The effect of bovine ephemeral fever on milk production

Finding potential inhibitors against RNA-dependent RNA polymerase (RdRp) of bovine ephemeral fever virus (BEFV): an in-silico study

The bovine ephemeral fever virus (BEFV) is an enzootic agent that affects millions of bovines and causes major economic losses. Though the virus is seasonally reported with a very high morbidity rate (80-100%) from African, Australian, and Asiatic continents, it remains a neglected pathogen in many of its endemic areas, with no proper therapeutic drugs or vaccines presently available for treatment. The RNA-dependent RNA polymerase (RdRp) catalyzes the viral RNA synthesis and is an appropriate candidate for antiviral drug developments. We utilized integrated computational tools to build the 3D model of BEFV-RdRp and then predicted its probable active binding sites. The virtual screening and optimization against these active sites, using several small-molecule inhibitors from a different category of Life Chemical database and FDA-approved drugs from the ZINC database, was performed. We found nine molecules that have docking scores varying between -6.84 to -10.43 kcal/mol. Furthermore, these complexes were analyzed for their conformational dynamics and thermodynamic stability using molecular dynamics simulations in conjunction with the molecular mechanics generalized Born surface area (MM-GBSA) scheme. The binding free energy calculations depict that the electrostatic interactions play a dominant role in the RdRp-inhibitor binding. The hot spot residues, such as Arg565, Asp631, Glu633, Asp740, and Glu707, were found to control the RdRp-inhibitor interaction. The ADMET analysis strongly suggests favorable pharmacokinetics of these compounds that may prove useful for treating the BEFV ailment. Overall, we anticipate that these findings would help explore and develop a wide range of anti-BEFV therapy.Communicated by Ramaswamy H. Sarma.

Hayes Yard virus: a novel ephemerovirus isolated from a bull with severe clinical signs of bovine ephemeral fever is most closely related to Puchong virus

Bovine ephemeral fever is a vector-borne disease of ruminants that occurs in tropical and sub-tropical regions of Africa, Asia and Australia. The disease is caused by a rhabdovirus, bovine ephemeral fever virus (BEFV), which occurs as a single serotype globally. Although several other closely related ephemeroviruses have been isolated from cattle and/or arthropods, only kotonkan virus from Nigeria and (tentatively) Mavingoni virus from Mayotte Island in the Indian Ocean have been previously associated with febrile disease. Here, we report the isolation of a novel virus (Hayes Yard virus; HYV) from blood collected in February 2000 from a bull (Bos indicus) in the Northern Territory of Australia. The animal was suffering from a severe ephemeral fever-like illness with neurological involvement, including recumbency and paralysis, and was euthanised. Histological examination of spinal cord and lung tissue identified extensive haemorrhage in the dura mata with moderate perineuronal oedema and extensive emphysema. HYV displayed cone-shaped morphology, typical of rhabdoviruses, and was found to be most closely related antigenically to Puchong virus (PUCV), isolated in 1965 from mosquitoes in Malaysia. Analysis of complete genome sequences of HYV (15 025 nt) and PUCV (14 932 nt) indicated that each has a complex organisation (3' N-P-M-G-G_NS-α1-α2-β-γ-L 5') and expression strategy, similar to that of BEFV. Based on an alignment of complete L protein sequences, HYV and PUCV cluster with other rhabdoviruses in the genus Ephemerovirus and appear to represent two new species. Neutralising antibody to HYV was also detected in a retrospective survey of cattle sera collected in the Northern Territory.

