Immunogenicity of a freeze-dried combined vaccine against Rift Valley fever and bovine ephemeral fever in cattle.

Background: The target of vaccination is to encourage a strong, covering and long-lasting immune response against antigens. For achieving these objectives; effective adjuvant and new vaccine strategies are demanded to make the vaccine sufficiently immunogenic to instigate a powerful immune response. Aim: This study was completed for elaboration and evaluation of freeze-dried combined vaccine against both Rift Valley fever (RVF) and bovine ephemeral fever (BEF) viruses using different stabilizers. Methods: Three formulae were prepared from such vaccine including: formula (1): stabilized with a mixture of 5% Lactalbumin Hydrolysate and 2.5% sucrose, formula (2): stabilized with a mixture of 50% the previous stabilizer and 50% of 1% Carbopol and formula (3): stabilized with 1% Carbopol solution. Samples of the three vaccine formulae were reconstituted on the time of experimental animal vaccination using saponin diluent which acts as an adjuvant for both RVFv and BEFv and as an inactivator BEF virus. The ratio between both viruses in all vaccine formulae was 1:1. Results: All vaccine batches were proved to be free of any foreign contaminants and unharmed for experimentally vaccinated animals. Each of the three groups of calves was vaccinated S/C with 2 ml of a reconstituted vaccine formula and their immune response was evaluated using serum neutralization test. The gained results revealed that the prepared combined freeze-dried vaccine with Carbopol elicited a better humoral immune response than the other two vaccine formulae. Conclusion: It could be recommended to use Carbopol as a stabilizer for the preparation of the aimed vaccine.

Effectiveness of the strain 919 bovine ephemeral fever virus vaccine in the face of a real-world outbreak: A field study in Israeli dairy herds.

Bovine ephemeral fever virus (BEFV) is a globally spread arthropod-borne RNA virus that has significant economic impacts on the cattle industry. A live attenuated commercial BEF vaccine, based on the Australian BEFV strain 919, is widely used in Israel and other countries. A previous study has suggested the high effectiveness of this vaccine (ULTRAVAC BEF VACCINE™ from Zoetis®), but anecdotal reports of high BEF morbidity among vaccinated dairy herds in Israel casted doubt on these findings. To resolve this uncertainty, a randomized controlled field vaccine effectiveness study was conducted in Israel during a BEF outbreak which occurred in 2021. Eleven dairy herds were enrolled and monitored for BEF-associated morbidity and rumination alteration patterns using electronic monitoring tags (HR Tags, SCR® Dairy, Netanya, Israel). Four of the herds were naturally infected with BEFV during the outbreak, resulting in a total of 120 vaccinated and 311 unvaccinated subjects that were included in the effectiveness study. A mixed-effect Cox proportional hazard regression model was used to calculate the overall hazard ratio between vaccinated and unvaccinated cattle. This analysis demonstrated an average vaccine effectiveness of 60 % (95 % CI = 38 %-77 %) for preventing clinical disease. In addition, a non-statistically significant trend (p = 0.1) towards protection from mortality was observed, with no observation of mortality among the vaccinated groups compared to 2.61 % mortality (7/311) among the unvaccinated subjects. One hundred and thirty vaccinated and unvaccinated calves from affected and non-affected herds and with different status of morbidity were sampled and analysed by serum-neutralization test. The highest titers of BEFV-neutralizing antibodies were found in subjects that were both vaccinated and clinically affected, indicating a booster effect after vaccination. The results of the study provide evidence for the moderate effectiveness of the ULTRAVAC BEF VACCINE™ for the prevention of BEF.

Development and validation of a DIVA ELISA for differentiating BEFV infected from vaccinated animals.

