Washing or washing and trypsin treatment is ineffective for removal of noncytopathic bovine viral diarrhea virus from bovine oocytes or embryos after experimental viral contamination of an in vitro fertilization system

Risk of pathogenic virus transmission by somatic cell nuclear transfer (SCNT): implications for xenotransplantation

Using somatic cell nuclear transfer (SCNT) for the generation of cloned and transgenic animals bears the risk of transmission of viruses, either by the oocyte or by the introduced donor cell. There is evidence that the zona pellucida (ZP) surrounding the oocyte prevents virus infection, however, virus infections despite intact ZP were reported. Furthermore, the protective ZP has to be penetrated in order to place the somatic cell in the oocyte's perivitelline space during SCNT. Transmission of viruses represents also a severe problem during in vitro fertilization (IVF). Genetically modified and IVF-produced pigs serve as an important biomedical model for numerous diseases and it is important to evaluate whether infections of the model animals can falsify the research data. Of special significance is this topic in the case of xenotransplantation using genetically modified pigs as donor animals, because transmission of porcine viruses may be harmful for the human recipient. This was repeatedly demonstrated in preclinical pig to non-human primate trials. Therefore, donor pigs, oocytes used for SCNT and genetically modified donor cells should be screened for potentially zoonotic viruses when creating genetically modified pigs designed for xenotransplantation.

Emerging diseases in international trade in embryos

A significant change in cattle production and germplasm exchange has occurred over the past 50 years. The growth of artificial reproductive technologies and their broad implementation has become commonplace. The production and subsequent import and export of semen and embryos throughout the world has increased significantly. The embryo transfer industry has reached a new record of growth, with approximately 1.5 million transferrable bovine embryos collected and/or produced in 2018. Over 1 million of these embryos were produced invitro . The increased production of invitro -produced embryos leads to greater opportunities involving international trade. However, further research concerning emerging pathogens is imperative to ensure the efficacy and safety of the embryo transfer industry. Appropriate biosecurity protocols, including reliable testing methodology and effective embryo processing procedures, are key in preventing disease due to emerging and re-emerging pathogens that can be transmitted via embryo transfer.

Alterações na morfologia e na viabilidade no desenvolvimento de embriões bovinos fecundados in vitro com sêmen contaminado experimentalmente à Escherichia coli produtora da toxina Shiga stx2

RESUMO:O objetivo deste trabalho foi avaliar, por meio de micros- copia óptica e eletrônica de transmissão, as alterações na morfologia e a viabilidade do desenvolvimento de embriões bovinos fecundados com sêmen contaminado experimentalmente à Escherichia coli produtora da toxina shiga stx2 (STEC). Para tanto, oócitos foram aspirados de ovários de vacas abatidas e selecionados para maturação in vitro. Após 20-24 horas de maturação, os oócitos foram divididos em 2 grupos. Sendo o primeiro grupo o controle (n = 418), fertilizado com sêmen testado e sem nenhum tipo de contaminante e o segundo, o grupo contaminado (n = 415), fertilizado com sêmen exposto a STEC. Cada sêmen foi tra tado pela técnica de gradiente descontínuo de Percoll. Após o período de fecundação, os embriões foram avaliados quanto a sua morfologia e viabilidade, com o auxílio da microscopia óptica e eletrônica. Na ava liação morfológica, os oócitos fecundados com o sêmen contaminado apresentaram retração citoplasmática, falhas na divisão, assimetria de blastômeros, ooplasma granuloso, coloração castanho-escuro, formação de vacúolos, degeneração e rompimento da zona pelúcida. Essas alte rações não foram observadas no grupo controle. A avaliação de todos oócitos incluídos mostrou taxas de clivagem de 70,3 e 52,8%, respec tivamente, para embriões controle e contaminado (p = 0,0001). Após o 5° dia de desenvolvimento embrionário foram observadas 44,7% de mórulas no grupo controle e 22,4% no grupo contaminado, apresen tando diferença significativa (p=0,0001). A presença da STEC interfere na taxa de clivagem dos embriões e também inviabiliza e provoca queda no desenvolvimento embrionário ao estádio de mórula, além de causar alterações morfológicas durante esse desenvolvimento.

Shaping the norms that regulate international commerce of embryos

As various embryo technologies in livestock were developed and evolved to a state of usefulness over the past 40 years, scientists with a specific interest in infectious diseases sought to determine the epidemiologic consequences of movement, especially international movement, of increasing numbers of embryos. Many of the foundational studies in this area were reported in Theriogenology, beginning in the 1970s and especially throughout the 1980s and 1990s. Unquestionably, Theriogenology has been a widely used venue for dissemination of basic information on this subject, which ultimately led to the development of the now universally accepted techniques for certification of embryo health. Today it is well-recognized that movement in commerce of embryos, especially in vivo-derived embryos, is a very low-risk method for exchange of animal germ plasm. This paper chronicles the evolution of strategies for health certification of embryos. An overview is provided of the calculated efforts of practitioners, scientists, and regulators to organize, forge necessary partnerships, stimulate needed research, provide purposeful analysis of the results, and, through these processes, guarantee the universal acceptance of efficient protocols for certifying the health of embryos intended for movement in international commerce.

Intrauterine inoculation of seronegative heifers with bovine viral diarrhea virus concurrent with transfer of in vivo-derived bovine embryos

Bovine viral diarrhea virus (BVDV) has been shown to be associated with single transferable in vivo-derived bovine embryos despite washing and trypsin treatment. Hence, the primary objective was to evaluate the potential of BVDV to be transmitted via the intrauterine route at the time of embryo transfer. In vivo-derived bovine embryos (n=10) were nonsurgically collected from a single Bos tarus donor cow negative for BVDV. After collection and washing, embryos were placed into transfer media containing BVDV (SD-1; Type 1a). Each of the 10 embryos was individually loaded into an 0.25-mL straw, which was then nonsurgically transferred into the uterus of 1 of the 10 seronegative recipients on Day 0. The total quantity of virus transferred into the uterus of each of the 10 Bos tarus recipients was 878 cell culture infective doses to the 50% end point (CCID(50))/mL. Additionally, control heifers received 1.5 x 10(6) CCID(50) BVDV/.5 mL without an embryo (positive) or heat-inactivated BVDV (negative). The positive control heifer and all 10 recipients of virus-exposed embryos exhibited viremia by Day 6 and seroconverted by Day 15 after transfer. The negative control heifer did not exhibit a viremia or seroconvert. At 30 d after embryo transfer, 6 of 10 heifers in the treatment group were pregnant; however, 30 d later, only one was still pregnant. This fetus was nonviable and was positive for BVDV. In conclusion, the quantity of BVDV associated with bovine embryos after in vitro exposure can result in viremia and seroconversion of seronegative recipients after transfer into the uterus during diestrus.

