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1.
In 5 herds in which bovine virus diarrhoea virus (BVDV) had been isolated, all animals were bled for virological and serological examination. After the herd blood test, follow up blood tests were made on calves born up to 6 months later in 1 herd, 9 months later in 1 herd and up to 12 months later in 3 herds. Persistently infected animals (PI animals) were removed and after a time period a small herd sample of 10 animals that were born after removal of the PI animals were examined for BVDV antibodies.At the herd blood test a total of 21 PI animals were detected. During the follow up period another 25 PI animals were born.Among animals in the small herd samples collected after removal of the PI animals, antibody positive animals were found in the 2 herds with the shortest follow up period. In the 3 herds with a 1 year follow up period there were no antibody carriers in the herd sample.It seems possible to prevent further spread of infection with BVDV if all animals in the herds as well as animals born during the following year are examined and PI animals removed.  相似文献   

2.
Routine Bovine Viral Diarrhoea Virus (BVDV) monitoring of a commercial beef herd in southern New South Wales over a 10-year period provided an opportunity to assess the impact of the introduction of BVDV on that herd. BVDV antibody testing provided strong evidence that the herd was initially free of BVDV (2009–2011). Testing from 2012 suggested BVDV had been introduced into the herd and this was confirmed in 2015 with the identification of persistently infected (PI) animals. Having become established in the herd, the owners then set out to eliminate BVDV from the herd. Antigen testing aimed at identifying PI animals revealed BVDV was already absent from the herd. Subsequent antibody testing confirmed that the herd was now free from BVDV. Despite the incursion of BVDV in this herd, there was little measurable impact on reproductive performance (pregnancy rates), although suspected increased calf losses from birth to calf marking were reported. This is the first time such self-clearance has been documented as part of a longitudinal study under Australian conditions.  相似文献   

3.
Neutralising serum antibodies against bovine virus diarrhoea virus (BVDV) were monitored for three years in 35 cattle that were infected with the virus as calves; 24 of the calves were inoculated intramuscularly or intranasally, and 11 contracted the infection naturally. All the experimentally infected calves seroconverted within 14 to 28 days after inoculation, and all the animals still had high serum levels of antibodies to BVDV three years after infection. Determinations of antibody levels in milk and blood samples excluded the possibility that the calves had been reinfected with BVDV during the study.  相似文献   

4.
A national eradication programme was designed with the aim of achieving total freedom from bovine viral diarrhea virus (BVDV) infection in the Swiss cattle population. The eradication programme consisted of testing every Swiss bovine for antigen, culling virus-positive animals and applying movement restrictions. Starting in 2008, the campaign achieved the goal of reducing the proportion of newborn calves that were virus-positive from 1.8% to under 0.2% within two years (situation in September 2010). Both good data flow between the parties involved as well as speed and efficiency (e.g. concerning the application of tests, movement restrictions and slaughter) are central to the success of the programme. Since the beginning of the programme 2.85 million cattle have been tested for bovine viral diarrhea virus (BVDV). The BVD-prevalence in cattle at the individual and herd levels following the implementation of the eradication programme was assessed. Using data collected during this campaign a risk factor analysis was conducted in order to identify factors associated with the appearance of virus positive newborn calves in herds where BVD had not previously been detected; these risk factors would allow targeting of future surveillance. Herd size, early death rate (i.e. the number of animals that either die before 15 days of age or are stillborn per number of newborns per year), buying in stock, using communal summer grazing, production type, age structure and management strategy were factors associated with the appearance of new cases of infection. Testing of newborn calves for antigen will continue to be conducted until the end of 2011, this is combined with outbreak investigation of newly infected herds (consisting of re-testing dams of virus-positive calves and if necessary all cattle on or that recently left the farm). This process is done to identify infected animals that may have been missed during prior testing (false negatives), it also serves to identify other factors that may be responsible for the introduction of BVDV onto the farm. Since October 2009, testing of calves for antigen combined with outbreak investigation has led to the detection of 55 infected animals that had tested negative (presumably false negative) during previous rounds of testing.  相似文献   

5.
Detection, genetic characterization, and control of bovine viral diarrhea virus (BVDV) disease in a large commercial dairy herd is reported. Precolostral BVDV serum antibody was detected in 5.3% (12/226) of newborn calves before the test and removal of persistently infected (PI) animals and in 0.4% (2/450) of newborn calves after the removal of PI heifers.  相似文献   

