A technique for the sequential isolation of RNA and DNA from embryos developed for screening for viruses

Risk of Chlamydia abortus transmission via embryo transfer using in vitro produced early bovine embryos

The objectives of this study were to determine (i) whether Chlamydia (C.) abortus would adhere to the intact zona pellucida (ZP-intact) of early in vitro produced bovine embryos; (ii) whether the bacteria would adhere to the embryos (ZP-free) after in vitro infection; and (iii) the efficacy of the International Embryo Transfer Society (IETS) washing protocol. The experimentation was made twice. For each replicate 100 (8-16-cell) bovine embryos produced in vitro were randomly divided into 10 batches. Height batches (4 ZP-intact and 4 ZP-free) of 10 embryos were incubated in a medium containing 4 × 10⁷Chlamydia/ml of AB7 strain. After incubation for 18 h at 37 °C in an atmosphere of 5% CO₂, the embryos were washed in accordance with the IETS guidelines. In parallel, two batches (1 ZP-intact and 1 ZP-free) of 10 embryos were subjected to similar procedures but without exposure to C. abortus as a control group. The 10 washing fluids from each batch were collected and centrifuged for 1 h at 13,000×g. Each batch of washed embryos and each wash pellets were tested using PCR. C. abortus DNA was found in all ZP-intact and ZP-free batches of 10 embryos after 10 successive washes. For ZP-intact infected embryos, Chlamydia-DNA was also detected in all 10 wash baths for two batches (2/8) of embryos, whereas for ZP-free infected embryos, Chlamydia-DNA was detected in all 10 wash baths for 6/8 batches of embryos. In contrast, none of the embryos or their washing fluids in the control batches was DNA positive. The bacterial load for batches of 10 embryos after the 10 wash baths was significantly higher for batches of ZP-free embryos (20.7 ± 9 × 10³ bacteria/mL) than for batches of ZP-intact embryos (0.47 ± 0.19 × 10³ bacteria/mL). These results demonstrate that C. abortus adheres to the ZP as well as the early embryonic cells of in vitro produced bovine embryos after in vitro infection, and that the standard washing protocol recommended by the IETS fails to remove it.

Can Chlamydia abortus be transmitted by embryo transfer in goats?

The objectives of this study were to determine (i) whether Chlamydia abortus would adhere to or penetrate the intact zona pellucida (ZP-intact) of early in vivo-derived caprine embryos, after in vitro infection; and (ii) the efficacy of the International Embryo Transfer Society (IETS) washing protocol for bovine embryos. Fifty-two ZP-intact embryos (8-16 cells), obtained from 14 donors were used in this experiment. The embryos were randomly divided into 12 batches. Nine batches (ZP-intact) of five embryos were incubated in a medium containing 4 × 10(7)Chlamydia/mL of AB7 strain. After incubation for 18 hours at 37 °C in an atmosphere of 5% CO2, the embryos were washed in batches in 10 successive baths of a phosphate buffer saline and 5% fetal calf serum solution in accordance with IETS guidelines. In parallel, three batches of ZP-intact embryos were used as controls by being subjected to similar procedures but without exposure to C. abortus. The 10 wash baths were collected separately and centrifuged for 1 hour at 13,000 × g. The washed embryos and the pellets of the 10 centrifuged wash baths were frozen at -20 °C before examination for evidence of C. abortus using polymerase chain reaction. C. abortus DNA was found in all of the infected batches of ZP-intact embryos (9/9) after 10 successive washes. It was also detected in the 10th wash fluid for seven batches of embryos, whereas for the two other batches, the last positive wash bath was the eighth and the ninth, respectively. In contrast, none of the embryos or their washing fluids in the control batches were DNA positive. These results report that C. abortus adheres to and/or penetrates the ZP of in vivo caprine embryos after in vitro infection, and that the standard washing protocol recommended by the IETS for bovine embryos, failed to remove it. The persistence of these bacteria after washing makes the embryo a potential means of transmission of the bacterium during embryo transfer from infected donor goats to healthy recipients and/or their offspring. Nevertheless, the detection of C. abortus DNA by polymerase chain reaction does not prove that the bacteria found was infectious. Further studies are required to investigate whether enzymatic and/or antibiotic treatment of caprine embryos infected by C. abortus would eliminate the bacteria from the ZP.

