Pestiviruses isolated from pigs, cattle and sheep can be allocated into at least three genogroups using polymerase chain reaction and restriction endonuclease analysis

A polymerase chain reaction-based assay capable of detecting a broad range of pestiviruses from pigs, cattle, or sheep was developed. Of six sets of primers selected from different parts of the pestivirus genome, the best results were provided by a pair from the highly conserved 5' non-coding region which gave amplification with all 129 isolates tested. This panel consisted of 33 isolates from pigs, 79 from cattle, and 17 from sheep. Differentiation between the viruses was achieved by cutting the PCR-amplified products with the restriction endonucleases AvaI and Bg1I. Using this procedure it was possible to distinguish at least 3 genogroups; group 1 (HCV) contained 32 of the pig isolates, group II (BVDV) contained all the cattle isolates tested plus 6 sheep isolates and group III (BDV) contained 11 sheep isolates and 1 pig isolate.

Bovine viral diarrhoea virus genotype 1 can be separated into at least eleven genetic groups

Seventy-eight bovine viral diarrhoea viruses (BVDV) recently collected in Austria, France, Hungary, Italy, Slovakia, Spain and UK were genetically typed in the 5'-untranslated (5'UTR) and autoprotease (Npro) regions of the pestivirus genome. Seventy-six of the isolates were BVDV-1 and two French isolates were of the BVDV-2 genotype. Phylogenetic analysis of the 5'UTR (245 nt), including additional BVDV-1 sequences from USA, Canada, Germany, New Zealand, Mozambique and Sweden, taken from GenBank and from our previous works, indicated that these viruses were clustered not only into the two generally accepted groups (BVDV-1a-"NADL like" and BVDV-1b-"Osloss like"), but altogether into 11 phylogenetic groups. Similar clustering was observed with Npro region sequences (385 nt) and the highest bootstrap values (over 95%) were obtained by phylogeny combining 5'UTR and Npro sequences. Some associations between the genetic grouping and the origin of the isolates were apparent, probably reflecting historical trade contacts. Considering the variability of isolates it is recommended that diagnostic PCR primers should be re-examined to ensure coverage of all BVDV-1 groups. The genogroups were less clearly differentiated by monoclonal antibody typing, suggesting significant antigenic similarities within the BVDV-1 genotype.

Genetic typing of classical swine fever virus

Three regions of the classical swine fever virus (CSFV) genome that have been widely sequenced were compared with respect to their ability to discriminate between isolates and to segregate viruses into genetic groups. Sequence data-sets were assembled for 55 CSFVs comprising 150 nucleotides of the 5' non-translated region, 190 nucleotides of the E2 envelope glycoprotein gene and 409 nucleotides of the NS5B polymerase gene. Phylogenetic analysis of each data-set revealed similar groups and subgroups. For closely related viruses, the more variable or larger data-sets gave better discrimination, and the most reliable classification was obtained with sequence data from the NS5B region. No evidence was found for intertypic recombination between CSFVs. A larger data-set was also analysed comprising 190 nucleotides of E2 sequence from 100 CSFVs from different parts of the world, in order to assess the extent and global distribution of CSFV diversity. Additional groups of CSFV are evident from Asia and the nomenclature of Lowings et al. (1996) [Lowings, P., Ibata, G., Needham, J., Paton, D., 1996. J. Gen. Virol. 77, 1311-1321] needs to be updated to accommodate these. A tentative assignment, adapting rather than overturning the previous nomenclature divides CSF viruses into three groups with three or four subgroups: 1.1, 1.2, 1.3; 2.1, 2.2, 2.3; 3.1, 3.2, 3.3, 3.4. The expanding data-base of CSFV sequences should improve the prospects of disease tracing in the future, and provide a basis for a standardised approach to ensure that results from different laboratories are comparable.