Endemic and emerging arboviral diseases of livestock in Nigeria: a review

Arthropod-borne viruses (arboviruses) are the largest biologic group of vertebrate viruses and constitute important emerging infectious disease agents globally. Arthropod transmission provides a way for viruses to cross species barriers since the same arthropod may bite animals that rarely or never come into close contact in nature. In Nigeria, arboviruses have, over several decades, caused severe diseases in livestock resulting in great economic losses and, sometimes, infection of humans leading to morbidity and mortality. In the present review, a computerized search of existing literature was conducted using the Google search engine and PubMed electronic database to identify and review relevant publications on arboviral diseases of livestock in Nigeria. The keywords used were 'arbovirus', 'arthropod-borne viral diseases' or 'livestock diseases' and 'Nigeria' while the Boolean operator 'OR' was used to combine and narrow the searches. Additional information was obtained by searching the veterinary libraries for journals not listed in the database. The available publications were thereafter reviewed and findings qualitatively described. Our findings revealed that although there were several studies on arboviruses and the livestock diseases they cause in Nigeria, most of such reports were made four to six decades ago, with only a few reported recently. Consequently, the true economic and public health impact of these diseases are likely to be underestimated, mainly due to under-reporting or lack of awareness of them. Thus, it is essential to update information on arboviral diseases in Nigeria in order to increase awareness of the diseases and facilitate their prompt identification and reporting. The importance of routine surveillance for arbovirus livestock diseases and sentinel herd monitoring as basis for development of an early warning and alert system to prevent future outbreaks is discussed.

Arbovirus infections of animals: congenital deformities, encephalitis, sudden death and blindness

Viruses from five different taxonomic families have been shown to be the cause of disease outbreaks in either domesticated or wild animals. These include viruses spread by both mosquitoes and biting midges from the genus Culicoides, especially C. brevitarsis. A number of arboviruses also present significant impediments to the international movement of live animals, semen and embryos.

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.

RNA interference targets arbovirus replication in Culicoides cells

Arboviruses are transmitted to vertebrate hosts by biting arthropod vectors such as mosquitoes, ticks, and midges. These viruses replicate in both arthropods and vertebrates and are thus exposed to different antiviral responses in these organisms. RNA interference (RNAi) is a sequence-specific RNA degradation mechanism that has been shown to play a major role in the antiviral response against arboviruses in mosquitoes. Culicoides midges are important vectors of arboviruses, known to transmit pathogens of humans and livestock such as bluetongue virus (BTV) (Reoviridae), Oropouche virus (Bunyaviridae), and likely the recently discovered Schmallenberg virus (Bunyaviridae). In this study, we investigated whether Culicoides cells possess an antiviral RNAi response and whether this is effective against arboviruses, including those with double-stranded RNA (dsRNA) genomes, such as BTV. Using reporter gene-based assays, we established the presence of a functional RNAi response in Culicoides sonorensis-derived KC cells which is effective in inhibiting BTV infection. Sequencing of small RNAs from KC and Aedes aegypti-derived Aag2 cells infected with BTV or the unrelated Schmallenberg virus resulted in the production of virus-derived small interfering RNAs (viRNAs) of 21 nucleotides, similar to the viRNAs produced during arbovirus infections of mosquitoes. In addition, viRNA profiles strongly suggest that the BTV dsRNA genome is accessible to a Dicer-type nuclease. Thus, we show for the first time that midge cells target arbovirus replication by mounting an antiviral RNAi response mainly resembling that of other insect vectors of arboviruses.

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.

Determination of the oral susceptibility of South African livestock-associated biting midges, Culicoides species, to bovine ephemeral fever virus

A total of 10 607 Culicoides midges (Diptera: Ceratopogonidae) were fed on either sheep or horse blood containing not less than 6.5 log10 TCID50/ml of bovine ephemeral fever virus (BEFV). Insects were collected during two consecutive summers from two distinct climatic areas. Two seed viruses, originating from either South Africa or Australia, were used separately in the feeding trials. Blood-engorged females were incubated at 23.5 degrees C for 10 days and then individually assayed in microplate BHK-21 cell cultures. Of the 4110 Culicoides that survived, 43% were C. (Avaritia) imicola Kieffer and 27% were C. (A.) bolitinos Meiswinkel. The remainder represented 18 other livestock-associated Culicoides species. Although BEFV was detected in 18.9% of midges assayed immediately after feeding, no virus could be detected after incubation. The absence of evidence of either virus maintenance or measurable replication suggests that most of the abundant livestock-associated Culicoides species found in South Africa are refractory to oral infection with BEFV. Future studies should be carried out using species of mosquitoes that are associated with cattle in the BEF endemic areas.

