The role of biotechnologically engineered vaccines and diagnostics in pseudorabies (Aujeszky's disease) eradication strategies

Bartha-K61 vaccine protects nursery pigs against challenge with novel european and asian strains of suid herpesvirus 1

The present study investigates the pathogenicity of two recently isolated strains of Suid herpesvirus 1 (SuHV1), the Greek strain Hercules and the Chinese strain HeN1, in unvaccinated pigs and in pigs vaccinated with a Bartha-K61 strain. In an experiment performed in negative pressure kiosks (isolators), 45-day old seronegative pigs previously oronasally /intramuscularly vaccinated with the Bartha-K61 vaccine strain, along with unvaccinated controls, were challenged either with the Hercules strain or the HeN1 strain of SuHV1. All animals were observed daily for clinical signs and body temperature and nasal swabs, faeces, blood and bodyweight were collected up to a maximum period of 20 days post-challenge (dpc). The results showed that, in the unvaccinated pigs, HeN1 strain was more virulent than the Hercules strain, with increased mortality, shorter time to death and higher group clinical score (p < 0.05). However, after vaccination with the Bartha-K61 vaccine, there was a drastic reduction in morbidity, mortality, bodyweight loss and virus excretion to almost a similar extent in both strains (p < 0.05). No significant differences were seen among the pigs of the two vaccinated groups compared to unvaccinated unchallenged controls, except a slight elevation in body temperature and in clinical score in the HeN1 vaccinees at 2 and 3 dpc, while bodyweight gain was similar to that of the negative control pigs. Our study showed that despite differences in virulence, the standard vaccination scheme with the Bartha-K61 strain could equally protect nursery pigs against both the European and Chinese strains.

Porcine Reproductive and Respiratory Syndrome Virus Reverse Genetics and the Major Applications

Porcine reproductive and respiratory syndrome virus (PRRSV) is a positive sense, single-stranded RNA virus that is known to infect only pigs. The virus emerged in the late 1980s and became endemic in most swine producing countries, causing substantial economic losses to the swine industry. The first reverse genetics system for PRRSV was reported in 1998. Since then, several infectious cDNA clones for PRRSV have been constructed. The availability of these infectious cDNA clones has facilitated the genetic modifications of the viral genome at precise locations. Common approaches to manipulate the viral genome include site-directed mutagenesis, deletion of viral genes or gene fragments, insertion of foreign genes, and swapping genes between PRRSV strains or between PRRSV and other members of the Arteriviridae family. In this review, we describe the approaches to construct an infectious cDNA for PRRSV and the ten major applications of these infectious clones to study virus biology and virus–host interaction, and to design a new generation of vaccines with improved levels of safety and efficacy.

Aujeszky's Disease and the Development of the Marker/DIVA Vaccination Concept

Aujeszky's disease or pseudorabies is an infection of animals caused by Suid alphaherpesvirus 1, also designated as pseudorabies virus (PrV). Whereas many mammals are susceptible to PrV, only pigs are able to survive productive infection. Early reports on this disease originate from cattle and companion animals with the hallmark sign of "mad itch", meaning development of pruritus. Although first reports date back to the early 19th century, it was Aladár Aujeszky who in 1902 described this disease, which has since been named after him, as a separate entity. AD expanded in the 20th century, despite efforts to control this infection in the growing pig farming industry. Live-attenuated vaccines were developed in the early 1960s, which assisted early eradication efforts. A major breakthrough in animal vaccinology occurred in the mid-1980s, when it was found that several live-attenuated PrV vaccine strains lacked a significant portion of the genome, including the gene encoding a major immunogenic viral envelope glycoprotein. Upon the development of a suitable serological assay, the first marker vaccine/DIVA concept (differentiating infected from vaccinated animals) was developed. Moreover, the first genetically modified live vaccines emanated from molecular work on PrV. Thus, AD serves as a hallmark for the history of veterinary virology as well as for pioneering novel strategies for controlling animal infectious diseases.

