adult goats (aged >1 year) from 165 herds located in various regions of Poland were serologically tested using a commercial ELISA. One hundred twenty eight herds were randomly selected while 37 were enrolled based on convenience non-random sampling. At least 1 seropositive result was obtained in 103 / 165 herds. For all these herds the probability that they were truly positive (herd-level positive predictive value) was calculated. It was ≥ 90% in 91 seropositive herds and 73% to < 90% in 12 herds in which only 1-4 goats were seropositive (22 goats in total). The seropositive goats in the latter herds were retested using a different commercial ELISA and 14 goats (9 males and 5 females) from 9 herds were confirmed to be seropositive (serial testing). The true herd-level seroprevalence was estimated at 61% (95% confidence interval [CI 95%]: 53%-68%). It differed significantly between herd size classes (p = 0.003): the highest prevalences were found in the medium (51 - 100 adult goats) and large herds (>100 adult goats) - 72% (CI 95%: 56-84%) and 86% (CI 95%: 67%-95%), respectively, while prevalences in very small (≤ 20 adult goats) and small herds (21 - 50 adult goats) were 46% (CI 95%: 34%-59%) and 57% (CI 95%: 43%-70%), respectively. The true herd-level seroprevalence differed significantly also between geographical regions of Poland (p = 0.003), with the highest values in the north-western and the lowest in the southern region of the country. The true within-herd seroprevalence estimated using a Bayesian approach ranged from 0.7% to 100% with the median (IQR) of 42% (17%-84%), and did not vary significantly between herd size classes (p = 0.393) or geographical regions of Poland (p = 0.570). Concluding, SRLV infection is widespread in the Polish goat population, the north-western region of Poland is most extensively infected, and herds counting > 50 adult goats are more often infected.

A Combined Approach for Detection of Ovine Small Ruminant Retrovirus Co-Infections

Jaagsiekte retrovirus (JSRV)-induced ovine pulmonary adenocarcinoma (OPA) is an important ovine respiratory disease in Switzerland. Furthermore, ovine lungs with OPA frequently exhibited lesions suggestive of maedi-visna virus (MVV) or caprine arthritis encephalitis virus (CAEV) infection, indicating that co-morbidities might occur. Lungs and pulmonary lymph nodes were sampled from suspected OPA cases, inflammatory lung lesions and control lungs (total of 110 cases). Tissues were (a) processed for histology and immunohistochemistry (IHC), and (b) underwent DNA extraction and real-time PCR for JSRV, MVV and CAEV. Peptide sequences were used to generate virus-specific customized polyclonal antibodies. PCR-positive OPA cases and formalin-fixed and paraffin-embedded MVV- and CAEV-infected synovial cell pellets served as positive controls. Fifty-two lungs were histologically diagnosed with OPA. Histological evidence of MVV/CAEV infection was detected in 25 lungs. JSRV was detected by PCR in 84% of the suspected OPA cases; six were co-infected with MVV and one with CAEV. MVV was detected by PCR in 14 cases, and four lungs were positive for CAEV. Three lungs had MVV/CAEV co-infection. In IHC, JSRV was detected in 91% of the PCR-positive cases, whereas MVV and CAEV immunoreactivity was seen in all PCR-positive lungs. Although PCR showed a higher sensitivity compared to IHC, the combined approach allows for investigations on viral cell tropism and pathogenic processes in co-morbidities, including their potential interdependency. Furthermore, an immunohistochemical tool for specific differentiation of MVV and/or CAEV infection was implemented.

Genetic Diversity of the LTR Region of Polish SRLVs and Its Impact on the Transcriptional Activity of Viral Promoters

A long terminal repeat (LTR) plays an indispensable role in small ruminant lentivirus (SRLV) gene expression. In this study, we present the LTR sequence of Polish SRLVs representing different subtypes, and analyzed their impact on SRLV promoter activity, as measured in transient transfection assays. Although certain nucleotide motifs (AML(vis), TATA box and the polyadenylation site (AATAAA)) were conserved across sequences, numerous mutations within the LTR sequences have been identified. Single nucleotide polymorphisms (SNPs) were detected in both regulatory (AP-1, AP-4, Stat and Gas) and non-regulatory sequences, and subtype-specific genetic diversity in the LTR region of Polish SRLVs was observed. In vitro assays demonstrated subtype-specific functional differences between the LTR regions of distinct SRLV subtypes. Our results revealed that the promoter activity of Polish strains was lower (1.64-10.8-fold) than that noted for the K1514 reference strain; however, the differences in most cases were not statistically significant. The lowest promoter activity was observed for strains representing subtype A5 (mean 69.067) while the highest promoter activity was observed for strain K1514 representing subtype A1 (mean 373.48). The mean LTR activities of strains representing subtypes A12, A17, A23, A18 and A24 were 91.22, 137.21, 178.41, 187.05 and 236.836, respectively. The results of the inter-subtype difference analysis showed that the promoter activity of strains belonging to subtype A5 was significantly lower than that for subtype A12 strains (1.32-fold; p < 0.00). The promoter activities of the A5 strain were 1.98-fold and 2.58-fold less active than that of the A17 and A23 strains, and the promoter activities of A12 strains were 1.955 and 1.5 times lower than the promoter activity of A23 and A17 strains, respectively. Furthermore, the promoter activity of A17 strains was 1.3 lower than the promoter activity of A23 strains. Our findings suggest that subtype-specific genetic diversity, mainly in the transcription factor's binding sites, has an impact on their transcriptional activity, producing a distinct activity pattern for the subtypes. This study provides new information that is important for better understanding the function of the SRLV LTR. However, further research including more strains and subtypes as well as other cell lines is needed to confirm these findings.

Emergence and pandemic spread of small ruminant lentiviruses

Small ruminant lentiviruses (SRLVs) cause chronic, persistent infections in populations of domestic sheep (Ovis aries) and goats (Capra hircus) worldwide. The vast majority of SRLV infections involve two genotypes (A and B) that spread in association with the emergence of global livestock trade. However, SRLVs have likely been present in Eurasian ruminant populations since at least the early Neolithic period. Here, we use phylogenetic and phylogeographic approaches to reconstruct the origin of pandemic SRLV strains and infer their historical pattern of global spread. We constructed an open computational resource ('Lentivirus-GLUE') via which an up-to-date database of published SRLV sequences, multiple sequence alignments (MSAs), and sequence-associated metadata can be maintained. We used data collated in Lentivirus-GLUE to perform a comprehensive phylogenetic investigation of global SRLV diversity. Phylogenies reconstructed from genome-length alignments reveal that the deep divisions in the SRLV phylogeny are consistent with an ancient split into Eastern (A-like) and Western (B-like) lineages as agricultural systems disseminated out of domestication centres during the Neolithic period. These findings are also consistent with historical and phylogeographic evidence linking the early 20^th century emergence of SRLV-A to the international export of Central Asian Karakul sheep. Investigating the global diversity of SRLVs can help reveal how anthropogenic factors have impacted the ecology and evolution of livestock diseases. The open resources generated in our study can expedite these studies and can also serve more broadly to facilitate the use of genomic data in SRLV diagnostics and research.

