An economic model to evaluate the mitigation programme for bovine viral diarrhoea in Switzerland

Economic analyses are indispensable as sources of information to help policy makers make decisions about mitigation resource use. The aim of this study was to conduct an economic evaluation of the Swiss national mitigation programme for bovine viral diarrhoea virus (BVDV), which was implemented in 2008 and concludes in 2017. The eradication phase of the mitigation programme comprised testing and slaughtering of all persistently infected (PI) animals found. First, the whole population was antigen tested and all PI cattle removed. Since October 2008, all newborn calves have been subject to antigen testing to identify and slaughter PI calves. All mothers of PI calves were retested and slaughtered if the test was positive. Antigen testing in calves and elimination of virus-carriers was envisaged to be conducted until the end of 2011. Subsequently, a surveillance programme will document disease freedom or detect disease if it recurs. Four alternative surveillance strategies based on antibody testing in blood from newborn calves and/or milk from primiparous cows were proposed by Federal Veterinary Office servants in charge of the BVDV mitigation programme. A simple economic spreadsheet model was developed to estimate and compare the costs and benefits of the BVDV mitigation programme. In an independent project, the impact of the mitigation programme on the disease dynamics in the population was simulated using a stochastic compartment model. Mitigation costs accrued from materials, labour, and processes such as handling and testing samples, and recording results. Benefits were disease costs avoided by having the mitigation programme in place compared to a baseline of endemic disease equilibrium. Cumulative eradication costs and benefits were estimated to determine the break-even point for the eradication component of the programme. The margin over eradication cost therefore equalled the maximum expenditure potentially available for surveillance without the net benefit from the mitigation programme overall becoming zero. Costs of the four surveillance strategies and the net benefit of the mitigation programme were estimated. Simulations were run for the years 2008-2017 with 20,000 iterations in @Risk for Excel. The mean baseline disease costs were estimated to be 16.04m CHF (1 Swiss Franc, CHF=0.73 € at the time of analysis) (90% central range, CR: 14.71-17.39m CHF) in 2008 and 14.89m CHF (90% CR: 13.72-16.08m CHF) in 2009. The break-even point was estimated to be reached in 2012 and the margin over eradication cost 63.15m CHF (90% CR: 53.72-72.82m CHF). The discounted cost for each surveillance strategy was found to be smaller than the margin, so the mitigation programme overall is expected to have a positive net economic benefit irrespective of the strategy adopted. For economic efficiency, the least cost surveillance alternative must be selected.     

Eradication of infectious bovine rhinotracheitis in Switzerland: review and prospects

Ten years after the first outbreak of infectious bovine rhinotracheitis (IBR) in Swiss dairy cows, the national cattle herd is almost free from infection with IBR virus (bovine herpesvirus 1, BHV 1). The national programme for the eradication of IBR was divided into four phases: (1) Prevention of transmission of the infection by restrictions on trade of bovines and assessment of the prevalence of cattle with antibodies to BHV 1. (2) Slaughtering animals with antibodies to BHV 1 in order to eradicate BHV 1 from breeding herds. (3) Detection and eradication of further BHV 1 reservoirs (e.g. fattening cattle). (4) Monitoring programme and legal actions in order to maintain the favourable situation. Approximately 50,000 animals were slaughtered in the course of the eradication of IBR. The total costs amounted to approximately SFr. 110,000,000 over 10 years. The costs for maintaining the situation are estimated at approximately SFr. 5,000,000 per annum.     

Predicted costs and benefits of eradicating BVDV from Ireland

Bovine viral diarrhoea virus (BVDV) causes an economically important endemic disease (BVD) of cattle in Ireland and worldwide. Systematic eradication by detection and removal of infectious (BVDV carrier) cattle has been successful in several regions. We therefore assessed the benefits (disease losses avoided) and costs (testing and culling regime) of a potential eradication programme in Ireland. Published bio-economic models of BVDV spread in beef suckler herds and dairy herds were adapted to estimate potential benefits of eradication in Ireland. A simple model of BVDV spread in beef finisher herds was devised to estimate the benefits of eradication in this sector. A six year eradication programme consisting of 5 inter-related virological and serological testing programmes is outlined and costed. We found that the annualised benefits of BVDV eradication in Ireland exceeded the costs by a factor of 5 in the beef suckler sector and a factor of 14 in the dairy sector. Corresponding payback periods were 1.2 and 0.5 years respectively. These results highlight the significant economic impact of BVDV on the Irish cattle industry and suggest a clear economic benefit to eradication using the proposed approach. This type of cost-benefit analysis is considered an essential prerequisite prior to undertaking an eradication campaign of this magnitude.     

