Risk factors associated with small-ruminant lentiviruses in sheepfold buildings

INTRODUCTION

Small-ruminant lentivirus (SRLV) infection is widespread across Europe. It causes substantial economic losses in sheep breeding. The main route of SRLV infection is through the mother's milk, especially colostrum However, infection can also occur via contact between infected and healthy animals. It should be noted that the mechanisms of contact infection are still relatively poorly understood. The virus can also spread through a flock via an aerogenic mechanism.

OBJECTIVE

Due to the increased risk of SRLV infection in sheep bred in an alcove system, this study sought to define the effect of various selected factors associated with alcove breeding on the frequency of SRLV infection in sheep.

MATERIAL AND METHODS

Risk factors associated with small-ruminant lentivirus (SRLV) infection were analyzed among flocks of sheep in central-eastern Poland. Ninety-eight sheep flocks were selected for detailed investigation and included 6,470 ewes and 15 breeds and lines. Serologic testing of blood samples was used to identify infected animals and evaluate the epidemiologic status of particular flocks. Specific antibodies for Maedi Visna Virus (MVV) were detected via ELISA. Questionnaires were used to gather information concerning risk factors.

RESULTS

The study's results indicate that factors associated with environmental conditions under which sheep are kept play a significant role in determining the risk of SRLV infection.

CONCLUSIONS

Special attention should be focused on airborne contamination associated with the technologies used in sheep breeding. Breeding technologies that limit airborne contamination in farm buildings should be employed. In developing programmes to eliminate SLRV in sheep flocks, improvement of zoohygenic conditions should also be considered.

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.

Genome-wide association identifies multiple genomic regions associated with susceptibility to and control of ovine lentivirus

BACKGROUND

Like human immunodeficiency virus (HIV), ovine lentivirus (OvLV) is macrophage-tropic and causes lifelong infection. OvLV infects one quarter of U.S. sheep and induces pneumonia and body condition wasting. There is no vaccine to prevent OvLV infection and no cost-effective treatment for infected animals. However, breed differences in prevalence and proviral concentration have indicated a genetic basis for susceptibility to OvLV. A recent study identified TMEM154 variants in OvLV susceptibility. The objective here was to identify additional loci associated with odds and/or control of OvLV infection.

METHODOLOGY/PRINCIPAL FINDINGS

This genome-wide association study (GWAS) included 964 sheep from Rambouillet, Polypay, and Columbia breeds with serological status and proviral concentration phenotypes. Analytic models accounted for breed and age, as well as genotype. This approach identified TMEM154 (nominal P=9.2×10(-7); empirical P=0.13), provided 12 additional genomic regions associated with odds of infection, and provided 13 regions associated with control of infection (all nominal P<1 × 10(-5)). Rapid decline of linkage disequilibrium with distance suggested many regions included few genes each. Genes in regions associated with odds of infection included DPPA2/DPPA4 (empirical P=0.006), and SYTL3 (P=0.051). Genes in regions associated with control of infection included a zinc finger cluster (ZNF192, ZSCAN16, ZNF389, and ZNF165; P=0.001), C19orf42/TMEM38A (P=0.047), and DLGAP1 (P=0.092).

CONCLUSIONS/SIGNIFICANCE

These associations provide targets for mutation discovery in sheep susceptibility to OvLV. Aside from TMEM154, these genes have not been associated previously with lentiviral infection in any species, to our knowledge. Further, data from other species suggest functional hypotheses for future testing of these genes in OvLV and other lentiviral infections. Specifically, SYTL3 binds and may regulate RAB27A, which is required for enveloped virus assembly of human cytomegalovirus. Zinc finger transcription factors have been associated with positive selection for repression of retroviral replication. DLGAP1 binds and may regulate DLG1, a known regulator of HIV infectivity.

Elimination of small ruminant lentivirus infection from sheep flocks and goat herds aided by health schemes in Great Britain

Over a period of 11 years, 33 sheep or goat holdings lost their maedi-visna or caprine arthritis-encephalitis accredited status (mean 2.8 per year [0.09 per cent] of the accredited holdings in Great Britain). Of these, 22 sheep flocks and two goat herds eradicated the infection and regained their accredited status. In addition, 10 sheep flocks and two goat herds managed to eradicate infection, having joined the scheme with infected animals. In flocks and herds with a high initial prevalence of infection, the adoption of an indirect ELISA, with greater sensitivity than the agar gel immunodiffusion test, improved success rates. A strategy was devised to interpret the ELISA results depending upon the prevalence of infection at the time. Eighteen of the 33 flocks/herds (54.5 per cent) that had introductions of infection also owned non-accredited stock.

Live attenuated lentivirus infection elicits polyfunctional simian immunodeficiency virus Gag-specific CD8+ T cells with reduced apoptotic susceptibility in rhesus macaques that control virus replication after challenge with pathogenic SIVmac239

HIV-specific CD8+ T cells that secrete multiple cytokines in response to Ag stimulation are associated with the control of virus replication during chronic HIV infection. To determine whether the presence of polyfunctional CD8+ T cell responses distinguishes protected and unprotected monkeys in a live attenuated lentivirus model, SIV Gag peptide-specific CD8+ T cell responses of simian HIV (SHIV) 89.6-vaccinated, SIVmac239-challenged rhesus macaques were compared in two monkeys that controlled challenge virus replication and two that did not. The ratio of Bcl-2+ Gag-specific CD8+ T cells to caspase-3+ Gag-specific CD8+ T cells was higher in the vaccinated-protected animals compared with unprotected monkeys. In addition, polyfunctional SIV-specific CD8+ T cells were consistently detected through 12 wk postchallenge in the protected animals but not in the unprotected animals. In the unprotected monkeys, there was an increased frequency of CD8+ T cells expressing markers associated with effector memory T cells. Further, there was increased annexin V expression in central memory T cells of the unprotected animals before challenge. Thus, monkeys that control viral replication after live attenuated SHIV infection have polyfunctional SIV-specific CD8+ T cells with an increased survival potential. Importantly, the differences in the nature of the SIV-specific CD8+ T cell response in the protected and unprotected animals are present during acute stages postchallenge, before different antigenic levels are established. Thus, the polyfunctional capacity and increased survival potential of CD8+ SIV-specific T cells may account for live attenuated, SHIV89.6-mediated protection from uncontrolled SIV replication.

