Degenerate and specific PCR assays for the detection of bovine leukaemia virus and primate T cell leukaemia/lymphoma virus pol DNA and RNA: phylogenetic comparisons of amplified sequences from cattle and primates from around the world

Inter-laboratory comparison of eleven quantitative or digital PCR assays for detection of proviral bovine leukemia virus in blood samples

Bovine leukemia virus (BLV) is the etiological agent of enzootic bovine leukosis and causes a persistent infection that can leave cattle with no symptoms. Many countries have been able to successfully eradicate BLV through improved detection and management methods. However, with the increasing novel molecular detection methods there have been few efforts to standardize these results at global scale. This study aimed to determine the interlaboratory accuracy and agreement of 11 molecular tests in detecting BLV. Each qPCR/ddPCR method varied by target gene, primer design, DNA input and chemistries. DNA samples were extracted from blood of BLV-seropositive cattle and lyophilized to grant a better preservation during shipping to all participants around the globe. Twenty nine out of 44 samples were correctly identified by the 11 labs and all methods exhibited a diagnostic sensitivity between 74 and 100%. Agreement amongst different assays was linked to BLV copy numbers present in samples and the characteristics of each assay (i.e., BLV target sequence). Finally, the mean correlation value for all assays was within the range of strong correlation. This study highlights the importance of continuous need for standardization and harmonization amongst assays and the different participants. The results underscore the need of an international calibrator to estimate the efficiency (standard curve) of the different assays and improve quantitation accuracy. Additionally, this will inform future participants about the variability associated with emerging chemistries, methods, and technologies used to study BLV. Altogether, by improving tests performance worldwide it will positively aid in the eradication efforts.

Bovine Leukaemia Virus: Current Epidemiological Circumstance and Future Prospective

Bovine leukaemia virus (BLV) is a deltaretrovirus that is closely related to human T-cell leukaemia virus types 1 and 2 (HTLV-1 and -2). It causes enzootic bovine leukosis (EBL), which is the most important neoplastic disease in cattle. Most BLV-infected cattle are asymptomatic, which potentiates extremely high shedding rates of the virus in many cattle populations. Approximately 30% of them show persistent lymphocytosis that has various clinical outcomes; only a small proportion of animals (less than 5%) exhibit signs of EBL. BLV causes major economic losses in the cattle industry, especially in dairy farms. Direct costs are due to a decrease in animal productivity and in cow longevity; indirect costs are caused by restrictions that are placed on the import of animals and animal products from infected areas. Most European regions have implemented an efficient eradication programme, yet BLV prevalence remains high worldwide. Control of the disease is not feasible because there is no effective vaccine against it. Therefore, detection and early diagnosis of the disease are essential in order to diminish its spreading and the economic losses it causes. This review comprises an overview of bovine leukosis, which highlights the epidemiology of the disease, diagnostic tests that are used and effective control strategies.

Interlaboratory Comparison of Six Real-Time PCR Assays for Detection of Bovine Leukemia Virus Proviral DNA

Quantitative real-time PCR (qPCR) is increasingly being used for the detection of bovine leukemia virus (BLV) proviral DNA. Nevertheless, quality control for the validation and standardization of such tests is currently lacking. Therefore, the present study was initiated by three Office International des Epizooties (OIE) reference laboratories and three collaborating laboratories to measure the interlaboratory variability of six already developed and available BLV qPCR assays. For that purpose, an international panel of 58 DNA samples reflecting the dynamic range of the majority of the assays was distributed to six testing centers. Based on qualitative results, the overall agreement among all six laboratories was moderate. However, significant variability in the measurement of the BLV proviral DNA copy number was observed among different laboratories. Quantitative PCR assays, even when performed by experienced staff, can yield large variability in BLV proviral DNA copy numbers without harmonization. Further standardization of different factors (i.e., utilization of unified protocols and unique calibrators) should increase interlaboratory agreement.

