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 recombinase polymerase amplification combined with lateral-flow dipstick assay for detection of bovine ephemeral fever virus

Bovine ephemeral fever virus (BEFV), identified as the causative pathogen of bovine ephemeral fever (BEF), is responsible for increasing numbers of epidemics/outbreaks and has a significant harmful effect on the livestock industry. Therefore, a rapid detection assay is imperative for BEFV diagnosis. In this study, we described the development of lateral-flow dipstick isothermal recombinase polymerase amplification (LFD-RPA) assays for detection of BEFV. RPA primers and LF probes were designed by targeting the specific G gene, and the amplification product can be visualized on a simple lateral flow dipstick with the naked eyes. The amplification reaction was performed at 38 °C for 20 min and LFD incubation time within 5 min. The detection limit of this assay was 8 copies per reaction, and there was no cross-reactivity with other bovine infectious viruses such as bovine viral diarrhea virus, infectious bovine rhinotracheitis virus, bovine respiratory syncytial virus, bovine coronavirus, bovine parainfluenza virus type 3, bovine vesicular stomatitis virus. In addition, the assay was performed with total 128 clinical specimens and the diagnostic results were compared with conventional RT-PCR, real-time quantative(q) PCR. The result showed that the coincidence rate of BEFV LFD-RPA and real-time qPCR was 96.09% (123/128), which was higher than conventional RT-PCR. The RPA combined with LFD assay probably provides a rapid and sensitive alternative for diagnosis of BEFV infections outbreak.

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RPA combined with LFD assay was developed first time to detect BEFV.

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The detection from cDNA could be completed within 30 min and be easily visualized with the naked eyes.

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The RPA combined with LFD assay probably provides a alternative for diagnosis of BEFV.

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.

Development of a reliable assay protocol for identification of diseases (RAPID)-bioactive amplification with probing (BAP) for detection of bovine ephemeral fever virus

A rapid, sensitive, and specific assay, RAPID-BAP assay, was developed to detect and quantify the G protein-encoding gene of bovine ephemeral fever virus (BEFV). This new technique uses a nested PCR and magnetic bead-based DNA probing assay. The optimal conditions for the assay were examined. By applying a nested PCR, a minimum of 1 copy/mul of the BEFV plasmid DNA could be detected by the assay. The optimal hybridization conditions at 50 degrees C in 5x SSC and 0.5% SDS with a 20-min incubation allowed clear discrimination between negative and positive controls. The assay was also highly specific as all negative controls failed to show any positive detection. The diagnostic sensitivity of the RAPID-BAP assay, real-time RT-PCR, and conventional RT-PCR in the detection of 34 clinical blood samples suspected to have BEFV infections were 72.73, 36.36, and 18.18%, respectively. The results indicated that the RAPID-BAP assay developed in this study was more sensitive than the conventional RT-PCR and real-time RT-PCR assays for the detection of BEFV. The novel RAPID-BAP assay is an excellent diagnostic tool with high sensitivity, specificity, and fast turnaround time.

A real-time RT-quantative(q)PCR for the detection of bovine ephemeral fever virus

A quantitative reverse-transcriptase real-time PCR assay, using TaqMan chemistry, for detecting bovine ephemeral virus (BEFV) is described. Available G gene sequences of viral RNA were aligned, and primers and probes were designed to recognize the virus. To quantitate the viruses, cDNA containing the real-time amplicon was prepared with a forward primer carrying the T7 promoter sequences. Run-off transcription from the T7 promoter amplicon template was used to prepare cRNA. Ten-fold dilutions of the run-off viral transcript were used as templates for the reaction in which they served as standards to quantitate unknown viral samples. By using this system it was shown that as few as 10-100 copies of a viral genome could be detected.

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.

Epizootics of bovine ephemeral fever on dairy farms in Saudi Arabia

In 1990 and 1996, field veterinarians suspected the clinical occurrence of bovine ephemeral fever among dairy and conventional cattle in different regions of Saudi Arabia. The disease has a seasonal occurrence; it begins in early summer (May) and ends in late autumn (November). The mortality rate is low: 0.3% to 0.6%. The morbidity rate ranged from 5% to 61% within the different age groups of one affected herd in the 1996 outbreaks and from 3.4% to 19% among four affected herds in the 1990 outbreaks. A sudden sharp drop in milk production occurred in lactating animals, some of which had become dry by the end of the outbreaks. Trials to isolate the causative virus in cell culture and in baby mice were unsuccessful. Serum neutralisation tests, which used a cell culture-adapted vaccine strain of bovine ephemeral fever virus as an antigen, revealed the presence of specific antibodies with significantly increased titres in the convalescent sera of affected animals. In addition, the testing of paired sera from non-affected heifers and from both dry and milking cows, performed twice, with an interval of 21 days, revealed the presence of neutralising antibodies. In the 1990 outbreaks, comparative serological studies indicated a high percentage (67.5%; 27/40) of seropositive animals in herds in which bovine ephemeral fever had been previously suspected. No antibodies were detected in animals of herds which had no recorded clinical history of bovine ephemeral fever. Following serological confirmation of the prevalence of bovine ephemeral fever in Saudi Arabia, some dairy farms started using a live imported vaccine to control the disease. This study discusses the epizootiological findings in regard to bovine ephemeral fever, as well as its economic impact on four affected dairy farms in 1990. In addition, the authors evaluate the efficacy of immunoprophylaxis in another dairy herd during the same outbreaks.

Epidemiology of bovine ephemeral fever virus infection in Taiwan

Sick animals with excessive nasal discharges and protruding tongue as a result of dyspnea were observed in the August of 1996. Eight strains of BEF virus were isolated from heparinized blood samples of the affected cattle. Most of the affected cattle were difficult to be treated and had a poor prognosis. A total of 516 farms in the 9 districts of Taiwan were affected in 1996. Among a population of 110,247 dairy cattle, 14,993 (13.6%) cattle were found to be clinically ill. During the epidemic, 1,685 (11.3%) affected cattle were culled or dead after the onset of the disease. Furthermore, a strain of Ibaraki virus was isolated from the blood sample of a sick cattle that showed pyrexia, labored respiration and solitary behavior in the affected farm. The cattle with Ibaraki virus infection had typical symptoms of BEF at the early stage of the disease, but neither stomatitis nor pharyngoesophageal paralysis was observed at the onset of the disease. The outbreak was presumably brought about by the low level or non-immune status of a large cattle population due to the negligence of BEF vaccination. Therefore, the disease easily recurred in Taiwan after a typhoon episode in the August of 1996, which resulted in the proliferation of biting midges in the field. No difference in the antigenicty was found between the new and the previous isolates of BEF virus. As analyzed by cross neutralization test, the isolated BEF viruses showed no relationship to the Kimberley and Berrimah viruses that were isolated from the blood of cattle and related to BEF virus in Australia. We have tried to advise farmers that they must vaccinate their cattle annually to prevent BEF outbreak in the future.