Inactivated vaccine is considered safe and used for prevention of bovine ephemeral fever in several endemic countries. To differentiate between BEFV-infected and vaccinated animals, we developed an ELISA capable of detecting infection-related antibodies against BEFV. Recombinant proteins, including N, P, M, L, GNS, α2, ß and γ, were expressed in E. coli and screened by Western blotting and ELISA. The results showed GNS, α2 and ß specifically reacted with sera from BEFV infected cattle but not sera from vaccinated cattle. A DIVA ELISA based on a C-terminal truncated form of GNS was developed, with 100% sensitivity and 98.0% specificity at a sample to positive-control optical density ratio (S/P) threshold of 0.18. Specificity analysis showed that the assay has no cross-reactivity with antisera of other common bovine viruses. Anti-GNS antibody appears at 3-4 days post infection (dpi) and persists up to 240-300 dpi in the experimentally infected cattle. Sero-epidemiological survey using sera collected from vaccinated cattle in an endemic area in Jiangsu Province revealed sero-positive rate of 2.36% (6/254), indicating that the DIVA ELISA could be used as a reliable diagnostic tool for differentiating BEFV infected from vaccinated animals.

Identification of Cytotoxic T lymphocyte (CTL) Epitope and design of an immunogenic multi-epitope of Bovine Ephemeral Fever Virus (BEFV) Glycoprotein G for Vaccine Development.

Bovine ephemeral fever (BEF), a vector-borne disease of cattle and water buffalo, is enzootic in tropical and subtropical zones of Asia, Australia, and Africa. Since cytotoxic T lymphocytes (CTL) responses may play a key role in the control of bovine ephemeral fever virus (BEFV) infection, it is important to identify and characterize the CTL target epitopes of BEFV antigens. The current study has been designed to identify and characterize the potential CTL epitopes using the Immuno-informatics tools, and it helped find the potent vaccine candidates against BEF. Antigenicity, toxicity, allergenicity, and immunogenicity testing of predicted CTL epitopes was done. Total four CTL epitopes for BEFV G protein, have been identified as potential epitopes. Prediction of the 3D structure of multi-epitope (final structure) was performed using I-TASSER server. Model 1 was selected as the best model with C-Score: -3.71. The modeled G protein structure and multi-epitope structure were validated by the Ramachandran plots Prosa and Verify 3D server. Epitopic regions of 3D protein structure were identified by Chimera UCSF software. Physicochemical properties of the Multi epitope were evaluated using ProtParam server. This is the first report of CTL epitope in the G protein of BEFV. In this manner, they would play an important role in evoking the immune response as well as vaccine development. However, in vitro and in vivo experimental studies are required for suggested epitopes verification. The multi-epitope was designed from regions of the G protein sequence that lacked mutation and genomic diversity. Therefore, it can be introduced as a protein vaccine from all strains of BEFV as a vaccine candidate for design.

Genome sequence of Bovine Ephemeral fever virus vaccine strain of South African origin.

Bovine Ephemeral fever virus (BEFV) is endemic in South Africa and has a negative economic impact on the meat and dairy industries. Bovine ephemeral fever or three-day stiff-sickness is controlled through annual vaccination with a live attenuated virus manufactured by Onderstepoort Biological Products (South Africa). We announce the genome sequences of two South African Bovine Ephemeral Virus strains; the live attenuated vaccine strain (14 876 nucleotides) and a field strain (14 883 nucleotides). A mutation in the alpha 3 open reading frame rendered the gene non-functional in both genomes. Phylogenetic analysis based on the glycoprotein gene showed that the two strains clustered with the South African lineage.

Expression and immunogenicity of secreted forms of bovine ephemeral fever virus glycoproteins applied to subunit vaccine development.