Molecular characterization of bovine leukemia virus from Moldovan dairy cattle

Bovine leukemia virus (BLV) is the causative agent of enzootic bovine leukosis (EBL), a disease that has worldwide distribution. Whilst it has been eradicated in most of Western Europe and Scandinavia, it remains a problem in other regions, particularly Eastern Europe and South America. For this study, in 2013, 24 cattle from three farms in three regions of Moldova were screened by ELISA and nested PCR. Of these cattle, 14 which were PCR positive, and these were molecularly characterized based on the nucleotide sequence of the env gene and the deduced amino acid sequence of the encoded gp51 protein. Our results demonstrated a low level of genetic variability (0-2.9%) among BLV field strains from Moldova, in contrast to that observed for other retroviruses, including human immunodeficiency virus (HIV) (20-38%) Mason IL (Trudy vologod moloch Inst 146–164, 1970) and equine infectious anemia virus (EIAV) (~40%) Willems L et al (AIDS Res Hum Retroviruses 16(16):1787–1795, 2000), where the envelope gene exhibits high levels of variation Polat M et al (Retrovirology 13(1):4, 2016). Sequence comparisons and phylogenetic analysis revealed that BLV genotype 7 (G7) is predominant in Moldova and that the BLV population in Moldovan cattle is a mixture of at least three new sub-genotypes: G7D, G7E and G4C. Neutrality tests revealed that negative selection was the major force operating upon the 51-kDa BLV envelope surface glycoprotein subunit gp51, although one positively selected site within conformational epitope G was detected in the N-terminal part of gp51. Furthermore, two functional domains, linear epitope B and the zinc-binding domain, were found to have an elevated ratio of nonsynonymous to synonymous codon differences. Together, these data suggest that the evolutionary constraints on epitopes G and B and the zinc-binding domains of gp51 differ from those on the other domains, with a tendency towards formation of homogenous genetic groups, which is a common concept of global BLV diversification during virus transmission that may be associated with genetic drift.

Identification and characterization of common B cell epitope in bovine leukemia virus via high-throughput peptide screening system in infected cattle

Background

Bovine leukemia virus (BLV) is the causative agent of enzootic bovine leukosis, the most common neoplastic disease of cattle. BLV is closely related to human T cell leukemia virus. B cell epitopes are important for the use of antibodies as therapeutic agents, the epitope-driven vaccine design, and immunological assays. A common B cell epitope for BLV has not yet been found due to individual differences in disease susceptibility.

Results

We used a peptide microarray with 156 synthetic 15-mer peptides covering the envelope glycoprotein gp51 and the Gag proteins p15, p24, and p12 to map B cell epitope and one B cell epitope, gp51p16, was recognized by all four cattle experimentally infected with BLV. A newly developed high-throughput peptide ELISA system revealed 590 (91.2 %) of 647 cattle naturally infected with BLV, carrying 25 different bovine leukocyte antigen class II DRB3 (BoLA-DRB3) alleles, responded to a 20-mer gp51p16-C peptide containing a C-terminal cysteine and gp51p16. Alanine mutation and comparison of the sequences at 17 amino acid positions within gp51p16-C revealed that R7, R9, F10, V16, and Y18 were the common binding sites to BLV antibodies, and two of these sites were found to be highly conserved. Transient expression in the cells of five infectious molecular clones of BLV with a single alanine mutation at five common antibody binding sites had no effect syncytia formation of the gp51 protein. In addition, the mutant proteins, R7A and R9A had no effect on the expression of gp51 protein; the gp51 protein expressions of F10A, V16A and Y18A were lower than that of the wild type protein.

Conclusions

This is the first report to identify a common B cell epitope in BLV by comprehensive screening of BLV-infected cattle with varied genetic backgrounds in BoLA-DRB3. Our results have important implications for disease control and diagnosis.

Development of an improved real time PCR for the detection of bovine leukaemia provirus nucleic acid and its use in the clarification of inconclusive serological test results

With the aim to erradicate Enzootic Bovine Leukosis from Poland, a more sensitive real-time polymerase chain reaction was required and developed to detect proviral Bovine leukaemia virus (BLV) DNA, the causative agent of Enzootic Bovine Leukosis (EBL). This new method proved more sensitive for our needs, than the current protocols available in the public domain. DNA was extracted from peripheral blood leukocytes of 51 cattle, which had given rise to doubtful serological test results by ELISA, and from mesenteric lymph nodes of six cattle that were slaughtered as EBL suspect cases. Additionally, fourteen DNA samples were obtained from animals with a strong BLV antibody response by ELISA. All real-time data were compared to results obtained from three different nested PCR methods. All 14 strongly positive ELISA samples were positive in all PCR tests. The real-time assay in comparison to the conventional PCR methods detected 7.8% (4/51) more specimens positive for BLV nucleic acid and showed a detection limit down to one copy. These observations represent the first report in the value of using a real-time method to help elucidate the disease status of animals when inconclusive ELISA results are obtained in the diagnostic laboratory. Thus, this method should be recommended for use in countries which have implemented an EBL-eradication programme, where a low level of BLV infection is evident.