The rodent uterotrophic assay: critical protocol features, studies with nonyl phenols, and comparison with a yeast estrogenicity assay

The major protocol features of the immature rat uterotrophic assay have been evaluated using a range of reference chemicals. The protocol variables considered include the selection of the test species and route of chemical administration, the age of the test animals, the maintenance diet used, and the specificity of the assay for estrogens. It is concluded that three daily oral administrations of test chemicals to 21- to 22-day-old rats, followed by determination of absolute uterus weights on the fourth day, provide a sensitive and toxicologically relevant in vivo estrogenicity assay. Rats are favored over mice for reasons of toxicological practice, but the choice of test species is probably not a critical protocol variable, as evidenced by the similar sensitivity of rats and mice to the uterotrophic activity of methoxychlor. Vaginal opening is shown to be a useful, but nondefinitive, adjunct to the uterotrophic assay. The ability of test chemicals to reduce or abolish the uterotrophic response of estradiol is suggested to provide a useful extension of the uterotrophic assay for the purpose of detecting antiestrogens. The results of a series of studies on the environmental estrogen nonyl phenol (NP), and its linear isomer n-nonyl phenol, confirm that branching of the aliphatic side chain is important for activity. 17beta-Desoxyestradiol is shown to be of similar activity to estradiol in the uterotrophic assay and is suggested to represent the "parent" estrogen of NP. Benzoylation of NP and 17-desoxyestradiol did not affect their uterotrophic activity, in contrast to the enhancing effect of benzoylation on estradiol. Selected chemicals shown to be active in the immature rat uterotrophic assay were also evaluated in an in vitro yeast human estrogen receptor transactivation assay. Most of the chemicals gave similar qualitative responses to those seen in the uterotrophic assay, and the detection of the estrogen methoxychlor by the yeast assay evidenced a degree of intrinsic metabolic competence. However, the assay had a reduced ability (compared to rodents) to hydrolyze the benzoate ester of estradiol, and the estrogenic benzoate derivative of NP was not active in the yeast assay. These last results indicate that current metabolic deficiencies of in vitro estrogenicity assays will limit the value of negative data for the immediate future. The results described illustrate the intrinsic complexity of evaluating chemicals for estrogenic activities and confirm the need for rigorous attention to experimental design and criteria for assessing estrogenic activity.

Comparative evaluation of six ELISAs for the detection of antibodies to the non-structural proteins of foot-and-mouth disease virus

To validate the use of serology in substantiating freedom from infection after foot-and-mouth disease (FMD) outbreaks have been controlled by measures that include vaccination, 3551 sera were tested with six assays that detect antibodies to the non-structural proteins of FMD virus. The sera came from naïve, vaccinated, infected and vaccinated-and-infected animals; two-thirds from cattle, the remainder from sheep and pigs. The assays were covariant for sensitivity, but not necessarily for specificity. A commercial kit from Cedi-diagnostics and an in-house assay from IZS-Brescia were comparable to the NCPanaftosa-screening index method described in the Diagnostic Manual of the World Animal Health Organisation. Using these three tests the specificity and sensitivity for the detection of carriers in vaccinated cattle approaches or exceeds 99% and 90%, respectively.

Transmission pathways of foot-and-mouth disease virus in the United Kingdom in 2007

Foot-and-mouth disease (FMD) virus causes an acute vesicular disease of domesticated and wild ruminants and pigs. Identifying sources of FMD outbreaks is often confounded by incomplete epidemiological evidence and the numerous routes by which virus can spread (movements of infected animals or their products, contaminated persons, objects, and aerosols). Here, we show that the outbreaks of FMD in the United Kingdom in August 2007 were caused by a derivative of FMDV O(1) BFS 1860, a virus strain handled at two FMD laboratories located on a single site at Pirbright in Surrey. Genetic analysis of complete viral genomes generated in real-time reveals a probable chain of transmission events, predicting undisclosed infected premises, and connecting the second cluster of outbreaks in September to those in August. Complete genome sequence analysis of FMD viruses conducted in real-time have identified the initial and intermediate sources of these outbreaks and demonstrate the value of such techniques in providing information useful to contemporary disease control programmes.