6.
Sera from 9 dairy herds with epizootic enteritis (winter dysentery) were examined for antibodies to bovine coronavirus (BCV) and bovine virus diarrhoea virus (BVDV). Cows in 8 of the 9 herds seroconverted to BCV alone, while the animals in the ninth herd, which showed severe symptoms of the disease, seroconverted both to BCV and BVDV. The BCV antibodies, which were present in high titres 1 year postinfection, were transferred to the offspring via the colostrum and were then detectable in sera of calves until these were approximately 5 months old. A serological survey of 549 Swedish heifers showed that 61% of the animals were reactors to BCV. The prevalence of seroreactors to BCV was equally distributed over Sweden but was commonly either high or low in herds. In conclusion, BCV is commonly detected in animals suffering from winter dysentery. A co-infection with BVDV appears to aggravate the disease.  相似文献   

7.
Previous reports on the spread of bovine virus diarrhoea virus (BVDV) from animals primarily infected with the agent are contradictory. In this study, the possibility of transmission of BVDV from calves simultaneously subjected to acute BVDV and bovine coronavirus (BCV) infection was investigated. Ten calves were inoculated intranasally with BVDV Type 1. Each of the 10 calves was then randomly allocated to one of two groups. In each group there were four additional calves, resulting in five infected and four susceptible calves per group. Virulent BCV was actively introduced in one of the groups by means of a transmitter calf. Two calves, susceptible to both BVDV and BCV, were kept in a separate group, as controls. All ten calves actively inoculated with BVDV became infected as shown by seroconversions, and six of them also shed the virus in nasal secretions. However, none of the other eight calves in the two groups (four in each) seroconverted to this agent. In contrast, it proved impossible to prevent the spread of BCV infection between the experimental groups and consequently all 20 study calves became infected with the virus. Following infection, BCV was detected in nasal secretions and in faeces of the calves and, after three weeks in the study, all had seroconverted to this virus. All calves, including the controls, showed at least one of the following clinical signs during days 3-15 after the trial started: fever (> or =40 degrees C), depressed general condition, diarrhoea, and cough. The study showed that BVDV primarily infected cattle, even when co-infected with an enteric and respiratory pathogen, are inefficient transmitters of BVDV. This finding supports the principle of the Scandinavian BVDV control programmes that elimination of BVDV infection from cattle populations can be achieved by identifying and removing persistently infected (PI) animals, i.e. that long-term circulation of the virus without the presence of PI animals is highly unlikely.  相似文献   

8.
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9.
In 1992, significant calf losses occurred between birth and weaning in a 650-cow Saskatchewan beef herd. These losses occurred subsequent to ill-thrift and disease, and every calf necropsied was found to be persistently infected with bovine viral diarrhea virus (BVDV). The objectives of this study were to describe the losses associated with fetal infection with BVDV in this herd and to determine why they occurred. For investigative purposes, blood samples were collected from the entire cow herd and the surviving calves at pregnancy testing in 1992, and tested by virus isolation for BVDV. Between 51 and 71 persistently infected calves were born in 1992. Bovine viral diarrhea virus was only isolated from calves. The only confirmed fetal infections with BVDV were recorded as the birth of persistently infected calves. However, abortions, reduced pregnancy rates, and delayed calvings were also recorded in the cow herd and may have been the result of fetal infections. The herd was monitored again in 1993. Fetal infections with BVDV were recorded as the birth of stunted, deformed, and persistently infected calves. The greatest losses due to fetal infection with BVDV in the 2 years of this study occurred in cows that were 3-years-old at calving (second calves). Bovine viral diarrhea virus appears to have remained endemic in this herd by transmission from persistently infected calves on young 3- and 4-year-old cows to naive calved 2-year-old cows that were mingled with them annually for rebreeding. Significant numbers of the 2-year-old cows remained naive to BVDV, because they were segregated from persistently infected calves at weaning, preventing cross-infection with BVDV.  相似文献   

