Veterinary vaccines for public health and prevention of viral and bacterial zoonotic diseases.

To meet with the increasing demand for food, the scale of world food production is increasing, as is the transport of animals and food products. At the same time, the contact of animals with the environment remains unchanged or, in the case of free-ranging animals, is even increasing. A number of microorganisms have established themselves in farmed animals, which although relatively harmless to animals are pathogenic to man. In this article, the options for reducing the risk of transferring zoonotic agents from animals (particularly farm animals) to man using veterinary vaccines against viral and bacterial diseases are described.

Studies on streptococci resembling Streptococcus milleri and on an associated surface-protein antigen.

Ninety-nine strains of streptococci were isolated from 97 cases of pyogenic infections, most of which involved the teeth. Physiological and serological tests were performed on these streptococci and on 37 strains of streptococci from culture collections. The results were used for a numerical classification. Seventy-nine of the strains isolated from patients formed a cluster with Streptococcus milleri and group-F reference strains, and were therefore considered as streptococci resembling S. milleri. By the use of an antiserum prepared against strain Z3, protein antigens were demonstrated in acid extracts of 65% of the strains of S. milleri. These antigens were in only five strains not included in the S. milleri cluster.

Infectious bursal disease of poultry: antigenic structure of the virus and control.

The present knowledge of genome organisation, structural basis of pathogenicity and antigenicity of infectious bursal disease virus (IBDV) are briefly reviewed. The current situation of IBDV infection in various countries is stated and recommendations for improved vaccination schemes are given.

Isolation of avian reovirus as a possible etiologic agent of osteoporosis ("brittle bone disease"; "femoral head necrosis") in broiler chickens.

Avian reovirus was isolated from intestines of 3-to-7-day-old broiler chickens with enteritis from broiler houses where osteoporosis was a problem. The virus was purified in a cesium chloride gradient (buoyant density 1.37 gm/ml) and identified as a reovirus by electron microscopy. Specific-pathogen-free (SPF) chickens and commercial broiler chickens with anti-reovirus maternal antibodies inoculated at 1 day of age with the reovirus isolate developed lesions of femoral head fractures and/or osteoporosis; reovirus could be reisolated from the bone marrow and intestinal tracts of experimentally infected SPF birds. The reovirus isolate, although isolated from intestines, induced development fo tenosynovitis lesions in SPF and commercial broiler chickens.

Protection of chickens from Newcastle and Marek's diseases with a recombinant herpesvirus of turkeys vaccine expressing the Newcastle disease virus fusion protein.

Recombinant strains of herpesvirus of turkeys (HVT) were constructed that contain either the fusion protein gene or the hemagglutinin-neuraminidase gene of Newcastle disease virus (NDV) inserted into a nonessential gene of HVT. Expression of the NDV antigens was regulated from a strong promoter element derived from the Rous sarcoma virus long terminal repeat. Recombinant HVT strains were stable and fully infectious in cell culture and in chickens. Chickens receiving a single intra-abdominal inoculation at 1 day of age with recombinant HVT expressing the NDV fusion protein had an immunological response and were protected (> 90%) against lethal intramuscular challenge at 28 days of age with the neurotropic velogenic NDV strain Texas GB. Recombinant HVT expressing the NDV hemagglutinin-neuraminidase provided partial protection (47%) against the same challenge. Chickens vaccinated with recombinant HVT vaccines had low levels of protection against NDV replication in the trachea when challenged ocularly. Recombinant HVT vaccines and the parent HVT strain provided similar levels of protection to chickens challenged with the very virulent RB1B strain of Marek's disease virus, indicating that insertion of foreign sequences into the HVT genome did not compromise the ability of HVT to protect against Marek's disease.

Active cross-protection induced by a recombinant baculovirus expressing chimeric infectious bursal disease virus structural proteins.

The VP2 structural gene encoded in the large genomic segment A of the variant GLS strain of infectious bursal disease virus (IBDV) was modified to encode a neutralization epitope (B69), found only on classic strains of IBDV. A chimeric cDNA clone of the large segment A, encoding VP3, VP4, and the modified variant IBDV VP2 structural proteins, was expressed in a recombinant baculovirus. The chimeric protein expressed was assessed with a panel of neutralizing monoclonal antibodies (MAbs), and it contained not only all previously MAb-defined GLS variant strain epitopes but also the B69 neutralization epitope found on classic IBDV strains. Complete active protection was afforded to specific-pathogen-free chickens by a subunit chimeric vaccine against virulent challenge with the classic IM and STC strains, as well as against the variant E/Del and GLS IBDV strains. Compared with a previously tested recombinant subunit vaccine, which incorporated unmodified baculovirus-expressed large-segment A GLS proteins, the recombinant chimeric subunit vaccine resulted in markedly improved active cross-protection against classic IBDV challenge.

The use in practice of inactivated oil emulsion vaccine against infectious bursal disease in broiler breeders and its influence on the progeny: a comparative field trial.