Transmission of bovine viral diarrhea virus (BVDV) via in vitro-fertilized embryos to recipients, but not to their offspring

The objective was to assess the potential of Day-7, IVP zona pellucida-intact blastocysts to transmit bovine viral diarrhea virus (BVDV) to embryo recipients. Embryos were exposed (1h) to two non-cytopathic (NCP) biotypes, either NY-1 (type 1) or two concentrations of PA-131 (type 2), washed 10 times, and transferred into recipients (two embryos/recipient) free of BVDV and its antibody. Six (30.0%) of the 20 pregnancies were lost after 30 d following transfer of the embryos exposed to the type 1 strain; none of the recipients or their 18 full term offspring seroconverted. Conversely, following exposure to the type 2 strain, 16 (51.6%) of the 31 pregnancies were lost >30 d after embryo transfer. Furthermore, 18 (51.4%) of 35 recipients receiving embryos exposed to type 2 seroconverted; 11 of those were pregnant at 30 d, but only 2 went to full term and gave birth to noninfected (seronegative) calves. Virus isolation tests were performed on single, virus-exposed, washed embryos (not transferred); 3 of 12 (25%) and 17 of 61 (28%) exposed to type 1 and type 2, respectively, were positive for live BVDV. Embryos exposed to type 2 virus had from 0 to 34 viral copies. In conclusion, a large proportion of recipients that received embryos exposed to BVDV, especially those exposed to a high concentration of type 2 virus, became infected after ET, and their pregnancies failed. However, term pregnancies resulted in calves free of both virus and antibody. Therefore, additional disinfection procedures are recommended prior to transferring potentially infected IVP embryos.

Normal reproductive capacity of heifers that originated from in vitro fertilized embryos cultured with an antiviral compound

Bovine viral diarrhea virus (BVDV) can associate with in vitro fertilized (IVF) bovine embryos despite washing and trypsin treatment. An antiviral compound, DB606 (2-(4-[2-imidazolinyl]phenyl)-5-(4-methoxyphenyl)furan), inhibits the replication of BVDV in bovine uterine tubal epithelial cells, Madin Darby bovine kidney cells, and fetal fibroblast cells. As well, DB606 in in vitro culture medium does not affect embryonic development. Antiviral-treated-IVF embryos placed into recipients developed into clinically normal calves. The objective of this project was to determine if these resultant heifer calves were capable of reproducing. Seven heifers from each of the treatment groups (natural breeding, IVF embryo, and IVF embryo cultured in DB606) of the previous study were used. At 20-27 months of age, the heifers were exposed to a fertile bull in a single pasture during a 63 d breeding season. Five of the seven heifers originating from natural breeding were pregnant 35 d after removal of the bull and calved. All of the heifers resulting from transfer of untreated IVF embryos were pregnant at 35 d; however, one aborted the fetus at 5-7 months of gestation. All of the heifers derived from transfer of IVF embryos cultured in DB606 were pregnant and calved. Offspring from dams of all treatment groups were clinically normal at birth. Adjusted 205 d weaning weights were not significantly different among the offspring of the treated and untreated dams. These results indicate that culture of bovine-IVF embryos in DB606 does not impair future reproductive capacity of resulting heifers.

Alteration in ultrastructural morphology of bovine embryos following subzonal microinjection of bovine viral diarrhea virus (BVDV)

The aim of the present study was to evaluate the development and ultrastructure of preimplantation bovine embryos that were exposed to bovine viral diarrhea virus (BVDV) in vitro. The embryos were recovered from superovulated and fertilized Holstein-Friesian donor cows on day 6 of the estrous cycle. Compact morulae were microinjected with 20 pl of BVDV suspension (10(5.16) TCID(50)/ml viral stock diluted 1:4) under the zona pellucida (ZP), then washed in SOF medium and cultured for 24-48 h. Embryos were evaluated for developmental stages and then processed immunocytochemically for the presence of viral particles, using fluorescent anti-BVDV-FITC conjugate. Ultrastructure of cellular organelles was analysed by transmission electron microscopy (TEM).After microinjection of BVDV under the ZP, significantly more (p<0.001) embryos (83.33%) were arrested at the morula stage compared with the intact control (30.33%). Immunocytochemical analysis localized the BVDV-FITC signal inside the microinjected embryos. TEM revealed: (i) the presence of virus-like particles in the dilated endoplasmic reticulum and in cytoplasmic vacuoles of the trophoblast and embryoblast cells; (ii) the loss of microarchitecture: and (iii) abnormal disintegrated nuclei, which lacked reticular structure and the heterochromatin area. In all, the embryo nuclear structure was altered and the microarchitecture of the nucleolus had disappeared when compared with the nuclei from control embryos. Dilatation of the intercellular space and the loss of the intercellular gap junctions were often observed in bovine BVDV-exposed embryos. These findings provide evidence for the adverse effect of BVDV virus on the development of bovine embryos, which is related to irreversible changes in the ultrastructure of cell organelles.

Development of a duplex quantitative polymerase chain reaction assay for detection of bovine herpesvirus 1 and bovine viral diarrhea virus in bovine follicular fluid

The objective of this study was to develop a duplex quantitative polymerase chain reaction (qPCR) assay for simultaneous detection of bovine herpesvirus 1 (BoHV-1) and bovine viral diarrhea virus (BVDV) type I and type II. Follicular fluid was collected from a BoHV-1 acutely infected heifer, a BVDV I persistently infected heifer, and from 10 ovaries recovered from an abattoir. Both the BoHV-1 and BVDV contaminated follicular fluid were diluted 1:5 to 1:10(7) using the pooled, abattoir-origin follicular fluid. Each dilution sample was analyzed using the duplex qPCR, virus isolation, reverse transcription-nested PCR (RT-nPCR), and BoHV-1 qPCR. The duplex qPCR was able to simultaneously detect BoHV-1 and BVDV I in the fluid diluted to 1:100 and 1:1000, respectively. These results corresponded with the reverse transcription-nested PCR and BoHV-1 qPCR. Therefore, the duplex qPCR might be used for quality assurance testing to identify these two viruses in cells, fluids and tissues collected from donor animals and used in reproductive technologies.

Bovine viral diarrhea virus (BVDV): Epidemiologic concerns relative to semen and embryos

Artificial insemination and embryo transfer are used commonly in cattle production and exchange of germplasm between populations of cattle. If properly monitored, assisted reproductive techniques can be used to prevent the spread of infectious agents. However, these techniques potentially represent unnatural routes for transmission of diseases. Bovine viral diarrhea virus (BVDV) is broadly distributed among the world's populations of cattle. Fluids, gametes and somatic cells from infected animals are likely contaminated with the virus. Thus, use of semen or embryos from infected animals could result in spread of BVDV. This paper provides an overview of the risks of transmitting this virus by AI or production and transfer of embryos and summarizes the precautions needed to prevent such transmissions of disease from occurring.

Disinfection procedures for controlling microorganisms in the semen and embryos of humans and farm animals

Semen and embryos generated by assisted reproductive techniques (ARTs) may be contaminated with numerous microorganisms. Contamination may arise from systemic or local reproductive tract infections in donors or the inadvertent introduction of microorganisms during ARTs, and may lead to disease transmission. This review describes sanitary procedures which have been investigated to ascertain whether they are effective in rendering semen and embryos free of pathogenic microorganisms, including internationally adopted washing procedures, which can be supplemented by antibiotics and enzymatic treatments. Other methods include treatment with antibodies or ozone, photoinactivation, acidification, and the use of novel antiviral compounds. In conclusion, despite the wide range of antimicrobial procedures available, none can be recommended as a universal disinfection method for rendering semen and embryos free from all potentially pathogenic microorganisms. However, some procedures are unsuitable, as they can compromise the viability of semen or embryos. In humans, washing by the gradient centrifugation method appears to be effective for reducing the microbial population in semen and is harmless to the spermatozoa. A useful procedure for embryos involving multiple washes in sterile medium has much to commend it for the prevention of disease transmission; furthermore, it is recommended by the International Embryo Transfer Society (IETS).