Longitudinal Study on Seroreactivity of Goats Exposed to Colostrum and Milk of Small Ruminant Lentivirus-infected Dams

Introduction

Small ruminant lentivirus (SRLV) causes caprine arthritis-encephalitis in goats and maedi-visna disease in sheep. Transmission is via ingestion of colostrum and milk from infected dams or long-term direct contact between animals. Lifelong seroconversion can occur several weeks after infection via ingestion. However, sub-yearling lambs that ingest contaminated colostrum may be able to clear the infection and become seronegative. Whether a similar phenomenon occurs in goats remains unknown. Therefore, the serological status of goats was studied longitudinally from the moment of natural exposure to colostrum and milk of SRLV-positive dams through the age of 24 months.

Material and Methods

Between February 2014 and March 2017 a dairy goat herd was studied which had been infected with SRLV for more than 20 years and carried maedi-visna virus-like genotype A subtype A17. Thirty-one kids born to dams seropositive for SRLV for at least a year beforehand were followed. They ingested colostrum immediately after birth and then remained with their dams for three weeks. The goats were tested serologically every month using two commercial ELISAs. The clinical condition of the goats was also regularly assessed.

Results

Out of 31 goats, 13 (42%) seroconverted at the age ranging from 3 to 22 months with a median of 5 months. Two goats seroconverted in the second year of life. The other eleven did so before the age of one year; two of these reverted to seronegative status. Only 9 out of 31 goats (29%) seroconverted in the first year of life and remained seropositive. They were early and stable seroreactors to which SRLV was transmitted lactogenically. The age at which they seroconverted ranged from 3 to 10 months with a median of 5 months. In 8 of the 18 persistently seronegative goats, a single isolated positive result occurred. No goats showed any clinical signs of arthritis. The level of maternal antibodies at the age of one week did not differ significantly between the stable seroreactors and the remainder.

Conclusion

Seroconversion appears to occur in less than 50% of goats exposed to heterologous SRLV genotype A via ingestion of colostrum and milk from infected dams and is delayed by 3-10 months. The natural lactogenic route of transmission of SRLV genotype A in goats appears to be less effective than this route of genotype B transmission reported in earlier studies.

Low transmission rates of Equine infectious anemia virus (EIAV) in foals born to seropositive feral mares inhabiting the Amazon delta region despite climatic conditions supporting high insect vector populations

Background

Marajó Island, within in the Amazon River Delta, supports numerous bands of feral equids including the genetically distinct Marajoara horses. Approximately 40% of the equids on the island are infected with Equine infectious anemia virus (EIAV). This high seropositivity rate coupled with the need to preserve rare breeds such as the Marajoara horse precludes euthanasia as the primary means for controlling EIAV in this region. In the absence of iatrogenic transmission, spread of this lentivirus is mediated primarily by hematophagous insects, whose year-round prevalence on the island is supported by favorable climatic conditions. In addition, cases of vertical EIAV transmission have been observed suggesting inclusion of seropositive mares in restorative breeding programs could result in their progeny becoming infected with this virus either pre-parturition or post-partum via hematophagous insects. Therefore, the aim of this study was to evaluate EIAV vertical and post-partum insect-mediated transmission rates among foals born to seropositive feral mares until natural weaning. Serum samples from foals born to seropositive feral mares within the Soure municipality, of Marajó Island, were collected to investigate their serological status, using an indirect ELISApgp45, with positive samples confirmed using the classical agar gel immunodiffusion (AGID) assay.

Results

The serological status of 28 foals were monitored over a 2-year period with some subjects, depending on their date of birth, being sampled up to six times. All foals remained with their respective mares until fully weaned at approximately 10 months of age. Only 2 foals (7.14%) in the study group became seropositive against EIAV.

Conclusion

The results demonstrate that in most cases it is possible to obtain seronegative foals born to and eventually weaned by EIA positive mares, even in equatorial regions where substantial rainfall and high temperatures favor the proliferation of insect vectors.

A novel strategy for developing vaccine candidate against Jaagsiekte sheep retrovirus from the envelope and gag proteins: an in-silico approach

BACKGROUND

Sheep pulmonary adenocarcinoma (OPA) is a contagious lung cancer of sheep caused by the Jaagsiekte retrovirus (JSRV). OPA typically has a serious economic impact worldwide. A vaccine has yet to be developed, even though the disease has been globally spread, along with its complications. This study aimed to construct an effective multi-epitopes vaccine against JSRV eliciting B and T lymphocytes using immunoinformatics tools.

RESULTS

The designed vaccine was composed of 499 amino acids. Before the vaccine was computationally validated, all critical parameters were taken into consideration; including antigenicity, allergenicity, toxicity, and stability. The physiochemical properties of the vaccine displayed an isoelectric point of 9.88. According to the Instability Index (II), the vaccine was stable at 28.28. The vaccine scored 56.51 on the aliphatic index and -0.731 on the GRAVY, indicating that the vaccine was hydrophilic. The RaptorX server was used to predict the vaccine's tertiary structure, the GalaxyWEB server refined the structure, and the Ramachandran plot and the ProSA-web server validated the vaccine's tertiary structure. Protein-sol and the SOLPro servers showed the solubility of the vaccine. Moreover, the high mobile regions in the vaccine's structure were reduced and the vaccine's stability was improved by disulfide engineering. Also, the vaccine construct was docked with an ovine MHC-1 allele and showed efficient binding energy. Immune simulation remarkably showed high levels of immunoglobulins, T lymphocytes, and INF-γ secretions. The molecular dynamic simulation provided the stability of the constructed vaccine. Finally, the vaccine was back-transcribed into a DNA sequence and cloned into a pET-30a ( +) vector to affirm the potency of translation and microbial expression.

CONCLUSION

A novel multi-epitopes vaccine construct against JSRV, was formed from B and T lymphocytes epitopes, and was produced with potential protection. This study might help in controlling and eradicating OPA.

The Prevalence of Histopathological Features of Pneumonia in Goats with Symptomatic Caprine Arthritis-Encephalitis

Chronic interstitial pneumonia (CIP) is a main pathology of sheep infected with small ruminant lentivirus (SRLV). Caprine arthritis-encephalitis (CAE) is caused by the same pathogen; however, the presence of CIP has been only occasionally reported in SRLV-infected goats. We carried out a cross-sectional study to determine the prevalence of histopathological lesions indicative of CIP in goats with symptomatic CAE, and to investigate whether CIP was associated with a higher prevalence of other types of pneumonia (purulent bronchopneumonia, fibrinous pleuropneumonia) or bacterial infections. Lung specimens and bronchial swabs were collected for histopathological and bacteriological examination, respectively, from 116 goats from a CAE-affected herd. All goats were euthanized due to severe clinical signs of CAE. The goats were seropositive for SRLV infection in two different ELISAs and the presence of SRLV antigen in the lung tissue was confirmed by immunohistochemistry. Histopathologically, pneumonia of any type was confirmed in 82 goats (70.7%) and CIP was present in 67 goats (57.8%). In most goats, the severity of the histopathological features of pneumonia was mild. Bacteria were detected in bronchial swabs from 73 goats (62.9%). CIP proved to be significantly positively linked to the occurrence of purulent bronchopneumonia (p < 0.001), fibrinous pleuropneumonia (p = 0.001), and of the infection of lungs with bacteria capable of causing pneumonia (p = 0.050). The causal character of these associations should be considered and warrants further investigation.