Options for control of foot-and-mouth disease: knowledge, capability and policy

Foot-and-mouth disease can be controlled by zoo-sanitary measures and vaccination but this is difficult owing to the existence of multiple serotypes of the causative virus, multiple host species including wildlife and extreme contagiousness. Although intolerable to modern high-production livestock systems, the disease is not usually fatal and often not a priority for control in many developing countries, which remain reservoirs for viral dissemination. Phylogenetic analysis of the viruses circulating worldwide reveals seven principal reservoirs, each requiring a tailored regional control strategy. Considerable trade benefits accrue to countries that eradicate the disease but as well as requiring regional cooperation, achieving and maintaining this status using current tools takes a great deal of time, money and effort. Therefore, a progressive approach is needed that can provide interim benefits along the pathway to final eradication. Research is needed to understand and predict the patterns of viral persistence and emergence and to improve vaccine selection. Better diagnostic methods and especially better vaccines could significantly improve control in both the free and the affected parts of the world. In particular, vaccines with improved thermostability and a longer duration of immunity would facilitate control and make it less reliant on advanced veterinary infrastructures.

Classical swine fever virus diversity and evolution

By analysing the nucleotide sequence data generated from both the E2 (gp55) and the NS5B genes of classical swine fever virus (CSFV), in addition to previously published data from the 5'NCR, we were able to divide 115 CSFV isolates into two major groups, five subgroups and two disparate isolates. Further discrimination was possible by analysis of sequence data from the E2 region. The three sequencing based methods were compared to monoclonal antibody (MAb) typing and to limited restriction enzyme (RE) mapping. Although both MAb and RE methods confirmed the previous classification the resolution was inferior. We estimated an approximate evolution rate for CSFV from an analysis of the virus variation observed in a single geographical area over a 6 year period. Applying this proposed rate to each of our deduced CSFV subgroups enabled us to calculate the approximate dates of divergence for each subgroup.

Porcine reproductive and respiratory syndrome: clinical disease, pathology and immunosuppression

Porcine reproductive and respiratory syndrome (PRRS) was first known as blue-eared pig disease in the United Kingdom and the causative agent as 'Lelystad virus'. The disease is characterised by very variable clinical signs, including reproductive failure and respiratory disease. The respiratory syndrome is often associated with severe infection with secondary bacterial agents including Pasteurella multocida, Haemophilus parasuis and Streptococcus suis. However, some seropositive herds show no clinical signs of disease. The secondary infections may be facilitated by the destruction of circulating lymphocytes, by the destruction of the mucociliary clearance system and, most importantly, by a large reduction in the numbers of alveolar macrophages. The clinical syndrome observed in a herd may therefore depend in part upon the other diseases present.

Integrating genetic and epidemiological data to determine transmission pathways of foot-and-mouth disease virus

Estimating detailed transmission trees that reflect the relationships between infected individuals or populations during a disease outbreak often provides valuable insights into both the nature of disease transmission and the overall dynamics of the underlying epidemiological process. These trees may be based on epidemiological data that relate to the timing of infection and infectiousness, or genetic data that show the genetic relatedness of pathogens isolated from infected individuals. Genetic data are becoming increasingly important in the estimation of transmission trees of viral pathogens due to their inherently high mutation rate. Here, we propose a maximum-likelihood approach that allows epidemiological and genetic data to be combined within the same analysis to infer probable transmission trees. We apply this approach to data from 20 farms infected during the 2001 UK foot-and-mouth disease outbreak, using complete viral genome sequences from each infected farm and information on when farms were first estimated to have developed clinical disease and when livestock on these farms were culled. Incorporating known infection links due to animal movement prior to imposition of the national movement ban results in the reduction of the number of trees from 41472 that are consistent with the genetic data to 1728, of which just 4 represent more than 95% of the total likelihood calculated using a model that accounts for the epidemiological data. These trees differ in several ways from those constructed prior to the availability of genetic data.