Detection of ovine lentivirus in the cumulus cells, but not in the oocytes or follicular fluid, of naturally infected sheep

The aim of this study was to examine the Maedi-Visna virus (MVV) infection status of oocytes, cumulus cells, and follicular fluid taken from 140 ewes from breeding flocks. MVV proviral-DNA and MVV RNA were detected using nested-PCR and RT-PCR MVV gene amplification, respectively in the gag gene. Nested-PCR analysis for MVV proviral-DNA was positive in peripheral blood mononuclear cells in 37.1% (52/140) of ewes and in 44.6% (125/280) of ovarian cortex samples. The examination of samples taken from ovarian follicles demonstrated that 8/280 batches of cumulus cells contained MVV proviral-DNA, whereas none of the 280 batches of oocytes taken from the same ovaries and whose cumulus cells has been removed, was found to be PCR positive. This was confirmed by RT-PCR analysis showing no MVV-viral RNA detection in all batches of oocytes without cumulus cells (0/280) and follicular fluid samples taken from the last 88 ovaries (0/88). The purity of the oocyte fraction and the efficacy of cumulus cell removal from oocytes was proved by absence of granulosa cell-specific mRNA in all batches of oocytes lacking the cumulus cells, using RT-PCR. This is the first demonstration that ewe cumulus cells harbor MVV genome and despite being in contact with these infected-cumulus cells, the oocytes and follicular fluid remain free from infection. In addition, the enzymatic and mechanical procedures we used to remove infected-cumulus cells surrounding the oocytes, are effective to generate MVV free-oocytes from MVV-infected ewes.

Seroconversion of calves following intravenous injection with embryos exposed to bovine viral diarrhea virus (BVDV) in vitro

Two recent studies demonstrated that a high-affinity isolate of BVDV (SD-1), remained associated with a small percentage of in vivo-derived bovine embryos following artificial exposure to the virus and either washing or trypsin treatment. Further, the embryo-associated virus was infective in an in vitro environment. Therefore, the objective of this study was to determine if the quantity of a high-affinity isolate of BVDV associated with single-washed or trypsin-treated embryos could cause infection in vivo. Twenty zona-pellucida-intact morulae and blastocysts (MB) were collected on day 7 from superovulated cows. After collection, all MB were washed according to International Embryo Transfer Society (IETS) standards, and all but 4 MB (negative controls) were exposed for 2 h to 10(5)-10(6) cell culture infective doses (50% endpoint) per milliliter (CCID(50)/mL) of viral strain SD-1. Following exposure, according to IETS standards, one half of the MB were washed and one half were trypsin treated. All MB were then individually sonicated, and sonicate fluids were injected intravenously into calves on day 0. Blood was drawn to monitor for viremia and(or) seroconversion. Seroconversion of calves injected with sonicate fluids from washed and trypsin-treated embryos occurred 38% and 13% of the time, respectively. Therefore, the quantity of a high-affinity isolate of BVDV associated with single-washed or trypsin-treated embryos was infective in vivo.

Evaluation of risks of viral transmission to recipients of bovine embryos arising from fertilisation with virus-infected semen

This scientific review was prompted by recent legislation to curtail the use of semen from potentially virus-infected bulls to produce embryos for import into the European Union. From studies in laboratory animals, humans and horses, it is apparent that viruses may sometimes attach to, or be integrated into, spermatozoa, although in domestic livestock, including cattle, this seems to be a rare phenomenon, and carriage of virus through the zona pellucida into the oocyte by fertilising sperm has never been described in these species. Four specific viruses; enzootic bovine leukosis (EBLV), bovine herpesvirus-1 (BoHV-1), bovine viral diarrhoea virus (BVDV) and bluetongue virus (BTV), all of which tend to cause subclinical infections in cattle, but which can occur in bovine semen, are examined with regard to the risks that use of infected semen might lead to production of infected embryos. With regard to in vivo-derived embryos, when internationally approved embryo processing protocols are used, the risks from EBLV- and BTV-infected semen are negligible, and the same is almost certainly true for semen infected with BoHV-1 if the embryos are also treated with trypsin. For BVDV, there is insufficient data on how the virus is carried in semen and how different BVDV strains can interact with sperm, oocytes and embryos. There is a potential, at least, that in vivo-derived embryos resulting from infected semen might carry BVDV, although field studies so far suggest that this is very unlikely. With regard to in vitro-produced embryos, use of semen infected with any of the four viruses, with the probable exception of EBLV, will often lead to contaminated embryos, and virus removal from these embryos is difficult even when the internationally approved embryo processing protocols are used. However, it has never been demonstrated that such embryos have resulted in transmission of infection to recipients or offspring.

Normal calves produced after transfer of in vitro fertilized embryos cultured with an antiviral compound

Bovine viral diarrhea virus (BVDV) replicates in embryo co-culture systems and remains associated with developing IVF bovine embryos, despite washing and trypsin treatment. Previous research demonstrated that 2-(4-[2-imidazolinyl]phenyl)-5-(4-methoxyphenyl)furan (DB606) inhibits replication of BVDV in cultured cells. The objective of this study was to evaluate the capability of IVF embryos to develop into normal, weaned calves after exposure to antiviral concentrations of DB606 during IVC. Oocytes were obtained from cows via transvaginal, ultrasound-guided follicular aspiration. Presumptive zygotes (n = 849) that resulted from fertilization of these oocytes were cultured for 7 d in medium supplemented with 0.4 microM DB606 or medium lacking antiviral agent. All blastocysts (n = 110) were transferred individually into the uterus of a synchronized recipient. The pregnancy status of recipients was determined using transrectal ultrasonography at 21-23 d after embryo transfer. Additional pregnancies as controls (n = 21) were initiated by natural breeding. Developing fetuses and resulting calves were evaluated every 27-34 d. Blastocyst development, pregnancies per transferred embryo, pregnancies maintained per pregnancies established, gestation length, gender ratio, birth weights, viability of neonates, complete blood counts, and serum chemistry profiles at 3 mo of age and adjusted 205 d weaning weights were compared for research treatments. Development to weaning after exposure to DB606 did not differ significantly from controls. In conclusion, bovine embryo cultures can be safely supplemented with antiviral concentrations of DB606; addition of DB606 agent might prevent viral transmission if BVDV were inadvertently introduced into the embryo culture system.

Evaluation of virus decontamination techniques for porcine embryos produced in vitro

The objective of this study was to explore approaches to decontaminate embryos either contaminated naturally or under experimental conditions with different viruses. Embryos were obtained from in vitro maturation and fertilisation of porcine oocytes. After 7 days of development, morula and blastocyst stages were exposed for 1 h to the following viruses: encephalomyocarditis virus (EMCV), porcine circovirus type 2 (PCV2), porcine parvovirus (PPV), porcine reproductive and respiratory syndrome virus (PRRSV), and bovine viral diarrhea virus (BVDV) at an infectivity of 100 TCID50/mL. Embryos samples were treated with different washing procedures, which all included the following standard washing solutions: PBS+0.4% BSA (five times for 10 s), Hank's+0.25% trypsin (two times for 60-90 or 120-150 s, or one time of 5 min), Hank's+0.1 mg/mL DNase 1+20 U/mL RNase One (one time of 30 min) and PBS+0.4% BSA again (five times for 10s). Two new approaches were used to improve trypsin treatment, 0.1% hyaluronidase (one time for 5 min) instead of trypsin and a pre-incubation with oviductal cells. Therefore, in the first experiment, oocytes received standard maturation treatments and in the second, they were also co-incubated with oviductal cells for the last 3 h of maturation. The effectiveness of the different washing techniques in removing viruses was evaluated by polymerase chain reaction (PCR) analysis. In the first experiment, trypsin treatment did not eliminate PRRSV, PPV, PCV, and EMCV from contaminated embryos. Surprisingly, treatment with hyaluronidase eliminated all tested viruses. In the second experiment, all viruses tested were removed from the oocytes following the different enzymatic treatments. In conclusion, in vitro embryo decontamination was more effective following exposure to oviductal secretions and hyaluronidase eliminated more virions than trypsin in washing techniques.