An outbreak of visna-maedi in a flock of sheep in Southern Brazil

Visna-maedi is a multisystemic and progressive inflammatory disease caused by a non-oncogenic retrovirus (Visna-maedi virus, VMV). An outbreak of visna-maedi occurred in Southern Brazil in sheep with clinical signs of blindness and stumbling gait. At post-mortem examination, all animals had similar lesions, including heavy non-collapsed lungs and multifocal yellow areas in the cerebral white matter, affecting mainly the periventricular region. These lesions corresponded histologically to lymphocytic interstitial pneumonia and histiocytic periventricular encephalitis surrounding areas of necrosis, in addition to significant demyelination in the brain. Serology was performed in all the sheep from the flock and 14% were seropositive for VMV. The presence of VMV was confirmed through PCR and partial sequencing of the 5'LTR. Sequencing demonstrated that the virus had 89.7 to 90.0% of nucleotide identity with VMV strains reported in the USA. This is the first description of clinical disease related to VMV in Brazil leading to economic losses. This study calls for the need to implement control measures to prevent the spread of small ruminant lentiviruses in Brazil.

Serological Survey of Small Ruminant Lentivirus Infections in Free-Ranging Mouflon and Chamois in Slovenia

Small ruminant lentiviruses (SRLVs) belong to the genus Lentivirus in the Retroviridae family, which are responsible for the diseases maedi-visna and caprine arthritis-encephalitis in sheep and goats worldwide and are also widespread in Slovenian sheep and goats. SRLVs cause lifelong infections with chronic inflammatory lesions in various organ systems. Cross-species transmission of SRLV strains in sheep and goats is well documented, but there are few data on the ability of these viruses to infect wild ruminants. The objective of this study was to investigate whether SRLVs circulate among wild small ruminants in Slovenia. During the 2017–2018 hunting season, a total of 38 blood samples were collected from free-ranging chamois (Rupicapra rupicapra) and European mouflon (Ovis ammon musimon). The serum samples were tested for antibodies against SRLV by enzyme-linked immunosorbent assay (ELISA). The serological tests revealed that of all tested mouflons, 1 animal (11.1%) was seropositive, while all samples from chamois were negative. Based on the results of this study and considering the results of previous studies in which SRLV infections were detected in mouflons with low seroprevalence, it is very likely that the detected seropositive animal was an incidental spillover host for SRLV. Although no seropositive samples were found in chamois, we cannot speculate on whether chamois may not be a host for SRLV infection because of the small sample size and the disadvantages of the ELISA assay used when applied to samples from chamois.

Supplementing Mannan Oligosaccharide Reduces the Passive Transfer of Immunoglobulin G and Improves Antioxidative Capacity, Immunity, and Intestinal Microbiota in Neonatal Goats

Successful establishment of passive immunity (PIT) and regulation of intestinal microbiota are crucial for ruminants to maintain body health and reduce the risk of disease during the neonatal period. Thus, the objective of this study was to investigate the effects of mannan oligosaccharide (MOS) supplementation on passive transfer of immunoglobulin G (IgG), serum inflammatory cytokines and antioxidant levels as well as bacteria composition in the ileal digesta. A total of 14 healthy neonatal Ganxi black goats with similar birth weight (BW: 2.35 ± 0.55 kg) were selected and allocated into two groups, only fed colostrum and milk replacer (CON, n = 7) and supplemented MOS (0.06% of birth BW) in the colostrum and milk replacer (MOS, n = 7). The results indicated that MOS supplementation significantly reduced (p < 0.05) serum IgG level at 3 and 6 h after colostrum feeding. Serum GLP-1 level of goats in the MOS group was significantly lower (p = 0.001) than that in the CON group. Goats in the MOS group had higher serum CAT and lower MDA level than those in the CON group (p < 0.05). Serum anti-inflammatory cytokine level of interleukin 4 (IL-4) was increased (p < 0.05), while pro-inflammatory cytokine IL-6 level was reduced (p < 0.05) in the MOS group when compared with the CON group. In addition, MOS supplementation remarkably increased (p < 0.05) the level of secretory IgA (sIgA) in the ileal digesta. Principal coordinate analysis of 16S rRNA sequence based on Brinary jaccard, Bray curtis, and weighted UniFrac distance of ileal microbiota showed a distinct microbial differentiation between the CON and MOS groups (p < 0.05). The relative abundance of Firmicutes in the MOS group was higher than that in the CON group, while the abundance of Verrucomicrobia was lower in the MOS group than that in the CON group at the phylum level (p < 0.05). The relative abundance of Proteobacteria tended to decrease (p = 0.078) in the MOS group at the phylum level. The results of LEfSe analysis showed that MOS group was characterized by a higher relative abundance of Lactobacillus, while the CON group was represented by a higher relative abundance of Akkermansia and Ruminiclostridium_5. Our findings demonstrated that MOS supplementation during the neonatal period increases antioxidant capacity and reduces the inflammatory response, and promotes IgA secretion and Lactobacillus colonization in the ileum. Thus, MOS induced positive effects are more pronounced in neonatal goats that might be an effective approach to maintain intestinal health and improve the surviving rate of neonatal ruminants.

Evaluation of Serological Methods and a New Real-Time Nested PCR for Small Ruminant Lentiviruses

Small ruminant lentiviruses (SRLVs), i.e., CAEV and MVV, cause insidious infections with life-long persistence and a slowly progressive disease, impairing both animal welfare and productivity in affected herds. The complex diagnosis of SRLVs currently combines serological methods including whole-virus and peptide-based ELISAs and Immunoblot. To improve the current diagnostic protocol, we analyzed 290 sera of animals originating from different European countries in parallel with three commercial screening ELISAs, Immunoblot as a confirmatory assay and five SU5 peptide ELISAs for genotype differentiation. A newly developed nested real-time PCR was carried out for the detection and genotype differentiation of the virus. Using a heat-map display of the combined results, the drawbacks of the current techniques were graphically visualized and quantified. The immunoblot and the SU5-ELISAs exhibited either unsatisfactory sensitivity or insufficient reliability in the differentiation of the causative viral genotype, respectively. The new truth standard was the concordance of the results of two out of three screening ELISAs and the PCR results for serologically false negative samples along with genotype differentiation. Whole-virus antigen-based ELISA showed the highest sensitivity (92.2%) and specificity (98.9%) among the screening tests, whereas PCR exhibited a sensitivity of 75%.

