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

Molecular Characterization of Small Ruminant Lentiviruses in Sheep and Goats: A Systematic Review

Small ruminant lentiviruses (SRLVs) are responsible for chronic and progressive multisystemic clinical forms, which significantly reduce flocks' productivity and have a considerable economic impact on the small ruminant industry. Due to the increase in genetic analysis studies and the potential for misclassification of certain strains, owing to the high genetic variability of these viruses, a systematic review was deemed necessary. This review explores the types of matrices used for molecular detection and phylogenetic studies, the genomic regions selected as targets, and the software utilized for phylogenetic analysis, assessing the geographical distribution of identified genotypes and subgenotypes over time. A thorough comparison of the diagnostic approaches highlights the strengths and limitations of each method, identifying gaps that need to be addressed. Additionally, recombination events and compartmentalization are examined to provide an updated, detailed, and comprehensive overview of SRLV phylogenesis.

The herd-level prevalence of caprine arthritis-encephalitis and genetic characteristics of small ruminant lentivirus in the Lithuanian goat population

Caprine arthritis-encephalitis (CAE) is a progressive disease of goats caused by small ruminant lentivirus (SRLV) and is considered as one of the most important threats for goat farming in developed countries. The disease prevalence has never been investigated in the Lithuanian goat population. Therefore, a descriptive cross-sectional study was carried out in 2021-2022 to determine if SRLV infection was present in the Lithuanian goat population and, in the case of a positive result, to estimate the true herd-level prevalence of SRLV infection and specify genotypes and subtypes of SRLV responsible for the infection. Thirty goat herds counting >5 adult goats were randomly selected and, in each herd, a representative sample of adult goats was blood-sampled and tested serologically for SRLV infection using a commercial ELISA. The herd was considered infected if at least one goat tested positive and the true herd-level prevalence of SRLV infection was estimated using the Bayesian approach. Seropositive animals were found in 17 / 30 herds (57 %; 95 % confidence interval: 39 %, 73 %). The true herd-level prevalence was 56 % (95 % credible interval: 36 %, 76 %). In 10 / 17 seropositive herds whose owners consented for resampling of seropositive goats, 1-5 seropositive goats were tested using the nested real-time PCR (nRT-PCR). Goats from 9 seropositive herds tested positive in the nRT-PCR: in 4 herds for genotype A, in 4 herds for genotype B, and in 1 herd - 2 goats for genotype B and 1 goat for genotype A. From each of 9 nRT-PCR-positive herds, 1 PCR product of each genotype was sequenced using Sanger method and the phylogenic tree was constructed using the neighbor-joining method in the Molecular Evolutionary Genetics Analysis software. Four herds turned out to be infected with B1 subtype (91 % identity with the prototypic strain), 3 herds with A2 subtype (90 %-92 % identity), and a herd with mixed infection was infected with B1 (91 % identity) and A2 subtype (90 % identity). In one herd, the only seropositive goat was found to be infected with the strain most closely related to the A1 subtype (80 % identity). This study shows for the first time that SRLV infection is present and widespread in the Lithuanian goat population and both classical SRLV genotypes, represented by quite typical subtypes A2 and B1, appear to be responsible for the infection.

Small Ruminant Lentiviruses and Caseous Lymphadenitis

Ovine progressive pneumonia and caprine arthritis encephalitis together are referred to as small ruminant lentiviruses (SRLVs). Along with caseous lymphadenitis (CL), SRLV are 2 of the so-called "iceberg diseases" of sheep and goats. In the case of SRLV, healthy tissue can be replaced with unproductive lymphoid tissue causing loss of milk, poor growth in lambs, swollen and painful joints, and shortened productive lives of infected animals. Understanding the characteristics of the SRLVs and the bacteria that causes CL and how to use the serologic tests available will help with prevention and eradication efforts.