AIMS: Vaccines for bovine ephemeral fever virus (BEFV) are available but are difficult to produce, expensive or suffer from genetic instability. Therefore, we designed constructs encoding C-terminally truncated forms (transmembrane anchoring region deleted) of glycoproteins G and GNS such that they were secreted from the cell into the media to achieve high-level antigen expression, correct glycosylation pattern and enable further simple purification with the V5 epitope tag. METHODS AND RESULTS: In this study, synthetic biology was employed to create membrane-bound and secreted forms of G and GNS glycoprotein. Mammalian cell culture was employed as an antigen expression platform, and the secreted forms of G and GNS protein were easily purified from media using a highly effective, single-step method. The V5 epitope tag was genetically fused to the C-termini of the proteins, enabling detection of the antigen through immunoblotting and immunomicroscopy. Our data demonstrated that the C-terminally truncated form of the G glycoprotein was efficiently secreted from cells into the cell media. Moreover the immunogenicity was confirmed in mice test. CONCLUSIONS: The immuno-dot blots showed that the truncated G glycoprotein was present in the total cell extract, and was clearly secreted into the media, consistent with the western blotting data and live-cell images. Our strategy presented the expression of secreted, epitope-tagged, forms of the BEFV glycoproteins such that appropriately glycosylated forms of BEFV G protein was secreted from the BHK-21 cells. This indicates that high-level expression of secreted G glycoprotein is a feasible strategy for large-scale production of vaccines and improving vaccine efficacy. SIGNIFICANCE AND IMPACT OF THE STUDY: The antigen expression strategy designed in this study can produce high-quality recombinant protein and reduce the amount of antigen used in the vaccine.

Genetically modified rabies virus vector-based bovine ephemeral fever virus vaccine induces protective immune responses against BEFV and RABV in mice.

Bovine ephemeral fever (BEF), caused by the bovine ephemeral fever virus (BEFV), is associated with an acute febrile infection in cattle and widespread in tropical and subtropical areas, leading to great economic losses to cattle and milk industry. However, no efficacious BEF vaccine is currently available in China. Herein, we generated a recombinant rabies virus (RABV) expressing BEFV glycoprotein (LBNSE-BG), utilizing a reverse genetics system based on the recombinant rabies virus strain LBNSE. It was found that mice immunized with LBNSE-BG produced robust neutralizing antibodies against both BEFV and RABV, and developed complete protection from lethal RABV challenge. Further studies showed that LBNSE-BG activated more dendritic cells (DCs), B cells and T cells in immunized mice than the parent virus LBNSE. Collectively, these findings demonstrate that the recombinant LBNSE-BG described here has the potential to be developed as a cost-effective and efficacious bivalent vaccine for cattle use in endemic areas of BEF and rabies.

The immunogenicity of the secretory GΔTM protein of bovine ephemeral fever virus stably expressed by mammalian cells.

Bovine ephemeral fever virus (BEFV) causes an acute febrile disease in cattle and water buffalo. The disease has an impact on dairy and beef production in tropical and subtropical countries. Vaccination is used for disease prevention and control. In this study, we developed a recombinant lentivirus to produce mammalian stable cells expressing histidine-tagged BEFV G protein with a deleted transmembrane domain (GΔTM) as a secretory protein. In addition, guinea pigs were immunised with the purified GΔTM protein and booster immunised at a 3-week interval. The mammalian stable cells were able to continuously produce GΔTM protein for a minimum of 25 passages. All of the mammalian stable cells expressing GΔTM protein could react specifically with a BEFV convalescent bovine serum. Serum samples from the immunised guinea pigs could react strongly and specifically with the purified GΔTM protein. Moreover, post-immunised guinea pig sera contained antibodies that could neutralise BEFV. These results indicate that the G protein without a transmembrane domain can be used as a subunit vaccine for the prevention and control of BEFV. The availability of the mammalian stable cells, which constitutively express GΔTM protein, could facilitate the potential use of the secretory protein for BEFV diagnosis and vaccine development.

Immunogenicity of a plasmid DNA vaccine encoding G1 epitope of bovine ephemeral fever virus G glycoprotein in mice.

