Diagnostic performance of ELISA and PCR in identifying SRLV-infected sheep and goats using serum, plasma and milk samples and in early detection of infection in dairy flocks through bulk milk testing

A systematic review and meta-analysis of the validation of serological methods for detecting anti-Toxoplasma gondii antibodies in humans and animals

Toxoplasma gondii is a paradigmatic zoonotic parasite from the One Health perspective, since it is broadly distributed and virtually infects all warm-blooded species. A wide variety of serological techniques have been developed to detect T. gondii infection in humans and animals. Our aim was to describe and compare the main characteristics of these serological tests and validation processes and to critically analyze whether these tests meet the standards required to ensure an accurate serological diagnosis. The current systematic review and meta-analysis included 134 studies that were published from 2013 to 2023. QUADAS 2 tool was used to evaluate the quality of the included studies. A total of 52 variables related to the characteristics of the techniques and analytical and diagnostic validation parameters were studied. A wider panel of tests was developed for humans, including techniques exclusively developed for humans that involve costly equipment and the measurement of different Ig isotypes that are considered biomarkers of congenital toxoplasmosis. Studies conducted in humans frequently employed commercial techniques as reference tests, measured different immunoglobulin isotypes with a predominance for IgG (>50%) and discriminated between acute and chronic infections. In animals, the most commonly used reference techniques were in-house tests, which almost exclusively detected IgG. Common limitations identified in a large number of studies were some misunderstandings of the terms "gold standard" and "reference test" and the absence of information about the negative and positive control sera used or the exact cutoff employed, which were independent of the quality of the study. There is a lack of analytical validation, with few evaluations of cross-reactivity with other pathogens. Diagnostic odds ratio values showed that indirect ELISA based on native or chimeric antigens performed better than other tests. The reproducibility of serological test results in both humans and animals is not guaranteed due to a lack of relevant information and analytical validation. Thus, several key issues should be considered in the future, including interlaboratory ring trials.

Phylogenetic analysis of small ruminant lentiviruses in Mongolian sheep supports an ancient east-west split for the genotype A

The ovine maedi-visna virus (MVV) and caprine arthritis-encephalitis virus (CAEV) are small ruminant lentiviruses (SRLVs) with striking genetic and structural similarities. The presence of SRLV in Mongolian sheep and goats was serologically demonstrated more than a decade ago; however, the viral genotype remains unknown. In total, 329 blood samples were collected from two sheep breeds (i.e., Khalkha and Sumber) in Tov, Govisumber, Arkhangay, Dornogovi, Zavkhan, and Sukhbaatar provinces, Mongolia. Serological and phylogenetic analyses were performed regardless of any apparent clinical signs, although most of the animals appeared healthy. All sheep in three of the six provinces were seronegative, whereas the seroprevalence in the Tov, Govisumber, and Zavkhan provinces averaged 7.9%. Genomic DNA from seropositive animals was tested using hemi-nested polymerase chain reaction, and sub-genomic SRLV sequences were determined from nine samples. Mongolian SRLV sequences clustered within the divergent subtype A22, which was previously found only in Fertile Crescent regions, including Lebanon, Jordan, and Iran, where the first sheep-domestication (Ovis aries) occurred. According to the phylogenetic analysis, genotype A has two ancestors from the ancient Fertile Crescent: (1) Turkish strains and (2) Iranian, Jordanian, and Lebanese strains. The first ancestor spread westward, whereas the second spread eastward, ultimately reaching Mongolia.

Differential gene expression and immune cell infiltration in maedi-visna virus-infected lung tissues

BACKGROUND

Maedi-visna virus (MVV) is a lentivirus that infects monocyte/macrophage lineage cells in sheep, goats, and wild ruminants and causes pneumonia, mastitis, arthritis, and encephalitis. The immune response to MVV infection is complex, and a complete understanding of its infection and pathogenesis is lacking. This study investigated the in vivo transcriptomic patterns of lung tissues in sheep exposed to MVV using the RNA sequencing technology.