Increased risk of BVDV infection of calves from pregnant dams on communal Alpine pastures in Switzerland

Skin biopsies and blood samples from 117 calves, the offspring of dams that had been pastured on communal Alpine pastures while pregnant, were examined for bovine viral diarrhoea virus (BVDV) antigen. Immunohistochemical evaluation of skin biopsy samples revealed BVDV antigen in nine (7.7%) calves, and ELISA testing of serum samples was positive for BVDV antigen in six (5.1%). Three calves with positive skin biopsy samples and negative serum results were < 11 days old; it was assumed that maternal antibody interfered with the ELISA testing. Serum samples that were collected at a later date from two of the three calves were positive for BVDV antigen. These results were significantly different from those of a previous study in which the prevalence of persistently infected calves in an average Swiss cattle population was 0.64%. It was concluded that the risk of infection with BVDV is high in cattle sharing a communal Alpine pasture.     

Immunohistochemistry used as a screening method for persistent bovine viral diarrhea virus infection.

Cattle persistently infected (PI) with bovine viral diarrhea virus(BVDV) are a major source of infection to herds. To successfully control BVDV, it is necessary to identify and cull those cattle PI with BVDV. Immunohistochemistry (IHC) is a useful tool for sensitive and specific detection of BVDV antigens in infected cattle.Skin of cattle PI with BVDV is one of the tissues where BVDV can be consistently identified by IHC and is readily accessible for sampling. Use of IHC on skin biopsies (in the form of ear notches)as a method to identify cattle PI with BVDV has resulted in a reliable, affordable technique for mass testing of cattle at an early age without maternal antibody interference. The ability to test large numbers of cattle to identify those Pl with BVDV will enable implementation of programs for control and eventual eradication of BVDV.     

Prevalence of BVDV infection in Greek dairy herds

Thirty-nine Greek dairy herds, totalling 6333 cattle, enrolled in a voluntary bovine viral diarrhoea virus (BVDV) eradication programme based on the identification and removal of persistently infected (PI) animals. The aim of this study was to estimate the prevalences of BVD antigen-positive and PI animals, and investigate the significance of the associations between the prevalence estimates and herd size. Initially, all animals were bled and examined for BVDV, using an antigen ELISA. A second sample was collected from the positive animals, after a period of at least three weeks. Animals retested positive were classified as PI. Antigen positive and PI animals were detected in all herds. The respective mean prevalences, adjusted for the test's accuracy and the herd-clustering effect, were 14% (95%CI: 11-18%) and 1.3% (0.8-1.8%), respectively. Herd size was not associated with the prevalence of antigen-positive or PI animals.     

Economic risk analysis model for bovine viral diarrhea virus biosecurity in cow-calf herds

A stochastic model was designed to calculate the cost-effectiveness of biosecurity strategies for bovine viral diarrhea virus (BVDV) in cow-calf herds. Possible sources of BVDV introduction considered were imported animals, including the calves of pregnant imports, and fenceline contact with infected herds, including stocker cattle raised in adjacent pastures. Spread of BVDV through the herd was modeled with a stochastic SIR model. Financial consequences of BVDV, including lost income, treatment costs, and the cost of biosecurity strategies, were calculated for 10 years, based on the risks of a herd with a user-defined import profile. Results indicate that importing pregnant animals and stockers increased the financial risk of BVDV. Strategic testing in combination with vaccination most decreased the risk of high-cost outbreaks in most herds. The choice of a biosecurity strategy was specific to the risks of a particular herd.     

Control of bovine viral diarrhea/mucosal disease in the district of Kamenz on a voluntary basis--ways, successes, limitations