10.
OBJECTIVE: To determine whether strict closure of a dairy herd and eradication of bovine viral diarrhea virus (BVDV) infection would decrease incidence of diarrhea in calves during the first 31 days after birth, whether specific risk factors were associated with incidence of diarrhea in calves, and whether diarrhea was associated with weight gain of the calves. DESIGN: 2-year cohort study. ANIMALS: 448 calves. PROCEDURE: Calves were monitored from birth to 31 days of age. Fecal samples were tested for rotavirus, blood samples were tested for BVDV and antibodies to BVDV, and serum samples were tested for IgG concentration. Risk factors were evaluated by means of survival analysis. RESULTS: Incidence of diarrhea in calves decreased significantly after strict closure of the herd and eradication of BVDV infection. Risk factors for diarrhea in calves interacted in a multifactorial way. Rotavirus infection and low serum IgG concentration increased the risk that calves would develop diarrhea. Calves that developed diarrhea gained significantly less weight than calves that did not develop diarrhea. CLINICAL IMPLICATIONS: To control diarrhea among calves in a dairy herd, emphasis should be on maintaining a strictly closed herd free from BVDV infection. However, other measures, such as measures to prevent rotavirus infection and to ensure that calves receive an appropriate amount of colostrum after birth, should also be taken.  相似文献   

11.
In January 1982 an outbreak of diarrhoea among adult dairy cows in a closed herd of approximately 200 milking animals was shown to be caused by the introduction of bovine virus diarrhoea virus (BVDV). Affected animals showed a significant reduction in milk yield. One animal died and four were culled. Eight cows aborted and one weak calf was born. Of 121 calves born that year, 26 died, mostly from pneumonia, but five aged from three weeks to five months had enteric lesions of mucosal disease. Subsequent investigations of the whole herd in 1983 and 1984 showed that virus spread among the adults was slow and that BVDV continued to make a major contribution to calf losses. Again the greatest cause of loss was suppurative or fibrinous pneumonia. Overall, BVDV was isolated from 36 animals. Isolation of virus from a wide range of tissues of individual animals confirmed that they were viraemic at death. Viruses from calves dying of pneumonia and from aborted fetuses were non-cytopathic in tissue culture. Isolates showing varying degrees of cytopathogenicity were obtained only from tissues of one calf with a congenital neurological defect and the seven animals with enteric lesions consistent with a diagnosis of mucosal disease. Blood from all 89 BVDV antibody-free animals older than three months was tested for the presence of BVDV. Altogether, 12 calves were identified as persistently viraemic and all were apparently healthy when bled. Only two matured normally, four grew poorly and six died.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   

12.
Knowing how bovine viral diarrhoea virus (BVDV) infection spreads via indirect contacts is required in order to plan large-scale eradication schemes against BVDV. In this study, susceptible calves were exposed to BVDV by an unhygienic vaccination procedure, by ambient air and from contaminated pens. Primary BVDV infection was observed in two calves vaccinated with a vaccine against Trichophyton spp that had been contaminated by smearing nasal secretion from a persistently infected (PI) calf on the rubber membrane and penetrating it twice with a hypodermic needle. Four other calves, housed in pairs in two separate housing units near a PI calf for one week--at distances of 1.5 and 10 m, respectively--became infected without having direct contact with the PI calf. Furthermore, two of the three calves housed in a pen directly after removal of a PI calf, but without the pen being cleaned and disinfected, also contracted primary BVDV infection, whereas two calves that entered such a pen four days after removal of another PI calf, did not. In herds where most animals are seronegative to BVDV, indirect airborne transmission of BVDV or contact with a contaminated housing interior may be an important factor in spreading of the virus, once a PI animal is present. However, the spreading of BVDV within herds can be stopped by identifying and removing PI animals and also by ensuring that susceptible breeding animals do not become infected during this procedure. In contrast, injectables contaminated with BVDV may prove to be a significant vector for spreading the infection, not only within an infected herd but, most importantly, also between herds. In our opinion, it is questionable whether medicine bottles, once opened and used within an infected herd, should be used in other herds. In any case, prior knowledge of a herd's BVDV status will help practising veterinarians and technicians to undertake appropriate hygienic measures.  相似文献   