RESULT

The results indicated that 2,739 genes were significantly differentially expressed, with 1,643 downregulated genes and 1,096 upregulated genes. Many variables that could be unique to MVV infections were discovered. Gene Ontology analysis revealed that a significant proportion of genes was enriched in terms directly related to the immune system and biological responses to viral infections. Kyoto Encyclopedia of Genes and Genomes analysis revealed that the most enriched pathways were related to virus-host cell interactions and inflammatory responses. Numerous immune-related genes, including those encoding several cytokines and interferon regulatory factors, were identified in the protein-protein interaction network of differentially expressed genes (DEGs). The expression of DEGs was evaluated using real-time polymerase chain reaction and western blot analysis. CXCL13, CXCL6, CXCL11, CCR1, CXCL8, CXCL9, CXCL10, TNFSF8, TNFRSF8, IL7R, IFN-γ, CCL2, and MMP9 were upregulated. Immunohistochemical analysis was performed to identify the types of immune cells that infiltrated MVV-infected tissues. B cells, CD4+ and CD8+ T cells, and macrophages were the most prevalent immune cells correlated with MVV infection in the lungs.

CONCLUSION

Overall, the findings of this study provide a comprehensive understanding of the in vivo host response to MVV infection and offer new perspectives on the gene regulatory networks that underlie pathogenesis in natural hosts.

A Combined Approach for the Characterization of Small Ruminant Lentivirus Strains Circulating in the Islands and Mainland of Greece

Small ruminant lentiviruses are a group of viruses infecting goat and sheep worldwide. These viruses exhibit an extraordinary degree of genetic and antigenic variability that severely influence in vivo and in vitro features, as well as diagnostic test results. Small ruminant farming is the most important animal farming business in Greece, with a high impact on the Greek primary economy. Although SRLV infection and its impact on animal production are well established in the country, little is known about the circulating SRLV strains and their prevalence. The aim of this study was to characterize SRLVs circulating in Greece with a combined serological and molecular approach, using the bulk milk matrix collected from 60 farms in different municipalities. This study allowed us to estimate a seroprevalence of around 52% at the herd level. The B1, B2 and A3 subtypes and a novel A viral cluster were identified. Moreover, the amplicon sequencing method allowed us to identify more than one viral subtype in a sample. These results again confirm the high variability of these viruses and highlight the importance of the constant monitoring of viral evolution, in particular in antigens of diagnostic interest.

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.

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.

Serological testing of an equal-volume milk sample - a new method to estimate the seroprevalence of small ruminant lentivirus infection?

BACKGROUND

In cattle attempts to evaluate within-herd prevalence of various infectious and parasitic diseases by bulk-tank milk (BTM) testing with ELISA have been made with moderate success. The fact that BTM is composed of variable and unknown volumes of milk from individual lactating animals weakens the relationship between numerical result of the ELISA and the within-herd prevalence. We carried out a laboratory experimental study to evaluate if a pooled milk sample created by mixing an equal volume of individual milk samples from seropositive and seronegative goats, henceforth referred to as an equal-volume milk sample (EVMS), would allow for accurate estimation of within-herd seroprevalence of caprine arthritis-encephalitis (CAE) using 3 different commercial ELISAs. By mixing randomly selected milk samples from seronegative and seropositive goats, 193 EVMS were created - 93 made of seronegative samples and 100 with the proportion of seropositive individual milk samples (EVMS%POS) ranging from 1 to 100%. EVMS%POS could be considered as a proxy for the within-herd seroprevalence. Then, OD of EVMS (ODEVMS) of the 193 EVMS was measured using 3 commercial ELISAs for CAE - 2 indirect and 1 competitive.

RESULTS

The cut-off values of ODEVMS indicating SRLV infection were determined. The regression functions were developed to link ODEVMS with EVMS%POS. A significant monotonic relationship between ODEVMS measured with 2 commercial indirect ELISAs and EVMS%POS was identified. Two regression models developed on this basis described approximately 90% of variability and allowed to estimate EVMS%POS, when it was below 50%. High ODEVMS indicated EVMS%POS of > 50%.

CONCLUSION

Our study introduces the concept of serological testing of EVMS as a method of detecting SRLV-infected herds and estimating the proportion of strongly seropositive goats. Further field studies are warranted to assess practical benefits of EVMS serological testing.