Development of a semi-nested PCR using degenerate primers for the generic detection of small ruminant lentivirus proviral DNA

A PCR assay was developed for the reliable detection of small ruminant lentivirus (SRLV) proviral DNA. The method involved the use of degenerate deoxyinosine-substituted primers and a second semi-nested PCR step that increased the polyvalency and sensitivity of the detection, respectively. Primers were designed from the pol gene conserved motifs of 85 SRLV isolates and were evaluated using different SRLV isolates together with Maedi-Visna virus (MVV) and caprine arthritis-encephalitis virus (CAEV) reference strains. The method successfully detected SRLV proviral DNA in total DNA extracts originating from whole blood samples, separated peripheral blood mononuclear cells (PBMCs) and tissue cultures. The semi-nested PCR was compared with the agar gel immunodiffusion test and proved to be highly sensitive, specific and capable of detecting many SRLV variants in infected or suspect animals. Therefore, it would be useful in the diagnosis of natural SRLV infections, in eradication programs and epidemiological studies. Whole blood samples can be used directly, thus alleviating the need for PBMC separation, and thereby enables a simple, fast and cost-effective analysis of a large number of samples.

Genomic characterization of a slow/low maedi visna virus

The complete genomic sequence of a sheep lentivirus isolate that presents a slow/low phenotype in vitro has been determined. The virus, designated P1OLV, was isolated from lung cells of a naturally infected sheep in Portugal. Three overlapping DNA fragments amplified by PCR, and encompassing the entire viral genome were cloned and sequenced. This isolate has an overall similarity of approximately 80% with the K1514 Maedi Visna virus (MVV) and approximately 70% with the caprine arthritis encephalitis virus (CAEV) Co strain. Phylogenetic analysis based on SU and RT nucleotide sequences grouped P1OLV with previously reported ovine MVV. To determine the virus replication rate, sheep choroid plexus (SCP) and lung cells, macrophages (MØ), and goat synovial membrane (GSM) cells were inoculated with either P1OLV or with the lytic North American strain WLC-1. Viral RNA in culture supernatants was measured by one-tube real time quantitative RT-PCR. Significant differences were observed between the replication rates of the two viruses, with WLC-1 growing rapidly and to high levels in all the cells tested, while P1OLV replicated more slowly and to lower levels inducing persistent infections in lung and SCP cells. The U3 region of the LTR of P1OLV lacks the sequence repeats that are present in the LTRs of WLC-1 and MVV prototype K1514 and that contain additional binding sites for the AML(vis) transcriptional factor. To evaluate the contribution of LTR in the virus replication rate in vitro, we measured the basal activity of the promoter from P1OLV and WLC-1 in a luciferase-driven gene expression assay and lower levels of expression were achieved for P1OLV. The genetic and biological properties of P1OLV will be useful for the study of virus transcriptional factors and genes that may be responsible for the slow/low phenotype.

Transmission of small ruminant lentiviruses

Small ruminant lentiviruses (SRLV) are classical slow retroviruses causing chronic inflammatory disease in a variety of target organs. The routes of transmission have been investigated and a large body of evidence has accumulated over many years. The main routes are through ingestion of infected colostrum and/or milk, or through inhalation of respiratory secretions. However, many studies also provide evidence that intrauterine infection may occur, though the extent and significance of this route is controversial. Embryos treated to IETS standards appear to pose very little risk of infection. SRLV have been detected in semen suggesting a potential source of transmission. However, such transmission has not been demonstrated to date. The application of control measures based on this information allows more efficient strategies to be developed which will reduce the rate of transmission.

Preventing experimental vertical transmission of scrapie by embryo transfer

This study investigated whether the transmission of naturally occurring scrapie in sheep can be prevented using embryo transfer. Embryos were collected from 38 donor ewes in a Suffolk sheep flock with a high incidence of naturally occurring scrapie, treated with a sanitary procedure (embryo washing) recommended by the International Embryo Transfer Society and then transferred to 58 scrapie-free recipient ewes. Ninety-four offspring were produced. None of the offspring or the recipient ewes developed scrapie. Furthermore, offspring derived from embryos collected from donor ewes bred to the immunohistochemically positive ram did not develop scrapie. We conclude that scrapie was not transmitted to offspring via the embryo nor was the infective agent transmitted to recipient ewes during embryo transfer procedures.

