Serological reactions in sheep and cattle experimentally infected with three Australian isolates of bluetongue virus

Serums from 103 sheep and 24 cattle experimentally infected with one of 3 serotypes of bluetongue virus isolated in Australia were tested for antibody to bluetongue virus in the serum neutralisation test and the agar gel diffusion precipitin test. Antibody to bluetongue virus was first detected by these tests 8 to 10 days after intravenous infection in 4 sheep that were bled daily for serum analysis. The agar gel diffusion test failed to detect antibody in 28% (29/103) of sheep which had seroconverted in the serum neutralisation test. A further 7% (7/103) of sheep serums were negative in both tests 14 to 22 d after infection. Both tests detected antibody to bluetongue virus in all cattle serums by 10 days after detection of viraemia. In comparison with the intravenous route of infection, extended prepatent periods for the commencement of viraemia resulting from intradermal, subcutaneous and intrauterine routes of infection in the cattle caused corresponding delays in the detection of antibody. For example, one cow that was infected by intrauterine inoculation did not become viraemic until 22 d after inoculation and antibody was not detected until 32 d after inoculation.     

Anti-idiotype technique: an alternative approach for immunodiagnosis of bluetongue

In development of a bluetongue alternative immunodiagnostic rest, the polyclonal anti-idiotypic antibodies were generated by the sequential immunization of rabbits with three monoclonal antibodies to VP7 of bluetongue virus. The anti-idiotypic antibodies recognize the idiotypes that are located within or near the antigen-combining sites and are associated with both heavy and light chains of the antibodies to VP7 of bluetongue virus. The anti-idiotypic antibodies mimic the VP7 antigen by recognizing the anti-VP7 antibodies from cattle and sheep that were infected with various serotypes of bluetongue viruses. The results indicate that the rabbit anti-idiotypic antibodies may be used as surrogate antigen in serological assays to detect the antibodies from different species of animals infected with various serotypes of bluetongue viruses.     

EPIZOOTIOLOGY OF BLUETONGUE: THE SITUATION IN THE UNITED STATES OF AMERICA

Bluetongue was first reported in the United States in 1948 in sheep in Texas. The virus has now been isolated from sheep in 19 States. When the disease first occurs in a flock, the morbidity may reach 50 to 75% and mortality 20 to 50%. In subsequent years, the morbidity may be only 1 to 2% with very few deaths. Difference in breed susceptibility has not been observed. Natural bluetongue infection has not been observed in Angora or dairy goats. Bluetongue virus was first isolated from cattle, in Oregon, in 1959. The virus has now been isolated from cattle in 13 States. In cattle, the disease is usually inapparent but can cause mild to severe clinical disease and neonatal losses. Natural clinical bluetongue has also been reported in bighorn sheep, exotic ruminants in a zoo, mule deer, and white-tailed deer. Serological evidence of exposure to the virus has also been found in other species of ruminants in the wild. Inoculation of virulent bluetongue virus, vaccine virus, or natural disease can cause congenital deformities and neonatal losses in calves, lambs, and white-tailed deer fawns. Culicoides is considered the important insect vector of bluetongue. The virus has also been isolated from sheep keds and cattle lice. U.S. field strains of the virus fit into four serologic groups. No cross reactions were found between bluetongue and epizootic haemorrhagic disease of deer viruses. Cattle are considered significant virus reservoirs. It is necessary to use washed erythrocytes, rather than whole blood, and to inoculate susceptible sheep, rather than embryonated chicken eggs, to detect longer-term viraemia in cattle.     

Bluetongue in exotic sheep in Cameroon

Bluetongue virus (BTV) was diagnosed in the Animal Research Institute, Mankon, Bamenda from tissue samples collected from five sheep of exotic breeds which had died of suspected bluetongue in a series of outbreaks between June and October 1982. Five serotypes BTV 1, 4, 5, 12 and 14 were isolated during the period mentioned. Similar disease occurred during June of the following year and BTV type 16 was isolated from a spleen sample from a dead sheep.     

