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.     

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.     

T lymphocyte subset alterations following bluetongue virus infection in sheep and cattle

To determine potential mechanisms of differential disease expression in ruminants infected with bluetongue virus (BTV), clinically normal, BTV-seronegative, yearling sheep and cattle were infected subcutaneously with a standardized insect-source inoculum of BTV serotype 17 (BTV-17) (three infected and one contact control each) or animal adapted BTV serotype 10 (BTV-10) (three sheep only). BTV was isolated from peripheral blood cell components of infected sheep and cattle and all infected animals showed evidence of seroconversion by 14 days post infection (PI). Sheep infected with both serotypes of BTV developed pyrexia, oral lesions, and leukopenia which were most severe on days 7-8 PI. Analysis of peripheral blood mononuclear leukocytes with specific monoclonal antibodies and flow cytometry revealed panlymphocytopenia on day 7 PI. This response was further characterized by an increase in the CD4/CD8 ratio (greater than 3) resultant from a greater decrease in absolute numbers of circulating SBU-T8(CD8+) ("cytotoxic/suppressor") lymphocytes compared to SBU-T4 (CD4)+ ("helper") lymphocytes. SBU-T19+ lymphocytes were also decreased below baseline values on days 5-14 post infection. On day 14 PI there were increased CD8+ lymphocytes and decreased CD4/CD8 ratios (approximately 0.6) in these sheep. Clinical and hematologic changes in cattle infected with BTV-17 were minimal and consisted of mild pyrexia (rectal temperature 103 degrees F) on day 9 PI in two of three infected animals and mild leukopenia on several days PI in one animal. This leukopenia was the result of a pan T lymphocytopenia with CD4/CD8 ratios in the expected range (1-2). Similar to infected sheep, infected cattle did have a shift (decrease, approximately 0.8) in the peripheral CD4/CD8 ratio associated with an increase in circulating BoT8 (CD8)+ lymphocytes on day 14 post infection. Lymphocytes in the peripheral blood of all sheep and cattle infected with BTV-17 proliferated in vitro in response to purified BTV-17. These results confirm and extend those of previous studies that indicate species differences in the hematologic response to an equivalent BTV infection in domestic ruminants.     

Nontransmission of bluetongue virus by embryos from bluetongue virus-infected sheep

Donor sheep were infected either by bites of bluetongue virus (BTV)-infected (serotype 11, "Texas Station strain") Culicoides variipennis or by inoculation with 100,000 median chicken embryo intravascular lethal doses of BTV (serotype 11) from a suspension made from infected C variipennis. Fourteen embryos from 4 BTV-infected ewes bred by rams not infected with BTV were transferred to 8 BTV-seronegative recipient ewes, and 35 embryos and 4 unfertilized eggs from 14 BTV-infected ewes bred by BTV-infected rams were transferred to 19 BTV-seronegative recipient ewes. Eleven pregnancies and 12 lambs resulted. None of the recipients or lambs seroconverted, and BTV was not isolated from the pregnant recipient ewes or their lambs at slaughter 30 days after parturition.     

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.     

Simulation analysis of the effect of herd immunity and age structure on infection of a cattle herd with bluetongue viruses in Queensland, Australia

A state-transition model based on Leslie matrix formulation was used to investigate the effects of herd immunity and age structure on the infection of a simulated cattle herd with bluetongue viruses under Australian climatic conditions. Increasing duration of immunity decreased the prevalence of infection. A duration of immunity of 33 months was consistent with prevalence estimates made from previous serological studies of bluetongue virus. Herd prevalence displayed slowly dampening cyclical variation over time (most pronounced when a short duration of immunity was simulated). Increasing calving and mortality risk rates in the simulated herd increased prevalence, whereas increasing age at first calving decreased prevalence. Manipulation of calving rates had the greatest effect on the predicted prevalence of infection in the herd. Simulation of a number of herd-management scenarios suggested that management systems in which cattle are bred early and where high calving rates are achieved are likely to contribute to high levels of infection with bluetongue viruses. Results confirm the importance of management factors in influencing the prevalence of infectious diseases in animal populations.     

Serologic and virologic evidence of bluetongue virus infection in cattle and sheep in Mexico

Three independent 1-year studies were conducted during 3 consecutive years to better define the prevalence of bluetongue virus (BTV) infection in Mexico. Serologic data were obtained by use of agar-gel immunodiffusion for identification of BTV group-reactive antibodies, and virologic data were obtained by virus isolation. Samples were obtained from sheep in 6 states over a 1-year period, with 9% seropositive; samples were obtained from cattle in 11 states during the same 1-year period, with 35% seropositive. Two years later, samples were obtained from cattle in 4 additional states, with 69% seropositive. Virus isolation was conducted on pooled blood samples obtained from cattle in 7 states. Six virus isolates were recovered and included 2 isolates each of BTV serotypes 11 and 13 and 1 isolate each of serotypes 10 and 17. All virus isolates were partially characterized by electrophoretic analysis of genomic RNA migration profiles (electropherotypes) in polyacrylamide gels. All Mexican isolates of BTV differed considerably in electropherotype profile, as compared with their respective US prototype strain of the same serotype. Such differences appeared to be much more extensive than those described to exist between numerous California isolates of the same serotype.     