First Molecular Characterization of Small Ruminant Lentiviruses in Hungarian Goat Population

In 2023, a molecular study was conducted on the Hungarian goat population to determine genotypes and subtypes of small ruminant lentiviruses (SRLV) infecting these herds. Ten goat herds seropositive for SRLV infection according to a serosurvey conducted earlier in Hungary were selected, and 135 adult goats (>1 year old) were blood sampled. The two-stage nested real-time PCR (nRT-PCR) was used to detect proviral DNA of SRLV and distinguish between two main viral genotypes (A and B). PCR products were submitted for Sanger dideoxy sequencing, and phylogenetic and molecular evolutionary analyses were conducted on the 200-250 bp-long proviral DNA sequences from the end of long terminal repeat (LTR) region and beginning of gag gene using the MEGA11 software. Reference strains included strains most identical to Hungarian sequences according to the Standard Nucleotide BLAST and prototypic strains for the relevant genotypes and subtypes. Proviral DNA of SRLV was detected in goats from all ten tested herds. A single SRLV genotype was detected in 6 herds-genotype A in three herds and B also in three herds. In four herds, mixed infection with genotypes A and B was confirmed. In total, 110/135 seropositive goats tested positive in the nRT-PCR (81.5%): 49/110 goats (44.5%) for genotype A, 54/110 goats (49.1%) for genotype B, and 7/110 goats (6.4%) for both genotypes. Hungarian sequences belonged to subtypes A1/A18, A2, and subtype B1. This is the first study which shows that Hungarian goats are infected by SRLV belonging to both genotypes A and B.

Comparison of serological and molecular methods for differentiation between genotype A and genotype B strains of small ruminant lentiviruses

Introduction

Small ruminant lentiviruses (SRLV) cause multisystemic, degenerative and chronic disease in sheep and goats. There are five genotypes (A, B, C, D and E), of which A and B are the most widespread. The purpose of this study was to evaluate the serotyping efficiency of the Eradikit SRLV Genotyping ELISA and the molecular typing efficiency of a newly developed nested real-time PCR targeting the long terminal repeat-gag (LTR-gag) region using samples from animals infected with subtypes of SRLV known to circulate in Poland.

Material and Methods

A total of 97 sera samples taken from 34 sheep and 63 goats were immunoassayed, and 86 DNA samples from 31 sheep and 55 goats were tested with the PCR. All ruminants were infected with known SRLV strains of the A1, A5, A12, A13, A16, A17, A18, A23, A24, A27, B1 and B2 subtypes.

Results

A total of 69 (80.2%, 95% confidence interval 71.6%-88.8%) out of 86 tested samples gave positive results in the PCR. In 17 out of the 86 (19.8%) samples, no proviral DNA of SRLV was detected. The differentiation between MVV (genotype A) and CAEV (genotype B) by PCR matched the predating phylogenetic analysis invariably. No cross-reactivity was observed. On the other hand, the proportion of samples genotyped the same by the older phylogenetic analysis and the Eradikit SRLV Genotyping ELISA was 42.3%. The test was unable to classify 40.2% of samples, and 17.5% of sera were incorrectly classified.

Conclusion

Our results showed that the Eradikit SRLV genotyping kit is not a reliable method for predicting SRLV genotype, while the nested real-time PCR based on the LTR-gag region did prove to be, at least for genotypes A and B.

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.

The genetic variability of small-ruminant lentiviruses and its impact on tropism, the development of diagnostic tests and vaccines and the effectiveness of control programmes

Introduction

Maedi-visna virus and caprine arthritis encephalitis virus are two closely related lentiviruses which cause multisystemic, progressive and persistent infection in goats and sheep. Because these viruses frequently cross the species barrier, they are considered to be one genetic group called small-ruminant lentiviruses (SRLV). They have in vivo tropism mainly for monocytes and macrophages and organ tropism with unknown mechanisms. Typical clinical signs are pneumonia in sheep, arthritis in goats, and mastitis in both species. Infection with SRLV cannot currently be treated or prevented, and control programmes are the only approaches to avoiding its spread. These programmes rely mainly on annual serological testing and elimination of positive animals. However, the high genetic and antigenic variability of SRLV complicate their early and definitive diagnosis. The objective of this review is to summarise the current knowledge of SRLV genetic variation and its implications for tropism, the development of diagnostic tests and vaccines and the effectiveness of control and eradication programmes.