Vaccines against pseudorabies virus (PrV)

Aujeszkýs disease (AD, pseudorabies) is a notifiable herpesvirus infection of pigs causing substantial economic losses to swine producers. AD in pigs is controlled by the use of vaccination with inactivated and attenuated live vaccines. Starting with classically attenuated live vaccines derived from low virulent field isolates, AD vaccination has pioneered novel strategies in animal disease control by the first use of genetically engineered live virus vaccines lacking virulence-determining genes, and the concept of DIVA, i.e. the serological differentiation of vaccinated from field-virus infected animals by the use of marker vaccines and respective companion diagnostic tests. The basis for this concept has been the molecular characterization of PrV and the identification of so-called nonessential envelope glycoproteins, e.g. glycoprotein E, which could be eliminated from the virus without harming viral replication or immunogenicity. Eradication of AD using the strategy of vaccination-DIVA testing has successfully been performed in several countries including Germany and the United States. Furthermore, by targeted genetic modification PrV has been developed into a powerful vector system for expression of foreign genes to vaccinate against several infectious diseases of swine, while heterologous vector systems have been used for expression of major immunogens of PrV. This small concise review summarizes the state-of-the-art information on PrV vaccines and provides an outlook for the future.

Growth properties and vaccine efficacy of recombinant pseudorabies virus defective in glycoprotein E and thymidine kinase genes

Pseudorabies virus (PRV) is an alphaherpesvirus that causes pseudorabies (PR), an economically important viral disease of pigs. Marker vaccines were widely used in PR prevention and eradication programs. The purpose of this study was to construct a novel recombinant virus with deletions at defined regions in the glycoprotein E (gE) and thymine kinase (TK) genes by homologous recombination. This study also evaluated the safety and efficacy of the virus for a live attenuated marker vaccine. No significant difference was observed in virus replication between gE gene-deleted (gE(-)), gE/TK double gene-deleted (gE(-)TK(-)), and wild-type PRV by growth curve analysis. However, gE(-)TK(-) PRV was completely attenuated in mice. To evaluate the immunogenicity of gE(-)TK(-) PRV, four 12-week-old specific-pathogen-free pigs per group were immunized intramuscularly with viral titers of 1×10(4), 1×10(5), or 1×10(6) TCID50, followed by intranasal challenge infection with virulent PRV (1×10(8) TCID50) at 3 weeks post vaccination. The gE(-)TK(-) PRV-vaccinated pigs displayed no general adverse effects after immunization and had protective immune responses after PRV challenge. Thus, gE(-)TK(-) PRV was safe and efficacious and might be a potential candidate for a live attenuated marker vaccine against PRV.

Emergence of a Pseudorabies virus variant with increased virulence to piglets

Pseudorabies virus (PRV) causes Pseudorabies (PR), an economically important disease in domestic swine. PR outbreaks on pig farms caused by PRV variant strains in Bartha-K61-vaccinated pigs have resulted in considerable economic losses in China since 2011. In this study, the pathogenicity of the PRV variant JS-2012 strain to pigs was investigated by experimentally inoculating piglets of different ages in comparison with a classic virulent PRV SC strain. The JS-2012 strain caused an earlier onset of clinical signs and higher mortality in 15, 30, and 60-day-old pigs, as compared with a classic virulent PRV SC strain. The Bartha-K61 vaccination provided complete protection against challenge with classical virulent PRV, but only partial protection against challenge with the JS-2012 strain in piglets. In conclusion, the increased virulence of the PRV variant may have partly contributed to the PR outbreak in China.

A novel gE-deleted pseudorabies virus (PRV) provides rapid and complete protection from lethal challenge with the PRV variant emerging in Bartha-K61-vaccinated swine population in China

The currently used Bartha-K61 strain is a very safe and effective vaccine against pseudorabies (PR) and has played a critical role in the control and eradication of PR worldwide. Since late 2011, however, PR reemerged among Bartha-K61-vaccinated pig population in many regions in China. Our previous studies demonstrated that the Bartha-K61 vaccine was unable to provide complete protection from the challenge with the PRV TJ strain (PRVTJ), a representative emerging PRV variant that was isolated from a Bartha-K61-immunized pig farm in Tianjin, China. Here, we generated a gE-deleted PRV, named as rPRVTJ-delgE, based on PRVTJ and evaluated its safety and immunogenicity in pigs. Our results showed that groups of piglets (n=5) immunized with 10(3), 10(4) or 10(5)TCID50 rPRVTJ-delgE did not exhibit clinical signs following immunization and challenge and were protected clinically and virologically from the lethal challenge with PRVTJ as early as 1 week post-immunization, in contrast with the incomplete protection provided by the Bartha-K61 vaccine. These indicate that rPRVTJ-delgE is a promising candidate vaccine for updating Bartha-K61 for the control of the currently epidemic PR in China.