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

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

Serological differentiation of FIV-infected cats from dual-subtype feline immunodeficiency virus vaccine (Fel-O-Vax FIV) inoculated cats

Feline immunodeficiency virus (FIV) vaccine, Fel-O-Vax FIV, was released for sale in the US in 2002. The antibodies of vaccinated cats interfere with serological assays by currently available FIV diagnostic kits. In this study, we investigated whether it is possible to distinguish serologically cats vaccinated with Fel-O-Vax FIV from cats experimentally or naturally infected with FIV. A total of 153 sera taken from 97 cats were used as serum samples. Enzyme linked immunosorbent assay (ELISA) was performed using whole FIV antigen and formalin treated whole FIV antigen, recombinant-gag (r-gag) antigen, and transmembrane (TM) peptide. Statistical analysis was performed using ELISA optical density (O.D.) values obtained with each antigen as variables. Except for the ELISA O.D. values obtained with r-gag antigen, a significant difference in ELISA O.D. values was observed between the vaccinated and the infected groups. However, it was not possible to distinguish both groups unequivocally. Using discriminant analysis, it was possible to distinguish the two groups with an accuracy of 97.1% with two discriminating variables (ELISA O.D. values obtained with formalin treated whole FIV antigen, and TM peptide), 97.8% with three discriminating variables (ELISA O.D. values obtained with whole FIV antigen, formalin treated whole FIV antigen, and TM peptide). Therefore, it was considered possible to distinguish cats vaccinated with Fel-O-Vax FIV from FIV-infected cats by ELISA using two types of antigens including formalin treated whole FIV antigen and TM peptide, or three types of antigens including formalin treated whole FIV antigen, TM peptide and whole FIV antigen.

Application of PCR technique in diagnosis of small ruminant lentivirus infection in sheep and goats

Detection of small ruminant lentiviruses (SRLVs) in sheep and goats usually relies on serological testing. In this study, we evaluated semi-nested PCR and nested PCR techniques applied as a diagnostic tool for detection of maedi-visna virus (MVV) and caprine arthritis-encephalitis virus (CAEV) in naturally infected sheep and goats, respectively. The examination of 193 ovine and 85 caprine serum samples by the ELISA revealed the presence of specific antibodies in 133 (69%) and 18 (21.2%) animals, respectively. Presence of proviral DNA was manifested in 103 (53.4%) sheep and 12 (14.2%) goats. Despite the relatively lower sensitivity of PCR, the fact of detection of proviral DNA in 19 out of 60 ovine samples and 7 out of 67 caprine samples collected from animals previously negative by ELISA was noteworthy. In conclusion, the data demonstrated that combinations of both ELISA and PCR might afford optimal detection of SRLVs infection.

Natural bovine lentiviral type 1 infection in Holstein dairy cattle. I. Clinical, serological, and pathological observations

Clinical, serological, and pathological abnormalities observed in Holstein cows naturally infected with bovine lentivirus 1 bovine immunodeficiency virus (BIV) and other infections were progressive and most commonly associated with weight loss, lymphoid system deficiency, and behavioral changes. Clinical evidence of meningoencephalitis was dullness, stupor, and occasional head or nose pressing postures. The polymerase chain reactions associated the BIV provirus with the lesions in the central nervous system and lymphoid tissues. Multiple concurrent infections developed in retrovirally infected cows undergoing normal stresses associated with parturition and lactation. A major functional correlate of the lymphoreticular alterations was the development of multiple secondary infections which failed to resolve after appropriate antibacterial therapy. The chronic disease syndrome in dairy cows associated with BIV may be useful as a model system for investigation of the pathogenesis of the nervous system lesions and lymphoid organ changes that occur in humans with lentiviral infection.

Tissues rich in macrophagic cells are the major sites of feline immunodeficiency virus uptake after intravenous inoculation into cats

To track the sites of feline immunodeficiency virus (FIV) clearance in cats and follow viral localization from 30 min until 48 h post-intravenous inoculation, several kinds of cells (PBMC, splenocytes, thymocytes, Kupffer cells (KC), lymph nodes, bone marrow and alveolar cells) were collected. After co-culture with uninfected PBMC, p24 antigen was detected. Reverse transcription (RT)-nested PCR and PCR were performed on all these cells and in situ RT-PCR on liver, spleen and isolated KC. Biochemical determinations showed that viral RNA was predominantly found during the first hour post-infection (p.i.) in PBMC, splenocytes and KC and later on (24-48 h) in thymocytes and lymph node cells. In addition, viral DNA was detected as early as 24 h post-inoculation in splenocytes and KC, whereas PBMC were positive at 48 h. Microscopic studies confirmed the presence of viral RNA in hepatic KC and also in the splenic red pulp rich in macrophages and dendritic cells. Our results enabled the early identification of the cell population infected and highlight the role played by macrophagic cells in the uptake of FIV and in viral dissemination.