13.
Wet BVDSim (a stochastic simulation model) was developed to study the dynamics of the spread of the bovine viral-diarrhoea virus (BVDV) within a dairy herd. This model took into account herd-management factors (common in several countries), which influence BVDV spread. BVDSim was designed as a discrete-entity and discrete-event simulation model. It relied on two processes defined at the individual-animal level, with interactions. The first process was a semi-Markov process and modelled the herd structure and dynamics (demography, herd management). The second process was a Markov process and modelled horizontal and vertical virus transmission. Because the horizontal transmission occurs by contacts (nose-to-nose) and indirectly, transmission varied with the separation of animals into subgroups. Vertical transmission resulted in birth of persistently infected (PI) calves. Other possible consequences of a BVDV infection during the pregnancy period were considered (pregnancy loss, immunity of calves). The outcomes of infection were modelled according to the stage of pregnancy at time of infection. BVDV pregnancy loss was followed either by culling or by a new artificial insemination depending on the modelled farmer’s decision. Consistency of the herd dynamics in the absence of any BVDV infection was verified. To explore the model behaviour, the virus spread was simulated over 10 years after the introduction of a near-calving PI heifer into a susceptible 38 cow herd. Different dynamics of the virus spread were simulated, from early clearance to persistence of the virus 10 years after its introduction. Sensitivity of the model to the uncertainty on transmission coefficient was analysed. Qualitative validation consisted in comparing the bulk-milk ELISA results over time in a sample of herds detected with a new infection with the ones derived from simulations.  相似文献   

14.
A BVD control programme based on the identification and removal of persistently infected (PI) animals is being undertaken in an area in the Rome province, where BVD outbreaks had been previously detected. It involves 174 mainly dairy herds, from which blood samples of all bovines older than 1 year are obtained through the national brucellosis and leukosis eradication programme. Samples sufficient to detect the presence of seropositive animals at a prevalence of 5% or more are initially screened for antibodies against BVD virus (BVDV) using an immunoenzymatic assay. Upon identification of seroreagents additional blood samples are tested from the 6-12-month age category not included in the initial samples. Animals are considered immunotolerant if BVDV is demonstrated twice at a minimum 30-day interval. When no seropositive animals are detected during the first serological screening the herd is declared BVD-free if a second testing, preferably carried on the same animals previously tested, confirms the seronegative status of the herd. At present 147 farms have been tested, of which 63 (42.9%) are negative with respect to antibodies against BVDV. Of the 84 remaining herds in which one or more seropositives are detected, 13 are classified as recently infected. In eight of these recently infected herds, 22 PI animals have been identified.  相似文献   

15.
Twenty-two heifers were infected intranasally with non-cytopathic bovine viral diarrhoea virus (BVDV) between days 74 and 82 of pregnancy. All animals had developed serum antibodies against BVDV 5 weeks later. No clinical effects were seen in the heifers, and they all delivered a live calf. The newborn calves were generally small, appeared unthrifty as typical 'poor doers', and some developed secondary infections with diarrhoea and signs of respiratory disease. Eighteen of the 22 calves were born without antibodies against BVDV and were persistently infected (PI) with the virus. One was weak at birth and died the following day. Four calves were born with serum antibodies against BVDV and with no detectable virus. Three of these showed signs and/or pathological changes indicating disease in the central nervous system. Otherwise, there were no obvious clinical differences between these calves and the PI calves, nor were there any apparent significant differences in blood parameters between these groups. In general, the calves showed low gamma-globulin values and thrombocytopaenia, but moderately increased fibrinogen values and relatively normal lymphocyte numbers.  相似文献   

16.
A spreadsheet model using Monte Carlo simulation was designed to evaluate the introduction of bovine viral diarrhea virus (BVDV) to cow-calf farms and the effect of different testing strategies. Risks were modeled to include imports to the cow-calf herd and stocker calves imported to adjacent pastures. The number of persistently infected (PI) animals imported and the probability of BVDV introduction were monitored for three herd sizes, four import profiles, and six testing strategies. Importing stockers and importing pregnant heifers were the biggest risks for introduction of BVDV. Testing for PI animals in stockers decreased the risk they posed, but testing pregnant heifers was not sufficient to decrease risk unless their calves were also tested. Test sensitivity was more influential than PI prevalence on the likelihood of BVDV introduction, when all imports were tested. This model predicts the risk of BVDV introduction for individual herds based on management decisions, and should prove to be a useful tool to help cow-calf producers in controlling the risk of importing BVDV to a na?ve herd.  相似文献   