Molecular characterization of ovine pestiviruses

Forty-two ovine pestivirus isolates, collected over a period of 18 years, were compared by phylogenetic analysis. The viruses were mostly field isolates from Britain; two others originated from Sweden and two from New Zealand. RT-PCR products were obtained from two genomic regions, one within the 5'-noncoding (5'-NC) region, and the other encompassing parts of the p20 (Npro) and C coding regions. Direct sequencing of the 5'-NC PCR products, followed by computer-assisted phylogenetic analysis, divided the ovine pestiviruses into three main genotypes. The results demonstrated that sheep may naturally be infected not only with border disease virus (BDV), but also with bovine viral diarrhoea virus (BVDV) types I and II. The BDV isolates segregated into two principal subtypes represented by the Moredun strain from Scotland and the 137/4 strain from England. The BVDV-I group was composed of three clusters, two of them represented by BVDV reference strains NADL and Osloss, respectively, and the third by ovine isolates D1120/1 and D1432/P. The grouping of ovine pestiviruses, based on comparative nucleotide sequence analysis of the 5'-NC region, was confirmed by comparative analysis of the p20 (Npro) and C coding regions, performed both at the nucleotide and at the amino acid level. The presence of three genotypes in sheep, including BVDV-I and BVDV-II, indicates the inadequacy of the current hostspecies-based nomenclature and classification of pestiviruses.

Molecular epidemiology of the foot-and-mouth disease virus outbreak in the United Kingdom in 2001

The objective of this study was to quantify the extent to which the genetic diversity of foot-and-mouth disease virus (FMDV) arising over the course of infection of an individual animal becomes fixed, is transmitted to other animals, and thereby accumulates over the course of an outbreak. Complete consensus sequences of 23 genomes (each of 8,200 nucleotides) of FMDV were recovered directly from epithelium tissue acquired from 21 farms infected over a nearly 7-month period during the 2001 FMDV outbreak in the United Kingdom. An analysis of these consensus sequences revealed very few apparently ambiguous sites but clear evidence of 197 nucleotide substitutions at 191 different sites. We estimated the rate of nucleotide substitution to be 2.26 x 10(-5) per site per day (95% confidence interval [CI], 1.75 x 10(-5) to 2.80 x 10(-5)) and nucleotide substitutions to accrue in the consensus sequence at an average rate of 1.5 substitutions per farm infection. This is a sufficiently high rate showing that detailed histories of the transmission pathways can be reliably reconstructed. Coalescent methods indicated that the date at which FMDV first infected livestock in the United Kingdom was 7 February 2001 (95% CI, 20 January to 19 February 2001), which was identical to estimates obtained on the basis of purely clinical evidence. Nucleotide changes appeared to have occurred evenly across the genome, and within the open reading frame, the ratio of nonsynonymous-to-synonymous change was 0.09. The ability to recover particular transmission pathways of acutely acting RNA pathogens from genetic data will help resolve uncertainties about how virus is spread and could help in the control of future epidemics.

Beyond the consensus: dissecting within-host viral population diversity of foot-and-mouth disease virus by using next-generation genome sequencing

The diverse sequences of viral populations within individual hosts are the starting material for selection and subsequent evolution of RNA viruses such as foot-and-mouth disease virus (FMDV). Using next-generation sequencing (NGS) performed on a Genome Analyzer platform (Illumina), this study compared the viral populations within two bovine epithelial samples (foot lesions) from a single animal with the inoculum used to initiate experimental infection. Genomic sequences were determined in duplicate sequencing runs, and the consensus sequence of the inoculum determined by NGS was identical to that previously determined using the Sanger method. However, NGS revealed the fine polymorphic substructure of the viral population, from nucleotide variants present at just below 50% frequency to those present at fractions of 1%. Some of the higher-frequency polymorphisms identified encoded changes within codons associated with heparan sulfate binding and were present in both foot lesions, revealing intermediate stages in the evolution of a tissue culture-adapted virus replicating within a mammalian host. We identified 2,622, 1,434, and 1,703 polymorphisms in the inoculum and in the two foot lesions, respectively: most of the substitutions occurred in only a small fraction of the population and represented the progeny from recent cellular replication prior to onset of any selective pressures. We estimated the upper limit for the genome-wide mutation rate of the virus within a cell to be 7.8 × 10(-4) per nucleotide. The greater depth of detection achieved by NGS demonstrates that this method is a powerful and valuable tool for the dissection of FMDV populations within hosts.