Bovine leukemia virus can be classified into seven genotypes: evidence for the existence of two novel clades

Previous studies have classified the env sequences of bovine leukemia virus (BLV) provirus from different locations worldwide into between two and four genetic groupings. These different studies gave unique names to the identified groups and no study has yet integrated all the available sequences. Thus, we hypothesized that many of the different groups previously identified actually correspond to a limited group of genotypes that are unevenly distributed worldwide. To examine this hypothesis, we sequenced the env gene from 28 BLV field strains and compared these sequences to 46 env sequences that represent all the genetic groupings already identified. By using phylogenetic analyses, we recovered six clades, or genotypes, that we have called genotypes 1, 2, 3, 4, 5 and 6. Genotypes 1–5 have counterparts among the sequence groupings identified previously. One env sequence did not cluster with any of the others and was highly divergent when compared with the six genotypes identified here. Thus, an extra genotype, which we named 7, may exist. Similarity comparisons were highly congruent with phylogenetic analyses. Furthermore, our analyses confirmed the existence of geographical clusters.

The complete genomic sequence of an in vivo low replicating BLV strain

DNA was extracted from lamb lymphocytes that were infected in vivo with a BLV strain after inoculation with the peripheral blood mononuclear cells from a persistently sero-indeterminate, low viral load, BLV-infected Holstein cow (No. 41) from Argentina. The DNA was PCR amplified with a series of overlapping primers encompassing the entire BLV proviral DNA. The amplified BLV ARG 41 DNA was cloned, sequenced, and compared phylogenetically to other BLV sequences including an in vivo high replicating strain (BLV ARG 38) from the same herd in Argentina. Characterization of BLV ARG 41's deduced proteins and its relationship to other members of the PTLV/BLV genus of retroviruses are discussed.

Human RNA "rumor" viruses: the search for novel human retroviruses in chronic disease

Retroviruses are an important group of pathogens that cause a variety of diseases in humans and animals. Four human retroviruses are currently known, including human immunodeficiency virus type 1, which causes AIDS, and human T-lymphotropic virus type 1, which causes cancer and inflammatory disease. For many years, there have been sporadic reports of additional human retroviral infections, particularly in cancer and other chronic diseases. Unfortunately, many of these putative viruses remain unproven and controversial, and some retrovirologists have dismissed them as merely "human rumor viruses." Work in this field was last reviewed in depth in 1984, and since then, the molecular techniques available for identifying and characterizing retroviruses have improved enormously in sensitivity. The advent of PCR in particular has dramatically enhanced our ability to detect novel viral sequences in human tissues. However, DNA amplification techniques have also increased the potential for false-positive detection due to contamination. In addition, the presence of many families of human endogenous retroviruses (HERVs) within our DNA can obstruct attempts to identify and validate novel human retroviruses. Here, we aim to bring together the data on "novel" retroviral infections in humans by critically examining the evidence for those putative viruses that have been linked with disease and the likelihood that they represent genuine human infections. We provide a background to the field and a discussion of potential confounding factors along with some technical guidelines. In addition, some of the difficulties associated with obtaining formal proof of causation for common or ubiquitous agents such as HERVs are discussed.

Natural genetic variations in bovine leukemia virus envelope gene: Possible effects of selection and escape

Bovine leukemia virus (BLV) is an oncogenic virus widespread in cattle. It belongs to the genus Deltaretrovirus of the family Retroviridae along with human and simian T-lymphotropic viruses. Here we report the addition of 28 new sequences to the current literature of 16 full-length BLV envelope gene sequences. The phylogenetic clustering, genotyping, and geographic distribution of BLV env variations corresponded in most cases. Most natural variations are mapped to the surface of the proposed conformational models of BLV gp51 N-terminus and gp30 external domain, overlapping with or adjacent to immunogenic epitopes. Analyses for evidence of possible selection pressures suggest the BLV env is under stringent negative selection overall, while strong positive selection is indicated for immunogenic epitope G. Natural env deletions bounded by similar flanking sequences were observed in multiple isolates and would result in truncated signal peptides, missing gp51, and aberrant coding frames for other proteins.