Novel and emerging therapies safeguarding health of humans and their companion animals: a review

Modern medicine has helped to a great extent to eradicate and cure several diseases of mankind and animals. But the existence of incurable diseases like cancer, Acquired Immunodeficiency Syndrome (AIDS), diabetes or rheumatoid arthritis, side effects of allopathic medicine, increasing trend of antibiotic resistance and chemicals and biopesticides causing dietary risk have made the situation more critical than ever before. Thus, it has become a matter of concern for the scientists and researchers to develop novel therapies. Bacteriophage therapy to treat pathogenic bacterial infections, virophage therapy for conservation of global system and avian egg yolk antibody therapy for designing prophylactic strategies against Gastrointestinal (GI) diseases are interesting approaches. Others include the use of cytokines as adjunctive immunomodulators, gene therapy focusing on diseases caused by single gene defects, RNAi technology to suppress specific gene of interest and apoptins for cancer treatment. Stem cell therapy against several diseases and ailments has also been discussed. The use of nanoparticles for better drug delivery, even though costly, has been given equal importance. Nevertheless, immunomodulation, be it through physiological, chemical or microbial products, or through essential micronutrients, probiotics, herbs or cow therapy prove to be cost-effective, causing minimum adverse reactions when compared to allopathy. Development in the field of molecular biology has created an enormous impact on vaccine development. The present review deals with all these novel and emerging therapies essential to safeguard the health of humans and companion animals.

Seroprevalence of porcine reproductive and respiratory syndrome, Aujeszky's disease, and porcine parvovirus in replacement gilts in Thailand

The present study investigated the seroprevalence of porcine reproductive and respiratory syndrome virus, Aujeszky's disease virus (ADV), and porcine parvovirus (PPV) in replacement gilts from selected five swine herds in Thailand. The study consisted of three parts. First, a retrospective data analysis on the seroprevalence of porcine reproductive and respiratory syndrome virus (PRRSV) and ADV glycoprotein I (gI) in gilts, sows, boars, nursery, and fattening pigs in five herds (n = 7,030). Second, a cross-sectional study on seroprevalence of PRRSV, ADV, and PPV (n = 200) in replacement gilts. Last, the seroprevalence of PRRSV, ADV, and PPV in gilts culled due to reproductive failure (n = 166). Across the herds, the seroprevalence of PRRSV and ADV was 79.3% and 5.3%, respectively. The cross-sectional study revealed that 87.5%, 4.0%, and 99.0% of the replacement gilts were infected with PRRSV, ADV, and PPV, respectively. In the gilts culled due to reproductive failure, the seroprevalence of PRRSV, ADV, and PPV was 73.5%, 28.3%, and 86.0%, respectively. Of these culled gilts, 75.5% had been infected with at least two viruses and 18.9% had been infected with all three viruses. It could be concluded that most of the replacement gilts were exposed to PRRSV (84%), PPV (97%), and ADV (4%) before entering the breeding house. PPV was an enzootic disease among the selected herds. The prevalence of ADV was higher in gilts culled due to reproductive disturbance than in the healthy gilts.

A study of the ability of a TK-negative and gI/gE-negative pseudorabies virus (PRV) mutant inoculated by different routes to protect pigs against PRV infection

The capacity of a TK-negative (TK-) and gI/gE-negative (gI/gE-) pseudorabies virus (PRV) mutant to protect pigs against Aujeszky's disease carried out by experimental infection with a virulent PRV strain, was tested. There were three groups, each of four susceptible pigs which were inoculated twice by two different schedules. Group 1 received the modified virus by the intradermal (first inoculation)-intramuscular (second inoculation) routes; group 2 was treated by the intranasal (first inoculation)-intramuscular (second inoculation) routes. The third group was left untreated as the control. All of the pigs were challenged intranasally with a virulent PRV strain and they were subsequently injected with dexamethasone. Two pigs in each group were necropsied on days 5 and 15 after dexamethasone inoculation. The challenge exposure resulted in mild clinical signs, increase in growth and a shorter period of virus shedding in vaccinated pigs, whereas the control group showed severe signs of Aujeszky's disease. No difference in the titre of the virulent virus which was excreted by pigs of all three groups, was observed and all animals seroconverted. Both the mutant strain and the wild-type virus established a latent infection although only the latter was reactivated and shed. Slight lesions were observed in target tissues of the vaccinated animals and no significant differences were detected between the two inoculation schedules.