The aim of this study was to investigate the immunogenicity of a plasmid deoxyribonucleic acid (DNA) vaccine encoding the G1 epitope of bovine ephemeral fever virus (BEFV) G glycoprotein in mice. A plasmid DNA carrying the G1 gene was constructed and designated as pcDNA3.1-G1. The expression of the target gene was confirmed in human embryonic kidney 293 (HEK 293) cells transfected with pcDNA3.1-G1 by indirect immunofluorescent staining. Immunisation experiments were intramuscularly carried out by vaccinating 6-week-old female mice in four groups, including the pcDNA3.1-G1 construct, pcDNA3.1 (+) plasmid alone, BEF-inactivated vaccine and phosphate-buffered saline (PBS) (1X) three times with 2-week intervals. Fourteen days after the last immunisation, the animals were bled and the resulting sera were tested for anti-G1-specific antibodies by immunoblotting analysis, indirect enzyme-linked immunosorbent assay (ELISA) and virus neutralisation (VN) test. Serological assays showed that the pcDNA3.1-G1 construct expressing G1 protein was able to elicit specific antibodies against this antigen. Virus neutralisation test showed that pcDNA3.1-G1 could induce anti-BEFV-neutralising antibodies in mice. Our findings indicated that a new dimension can be added to vaccine studies for bovine ephemeral fever (BEF) using eukaryotic expression plasmids encoding the G1 antigen in the future.

Resurgence of bovine ephemeral fever in mainland Japan in 2015 after a 23-year absence.

In September and October 2015, suspected cases of bovine ephemeral fever (BEF) were reported in the mainland region of Kagoshima Prefecture and on Tanegashima Island. The genome of the BEF virus (BEFV) was detected in the diseased cows and the cows that had recovered. The serum obtained from the affected cows contained high titers of BEFV-neutralizing antibody. In total, 18 affected cows were demonstrated to be infected with BEFV during the outbreak. Our findings showed evidence that BEF occurred in mainland Japan after a 23-year absence. Phylogenetic analysis based on the surface glycoprotein (G) gene revealed that BEFVs detected in the affected cows were genetically distinct from previous Japanese BEFVs, but were close to BEFVs circulating in Taiwan and mainland China in recent years. Amino acid substitution in the neutralizing epitope domains of the G protein was limited between the detected viruses and the vaccine strain (YHL isolate), and high titers of the neutralizing antibody against the YHL isolate were induced in the infected cattle during the disease occurrences. Therefore, current BEF vaccines probably elicit protective immunity against the BEFVs detected in 2015, although their effectiveness should be assessed. Since the BEFV vaccination rates are estimated to be low, a BEF outbreak should be considered a possibility in mainland Japan.

Characterization of a recombinant Newcastle disease virus expressing the glycoprotein of bovine ephemeral fever virus.

Bovine ephemeral fever (BEF) is caused by the arthropod-borne bovine ephemeral fever virus (BEFV), which is a member of the family Rhabdoviridae and the genus Ephemerovirus. BEFV causes an acute febrile infection in cattle and water buffalo. In this study, a recombinant Newcastle disease virus (NDV) expressing the glycoprotein (G) of BEFV (rL-BEFV-G) was constructed, and its biological characteristics in vitro and in vivo, pathogenicity, and immune response in mice and cattle were evaluated. BEFV G enabled NDV to spread from cell to cell. rL-BEFV-G remained nonvirulent in poultry and mice compared with vector LaSota virus. rL-BEFV-G triggered a high titer of neutralizing antibodies against BEFV in mice and cattle. These results suggest that rL-BEFV-G might be a suitable candidate vaccine against BEF.

Effectiveness of a BHV-1/BEFV bivalent vaccine against bovine herpesvirus type 1 infection in cattle.