Molecular characterization of the env gene from Brazilian field isolates of Bovine Leukemia Virus

Molecular characterization of Bovine leukemia virus (BLV) isolates from Brazil using the env gene sequences revealed a high conservation of this gene. In most cases the substitutions corresponded to silent transitions. In addition, cystein residues, potential glycosylation sites, neutralization domains and other critical residues involved with the envelope structural domains and viral infectivity were conserved. Most of the substitutions found in the aminoacid sequences of the gp51 protein were localized in the G and H epitopes. Using the SIFT software, it was predicted that they should not alter the protein functions. Phylogenetic analyses showed that partial or complete env gene sequences grouped in three or four phylogenetic clusters, respectively. The sequences from the Brazilian isolates had similar mutation rates as compared to samples from other countries, and belonged to at least two phylogenetic clusters.

Mechanisms of leukemogenesis induced by bovine leukemia virus: prospects for novel anti-retroviral therapies in human

In 1871, the observation of yellowish nodules in the enlarged spleen of a cow was considered to be the first reported case of bovine leukemia. The etiological agent of this lymphoproliferative disease, bovine leukemia virus (BLV), belongs to the deltaretrovirus genus which also includes the related human T-lymphotropic virus type 1 (HTLV-1). This review summarizes current knowledge of this viral system, which is important as a model for leukemogenesis. Recently, the BLV model has also cast light onto novel prospects for therapies of HTLV induced diseases, for which no satisfactory treatment exists so far.

tax and rex Sequences of bovine leukaemia virus from globally diverse isolates: rex amino acid sequence more variable than tax

Bovine leukaemia virus (BLV) is an important agricultural problem with high costs to the dairy industry. Here, we examine the variation of the tax and rex genes of BLV. The tax and rex genes share 420 bases and have overlapping reading frames. The tax gene encodes a protein that functions as a transactivator of the BLV promoter, is required for viral replication, acts on cellular promoters, and is responsible for oncogenesis. The rex facilitates the export of viral mRNAs from the nucleus and regulates transcription. We have sequenced five new isolates of the tax/rex gene. We examined the five new and three previously published tax/rex DNA and predicted amino acid sequences of BLV isolates from cattle in representative regions worldwide. The highest variation among nucleic acid sequences for tax and rex was 7% and 5%, respectively; among predicted amino acid sequences for Tax and Rex, 9% and 11%, respectively. Significantly more nucleotide changes resulted in predicted amino acid changes in the rex gene than in the tax gene (P < or = 0.0006). This variability is higher than previously reported for any region of the viral genome. This research may also have implications for the development of Tax-based vaccines.

Human T-lymphotropic virus type I/II infections in volunteer blood donors from Northern and Western Greece: increased prevalence in one blood bank unit

BACKGROUND: Blood donors are routinely screened for antibodies to human T-cell lymphotropic viruses type I and II (HTLV-I and HTLV-II) in the United States, Canada, Japan, and some European countries. Previous reports from our group in relatively small numbers of donors have shown a zero prevalence of HTLV-I/II markers in our region. In this study, seven blood banks in the north and west of Greece participated in order to determine whether mandatory screening of blood donations for HTLV-I/II infection should be established. METHODS: Sera from 51,714 consecutive donors were investigated for anti-HTLV-I/II using two commercially available enzyme immunoassays (EIAs). Reactive samples in one or both EIAs were repeatedly evaluated further by Western blot, which is specific for both confirmation and differentiation of HTLV-I and HTLV-II seroreactivities. Investigation for HTLV DNA was also done in all EIA-reactive donors, irrespective of the WB result, using a combination assay based on the polymerase chain reaction (PCR) and a DNA EIA. RESULTS: A total of 115 donors (0.222%; 95% CI 0.018-0.26%) were initially considered reactive for anti-HTLV-I/II by EIAs. However, only 7 of the 115 were confirmed as positive by WB (five HTLV-I and two HTLV-I/II). Thus, the prevalence of anti-HTLV-I/II in donors from northern and western Greece was 0.013% (95% CI 0.003-0.023%). Interestingly, the majority of WB-confirmed anti-HTLV-positive individuals were detected in the blood bank of Corfu (5/7, all anti-HTLV-I). This prevalence (5/15383; 0.032%; 95% CI 0.004-0.061%) was six times the prevalence found at the other blood banks combined (2/36331; 0.0055%; 95% CI 0-0.013%), but it was not statistically significant. None of the EIA-reactive donors had detectable HTLV DNA. CONCLUSIONS: The very low prevalence of confirmed anti-HTLV-I/II infection markers in northern and western Greek blood donors, together with the negative PCR results in EIA-reactive subjects, indicates that anti-HTLV-I/I routine screening is not really justified in this area of our country. However, the increased prevalence of WB-confirmed anti-HTLV-I-positive donors in the Corfu blood bank calls for further prospective and careful investigation in order to address whether this finding represents a real cluster phenomenon of HTLV infection.