Effects of aromatic cationic molecules on bovine viral diarrhea virus and embryonic development

Bovine viral diarrhea virus (BVDV) has been shown to replicate in embryo culture systems and remain associated with bovine embryos developing in vitro. In this study, novel antiviral agents were evaluated for capability to inhibit replication of BVDV without affecting embryonic development. Serial concentrations of 2-[5(6)-{2-imidazolinyl}-2-benzimidazolyl]-5-(4-aminophenyl)furan (DB456) or 2-(4-[2-imidazolinyl]phenyl)-5-(4-methoxyphenyl)furan (DB606) were prepared in IVC medium. Then, bovine uterine tubal epithelial cells (UTC) were placed in IVC media with varying concentrations of DB456 or DB606. Within 1h, a genotype I or II strain of BVDV was added to the cultures. Cultures were maintained for 7 days. Infectious virus was quantitated in IVC media collected on days 3 and 7 and in UTC lysates harvested on day 7. The effective antiviral concentrations of DB606 were much lower than effective antiviral concentrations of DB456. In subsequent experiments, IVF presumptive zygotes were cultured in IVC medium with or without DB456 or DB606 at multiple concentrations for 7 days to evaluate effect of the compound on conceptus development. On day 7, stage of embryonic development was observed, and blastocysts were harvested and stained using Hoechst 33342 to enumerate embryonic cells. While DB456 inhibited blastocyst development, DB606 at 20 times the effective antiviral concentration did not hinder blastocyst development or reduce the mean number of cells per blastocyst. These preliminary results indicated that bovine embryo cultures might be safely supplemented with effective concentrations of an antiviral agent.

Different strains of noncytopathic bovine viral diarrhea virus (BVDV) vary in their affinity for in vivo-derived bovine embryos

Washing procedures (without trypsin treatment) recommended by the International Embryo Transfer Society (IETS) for use on in vivo-derived embryos effectively removed a cytopathic strain (NADL) of bovine viral diarrhea virus (BVDV) after artificial exposure. However, these washing procedures have not been evaluated using other isolates of BVDV, including representative non-cytopathic strains. Thus, the objective of this study was to evaluate the efficacy of the IETS procedures following artificial exposure of in vivo-derived bovine embryos to two different strains and biotypes of BVDV. One hundred and twenty-nine zona pellucida-intact (ZP-I) morulae and blastocysts (MB) and 56 non-fertile and degenerated (NFD) ova were collected 7 days following exposure to bulls from 32, BVDV-negative, superovulated cows. After collection, all MB and NFD ova were washed according to IETS standards. Subsequently, half of the MB and NFD ova were exposed for 1h to approximately 10(6)-cell culture infective doses (50% endpoint) per milliliter of viral strain SD-1, and the other half were exposed to the same concentration of CD-87. After exposure, groups of > or =3 and < or = 10 MB or NFD ova were washed using methods that met or exceeded IETS standards. Then, the washed groups were sonicated, and sonicate fluids were assayed for presence of virus using virus isolation and a reverse transcription nested polymerase chain reaction. No virus was detected in any group of MB or NFD ova that had been exposed to the CD-87 isolate. However, virus was detected in association with 50% of the groups of MB and 33% of the groups of NFD ova that had been exposed to the SD-1 isolate. Therefore, standard embryo-washing procedures recommended by the IETS are more effective for removal of some isolates of BVDV than for others. It remains to be determined if the quantity of a high-affinity isolate of BVDV associated with individual washed embryos would infect recipients via the intrauterine route. Further, it should be determined if an alternative embryo processing procedure, washing and trypsin treatment, would be more effective for removal of high-affinity isolates.

Bovine viral diarrhea virus in embryo and semen production systems

Although BVDV-free offspring have been produced from persistently infected bulls and heifers via advanced reproductive techniques, embryos and semen can potentially transmit the virus. Due to this potential for transmission, appropriate testing is necessary to ensure freedom of semen and embryos from BVDV. In the future, less constraining quality control measures may ensure freedom of embryos and semen from BVDV. These quality control measures require additional research to be validated.

Biosecurity issues associated with current and emerging embryo technologies

A variety of procedures associated with in vivo and in vitro embryo production, as well as cloning and transgenics, are in current use by both researchers and practitioners. Biohazards associated with these procedures could influence clinical proficiency and the outcome of basic research or result in unusual distribution of pathogens in populations of animals. By their nature, embryo technologies are vulnerable to contamination from numerous sources. Although pathogens can originate in the physical environments in which embryo technologies are applied, they are more likely to be introduced via animals or materials of animal origin. However, it is important to note that both the occurrence and consequences of contamination are heavily influenced by environmental circumstances. This paper represents a philosophical description of biohazards associated with three generations of embryo technologies using the cow as a model species. Emphasis is placed on sources of contamination, current or suggested preventive actions and the issue of environmental changes as they relate to the emergence of biohazards and the implementation of biosecurity measures. Some specific pathogens are discussed for illustration. In addition, details of the risks associated with introducing bovine viral diarrhoea virus in each of three generations of embryo technologies are described.

Bovine viral diarrhea virus (BVDV) and anti-BVDV antibodies in pooled samples of follicular fluid

Bovine viral diarrhea virus (BVDV) can be found in cells and fluids from ovaries collected at the abattoir. On the other hand, immunoglobulins are also found in the fluid of ovarian follicles. Anti-BVDV antibodies in follicular fluid might reduce cross-contamination of COCs at the time of collection or hinder the use of virus isolation to test for the presence of virus. One objective of this study was to determine the frequency with which BVDV could be found in pooled follicular fluid collected during the periodic aspiration of COCs from abattoir-origin ovaries. A second objective was to determine the prevalence and neutralizing activity of anti-BVDV antibodies in these blended samples. We collected samples of pooled follicular fluid (n = 55) over a 20-month period as part of our routine oocyte collection activities. We assayed each sample for BVDV using virus isolation as well as reverse transcription nested polymerase chain reaction (RT-nPCR) procedures. We also tested follicular fluid for antibody that would neutralize four representative strains of BVDV (SD-1, a genotype 1a strain; NY-1, a genotype lb strain; CD-87, a genotype 2 strain, and PA-131, a divergent genotype 2 strain). We detected no BVDV by virus isolation, but we did identify the virus by RT-nPCR in one of the 55 samples of follicular fluid. Automated dye terminator nucleotide sequencing of the amplified portion of the viral genome indicated a genotype 1 strain that was distinct from any of our laboratory strains. In addition, each of the samples of follicular fluid contained sufficient antibody to neutralize large quantities of each of the four laboratory strains that were used. Finding BVDV in just 1 of 55 samples was consistent with reports of similar studies in which the occurrence of BVDV in abattoir-origin materials ranged from 0.9 to 12%. We presumed that failure to isolate the virus was due to neutralizing antibody in the sample. Thus, the incidence of BVDV contamination of our IVF system at the level of pooling of follicular fluid was low for the 20-month period. The presence of anti-BVDV antibody in pooled follicular fluid provided a coincidental means of neutralizing BVDV when it was introduced in fluid aspirated from infected ovaries.