17.
OBJECTIVE: To determine whether use of serologic evaluation of a sentinel sample of calves or cows for antibodies against bovine viral diarrhea virus (BVDV) would accurately predict whether an animal persistently infected with BVDV could be detected in beef herds. SAMPLE POPULATION: 27 cow-calf herds in which the status of persistently infected calves was not known and 11 herds known to have persistently infected calves. Procedure-Detection of persistently infected calves was determined through immunohistochemical testing of tissue obtained at necropsy of all calves that died during calving season and skin (ear notch) specimens obtained from all young stock in the fall of 2002. Serum samples were collected from 30 spring-born calves and 10 mature cows. RESULTS: Optimum serologic test performance at time of weaning was detected when 10 calves were evaluated. At least 3 of 10 randomly selected calves were likely to have a titer > 1:1000 against BVDV type I or II in 53% of herds in which a persistently infected calf was detected during that year (sensitivity, 53%). However, at least 3 of 10 randomly selected calves were also likely to have a titer > 1:1000 in 20% of herds that did not have a persistently infected calf detected during that year (specificity, 80%). CONCLUSIONS AND CLINICAL RELEVANCE: Despite the use of a number of various cutoff values and sample sizes, serologic evaluation of a small number of calves or cows could not be used to accurately predict the presence of persistently infected cattle in a herd.  相似文献   

18.
A double polymerase chain reaction (PCR) assay has been devised for the direct detection of bovine leukemia virus (BLV). The assay was directly performed on blood leukocytes, avoiding the DNA-purification procedures. The PCR products were identified by gel-electrophoresis and the specificity of the test was confirmed by hybridization with a biotinylated oligonucleotide probe. When testing the sensitivity of PCR, less than eight genome copies of the provirus were detected in the background of two million negative lymphocytes. In a BLV infected herd 22 animals of various age groups were examined by the indirect (serological) diagnostic tests of agar-gel immunodiffusion and indirect ELISA as well as by the direct detection method of PCR. The tests were repeated at monthly intervals on five occasions. When examining the specimens from cows and heifers, a close agreement was found between the results of the various methods. The newborn calves, which were the offspring of BLV infected mothers, were consequently negative in PCR throughout the experimental period. However, in the indirect tests the calves were positive during the first samplings and became negative only around four months of age. Since the indirect tests can not discriminate infection from colostral immunity, PCR proved to be a useful complementary assay for the safe diagnosis of BLV infection in young calves.  相似文献   

19.
Models have been developed to represent the spread of bovine viral diarrhoea virus (BVDV) in cattle herds. Whereas the herd dynamics is well known, biological data are missing to estimate the parameters of the infection process. Our objective was to identify the parameters of the infection process that highly influence the spread of BVDV in a dairy herd. A stochastic compartmental model in discrete time represented BVDV infection in a typical Holstein dairy herd structured into five groups (calves, young versus older heifers, lactating versus dry cows). Model sensitivity was analysed for variations in the probability of birth of persistently infected (P) calves (b(P)), mortality of P animals (m(P)), within- and between-group transmission rates for P and transiently infected (T) animals (respectively, beta(w)(P),beta(b)(P),beta(w)(T),beta(b)(T)). Three to five values were tested per parameter. All possible combinations of parameter values were explored, representing 3840 scenarios with 200 runs for each. Outputs were: virus persistence 1 year after introduction, time needed to reach a probability of 80% for the herd to be virus-free, epidemic size, mean numbers of immune dams carrying a P foetus, of P and of T animals in infected herds. When considered together, m(P) and beta(b)(P) accounted for 40-80% of variance of all outputs; b(P) and beta(w)(T) accounted each for less than 20% of variance; beta(b)(T) and beta(w)(P) accounted for almost no percent of variance of the outputs. Parameters beta(w)(T) and b(P) needed to be more precisely estimated. The influence of m(P) indicated the effectiveness of culling P calves, the influence of beta(b)(P) indicated the role of the herd structure in BVDV spread, whereas the influence of b(P) indicated the possible role of vaccination programs in controlling within-herd BVDV spread.  相似文献   

20.
Nine pregnant heifers, in early gestation (63 to 107 days), were infected intranasally or in utero with cytopathic bovine virus diarrhoea virus (BVDV) and each dam seroconverted. All nine calves developed to full term; four were stillborn, of which one had seroconverted but virus was not recovered from their tissues. One of the five liveborn calves appeared to have seroconverted in utero to an adventitious BVDV infection in late pregnancy but the remaining four were not viraemic and showed a normal secondary antibody response to BVDV infection at about six months old. Thus, in contrast to results with noncytopathic virus there was no evidence that infection in utero with cytopathic virus could result in a persistent viraemia or immunotolerance. It is suggested that cells able to support a persistent viraemia with cytopathic virus may not be developed in the young fetus.  相似文献   

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