Species-Specific Humoral Immune Responses in Sheep and Goats upon Small Ruminant Lentivirus Infections Inversely Correlate with Protection against Virus Replication and Pathological Lesions

Maedi-Visna-like genotype A strains and Caprine arthritis encephaltis-like genotype B strains are small ruminant lentiviruses (SRLV) which, for incompletely understood reasons, appear to be more virulent in sheep and goats, respectively. A 9-month in vivo infection experiment using Belgian genotype A and B SRLV strains showed that almost all homologous (genotype A in sheep; genotype B in goats) and heterologous (genotype A in goats; genotype B in sheep) intratracheal inoculations resulted in productive infection. No differences in viremia and time to seroconversion were observed between homologous and heterologous infections. Higher viral loads and more severe lesions in the mammary gland and lung were however detected at 9 months post homologous compared to heterologous infection which coincided with strongly increased IFN-γ mRNA expression levels upon homologous infection. Pepscan analysis revealed a strong antibody response against immune-dominant regions of the capsid and surface proteins upon homologous infection, which was absent after heterologous infection. These results inversely correlated with protection against virus replication in target organs and observed histopathological lesions, and thus require an in-depth evaluation of a potential role of antibody dependent enhancement in SRLV infection. Finally, no horizontal intra- and cross-species SRLV transmission to contact animals was detected.

Initial multi-target approach shows importance of improved caprine arthritis-encephalitis virus control program in Russia for hobbyist goat farms

Background and Aim:

Several reports described the detection of specific caprine arthritis-encephalitis virus (CAEV) antibodies in Russian goat populations, which indicates the circulation of CAEV in Russian goat farms. The aim of this study was to use a multi-target approach to testing with both serological tests and an in-house real-time (RT) molecular test to investigate the prevalence of CAEV in goats from three hobbyist farms in the Republic of Tatarstan, Russia.

Materials and Methods:

We applied a multi-target approach to testing with both enzyme-linked immunosorbent assay (ELISA) and an in-house RT polymerase chain reaction test to investigate the prevalence of CAEV in goats. Animals from the three hobbyist farms were used in this study. The animals from two farms (n=13 for F1 and n=8 for F2) had clinical signs of arthritis and mastitis. In the third farm (n=15 for F3), all goats were home-bred and had no contact with imported animals.

Results:

CAEV antibodies (ELISA targets TM env and gag genes) were detected in serum samples from two farms (F1 and F2), indicating seroprevalence of 87.50-92.31%. Specific CAEV antibodies were also detected in milk samples. CAEV proviral DNA was detected in 53.85-62.50%. The results from all tests performed in the third farm (F3) were negative, indicating that all tests were 100% specific.

Conclusion:

The results showed that CAEV is circulating and present in small hobbyist goat farms in Russia. Serological and molecular tests could be important for programs to control and eradicate CAEV in Russia for hobbyist goat farms.

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.

Accurate Diagnosis of Small Ruminant Lentivirus Infection Is Needed for Selection of Resistant Sheep through TMEM154 E35K Genotyping

Small ruminant lentiviruses (SRLV) cause an incurable multiorganic disease widely spread in sheep and goats that disturbs animal welfare and production. In the absence of a vaccine, control measures have been traditionally based on early diagnosis and breeding with virus-inactivated colostrum with segregation of seropositive animals. However, antigenic heterogeneity, poor antibody production due to low viral load, and single strain design of most available ELISA, pose a threat to SRLV diagnosis. Genome-wide association studies have described TMEM154 E35K polymorphism as a good genetic marker for selection of resistant animals in some American and European breeds. In this study, a multitargeted serological and virological screening of more than 500 animals from four different breeds (latxa, raza Navarra, assaf, and churra) attending to SRLV infection status was performed. Then, animals were genotyped to characterize TMEM154 E35K polymorphism. ELISA procedures, individually considered, only identified a proportion of the seropositive animals, and PCR detected a fraction of seronegative animals, globally offering different animal classifications according to SRLV infection status. TMEM154 allele frequency differed substantially among breeds and a positive association between seroprevalence and TMEM154 genotype was found only in one breed. Selection based on TMEM154 may be suitable for specific ovine breeds or SRLV strains, however generalization to the whole SRLV genetic spectrum, ovine breeds, or epidemiological situation may need further validation.

Accurate Diagnosis of Small Ruminant Lentivirus Infection Is Needed for Selection of Resistant Sheep through TMEM154 E35K Genotyping

Small ruminant lentiviruses (SRLV) cause an incurable multiorganic disease widely spread in sheep and goats that disturbs animal welfare and production. In the absence of a vaccine, control measures have been traditionally based on early diagnosis and breeding with virus-inactivated colostrum with segregation of seropositive animals. However, antigenic heterogeneity, poor antibody production due to low viral load, and single strain design of most available ELISA, pose a threat to SRLV diagnosis. Genome-wide association studies have described TMEM154 E35K polymorphism as a good genetic marker for selection of resistant animals in some American and European breeds. In this study, a multitargeted serological and virological screening of more than 500 animals from four different breeds (latxa, raza Navarra, assaf, and churra) attending to SRLV infection status was performed. Then, animals were genotyped to characterize TMEM154 E35K polymorphism. ELISA procedures, individually considered, only identified a proportion of the seropositive animals, and PCR detected a fraction of seronegative animals, globally offering different animal classifications according to SRLV infection status. TMEM154 allele frequency differed substantially among breeds and a positive association between seroprevalence and TMEM154 genotype was found only in one breed. Selection based on TMEM154 may be suitable for specific ovine breeds or SRLV strains, however generalization to the whole SRLV genetic spectrum, ovine breeds, or epidemiological situation may need further validation.

Vertical transmissibility of small ruminant lentivirus

This study aimed to evaluate by means of Nested Polymerase Chain Reaction (nPCR), co-cultivation and sequencing, with genetic comparison between strains (mother/newborn), the occurrence of vertical transmission of Small Ruminant Lentiviruses (SRLV) from naturally occurring nannies infected for their offspring. For the detection of SRLV seropositive progenitors, blood was collected from 42 nannies in the final third of gestation in tubes with and without anticoagulant. The diagnostic tests used were Western Blot (WB) and nPCR. During the period of birth, the same blood collection procedure was performed on 73 newborns at zero hours of birth, with the same diagnostic tests. Seventeen blood samples from seven-day-old kids, proven positive for SRLV by nPCR, chosen at random, were subjected to coculture in goat synovial membrane (GSM) cells for 105 days. The pro-viral DNA extracted from the cell supernatant from the coculture was subjected to nPCR. For DNA sequencing from the nPCR products, nine positive samples were chosen at random, four nannies with their respective offspring, also positive. Each sample was performed in triplicate, thus generating 27 nPCR products of which only 19 were suitable for analysis. Among the 42 pregnant goats, in 50% (21/42) pro-viral DNA was detected by nPCR, while in the WB, only 7.14% (3/42) presented antibodies against SRLV. Regarding neonates, of the 73 kids, 34 (46.57%) were positive for the virus, using the nPCR technique, while in the serological test (WB), three positive animals (4.10%) were observed. The coculture of the 17 samples with a positive result in the nPCR was confirmed in viral isolation by amplification of the SRLV pro-viral DNA. When aligned, the pro-viral DNA sequences (nannies and their respective offspring) presented homology in relation to the standard strain CAEV Co. It was concluded that the transmission of SRLV through intrauterine route was potentially the source of infection in the newborn goats.