Loss of Caprine Arthritis Encephalitis Virus (CAEV) Herd Accreditation: Characteristics, Diagnostic Approach, and Specific Follow-Up Scenarios on Large Dairy Goat Farms

The retrovirus causing caprine arthritis encephalitis (CAE), a slowly progressive inflammatory disease in goats, belongs to the group of small ruminant lentiviruses (SRLVs) which cause lifelong infections that ought to be avoided for animal welfare as well as economic reasons. SRLV accreditation has been in place for forty years in The Netherlands and is based on the screening of small ruminant sera for specific antibodies. This paper evaluates 38 dairy goat herds that lost CAEV accreditation between 2012 and 2022. The characteristics of these herds are discussed, and specific follow-up scenarios, depending on desired goals, are introduced. The herd size of the participating herds varies from approximately 400 to 4600 adult dairy goats. The larger herds tended to be more prone to lose herd accreditation and had more difficulties regaining accreditation. Possible routes of introduction are lined up. The Royal GD's tailor-made approach and advice to support livestock farmers with herds that have lost CAE accreditation are discussed in detail. Specific emphasis is placed on the strategic deployment of various diagnostic tests (such as antibody ELISAs and PCR) in different media, such as (pooled) sera, (bulk)milk and tissue samples. Special attention is paid to the added value of retrospective bulk milk testing or the specific testing of groups based on housing and management, which enables the investigation of the moment of viral introduction and route of transmission into a herd. Furthermore, the prospective implementation of bulk milk and strategic pooled milk sample testing in the Dutch SRLV accreditation programs intensifies surveillance and enables the taking of swift action to prevent further transmission within and between herds. An appeal is made to share experiences to improve programs collectively, and to start research into the underlying mechanisms.

Clearance of Maedi-visna infection in a longitudinal study of naturally infected rams is associated with homozygosity for the TMEM154 resistance allele

Maedi-visna (MV) is a lentiviral disease of sheep responsible for severe production losses in affected flocks. There are no vaccination or treatment options with control reliant on test and cull strategies. The most common diagnostic methods used at present are combination ELISAs for Gag and Env proteins with virus variability making PCR diagnostics still largely an experimental tool. To assess variability in viral loads and diagnostic tests results, serology, DNA and RNA viral loads were measured in the blood of 12 naturally infected rams repeatedly blood sampled over 16 months. Six animals tested negative in one or more tests at one or more time points and would have been missed on screening programmes reliant on one test method or a single time point. In addition the one animal homozygous for the ‘K’ allele of the TMEM154 E35K SNP maintained very low viral loads in all assays and apparently cleared infection to below detectable limits at the final time point it was sampled. This adds crucial data to the strong epidemiological evidence that this locus represents a genuine resistance marker for MV infection and is a strong candidate for selective breeding of sheep for resistance to disease.

Detection of anti-Neospora caninum antibodies in sheep's full-cream milk by a time-resolved fluorescence immunoassay

Ovine neosporosis, caused by the Apicomplexan parasite Neospora caninum, leads to reproductive failure worldwide. Nowadays, there is a trend to develop diagnostic techniques using non-invasive samples, such as milk, in order to reduce animal stress, sample collection effort, and costs. The objective of this study was to develop and validate a highly sensitive and specific serological technique, based on a time resolved-fluorescence immunoassay using a N. caninum GRA7 antigen (GRA7-TRFIA), for the detection of anti-N. caninum immunoglobulins G on sheep' full-cream milk samples. An analytical validation was performed, including intra- and inter-assay precision, analytical sensitivity and accuracy. The diagnostic performance of the assay was evaluated by studying the positive-negative discrimination by Mann Whitney U tests. In additon optimal cut-offs, diagnostic sensitivity and specificity, and areas under the curve were calculated by three Receiver Operating Curve (ROC) analyses, using GRA7-TRFIA and a N. caninum tachyzoite soluble extract-based ELISA (NcSALUVET-ELISA) in blood sera, and the coinciding results of both techniques, as reference techniques. Moreover, Spearman's correlation of GRA7-TRFIA in milk with the techniques in sera and agreement (kappa values) were also estimated. GRA7-TRFIA for milk samples showed an adequate precision, with high analytical sensitivity and accuracy. Regarding ROC analyses, at the optimal cut-offs, the diagnostic sensitivity and specificity were more than 90 % in all cases. In addition, GRA7-TRFIA values in milk were more positively correlated to GRA7-TRFIA values in blood sera than in the case of values obtained with NcSALUVET-ELISA. GRA7-TRFIA in milk showed an almost perfect agreement with GRA7-TRFIA in blood sera (kappa = 0.98) and with the coinciding results of GRA7-TRFIA and NcSALUVET in blood sera (kappa = 1.00), while it has a substantial agreement with NcSALUVET-ELISA (kappa = 0.69). In the light of these results, GRA7-TRFIA in full-cream milk samples is a highly sensitive technique that could be used for screening anti-N. caninum antibodies in sheep flocks.

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.