Field trials were conducted to establish the effect of the use of an inactivated oil emulsion vaccine against Infectious Bursal Disease (IBD OEV) in broiler breeder hens, and its effects on their progeny. The performance of 18 broiler flocks, which were the progeny of the IBD OEV vaccinated breeder hens, but which were not vaccinated with a live vaccine against IBD, was equal to that of broiler flocks which were vaccinated with a live IBD vaccine and originated from parent stock that had been vaccinated only against IBD with a live vaccine. In none of the 18 flocks, progeny of IBD OEV vaccinated parents, was IBD diagnosed. In a second stage, 15 broiler flocks were included in the trial: these were derived partly from IBD OEV vaccinated parents, and partly from parents that received only live IBD vaccine at 8-10 days of age. No cases of IBD occurred and all flocks were positive for IBD precipitins at slaughter age. Vaccination with a live vaccine against IBD at the age of 8-10 days had no influence on NCD antibody development after a NCD vaccination at 7 days. No immunosuppressive effect from this type of live live IBD vaccine could be determined under field conditions.

Isolation of a new serotype of avian reovirus associated with malabsorption syndrome in chickens.

This paper describes the isolation and identification of a novel class of reoviruses, the so-called enteric reovirus strains (ERS). The pathogenicity, dissemination, induction of malabsorption syndrome (MAS), reaction pattern with different monoclonal antibodies, and serotype properties are reported. Upon screening of reoviruses in the field, it was observed that these reovirus strains were also present in other countries and were usually isolated from birds with MAS. Based on the data presented here, it is proposed that the so-called ERS are associated with MAS.

Viral diseases of the immune system and strategies to control infectious bursal disease by vaccination.

Viral infections which are immunosuppressive can affect the economics of poultry production, often as a result of the chicken's increased susceptibility to secondary infections and sub-optimal response to vaccinations. The mechanism of this immunosuppression has been studied in detail for certain chicken viruses. The replicating virus can have both direct and indirect effects on the cells of the immune system. The special role of the bursa of Fabricius, as a lympho-epithelial organ, will be mentioned. The effects of oncogenic viruses (MDV, REV and ALV) on the immune system will be discussed as will the present status of our knowledge on the immunosuppressive effects of certain respiratory viruses such as ILT, NDV and reovirus. Two major immunosuppressive agents are CAV and IBDV. The effects of IBDV will be described in more detail because of its economic importance. Advances made in the molecular biology of both the virus and the immune system give new opportunities to control the disease by vaccination. Successful vaccination strategies applied in the past and options for the future will be discussed.

Intradermal application of Aujeszky's disease virus strain Begonia with tocopherol-based adjuvant and a novel design injection device.

Initially the use of intradermal application of Aujeszky's disease vaccines was shown to be very effective. However, for thus far unknown reasons the gI-deleted vaccines were much less efficacious by using this route of vaccination as compared to gI-positive vaccines. By the use of a tocopherol-based adjuvant and an improved design of the intradermal injection device it now appeared feasible to obtain the same efficacy both in specific pathogen free pigs and in pigs with material antibodies as found before when intramuscular administration was performed. With respect to safety we found a complete lack of skin lesions, no adverse systemic reactions (e.g. body temperatures) and no effect on growth rates. Last but not least, the easiness of intradermal injections is of great advantage in large-scale vaccination programs.

Antigenic characterization of IBDV field isolates by their reactivity with a panel of monoclonal antibodies.

Recently Infectious Bursal Disease Virus isolates have been described in USA displaying an antigenic drift. Many of the new isolates were very virulent for chickens. In several European countries severe outbreaks of Gumboro disease have also been reported from vaccinated and non-vaccinated flocks. Since vaccinated SPF birds were shown to be protected against challenge infection with the new isolates under laboratory conditions, a more detailed investigation of the European isolates is wanted. The similarity between the European and US field situation got us to use a panel of monoclonal antibodies (MCAs) previously applied to characterize US strains for testing European isolates. An antigen capture ELISA has been carried out directly on bursa homogenates of chickens form the field. One European (F52/70) and two US (Var. E and GLS-5) strains have been included as reference viruses. From the results presented here it can be concluded that the European isolates (Netherlands, France, UK, Germany, Jugoslavia and Spain) did not undergo the same antigenic drift as the US strains. A more extensive analysis of the isolates will be done to elucidate their role for disease outbreaks.

The results of field trials conducted with an inactivated vaccine against the egg drop syndrome 76 (EDS 76).

The results of six vaccination trials carried out with a formalin inactivated oil adjuvant Egg Drop Syndrome 76 (EDS 76) vaccine prepared from strain BC14 are presented. The trials carried out in breeding and laying flocks of fowls always included vaccinated and unvaccinated birds. The birds were vaccinated once during the rearing period by intramuscular injection. Field infection with EDS 76 virus was confirmed by the sero-logical conversion to EDS antibody positive in the unvaccinated birds. In the unvaccinated birds field challenge was followed by typical EDS 76 symptoms, whereas the vaccinated birds were protected and layed normally throughout the trials.

Typing of Group A streptococci from an urban area (Köln) in West Germany.