Epidemiology and control of maedi-visna virus: Curing the flock

Maedi-visna (MV) is a complex lentiviral disease syndrome characterised by long immunological and clinical latencies and chronic progressive inflammatory pathology. Incurable at the individual level, it is widespread in most sheep-keeping countries, and is a cause of lost production and poor animal welfare. Culling seropositive animals is the main means of control, but it might be possible to manage virus transmission effectively if its epidemiology was better quantified. We derive a mathematical epidemiological model of the temporal distributions of seroconversion probabilities and estimate susceptibility, transmission rate and latencies in three serological datasets. We demonstrate the existence of epidemiological latency, which has not explicitly been recognised in the SRLV literaure. This time delay between infection and infectiousness apparently exceeds the delay between infection and seroconversion. Poor body condition was associated with more rapid seroconversion, but not with a higher probability of infection. We estimate transmission rates amongst housed sheep to be at about 1,000 times faster than when sheep were at grass, when transmission was negligible. Maternal transmission has only a small role in transmission, because lambs from infected ewes have a low probability of being infected directly by them, and only a small proportion of lambs need be retained to maintain flock size. Our results show that MV is overwhelmingly a disease of housing, where sheep are kept in close proximity. Prevalence of MV is likely to double each year from an initial low incidence in housed flocks penned in typically-sized groups of sheep (c. 50) for even a few days per year. Ewes kept entirely at grass are unlikely to experience transmission frequently enough for MV to persist, and pre-existing infection should die out as older ewes are replaced, thereby essentially curing the flock.

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.

Short communication: Genetic parameter estimates for caprine arthritis encephalitis in dairy goats

Caprine arthritis encephalitis (CAE) is a chronic disease caused by a retrovirus from the Lentivirus genus. No effective vaccines or treatments exist, and therefore genetic selection for CAE resistance might be a feasible alternative. To our best knowledge, no other studies have investigated the genetic architecture of CAE resistance in dairy goats. In this context, this study was designed to estimate genetic parameters for CAE infection in Alpine and Saanen goats using a Bayesian threshold model. A total of 542 adult goats (and >3-generation pedigree), which were group-housed in a population with high CAE prevalence, were tested based on a serological infection assessment test (negative = 1 or positive = 2) and used for this study. Genetic parameters were estimated using the BLUPF90 family programs. There was considerable genetic variability for CAE resistance, and pedigree-based heritability was significantly different from zero (0.026 < heritability < 0.128). Our findings indicate that the prevalence of CAE in goat herds can be reduced or eliminated through direct genetic selection for CAE resistance in addition to proper management strategies.

Etiology, Epizootiology and Control of Maedi-Visna in Dairy Sheep: A Review

Maedi-visna (MV) in sheep is caused by maedi-visna virus (MVV), a small ruminant lentivirus (SRLV) that causes chronic infection and inflammatory lesions in infected animals. Pneumonia and mastitis are its predominant clinical manifestations, and the tissues infected by MVV are mainly the lungs, the mammary gland, the nervous system and the joints. MV has a worldwide distribution with distinct MVV transmission patterns depending on circulating strains and regionally applied control/eradication schemes. Nevertheless, the prevalence rate of MV universally increases. Currently, gaps in understanding the epizootiology of MV, the continuous mutation of existing and the emergence of new small ruminant lentiviruses (SRLVs) strains, lack of an effective detection protocol and the inefficiency of currently applied preventive measures render elimination of MV an unrealistic target. Therefore, modifications on the existing MV surveillance and control schemes on an evidentiary basis are necessary. Updated control schemes require the development of diagnostic protocols for the early and definitive diagnosis of MVV infections. The objectives of this review are to summarize the current knowledge in the epizootiology and control of MV in dairy sheep, to describe the research framework and to cover existing gaps in understanding future challenges regarding MV.

Phylogenetic Analysis of Belgian Small Ruminant Lentiviruses Supports Cross Species Virus Transmission and Identifies New Subtype B5 Strains

Small ruminant lentiviruses (SRLV) are a group of highly divergent viruses responsible for global and fatal infections in sheep and goats. Since the current phylogenetic classification of these viruses was proposed in 2004, it nowadays consists out of 5 genotypes and 28 subtypes. In support of our national SRLV control program, we performed the genetic characterization of SRLV strains circulating in the Belgian sheep and goat population. Fourteen sheep and 9 goat strains were sequenced in the gag-pol and pol regions using the method described by Shah. Most SRLV strains from sheep and goats belonged to prototype A1 and B1 subtypes, respectively. We, however, also found indications for cross-species transmission of SRLV strains between sheep and goats and vice versa, and identified a new subtype designated as B5. An in-depth analysis of the current SRLV phylogeny revealed that many subtypes have been defined over the years based on limited sequence information. To keep phylogeny as a useful tool, we advocate to apply more rigorous sequencing standards to ensure the correct classification of current and new emerging strains. The genetic characterization of Belgian SRLV strains will help in the development of appropriate diagnostic tools to assist the national control program.

Phylogenetic analysis of small ruminant lentiviruses in Germany and Iran suggests their expansion with domestic sheep

Small ruminant lentiviruses (SRLVs) are found in sheep in Germany and Iran. SRLVs have been classified into four genotypes: A-C and E. Genotype A has been subdivided into 20 subtypes. Previous studies suggested that, first, the ancestors of genotype A are those SRLVs found in Turkey, second, the evolution of SRLVs is related to the domestication process, and, third, SRLV infection was first observed in sheep in Iceland and the source of that infection was a flock imported from Germany. This study generated, for the first time, partial SRLV sequence data from German and Iranian sheep, enhancing our knowledge of the genetic and evolutionary relationships of SRLVs, and their associations with the domestication process. Based on 54 SRLV sequences from German and Iranian sheep, our results reveal: (1) SRLV subtypes A4, A5, A11, A16 and A21 (new) are found in German sheep and A22 (new) in Iranian sheep. (2) Genotype A has potentially an additional ancestor (A22), found in Iran, Lebanon and Jordan. (3) Subtype A22 is likely an old version of SRLVs. (4) The transmission routes of some SRLVs are compatible with domestication pathways. (5) This study found no evidence of Icelandic subtype A1 in German sheep.