Photosensitive chemical and laser light treatments decrease epizootic hemorrhagic disease virus associated with in vitro produced bovine embryos

Photoinactivation was employed to eliminate EHDV-2 from in vitro produced bovine embryos experimentally exposed to this virus. Immature oocytes were matured, fertilized, and cultured in chemically defined conditions. All treatments were performed on zygotes. Developmental potential of zygotes and cell numbers of resulting hatched blastocysts were assessed after exposure to a 1 mW helium neon laser (633 nm, red) for 1, 5, 10, and 15 min; the photosensitive chemicals hematoporphyrin (15 microM) and hypericin (1 and 10 microM) for 15 min; a combination of 10 microM hypericin and laser light for 1, 3, or 5 min; and a combination of 15 microM hematoporphyrin and laser light for 1, 2, or 3 min. There were no significant differences among proportions of embryos developing or cell numbers after treatment with or without exposure to laser light alone for up to 10 min. No differences were observed after exposure of zygotes to photosensitive chemicals alone. Exposure to 10 microM hypericin and 5 min of laser light or 15 microM hematoporphyrin and 2 min of laser light compromised zygote developmental potential. After exposure to 10(6) TCID50/mL EHDV-2 for 90 min groups of 10 zygotes were exposed to 10 microM hypericin or 15 microM hematoporphyrin and laser light to inactivate the virus. Hematoporphyrin was effective with 3 min light exposure at reducing the percentage of EHDV-2 contaminated zygote pools (16.7%) as compared to EHDV-2 exposed pools without treatment (88.9%) but hematoporphyrin + 1 min light was ineffective. Hypericin + 3 min light provided an intermediate effect (55.6%).

A strategy for rapid cooling of mouse embryos within a double straw to eliminate the risk of contamination during storage in liquid nitrogen

Double packaging, in which an inner straw containing the specimen is inserted into an outer, larger straw (here termed 'straw-in-straw') to prevent the inner straw from coming into direct contact with liquid nitrogen provides a simple strategy for reducing or eliminating the potential contamination risk associated with storage in liquid nitrogen. This approach has in the past been used in conjunction with cryopreservation by slow cooling, but has not previously been tested for use throughout an entire rapid cooling and warming procedure. This study determined whether keeping the straw containing the embryos inside a second protecting container throughout the cryopreservation and storage protocol would compromise embryo viability. We established that a cryoprotectant containing a high polymer concentration (35% dextran or Ficoll) together with 25% ethylene glycol (as the penetrating cryoprotectant) was highly effective for day 2 and day 3 mouse embryos in both single and double straws. The survival and development of all cryopreserved embryos, as assessed both in vitro and in vivo, was not statistically different to their untreated controls. This established that a protein/serum-free cryoprotectant solution supplemented with polymers could provide complete protection of mouse embryos. It also shows, for the first time, that embryos can be cooled by direct immersion in liquid nitrogen and warmed by direct immersion into a waterbath within a double straw arrangement to reduce the likelihood of contamination.

Replication and persistence of different strains of bovine viral diarrhea virus in an in vitro embryo production system

Recent studies have shown that exposed, in vitro-derived embryos remain contaminated with bovine viral diarrhea virus (BVDV) after washing. However, introduction of a Genotype II versus Genotype I strain of BVDV into an IVF system was reported to provide greater potential for transmission of disease. The primary objective of this study was to compare the potentials for different strains of noncytopathic BVDV to replicate in an IVF system, associate with IVF embryos and infect co-cultured cells via association with washed embryos. The secondary objective was to compare the effect of different strains of BVDV on embryonic development. Two Genotype I (SD-1 and NY-1) and 2 Genotype II (CD-87 and PA-131) strains of BVDV were evaluated. After IVM and IVF of oocytes, presumptive zygotes were washed and transferred into in vitro cultures containing uterine tubal cells (UTC) and medium that was free of BVDV-neutralizing activity. Immediately before addition of zygotes, the cultures were inoculated with 10(5) cell culture infective doses (50%, CCID50) of a strain of BVDV or maintained as a negative control. Cultures of zygotes were then incubated for 7 d. Embryonic development was observed on Days 3 and 7, and attempts were made to isolate BVDV from UTC and medium on Day 7. Also on Day 7, groups of intact, washed blastocysts were either transferred into virus-free secondary cultures containing UTC or sonicated with sonicate fluid assayed by both virus isolation and single-closed-tube reverse transcription nested polymerase chain reaction (RT-nPCR). After 3 d in secondary culture, hatched embryos were enumerated, and medium from the cultures, washed UTC and embryos were tested for BVDV by virus isolation. In addition, washed UTC and embryos were tested for BVDV using RT-nPCR. All strains of BVDV persisted and replicated in the embryo culture environment, but cleavage beyond the 4-cell stage, blastocyst development and hatching varied among cultures contaminated with different strains of virus. Further, the quantity of BVDV associated with washed embryos from both initial and secondary cultures varied among strains, but the variation was unrelated to difference in genotype (SD-1 and PA-131 greater than NY-1 and CD-87). Although all strains of BVDV replicated in UTC in the initial in vitro cultures and remained associated with washed blastocysts, susceptible UTC in the secondary in vitro cultures were seldom infected by any strain of virus.

Epidemiologic concerns relative to in vivo and in vitro production of livestock embryos

Evidence indicates low potential for transmission of pathogens with in vivo-derived embryos of cattle when appropriate precautions are taken. In apparent contrast, results of research with in vivo-derived embryos of small ruminants and swine and with in vitro-derived embryos of cattle suggest a greater tendency for their association with pathogens after artificial exposure. However, regardless of donor species, investigations involving collection of embryos from artificially or naturally infected animals and assessment of health of recipients and offspring after transfer of these embryos have indicated low potential for transmitting disease. In this paper, results of embryo-pathogen research are summarized, emphasizing potential for spread of pathogens under natural circumstances. Also, safe embryo handling practices and their application to multiple species are discussed.

Viral contamination of embryos cryopreserved in liquid nitrogen

Despite the worldwide application of embryo-freezing technology as the means of preserving germplasm of mammalian species, there is no information available on the possible transmission of infectious agents to cryopreserved embryos via contaminated liquid nitrogen (LN). Recently, it has been reported that new methods of cryopreservation which employ ultrarapid freezing or vitrification require direct contact between the freezing medium containing oocytes or embryos and liquid phase nitrogen (LPN). As models for human and animal viral pathogens three bovine viruses, bovine viral diarrhea virus (BVDV), bovine herpesvirus-1 (BHV), and bovine immunodeficiency virus (BIV), were employed to study the potential for their transmission by experimentally contaminated LN to embryos frozen and stored in open freezing containers. Bovine embryos in a mixture of 20% ethylene glycol, 20% ME(2)SO, and 0.6% sucrose were vitrified in either unsealed standard 0.25 ml or modified open pulled straws or in plastic cryovials and then plunged into contaminated LPN. After 3-5 weeks of storage in LN, embryos were thawed and sequentially washed and only those with intact ZP were pooled together and tested in batches of three for viral contamination. From this pool of 83 batches, 13 of 61 (21.3%) batches exposed to BVDV and BHV-1 tested positive for viral association while all 22 batches exposed to BIV in unsealed containers tested negative. All control embryos vitrified in sealed cryovials and straws were free from viral contamination.