Two-hundred and twenty strains of Streptococcus pyogenes (group A streptococcus) from the urban area of Köln, West Germany have been typed by M precipitin and T agglutination tests. Determination of streptococcal nicotinamide adenine dinucleotide glycohydrolase (NADase) production and the serum opacity reaction (SOR) have also been performed. 65.5% of the isolates could be typed by the M precipitin reaction. 92.1% of the remaining strains could be identified by their T protein antigens and could be further subdivided according to their NADase/SOR pattern. Most of the M typable strains originated from upper respiratory tract infections (including scarlet fever), whereas the majority of the M nontypable streptocci had been isolated from skin, wound, and other non-respiratory sites.

Serological classification of recent infectious bronchitis virus isolates by the neutralization of immunofluorescent FOCI.

The neutralisation of immunofluorescent foci test was adapted to the grouping of 14 recent Dutch infectious bronchitis virus isolates. This test provides a distinct grouping of the isolates and the corresponding sera. Evaluation of the tests was carried out by means of the computer program called 'Taxonomic', designed for the calculation of taxonomic order from serological data. The taxonomic order, depicted in the form of a tree, facilitates the judgement of the degree of resemblance between viruses or groups of viruses as well as sera. Using this test the isolates of infectious bronchitis virus can be classified into distinct groups.

Application of a new method for detecting streptococcal nicotinamide adenine dinucleotide glycohydrolase to various M types of Streptoccus pyogenes.

The production of extracellular nicotinamide adenine dinucleotide glycohydrolase (NADase) by Streptococcus pyogenes can easily be demonstrated using the fluorescence of nicotinamide adenine dinucleotide in ultraviolet light occurring on addition of strong alkali. The new method described here uses microtiter plates and can be read with the naked eye. It permits the screening of large numbers of strains in a short time and with minimal amounts of reagents. The sensitivity of the new method proved to be good in comparison with the bisulfite spectrophotometric method. Culture supernatants of 177 group A streptococci were tested for NADase production by the microtiter fluorescence method. We could confirm former findings that strains within a certain M type of S. pyogenes are usually either producers or nonproducers of the enzyme. The usefulness of the test for screening of streptococcal NADase production is discussed.

Bovine viral diarrhea virus with deletions in the 5'-nontranslated region: reduction of replication in calves and induction of protective immunity.

Bovine viral diarrhea virus (BVDV) with deletions in the 5'-nontranslated region (5'-NTR) were tested for their suitability as live BVD vaccines. Firstly, the genetic stability of the mutants was established by culturing over 15 passages in bovine cells. Secondly, two deletion mutants and the parent strain CP7-5A were characterised with respect to in vivo replication competence, attenuation and induction of protective immunity against BVDV. Naïve calves (n = 5 per group) were inoculated with mutants d2-31 and d5-57 or CP7-5A and 5 weeks later, a challenge with the BVDV type 1 strain New York was performed. The mutants were found to be genetically and phenotypically stable. Moreover, the results indicate that the mutants were attenuated with regard to effects including pyrexia and drop in leucocyte counts. Infection with the mutants induced moderate to high titers of BVDV neutralizing antibodies and completely prevented viremia after challenge infection with a heterologous BVDV strain. Taken together, the 5'-NTR deletion mutants combine a good safety profile with good efficacy and are therefore well suited as candidate live vaccines.

Active and passive protection against variant and classic infectious bursal disease virus strains induced by baculovirus-expressed structural proteins.

Infectious bursal disease virus (IBDV) is responsible for a highly immunosuppressive disease in young chickens which causes significant economic losses to the poultry industry worldwide. The structural protein genes (VP2, VP3 and VP4) of a variant IBDV strain (GLS) were expressed in insect cells using a baculovirus expression system. Susceptible chickens vaccinated with a single dose of the recombinant IBDV antigens were completely protected against challenge with two variant strains of IBDV (GLS and Delaware), and partially protected against the standard challenge strain (STC). A booster dose of the recombinant antigens induced higher levels of neutralizing antibodies and afforded complete protection against both variant and standard virus challenges. Specific-pathogen-free hens vaccinated with a single dose of the same subunit vaccine produced virus-neutralizing antibodies that were capable of passively protecting the progeny from infection with variant IBDV.

Pseudorabies virus glycoprotein gI: in vitro and in vivo analysis of immunorelevant epitopes.

Overlapping fragments of the gene encoding glycoprotein gI of pseudorabies virus (PRV; herpesvirus suis 1) were expressed in bacteria. Using the fusion proteins and a panel of monoclonal antibodies (MAbs) against gI as well as swine sera we found that the N-terminal part of gI (residues 33 to approximately 100) contains a highly antigenic and immunogenic domain. Transfer of antibodies binding to this region as well as vaccination with fusion proteins containing the N terminus of gI are able to confer protection to mice against a lethal challenge of virus. The results show that gI, which is non-essential for virus replication in tissue culture, can induce neutralizing and protective antibodies. The potential suitability of fusion proteins encompassing N-terminal parts of gI as diagnostic tools is demonstrated.