Seroprevalence of small ruminant lentivirus (SRLV) infection in wild cervids in Poland

Small ruminant lentiviruses (SRLV) are widespread amongst domesticated sheep and goats worldwide. Infection of wild ruminants in close contact with affected domesticated small ruminants has been proposed as an actor in SRLV epidemiology, but studies are limited. The aim of this study was to estimate the apparent (AP) and estimated prevalence (EP) of exposure to SRLV infection in wild ruminants from Poland. Samples originating from 198 free-living cervids comprising 142 European red deer and 56 roe deer were serologically tested using a multi-epitope recombinant antigen ELISA representing subtypes A1, A13, B1, and B2 of SRLV and a commercial ELISA test. The estimated prevalence of SRLV infection was estimated using the Bayesian approach with models that adjusted for the misclassification of animals because of a small population and lack of sampling method, the imperfect performance of the ELISAs and because sera of different species were tested. The calculated estimated prevalence ranged from 5.3 % (95 % CI 0.3, 12.5) to 24.6 % (95 % CI 3.3, 38.5) for the ELISA with multi-epitope antigens while estimated prevalence using the commercial ELISA was 2.5 % (95 % CI 0.2, 6.6). These results may suggest the existence of a new SRLV reservoir in Poland and highlight the importance of surveilling and controlling SRLV infection in domestic and wild ruminants sharing pasture areas.

(Non-)Sense of Milk Testing in Small Ruminant Lentivirus Control Programs in Goats. Comparative Analysis of Antibody Detection and Molecular Diagnosis in Blood and Milk

Small ruminant lentivirus (SRLV) control programs are mainly based on diagnostic tests performed on blood samples collected from sheep and goats. Since blood sampling is costly and stressful for the animals, we evaluated whether milk could be used as an inexpensive and easily collectable matrix for SRLV detection. We therefore compared SRLV detection via two commercial enzyme-linked immunosorbent assays (ELISAs) and quantitative polymerase chain reaction (qPCR) in blood and corresponding milk samples from 321 goats originating from eight different SRLV-infected farms in Flanders (Belgium). The IDscreen^® ELISA had a better relative sensitivity (97% vs 93%) and specificity (100% and 97%) than the Elitest^® ELISA for SRLV-specific antibody detection in milk compared to serum. The higher sensitivity correlates with a 10-fold higher analytical sensitivity of the IDscreen^® test. In contrast to the overall good ELISA results, qPCR on milk cell pellets lacked sensitivity (81%) and specificity (88%), compared to molecular detection in blood leucocyte pellets. Our results show that serology is more suitable than qPCR for SRLV diagnosis, and that milk may represent an interesting matrix for a preliminary evaluation of a herd’s infection status. Serum remains however the sample of choice for control programs where it is important to identify positive animals with the highest sensitivity.

Compartmentalization of Subtype A17 of Small Ruminant Lentiviruses between Blood and Colostrum in Infected Goats Is Not Exclusively Associated to the env Gene

The compartmentalization of small ruminant lentiviruses (SRLVs) subtype A17 was analyzed in colostrum and peripheral blood leukocyte cells of three naturally infected goats. This study aimed to analyze heterogeneity of the SRLV env (V4V5) gene, which encodes neutralizing epitopes of SU glycoprotein, the gag gene encoding capsid protein (CA), and LTR, a noncoding region, responsible for determination of cell tropism. Compartmentalization was assessed using six established tree or distance-based methods, including permutation test to determine statistical significance. We found statistical evidence of compartmentalization between blood and colostrum in all infected goats although phylogenetic evidence of such compartmentalization was not obvious. Our study demonstrated that compartmentalization is not exclusively specific to the env gene, as we revealed that gag and LTR sequences are also compartmentalized between blood and colostrum. The work also confirms the combined use of different methods as essential for reliable determination of intrahost viral compartmentalization. Identifying and characterizing distinct viral subpopulations and the genetic evolution of SRLV in specific anatomical sites enhances our overall understanding of SRLV pathogenesis, immune control, and particularly virus transmission.

Molecular analysis of small-ruminant lentiviruses in Polish flocks reveals the existence of a novel subtype in sheep

Small-ruminant lentivirus (SRLV) infections are widespread in Poland, and circulation of subtypes A1, A12, A13, A16, A17, B1 and B2 has been documented. The aim of this study was to characterize the SRLV strains circulating in sheep and goats in mixed flocks in the Malopolska region, where the highest seroprevalence has been detected. Phylogenetic analysis revealed that most of the isolates from sheep belonged to subtype A13, suggesting that this subtype may be predominant in the Malopolska region. Furthermore, the existence of a new subtype, tentatively designated as A18, was described for the first time. This work extends the current knowledge on the distribution of SRLV subtypes in sheep and goats in Poland and provides further information on the genetic diversity of SRLV. The new data are important for both epidemiological studies and eradication programs and provide insight into the evolution of SRLV.

Comparative Analysis of Different Serological and Molecular Tests for the Detection of Small Ruminant Lentiviruses (SRLVs) in Belgian Sheep and Goats

Countries rely on good diagnostic tests and appropriate testing schemes to fight against economically important small ruminant lentivirus (SRLV) infections. We undertook an extensive comparative analysis of seven commercially available serological tests and one in-house real-time PCR (qPCR) detecting genotype A and B strains using a large panel of representative Belgian field samples and samples from experimentally infected sheep and goats. ELISAs generally performed well and detected seroconversion within three weeks post experimental infection. Two enzyme-linked immunosorbent assays (ELISAs) (Elitest and IDscreen^® kits) showed the highest sensitivities (>96%) and specificities (>95%) in both species, and their combined use allowed to correctly identify the infection status of all animals. Individual agar gel immunodiffusion (AGIDs) kits lacked sensitivity, but interestingly, the combined use of both kits had a sensitivity and specificity of 100%. qPCRs detected SRLV infection before seroconversion at two weeks post infection and showed a specificity of 100%. Sensitivity however remained suboptimal at 85%. These results allow to propose a faster and cheaper diagnostic testing strategy for Belgium by combining a first ELISA screening, followed by confirmation of positive samples in AGID and/or a second ELISA. Since genotypes A and B strains are predominant in many countries, these results are interesting for other countries implementing SRLV control programs.

Maedi-Visna virus: current perspectives

Maedi-Visna virus (MVV) and caprine arthritis-encephalitis virus are commonly known as small ruminant lentiviruses (SRLVs) due to their genetic, structural, and pathogenic similarities. They produce lifelong lasting infections in their hosts, which are characterized by slow progression till overt disease happens. There are four major clinical forms derived from a chronic inflammatory response due to the constant low grade production of viruses from monocyte-derived macrophages: respiratory (caused by interstitial pneumonia), mammary (which may produce a decrease in milk production due to subclinical mastitis), joint (characterized by lameness), and neurological (characterized by chronic nonpurulent meningoencephalomyelitis). There are three levels which try to eliminate the virus: cellular, body, and the flock level. However, SRLVs have ways to counteract these defenses. This review examines some of them.