Differential levels of mRNAs for cytokines, the interleukin-2 receptor and class II DR/DQ genes in ovine interstitial pneumonia induced by maedi visna virus infection

The relative levels of selected cytokine, interleukin-2 receptor, class II DR and DQ RNAs, and maedi visna virus (MVV) RNA were measured by reverse-transcriptase polymerase chain reaction (RT-PCR) in the lungs of sheep with natural maedi visna virus infection (n = 8) and a group of age/sex/breed-matched MVV seronegative sheep (n = 4). These animals were divided into two groups, irrespective of serostatus, according to the severity of lymphocytic interstitial pneumonia. The severity of lung lesions was determined by clinical sign, lung weight, and lesion sore in the lungs measured by three pathologic parameters. Sheep with lung lesions showed hyperelevated levels of granulocyte-macrophage colony-stimulating factor upregulated gamma-interferon, interleukin 2 receptor, and interleukins 1 beta, 4, and 10 mRNAs. Class II mRNAs were found not to be elevated in the lungs of sheep with lung lesions. Tumor necrosis factor alpha and transforming growth factor beta 1 mRNA levels were similar in all sheep lungs studied. We discuss the major roles played by granulocyte-macrophage colony-stimulating factor and type 2 cytokines in the pathogenesis of this disease and the possible stimulation of the production of these cytokines by viral surface glycoproteins.

A review on disease transmission studies in relationship to production of embryos by in vitro fertilization and to related new reproductive technologies

This paper addresses the circumstances of germplasm contamination and updates on transmission of pathogenic agents by embryos produced in vitro and by associated techniques. It has been shown that some pathogenic agents might have been associated with the follicular oocytes and oviductal cells, collected for in vitro fertilization (IVF), resulting in infected embryos. Experimental introduction of pathogenic agent with oocytes or infected semen into the IVF system allows, in most cases, for the fertilization of eggs and for the production of some transferable quality embryos. Rendering of oocytes and embryos free of infectious pathogens, using the standard sequential washing or enzymatic treatment, is inconsistent and more difficult in the presently used in vitro fertilization system as compared to in vivo produced embryos.

Characterization of enzootic nasal tumor virus capsid antigen

The RT-PCR was carried out on tumor tissue from sheep with enzootic nasal tumor (ENT), using primers designed from conserved amino acid regions of related type D retroviruses. A 591 bp PCR fragment, corresponding to 90% of the capsid antigen was cloned, sequenced and expressed in E. coli. Alignment with ovine pulmonary carcinoma (OPC) virus showed 93% nucleotide and 96% amino acid homology. No amplification occurred when DNA from ovine fetal cell line was used as template. The recombinant protein, highly expressed in prokaryotic system, reacted in immunoblot with mouse antiserum to Mason Pfizer monkey virus (MPMV) p27, as well as sera from OPC and ENT diseased animals. Preliminary application of this antigen in ELISA suggested its potential use to detect seropositive animals in infected flocks.

Increased intestinal TNF-alpha, IL-1 beta and IL-6 expression in ovine paratuberculosis

Mycobacterium avium subspecies paratuberculosis is an intracellular parasite of intestinal macrophages and causes a chronic granulomatous enteritis in sheep and other ruminants (paratuberculosis or Johne's disease). Macrophages can be produced a variety of immunoregulatory cytokines that may influence mycobacterial killing and produce disordered inflammation within the gut. In this study, messenger RNA (mRNA) was extracted from intestinal tissue from control and multibacillary diseased sheep and profiles for the cytokines tumour necrosis factor-alpha (TNF-alpha), interleukin-1 beta (IL-1 beta), IL-6, transforming growth factor-beta1 (TGF-beta1) and granulocyte-macrophage colony stimulating factor (GM-CSF) were semi-quantified using reverse transcriptase polymerase chain reactions (RT-PCR). Infected intestinal tissues had significantly increased mRNA for TNF-alpha, IL-1beta and IL-6 but TGF-beta1 and GM-CSF mRNA levels were significantly different from controls. Supernatants from in vitro intestinal cultures were assayed for TNF-alpha activity using the PK(15)-1512 cytotoxicity bioassay and levels were significantly raised in diseased samples. TNF-alpha was not detected in any serum samples. Further analysis on intestinal tissues from sheep with the different, paucibacillary, form of the disease showed significant elevation of TNF-alpha mRNA but not other cytokines tested. Increased pro-inflammatory cytokine expression in the intestine coincident with a failed or misdirected immune response may contribute to the pathogenesis of paratuberculosis and the persistence of a chronic inflammatory state.