Quality controls for bovine viral diarrhea virus-free IVF embryos

Introduction of bovine viral diarrhea virus (BVDV) with cumulus-oocyte-complexes (COCs) from the abattoir is a concern in the production of bovine embryos in vitro. Further, International Embryo Transfer Society (IETS) guidelines for washing and trypsin treatment of in-vivo-derived bovine embryos ensure freedom from a variety of pathogens, but these procedures appear to be less effective when applied to IVF embryos. In this study, COCs were exposed to virus prior to IVM, IVF and IVC. Then, virus isolations from cumulus cells and washed or trypsin-treated nonfertile and degenerated ova were evaluated as quality controls for IVF embryo production. The effect of BVDV on rates of cleavage and development was also examined. All media were analyzed prior to the study for anti-BVDV antibody. Two approximately equal groups of COCs from abattoir-origin ovaries were washed and incubated for 1 h in minimum essential medium (MEM) with 10% equine serum. One group was incubated in 10(7) cell culture infective doses (50% endpoint) of BVDV for 1 h, while the other was incubated without virus. Subsequently, the groups were processed separately with cumulus cells, which were present throughout IVM, IVF and IVC. Cleavage was evaluated at 4 d and development to morulae and blastocysts at 7 d of IVC. After IVC, groups of nonfertile and degenerated ova or morulae and blastocysts were washed or trypsin-treated, sonicated and assayed for virus. Cumulus cells collected at 4 and 7 d were also assayed for virus. Anti-BVDV antibody was found in serum used in IVM and IVC but not in other media. A total of 1,656 unexposed COCs was used to produce 1,284 cleaved embryos (78%), 960 embryos > or = 5 cells (58%), and 194 morulae and blastocysts (12%). A total of 1,820 virus-exposed COCs was used to produce 1,350 cleaved embryos (74%), 987 embryos > or = 5 cells (54%), and 161 morulae and blastocysts (9%). Rates of cleavage (P = 0.021), cleavage to > or = 5 cells (P = 0.026) and development to morula and blastocyst (P = 0.005) were lower in the virus-exposed group (Chi-square test for heterogeneity). No virus was isolated from any samples from the unexposed group. For the exposed group, virus was always isolated from 4- and 7-d cumulus cells, from all washed nonfertile and degenerated ova (n = 40) and morulae and blastocysts (n = 57) and from all trypsin-treated nonfertile and degenerated ova (n = 80) and morulae and blastocysts (n = 91). Thus, virus persisted in the system despite the presence of neutralizing antibody in IVM and IVC media, and both washing and trypsin treatment were ineffective for removal of the virus. Presence of virus in 4- and 7-d cumulus cells as well as in nonfertile and degenerated ova were good indicators of virus being associated with morulae and blastocysts.

Infectious agents in bovine embryo production: hazards and solutions

Infectious agents in systems for producing bovine embryos might reduce the number and quality of embryos generated, result in transmission of disease to recipients and offspring, or confound findings of research. Embryo-associated pathogens might also jeopardize human health when the goal of embryo production is creating transgenic animals intended to be a source of pharmaceuticals or organs. This paper addresses risks and resulting hazards of pathogen and microbial contaminant introduction into in vivo or in vitro embryo production systems. Additionally, methods for prevention and quality control are discussed.

Effect of bovine herpesvirus-1 or bovine viral diarrhea virus on development of in vitro-produced bovine embryos

In previous experiments, zona pellucida (ZP)-intact in vitro-produced (IVP) embryos incubated for 1 hr with 10(6.3) TCID(50)/ml bovine herpes virus-1 (BHV-1), 10(5.3) TCID(50)/ml cytopathic (CP) bovine viral diarrhea virus (BVDV) or 10(5.3) TCID(50)/ml noncytopathic (NCP) BVDV showed no signs of virus replication or embryonic degeneration. The aims of the present study were to investigate whether a prolonged presence (24 hr or 8 days) of 10(6.3) TCID(50)/ml BHV-1 or 10(5.3) TCID(50)/ml BVDV in an in vitro embryo production system affected the rate of cleavage and embryonic development of ZP-intact embryos, and to point out eventual causes of adverse effects. When virus was present in each step of an IVP system, significantly lower rates of cleavage and blastocyst formation of virus-exposed embryos were observed, in comparison with control embryos (P < 0.01). When embryos were only exposed to virus during the in vitro fertilization (IVF), the rates of cleavage and blastocyst formation were significantly affected. The introduction of BHV-1 or BVDV during in vitro maturation (IVM) or in vitro culture (IVC) resulted only in significantly lower rates of blastocyst (P < 0.01). In all experiments, virus replication was not detected in the embryonic cells. On the other hand, virus replication was clearly demonstrated in oviductal cells in the co-culture system, resulting in a degeneration of these cells. In an additional experiment, synthetic oviduct fluid (SOF) without somatic cells was used as an alternative culture system. Even when SOF-embryos were exposed to 10(6.3) TCID(50)/ml BHV-1 or 10(5.3) TCID(50)/ml CP, and NCP BVDV, the rates of blastocyst formation of the BHV-1-, CP-, and NCP BVDV-exposed embryos were not different from the unexposed control embryos, 23%, 24%, and 24%, respectively, vs. 27%. Taken together, it can be concluded that the virus-induced adverse effects on embryonic development in conventional co-cultures were due to changes in the embryonic environment caused by infection of oviductal cells.

Quantity and infectivity of embryo-associated bovine viral diarrhea virus and antiviral influence of a blastocyst impede in vitro infection of uterine tubal cells

In previous studies, bovine viral diarrhea virus (BVDV) remained associated with IVF embryos after viral exposure and washing. However, uterine tubal cells (UTC) were not infected when exposed embryos were washed and individually co-cultured with them. The objective of this study was to evaluate quantity and infectivity of embryo-associated virus and antiviral influence of a blastocyst as possible explanations for failure to infect the UTC in vitro. Morulae and blastocysts were produced in vitro and washed. A portion of the embryos were incubated for 2 h in medium containing 10(6) to 10(8) cell culture infective doses (50%, CCID50) of a genotype I, noncytopathic BVDV per milliliter and then washed again. Virus isolation was attempted on sonicated negative (virus unexposed) and positive (virus exposed) control embryo groups after washing. The influence of quantity and infectivity of embryo-associated virus was evaluated by transferring exposed, washed embryo groups (2, 5, and 10 embryos/group) or sonicate fluid of exposed, washed, sonicated embryo groups (2, 5, and 10 embryos/group) to cultures containing bovine UTC in IVC medium that was free of BVDV neutralizing activity. The antiviral influence of an embryo was evaluated by adding 1 to 10(5) CCID50 of BVDV to UTC in the presence or absence of a single unexposed blastocyst in IVC medium. After 2 d in co-culture, the UTC, IVC medium and washed embryos (when present) were tested separately for the presence of BVDV using virus isolation. Virus was isolated from sonicate fluids of all positive but no negative controls. Virus was not isolated from any UTC following 2 d of culture with virally exposed groups of intact embryos. However, virus was isolated from UTC cultured with sonicate fluids from some groups of 5 (60%) and 10 (40%) embryos. Infective virus also remained associated with some groups of 2 (20%), 5 (40%) and 10 (60%) intact embryos after 48 h of post-exposure culture. Finally, primary cultures of UTC were more susceptible to infection with BVDV in the absence of a blastocyst (P = 0.01). Results indicate that insufficient quantity and reduced infectivity of embryo-associated virus as well as an antiviral influence of intact IVF blastocysts may all contribute to failure of embryo-associated virus to infect UTC in vitro.