A comparison of penetrating keratoplasty and lamellar keratoplasty in the surgical management of keratoconus

A retrospective study of patients who underwent keratoplasty for keratoconus was done in 100 consecutive cases, of which 50 were penetrating keratoplasty procedures, and 50 were lamellar keratoplasty procedures. Each case was done by the same surgeon in both series. Criteria for patient selection were essentially the same. Postoperative care differed primarily in the time before suture removal, being an average of ten months in the penetrating keratoplasty group and three months in the lamellar keratoplasty group. Of those patients who underwent penetrating keratoplasty, the mean best-corrected visual acuity was 6/6 (20/20-) and the average corneal astigmatism was + 5.00 diopters. Of those patients who received lamellar keratoplasty, the mean best-corrected visual acuity was 6/9 (20/30-), and the average corneal astigmatism was +3.25 diopters. The most frequent complications of both techniques were wound separations that responded well to resuturing.

Multiple origins of foot-and-mouth disease virus serotype Asia 1 outbreaks, 2003-2007

Viruses in 6 genetic groups have caused recent outbreaks in Asia.

We investigated the molecular epidemiology of foot-and-mouth disease virus (FMDV) serotype Asia 1, which caused outbreaks of disease in Asia during 2003–2007. Since 2004, the region affected by outbreaks of this serotype has increased from disease-endemic countries in southern Asia (Afghanistan, India, Iran, Nepal, Pakistan) northward to encompass Kyrgyzstan, Tajikistan, Uzbekistan, several regions of the People’s Republic of China, Mongolia, Eastern Russia, and North Korea. Phylogenetic analysis of complete virus capsid protein 1 (VP1) gene sequences demonstrated that the FMDV isolates responsible for these outbreaks belonged to 6 groups within the Asia 1 serotype. Some contemporary strains were genetically closely related to isolates collected historically from the region as far back as 25 years ago. Our analyses also indicated that some viruses have spread large distances between countries in Asia within a short time.

Classical swine fever--an update

Classical swine fever (CSF) is a serious and contagious viral disease of pigs and wild boar with a widespread worldwide distribution. The immunopathology of the disease is poorly understood, but the ability of the CSF virus to infect cells without triggering apoptosis and to kill uninfected cells is probably highly significant. The virus may be spread by various direct and indirect methods, but in most cases the exact mechanisms involved in local spread between farms are not known. Excellent diagnostic tools and typing methods are available, but tests that could be performed on-farm, in pre-clinically infected pigs or on meat would also be advantageous. A more complete picture of the viruses circulating in different parts of the world is needed. There is great interest to develop and use marker vaccines for the control of CSF in domestic pigs and in wild boar. Epidemiological modelling is increasingly used to evaluate control options.

Application of non-structural protein antibody tests in substantiating freedom from foot-and-mouth disease virus infection after emergency vaccination of cattle

There has been much debate about the use of the so-called "vaccinate-to-live" policy for the control of foot-and-mouth disease (FMD) in Europe, according to which, spread of the FMD virus (FMDV) from future outbreaks could be controlled by a short period of "emergency" vaccination of surrounding herds, reducing the need for large-scale preemptive culling of at-risk animals. Since vaccinated animals may become subclinically infected with FMDV following challenge exposure, it is necessary to either remove all vaccinates (vaccinate-to-kill) or to detect and remove vaccinates in which virus is circulating or has established persistent infections (vaccinate-to-live), in order to rapidly regain the most favoured trading status of FMD-free without vaccination. The latter approach can be supported by testing vaccinated animals for the presence of antibodies to certain non-structural proteins (NSP) of FMDV, which are induced by infection with the virus, but not by vaccination with purified FMD vaccines. Using test sensitivity and specificity data established at a recent workshop on NSP assays [Brocchi E, Bergmann I, Dekker A, Paton DJ, Sammin DJ, Greiner M, et al. Comparative performance of six ELISAs for antibodies to the non-structural proteins of foot-and-mouth disease. Vaccine, in press], this paper examines the ways in which serological testing with NSP ELISAs can be used and interpreted and the effect that this will have on the confidence with which freedom from infection can be demonstrated within guidelines specified by the World Animal Health Organisation and the European Commission.