Further Insights Into Caprine Arthritis Encephalitis (CAE): The Current Status of Seroprevalence Among Small Ruminants in Two Selected States of Peninsular Malaysia

Caprine arthritis-encephalitis virus (CAEV) is a member of the genus lentivirus causing caprine arthritis-encephalitis (CAE), a chronic inflammatory condition affecting the lungs, joints, udder and central nervous system of small ruminants such as sheep and goats. CAE is distributed worldwide and is recognised as a significant cause of morbidity and decreased milk production in dairy goats. Earlier studies highlighted the clinicopathological features and supplied preliminary serological evidence for the existence of CAE among selected goat herds in Malaysia. Therefore, this study aims to provide further insights into the seroprevalence and contributing factors of CAE among sheep and goat herds in two states of Peninsular Malaysia. The blood samples and biodata were randomly collected from a total of 262 individual sheep (40) and goat (222) in seven smallholder farms. Blood sera were tested for specific anti-CAEV antibodies using Qayee-Bio CAEV sandwich-ELISA test kits according to standard procedures. Our results of the study revealed 21.4% (95% CI: 15.8-28.6) apparent and 20.6% (95% CI: 14.5-27.8) true seroprevalence with significant differences (p < 0.05) in seroconversion rates between the states, farms, production systems and breeds of small ruminants. The prevalence of CAE in the Malaysian Peninsular is a potential threat to the small ruminant industry and developing agricultural economy. Further studies are required to determine the genetic characteristics, distribution and risk factors of CAEV for effective prevention and control in Malaysia.

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

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

Worldwide Prevalence of Small Ruminant Lentiviruses in Sheep: A Systematic Review and Meta-Analysis

Small Ruminant Lentiviruses (SRLV) are highly prevalent retroviruses with significant genetic diversity and antigenic heterogeneity that cause a progressive wasting disease of sheep called Maedi-visna. This work provides a systematic review and meta-analysis of the last 40 years (1981-2020) of scientific publications on SRLV individual and flock prevalence. Fifty-eight publications and 314 studies were included. Most articles used a single diagnostic test to estimate prevalence (77.6%), whereas articles using three or more tests were scarce (6.9%). Serological tests are more frequently used than direct methods and ELISA has progressively replaced AGID over the last decades. SRLV infection in sheep is widespread across the world, with Europe showing the highest individual prevalence (40.9%) and being the geographical area in which most studies have been performed. Africa, Asia, and North America show values between 16.7% to 21.8% at the individual level. South and Central America show the lowest individual SRLV prevalence (1.7%). There was a strong positive correlation between individual and flock prevalence (ρ = 0.728; p ≤ 0.001). Despite the global importance of small ruminants, the coverage of knowledge on SRLV prevalence is patchy and inconsistent. There is a lack of a gold standard method and a defined sampling strategy among countries and continents.

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.

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

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

(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.

Serological Diagnosis of Lentivirus Infection in Goats Raised in Algeria

Introduction

Infection of goats with caprine arthritis encephalitis virus (CAEV) has been detected in variable proportions in many countries all over the world. Here, we investigated the seroprevalence of CAEV in goats raised in Algeria.

Material and Methods

A serological survey was performed on serum samples from 1,313 goats, including the local breeds (Arabia and Dwarf of Kabylia) and imported European breeds (Alpine and Saanen). Blood samples were taken from goats on 38 farms distributed across four different geographical regions of Algeria. Serum samples were tested for CAEV antibodies using a commercial ELISA.

Results

A total of 390 serum samples were found to be positive for CAEV, giving an overall seropositivity rate of 29.7% in individual animals and 97.37% (37/38) at the goat farm level.

Conclusion

These results provide the first large-scale serological evidence for the presence of CAEV infection in both the local and imported breeds of goats raised in Algeria, indicating that the virus infection is widespread.

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.

Seroprevalence of small ruminant caprine arthritis encephalitis lentivirus among goats from selected small ruminant farms in Selangor, Malaysia

Background and Aim:

Caprine arthritis encephalitis (CAE) is an important viral disease of small ruminants particularly in dairy goats with severe social and economic implication. Hence, this study was designed to determine the seroprevalence of CAE virus (CAEV) among goat population in selected small ruminant farms in Selangor and the risk factors associated with the occurrence of the disease.

Materials and Methods:

Blood samples were collected from a total of 91 goats selected at random. Blood serum was harvested and used for competitive enzyme-linked immunosorbent assay test to detect antibodies against CAE virus.

Results:

The result obtained showed that 8/91 (8.8%) of the goats were seropositive for CAEV. In addition, biosecurity management, source of origin and sex of the animal were observed to be important risk factors associated with the occurrence of CAE in goats.