An outbreak of enzootic bovine leukosis in upper Egypt: clinical, laboratory and molecular-epidemiological studies

In 1989, 220 Holstein Friesian cattle (212 heifers and eight bulls) were imported from Minnesota, USA, to form a closed dairy herd in Arab El-Aoumar, Assiut, Upper Egypt. In November 1996, some abnormal signs such as loss of weight, decreased milk yield, external lymphadenopathy and decreased appetite were observed on this farm. Serological screening by enzyme-linked immunosorbent assay revealed a seroprevalence of antibodies directed against bovine leukaemia virus (BLV) of 37.7% in cattle under 2 years old and of 72.8% in animals more than 2 years old. Diagnosis was confirmed by the detection of BLV proviral DNA using polymerase chain reaction with primers amplifying a fragment of the env gene. Out of 21 tested leucocyte fractions from individual animals, 15 were positive showing a BLV-specific amplicon of 444 base pairs. Analysis of the amplicons for restriction fragment length polymorphisms and DNA sequencing results allowed the isolates to be typed. Since this was the first recorded case of enzootic bovine leukosis in Upper Egypt, strict quarantine measures were adopted and all serologically positive animals in the herd were culled.

Development and evaluation of a highly sensitive and specific blocking enzyme-linked immunosorbent assay and polymerase chain reaction assay for diagnosis of bovine leukemia virus infection in cattle

OBJECTIVE

To develop a blocking ELISA for detection of bovine leukemia virus (BLV) antibodies that is comparable to a radioimmunoprecipitation (RIP) assay, to evaluate use of this ELISA for identification of BLV-infected herds, and to develop a polymerase chain reaction (PCR) assay for direct diagnosis of infection with BLV.

SAMPLE POPULATION

Serum samples and pooled bulk-tank milk samples from cattle.

PROCEDURE

The blocking ELISA was developed, using BLV gp51 as antigen, captured by a selected bovine polyclonal serum. A nested PCR was conducted with primers specific for a segment of the pol region of the BLV genome.

RESULTS

Sensitivity and specificity of the ELISA were comparable to those of the RIP assay. Use of the ELISA on pooled milk samples allowed identification of herds in which prevalence of BLV infection among lactating cows was as low as 2.5%. Pooled milk samples from BLV-free herds did not react in the ELISA. All cattle that had positive results for the nested PCR had BLV antibodies, but cattle with consistantly low antibody titers required examination of sequential DNA samples to detect viral sequences. None of the 63 antibody-negative cattle had positive results for the PCR.

CONCLUSIONS AND CLINICAL RELEVANCE

This ELISA is a highly specific and sensitive assay for the detection of BLV antibodies in serum and milk samples of cattle. Examination of pooled milk samples with the ELISA provides a reliable, practical, and economic procedure for identification of BLV-infected herds. The nested PCR also constitutes a specific procedure for direct diagnosis of infection with BLV.

A PCR primer system for detecting oncoretroviruses based on conserved DNA sequence motifs of animal retroviruses and its application to human leukaemias and lymphomas

Many C- and D-type retroviruses are known to cause a broad spectrum of malignant diseases in animals. Certain genome regions of these animal retroviruses are highly conserved between different animal species. It should be possible to detect new members of the retrovirus family with consensus PCR primers derived from these conserved sequence motifs. The consensus PCR primers developed in this study are generic enough to detect nearly all known oncogenic mammalian and avian exogenous C- and D-type retroviruses but do not amplify human endogenous retroviral sequences. In contrast to previous investigations, the present study involved highly stringent PCR conditions and truly generic PCR primers. Forty-four samples from patients with various immunophenotyped malignant diseases (acute and chronic T-/B-cell lymphocytic leukaemias, acute myeloid leukaemias, T-/B-cell lymphomas, chronic myeloproliferative disorders) and three cell lines (Hodgkin's lymphoma, Burkitt's lymphoma) have thus far been investigated using these PCR primers. The fact that no retroviruses have been found argues against an involvement of known animal oncoretroviruses or related hitherto undetected human retroviruses in the aetiopathogenesis of these diseases. The retrovirus detection system developed here may be used to confirm suspected retroviral involvement in other (malignant or nonmalignant) human diseases as well as to identify new animal retroviruses.