In 69 dairy and beef herds in the district of Kamenz, Saxony, with a total number of 21,783 and 89.6% of the district's cattle, a voluntary BVDV eradication protocol was implemented from 2000 to 2007. The aim was to achieve eradication as comprehensive as possible and to prepare the herds for the mandatory eradication program. Essential preconditions for the accreditation of a herd as "free of BVD virus" were the antigen test of all cattle and their offspring for 12 months including completeness check and a negative serological random sampling of young cattle. Mean eradication period of infected herds lasted 45.6 months, herd size, and the number of newly purchased cattle were found to have a significant influence. In five infected farms calf losses significantly decreased after termination of the eradication. further examination of the 126 antigen test positive animals from 15 herds resulted in 87 persistently infected (PI) and 15 transiently infected (TI) individuals, 24 animals missed the second test. Furthermore, out of the 87 PI's 30 individuals (34%) had antibodies against BVDV. Eight farms vaccinated their whole herd, seven only the young stock before first breeding, and 54 herds did not vaccinate, respectively. Concluding from this study, the epidemiological particularities of the farms should be taken in account. Testing of all cattle in a minimum of time including, official monitoring of immediate culling of PI's, immediate epidemiological research, and serological monitoring of the eradication process is necessary.     

Eradication programme for bovine viral diarrhoea virus in Orkney 2001 to 2008

The strategies used and the results obtained in Orkney's bovine viral diarrhoea virus (BVDV) eradication programme over eight years (2001 to 2008) are presented and discussed. The venture was undertaken by local veterinary practices and the Orkney Livestock Association (OLA) with the financial support of the Orkney Islands Council. Participation is voluntary; the programme comprises screening of youngstock, a whole-herd test if required, elimination of persistently infected animals and strict biosecurity measures and/or vaccination. BVDV-free herds are certified, and certification is updated annually by retesting the youngstock. The programme aims to minimise economic losses, thereby increasing the competitiveness of the Orcadian cattle industry and to improve animal health and welfare by eliminating virus circulation. Information from databases of the Scottish Agricultural College, Biobest Laboratories and OLA show that despite a significant reduction in the overall prevalence of BVDV on Orkney during the initial stages of the eradication programme, there has been little progress made since 2006 and that some difficulties have been encountered, with herd BVDV breakdowns following initial eradication. These results highlight the need for continued motivation of farmers, strict application of biosecurity measures and/or systematic vaccination of all seronegative breeding animals.     

Transmission of bovine viral diarrhoea virus by unhygienic vaccination procedures,ambient air,and from contaminated pens

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.     

Prevalence of bovine viral diarrhea virus (BVDV) in persistently infected cattle and BVDV subtypes in affected cattle in beef herds in south central United States

The prevalence of bovine viral diarrhea virus (BVDV) in persistently infected (PI) cattle in beef breeding herds was determined using 30 herds with 4530 calves. The samples were collected by ear notches and tested for BVDV antigens using immunohistochemistry (IHC) and antigen capture enzyme-linked immunosorbent assay (ACE). Animals with initial positives on both IHC and ACE were sampled again using both tests and serums were collected for viral propagation and sequencing of a viral genomic region, 5′-untranslated region (5′-UTR) for viral subtyping. Samples were also collected from the dams of PI calves. There were 25 PI calves from 4530 samples (0.55%) and these PI calves were from 5 of the 30 herds (16.7%). Two herds had multiple PI calves and 3 herds had only 1 PI calf. Only 1 of the 25 dams with a PI calf was also PI (4.0%). The subtype of all the PI isolates was BVDV1b. Histories of the ranches indicated 23 out of 30 had herd additions of untested breeding females. Twenty-four of the 30 herds had adult cowherd vaccinations against BVDV, primarily using killed BVDV vaccines at pregnancy examination.     

Epidemiological Study of Pestiviruses in South American Camelids in Switzerland

Background: In the context of the ongoing eradication campaign for bovine viral diarrhea virus (BVDV) in cattle in Switzerland, the role of South American camelids (SAC) as a possible virus reservoir needed to be evaluated. Objective: To assess and characterize the prevalence of pestivirus infections in SAC in Switzerland. Animals: Serum samples collected from 348 animals (40 herds) in 2008 and from 248 animals (39 herds) in 2000 were examined for antibodies against pestiviruses and for the presence of BVDV viral RNA. Methods: Cross‐sectional study using stratified, representative herd sampling. An indirect BVDV‐ELISA was used to analyze serum samples for pestivirus antibodies, and positive samples underwent a serum neutralization test (SNT). Real‐time RT‐PCR to detect pestiviral RNA was carried out in all animals from herds with at least 1 seropositive animal. Results: In 2008, the overall prevalence of animals positive for antibodies (ELISA) and pestiviral RNA or was 5.75 and 0%, respectively. In 2000, the corresponding prevalences were 3.63 and 0%, respectively. The seroprevalences (SNT) for BVDV, border disease virus or undetermined pestiviruses were estimated to be 0, 1.73, and 4.02% in 2008, and 0.40, 1.21, and 2.02% in 2000, respectively. Conclusions and Clinical Importance: At the present time, SAC appear to represent a negligible risk of re‐infection for the BVDV eradication program in cattle in Switzerland.     

