Incursion of bluetongue virus into the Okanagan Valley, British Columbia.
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Bluetongue virus was isolated from a sentinel herd in British Columbia. Virus isolation was by intravenous inoculation of embryonated chicken eggs and subculture in BHK-21 cells. The cytopathic agent was identified as bluetongue virus by electron microscopy and the immunoperoxidase test. The serotype was identified as serotype 11 by virus neutralization. (+info)
Malignant catarrhal fever: polymerase chain reaction survey for ovine herpesvirus 2 and other persistent herpesvirus and retrovirus infections of dairy cattle and bison.
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Using a polymerase chain reaction (PCR) test for sequences of ovine herpesvirus 2 (OHV2), this virus was shown to be significantly associated with sheep-associated malignant catarrhal fever (SA-MCF) in terminal cases of disease in 34 cattle and 53 bison. Ovine herpesvirus 2 was not detected in cattle (38) and bison (10) that succumbed to other diseases. Other persistent herpesviruses, retroviruses, and pestivirus, some of which have been previously isolated from cases of SA-MCF, were not associated with the disease. These included bovine herpesvirus 4 (BHV4), bovine lymphotrophic herpesvirus (BLHV), bovine syncytial virus (BSV, also known as bovine spumavirus), bovine immunodeficiency virus (BIV), and bovine viral diarrhea virus (BVDV). A PCR survey for OHV2 in DNA from individual cow's peripheral blood lymphocytes in 4 dairies showed that the 1 dairy that was in close contact to sheep had a prevalence of OHV2 of 21.3%, whereas the 3 other dairies had no OHV2. Prevalence of the other herpesviruses and retroviruses in the dairy cows was variable, ranging from 2% to 51% for BHV4, 52% to 78.7% for BLHV, and 10% to 34% for BSV. Bovine lymphotrophic herpesvirus and BSV were also found in a few (1-4 of 21 tested) cases of terminal SA-MCF, but BIV and BVDV were not found in either the dairy cows sampled, or in the cases of SA-MCE No significant correlation was found between the presence of any 2 viruses (OHV2, BHV4, BLHV, BSV) in the dairy cows or terminal cases of SA-MCE (+info)
Maximal predicted duration of viremia in bluetongue virus-infected cattle.
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Central to the development of rational trade policies pertaining to bluetongue virus (BTV) infection is determination of the risk posed by ruminants previously exposed to the virus. Precise determination of the maximal duration of infectious viremia is essential to the development of an appropriate quarantine period prior to movement of animals from BTV-endemic to BTV-free regions. The objective of this study was to predict the duration of detectable viremia in BTV-infected cattle using a probabilistic modeling analysis of existing data. Data on the duration of detectable viremia in cattle were obtained from previously published studies. Data sets were created from a large field study of naturally infected cattle in Australia and from experimental infections of cattle with Australian and US serotypes of BTV. Probability distributions were fitted to the pooled empirical data, and the 3 probability distributions that provided the best fit to the data were the gamma, Weibull, and lognormal probability distributions. These asymmetric probability distributions are often well suited for decay processes, such as the time to termination of detectable viremia. The analyses indicated a > 99% probability of detectable BTV viremia ceasing after < or = 9 weeks of infection in adult cattle and after a slightly longer interval in BTV-infected, colostrum-deprived newborn calves. (+info)
Occurrence of genetic drift and founder effect during quasispecies evolution of the VP2 and NS3/NS3A genes of bluetongue virus upon passage between sheep, cattle, and Culicoides sonorensis.
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Bluetongue virus (BTV) is the cause of an insect-transmitted virus infection of ruminants that occurs throughout much of the world. Individual gene segments differ between field strains of BTV; thus, we hypothesized that key viral genes undergo genetic drift during alternating passage of BTV in its ruminant and insect hosts. To test this hypothesis, variation in the consensus sequence and quasispecies heterogeneity of the VP2 and NS3/NS3A genes of a plaque-purified strain of BTV serotype 10 was determined during alternating infection of vector Culicoides sonorensis and a sheep and calf. Consensus sequences were determined after reverse transcriptase-nested PCR amplification of viral RNA directly from ruminant blood and homogenized insects, and quasispecies heterogeneity was determined by the sequencing of clones derived from directly amplified viral RNA. Comparison of these sequences to those of the original BTV inoculum used to initiate the cycle of BTV infection demonstrated, for the first time, that individual BTV gene segments evolve independently of one another by genetic drift in a host-specific fashion, generating quasispecies populations in both ruminant and insect hosts. Furthermore, a unique viral variant was randomly ingested by C. sonorensis insects that fed on a sheep with low-titer viremia, thereby fixing a novel genotype by founder effect. Thus, we conclude that genetic drift and founder effect contribute to diversification of individual gene segments of field strains of BTV. (+info)
Studies on the epidemiology of bluetongue virus in China.