Comparative study of PCR as a direct assay and ELISA and AGID as indirect assays for the detection of bovine leukaemia virus

The choice of a diagnostic method depends on the characteristics of the herd to be analysed. Two herds with different prevalences of enzootic bovine leukaemia were chosen to study the concordance between agar gel immunodiffusion (AGID), enzyme-linked immunosorbent assay (ELISA) and polymerase chain reaction (PCR) methods. PCR, an increasingly used virological method, was performed with four sets of primers, amplifying different genomic regions (env, pol and tax), from DNA extracted either from peripheral blood monocytes (PBMCs) or milk leucocytes. The highest percentage of positive animals was obtained using PCR performed with DNA extracted from PBMCs using primers which amplified either env or pol, followed by PCR using PBMCs and primers which hybridized with tax, then ELISA using serum and finally AGID. The results of PCR were more consistent with PBMCs than when milk leucocytes were used.

The complete genomic sequence of a BLV strain from a Holstein cow from Argentina

DNA was extracted from the peripheral blood of a seropositive, PCR-positive, BLV-infected Holstein cow (No. 38) from Argentina. The DNA was amplified via PCR with a series of overlapping primers encompassing the entire BLV proviral DNA. The amplified BLV ARG 38 DNA was cloned, sequenced, and compared phylogenetically to three other full-length BLV sequences. Characterization of its deduced proteins and its relationship to other members of the PTLV/BLV genus of retroviruses are discussed.

Detection of reverse transcriptase activity in the serum of patients with motor neurone disease

The recognition that both human and murine retroviruses can cause motor neurone disease-like syndromes has raised the possibility that a retrovirus may be involved in the aetiology of motor neurone disease. This possibility was explored by looking for evidence of reverse transcriptase in the serum of motor neurone disease patients. Sera from 56 patients with motor neurone disease and 58 controls were tested by the product-enhanced reverse transcriptase assay, a technique that is approximately a million fold more sensitive than conventional reverse transcriptase assays and capable of detecting very low numbers of retroviral particles. Cell-free reverse transcriptase activity was detected in the serum of 33 of the 56 motor neurone disease patients (59%) but in only 3 of the controls (P < 0.00001). The reverse transcriptase activity was detectable in the presence of a large excess of an effective inhibitor of human cellular DNA polymerases and was therefore tentatively considered to be compatible with a retroviral origin. The reverse transcriptase activity, however, was not found to be due to the presence of known human exogenous retroviruses including HIV-1, HIV-2, HTLV-I, HTLV-II, HRV-5 or human foamy virus, as assessed by PCR-based assays. Further investigations will be required to determine the source of the reverse transcriptase activity observed in these motor neurone disease patient sera.

Lack of BLV and PTLV DNA sequences in the majority of patients with large granular lymphocyte leukaemia

The primate T-cell lymphoma/leukaemia viruses (PTLV) and bovine leukaemia virus (BLV) comprise a unique genus of retroviruses, infection with which induces seroreactivity in the host against conserved epitopes in their p24 gag and gp21 env cognate proteins. Herein, we have confirmed this serocrossreactivity. Patients with large granular lymphocyte (LGL) leukaemia have frequent seroreactivity to the p24 and gp21 env proteins of human T-cell lymphoma/leukaemia virus I (HTLV-I), one of the species in the genus. However, only a small minority of patients are actually infected with prototypic HTLV-I or HTLV-II, another species within the group. In an attempt to determine whether LGL leukaemia might be associated with other members of the PTLV/BLV genus, we examined the peripheral blood mononuclear cell DNA of 22 HTLV p24 and/or gp21 seropositive LGL leukaemia patients via PCR using degenerate and specific primer pair/probe systems capable of detecting all known members of the PTLV/BLV genus. None of the samples was positive. These data indicate that although HTLV-II may be associated with some cases of LGL leukaemia most patients are not infected with a PTLV or BLV virus.

