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

Potential applications for antiviral therapy and prophylaxis in bovine medicine

Viral disease is one of the major causes of financial loss and animal suffering in today's cattle industry. Increases in global commerce and average herd size, urbanization, vertical integration within the industry and alterations in global climate patterns have allowed the spread of pathogenic viruses, or the introduction of new viral species, into regions previously free of such pathogens, creating the potential for widespread morbidity and mortality in naïve cattle populations. Despite this, no antiviral products are currently commercially licensed for use in bovine medicine, although significant progress has been made in the development of antivirals for use against bovine viral diarrhea virus (BVDV), foot and mouth disease virus (FMDV) and bovine herpesvirus (BHV). BVDV is extensively studied as a model virus for human antiviral studies. Consequently, many compounds with efficacy have been identified and a few have been successfully used to prevent infection in vivo although commercial development is still lacking. FMDV is also the subject of extensive antiviral testing due to the importance of outbreak containment for maintenance of export markets. Thirdly, BHV presents an attractive target for antiviral development due to its worldwide presence. Antiviral studies for other bovine viral pathogens are largely limited to preliminary studies. This review summarizes the current state of knowledge of antiviral compounds against several key bovine pathogens and the potential for commercial antiviral applications in the prevention and control of several selected bovine diseases.

Antiviral treatment of calves persistently infected with bovine viral diarrhoea virus

BACKGROUND

Animals persistently infected (PI) with bovine viral diarrhoea virus (BVDV) are a key source of viral propagation within and among herds. Currently, no specific therapy exists to treat PI animals. The purpose of this research was to initiate evaluation of the pharmacokinetic and safety data of a novel antiviral agent in BVDV-free calves and to assess the antiviral efficacy of the same agent in PI calves.

METHODS

One BVDV-free calf was treated with 2-(2-benzimidazolyl)-5-[4-(2-imidazolino)phenyl]furan dihydrochloride (DB772) once at a dose of 1.6 mg/kg intravenously and one BVDV-free calf was treated three times a day for 6 days at 9.5 mg/kg intravenously. Subsequently, four PI calves were treated intravenously with 12 mg/kg DB772 three times a day for 6 days and two PI control calves were treated with an equivalent volume of diluent only.

RESULTS

Prior to antiviral treatment, the virus isolated from each calf was susceptible to DB772 in vitro. The antiviral treatment effectively inhibited virus for 14 days in one calf and at least 3 days in three calves. Subsequent virus isolated from the three calves was resistant to DB772 in vitro. No adverse effects of DB772 administration were detected.

CONCLUSIONS

Results demonstrate that DB772 administration is safe and exhibits antiviral properties in PI calves while facilitating the rapid development of viral resistance to this novel therapeutic agent.

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.

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.

Risk assessment of transmission of bovine viral diarrhea virus (BVDV) in abattoir-derived in vitro produced embryos

Bovine virus diarrhea virus (BVDV) is a pathogen of the bovine reproductive system causing reduced conception rates, abortions and persistently infected calves. Most if not all strains of BVDV are transmissible by natural mating and AI. For international trade, it is recommended that in vitro fertilized embryos be washed according to the IETS Manual. However, BVDV may not be entirely washed out, resulting in possible transmission risks to recipients. Donor cows, donor bulls and biological agents are all possible sources of contamination. The process for producing in vitro produced (IVP) embryos is complex and non-standard, and some procedures can contribute to spread of BVDV to uninfected embryos. The structure of the zone pellucida (ZP) of IVP embryos permits adherence of BVDV to the ZP. To estimate the risk of producing infected recipients and persistently infected calves from abattoir-derived IVP embryos, a quantitative risk assessment model using Microsoft Excel and Palisade @Risk was developed. Assumptions simplified some of the complexities of the IVP process. Uncertainties due to incomplete or variable data were addressed by incorporating probability distributions in the model. Model variables included: disease prevalence; the number of donor cows slaughtered for ovaries; the number of oocytes collected, selected and cultured; the BVDV status of ovaries, semen, biological compounds and its behavior in the IVP embryo process. The model used the Monte Carlo method to simulate the IVP process. When co-culture cells derived from donor cows of unknown health status were used for in vitro culture (IVC), the probability of a recipient cow at risk of infection to BVDV per oocyte selected for IVP processing averaged 0.0006. However, when co-culture free from BVDV was used, the probability was 1.2 x 10(-5). Thus, for safe international trade in bovine IVP embryos (i.e. negligible risks of transmission of BVDV), co-culture cells, if used during IVC for producing IVP embryos, should be disease-free.

Sanitary control in bovine embryo transfer How far should we go? A review

Embryo transfer is a globally executed technique which, when properly done, has both economic and sanitary advantages. International guidelines are available to prevent infection of the embryo with pathogens, both originating from the donor animals as from the environment. This manuscript describes the bacteria, viruses, protozoa, fungi and prions that are of major concern in the context of embryo transfer in cattle. In addition, the actual scientific knowledge on these pathogens is evaluated in terms of the current international and national guidelines and legislation.

Biosecurity and the various types of embryos transferred

The aim of the present paper was to review some features related to the risk analysis of three types of embryos to be transferred, namely the in vivo derived, the in vitro produced and the cloned ones. For in vivo-collected embryos, a considerable number of experiments and scientific investigations have been performed and hundreds of thousands of embryos are transferred annually with no contamination of associated diseases. Provided that the code of practice such as that published by the International Embryo Transfer Society is strictly followed by the embryo transfer practitioners, the statement made some 17 years ago saying that the in vivo-derived embryo transfer was the safest way of exchanging genes remains entirely true, thanks to the professionalism of the embryo transfer industry. For the in vitro-produced embryos, some particular rules have to be followed because of specific risks for some pathogens to strongly adhere to the zona pellucida of such embryos. There are some means to monitor and control those effects, and the transfer of in vitro-produced embryos can also be a very safe way to exchange genes around the world. The third type of embryos, the cloned ones, is a quite different category and the risk analysis to be soundly made still needs a lot of investigations so as to characterize the potential risks if there are, in terms not only of disease transmission but also in terms of public health, zoonotic risks as well as those related to quality and safety of food. The problem in this regard, is more directly addressed for offspring of clones than to the cloned embryos themselves. Published data on this issue are increasing in numbers so that progress in that area is expected in the few years to come.

Synthesis and Anti-BVDV Activity of Acridones As New Potential Antiviral Agents

In this study we report the design, synthesis, and activity against bovine viral diarrhea virus (BVDV) of a novel series of acridone derivatives. BVDV is responsible for major losses in cattle. The virus is also considered to be a valuable surrogate for the hepatitis C virus (HCV) in antiviral drug studies. Some of the synthesized acridones elicited selective anti-BVDV activity with EC(50) values ranging from 0.4 to 4 microg/mL and were not cytotoxic at concentrations that were 25- to 200-fold higher (CC(50) >100 microg/mL). It was proven that the most potent acridone derivative 10 was able to not only protect cells from virus-induced cytopathic effect but also reduce the production of infectious virus and extracellular viral RNA. Furthermore, compound 10, as well as a number of other analogues, inhibited HCV replication to some extent. However, there was no direct correlation between anti-BVDV and anti-HCV activity. Thus, the acridone scaffold, when appropriately functionalized, can yield compounds with selective activity against pestiviruses and related viruses such as the HCV.

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.