The influence of chemical structure on the extent and sites of carcinogenesis for 522 rodent carcinogens and 55 different human carcinogen exposures

Gold and her colleagues have tabulated the results of rodent bioassays on 522 chemicals and have analysed the data. The present study complements those analyses by providing a perspective from the viewpoint of the chemical structure of the carcinogens. The chemical structure of each of the carcinogens is displayed and the Gold database is represented with the test agents as the primary variable. The carcinogens are gathered into six chemical classes and each chemical is assessed for structural alerts to DNA reactivity. The database is then analysed using an integration of the following parameters: bioassay in rat, mouse or both; structural alert status; chemical class; sites and multiplicity of carcinogenesis, and trans-species carcinogenicity. A series of Figures is presented that enables rapid acquaintance with what represents the core database of rodent carcinogenicity. The several analyses presented combine in endorsing the reality of two broad classes of rodent carcinogen--presumed DNA-reactive and others (putative genotoxic and non-genotoxic carcinogens, but semantics have been largely avoided). Vainio and his colleagues have tabulated 55 situations in which humans have succumbed to chemically induced cancer, and have listed the tissues affected. This database of human carcinogens has been analysed in the present study as done for the rodent carcinogen database, and comparisons made between the two. The predominance of putative genotoxic carcinogens in the human database was confirmed, as was the reality of putative non-genotoxic carcinogenicity in humans. It is concluded that putative genotoxic rodent carcinogenesis can be correlated both with chemical structure and the extent and nature of the induced effect, and that it is of clear relevance to humans. In contrast, it is concluded that putative non-genotoxic rodent carcinogenesis is more closely related to the test species than to the test chemical, and that it is essentially unpredictable in the absence of mechanistic models. In the absence of such models nongenotoxic carcinogenic effects should be extrapolated to humans with caution. Progress in the accurate prediction and extrapolation of rodent carcinogenicity will be helped by a common, if only temporary, enabling acceptance that not all carcinogens are intrinsically genotoxic.

The effects of bovine viral diarrhoea virus on cattle reproduction in relation to disease control

Bovine viral diarrhoea virus (BVDV) is a major reproductive pathogen in cattle. Infection of the bull can lead to a fall in semen quality and the isolation of infectious virus in the ejaculate, while infection in the cow leads to poor conception rates, abortions and congenital defects. BVDV also reduces the animal's resistance to other respiratory and enteric pathogens. The prevalence of BVDV is primarily due to the efficiency with which the virus crosses the placenta of susceptible females. Calves that survive infection during the first trimester of pregnancy are born with a persistent and lifelong infection. These persistently infected (PI) animals represent between 1.0% and 2.0% of the cattle population and continuously shed infectious virus. The availability of reliable diagnostic ELISA and PCR techniques, which can test milk or serum samples for virus or antibodies, has simplified BVDV surveillance and improved the prospects for control. Although PI animals are the principal vectors within and between herds, they can be readily identified and removed. By contrast, cows carrying a PI foetus are particularly problematic. These animals have been compared to 'Trojan Horses' because they are virus-negative and antibody-positive but they deliver PI calves. In general, acutely infected cattle are much less efficient vectors but infections at the onset of puberty have resulted in a localised and persistent infection within the testes. Under these circumstances, virus shedding into the semen may remain undetected. Transmission of BVDV can be controlled through vaccination or eradication. BVDV vaccine technology has been developing over the past 30 years, but currently available vaccines are still of the conventional inactivated or attenuated sort. In general, vaccination has not been applied with sufficient rigor to make a significant impact on the level of circulating virus, unlike the national and regional eradication programmes established in areas such as Scandinavia, Austria, the Netherlands and Scotland. Eradication confers the added advantage of improved herd health; however, it also creates a susceptible cattle population that needs to be protected by stringent biosecurity. In this article, we discuss how BVDV influences reproductive function, the potential for viral transmission during breeding and the measures that must be taken to avoid the spread of infection to susceptible cattle populations via semen, embryos, culture fluids and infected cows.