Conclusion:

The findings of this study affirmed that the seroprevalence of CAEV infection among goat population in small ruminant farms in Selangor, Malaysia, is low. However, there is need to institute strict control measures such as testing and culling positive animals or separation of infected animals from those that tested negative to the disease for effective eradication of the disease.

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

Aim

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

Materials and Methods

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

Results

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

Conclusion

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

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

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

Research And Practice: Quantification Of Raw And Heat-Treated Cow Milk in Sheep Milk, Cheese And Bryndza By ELISA Method

The aim of this study was to test the reliability of commercial ELISA tests (RC-bovino) within raw and heat treated cow milk detection in sheep milk and cheese in order to obtain a high-quality, reliable and economically beneficial method suitable for routine application in practice. These tests were subsequently used for quantification of cow milk in commercial "Bryndza". Raw sheep milk, cow milk and heat-treated cow milk (pasteurisation at 72 °C for 15 sec or at 85 °C for 3 sec) were mixed in precisely defined proportions (0 - 100% cow milk in sheep milk). The milk mixtures were sampled to detect adulteration and subsequently cheese was made. By ELISA tests was possible to determine these amounts of raw cow milk in sheep milk: 0.5% (0.2%), 5 % (4.81%), 50% (42.08%) and 75% (56.52%). The pasteurized samples in different combinations gave lower optical density responses than those prepared from raw milk (by approximately 60%). In context with the above mentioned, the relationship between the real and detected amount of cow milk (%) in different production stages (milk, cheese) using a regression analysis was examined. However, a lower reliability of the detection was indicated by R2 values, which ranged from 0.4058 (cheese) to 0.5175 (milk). In practice this means that although individual percentage (%) of cow milk in the sample can be detected, but in the unknown sample it can not be clearly confirm whether the cow milk was raw or heat-treated. In this context, the results can be inaccurate and may not correspond to the real situation. Within monitoring phase of this research, 9 samples of bryndza were analysed with the results of detected cow milk ranged from 11.56% to 14.3%. The obtained results confirm that the appropriate selection of ELISA tests can become an important factor in the setting of analytical capabilities for the detection of milk and cheese adulteration.

Small ruminant lentivirus infections and diseases

Small ruminant lentiviruses include viruses with diverse genotypes that frequently cross the species barrier between sheep and goats and that display a great genetic variability. These characteristics stress the need to consider the whole host range and to perform local surveillance of the viruses to opt for optimum diagnostic tests, in order to establish control programmes. In the absence of effective vaccines, a comprehensive knowledge of the epidemiology of these infections is of major importance to limit their spread. This article intends to cover these aspects and to summarise information related to characteristics of the viruses, pathogenesis of the infection and description of the various syndromes produced, as well as the diagnostic tools available, the mechanisms involved in transmission of the pathogens and, finally, the control strategies that have been designed until now, with remarks on the drawbacks and the advantages of each one. We conclude that there are many variables influencing the expected cost and benefits of control programs that must be evaluated, in order to put into practice measures that might lead to control of these infections.

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

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

Caprine arthritis encephalitis and caseous lymphadenitis in goats: use of bulk tank milk ELISAs for herd-level surveillance

The objective of this study was to evaluate the diagnostic performance of two ELISA tests applied to bulk tank milk (BTM) as the first part of a two-step test scheme for the surveillance of caprine arthritis encephalitis (CAE) and caseous lymphadenitis (CLA) infections in goats. The herd-level BTM tests were assessed by comparing them to the test results of individual serological samples. The potential for refining the cut-off levels for BTM tests used as surveillance tools in a population recently cleared of infection was also investigated. Data was gathered on serum (nCAE =9702 and nCLA=13426) and corresponding BTM (nCAE=78 and nCLA=123) samples from dairy goat herds enrolled in the Norwegian disease control and eradication programme 'Healthier Goats'. The results showed that the sensitivity and specificity of the CAE ELISA BTM test with respect to detecting ≥2 per cent within-herd prevalence were 72.7 per cent and 86.6 per cent, respectively. For the CLA ELISA BTM the sensitivity and specificity were 41.4 per cent and 81.7 per cent, respectively, for the same goal of detection. The results suggest that BTM testing can be applied as a cost-effective first step for early detection of CAE and CLA infection.