Preliminary characterisation of extracellular serine proteases of Dermatophilus congolensis isolates from cattle,sheep and horses

Dermatophilus congolensis is a filamentous branching actinomycete that causes dermatophilosis, an exudative dermatitis in ruminants. The pathogenesis of this disease is poorly understood and virulence factors of D. congolensis have not been characterised. Culture filtrate (CF) of 14 D. congolensis isolates from cattle, 15 from sheep and four from horses were examined for proteolytic activity using azocasein as a non-specific substrate. The isolates were from a variety of geographical locations. All the isolates examined produced extracellular proteolytic activity. CF from 24 and 48 h cultures and from first and third passages contained proteases. Proteolytic activity was greatest in neutral to alkaline pH (pH 7–10). CF of bovine isolates contained more proteolytic activity than that of ovine isolates. Furthermore, in substrate SDS-PAGE gels containing azocasein the number of proteolytic bands and their molecular weights in CF of bovine, ovine and equine isolates were different, giving distinctive band patterns for isolates from each host species. Three out of four bovine isolates from Antigua gave a fourth band pattern. Bands of equivalent molecular weights to the proteases could not be identified in silver stained SDS-PAGE gels of CF. Serine protease inhibitors had a concentration-dependent inhibitory effect on proteolytic activity in CF and inhibited activity of all proteolytic bands in substrate gels. With the exception of EDTA which had a variable-enhancing effect on activity, inhibitors of other classes of protease had no effect on activity. We conclude that D. congolensis produces a number of extracellular alkaline serine proteases, our results suggest the presence of host-specific variation between isolates and to a lesser extent between isolates from the same host species.     

Association between risk of seroconversion of sentinel cattle to bluetongue viruses and Culicoides species (Diptera: Ceratopogonidae) in Queensland, Australia

The association between risk of seroconversion of sentinel cattle to bluetongue viruses and the number of Culicoides brevitarsis Kieffer and C. wadai Kitaoka caught by light traps was investigated using survival analysis. Eight sentinel herds that seroconverted to bluetongue viruses between 1990 and 1994, and for which insect-trapping data were available, were selected for inclusion in the study. These herds were located at six sites along the eastern coast of Queensland, Australia, from approximately latitude 10 °South to 25 °South. C. brevitarsis was detected at all locations where sentinel herds were maintained, whereas C. wadai was detected at only two locations in northern Queensland where four sentinel herds were maintained during the study period. The mean number of C. brevitarsis and C. wadai caught per month was 230 and 21, respectively. A significant (P = 0.05) positive association was found between the risk of seroconversion of sentinel cattle to bluetongue viruses and the number of C. wadai caught in the same month.     

Susceptibility of Sudanese sheep to a bluetongue virus isolated from apparently healthy cattle in the Sudan

This study intends to clarify the role of apparently healthy cattle as a reservoir of bluetongue (BT) virus to sheep in the Sudan. It confirms earlier work and establishes that cattle can harbour bluetongue virus to which sheep are susceptible in the country. Experimental transmission of BT virus between the two species suggests that the best indicator to determine viraemia in apparently healthy cattle is to inoculate susceptible sheep with suspected cattle virus. The condition of the viraemia and the virus survival in the field are discussed.     

Genotypic characterisation of Indian cattle, buffalo and sheep isolates of Echinococcus granulosus

Twelve isolates of Echinococcus granulosus, collected from domestic animals, including cattle, buffalo and sheep were analysed for DNA nucleotide sequence variation within mitochondrial cytochrome c oxidase I (coxI), NADH dehydrogenase subunit I (nadI) and internal transcribed spacer gene I (ITS1). After analysis of sequence information this was found that the fragment size of ITS1 of buffalo isolate was more in comparison to cattle and sheep isolates. Based on the nadI genotype this was found that Indian cattle, buffalo and sheep isolates could be grouped into E. granulosus sensu stricto. Based on coxI genotype two sheep isolates and one buffalo isolate were homologous to G2 genotype. Rests of the isolates were microvariants of G2 genotype. Presence of G2 genotype in buffalo is the first report of this genotype from this host.     

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.     

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.