Prevalence of antibodies to bovine virus diarrhoea virus and other viruses in bulk tank milk in England and Wales

Bulk tank milk samples from 1070 dairy herds in England and Wales were tested by ELISA for antibodies to bovine virus diarrhoea virus (BVDV). A subset of 341 herds was tested by ELISA for antibodies to bovine herpesvirus 1 (BHV-1), bovine respiratory syncytial virus (BRSV) and bovine coronavirus (BCV). None of the herds had less than 40 dairy cows and none had been vaccinated against BVDV. The prevalence of BVDV antibody-positive herds in the national population was estimated at 95 per cent and approximately 65 per cent of the herds had a high level of bulk tank antibody suggestive of recent infection with BVDV. Dairy herds in East Anglia and the south-east of England had a significantly lower risk of being BVDV antibody-positive than herds in the rest of England and Wales. However, these regional differences tended to diminish with increasing herd size. Around 69 per cent of the herds were BHV-1 antibody-positive and all the herds were antibody positive to BRSV and BCV. Comparison with earlier serological surveys revealed that there had been little change in the prevalence and distribution of BVDV antibody-positive herds in England and Wales over the last 20 years, but that there had been an increase in the prevalence of BHV-1 antibody-positive herds.

Subdivision of the pestivirus genus based on envelope glycoprotein E2

Conventionally, the genus Pestivirus of the family Flaviviridae has been divided into bovine viral diarrhea virus (BVDV), classical swine fever virus (CSFV), and border disease virus (BDV). To date, BDV and BVDV have been isolated from different species, whereas CSFV seems to be restricted to swine. Pestiviruses are structurally and antigenically closely related. Envelope glycoprotein E2 is the most immunogenic and most variable protein of pestiviruses. We cloned E2 genes of many different pestivirus strains, including those from a deer and a giraffe. The E2 genes were transiently expressed, characterized with monoclonal antibodies, sequenced, and compared. Based on these data, we can delineate six major groups within the Pestivirus genus. Four groups correspond to defined genotypes, whereas the two other groups could be new genotypes within the Pestivirus genus. One group comprises CSFV strains isolated from swine. A second group consists of BDV strains Moredun, L83, and X818, which have been isolated from sheep, and strain F from swine. A third group contains strain BD78 from sheep, strain 5250 from swine, and strain 178003 from cattle. On the basis of E2, these viruses are very similar to BVDV strains associated with acute severe outbreaks of bovine viral diarrhea, so-called type 2 BVDV. The fourth group consists of BVDV strains originating predominantly from cattle. This BVDV group can be divided into two subtypes or subgroups BVDV Ia and Ib: BVDV Ia contains viruses from the United States, such as like NADL and Oregon, and some others, such as 150022 and 1138 from Europe. Subgroup BVDV Ib contains strain Osloss and several Dutch isolates. The fifth and sixth "groups" could be proposed as two new genotypes and contain strains Deer and Giraffe, respectively.

Structure activity relationships in skin sensitization using the murine local lymph node assay

Murine local lymph assay node data for 106 chemicals are listed. Among these, 73 are active in the assay indicating their potential as skin sensitizing agents. Broad structure activity relationships (SAR) are suggested based on the electrophilic theory of skin sensitization suggested by Landsteiner and Jacobs in 1936, and elaborated by Dupuis and Benezra in 1982. Eight classes of agent are discerned; electrophiles, potential electrophiles after metabolism, Michael-reactive agents, benzoylating agents, ionic chemicals and miscellaneous agents. The electrophilic theory cannot at present fully explain the activity of agents in the last two classes. That fact will hopefully focus research into their mode of action. Some chemicals fit equally into more than one class, and such agents are entered into the several classes in order not to bias the analysis. Attention is given to why not all chemicals of a class are active in the assay. It is concluded that a combination of inappropriate lipophilicity, molecular size and metabolic detoxification are responsible for these inactivities. Given a sufficient number of analogues tested within each class it should be possible eventually to predict with accuracy the skin sensitizing potential of new members of the class. However, the present analysis is qualitative, not quantitative. Finally, the parallelism between sensitizing potential and mutagenic potential for chemicals is explored further.