Study on Correlation of Maedi-Visna Virus (MVV) with Ovine Subclinical Mastitis in Iran

Maedi-Visna is an important slow viral disease of sheep leading to progressive pneumonia, encephalitis and mastitis. Udder is one of the organs affected by MVV. Despite the fact that in Iran Maedi-Visna is known since 2000, to the authors' knowledge correlation of subclinical mastitis and infection with MVV has not been assayed. In this study 50 milk samples from 10 flocks in East Azerbaijan Province of Iran were tested. None of the animals exhibited any clinical signs of the disease. Forty samples were collected from CMT positive ewes and ten were taken from CMT negative ewes. Milk samples were analyzed using PCR targeting gag sequence. Presence of provirus DNA was detected in one sample from CMT negative and seven samples from CMT positive ewes. These data demonstrate that 16.5 % of sheep with subclinical mastitis were infected to MVV. Thus this virus can be considered one of the main pathogenic agents of mastitis and can be dramatically transmitted to lambs by milk.

Evolution of specific antibodies and proviral DNA in milk of small ruminants infected by small ruminant lentivirus

The diagnosis of Small Ruminant Lentivirus (SRLV) is based on clinical signs, pathological lesions and laboratory testing. No standard reference test for the diagnosis of maedi visna has been validated up to the present, and it is puzzling that tests which detect antibodies against the virus and tests which detect the proviral genome may render opposite results. The aim of this study was to evaluate the presence in milk throughout a lactation period of specific antibodies by ELISA and of SRLV proviral DNA by a PCR of the highly conserved pol region. A six-month study was conducted with the milk of 28 ewes and 31 goats intensively reared. The percentage of animals with antibodies against SRLV increased throughout the study period. Seroprevalence in sheep was 28% at the beginning of the study and by the end it had increased up to 52.4%. In goats, initial seroprevalence of 5.6% increased to 16%. The percentage of PCR positive ewes was stable throughout the study period. Of the positive sheep, 21.4% were PCR-positive before antibodies could be detected and most of them became PCR-negative shortly after the first detection of antibodies. This might suggest that antibodies have a neutralizing effect. In addition, an equal percentage of sheep were always PCR-negative but either became ELISA-positive or was always ELISA-positive, which might support this hypothesis. On the other hand, the PCR results in goats did not follow any pattern and oscillated between 35.3% and 55.6% depending on the month. Most goats positive by PCR failed to develop antibodies in the 6 months tested. We may conclude that the infection and the antibody response to it follow a different trend in sheep and goats.

Small ruminant lentiviruses (SRLVs) break the species barrier to acquire new host range

Zoonotic events of simian immunodeficiency virus (SIV) from non-human primates to humans have generated the acquired immunodeficiency syndrome (AIDS), one of the most devastating infectious disease of the last century with more than 30 million people dead and about 40.3 million people currently infected worldwide. Human immunodeficiency virus (HIV-1 and HIV-2), the two major viruses that cause AIDS in humans are retroviruses of the lentivirus genus. The genus includes arthritis-encephalitis virus (CAEV) and Maedi-Visna virus (MVV), and a heterogeneous group of viruses known as small ruminant lentiviruses (SRLVs), affecting goat and sheep. Lentivirus genome integrates into the host DNA, causing persistent infection associated with a remarkable diversity during viral replication. Direct evidence of mixed infections with these two closely related SRLVs was found in both sheep and goats. The evidence of a genetic continuum with caprine and ovine field isolates demonstrates the absence of an efficient species barrier preventing cross-species transmission. In dual-infected animals, persistent infections with both CAEV and MVV have been described, and viral chimeras have been detected. This not only complicates animal trade between countries but favors the risk that highly pathogenic variants may emerge as has already been observed in the past in Iceland and, more recently, in outbreaks with virulent strains in Spain. SRLVs affecting wildlife have already been identified, demonstrating the existence of emergent viruses adapted to new hosts. Viruses adapted to wildlife ruminants may acquire novel biopathological properties which may endanger not only the new host species but also domestic ruminants and humans. SRLVs infecting sheep and goats follow a genomic evolution similar to that observed in HIV or in other lentiviruses. Lentivirus genetic diversity and host factors leading to the establishment of naturally occurring virulent versus avirulent infections, in addition to the emergence of new strains, challenge every aspect of SRLV control measures for providing efficient tools to prevent the transmission of diseases between wild ungulates and livestock.