Detection of feline immunodeficiency virus RNA by two nucleic acid sequence based amplification (NASBA) formats

Feline immunodeficiency virus (FIV) is an AIDS-inducing lentivirus that infects domestic cats worldwide. Because of its clinicopathologic similarities to human immunodeficiency virus type 1 (HIV-1) infection, the FIV/cat infection system is a valuable animal model for investigating comparative aspects of HIV-1 biology. An assay that detects quickly and efficiently FIV RNA in relatively small volume samples of feline blood or other body fluids would be of benefit in studies of viral transmission and antiviral interventions. Nucleic acid sequence based amplification (NASBA) technology is particularly suited for the detection of RNA in a variety of body fluids. In this report, the development of two rapid, sensitive and versatile NASBA formats is described for the detection of FIV gag RNA in plasma from infected cats. RNA detection by either format was unaffected by the presence of feline plasma. The limits of detection were at least 200 copies of input RNA for both formats. Results from seropositive and seronegative feline plasma samples were clearly distinguishable. These results demonstrate that NASBA provides a rapid and sensitive alternative to RT-PCR and culture isolation for detecting FIV RNA in infected feline plasma.

Involvement of cytolytic and non-cytolytic T cells in the control of feline immunodeficiency virus infection

The appearance of non-cytolytic T cells that suppressed feline immunodeficiency virus (FIV) replication in vitro, and FIV-specific cytotoxic T cell (CTL) responses was compared in a group of seven, specific pathogen free (SPF) domestic cats following primary infection with the Glasgow(8) isolate of FIV (FIV(GL-8)). FIV proviral burdens were quantified in the blood and lymphoid tissues by real-time PCR. Non-cytolytic T cell suppression of FIV replication was measured by co-cultivating lymphoblasts prepared from the cats at different time-points during infection with FIV-infected MYA-1 cells in vitro. Non-cytolytic suppressor activity was detected as early as 1 week after infection, and was evident in all the lymphoid tissues examined. Further, this activity was present in subpopulations of T cells in the blood with normal (CD8(hi)) or reduced (CD8(lo)) expression of the CD8 molecule, and temporal modulations in non-cytolytic suppressor activity were unrelated to the circulating CD8(+) T cell numbers. Virus-specific CTL responses, measured by (51)Cr release assays, were not detected until 4 weeks after infection, with the emergence of FIV-specific effector CTLs in the blood. Throughout infection the response was predominantly directed towards FIV Gag-expressing target cells, and by 47 weeks after infection CTL responses had become localised in the lymph nodes and spleen. The results suggest that both non-cytolytic T cell suppression of FIV replication and FIV-specific CTL responses are important cellular immune mechanisms in the control of FIV replication in infected asymptomatic cats.

Feline immunodeficiency virus-infected cat sera associated with the development of broad neutralization resistance in vivo drive similar reversions in vitro

We previously reported that, upon reinoculation into cats, a neutralization-sensitive, tissue culture-adapted strain of feline immunodeficiency virus constantly reverted to the broad neutralization resistance typical of primary virus isolates and identified residue 481 in the V4 region of the surface glycoprotein as a key determinant of the reversion. Here, we found that well-characterized immune sera, obtained from cats in which such reversion had occurred, selected in tissue culture in favor of virus variants that also had a neutralization-resistant phenotype and had amino acid 481 changed, thus indicating that the host's humoral immune response is capable of driving the reversion in the absence of other intervening factors. In contrast, a second group of immune sera, elicited by a virus variant that had already reverted to neutralization resistance in independent cats, induced the emergence of escape mutants lacking broad neutralization resistance and neutralized fewer virus variants. It is proposed that the viral variants used to produce the two sets of sera may have generated different antibody repertoires.

Feline babesiosis: signalment, clinical pathology and concurrent infections

Fifty-six cats with naturally occurring Babesia felis infection were studied. No breed or sex predilection could be identified, but there was an apparent predilection for young adult cats less than 3 years of age. Macrocytic, hypochromic, regenerative anaemia was present in 57% of the cats and in-saline agglutination tests were positive in 16%. No characteristic changes were observed in total or differential leukocyte counts. Thrombocyte counts were variable and thrombocytopaenia was an inconsistent finding. Hepatic cytosol enzyme activity and total bilirubin concentrations were elevated in the majority of cats. Serum protein values were mostly normal, but increased values were occasionally observed and polyclonal gammopathies were observed in all cats with increased total globulin concentrations. No remarkable changes in renal parameters were observed. A variety of electrolyte abnormalities occurred in a number of cats, but no consistent pattern of change could be identified. A close correlation was evident between peripheral and central parasite counts. Concurrent infections with Haemobartonella felis, feline immunodeficiency virus and/or feline leukemia virus were identified in a number of cats.

Monoclonal antibodies to conformational epitopes of the surface glycoprotein of caprine arthritis-encephalitis virus: potential application to competitive-inhibition enzyme-linked immunosorbent assay for detecting antibodies in goat sera