Akabane and bovine ephemeral fever virus infections

Akabane and bovine ephemeral fever viruses are exotic to the American continent. Both viruses are spread by insect vectors, and each causes disease of varying severity in food-producing animals. However, there are few other similarities between the agents and the diseases that they cause. They do not share the same insect vectors, the mammalian host range is different, and the clinical manifestations of virus infection vary markedly. Akabane virus is a cause of severe congenital defects, but adult animals show no signs of infection. In contrast, bovine ephemeral fever virus causes a febrile illness affecting mainly mature animals. If introduced to North America, it is probable that there would be significant economic losses, at least until endemic virus transmission patterns were established. Subsequently, it is likely that there would be patterns of alternate disease outbreaks followed by interepidemic periods in which there is a minor clinical effect.

Epidemiological investigations of outbreaks of bovine ephemeral fever in Israel

In two epidemics of bovine ephemeral fever (BEF) in Israel, one in 1990 and one in 1999, the virus was probably carried by vectors transported by air currents across the Rift Valley and through the Red Sea trough. The disease broke out under optimal ecological conditions among vulnerable cattle populations and spread rapidly; it developed in the spring and summer and ended soon after the daily average ambient temperature fell below 16 degrees C in late autumn. The proportion of herds affected reached 78.4 and 97.7 per cent in 1990 and 1999, respectively. The highest rates of incidence, morbidity and mortality were recorded in dairy cattle herds in the Jordan Valley, the initial focus of the outbreaks, with a morbidity of 20 and 38.6 per cent in 1990 and 1999, respectively, and mortality among the affected animals of 2 and 8.6 per cent in 1990 and 1999, respectively. In 1991, the disease recurred sporadically in the central and southern regions of Israel in only three herds, but in 2000 the disease returned on an epidemic scale, and 85 per cent of herds were affected, with morbidity and mortality rates of 4-3 and 0-3 per cent, respectively. In the 1999 epidemic, the morbidity rate decreased from 38-6 per cent on average in the Jordan Valley to 12.8 per cent in the inner valleys and 5.3 per cent on the Mediterranean coastal plain, but the mortality rate increased from 8-6 per cent in the Jordan Valley to 14-3 per cent in the inner valleys, and to 28 per cent on the Mediterranean coastal plain, where the outbreak declined. An average of 2-7 per cent of the animals experienced a second attack of the disease two to six weeks later. The epidemic in 2000 was milder and shorter than that in 1999. All the cattle affected in both outbreaks were more than three months old. The vector(s) is not known for certain but the available evidence indicates that mosquitoes, and not Culicoides species, are the natural vectors of BEF virus in Israel.

Bovine ephemeral fever: a review

Bovine ephemeral fever is a viral disease of cattle and buffaloes besides subclinical involvement of a variety of ruminant species. The subtropical and temperate regions of Africa, Asia and Australia have experienced the major epidemic of the bovine ephemeral fever but the occurrence in the tropics can not be overlooked. Although the substantial role played by the vectors viz., mosquitoes and culicoides in bovine ephemeral fever perpetuation and dissemination, other vector involvement if any should be extensively studied. The clinical severity of the disease is not apparent and the mortality is low. However, high morbidity, enormous economic losses in terms of significant reduction in production, disruption of national and international trade and finally a variety of complications resulting from the disease have drawn appreciable attention from the researchers around the world to resolve the unsolved questions in this area. In this review, detailed informations of all the aspects of the disease has been provided in a simple, lucid and easily understandable manner.

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.