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Sentinel herds of large ruminants were established at five centres in Yunnan Province, Peoples Republic of China, between 1995 and 1997. The application of a sensitive antigen capture ELISA to facilitate virus isolation procedures led to the isolation of 108 strains of bluetongue (BLU) virus. Serotypes isolated included types 1, 2, 3, 4, 9, 11, 12, 15, 16, 21 and 23. Virus transmission occurred over a period of 1-3 months at each of the four positive sites, giving an overall BLU virus transmission period for the province of 5 months, from early June to early November. The greatest level of transmission took place in July and August. The duration of viraemia in individual animals varied from 1 to 7 weeks, with a mean calculated for each serotype between 6 and 20 days. The study represents the first detailed investigation of the epidemiology of BLU in China utilizing sentinel herds. (+info)
The role of endothelial cell-derived inflammatory and vasoactive mediators in the pathogenesis of bluetongue.
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Bluetongue is an insect-transmitted disease of sheep and wild ruminants that is caused by bluetongue virus (BTV). Cattle are asymptomatic reservoir hosts of BTV. Infection of lung microvascular endothelial cells (ECs) is central to the pathogenesis of BTV infection of both sheep and cattle, but it is uncertain as to why sheep are highly susceptible to BTV-induced microvascular injury, whereas cattle are not. Thus, to better characterize the pathogenesis of bluetongue, the transcription of genes encoding a variety of vasoactive and inflammatory mediators was quantitated in primary ovine lung microvascular ECs (OLmVECs) exposed to BTV and/or inflammatory mediators. BTV infection of OLmVECs increased the transcription of genes encoding interleukin- (IL) 1 and IL-8, but less so IL-6, cyclooxygenase-2, and inducible nitric oxide synthase. In contrast, we previously have shown that transcription of genes encoding all of these same mediators is markedly increased in BTV-infected bovine lung microvascular ECs and that BTV-infected bovine ECs produce substantially greater quantities of prostacyclin than do sheep ECs. Thus, sheep and cattle were experimentally infected with BTV to further investigate the role of EC-derived vasoactive mediators in the pathogenesis of bluetongue. The ratio of thromboxane to prostacyclin increased during BTV infection of both sheep and cattle, but was significantly greater in sheep (P = 0.001). Increases in the ratio of thromboxane to prostacyclin, indicative of enhanced coagulation, coincided with the occurrence of clinical manifestations of bluetongue in BTV-infected sheep. The data suggest that inherent species-specific differences in the production and activities of EC-derived mediators contribute to the sensitivity of sheep to BTV-induced microvascular injury. (+info)
A possible overwintering mechanism for bluetongue virus in the absence of the insect vector.
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Bluetongue virus (BTV) and several other Orbivirus species are transmitted between mammalian hosts via bites from adults of certain species of Culicoides midges. However, BTV can survive for 9-12 months (typically during the winter), in the absence of adult vectors, with no detectable cases of viraemia, disease or seroconversion in the host. The survival of the virus from one 'vector season' to the next is called 'overwintering' but the mechanism involved is not fully understood. It is demonstrated that BTV can persistently infect ovine gammadelta T-cells in vitro, a process that may also occur during infection and viraemia in mammalian hosts, thus providing a mechanism for virus persistence. Interaction of persistently BTV-infected gammadelta T-cells with antibody to the gammadelta T-cell-specific surface molecule WC-1 resulted in conversion to a lytic infection and increased virus release. Skin fibroblasts induce a similar conversion, indicating that they express a counter ligand for WC-1. Feeding of Culicoides midges induces skin inflammation, which is accompanied by recruitment of large numbers of activated gammadelta T-cells. The interaction of persistently infected gammadelta T-cells with skin fibroblasts would result in increased virus production at 'biting sites', favouring transmission to the insect vector. This suggested mechanism might also involve up-regulation of the WC-1 ligand at inflamed sites. It has been shown previously that cleavage of virus surface proteins by protease enzymes (which may also be associated with inflammation) generates infectious subvirus particles that have enhanced infectivity (100 times) for the insect vector. (+info)
Competitive ELISA for serodiagnosis of bluetongue: evaluation of group-specific monoclonal antibodies and expressed VP7 antigen.
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The performance of 2 competitive enzyme-linked immunosorbent assays (C-ELISA) was compared with the reference C-ELISA I for the detection of antibodies to bluetongue virus (BTV). One of the assays (C-ELISA II) used a group-specific monoclonal antibody (MAb) to BTV, obtained from the American Type Culture Collection (8A3B-6) and tissue culture (TC)-derived BTV antigen (Ag), and the other assay (C-ELISA III) used BTV core protein VP7 (expressed in yeast) and the reference MAb (Pirbright Laboratory, 3-17-A3). Test sera were obtained by sequential blood samples from 22 calves, each inoculated with a different serotype (T) of BTV (South African [SA] T-1-T-16 and T-18-T-20 and USA T-11, T-13, and T-17). Sera were also obtained from 4 calves and 4 sheep inoculated with USA BTV T-10 and from several groups of calves exposed to single or multiple doses of epizootic hemorrhagic disease virus (EHDV) T-1-T-4 grown in TC (BHK-21) or suckling mouse brain (SMB). A total of 618 bovine and ovine field sera collected from BT-free and BT-endemic areas were also tested. The C-ELISA III was more sensitive than the C-ELISA II in the detection of anti-BTV antibody in sera from cattle and sheep early after infection with BTV. Seroconversion was demonstrated by the 3 C-ELISAs in all animals inoculated with BTV by 20 days postinfection (DPI), except in calves that received SA T-3 or USA T-13, which became positive at 40 DPI.(ABSTRACT TRUNCATED AT 250 WORDS) (+info)