Serological studies of two additional Australian blue-tongue virus isolates CSIRO 154 and CSIRO 156

Serological surveys revealed that some cattle in northern Australia possessed bluetongue virus (BTV) group-reactive (agar gel diffusion precipitin, AGDP, and complement-fixing, CF) antibodies, but not serum neutralizing (SN) antibodies, to BTV20, a new type previously found in Australia. Attempts were made during 1979 to isolate viruses causing these reactions. There was one isolate of a virus (CSIRO 154) and eight isolates of another virus (CSIRO 156) made from the blood of healthy cattle in the Northern Territory. These viruses could not be distinguished from BTV20 by AGDP, CF or fluorescent-abtibody tests and hence were designated members of the bluetongue serogroup. Serotyping was carried out using the plaque-inhibition and plaque-reduction SN tests. CSIRO 156 virus could not be distinguished from BTV1 by any of the SN tests and it was concluded that it was an Australian isolate of the BTV1 serotype. CSIRO 154 virus was found to be related to, but not identical with, BTV6. It is probably not one of the known 20 BTV serotypes and may represent a new BTV serotype. None of the three Australian BTV isolates is known to cause clinical disease in sheep or cattle under natural conditions, and biochemical comparisons with the African BTV serotypes may show differences not revealed by these serological studies.     

Isolation of an exotic serotype of bluetongue virus from imported cattle in quarantine.

In 1980, 60 zebu cattle from Brazil were admitted into quarantine in Florida for 150 days. During the 30 days between their last test in Brazil and their first test in Florida, four animals developed antibody to bluetongue virus detectable by agar gel immunodiffusion test. Within 62 days after arrival in Florida, three more seroconverted and one more was positive by the 86th day. Virus neutralizing titers of serums from the first four cattle were highest against bluetongue virus serotype 4 and 20; both of these serotypes are exotic to the United States. A bluetongue virus serotype 4 was isolated from one of these animals. The eight positive reactors were slaughtered; the other 52 cattle, which did not develop detectable antibody titers to bluetongue virus, were released into the United States.     

A study on bluetongue virus infection in Saudi Arabia using sentinel ruminants

Four sentinel herds comprising cattle, sheep and goats were established at various localities in Saudi Arabia. Maternal bluetongue antibodies were detected in all four sentinel herds but disappeared in 4-6 months, immediately followed by seroconversion in all. Serological results indicated that the animals were recently exposed to BT virus serotypes 10, 12, 15 and 20. The epidemiology of the disease in Saudi Arabia is discussed.     

Recovery of dual serotypes of bluetongue virus from infected sheep and cattle

Dual serotypes of bluetongue virus (BTV) were recovered from field-collected samples of sheep and cattle blood. Two sheep, each infected with both BTV serotypes 10 and 17, were found in a flock with bluetongue disease associated with these two serotypes. One sheep infected with BTV serotypes 11 and 17 was found in a second flock; it was the only viremic sheep detected and was clinically ill. Dual serotype infections of one beef and two dairy cattle were found in three geographically separate herds; mixtures recovered were of BTV serotypes 10 and 17 and serotypes 11 and 17. Clinical signs of illness were absent in the cattle in two herds, but severe conjuctivitis was seen in several cows in a third herd, including the cow with a dual serotype infection (BTV 11 and 17). Two of the cattle with dual infections had no serological evidence of BTV as determined by the agar gel precipitin test; serum was not available from the other cow with a dual serotype infection. The significance of dual infections and immune tolerance are discussed.     

Serological studies of Australian and Papua New Guinean cattle and Australian sheep for the presence of antibodies against bluetongue group viruses

Following isolation of a virus (CSIRO19) from insects in Australia and its identification as bluetongue virus serotype 20 (BTV20), a nationwide survey of antibodies in cattle and sheep sera was undertaken. Initial studies using the serum neutralization (SN) test showed that the distribution of BTV20 antibodies in cattle was confined to the northern part of Australia. Group-reactive antibody tests (agar gel diffusion precipitin, AGDP, and complement-fixation, CF) showed group-reactive cattle sera south of the BTV20 zone (northern Australia), and southwards from Queensland to New South Wales. Very few group-reactive sheep sera (45 out of 16213) were found and these were of doubtful epidemiological significance. Some of these BTV group-reactive, BTV20-negative, sera were tested in SN tests against BTV1 to 17 and Ibaraki (IBA) virus. The results indicated that BTV1, or a closely related orbivirus, was active in cattle in Queensland, northern Western Australia, and New South Wales, and that antibody to BTV15 was present in some of the cattle sera in northern Western Australia and the Northern Territory. Antibody to IBA virus was present in some cattle sera in Queensland, northern Western Australia and New South Wales. SN antibody titres ?60 were also found to a number of other BTV serotypes in cattle sera in northern Western Australia and Queensland (principally, BTV2 and BTV7). Low level reactions were commonly observed against these and a number of other BTV serotypes, often in the same serum samples. Further, 22% of the group-reactive cattle sera did not react with any of the viruses in the SN tests. Such results were difficult to interpret in terms of known Australian BTV or BTV-related isolates.     