Genetic characterisation of small ruminant lentiviruses in sheep and goats from the Czech Republic

The aim of this study was to determine the prevalence of small ruminant lentivirus (SRLV) infections on sheep and goat farms which are exempt from state monitoring and carry molecular characterisation of strains circulating amongst these farms without SRLV eradication. A total number of 3,410 blood samples of sheep and goats from 21 herds were collected for the purpose of the project. The detected serological prevalence of maedi visna in sheep was 19.9% (556/2801) and the seroprevalence of caprine arthritis and encephalitis in goats was 14.1% (86/609). All positive animals were tested by the nested polymerase chain reaction (nPCR) method for the presence of provirus in the buffy-coats from EDTA-blood samples. Phylogenetic analysis of 93 SRLV strains identified the genotype in 77 sequences, where 60 of them were genotype A and 17 belonged to genotype B. Whereas all of the genotype B sequences were classified in subtype B2, the genotype A group of isolates showed higher variability and were related to subgenotypes A2 and A3. This study represents the first report of genetic characterisation of SRLV strains circulating in the territory of the Czech Republic.

A cross-sectional study to identify a set of risk factors for caprine herpesvirus 1 infection

BACKGROUND

Caprine herpesvirus 1 (CpHV-1) causes neonatal mortality and reproductive failure in goats. Despite its impact on herd reproductive performance, few studies have investigated the risk factors associated with CpHV-1 infection. The aim of this cross-sectional study was to identify potential herd- and host-level risk factors associated with CpHV-1 prevalence in a goat population with heterogeneous seropositivity for CpHV-1.

RESULTS

Blood samples and individual data from 4542 goats were collected from 255 herds in Piedmont, Italy. Enzyme-linked immunosorbent assay (ELISA) and serum neutralization tests were carried out to detect antibodies against CpHV-1. A mixed-effects model was applied to identify any statistical association between CpHV-1 seropositivity and a set of putative host-level and herd-level risk factors. A total of 630 samples tested were found positive by ELISA (prevalence = 13.9%; 95% confidence interval (CI) 12.9-14.9). Of the 255 tested herds, 85 were classified as positive for the presence of at least one gB-positive animal (herd prevalence 33.3%, 95% CI 27.5-39.2), with a within-herd prevalence between 0.7 and 100% (Q1 = 17.6%; median = 32.3%; Q3 = 50%) (Q = quartiles). The prevalence ratios showed a statistical association with the following risk factors: breeds other than Saanen, older age, larger herd size, meat and extensive herds, and co-existence of CAEV-infected animals.

CONCLUSIONS

Results from this cross sectional study may help to elucidate the natural history of the infection and inform targeted strategies to control a disease with a potentially important impact on animal health and goat farming economy.

Evaluation of caprine arthritis-encephalitis virus transmission in newborn goat kids

ABSTRACT: Caprine arthritis encephalitis causes considerable losses in goat production. The main form of the caprine arthritis encephalitis virus transmission is through the ingestion of colostrum or milk from infected females. However, some transmissions cannot be explained in this manner. Therefore, this study aimed to evaluate transplacental transmission of caprine arthritis encephalitis virus. Blood samples were collected from 283 newborn kids of Anglo-Nubian and Saanen breeds born from seropositive and seronegative goats. Samples were collected immediately after birth and analyzed with agarose gel immunodiffusion and western blot. All samples were negative in the agarose gel immunodiffusion. However, the western blot test demonstrated that four kids were born positive for caprine arthritis encephalitis virus. This result indicates that although in a low frequency (1.4%), there is a possibility of transplacental transmission of small ruminant lentivirus.

Viral load, tissue distribution and histopathological lesions in goats naturally and experimentally infected with the Small Ruminant Lentivirus Genotype E (subtype E1 Roccaverano strain)

Small Ruminant Lentivirus (SRLV) subtype E1, also known as Roccaverano strain, is considered a low pathogenic virus on the basis of natural genetic deletions, in vitro properties and on-farm observations. In order to gain more knowledge on this atypical lentivirus we investigated the in vivo tropism of Roccaverano strain in both, experimentally and naturally infected goats. Antibody responses were monitored as well as tissue distribution and viral load, evaluated by real time PCR on single spliced (gag/env) and multiple spliced (rev) RNA targets respectively, that were compared to histopathological lesions. Lymph nodes, spleen, alveolar macrophages and mammary gland turned out to be the main tissue reservoirs of genotype E1-provirus. Moreover, mammary gland and/or mammary lymph nodes acted as active replication sites in dairy goats, supporting the lactogenic transmission of this virus. Notably, a direct association between viral load and concomitant infection or inflammatory processes was evident within organs such as spleen, lung and testis. Our results validate the low pathogenicity designation of SRLV genotype E1 in vivo, and confirm the monocyte-macrophage cell lineage as the main virus reservoir of this genotype. Accordingly, SRLV genotype E displays a tropism towards all tissues characterized by an abundant presence of these cells, either for their own anatomical structure or for an occasional infectious/inflammatory status.

Seroprevalence and risk factors related to small ruminant lentivirus infections in Belgian sheep and goats

Maedi-Visna virus (MVV) and caprine arthritis encephalitis virus (CAEV) are two prototype members of the group of small ruminant lentiviruses (SRLVs). Both result in progressive and persistent infections of sheep and goats that impact animal health and cause economic losses. In Belgium, the sheep and goat sector is small and consists mostly of hobbyist farmers keeping few animals. A voluntary control program however exists, but less than 2% of the farmers participate to the program. The current lack of SRLV seroprevalence data and knowledge on risk factors related to SRLV seropositivity in this hobbyist sector makes it difficult to evaluate the risk of SRLV transmission from non-certified to SRLV free certified farms. We performed a nationwide SRLV seroprevalence study based on a stratified sampling proportional to the number of sheep and goat holders per province. Randomly selected sheep and goat owners were invited to participate and subject to a short questionnaire to collect information about flock size, animal health condition, age, flock constitution and housing conditions. Samples were collected from maximum 7 animals per farm and tested in a commercial ELISA. In total, we received samples from 87 sheep and 76 goat farms. Sheep flocks showed an overall seroprevalence of 9% (CI _95%: 5-15) and a between-herd seroprevalence of 17% (CI _95%:11-27). Seroprevalence at animal level in goat flocks was 6% (CI _95%: 3-12) and the between-herd seroprevalence was 13% (CI _95%: 7-23). Multiple sheep and goat breeds were found SRLV seropositive. Answers provided during the questionnaire confirmed the mostly hobbyist nature of the sector and showed that more than 65% of sheep and goat farmers had never heard of the disease. The only risk factor found to be related to SRLV seroprevalence was flock size. Herds of more than 10 goats had significantly higher chance to harbor seropositive animals (OR: 4.36; CI: 1.07; 17.73). In conclusion, it was shown that participants to the SRLV free certification program are at risk for reintroduction of the disease in their herds since SRLVs are present on about 15%-20% of non-certified farms. Except from flock size, no clear risk factors were found that are helpfull to identify flocks at risk. Greater effort should be made to inform sheep and goat farmers about the existence and consequences of this disease in order to promote the voluntary control program and further reduce the disease prevalence.