Uterine tubal cells remain uninfected after culture with in vitro-produced embryos exposed to bovine viral diarrhea virus

Bovine viral diarrhea virus (BVDV) has been isolated from washed and sonicated, in vitro-produced embryos, but the infectivity of BVDV associated with intact, developing, embryos has not been demonstrated. The objective of this study was to determine if a dose of BVDV infective for co-culture cells was associated with individual, developing embryos, following artificial exposure to the virus and washing. In 5 replicates, zona pellucida-intact, in vitro-produced embryos were assigned to a negative control embryo group, or were incubated in 10(5)-10(6) cell culture infective doses (50%, CCID50) per milliliter of a type I, noncytopathic (strain SD-1) BVDV for 2 h. Unexposed negative control embryos and exposed positive control embryos were washed, sonicated and assayed for BVDV using virus isolation with immunoperoxidase monolayer assay. Immediately or following cryopreservation, remaining virally-exposed, washed embryos were co-cultured individually with BVDV-negative cultures of bovine uterine tubal cells in a medium free of BVDV-neutralizing activity. After two days in culture, uterine tubal cells and embryos (including the zona pellucida) were separated and washed. The culture medium, uterine tubal cells and embryos were then assayed for BVDV. Bovine viral diarrhea virus was not isolated from any negative control embryo group, but was isolated from all positive control embryo groups. Although all uterine tubal cell populations were confirmed to be susceptible to BVDV, virus was never isolated from uterine tubal cells or embryos from post-exposure culture. In conclusion, although BVDV remains associated with washed in vitro-produced embryos, the virus associated with unsonicated embryos was not infective for uterine tubal cells in vitro.

The effect of high concentrations of cryoprotectants on the passage of bovine viral diarrhea virus through the zona pellucida of in vitro fertilized embryos

The effect of high concentrations of cryoprotectants on the passage of bovine viral diarrhea virus (BVDV) through the zona pellucida (ZP) of intact bovine embryos during the pre-freezing step of cryopreservation was investigated in a series of experiments. In vitro fertilized (IVF) embryos at the blastocyst stage were exposed to 10(6) TCID50 BVDV (non-cytopathic NY-1 strain) in a 30% suspension of either ethylene glycol, glycerol, DMSO, or 2 M sucrose in physiological saline for 10 min at 20 degrees C. Subsequently, the embryos were washed free of residual unbound viral particles, and the ZP of some embryos were removed by micromanipulation. Groups of ZP-intact embryos, ZP-free embryonic cells and their respective ZP were then tested separately for the presence of virus. The infectious virus was detected in association with 81% (17/21) of samples containing non-micromanipulated ZP-intact embryos which were exposed to the virus and cryoprotectants and then washed 10 times and in 83% (43/53) of the samples containing only ZP from micromanipulated embryos (P > 0.05). The virus was not found in the samples containing the corresponding embryonic cells of embryos exposed previously to the virus and cryoprotectants. It was concluded that the transfer of embryos from the isotonic PBS solution into a highly hypertonic cryoprotectant solution did not cause the passage of BVDV through ZP and its entry to embryonic cells.

Principles for eradication of bovine viral diarrhoea virus (BVDV) infections in cattle populations

Systematic eradication of BVDV without vaccination started in Scandinavia in 1993. In principle, the schemes include; (1) identification of non-infected and infected herds using different combinations of serological herd tests such as bulk milk tests and spot tests (sample of animals in a certain age), (2) monitoring/certification of non-infected herds by repeated sampling, applying one of the above-mentioned methods and (3) virus clearance in infected herds aimed at removing persistently infected (PI) animals in a cost- and time-efficient manner. In the virus clearance protocol described, an initial test is performed on all animals with subsequent follow-up of calves born as well as of dams seronegative in the initial test. It is generally recommended to perform an initial antibody test on all samples. This should be done not only to screen for seronegative animals on which virus isolation should be attempted (i.e. possible PI animals), but more in order to identify non-immune animals in reproductive age, that is, the key animals in herd-level persistence of infection. In Sweden, a common finding has been self-clearance, where the infection ceases without any other intervention than controlled introduction of new animals. Other epidemiological observations concern the course of events following virus introduction. Important risk factors for spreading BVDV are discussed, where livestock trade is perceived as the most central to control. Live vaccines, imported semen and embryos constitute special hazards, since they may act as vehicles for the introduction of new BVDV strains. The importance of making farmers aware of herd biosecurity and their own responsibility for it is stressed, and in order to maintain a favourable situation after a scheme has been concluded, effort must be put into establishing such a persisting attitude in the farming community.

Epidemiological features and economical importance of bovine virus diarrhoea virus (BVDV) infections

Infections with bovine virus diarrhoea virus (BVDV) are widespread throughout the world. Although the prevalence of infection varies among surveys, the infection tends to be endemic in many populations, reaching a maximum level of 1-2% of the cattle being persistently infected (PI) and 60-85% of the cattle being antibody positive. Persistently infected cattle are the main source for transmission of the virus. However, acutely infected cattle as well as other ruminants, either acutely or persistently infected, may transmit the virus. Transmission is most efficient by direct contact. However, as infections have been observed in closed, non-pasturing herds, other transmission routes seem likely to have some practical importance. Differences in BVDV prevalence among regions or introduction of virus in herds previously free of BVDV are often associated with particular epidemiological determinants such as cattle population density, animal trade and pasturing practices. However, on a few occasions there have been no obvious explanations for infection of individual herds. Estimates of economic losses due to BVDV infection vary depending on the immune status of the population and the pathogenicity of the infecting virus strains. Introduction of the infection into a totally susceptible population invariably causes extensive losses until a state of equilibrium is reached. Infection with highly virulent BVDV strains causing severe clinical signs and death after acute infection gives rise to substantial economical losses. At an estimated annual incidence of acute infections of 34%, the total annual losses were estimated as US$ 20 million per million calvings when modeling the losses due to a low-virulent BVDV strain. At the same incidence of infection, the losses due to a high-virulent BVDV strain were estimated as US$ 57 million per million calvings. Low-virulent BVDV infections caused maximum losses at an incidence of 45%, whereas high-virulent BVDV infections caused maximum losses at an incidence of 65%. Thus, cost-benefit analyses of control programs are highly dependent on the risks of new infections under different circumstances and on the strains of the virus involved.