Absence of evidence of infection with divergent primate T-lymphotropic viruses in United States blood donors who have seroindeterminate HTLV test results

BACKGROUND

Recent identification of divergent simian or primate T-lymphotropic viruses (STLVs; PTLVs) in bonobos (formerly called pygmy chimpanzees; Pan paniscus; viruses: STLVpan-p and STLVpp1664) and a baboon (Papio hamadryas; viruses: STLVph969 or PTLV-L) have raised the possibility of human infection with these viruses. Divergent PTLV-infected primate sera show p24 bands on HTLV-I Western blots (WBs). It was investigated whether infection by divergent PTLV-like viruses could explain a subset of United States blood donors who reacted on HTLV-I EIAs and had indeterminate HTLV-I WBs with p24 bands.

STUDY DESIGN AND METHODS

Epidemiologic characteristics of 1889 donors with HTLV-I-indeterminate WBs were compared to those of donors with confirmed retrovirus infections (393 with HIV, 201 with HTLV-I, 513 with HTLV-II) and 1.6 million donors with nonreactive screening tests. To directly probe for infection with divergent PTLVs, 2 HTLV-I-indeterminate donors born in Africa and 269 representative non-African-born donors with p24 bands on HTLV-I WBs (previously shown to be negative for HTLV-I and -II DNA by PCR) were selected for PTLV PCR analysis. DNA from peripheral blood MNC samples was tested for a proviral tax sequence by PCR using generic primers that amplify HTLV-I, HTLV-II, and the divergent PTLVs. Amplified tax sequences were detected by Southern blot hybridization to a (32)P-labeled generic PTLV probe. PCR-positive samples could then be typed by hybridization with virus-specific internal probes that differentiate HTLV-I, HTLV-II, PTLV-L, and STLVpan-p.

RESULTS

In the epidemiologic analysis, HTLV-indeterminate status was independently associated with age of at least 25 years (OR = 2.19; 95% CI, 1.93-2.49), black (OR = 3.27; 95% CI, 2.90-3.67) or Hispanic (OR = 1.82; 95% CI, 1.52-2.16) race or ethnicity, and donation at one blood center (Baltimore) (OR = 1. 30; 95% CI, 1.11-1.53). None of the 271 HTLV-I WB-indeterminate samples tested positive by generic PTLV PCR analysis.

CONCLUSION

Although the epidemiologic data suggest the possibility of undiagnosed HTLV-I, HTLV-II, or a cross-reactive virus such as PTLV among older, black, and Hispanic blood donors, the PCR data do not support the presence of divergent PTLV infection among US blood donors with HTLV-I-indeterminate results.

A rapid and sensitive diagnosis of bovine leukaemia virus infection using the nested shuttle polymerase chain reaction

Bovine leukaemia virus (BLV) is the causative agent of enzootic bovine leukosis (EBL). In Argentina, where a program to eradicate EBL has been introduced, sensitive and reliable diagnosis has attained high priority. Although the importance of the agar gel immunodiffusion test remains unchanged for routine work, an additional diagnostic technique is necessary to confirm cases of sera with equivocal results or of calves carrying maternal antibodies.Utilizing a nested shuttle polymerase chain reaction, the proviral DNA was detected from cows experimentally infected with as little as 5 ml of whole blood from BLV seropositive cows that were nonetheless normal in haematological terms. It proved to be a very sensitive technique, since it rapidly revealed the presence of the provirus, frequently at 2 weeks postinoculation and using a two-round procedure of nested PCR taking only 3 hours. Additionally, the primers used flanked a portion of the viral genome often employed to differentiate BLV type applying BamHI digestion. It is concluded that this method might offer a highly promising diagnostic tool for BLV infection.

Emerging Viruses

Diseases caused by microbial infections are present throughout human evolution. Large proportions are the result of virus infections. A commonly cited example of resurgent or recurrent disease is the yearly appearance of new antigenically different influenza viruses. These new variants are able to evoke disease in their host while causing the centuries-old symptoms of influenza. However, conventional virological techniques have failed to identify the agent, even though evidence suggested non-A, non-B hepatitis (NANBH) is caused by a blood-borne, small enveloped virus, readily transmissible to chimpanzees. Modern molecular biology techniques are used to identify completely new viruses. These viruses can be associated with a new disease or associated with a well-characterized disease present in humans for many years. In identifying an emerging virus, one is often presented with epidemiological data and clinical specimens that have no reactivity with diagnostic reagents available for known pathogens. The primary aim therefore is to identify any new infectious agent and build a body of data to support the existence of a causal link between organism and disease.