Achievements of an eradication programme against caprine arthritis encephalitis virus in South Tyrol, Italy

Small ruminant lentivirus infections in goats affect both production and animal welfare. This represents a threat to the qualitative and quantitative growth of goat farming, recently observed in mountainous regions such as the Autonomous Province of Bolzano – South Tyrol (Italy). To monitor and eradicate the caprine arthritis encephalitis virus in this goat population, a compulsory eradication campaign was launched, based on a strict census of small ruminants and yearly serological testing of all animals, followed by the consequent culling of seropositive individuals. The campaign succeeded in completely eliminating cases of clinical disease in goats, while drastically reducing the seroprevalence at the herd as well as individual animal level. The serological outcome of the introduced control measures was determined using commercially available ELISA kits, demonstrating their suitability for use in this type of campaign, aimed at reducing seroprevalence as well as clinical manifestations of these infections. However, this clear success is diminished by the failure to achieve a complete eradication of these viruses. The reasons leading to the observed tailing phenomenon and the occurrence of new infections in already sanitised flocks are discussed and implementation of further measures are proposed.

Bayesian estimation of seroprevalence of small ruminant lentiviruses in sheep from Poland

In Poland, no systematic survey of ruminant lentiviruses (SRLVs) infection was performed, neither at the national nor at the regional level and only limited knowledge exists on the prevalence of SRLVs among sheep. The aim of the present study was to establish the true prevalence of SRLVs infection in sheep from Poland at the animal and herd-levels. The blood samples used for this study were the fraction of samples collected by Veterinary Inspection during an official sampling for the national monitoring program for brucellosis. Under this program the animals and herds were randomly selected using the data available from ARMA (Agency for Restructuring and Modernisation of Agriculture). The sampling unit was the herd and the target population included at least 5% of sheep, over 6 months old, from each of 16 voievodships (provinces) of Poland. Two-stage cluster sampling design was performed in this study offering the possibility to determine the prevalence of SRLVs infection, when only a fraction of herds and a fraction of animals in the herds are tested. In total, 8233 sheep serum samples coming from 832 herds were tested by indirect ELISA. 1474 (17.9%) samples were positive and 261 (31.4%) herds with at least one seropositive animals were identified. The overall true prevalence estimated by the Bayesian framework was 9.3% (95% CI 6.8, 11.3) and 33.3% (95% CI 26.5, 38.2) on the animal and herd level, respectively. Large variation in the animal and herd prevalence between the voivodships was observed. True prevalence on the herd level varied from 0.0% (95% CI 0.0, 0.0) to 71.6% (95% CI 67.6, 75.9) whereas true prevalence on the animal level ranged from 0.0% (95% CI 0.0, 0.0) to 55.3% (95% CI 50.0, 61.2). The true prevalence of SRLVs infection at animal and herd level increased according to herd size as was proved by posterior probabilities (POPR).

Investigação sorológica das lentiviroses de pequenos ruminantes nas microrregiões homogêneas do Alto Médio Canindé, Picos e Floriano, Piauí, Brasil

RESUMO: Lentivírus de pequenos ruminantes (LV) é o termo genérico utilizado para designar os vírus da artrite encefalite caprina e Maedi-Visna, os quais pertencem à família Retroviridae, subfamília Orthoretrovirinae, gênero Lentivirus. Tais vírus infectam caprinos e ovinos, causando enfermidades de curso lento com lesões inflamatórias, crônicas e degenerativas que podem atingir vários órgãos, provocando caquexia e morte. Os animais infectados eliminam o vírus sobretudo por meio de secreções e excreções e transmitem-no especialmente em situações de estreito contato. Não há tratamento até o momento. O controle é baseado na criação segregada, no manejo e no sacrifício dos positivos. Esse agente infeccioso já foi relatado em várias partes do mundo, sendo responsável por perdas econômicas significativas. Por o agente ter sido verificado em vários estados do Brasil e por não existirem dados soroepidemiológicos nas mesorregiões sudeste e sudoeste piauiense, esta pesquisa teve por objetivo realizar inquérito sorológico para investigar a ocorrência de anticorpos para o LV em ovinos e caprinos nas microrregiões do Alto Médio Canindé, Picos e Floriano, no Piauí. Para tanto, foram coletadas 1.280 e 1.360 amostras de soro caprino e ovino, respectivamente, oriundos de 20 municípios, distribuídos nas três microrregiões, sendo o número de amostras proporcional ao rebanho efetivo de cada município. As amostras de soro foram analisadas utilizando o teste de imunodifusão em gel de agarose (IDGA). Nenhum dos soros pesquisados reagiu positivamente, constatando-se soroprevalência nula. Ressalta-se a importância da implantação de um rigoroso programa de controle para que se possa evitar a introdução e/ou a disseminação desse agente infeccioso nessas microrregiões.

A census to determine the prevalence and risk factors for caprine arthritis-encephalitis virus and visna/maedi virus in the Swiss goat population

In Switzerland, viruses belonging to two different phylogenetic groups of small ruminant lentiviruses (SRLV) are currently circulating: the caprine arthritis-encephalitis virus (CAEV) and visna/maedi virus (VMV). In the past two decades, a mandatory national control program has led to a very low prevalence of seropositivity, while completely eliminating CAE as a clinical manifestation. However, in order to reduce the high costs and effort associated with this program, adjustments based on the most recent epidemiological knowledge are needed. The purpose of this study was to estimate the seroprevalence of CAEV and VMV using the newest diagnostic tools available, and to identify potential risk factors for infection with these viruses in Switzerland. For the prevalence estimation, a census was carried out including 10,696 farms with a total of 85,454 goats. Blood samples were analysed using a 3-step serological testing algorithm consisting of Chekit ELISA, Western Blot and SU5 ELISA. A risk factor analysis was conducted using logistic regression models built with data obtained from a mail questionnaire, and serological results from the census. The apparent herd-level prevalences were 0.38%, 2.77%, and 3.04% for CAEV, VMV and SRLV, respectively. Animal-level prevalences were 0.06% for CAEV, 0.55% for VMV, and 0.61% for SRLV. No statistically significant risk factors associated with CAEV or VMV infection were identified. However, the proportional high number of CAEV seropositive dwarf goats, in relation to their population size, could indicate that these hobby breeds may slip through some of the official controls. For an infection with SRLV, a medium herd size (7-40 goats) was found to be protective, compared with smaller (OR=1.90, p=0.034) and larger herds (OR=1.95, p=0.038). In conclusion, considering that all CAEV positive animals were culled, these results imply that CAEV is no longer actively spreading and has successfully been controlled in Switzerland. However, given the uncertain pathogenic potential of VMV in goats, future surveillance should also be taking into account the not insignificant number of VMV circulating in the Swiss goat population.

High prevalence of caprine arthritis encephalitis virus (CAEV) in Taiwan revealed by large-scale serological survey

In this study, a large-scale serological survey of caprine arthritis encephalitis virus (CAEV) infection was conducted between March 2011 and October 2012. 3,437 goat blood or milk samples were collected from 65 goat farms throughout Taiwan. A commercial ELISA kit was used to detect antibodies against CAEV. The overall seropositive rate was 61.7% (2,120/3,437) in goats and in 98.5% (64/65) of goat farms. These results provide the first large-scale serological evidence for the presence of CAEV infection, indicating that the disease is widespread in Taiwan.