Bovine herpesvirus type 1 (BHV-1) causes acute febrile respiratory diseases (infectious bovine rhinotracheitis, IBR), decreased milk production, weight loss and abortion. Bovine ephemeral fever virus (BEFV) causes acute febrile respiratory disease, with pulmonary emphysema and pulmonary edema as the main signs. These viruses infect domesticated herds and lead to significant economic losses. In our previous study, an inactivated BHV-1 and BEFV bivalent vaccine was formulated with water-in-oil-in-water adjuvant, and vaccine efficacy was evaluated in guinea pigs. In this study, we evaluated the efficacy of the bivalent vaccine in cattle. Results showed that immunized cattle had a significantly higher level of total anti-BHV-1 antibody response (S/P ratio of 12.7) than the control group (S/P ratio of 0.07) 32weeks post-vaccination. The immunized group also showed higher neutralizing antibody levels against BHV-1 (SN=23.8) and BEFV (SN=24.6) than the control group (SN<2) 4 to 32weeks post-vaccination (p<0.05). In a BHV-1 challenge experiment, immunized cattle showed low virus shedding (101.2TCID50/mL) and a significant reduction in pathological lesion scores (p<0.01). In conclusion, the BHV-1+BEFV+w/o/w vaccine not only improved long-term antibody immune response but also significantly reduced clinical signs in a BHV-1 challenge experiment. Our approach may be feasible for developing an effective vaccine against bovine herpesvirus type 1 and bovine ephemeral fever virus.

Risk analysis and seroprevalence of bovine ephemeral fever virus in cattle in the Kingdom of Saudi Arabia.

Bovine ephemeral fever virus (BEFV) is an arthropod-borne rhabdovirus that causes disabling clinical signs and major economic losses in cattle and water buffalo. The disease is well documented in Asia, Africa, and the Middle East; however, the seroprevalence of BEFV in different regions and bovine breeds in the Kingdom of Saudi Arabia (KSA) is unknown. The aim of this study was to analyze risk factors which affect the prevalence of antibodies against BEFV in small herds of cattle in four geographical regions of KSA. A total of 1480 serum samples from non-BEFV vaccinated small herds of cattle were collected from the Eastern, Jizan, Qasim, and Riyadh regions (370 samples per region) during the summer of 2010. Serum neutralization test was used to detect antibodies against BEFV. There was a significant effect of region, breed, sex, and age on the seroprevalence of BEFV. Seropositive ratios were 18, 18, 26, and 12 % for the Eastern, Jizan, Qasim, and Riyadh regions, respectively (P = 0.00002); 23.2 % for dairy and 13.7 % for non-dairy breeds (P = 0.00004); 24.4 % for males and 14.6 % for females (P = 0.00004); and 15.4, 29.1, and 11.4 % for animals <1 year, 1-3 years, and >3 years, respectively (P < 0.001). Risk analysis showed a significant effect of different regions of KSA on the seroprevalence of BEFV. Host risk factors (age, sex, and breed) showed also a significant effect on the seroprevalence of BEFV. This indicates active circulation of this virus in small herds of cattle. Insect control strategies and BEFV vaccination programs during the spring are recommended to reduce the spread of BEFV and minimize subsequent economic losses as this is adopted in many enzootic countries.

Epidemiology and control of bovine ephemeral fever.

Bovine ephemeral fever (or 3-day sickness) is an acute febrile illness of cattle and water buffaloes. Caused by an arthropod-borne rhabdovirus, bovine ephemeral fever virus (BEFV), the disease occurs seasonally over a vast expanse of the globe encompassing much of Africa, the Middle East, Asia and Australia. Although mortality rates are typically low, infection prevalence and morbidity rates during outbreaks are often very high, causing serious economic impacts through loss of milk production, poor cattle condition at sale and loss of traction power at harvest. There are also significant impacts on trade to regions in which the disease does not occur, including the Americas and most of Europe. In recent years, unusually severe outbreaks of bovine ephemeral fever have been reported from several regions in Asia and the Middle East, with mortality rates through disease or culling in excess of 10-20%. There are also concerns that, like other vector-borne diseases of livestock, the geographic distribution of bovine ephemeral fever could expand into regions that have historically been free of the disease. Here, we review current knowledge of the virus, including its molecular and antigenic structure, and the epidemiology of the disease across its entire geographic range. We also discuss the effectiveness of vaccination and other strategies to prevent or control infection.

The protective effectiveness of an inactivated bovine ephemeral fever virus vaccine.

