Experimental infection with bovine ephemeral fever virus and analysis of its antibody response cattle

The Development of Dual Vaccines against Lumpy Skin Disease (LSD) and Bovine Ephemeral Fever (BEF)

Dual vaccines (n = 6) against both lumpy skin disease (LSD) and bovine ephemeral fever (BEF) were constructed, based on the BEFV glycoprotein (G) gene, with or without the BEFV matrix (M) protein gene, inserted into one of two different LSDV backbones, nLSDV∆SOD-UCT or nLSDVSODis-UCT. The inserted gene cassettes were confirmed by PCR; and BEFV protein was shown to be expressed by immunofluorescence. The candidate dual vaccines were initially tested in a rabbit model; neutralization assays using the South African BEFV vaccine (B-Phemeral) strain showed an African consensus G protein gene (Gb) to give superior neutralization compared to the Australian (Ga) gene. The two LSDV backbones expressing both Gb and M BEFV genes were tested in cattle and shown to elicit neutralizing responses to LSDV as well as BEFV after two inoculations 4 weeks apart. The vaccines were safe in cattle and all vaccinated animals were protected against virulent LSDV challenge, unlike a group of control naïve animals, which developed clinical LSD. Both neutralizing and T cell responses to LSDV were stimulated upon challenge. After two inoculations, all vaccinated animals produced BEFV neutralizing antibodies ≥ 1/20, which is considered protective for BEF.

Endemic and Emerging Arboviruses in Domestic Ruminants in East Asia

Epizootic congenital abnormalities caused by Akabane, Aino, and Chuzan viruses have damaged the reproduction of domestic ruminants in East Asia for many years. In the past, large outbreaks of febrile illness related to bovine ephemeral fever and Ibaraki viruses severely affected the cattle industry in that region. In recent years, vaccines against these viruses have reduced the occurrence of diseases, although the viruses are still circulating and have occasionally caused sporadic and small-scaled epidemics. Over a long-term monitoring period, many arboviruses other than the above-mentioned viruses have been isolated from cattle and Culicoides biting midges in Japan. Several novel arboviruses that may infect ruminants (e.g., mosquito- and tick-borne arboviruses) were recently reported in mainland China based on extensive surveillance. It is noteworthy that some are suspected of being associated with cattle diseases. Malformed calves exposed to an intrauterine infection with orthobunyaviruses (e.g., Peaton and Shamonda viruses) have been observed. Epizootic hemorrhagic disease virus serotype 6 caused a sudden outbreak of hemorrhagic disease in cattle in Japan. Unfortunately, the pathogenicity of many other viruses in ruminants has been uncertain, although these viruses potentially affect livestock production. As global transportation grows, the risk of an accidental incursion of arboviruses is likely to increase in previously non-endemic areas. Global warming will also certainly affect the distribution and active period of vectors, and thus the range of virus spreads will expand to higher-latitude regions. To prevent anticipated damages to the livestock industry, the monitoring system for arboviral circulation and incursion should be strengthened; moreover, the sharing of information and preventive strategies will be essential in East Asia.

A SYBR green I-based quantitative RT-PCR assay for bovine ephemeral fever virus and its utility for evaluating viral kinetics in cattle

We developed a SYBR green I-based reverse-transcription quantitative PCR (RT-qPCR) assay for bovine ephemeral fever virus (BEFV). Analytical sensitivity of the assay was ~ 100 times higher than conventional RT-PCR. The precision of the RT-qPCR established for RNA standards was high, with intra-assay and inter-assay coefficients of variation of 0.23-0.89% and 0.23-1.02%, respectively. The test was highly specific for BEFV strains, with no cross-reactivity with other viruses of veterinary significance. The assay detected BEFV RNA as early as 1 d post-infection (dpi) and up to 7-8 dpi in the blood samples of experimentally infected cattle. The most stable reference gene, peptidylprolyl isomerase A (PPIA), was selected for the quantification of BEFV. Viral RNA loads reached peak level at 3-5 dpi and then decreased rapidly through 7-8 dpi. Our assay provides a reliable approach for the detection of BEFV in the early infection stage and for use in the profiling of BEFV kinetics in vivo.

Development of a quick dot blot assay for the titering of bovine ephemeral fever virus

Background

Bovine ephemeral fever virus (BEFV) causes fever and muscle stiffness in cattle, resulting in negative economic impact for cattle and dairy farms. During the manufacturing process of inactivated vaccine for virus control, it is important to determine the virus titer, but traditional methods such as plaque assay and TCID₅₀ assay require days of waiting time. We sought to develop a quick dot blot assay for BEFV titering.

Results

Three different kinds of BEFV antigens were prepared to raise primary antibodies for BEFV detection in dot blot assays: 1) purified BEFV particles, 2) Escherichia coli (E. coli)-expressed BEFV G1 region, and 3) E. coli-expressed BEFV N protein. Results showed that antibodies raised against purified BEFV particles can detect BEFV particles, but it also showed a high background level from the proteins of BHK-21 cells. Antibodies raised against E.coli-expressed BEFV G1 region could not detect BEFV particles in dot blot assays. Finally, antibodies raised against E.coli-expressed BEFV N protein detected BEFV particles with a high signal-to-noise ratio in dot blot assays.

Conclusions

E.coli-expressed N protein is a suitable antigen for the production of antiserum that can detect BEFV particles with a high signal-to-noise ratio. A dot blot assay kit using this antiserum can be developed as a quick and economical way for BEFV titering.

Electronic supplementary material

The online version of this article (10.1186/s12917-019-2059-6) contains supplementary material, which is available to authorized users.

Complete genome analysis of highly pathogenic bovine ephemeral fever virus isolated in Turkey in 2012

Relatively high prevalence and mortality rates of bovine ephemeral fever (BEF) have been reported in recent epidemics in some countries, including Turkey, when compared with previous outbreaks. A limited number of complete genome sequences of BEF virus (BEFV) are available in the GenBank Database. In this study, the complete genome of highly pathogenic BEFV isolated during an outbreak in Turkey in 2012 was analyzed for genetic characterization. The complete genome of the Turkish BEFV isolate was amplified by reverse transcription-polymerase chain reaction (RT-PCR) and sequenced. It was found that the complete genome of the Turkish BEFV isolate was 14,901 nt in length. The complete genome sequence obtained from the study showed 91-92% identity at nucleotide level to Australian (BB7721) and Chinese (Bovine/China/Henan1/2012) BEFV isolates. Phylogenetic analysis of the glycoprotein gene of the Turkish BEFV isolate also showed that Turkish isolates were closely related to Israeli isolates. Because of the limited number of complete BEFV genome sequences, the results from this study will be useful for understanding the global molecular epidemiology and geodynamics of BEF.

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.