Four immunoglobulin G1 monoclonal antibodies (MAbs) to the gp135 surface envelope glycoprotein (SU) of the 79-63 isolate of caprine arthritis-encephalitis virus (CAEV), referred to as CAEV-63, were characterized and evaluated for their ability to compete with antibody from CAEV-infected goats. Three murine MAbs (MAbs GPB16A, 29A, and 74A) and one caprine MAb (MAb F7-299) were examined. All MAbs reacted in nitrocellulose dot blots with native CAEV-63 SU purified by MAb F7-299 affinity chromatography, whereas none reacted with denatured and reduced SU. All MAbs reacted in Western blots with purified CAEV-63 SU or the SU component of whole-virus lysate following denaturation in the absence of reducing agent, indicating that intramolecular disulfide bonding was essential for epitope integrity. Peptide-N-glycosidase F digestion of SU abolished the reactivities of MAbs 74A and F7-299, whereas treatment of SU with N-acetylneuraminate glycohydrolase (sialidase A) under nonreducing conditions enhanced the reactivities of all MAbs as well as polyclonal goat sera. MAbs 29A and F7-299 were cross-reactive with the SU of an independent strain of CAEV (CAEV-Co). By enzyme-linked immunosorbent assay (ELISA), the reactivities of horseradish peroxidase (HRP)-conjugated MAbs 16A and 29A with homologous CAEV-63 SU were <10% of that of HRP-conjugated MAb 74A. The reactivity of HRP-conjugated MAb 74A was blocked by sera from goats immunized with CAEV-63 SU or infected with CAEV-63. The reactivity of MAb 74A was also blocked by sera from goats infected with a CAEV-Co molecular clone, although MAb 74A did not react with CAEV-Co SU in Western blots. Thus, goats infected with either CAEV-63 or CAEV-Co make antibodies that inhibit binding of MAb 74A to CAEV-63 SU. A competitive-inhibition ELISA based on displacement of MAb 74A reactivity has potential applicability for the serologic diagnosis of CAEV infection.

Failure to detect bovine immunodeficiency virus contamination of stud bull spermatozoa, blood leukocytes, or semen leukocytes in samples supplied by artificial insemination centers

OBJECTIVE

To determine whether bovine immunodeficiency virus (BIV) infection could be detected in spermatozoa, blood leukocytes, or semen leukocytes from stud bulls in artificial insemination centers.

ANIMALS

30 bulls at 3 artificial insemination centers.

PROCEDURE

Polymerase chain reaction testing that used 3 sets of primer pairs targeting pol and env regions of the BIV proviral genome was performed on DNA extracted from semen leukocytes, spermatozoa, and blood leukocytes from each bull. Southern blot analysis was performed to increase sensitivity of detection. Western blot analysis of plasma samples was used to detect antibodies against BIV.

RESULTS

BIV provirus was not detected in DNA samples obtained from semen leukocytes, spermatozoa, or blood leukocytes, and antibodies against BIV were not detected.

CONCLUSIONS AND CLINICAL RELEVANCE

Contrary to our report of high point prevalence of BIV contamination of semen from a single artificial insemination center, bulls of the study reported here did not appear to be infected. Maximum risk of BIV infection in similar bulls was estimated at 10% with a confidence level of 95%.

A viral transmembrane recombinant protein-based enzyme-linked immunosorbent assay for the detection of bovine immunodeficiency virus infection

The expression of bovine immunodeficiency virus (BIV) truncated transmembrane envelope protein (designated hereafter tTM) in insect cells has been described previously (Abed, Y., St-Laurent, G., Zhang, H., Jacobs, R.M., Archambault, D., 1999. Development of a Western blot assay for detection of bovine immunodeficiency-like virus using capsid and transmembrane proteins expressed from recombinant baculovirus. Clin. Diagn. Lab. Immunol. 6, 168-172). In this study, a tTM-based enzyme-linked immunosorbent assay (ELISA) was developed for the serodetection of BIV infection. A total of 109 bovine sera including 86 BIV-negative and 23 BIV-positive serum samples were tested. The ELISA results were compared with those of three Western blot assays using, as test antigens, cell culture-derived whole virus proteins (WB1), and the tTM (WB2) and p26 (WB3) fusion proteins expressed from recombinant baculovirus in insect cells, respectively. The concordances of the ELISA results with those of the WB1, WB2, and WB3 were 97.2, 100 and 97.2%, respectively. The tTM protein-based ELISA and Western blot permitted the detection of BIV infection in cattle whose sera failed to react with the p26 fusion protein and the whole virus protein preparation. The tTM recombinant protein was also used to study the kinetics of appearance of antibodies against BIV transmembrane envelope protein in rabbits infected experimentally with BIV. Antibodies to tTM were detected at 28 days post-infection and persisted through the entire 36-39.5 months experimental time period. The results of this study showed that the tTM-ELISA might be useful for the serodetection of BIV-infected animals, and for basic studies on BIV replication life cycle.

Acute-phase proteins and hematologic values in ovine lentivirus-infected lambs treated with recombinant ovine IFN-tau

To evaluate changes in complete blood cell (CBC) counts, haptoglobin and fibrinogen in ovine lentivirus (OvLV)-infected lambs treated with recombinant ovine interferon-tau (rOVIFN-tau), 24 lambs were allocated to one of four groups (n = 6 per group): (1) virus + rOvIFN-tau, VI, (2) virus + placebo, VP, (3) no virus + rOVIFN-tau, NVI, and (4) no virus + placebo, NVP. Three lambs in each group were treated once a day for 12 weeks, and the remaining 3 lambs were treated for 33 weeks. Blood was collected at days 0, 7, and 10 and at weeks 2-10, 12, 32, and 33 to determine CBC counts, as well as haptoglobin and fibrinogen levels. Hematologic values remained within normal limits in all groups. However, hemoglobin (Hb), mean corpuscular volume (MCV), mean corpuscular hemoglobin concentration (MCHC), and packed cell volume (PCV) values decreased (p < 0.05) in the two rOvIFN-tau-treated groups (VI and NVI) compared with the placebo-treated (VP and NVP) groups. Both rOvIFN-upsilon and OvLV had a mild negative effect on neutrophil numbers. Although Hb, MCV, MCHC, PCV, and neutrophil values declined in the rOvIFN-tau-treated lambs compared with the placebo-treated lambs, these values remained within the reference range for sheep. Experimental lambs did not show adverse clinical signs associated with OvLV infection or as a result of rOvIFN-tau treatment. The lack of significant side effects of high-dose rOvIFN-tau in sheep and previous reports of broad-spectrum and cross-species antiviral activity suggest that rOvIFN-tau warrants further investigation as an antiviral therapeutic agent.

