Vaccines for bluetongue

Isolation of 8 serotypes of bluetongue virus (BTV) in Australia has led to widespread debate on how to prepare for an outbreak of bluetongue disease and the type of vaccine best suited to control bluetongue in Australia. This article describes the vaccine options under consideration by research workers and animal health administrators. The most widely discussed options are live attenuated virus, killed virus and virus-like particles (VLP) generated by recombinant baculoviruses. Attenuated virus vaccines are cheap and easy to produce and are administered in a single dose. They replicate in sheep without causing significant clinical effects and provide protection against challenge with virulent virus of the same serotype. The possibility that insects could acquire vaccine virus by feeding on vaccinated animals and transmit it to sheep or cattle cannot be eliminated. This poses a risk because attenuated viruses are teratogenic if ewes are infected in the first half of pregnancy. In addition, vaccine virus replication in insects and ruminants may lead to a reversion to virulence. Killed virus vaccines have been shown to be efficacious in small laboratory trials and cannot be transmitted to other animals in the field, but are significantly more expensive to produce than attenuated viruses and require at least 2 doses with adjuvant to elicit an immune response. More work is needed to properly assess their effectiveness and determine their cost of production. Recombinant VLP contain the 4 major structural proteins of BTV but no nucleic acid. VLP are relatively easy to isolate, but it is unlikely that the purification methods currently used in laboratories will be adapted for use commercially. Despite the enthusiasm of recent years, little commercial progress appears to have been made. Although scientific research in Australia and overseas has provided a number of options for development of bluetongue vaccines, the decisions on which to use in an outbreak are complex and will require, not only consideration of factors discussed here, but also agreement from industry and government.     

Vaccines against veterinary helminths

The majority of attempts to develop commercial vaccines for veterinary helminths have focussed on identifying protein antigens, which could be formulated as protective vaccines. Notable successes have been achieved for some cestode parasites, where recombinant proteins have been developed into highly effective vaccines. Although effective protection can also be obtained using some nematode proteins in their native forms, it has not yet been possible to formulate commercially successful vaccines for other helminth parasites of veterinary significance. Increasing evidence suggests that parasite glycan moieties may provide an alternative source of vaccine antigens, and increased attention is now being given to this class of compounds. In addition to identifying candidate protective antigen(s), an increased research effort is needed to develop appropriate strategies for the formulation and delivery of helminth vaccines.     

An experimental inactivated vaccine against bluetongue.

Bluetongue virus grown in BHK cells was shown to be inactivated in concentrations of betapropiolactone (BPL) higher than 0-15 per cent. When the virus, inactivated with 0-2 per cent BPL and prepared as a double emulsion vaccine, was injected into Cypriot sheep, no untoward reactions were observed and neutralising antibodies developed. The antibody titre reached a high level and persisted for at least a year. After re-vaccination, a secondary response was observed. A bivalent vaccine elicited a response to both virus types incorporated. The possibilities of using a polyvalent inactivated vaccine are discussed.     

Vaccines against cysticercosis and hydatidosis.

The recombinant vaccines that have been developed against cysticercosis and hydatidosis in sheep and cattle are remarkable for their effectiveness and are prominent as examples of the very few non-living vaccines against parasitic diseases. Their development has been through practical application of molecular parasitology, utilising immunochemical techniques in antigen identification and recombinant DNA methods in antigen production. This brief overview discusses the contribution of molecular techniques to the successful development of recombinant vaccines against Taenia ovis, Taenia saginata and Echinococcus granulosus as well as the immunological and genomic studies that have arisen from their development.     