Bovine ephemeral fever (BEF) is an important viral disease of cattle. Despite the extensive use of inactivated vaccines for the prevention of BEF, a controlled study of their field effectiveness has never been performed. We conducted a large field effectiveness study of a BEF inactivated vaccine, during a large BEF outbreak. Neutralizing antibody titers measured in 385 heifers and calves 1 month after 2(nd) vaccination averaged 1:91.8 (CI95%=76.6-110). The effectiveness study enrolled 2780 cows in nine herds. In two herds cows vaccinated twice, 1 year before the outbreak and once 2-3 months before outbreak onset were compared with non-vaccinated cows. Average vaccine effectiveness of three vaccine doses compared to no vaccination was 47% (CI95%=34-57) in these herds. In two other herds cows vaccinated twice 1 year before the outbreak and twice again 2-3 months before outbreak were compared with cows vaccinated only twice 2-3 months prior to the outbreak. Average vaccine effectiveness of four doses compared to two doses was 49% (CI95%=25-65) in these herds. In five herds cows vaccinated twice 2-3 months before outbreak onset were compared with non-vaccinated cows. This vaccination schedule was shown to be non-effective (average effectiveness=2%, CI95%=-14-17). Milk production analysis on one of the effected herds, in which 56% vaccine effectiveness and an absolute reduction of 27% in morbidity were documented, revealed a net milk production loss of 175.9kg/sick cow (CI95%=127.9-223.9) and an average gain of 37kg for each vaccinated cow (CI95%=-3.6-77.7). This study indicates that despite the fact that two vaccine doses of the tested inactivated vaccine elicited high titers of neutralizing antibodies, partial protection was induced only when at least 3 doses were administrated before natural challenge.

Safety, immunogenicity and duration of immunity elicited by an inactivated bovine ephemeral fever vaccine.

Bovine ephemeral fever (BEF) is an economically important viral vector-borne cattle disease. Several live-attenuated, inactivated and recombinant vaccines have been tested, demonstrating varying efficacy. However, to the best of our knowledge, duration of immunity conferred by an inactivated vaccine has never been reported. In the last decade, Israel has faced an increasing number of BEF outbreaks. The need for an effective vaccine compatible with strains circulating in the Middle East region led to the development of a MONTANIDE™ ISA 206 VG (water-in-oil-in-water), inactivated vaccine based on a local strain. We tested the safety, immunogenicity and duration of immunity conferred by this vaccine. The induced neutralizing antibody (NA) response was followed for 493 days in 40 cows vaccinated by different protocols. The vaccine did not cause adverse reactions or a decrease in milk production. All cows [except 2 (6.7%) which did not respond to vaccination] showed a significant rise in NA titer of up to 1:256 following the second, third or fourth booster vaccination. Neutralizing antibody levels declined gradually to 1:16 up to 120 days post vaccination. This decline continued in cows vaccinated only twice, whereas cows vaccinated 3 or 4 times showed stable titers of approximately 1:16 for up to 267 days post vaccination. At least three vaccinations with the inactivated BEF vaccine were needed to confer long-lasting immunity. These results may have significant implications for the choice of vaccination protocol with inactivated BEF vaccines. Complementary challenge data should however be added to the above results in order to determine what is the minimal NA response conferring protection from clinical disease.

DNA sequence analysis of glycoprotein G gene of bovine ephemeral fever virus and development of a double oil emulsion vaccine against bovine ephemeral fever.

The surface glycoprotein G is considered as the major neutralizing and protective antigen of bovine ephemeral fever virus (BEFV). Comparison of the deduced amino acid sequence of G protein of BEFV isolates during the period 1984-2004 outbreaks in Taiwan showed amino acid substitutions in the neutralizing epitopes. All the isolates differ markedly in the neutralizing epitope at the same amino acid positions compared to the currently available killed vaccine strain (Tn73). Tn88128 strain isolated in 1999 showed the maximum variability of 12 amino acids, 5 amino acid in the neutralization epitope and 7 apart from, respectively. Combinations of both Tn88128 (1999) and commercially available vaccine strain (Tn73) were developed and its safety was evaluated in mice, guinea pigs, calves, and pregnant cows. None of the animals showed any adverse effect or clinical signs. Calves were immunized with commercial vaccine (Tn73) and, combined vaccine (Tn73 and Tn88128), respectively, with adjuvants such as Al-gel and water-in-oil-in-water (w/o/w) oil and PBS alone and challenged with Tn88128 strains. Except PBS administered animals, all the vaccinated animals showed protective immune response. However, animals immunized with combined vaccine plus w/o/w adjuvant elicited stronger neutralization antibodies and long lasting immunity compared to other vaccines.