Washing and trypsin treatment of in vitro derived bovine embryos exposed to bovine viral diarrhea virus

Gametes, somatic cells and materials of animal origin in media are potential sources for introducing bovine viral diarrhea virus (BVDV) into systems for production of IVF bovine embryos. Further, the efficacy of washing and trypsin treatment for removal of BVDV from IVF embryos is questionable. Washing and trypsin treatments recommended by the International Embryo Transfer Society for in vivo-derived embryos were applied to in vitro-derived, virus-exposed, bovine embryos in this side-by-side comparison of treatments. Embryos for the study were produced in a virus-free system in which follicular oocytes were matured and fertilized in vitro and presumptive zygotes were co-cultured with bovine uterine tubal cells for 7 d. A total of 18 trials was performed, 9 using a noncytopathic BVDV and 9 using a cytopathic BVDV. In each trial, 4 equal groups of 10 or less, zona pellucida-intact embryos/ova were assembled, including 2 groups of morulae and blastocysts (M/B) and 2 groups of nonfertile or degenerated ova (NFD). Each group was prewashed and exposed to 10(4) to 10(6) TCID50/mL of either noncytopathic (SD-1) or cytopathic (NADL) BVDV for 2 h. Following in vitro viral exposure, one group of M/B and one group of NFD were washed. The other groups of M/B and NFD were trypsin-treated. Both treatments were consistent with IETS guidelines. After in vitro exposure to noncytopathic BVDV and washing, viral assays of 100% (9/9) and 78% (7/9) of the groups of M/B and NFD ova, respectively, were positive. After in vitro exposure to cytopathic BVDV and washing, viral assay of 33% (3/9) of the groups of both M/B and NFD ova were positive. After in vitro exposure to noncytopathic BVDV and trypsin treatment, viral assay of 44% (4/9) of groups of M/B and 67% (6/9) of groups of NFD ova were positive. Finally, after in vitro exposure to cytopathic BVDV and trypsin treatment, viral assay of 22% (2/9) of the groups of M/B and 44% (4/9) of the groups of NFD ova were positive. Contingency table analysis, in which data was stratified by embryo type and virus biotype, was used to compare results. While a difference existed between results of the 2 treatments of groups of M/B within the noncytopathic biotype (P = 0.01, Mantel Haenszel Chi-square), no difference was observed between comparison of treatment between all groups in both biotypes (P > 0.05).

Noncytopathogenic bovine viral diarrhea virus (BVDV) reduces cleavage but increases blastocyst yield of in vitro produced embryos

The growing application of in vitro embryo production systems that utilize slaughterhouse tissues of animals of unknown health status conveys the risk of disease transmission. One pathogen of concern in this regard is bovine viral diarrhea virus (BVDV), and the objective of this study was to investigate the effect of BVDV on in vitro embryonic development. A bovine in vitro embryo production system was experimentally infected with BVDV at 2 stages: prior to in vitro maturation by incubating cumulus-oocyte complexes (COC) with virus (strain Pe515; titer 10(6.2) tissue culture infective dose (TCID)50/mL) or vehicle for 2 h, and then during in vitro culture by the use of BVDV infected granulosa cells. Exposure to BVDV throughout in vitro production reduced cleavage rates (P = 0.01) but increased (P = 0.05) the number of embryos that reached the 8-cell stage when expressed as a percentage of cleaved oocytes. Blastocyst yield was increased by the presence of virus when expressed as a proportion of oocytes (P = 0.0034) or of those cleaved (P < 0.0001). The percentage of total blastocyst yield on Days 7, 8 and 9 for the control and virus treatments was 20, 51, 29 and 29, 41, and 29%, respectively, indicating that the rate of blastocyst development was nonsignificantly faster in the virus-treated group (P = 0.06). These results indicate that the presence of non-cytopathogenic BVDV in an in vitro production system may reduce cleavage rates but allow those cleaved to develop to blastocysts at a higher rate.

Immunohistochemical evidence for the localization of bovine viral diarrhea virus, a single-stranded RNA virus, in ovarian oocytes in the cow

Bovine viral diarrhea virus (BVDV) is a single-stranded RNA virus responsible for enteric disease and reproductive failure in cattle. The virus can pass vertically from cow to fetus, causing abortion, birth of malformed calves, and calves born with persistent and life-long infections. In this study, we investigated the tropism of BVDV in ovarian tissue from persistently infected animals. Three heifers persistently infected with BVDV were euthanatized and their ovaries were recovered. A specimen of each ovary was taken (n = 6) for virus isolation, and the remaining ovarian tissue was stored at -70 C. Cryosections (6 microm) cut from each ovary were analyzed for the presence of BVDV antigens by indirect immunofluorescence. The immunofluorescent analysis employed two monoclonal antibodies, WB103 and WB162, previously raised against the nonstructural protein NS3 and the envelop glycoprotein E2, respectively. High titers (6.97 +/- 0.17 log10 tissue culture infective dose50/ml) of BVDV were recovered from 6/6 ovarian samples; NS3 and E2 were widely distributed within the ovarian stroma, the cumulus cell population, and the oocytes maturing in primordial, primary, and secondary follicles. Overall, 362/1,939 (18.7%) of the oocytes contained BVDV antigens, and there was no significant (P > 0.05) difference in the proportion of BVDV-infected oocytes recorded within the primordial (227/1,247, 18.2%), primary (122/630, 19.4%), and secondary (13/62, 21.0%) follicle populations. Although the developmental potential of the infected oocytes could not be established in the present study, we conclude that bovine oocyte and the cumulus cells are susceptible to BVDV infection.

Association of bovine embryos produced by in vitro fertilization with a noncytopathic strain of bovine viral diarrhea virus type II

In the first experiment, heifers were infected experimentally with bovine viral diarrhea virus type II (BVDV-type II, strain CD87; characterized by high morbidity and mortality). Subsequently, in vitro fertilized embryos were produced from oocytes collected on Day 4, 8, and 16 post infection. In a total of 29 heifers, the infectious virus was detected in 55% of the samples of the follicular fluid, in 10% of the oviductal cells, in 10% of the uterine flushes and in 41% of the in vitro fertilized embryos. The highest number of embryos associated with the virus was detected in the group of animals slaughtered on Day 8 post infection (58%). The amount of the virus (10(1.5-2.0) TCID50/mL) associated with the washed single embryos generated from oocytes of heifers 8 and 16 d post infection was sufficient for disease transmission by intravenous inoculation to the seronegative recipients (6/15). In the second experiment, uninfected oocytes were exposed in vitro to BVDV (10(5) TCID50/mL) in the maturation medium and then fertilized and cultured prior to viral assay. Virus was detected in 4 of 7 samples containing embryos but not in samples of embryos produced from the control group of uninfected oocytes. The presence of BVDV in the IVF system did not affect embryonic development in vitro. In conclusion, it appears that BVDV-type II has the ability to be transferred with oocytes through the IVF system, resulting in infectious embryos with normal morphological appearance which may have a potential for disease transmission.

Persistent bovine pestivirus infection localized in the testes of an immuno-competent, non-viraemic bull

A post-pubertal bull on an artificial insemination station was found to be persistently shedding bovine viral diarrhoea virus (BVDV) in semen over a period of eleven months, while demonstrating no viraemia. Circulating antibodies to BVDV were consistently high, suggesting that the immune system was challenged repeatedly. Post-mortem findings confirmed that the virus was sequestered in the testes of the bull. It is hypothesized that the BVDV in this immuno-competent bull was protected from the bull's immune response by the blood-testes barrier. The barrier becomes functional only at puberty when tight junctions form between adjacent Sertoli cells, suggesting that this bull became persistently infected with BVDV during puberty.