Small ruminant lentiviruses: genetic variability, tropism and diagnosis

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

An insight into a combination of ELISA strategies to diagnose small ruminant lentivirus infections

A single broadly reactive standard ELISA is commonly applied to control small ruminant lentivirus (SRLV) spread, but type specific ELISA strategies are gaining interest in areas with highly prevalent and heterogeneous SRLV infections. Short (15-residue) synthetic peptides (n=60) were designed in this study using deduced amino acid sequence profiles of SRLV circulating in sheep from North Central Spain and SRLV described previously. The corresponding ELISAs and two standard ELISAs were employed to analyze sera from sheep flocks either controlled or infected with different SRLV genotypes. Two outbreaks, showing SRLV-induced arthritis (genotype B2) and encephalitis (genotype A), were represented among the infected flocks. The ELISA results revealed that none of the assays detected all the infected animals in the global population analyzed, the assay performance varying according to the genetic type of the strain circulating in the area and the test antigen. Five of the six highly reactive (57-62%) single peptide ELISAs were further assessed, revealing that the ELISA based on peptide 98M (type A ENV-SU5, consensus from the neurological outbreak) detected positives in the majority of the type-A specific sera tested (Se: 86%; Sp: 98%) and not in the arthritic type B outbreak. ENV-TM ELISAs based on peptides 126M1 (Se: 82%; Sp: 95%) and 126M2 0,65 0.77 (Se: 68%; Sp: 88%) detected preferentially caprine arthritis encephalitis (CAEV, type B) and visna/maedi (VMV, type A) virus infections respectively, which may help to perform a preliminary CAEV vs. VMV-like typing of the flock. The use of particular peptide ELISAs and standard tests individually or combined may be useful in the different areas under study, to determine disease progression, diagnose/type infection and prevent its spread.

Lentivírus em caprinos leiteiros do semiárido paraibano: prevalência de anticorpos, fatores de risco e detecção molecular

Os objetivos do presente trabalho foram determinar a prevalência de caprinos leiteiros soropositivos para a infecção por Lentivirus de pequenos ruminantes no semiárido do Estado da Paraíba, Nordeste do Brasil, identificar fatores de risco associados à prevalência de rebanhos positivos, e realizar a detecção molecular do agente. Foram utilizadas 1047 cabras leiteiras de 110 propriedades selecionadas aleatoriamente no Município de Monteiro, Estado da Paraíba, no período de março de 2009 a dezembro de 2011. Para o diagnóstico da infecção por Lentivirus, foi utilizado o teste de imunodifusão em gel de ágar (AGID). Um ano após foi realizada nova sorologia, e PCR em tempo real foi aplicada em amostras de sangue e leite de 48 cabras procedentes de quatro propriedades com animais soropositivos. As prevalências de propriedades positivas e de animais soropositivos na AGID foram 44,6% (IC 95% = 35,1% - 54,3%) e 8,1% (IC 95% = 5,6% - 16,8%), respectivamente. Realizar corte e desinfecção de umbigo (odds ratio = 2,44; p = 0,048) e condições de aglomeração de animais (odds ratio = 3,45; p = 0,048) foram associadas com a prevalência de propriedades positivas. Um ano após a realização do inquérito sorológico, foi verificada a permanência de animais infectados, detectados por PCR em tempo real a partir de amostras de sangue e leite. A PCR em tempo real das amostras de leucócitos circulantes apresentou boa performance, com sensibilidade de 100%, especificidade de 92,86%, concordância de 93,75% e indicador Kappa de 0,765. Sugere-se que seja realizado um trabalho de educação sanitária junto aos produtores sobre medidas de prevenção com o objetivo de reduzir a disseminação da infecção nos rebanhos.

Molecular and genetic characteristics of small ruminant lentiviruses in Slovenia

Small ruminant lentiviruses (SRLV) are spread throughout the world, including Slovenia, where the first evidence of caprine arthritis encephalitis virus (CAEV) infection was found in 1996. This study was conducted to investigate the molecular and genetic characteristics of SRLV infection in Slovenia in order to classify our strains in relation to other known SRLV strains worldwide as well as to establish molecular techniques in concordance with serology. In this study, 340 goats and sheep were tested. Serological examination revealed that 57% of the goats and only 14% of the sheep were seropositive. The results of this study also show that the polymerase chain reaction (PCR) used in this study is less reliable than ELISA, with only 60.6% of the seropositive animals being PCR positive. Thirty-eight nucleotide sequences of the gag region encoding the matrix protein were determined and compared to sequences derived from the GenBank, revealing that Slovenian SRLV strains belong to sequence groups A and B, being maedivisna virus (MVV) and CAEV-like, respectively. In one goat herd, the presence of more than one genotype was confirmed and the majority of goat SRLV sequences were more closely related to MVV than to CAEV prototype strains.