Bovine ephemeral fever in Australia and the world.

Bovine ephemeral fever (BEF) is a disabling viral disease of cattle and water buffaloes. It can cause significant economic impact through reduced milk production in dairy herds, loss of condition in beef cattle and loss of draught animals at the time of harvest. Available evidence indicates clinical signs of BEF, which include bi-phasic fever, anorexia, muscle stiffness, ocular and nasal discharge, ruminal stasis and recumbency, are due primarily to a vascular inflammatory response. In Australia, between 1936 and 1976, BEF occurred in sweeping epizootics that commenced in the tropical far north and spread over vast cattle grazing areas of the continent. In the late 1970s, following several epizootics in rapid succession, the disease became enzootic in most of northern and eastern Australia. In Africa, the Middle East and Asia, BEF occurs as also epizootics which originate in enzootic tropical areas and sweep north or south to sub-tropical and temperate zones. The causative virus is transmitted by haematophagous insects that appear to be borne on the wind, allowing rapid spread of the disease. Bovine ephemeral fever virus (BEFV) has been classified as the type species of the genus Ephemerovirus in the Rhabdoviridae. It has a complex genome organization which includes two glycoprotein genes that appear to have arisen by gene duplication. The virion surface glycoprotein (G protein) contains four major antigenic sites that are targets for neutralizing antibody. An analysis of a large number of BEFV isolates collected in Australia between 1956 and 1992 has indicated remarkable stability in most neutralization sites. However, epitope shifts have occurred in the major conformational site G3 and these have been traced to specific mutations in the amino acid sequence. BEFV isolates from mainland China and Taiwan are closely related to Australian isolates, but some variations have been detected. Natural BEFV infection induces a strong neutralizing antibody response and infection usually induces durable immunity. Several forms of live-attenuated, inactivated and recombinant vaccines have been reported but with variable efficacy and durability of protection. The BEFV G protein is a highly effective vaccine antigen, either as a purified subunit or expressed from recombinant viral vectors.

Bovine ephemeral fever in Taiwan (2001-2002).

Bovine ephemeral fever (BEF), a vector-borne disease of cattle, is caused by the Ephemerovirus of the family Rhabdoviridae. In the past 40 years, Taiwan has had seven BEF epizootics, and we have previously reported the first five. This study summarizes the 2001 and 2002 epizootics; conducted case-control serologic studies on 10 herds involved in the 2001 epizootic; determined whether the recent BEF viruses have varied significantly; and discusses the relationship between epizootic patterns and possible variant BEF viruses. For mature cows that had received at least 2 doses of vaccine before the study, a negative correlation between the prevaccinated (the 3rd dose and after) serum neutralization antibody (SNA) titers and their postvaccinated peak rates was found. When prevaccinated SNA levels were at < or = 32, their postvaccinated SNA levels increased significantly faster (P<0.01) than for those at > or = 32. The glycoprotein gene of isolates from 1999, 2001, and 2002 had a 99.2-99.9% homology, without consistent amino acid variations in the neutralization sites. Phylogenetic analysis of Taiwanese isolates revealed 2 distinct clusters, the 1983-1989 and 1996-2002 isolates. Cross-neutralization tests confirmed the glycoprotein gene sequence analysis results. In conclusion, annual boosters at SNA levels > 32, at more than 2 doses, or at intervals shorter than 6 months are not advisable. The occurrence of frequent small epizootics implies the dominance of BEF virus over host immunity, but not a variant virus.