Vaccination with experimental feline immunodeficiency virus vaccines, based on autologous infected cells, elicits enhancement of homologous challenge infection

Cats were vaccinated with fixed autologous feline immunodeficiency virus (FIV)-infected cells in order to present viral proteins to the immune system of individual cats in an MHC-matched fashion. Upon vaccination, a humoral response against Gag was induced. Furthermore, virus-neutralizing antibodies were detected in a Crandell feline kidney cell-based neutralization assay, but not in a neutralization assay based on primary peripheral blood mononuclear cells. Despite the induction of these FIV-specific responses, vaccinated cats were not protected. Instead, accelerated virus replication was found, an observation similar to what previous experiments using other vaccine candidates have shown. Here, the results of the present study are discussed in the light of enhancement of lentivirus infections as a complicating factor in lentivirus vaccine development.

Detection of bovine immunodeficiency-like virus infection in experimentally infected calves

Detection of BIV virus infection by serological means, PCR and virus isolation in experimentally infected calves is described. Viral sequences were specifically detected by PCR in peripheral blood mononuclear cells (PBMCs), with primer systems located in the gag, pol and tat regions of the viral genome. An enzyme-linked oligosorbent assay (ELOSA) in microtiter plates is described, for the detection of PCR products, the sensitivity of which was shown to be comparable to that of membrane hybridization detection. Serological response of the animals against the BIV p26 protein was shown, using a recombinant fusion protein ((His)6p26) expressed in E. coli and purified by metal affinity chromatography, in ELISA and Western blot studies. The presence of infectious virus was demonstrated by its rescue, by virus isolation in cell cultures, from PBMCs during a one year follow-up.

Longitudinal studies of immune function in cattle experimentally infected with bovine immunodeficiency-like virus and/or bovine leukemia virus

The effects of single or dual infection with bovine immunodeficiency-like virus (BIV) and/or, bovine leukemia virus (BLV) on bovine immune function were examined over a 4 year period. Holstein calves were infected with BIV (four calves), BLV (five calves), BIV and BLV (five calves), or sham inoculated (three calves). Lymphocyte blastogenesis to mitogens, seven tests of neutrophil function, and mononuclear cell subset analysis by flow cytometry (BoCD4, BoCD8, BoCD2, BoWC1, sIgM+, and monocytes) were performed at regular intervals to 49 months post-infection. These data were analyzed for main effects of each virus and interaction as a 2 x 2 factorial. BIV infected cattle had lower neutrophil antibody-dependent cell-mediated cytotoxicity and iodination responses during 2 of the 4 years post-infection (P < 0.05). BIV infection was not associated with any long-term significant changes in lymphocyte blastogenesis to mitogens or changes in mononuclear cell subset numbers in blood. There was a tendency for animals infected with BIV alone to have decreased lymphocyte blastogenic responses to mitogens, but this was not statistically significant. BLV infection caused an increase in total mononuclear cells with no dramatic shift in the relative proportions of the various subsets. Co-infection with BIV and BLV did not consistently cause a different response than either virus did individually. One BIV infected animal died of non-BLV lymphosarcoma 7 months after infection. All other animals had no unusual clinical signs. In summary, infection with BIV caused a significant, temporary decrease in neutrophil function with no consistent statistically significant alteration in lymphocyte blastogenesis or mononuclear cell numbers during the first 4 years after infection. BLV infection caused an increase in lymphocyte numbers, and there appeared to be no synergism between the viruses.

Mucosal transmission of cell-associated and cell-free feline immunodeficiency virus

Mucosal infection by feline immunodeficiency virus (FIV) was assessed via a single exposure of the vaginal or rectal mucosa to either infectious peripheral blood mononuclear cells (PBMCs), infectious plasma, or cell-free cultured virus. All cats inoculated with cell-free cultured virus (100 or 400 TCID) and 9 of 10 cats inoculated with infected PBMCs (2 x 10(7) or 2 x 10(5)) became persistently viremic within 3 weeks. Neither cat inoculated with 2 x 10(3) PBMCs became viremic. Rectal and vaginal exposure were equally effective routes to induce viremia. CD4+ T cells and mitogen-stimulated PBMC proliferation declined in all infected cats. However, a transient PBMC proliferative response to FIV p24gag occurred in most virus-exposed cats, especially those that did not develop detectable infection. FIV was not transmitted by mucosal exposure to infectious virus in plasma (100 TCID), a dose > 10-fold that needed for infection by parental injection. In vitro studies suggested that a plasma heat-stable virus-neutralizing factor may be associated with failure of plasma virus to establish infection via the mucosal route. Mucosal FIV infection provides a new model with which to study early stages of infection and intervention in transmucosal lentivirus infections.