A comparative study of pseudorabies virus (PRV) strains with defects in thymidine kinase and glycoprotein genes

In the course of two experiments, an examination was made of the virulence and neuroinvasiveness for pigs of two pseudorabies virus mutants (strain 6C2TK(-), with a defect in thymidine kinase (TK) function; and strain 6C2TK(-), gI(-)/gE(-), with defects in TK and glycoproteins I and E) and of the wild-type parent strain (86/27V). At various times after intranasal inoculation, pigs were killed and samples of tonsil, lung and different levels of the trigeminal and olfactory nervous pathways were examined by methods that included viral isolation, polymerase chain reaction assay and immunohistochemistry. Both mutant viruses were of reduced virulence, as indicated by no more than moderate clinical signs and lesions, and only sporadic isolation of virus; moreover, unlike the wild-type parent strain, the mutant viruses were not reactivated from the latent state by corticosteroid treatment. In addition, migration of the mutant strains to the central nervous system (olfactory and trigeminal nervous pathways) was reduced as compared with that of the wild-type strain. Thus, mutations in the genes encoding the TK enzyme and the gI/gE complex were associated with reduced virulence, reduced replication in peripheral target tissues, and reduced migration to the olfactory and trigeminal pathways.

Vaccine delivery to animals

For many years vaccination of animals has been practiced to prevent infectious diseases using inactivated organisms or modified live organisms. The live vaccines were effective but lacked safety. The vaccines made with inactivated organisms required an adjuvant to induce an immune response that was not as effective as either the clinical disease or live vaccines. An 'ideal' vaccine would induce effective immunity specific for the type of infection, have long duration, require minimal or no boosters, have impeccable safety, would not induce adverse reactions, and be easy to administer. The desire to meet these criteria, and especially safety, has resulted in the development of vaccines that do not depend on the use of the viable disease agent. The emphasis on subunit or inactivated vaccines that meet the desired criteria of a perfect vaccine has resulted in a critical need for better adjuvants and delivery systems. This has resulted in a technological innovation revolution with development of a wide array of different technologies to generate effective vaccines. This review will describe the historical relevance of adjuvants used for parenterally administered inactivated/subunit vaccines as well as describe some of the exciting technological advances including adjuvants (ISCOMS), delivery systems (recombinant vectors, microparticles), and novel approaches (transgenic plants, naked DNA) that are currently being, or will be used in the future, in the search for better, more effective vaccines that meet the current and future needs of veterinary medicine.

Out on the farm with DNA vaccines

DNA vaccination is a rapidly developing technology that offers new approaches for the prevention of disease. This technology may permit the production of new vaccines against diseases that have no current vaccine, as well as allowing the development of improved vaccines to replace existing products. We describe how DNA vaccination is being developed for use in commercial animal production, with an emphasis on viral diseases, and discuss the existing hurdles to its development and use.

Synthesis and antiviral evaluation of analogs of adenosine-N1-oxide and 1-(Benzyloxy)adenosine

The activity of a series of compounds related to adenosine-N1-oxide (1) and 1-(benzyloxy)adenosine (42) against vaccinia virus has been determined both in vitro and in a vaccinia mouse tailpox model. Significant activities have been found both in vitro and in vivo for a number of the synthetic compounds.

The probability of in vivo reactivation of herpes simplex virus type 1 increases with the number of latently infected neurons in the ganglia

The purpose of this study was to define the relationship between herpes simplex virus (HSV) latency and in vivo ganglionic reactivation. Groups of mice with numbers of latently infected neurons ranging from 1.9 to 24% were generated by varying the input titer of wild-type HSV type 1 strain 17syn+. Reactivation of the virus in mice from each group was induced by hyperthermic stress. The number of animals that exhibited virus reactivation was positively correlated with the number of latently infected neurons in the ganglia over the entire range examined (r = 0.9852, P < 0. 0001 [Pearson correlation]).