Clinical syndromes associated with the circulation of multiple serotypes of bluetongue virus in dairy cattle in Israel

From 2008 to 2011, seven distinct bluetongue virus (BTV) serotypes (BTV-2, BTV-4, BTV-5, BTV-8, BTV-15, BTV-16 and BTV-24) have been identified to be circulating in diseased sheep and cattle in Israel. This paper describes the array of clinical manifestations caused by BTV in cattle in Israel. Each set of clinical manifestations has been categorised as a syndrome and six distinct clinical syndromes have been observed in dairy cattle: 'footrot-like syndrome', 'sore nose syndrome', 'subcutaneous emphysema syndrome', 'red/rough udder syndrome', 'bluetongue/epizootic haemorrhagic disease systemic syndrome' and 'maladjustment syndrome'.     

Spatial analysis of seroconversion of sentinel cattle to bluetongue viruses in Queensland

Objective To assess quantitatively the spatial distribution of seroconversion of Queensland cattle to bluetongue viruses.
Design A sentinel herd study. Sample population Sixty-nine sentinel herds at 30 locations.
Procedure Spatial clustering of seroconversion to blue-tongue viruses was investigated during the period from 1990 to 1994.
Results Seroconversion to only two bluetongue virus serotypes, 1 and 21, was observed. The 14 herds, in which seroconversion to bluetongue virus serotype 1 was detected, were located only along the eastern coastal and subcoastal region of Queensland, and were significantly (P < 0.05) clustered. Locations at which seroconversion to serotype 21 was detected, were not significantly clustered. The results generally agree with field observations, except for the failure to detect seroconversion to bluetongue viruses in north-western Queensland.
Conclusion Bluetongue infection of cattle in north-western Queensland may be temporally sporadic. The dominance of serotype 1 in the Queensland cattle population may be the result of differential transmission by potential vector species. Long-term surveillance programs are important for defining disease status of animal populations.     

Replication of bluetongue virus and epizootic hemorrhagic disease virus in pulmonary artery endothelial cells obtained from cattle,sheep, and deer

OBJECTIVE: To compare replication of bluetongue virus (BTV) and epizootic hemorrhagic disease virus (EHDV) in pulmonary artery endothelial cells (ECs) obtained from juvenile cattle, sheep, white-tailed deer (WTD; Odocoileus virginianus), and black-tailed deer (BTD; O hemionus columbianus). SAMPLE POPULATION: Cultures of pulmonary artery ECs obtained from 3 cattle, 3 sheep, 3 WTD, and 1 BTD. PROCEDURE: Purified cultures of pulmonary artery ECs were established. Replication, incidence of infection, and cytopathic effects of prototype strains of BTV serotype 17 (BTV-17) and 2 serotypes of EHDV (EHDV-1), and (EHDV-2) were compared in replicate cultures of ECs from each of the 4 ruminant species by use of virus titration and flow cytometric analysis. RESULTS: All 3 viruses replicated in ECs from the 4 ruminant species; however, BTV-17 replicated more rapidly than did either serotype of EHDV. Each virus replicated to a high titer in all ECs, although titers of EHDV-1 were significantly lower in sheep ECs than in ECs of other species. Furthermore, all viruses caused extensive cytopathic effects and a high incidence of cellular infection; however, incidence of cellular infection and cytopathic effects were significantly lower in EHDV-1-infected sheep ECs and EHDV-2-infected BTD ECs. CONCLUSIONS AND CLINICAL RELEVANCE: There were only minor differences in replication, incidence of infection, and cytopathic effects for BTV-17, EHDV-1, or EHDV-2 in ECs of cattle, sheep, BTD, and WTD. It is not likely that differences in expression of disease in BTV- and EHDV-infected ruminants are attributable only to species-specific differences in the susceptibility of ECs to infection with the 2 orbiviruses.     