Spontaneous programmed cell death (PCD) process of lymphocytes of FIV-infected cats: pharmacological modulation in vitro

We previously reported that unstimulated lymphocytes in culture from FIV-infected cats undergo spontaneous apoptosis in vitro as indicated by internucleosomal DNA fragmentation and hypodiploid DNA content of nuclei. Unlike what is reported in HIV-infected individuals, we observed that cell death of cat lymphocytes was inhibited by activation. Spontaneous apoptosis was reduced by the addition of cat serum, interleukins [interleukin (IL)1, Il2, IL6 and interferon-gamma (IFN gamma)] and after activation by phorbol ester [phorbol myristyl acetate (PMA)], superantigens [staphylococcal enterotoxin B (SEB), staphylococcal enterotoxin A (SEA)], and to a lesser extent by mitogens such as Concanavalin A and pokeweed mitogen, IN contrast, apoptosis of lymphocytes from FIV-infected, but not from control cats was increased in the presence of calcium ionophore (ionomycin). In this study, we studied the spontaneous programmed cell death (PCD)-inducing pathways, and the mechanisms of action of PMA, SEB and SEA. Spontaneous lymphocyte apoptosis of FIV-infected cats was inhibited by cycloheximide, ZnSO4 and N-acetyl-cystein. The preventive effect of SEB and SEA was inhibited by actinomycin, but not by inhibitors of kinases. Calyculin, an inhibitor of phosphatase, had no effect either on spontaneous apoptosis, or on the action of PMA, SEB and SEA. Ionomycin-induced apoptosis was found sensitive to PMA and cytokines. In FIV-infected cats, these data suggest that the mature lymphocytes appear programmed to die by apoptosis, unless rescued by specific agents, such as protein kinase C activators or growth factors, and that spontaneous PCD seems to be dependent of de nove protein synthesis (see effect of cycloheximide). The effects of PMA, SEB and SEA are probably mediated by de novo proteins which for PMA, undergo a phosphorylation involving serine-threonine and/or tyrosine groups. Our data suggest a clear difference between lymphocytes from FIV-infected cats and lymphocytes from HIV-infected humans, with regard to their metabolic regulations.

Size variation within the second hypervariable region of the surface envelope gene of the bovine lentivirus BIV in experimentally and naturally infected cattle

The bovine lentivirus also known as the bovine immunodeficiency-like virus (BIV) has conserved and hypervariable regions in the surface envelope (SU) gene. Size variation between isolates can be as large as 200 bp, mostly occurring in the second hypervariable (V2) gene region of the SU gene. The V2 region was cloned and sequenced from both experimentally and naturally infected cattle. Temporal evaluation of provirus from an experimentally inoculated cow showed two different-sized variants that appeared over time. The variation appeared to result from a recombinational event resulting in an apparent direct repeat. Cloned proviral nucleotide sequence diversity increased over time. Virus that was cultured and then cloned and sequenced showed progressive change from the inoculum virus, but culturing reduced the diversity of the clones as compared with direct amplification of provirus from leukocyte samples from the cow. The quasispecies phenomenon was evident in clones sequenced from a cow naturally infected with BIV. Of 10 clones examined from the V2 region, 6 different-size clones were present with nine different patterns of sequence rearrangement. Sequence length of different clones varied by as much as 43 amino acids (aa), with 21- and 15-aa direct repeats accounting for most of the size variation. Similar to other lentiviruses, BIV appears to mutate rapidly, which may be important in viral persistence and pathogenesis.

Laboratory diagnostic tests for retrovirus infections of small ruminants

The most practical and reliable approach to confirming a diagnosis of OPPV or CAEV infection is a combination of serology and clinical evaluation. Although serology represents the most cost effective method of diagnosing persistently infected, clinically normal animals, testing errors occur; the frequency of error depends on the performance data of the particular serologic assay being used. When PCR detection of OPPV and CAEV becomes routinely available, this detection method can be used in rigorous eradication programs to determine the infection status of animals that cannot be definitively diagnosed by serology. The important aspects of OPPV and CAEV infection that must be considered in designing programs to prevent transmission are (1) OPPV and CAEV persist for life in the infected host, (2) a major route of transmission is to lambs and kids via colostrum and milk during nursing, (3) contact transmission among adults can occur, and (4) time variability can exist among individual sheep and goats from infection to the appearance of detectable antibodies.

Bovine lentivirus induces early transient B-cell proliferation in experimentally inoculated cattle and appears to be pantropic

Bovine immunodeficiency-like virus (BIV) was first isolated in 1972 (M. J. VanDerMaaten et al., J. Natl. Cancer Inst. 49:1649-1657, 1972). Much work has been done on the molecular characterization of BIV in studies using the original BIV R29 isolate; however, R29 is believed to be attenuated since it no longer causes either mononuclear cell number increases or detectable enlargement of lymphatic nodules in experimentally infected cattle. The host cell tropism and changes in host peripheral blood lymphocyte populations following infection with BIV are unknown. Recently, we isolated and characterized a field isolate of BIV, FL112 (D. L. Suarez et al., J. Virol. 67:5051-5055, 1993) that causes a transient, mononuclear cell lymphocytosis in experimentally infected cattle. In the present study, cattle were inoculated with BIV FL112, and data from flow cytometry showed that BIV causes a B-cell lymphocytosis with no consistent, significant changes in other mononuclear cell populations, including CD3+, CD4+, and CD8+ cells. Cell sorting and PCR amplification were used to show that BIV may be pantropic. Proviral DNA was present in CD3+, CD4+, CD8+, and B-cells, monocytes, and WC1 cells (gamma/delta T cells, null cells) by 3 to 6 days postinoculation and also at 2.5 years postinoculation.

Detection of antibodies against bovine immunodeficiency-like virus in daily cattle in Hokkaido

Serological survey of bovine immunodeficiency-like virus (BIV) infection was performed in cattle of 3 different farms in Hokkaido, where a relatively high seroprevalence was recorded for bovine leukemia virus (BLV). About a half of 120 cattle tested were seropositive for BLV, while 7.5% of the cattle were seropositive for BIV. Though increased numbers of leukocytes were frequently observed in BLV-seropositive cows, no such changes were observed in BIV-positive but BLV-negative cows. No correlation was demonstrated between BIV- and BLV-seroprevalence of the cattle.