Genetic diversity of international bovine viral diarrhoea virus (BVDV) isolates: identification of a new BVDV-1 genetic group

In the last decade, several studies were performed to characterise bovine viral diarrhoea virus (BVDV) isolates and define genetic groups by genotyping. Much data is now available from GenBank, predominantly sequences from the 5' untranslated region (5'-UTR). In order to find out whether genetic grouping of isolates from different countries could be harmonised, 22 new isolates from five countries were analysed in combination with published sequences. Eighteen of these isolates were typed as BVDV genotype 1 (BVDV-1), and one isolate from Argentina and three isolates from Brazil were typed as BVDV-2. BVDV-1 isolates were clustered into five previously defined genetic groups: BVDV-1a, b, d, e and f. Two isolates from Finland and one from Egypt formed a group which was tentatively labelled as BVDV-1j, since statistical support was low. By using a fragment of the Npro gene for typing, we found that these isolates fall into the same group as a deer strain, and are statistically significant. Some Swiss BVDV strains taken from GenBank were found in a new genetic group which was designated as BVDV-1k. The BVDV-2 isolates included in this study seemed to fall into two genetic groups.

Global FMD control--is it an option?

The outbreaks of foot-and-mouth disease (FMD) in Europe in 2001 identified the vulnerability of the intensive agricultural industries in Europe and North America to the economic consequences of the introduction of a highly infectious animal disease. The very large illegal international trade in animal products bypasses the safeguards recommended by World Animal Health Organization (OIE) and put in place by governments to prevent the importation of foreign pathogens. If it is not possible to stop the entry of FMD virus, what are the options to mitigate the risk by reducing the area of the globe in which FMD is endemic? There are a number of constraints that would prevent global control of FMD; current vaccines are expensive, have a narrow antigenic spectrum, provide only short term immunity and are very fragile; diagnostics are also expensive, require training to use and if not handled properly lose sensitivity and specificity; we still do not understand the significance of carrier animals in the epidemiology of FMD, and whether it is necessary or possible to prevent the carrier state; and many decision support tools, such as models are currently more dangerous than useful in that they fail to fully accommodate all the complexities of the disease. The four national foreign animal disease laboratories in USA, Canada, UK and Australia together with the International Livestock Research Institute have put forward a proposal to address some of these constraints (the Global FMD Research Alliance, GFRA), not only to protect their own national livestock industries, but also to support FMD control programs in countries in which the disease is present.

Porcine reproductive and respiratory syndrome (PRRS): a review, with emphasis on pathological, virological and diagnostic aspects

Despite early attempts to control the spread of the disease, porcine reproductive and respiratory syndrome (PRRS) has now become endemic in many countries including Britain. The occurrence of subclinical herd infections, the prolonged circulation of virus within herds and probable aerogenic virus spread all mitigated against the success of control measures. The origin of the disease is unknown but the causative agent has been shown to be an arterivirus with shared features to lactate dehydrogenase virus of mice. There is evidence of extreme genetic and antigenic variability between American and European isolates. PRRS virus has a predilection for alveolar macrophages and does not grow in most cell lines. In infected pigs, viraemia can persist for many weeks in the face of circulating antibodies and little is known about the mechanisms by which immunity to infection develops. A wide spectrum of disease has been reported from the field, accompanied in some cases by heavy economic losses. Reproductive and perinatal losses were most prominent when the disease first appeared. In the endemic phase, PRRS may be more significant as a contributory factor to a post-weaning respiratory syndrome of young pigs of 3-8 weeks. On-farm techniques have been developed to reduce the recycling of PRRS virus from older infected nursery pigs to the younger newly weaned pig. Vaccines are now marketed for the control of PRRS, but are not licensed for use in Britain. Improvements in knowledge of virion composition and antigenic stability and in the nature of the immune response of the pig should result in genetically engineered subunit vaccines becoming available. Diagnosis of PRRS is still difficult as many animals do not show clinical signs and may only be detected by serology and often only when other respiratory diseases are being investigated. Now that the infection is widespread, serological testing must be properly targeted and interpreted to give meaningful results about virus circulation. An increasing arsenal of diagnostic methods are becoming available to detect virus in both fresh and fixed specimens. The pathogenic mechanisms of PRRS remain poorly defined and more work is needed to reveal the nature of the interaction between PRRS virus and other factors in disease.