Vaccines against bluetongue in Europe

After the incursion of bluetongue virus (BTV) into European Mediterranean countries in 1998, vaccination was used in an effort to minimize direct economic losses to animal production, reduce virus circulation and allow safe movements of animals from endemic areas. Vaccination strategies in different countries were developed according to their individual policies, the geographic distribution of the incurring serotypes of BTV and the availability of appropriate vaccines. Four monovalent modified live virus (MLV) vaccines were imported from South Africa and subsequently used extensively in both cattle and sheep. MLVs were found to be immunogenic and capable of generating strong protective immunity in vaccinated ruminants. Adverse side effects were principally evident in sheep. Specifically, some vaccinated sheep developed signs of clinical bluetongue with fever, facial oedema and lameness. Lactating sheep that developed fever also had reduced milk production. More severe clinical signs occurred in large numbers of sheep that were vaccinated with vaccine combinations containing the BTV-16 MLV, and the use of the monovalent BTV-16 MLV was discontinued as a consequence. Abortion occurred in <0.5% of vaccinated animals. The length of viraemia in sheep and cattle that received MLVs did not exceed 35 days, with the single notable exception of a cow vaccinated with a multivalent BTV-2, -4, -9 and -16 vaccine in which viraemia persisted at least 78 days. Viraemia of sufficient titre to infect Culicoides insects was observed transiently in MLV-vaccinated ruminants, and natural transmission of MLV strains has been confirmed. An inactivated vaccine was first developed against BTV-2 and used in the field. An inactivated vaccine against BTV-4 as well as a bivalent vaccine against serotypes 2 and 4 were subsequently developed and used in Corsica, Spain, Portugal and Italy. These inactivated vaccines were generally safe although on few occasions reactions occurred at the site of inoculation. Two doses of these BTV inactivated vaccines provided complete, long-lasting immunity against both clinical signs and viraemia, whereas a single immunization with the BTV-4 inactivated vaccine gave only partial reduction of viraemia in vaccinated cattle when challenged with the homologous BTV serotype. Additional BTV inactivated vaccines are currently under development, as well as new generation vaccines including recombinant vaccines.     

Serologic responses of calves to sequential infections with epizootic hemorrhagic disease virus serotypes

Six calves were inoculated with 1 of 2 North American serotypes of epizootic hemorrhagic disease virus (EHDV) and then inoculated with the second serotype 16 weeks later. One calf did not develop an immune response to EHDV after primary inoculation and was removed from the study. Viremia after primary inoculation was transient. Although each infected calf developed a high serum neutralizing antibody titer to EHDV, at no time after inoculation with one or both viruses was antibody detected that neutralized any US serotypes of bluetongue virus. After exposure to both serotypes of EHDV, 4 of 5 calves developed antibodies that cross-reacted with group-specific bluetongue virus antigens.     

Antibodies against certain bluetongue and epizootic haemorrhagic disease viral serotypes in Indonesian ruminants.

The orbiviruses contain several important viruses of livestock including bluetongue (BT) and epizootic haemorrhagic disease of deer (EHD) which share some group antigens. Preliminary screening of sera for antibodies to orbiviruses by the agar gel immunodiffusion (AGID) test has previously revealed widespread infections with the BT group in Indonesia. However serum neutralization (SN) tests give a more accurate estimate of exposure to each serotype in the BT and EHD groups, and in this study were applied to sera that had reacted previously in the AGID test. Five different serotypes of BT and one serotype of EHD virus were studied. Reactors to BT serotype 20 were the most prevalent, followed by EHD type 5 and BT types 21, 12, 1 and 17. Antibodies against BT serotype 20 were present in cattle, buffaloes, goats and sheep, but were most common in buffaloes. Buffaloes showed the highest exposure to the BT serotypes tested. Antibody to EHD type 5 occurred most frequently in cattle. Antibodies against all BT and EHD serotypes tested were found in buffaloes and cattle while goats had antibodies against BT types 20, 21 and EHD type 5 and sheep had antibodies only against BT type 20.     

Infection of cattle in Queensland with bluetongue viruses: 1. prevalence of antibodies

SUMMARY A survey of nearly 20 000 cattle in Queensland was conducted to describe the prevalence and distribution of infection by serotypes of bluetongue virus. The overall prevalence of serum antibodies to one or more bluetongue viruses was 8.7% (95% confidence interval 8.3 to 9.1). Sera from cattle contained neutralising activity against 2 serotypes, 1 and 21. No evidence was found of infection with other serotypes previously isolated in Australia. The overall prevalence of serotype 1 antibodies was 7.7% (95% CI 7.3 to 8.0) and the prevalence of serotype 21 antibodies was 3.3% (95% CI 3.1 to 3.6). The prevalence of serotype 1 antibodies was significantly (P < 0.05) higher than that of serotype 21 in every region of the State, except in the central highlands and south-west Queensland. Overall, 3 significantly (P < 0.05) different zones of prevalence were found: high prevalence (> 20%) in far north Queensland, moderate (5 to 20%) in north-west, northern and southern coastal Queensland, and low (< 5%) in the central highlands, Darling Downs and south-west Queensland.     