The transmission of Jembrana disease, a lentivirus disease of Bos javanicus cattle

Methods of transmission of Jembrana disease, an acute and severe disease of Bali cattle (Bos javanicus) caused by a recently-identified bovine lentivirus known as Jembrana disease virus, are described. During the acute disease virus can be detected in saliva and milk. There is evidence of direct transmission from acutely affected animals in close contact with susceptible cattle, possibly by virus in these secretions infecting cattle by the conjunctival, intranasal or oral routes, by which it was possible to infect cattle experimentally. During the acute disease the titre of infectious virus in blood is high, about 10(8) 50% cattle infectious units (ID50)/ml, and it is probable that the virus is also transmitted mechanically by haematophagous arthropods. Recovered cattle are also a potential but probably infrequent source of infection; recovered cattle are persistently viraemic but the titre of infectious virus in blood decreases to about 10(1) ID50/ml by 60 days after recovery from the acute disease, and virus cannot be detected in secretions.

Possible role of bovine immunodeficiency virus in bovine paraplegic syndrome: evidence from immunochemical, virological and seroprevalence studies

Bovine paraplegic syndrome (BPS) is a debilitating cattle disease of unknown origin that is characterized by leukocytosis, lymphocytopenia and monocytopenia. The major clinical signs are difficulties in locomotion affecting hind limbs, hypoalgesia in the hind quarters, posterior paralysis and death within 72 to 96 hours after recumbency. To investigate the aetiological basis of BPS, we examined a possible association of the syndrome with infection by bovine immunodeficiency virus (BIV), a lentivirus implicated in immune system dysfunction and central nervous system lesions in cattle. Serum samples (n = 1,278) were collected from both healthy and BPS-prevalent cattle herds in Venezuela, and organ extracts were prepared from euthanized animals (n = 11) suspected of having BPS. Sera were analysed for reactivity to recombinant BIV and bovine leukaemia virus gag precursor proteins by immunoblot procedures. Serum reactivity to BIV ranged from 12 to 66% between groups of BPS prevalent herds. The percentage of samples reactive to BLV antigen was much lower (2 to 17%). Rabbits inoculated with extracts from BPS-afflicted animals exhibited an anamnestic immune response to BIV antigens as well as the presence of BIV gag antigens in their tissues. We present evidence for a possible association between BPS disease and a viral agent related to BIV. The role of BIV, in combination with malnutrition, in BPS is discussed.

Longitudinal assessment of feline immunodeficiency virus kinetics in plasma by use of a quantitative competitive reverse transcriptase PCR

Cats infected with feline immunodeficiency virus (FIV) develop a disease syndrome similar to that caused by human immunodeficiency virus type 1 (HIV-1) infection in humans. HIV-1 replication has been shown to correlate with the disease stage and progression. To assess replication kinetics and disease progression in early FIV infection, we developed a quantitative competitive reverse transcriptase PCR to measure the plasma virus load at serial time points after virus exposure. We found that an early peak viremia immediately preceded the onset of acute-phase symptoms in infected cats. Plasma virus levels remained high throughout the symptomatic phase of infection, which lasted for 8 to 10 weeks, and then declined as clinical symptoms resolved; however, all cats maintained significant plasma virus titers through 36 weeks postinfection. Early peak viral replication coincided with the initial precipitous decline in circulating CD4+ T lymphocytes. These results indicate that FIV kinetics are similar to those of HIV-1 during the acute and secondary phase of infection and that the plasma FIV load correlates with the disease stage. These results serve to further develop the FIV model and to enhance its usefulness for pathogenesis, vaccine development, and therapeutic studies related to HIV.

Pathogenic mechanisms of caprine arthritis-encephalitis virus

Goats infected with caprine arthritis-encephalitis virus (CAEV) show chronic arthritis and cachexia, which are progressive in nature. The immunopathogenic mechanisms responsible for these progressive clinical symptoms have not been fully elucidated. Various haematological and immunological parameters were evaluated in experimentally-infected goats showing typical signs of CAEV-induced disease. Infected goats showed recurrent lymphocytosis that may be due to constant presentation of antigen by infected cells of a monocyte/macrophage lineage. The serum alkaline phosphatase and gamma-glutamyl transferase concentrations were elevated in infected goats, a characteristic of hepatic and bone disorders. All other serum chemistry parameters were similar between infected and control goats. Importantly, the serum tumour necrosis factor-alpha (TNF-alpha) levels were higher in infected goats. The cachexia seen in infected goats may be at least partly due to altered metabolism as a result of prolonged elevation of serum TNF-alpha levels. Depressed natural killer cell activity was observed in infected goats and may contribute towards the establishment of a persistent infection with CAEV.

Oligopeptide-based enzyme immunoassay for ovine lentivirus antibody detection

Ovine progressive pneumonia virus (OPPV) is a lentivirus which causes a progressive disease in sheep. Immunodominant epitopes have been identified in the envelope gp40 glycoprotein. Synthetic peptides representing these regions are able to detect the presence of OPPV antibodies in 96% of infected sheep.