Studies on the pathogenesis of bovine ephemeral fever. IV: A comparison with the inflammatory events in milk fever of cattle

The study of ephemeral fever in cattle has defined a range of haematological and biochemical changes in blood which are characteristic of an inflammatory response. One of the clinical signs of ephemeral fever, a temporary paralysis reversible by treatment with calcium borogluconate, is similar to that in milk fever (parturient paresis), a disease of multiparous dairy cows. Three separate groups of cows were studied. Four multiparous cows were observed and sampled repeatedly during calving, three similar cows and one cow calving for the first time in a dairy herd were sampled daily before and after calving; and, in other dairy herds, seven cows with milk fever were sampled during illness. One of the cows under repeated observation during calving developed milk fever. The results showed that all the inflammatory indicators in blood were present in the multiparous cows at calving and that these were essentially similar to those established in ephemeral fever. The similarities in the four cows sampled repeatedly during the periparturient period were: a rectal temperature rise of 1 to 1.2 degrees C; rise in circulating neutrophils to peaks between 5700 and 11200 l-6; disappearance of eosinophils for 1 day; hypocalcaemia (plasma Ca < 2.0 mM l-1); fall of plasma zinc to low levels immediately after calving (plasma Zn < 500 micrograms l-1); fall of inorganic phosphate (plasma P < 0.9 mM l-1); rises in copper (plasma Cu > 1000 micrograms l-1) and plasma fibrin to > 8.75 g l-1. Plasma glucose peaked at calving between 5.7 and 8.9 mM l-1 then fell to levels ranging between 3.4 and 3.8 mM l-1. Plasma iron rose in one cow to 1220 micrograms l-1, was unchanged in one cow and fell in the other two to 440 and 860 micrograms l-1 respectively. The three multiparous cows which were sampled daily and calved normally showed similar haematological, macro and micromineral changes and fibrin response as did the seven milk fever cases. In the periparturient period, milk fever cows differed from multiparous cows calving normally, in degree but not in kind, of inflammatory response. It is postulated that an inflammatory event occurs in the periparturient period of multiparous cows which partially accounts for the falls in plasma calcium. This can precipitate a paralysis and other hypocalcaemic signs similar to that seen in acute ephemeral fever.

Preliminary observations on the epidemiology of bovine ephemeral fever in China

Bovine ephemeral fever (BEF) is a viral disease of cattle and water buffalo recognised for the first time in China in 1955. The disease has been endemic in south China with 13 epidemics since 1955, seven epidemics reaching central China and one extending into north-east China (40 degrees N). The outbreaks have been seasonal with all occurring in the warmer summer/autumn months of June to October when possible insect vectors are active. Reports of clinical disease were confirmed as BEF by the detection of virus-neutralising antibody. The economic impact of the disease includes loss of milk production, late-term abortions and the loss of draught animal power.

Bovine ephemeral fever

Ephemeral fever remains a viral disease of considerable importance to many countries including Australia. The virus has been only partly characterised and still awaits final classification. Although BEF virus was first thought to contain 6 structural proteins there is increasing evidence to suggest that it contains the 5 proteins characteristic of the Rhabdoviridae. Although BEF is thought to be arthropod borne, the vector has yet to be identified but it is clear from the distribution of BEF that more than one vector is capable of transmitting the disease. Despite rigorous investigation of the clinical signs and the pathology of ephemeral fever, little progress has been made on the pathogenesis of the disease. This has been partly due to the difficulty of propagating BEF virus in vitro and the inability to define the site of replication. However, there is mounting evidence to suggest that BEF is immunopathologic in nature and that the clinical expression of the disease is influenced by the release of one or more mediators of inflammation. The disease is characterised by a number of haematological and biochemical changes and early and prolonged treatment with phenylbutazone is capable of reversing a number of these changes. The intravenous administration of calcium can now be considered a justifiable addition to the treatment regimen together with prolonged phenylbutazone therapy. The vaccines currently available are prepared from either live attenuated or killed virus and may be less than reliable. There appears to be a need for a reliable, inexpensive, cold-chain independent alternative vaccine.