Material and Methods

Subject literature was selected from the PubMed and the Google Scholar databases.

Results

The high genetic diversity of SRLV affects the performance of diagnostic tools and therefore control programmes. For the early and definitive diagnosis of SRLV infection, a combination of serological and molecular tests is suggested. Testing by PCR can also be considered for sub-yearling animals. There are still significant gaps in our knowledge of the epidemiology, immunology and biology of SRLV and their impact on animal production and welfare.

Conclusion

This information may aid selection of the most effective SRLV spread reduction measures.

First Molecular Characterization of Small Ruminant Lentiviruses Detected in Romania

Small ruminant lentiviruses (SRLVs) are a group of retroviruses that cause multisystem chronic diseases in goats and sheep and lead to production losses in these animals, negatively affecting animal health and welfare. Although molecular characterization of SRLV field isolates has been performed in many countries, there is currently no information on SRLV genotypes circulating in sheep and goats in Romania. Therefore, the main objective of this study was to conduct a molecular and phylogenetic analysis of SRLVs from Romania and determine the degree of genetic relatedness of the obtained sequences to other known SRLV reference strains. A total of 81 sheep lung tissue samples and 41 sheep lung lymph node samples were tested using nested real-time PCR, and samples positive for real-time PCR were used to amplify an 800 bp gag-pol fragment and an overlapping 625 bp fragment of the gag gene. Pairwise DNA distance and phylogenetic analysis showed that the Romanian SRLV strains were closely related to the A2 and A3 strains based on gag-pol sequences and to the A3 and A17 subtypes based on gag sequences. No recombination events were found. Our results revealed that the Romanian sequences have similar epitope patterns to other existing subtypes, although E/K and R/K mutations in epitope 3 were found only in the Romanian sequences, which may have potential value in serological diagnosis. This study is the first report on the genetic characterization of SRLV strains circulating in Romania and provides new information on SRLV heterogeneity. Further detailed studies should be conducted to better understand the divergence of SRLV Romanian strains.

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.

[Indurative mastitis in a herd of Dorper sheep caused by an infection with Maedi Visna virus]

This case report describes indurative mastitis in a herd of sheep caused by Maedi Visna virus (MVV) infection. Reduced udder formation after delivery, small, indurated udders and increased losses of lambs were observed in a herd of Dorper sheep. Examination of the mammary gland and milk did not reveal findings characteristic of chronic bacterial mastitis. The protein supply was insufficient which may have contributed to reduced milk yield, but was considered unlikely as cause for the induration of the mammary gland. Nineteen of the 21 mothers were positive for MVV by serology. Mammary gland and supramammary lymph nodes were collected in a sheep with indurated udder at the time of slaughter. Meat inspection did not reveal lesions in any other organs. One part of the mammary gland showed a mild to moderate multifocal lymphohistiocytic mastitis, the other exhibited a severe diffuse lymphohistiocytic mastitis with atrophy of the glandular acini, vasculopathy, fibrosis and calcification. MVV antigen was visualized by immunohistochemistry in macrophages, dendritic cells, epithelial cells and endothelial cells in the mammary gland, and macrophages and dendritic cells in the supramammary lymph nodes. A large amount of MVV provirus was detected in the supramammary lymph nodes and the severely indurated part of the mammary gland by PCR. In conclusion, indurative mastitis as a result of a systemic infection may occur independently of the commonly known manifestations of Maedi Visna in the lung and central nervous system. MVV should be considered as differential diagnosis in mastitis of sheep. The MVV status of the herd can be tested by serological detection of specific antibodies. Additionally, characteristic histological lesions are present in the mammary gland. MVV antigen can also be detected by immunohistochemistry and MVV provirus by PCR in the altered mammary gland and regional lymph nodes.

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.

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.