Serological differentiation of five bluetongue virus serotypes in indirect ELISA.

The serological reactivity in indirect ELISA of five different bluetongue virus (BTV) serotypes (4, 10, 15, 16 & 20) was compared using polyclonal antisera raised against virus particles and an outer structural protein, VP2. Rabbit and sheep antisera against BTV-10 produced higher ELISA values with their homologous antigens than with heterologous serotypes. A hyperimmune rabbit serum specific for virus particles was able to distinguish heterologous serotypes from each other, but a sheep serum from an infected animal was not. An antiserum directed against VP2, the protein responsible for serotype specificity in neutralization tests, was not serotype-specific in ELISA and cross-reacted with other serotypes. The discriminatory ability of a BTV-4 antiserum was improved by cross-absorption with heterologous antigens. This greatly reduced the ELISA signals with heterologous serotypes and produced an antiserum that was effectively serotype-specific.     

Arboviruses recovered from sentinel livestock in northern Australia

Over 700 arboviruses were recovered between 1981 and 1987 from the blood of sentinel livestock near Darwin. Twenty-three isolates were made from sheep, goats, swamp buffalo (Bubalus bubalis) and horses, and the remainder were from cattle. The isolates have been typed as 27 separate viruses belonging to the bluetongue, epizootic haemorrhagic disease, Palyam, Simbu, bovine ephemeral fever, Tibrogargan and alphavirus groups. Ten of these viruses have not been isolated elsewhere in Australia and four have been isolated only in Darwin. Considerable annual variations in virus activity and in the durations of detectable viraemia were observed.     

The immunological response to intact and dissociated blue-tongue virus in mice.

Antigenic fractions of bluetongue virus were separated by ultracentrifugation in Tris-buffered CsCl gradients at pH 6, 7 or 8 and the bluetongue virus polypeptide composition of the bands isolated from these gradeints was monitored by polyacrylamide gel slab electrophoresis. The immunological response to these fractions in mice was determined by a haemolytic plaque-forming cell assay, using sheep erythrocytes onto which intact bluetongue virus was adsorbed as lytic indicator cells. Isolated outer layer bluetongue virus polypeptide 2, from gradients at pH 6, and polypeptides 2 and 5, from gradients at pH 7, produced a strong primary IgM plaque-forming cell response. The subviral particles of density 1, 39 g.cm-3 and the bluetongue virus core particles of density 1,42 g.cm-3 also stimulated an IgM response at least as strong as that to intact bluetongue virus of density 1,38 g.cm-3. The isolated bluetongue virus fractions therefore appear to maintain their immunogenic integrity as effectively as those of intact bluetongue virus. The pattern of the immune response to bluetongue virus type 4 is similar to that of type 10.     

Neutralizing antibody responses to bluetongue and epizootic hemorrhagic disease virus serotypes in beef cattle

Blood samples were obtained from sentinel beef cattle at monthly intervals, and the sera were tested for antibodies, using a bluetongue virus (BTV) immunodiffusion test (IDT) and virus-neutralization test (VNT), for 5 BTV serotypes (2, 10, 11, 13, and 17) and 2 epizootic hemorrhagic disease virus (EHDV) serotypes (1 and 2). The cattle tested were transported from Tennessee to Texas in 1984 and 1985. All cattle were seronegative by the BTV IDT at the initial bleeding in Texas in 1984 and 1985. In 1984, 16 of 40 (40%) cattle seroconverted as assessed by results of the BTV IDT. In the 16 seropositive cattle in 1984, neutralizing antibodies were detected to BTV serotypes 10 (n = 7), 11 (n = 3), and 17 (n = 11), and EHDV serotypes 1 (n = 1) and 2 (n = 7). In 1984, no cattle seroconverted to BTV-2 or BTV-13. In 1985, 10 of 36 (27.8%) cattle seroconverted as assessed by results of the IDT. Of the 10 seropositive cattle in 1985, neutralizing antibodies were detected to BTV serotypes 10 (n = 10), 11 (n = 10), 13 (n = 7), and 17 (n = 5), and EHDV serotypes 1 (n = 1) and 2 (n = 7). In 1985, no cattle seroconverted to BTV-2. Clinical diseases attributable to BTV or EHDV was not detected in these cattle in 1984 or 1985.