Prediction of bluetongue vector distribution in Europe and north Africa using satellite imagery

Bluetongue is an infectious, non-contagious arboviral disease thought to infect all known ruminant species. Since 1998, an unprecedented epizootic of the disease has occurred in the Mediterranean region, resulting in the deaths of over 800,000 sheep to date. Bluetongue virus (BTV) is transmitted by biting midges of which one species, Culicoides imicola, is the major vector in the old world. C. imicola was trapped for 2 years at 87 sites across Portugal and models were developed for predicting the presence and abundance of the midge at these sites. Discriminant analysis was used to identify the best models from 40 temporally Fourier-processed 1 km spatial resolution remotely-sensed variables. The best models correctly predicted presence and absence at 83 of the 87 sites, and abundance at 76 sites. The models were then used to predict C. imicola presence and abundance elsewhere across Europe and north Africa. C. imicola was predicted to be present and in high abundance at the majority of areas affected in the recent bluetongue epizootic, including the Balearics, Sardinia, Corsica, Sicily, areas of mainland Italy, large areas of Greece, western Turkey and northern Algeria and Tunisia.     

鸡球虫疫苗研究进展

鸡球虫病是生产中严重危害养禽业的寄生虫病,长期以来以药物防治为主。目前,由于球虫耐药性的普遍存在,加上消费者对禽产品药物残留问题的关注,采用疫苗防治球虫病为人心所向。球虫活苗在实际生产中发挥了一定的作用,但由于球虫活苗存在“复壮”的可能且使用麻烦,人们将目光转向了分子疫苗。球虫基因组学研究为基因工程苗开发奠定了基础,目前已经筛选了上百个功能抗原基因。受表达系统的限制,原核表达的重组蛋白抗原性较差,虽有较多尝试,但鲜有成功。人们在探索体外真核表达(如酵母、杆状病毒表达系统等)的同时,核酸疫苗以其独特的诱发高水平细胞免疫反应的能力而倍受青睐,近几年发展较快。     

Establishment of an early warning system against bluetongue virus in Switzerland

Bluetongue (BT) is a vector-borne animal disease of economical importance due to the international trade restrictions likely to be put into place in a country once the infection is discovered. The presence of BT and its vectors in countries adjacent to Switzerland stresses the need of implementing a surveillance system and to raise disease awareness among potential stakeholders. A national survey in Switzerland 2003 indicated freedom of Bluetongue virus (BTV), although a single individual of the main BT vector Culicoides imicola was caught in the canton of Ticino. The survey also demonstrated that potential BT vectors, C. obsoletus and C. pulicaris are locally abundant in Switzerland. Therefore, a new surveillance method based on sentinel herds in high risk areas was implemented in 2004 for the early detection of both an incursion of BT vectors into Switzerland, and potential virus circulation among cattle.     

Quantitative analysis of transmission parameters for bluetongue virus serotype 8 in Western Europe in 2006

ABSTRACT: The recent bluetongue virus serotype 8 (BTV-8) epidemic in Western Europe struck hard. Controlling the infection was difficult and a good and safe vaccine was not available until the spring of 2008. Little was known regarding BTV transmission in Western Europe or the efficacy of control measures. Quantitative details on transmission are essential to assess the potential and efficacy of such measures.To quantify virus transmission between herds, a temporal and a spatio-temporal analysis were applied to data on reported infected herds in 2006. We calculated the basic reproduction number between herds (Rh: expected number of new infections, generated by one initial infected herd in a susceptible environment). It was found to be of the same order of magnitude as that of an infection with Foot and Mouth Disease (FMD) in The Netherlands, e.g. around 4. We concluded that an average day temperature of at least 15°C is required for BTV-8 transmission between herds in Western Europe. A few degrees increase in temperature is found to lead to a major increase in BTV-8 transmission.We also found that the applied disease control (spatial zones based on 20 km radius restricting animal transport to outside regions) led to a spatial transmission pattern of BTV-8, with 85% of transmission restricted to a 20 km range. This 20 km equals the scale of the protection zones. We concluded that free animal movement led to substantial faster spread of the BTV-8 epidemic over space as compared to a situation with animal movement restrictions.     

猪支原体肺炎疫苗的研究进展

本文介绍了国内外猪支原体肺炎疫苗的研究概况，包括国内外常规疫苗、基因工程疫苗等，并对猪支原体肺炎疫苗的进一步的研究工作提出了建议。