Evaluation of agar gel immunodiffusion serology using caprine and ovine lentiviral antigens for detection of antibody to caprine arthritis-encephalitis virus

The sensitivity of the agar gel immunodiffusion (AGID) test for the detection of antibody to caprine arthritis-encephalitis virus (CAEV) was investigated with CAEV or ovine progressive pneumonia virus (OPPV) as the source of antigen. A total of 218 goat serum specimens were tested for anti-CAEV antibody by AGID and immunoprecipitation of [35S]methionine-labeled CAEV. In comparison with that of immunoprecipitation, the sensitivity of the CAEV AGID test was 0.91, and that of the OPPV AGID test was 0.56. The AGID test with either antigen was 100% specific. The lower sensitivity of the OPPV AGID test in detecting caprine antibody to CAEV indicates that OPPV antigen is of limited value for use in CAEV diagnosis and control programs.

Plasma amino acid dysregulation after lentiviral infection

The absence of AIDS-like symptoms in HIV-infected chimpanzees and SIV-infected African Green monkeys (AGMs) may provide important clues about the pathogenic mechanism of AIDS and about mechanisms of resistance. HIV-infected persons and SIV-infected rhesus macaques have, on the average, markedly decreased cysteine, cystine, and glutathione levels and elevated plasma glutamate concentrations. Glutamate inhibits the membrane transport of cystine and a combination of low plasma glutamate and high cystine levels was found to be correlated with high CD4+ T cell numbers even in HIV-negative healthy human individuals. We have now found that glutamate and cystine levels are also correlated with CD4+ T cell numbers in chimpanzees. But infection of chimpanzees, AGMs, and goats with HIV-1, SIV, and caprine arthritis encephalitis virus (CAEV), respectively, does not induce significant changes in plasma cystine or glutamate levels, although infected AGMs and goats have, on the average, significantly elevated plasma levels of the biochemically related amino acid proline.

Feline immunodeficiency virus infection. Clinicopathologic findings in 90 naturally occurring cases

In 90 cats with naturally occurring feline immunodeficiency virus (FIV) infection, the clinicopathologic changes seen at the time of first diagnosis of FIV infection included lymphopenia (29%), neutrophilia (27%), monocytosis (23%), anemia (18%), leukocytosis (13%), leukopenia (13%), neutropenia (11%), hyperproteinemia (38%), and hyperglobulinemia (25%). Forty-nine (54%) of the cats showed multiple hematologic abnormalities, and a further 24 (17%) had a single abnormality. The most consistent changes in serum protein electrophoretic patterns were increases in the concentrations of alpha 2 globulin and gammaglobulin subfractions. Although there is no established system for staging the degree of immunosuppression in cats infected with FIV, cytopenias appeared to be more common in cats with advanced clinical signs of disease.

Infection and dysfunction of monocytes induced by experimental inoculation of calves with bovine immunodeficiency-like virus

Three calves were experimentally inoculated with bovine immunodeficiency-like virus (BIV) to examine BIV pathogenesis. Inoculated calves produced specific antibody that could be detected from 3 to 5 weeks up to 1 year postinoculation (pi). Virus was isolated from peripheral blood mononuclear cells (PBMC) 3-4 weeks pi by syncytia assay. Thereafter, the virus could be continually isolated. BIV could be isolated from monocytes but not from T cells. Likewise, monocytes could be infected with BIV in vitro. Various monocyte functions of these BIV-infected calves and age-matched uninfected calves were tested; superoxide anion release, phagocytic activity, and chemotactic responsiveness of monocytes were depressed in BIV-infected calves compared with control calves. A slight delay in the humoral immune response against mouse serum protein was also evident. During the observation period of approximately 1 year, no significant clinical symptoms could be observed. One calf, however, was killed at 15 months pi. At the time of necropsy, BIV could be isolated from PBMC as well as from cells of the spleen, liver, and lymph nodes.

Persistent infection of rabbits with bovine immunodeficiency-like virus

Chronic infection of rabbits was induced by a single intraperitoneal injection of bovine immunodeficiency-like virus (BIV)-infected cells. Ten BIV-infected animals were monitored serologically for up to 2 years. Results of serologic and virus rescue assays indicated that all animals became infected and demonstrated a rapid and sustained BIV-specific humoral response. BIV was rescued by cocultivation from spleen, lymph nodes, and peripheral blood leukocytes of infected animals. Viral DNA in immune tissues was confirmed by polymerase chain reaction amplification of BIV sequences. These data and specific immunohistochemical staining of mononuclear cells of the spleen for BIV antigen suggest that the infection is targeted to immune system cells.

Feline immunodeficiency virus: quantification in peripheral blood mononuclear cells and isolation from plasma of infected cats

The titer of feline immunodeficiency virus in peripheral blood mononuclear cells (PBMC) and the presence of infectious virus in plasma was investigated over 20 week period in 8 experimentally infected cats, 3 uninfected cats and 2 naturally infected cats by end point dilution cultures using a feline T-lymphoblastoid cell line (MYA-1). FIV was isolated from PBMC of all infected cats, but not from the uninfected cats. FIV was also isolated consistently from 100 microliters plasma from most of the experimentally infected cats, but not from the 2 naturally infected cats. The virus titer in PBMCs in both experimentally and naturally infected cats was comparatively high, ranging from 10 TCID/10(6) PBMC to 14,286 TCID/10(6) PBMC. The titers in PBMC of individual cats remained unchanged or varied only slightly over the 20 week period. In contrast, the titers varied substantially between cats, with significantly higher titers in the youngest litter (4 cats) than in the oldest litter (3 cats). This suggests that there is an age-related factor influencing the level of PBMC virus titers in experimental infection with FIV. A similar age-related susceptibility has been shown with feline leukemia virus. More importantly, the sustained titers in the experimentally infected cats bear close resemblance to infection of children with human immunodeficiency virus. These data reinforce suggestions that age and immune maturity have a fundamental influence on PBMC and plasma titers in lentivirus infections.