Quantitative estimation of the impact of caprine arthritis encephalitis virus infection on milk production by dairy goats

This retrospective study investigated milk production losses associated with serological evidence (serostatus) of caprine arthritis encephalitis virus (CAEV) infection over one lactation in 4543 Murciano-Granadina goats from 22 herds in Spain. The seroprevalence of infection was 18%, ranging from 0% to 2% in 11 herds, 7% to 60% in 10 herds and was 100% in one herd. Seropositive does had significantly shorter lactations, produced less milk and milk fat, lactose and dry extract and had higher somatic cell counts than their seronegative counterparts, although differences in milk production between seropositive and seronegative animals were noted between herds. Mixed regression models confirmed the association between CAEV seropositivity and reduced milk production. The adjusted, least squares mean (LSM) test-day milk yield was 10% less in seropositive compared to seronegative does and this difference varied according to lactation number. In contrast, differences in the LSM of milk fat, lactose and dry extract percentages between seropositive and seronegative goats were only between 0.1% and 0.2% and did not increase with lactation number. The findings of this study provide strong evidence that CAEV-infection can be a major cause of reduction in milk yield in goats and its control should be considered as part of dairy goat herd health schemes.

Comparison of two PCR and one ELISA techniques for the detection of small ruminant lentiviruses (SRLVs) in milk of sheep and goats

The aim of the present study was to compare the efficiency of two PCR techniques for the diagnosis of small ruminant lentiviruses (SRLVs). Detection of the proviral genome by PCR, though sensitive, is difficult due to the heterogeneity of the SRLV genomes. One of the PCR techniques amplifies a fragment in the pol gene (pol-PCR) and the other PCR targets the LTR region of the proviral genome (LTR-PCR). Milk from 194 sheep and 163 goats from farms in the Central Spain was analyzed by both techniques and compared to results obtained by ELISA. When compared to the serologic assay, the agreement of both PCR techniques was very low (0.024 and 0.020 in sheep, and 0.124 and 0.114 in goats). In view of these results, it may be concluded that the efficacy of PCR for the diagnosis of SRLVs is low and a combination of PCR and ELISA should be used for diagnosis.

First molecular characterization of visna/maedi viruses from naturally infected sheep in Turkey

Recent worldwide serological and genetic studies of small ruminant lentiviruses (SRLV) have led to the description of new genotypes and the development of new diagnostic tests. This study investigated the detection and molecular characterization of visna/maedi virus (VMV) infection in serum and blood samples from pure and mixed sheep breeds acquired from different regions in Turkey using ELISA and PCR techniques. The prevalence of VMV was 67.8 % by ELISA and/or LTR-PCR with both assays showing a medium level of agreement (kappa: 0.26; ± 0.038 CI). Positivity of VMV in sheep increased according to the age of the animal, although PCR positivity was higher than ELISA in young individuals. Phylogenetic analysis of 33 LTR sequences identified two distinct clades that were closely related to American and Greek LTR sequences. Phylogenetic analysis of 10 partial gag gene sequences identified A2, A3, A5, A9, A11 subtypes of genotype A SRLVs. In vitro culture of all isolates in fetal sheep lung cells (FSLC) showed a slow/low phenotype causing less or no lytic infection compared with infection with the WLC-1 American strain characterized by a rapid/highly lytic phenotype. Phylogenetic analysis revealed that Turkish VMV sequences preceded the establishment of American or Greek strains that were associated with the migration of sheep from the Middle East to Western Europe several centuries ago. This is the first study that describes Turkish VMV sequences with the molecular characterization of LTR and gag genes, and it strongly suggests that SRLV-genotype A originated in Turkey.

Serological evidence of caprine arthritis-encephalitis virus (CAEV) infection in indigenous goats in the Sultanate of Oman

Caprine arthritis encephalitis (CAE) is a chronic debilitating disease of goats caused by a lentivirus responsible for economic losses as a result of a drop in milk production and weight loss. The objective of the study was to determine if indigenous goats from five different regions in the Sultanate of Oman exhibit serological evidence of exposure to CAEV using a competitive-inhibition ELISA technique. Blood samples were collected from slaughtered goats (N=1,110) and from the National Serum Bank (n=528). In total, 83 (5.1%) of screened samples were classed as seropositive. The results provide the first serological evidence for the presence of CAEV in Oman.