奶牛场病毒性腹泻清除计划的实施

对北京某牛场977头牛采用抗原捕获ELISA方法进行牛病毒性腹泻病毒持续感染牛的筛查,共检出8头阳性牛,其中后备牛7头、成母牛1头。在后续新生犊牛检测中检出1头阳性犊牛。后备持续感染牛表现不同程度的发育迟缓,配种延迟,与国外报道一致。以抗原检测为手段的持续感染牛的清除计划,可用于奶牛场病毒性腹泻的清除与控制。     

Field application of the combination of neutralizing test and virus isolation, so-called spot test, to detect herds including cattle persistently infected with bovine viral diarrhea virus

To detect herds including cattle persistently infected (PI) with bovine viral diarrhea virus (BVDV), application of the combination of neutralizing antibody detection and virus isolation, so-called spot test, were performed on sera of 3 calves selected from each of 26 farms. Nine farms were judged as positive because 64 or more antibody titers were detected from 2 or more calves or BVDV was isolated from one or more calves. PI cattle were detected from 8 of the 9 farms. The positive judgment on one farm was obtained only when the indicator virus used on the neutralizing test was genotypically identical with the isolate from the farm. These results suggest that the spot test can be effective in detecting herds with PI cattle and that the accuracy may be influenced by the genotypes of the indicator viruses.     

Prevalence and epidemiological features of bovine viral diarrhoea virus infection in Lithuania

The objectives of the present work were to estimate the level of bovine viral diarrhoea virus (BVDV) infection in cattle herds at the different Lithuanian districts and to determine factors influencing the course of BVDV infection. The studies were explored in 147 intensive dairy cattle breeding herds from 27 different Lithuanian regions in 1997-2001. BVDV infection was diagnosed in all investigated regions. The existing variations in the structure of cattle population determined different distribution patterns of BVDV infection. The number of seropositive animals ranged from 11.9 to 100%. It must be pointed out that 29.9% of the herds were not infected with BVDV and in 32.7% of the herds from 70 to 100% of cattle were seropositive to BVDV. A positive correlation between the number of seropositive cattle, and the size of herds and age of animals was determined. Sex of animal had no influence on the prevalence of BVDV. It was estimated that the annual incidence risk of infection with BVDV decreases with the animal age.     

Use of serologic evaluation for antibodies against bovine viral diarrhea virus for detection of persistently infected calves in beef herds

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.     

Control and eradication programme of enzootic bovine leucosis (EBL) from selected dairy herds in Turkey

Serum samples of 15,909 cattle from 31 dairy herds located in various regions of Turkey were tested for the presence of antibodies against bovine leucosis virus (BLV) using Agar Gel Immuno-diffusion technique (AGID). 48.3% (15/31) of the herds had seropositive animals and positivity rates were detected from 0.5-34.4% in these herds. In an EBL control/eradication programme all seropositive animals were culled in the infected herds. Thereafter, a total of 74,347 sera were tested for the presence of BLV specific antibodies. The serological results and detail of EBL control/eradication programme were shown in this paper.     

Detection of bovine viral diarrhea virus (BVDV) in seropositive cattle

Detection of bovine virus diarrhoea virus (BVDV) in one vaccinated beef cattle and three non-vaccinated dairy herds was investigated on peripheral blood leukocytes (PBL) with or without previous treatment followed by a capture ELISA (cELISA). Using the combination of PHA and polycation treatment, PBL from 229 seropositive cattle were studied and could be classified in four different states of BVDV infection. Lysed PBL from four animals were directly positive in cELISA (Category I), PBL of 17 animals were positive after PHA stimulation (Category II), 15 animals were positive only after PHA stimulation plus polycation treatment (Category III), while virus could not be detected in 193 seropositive cattle. Wild-type BVDV strains were isolated by co-culture on polycation-treated MDBK cells from 11 of these seropositive animals. BVDV antibodies of these same animals were able to neutralize their own virus, indicating that virus persists in PBL in spite of strain-specific antibodies. No apparent change of leukocyte subpopulations could be detected in any category of virus-positive animals. Thus, BVDV may be present in the PBL of some cattle, even in the presence of a specific active immune response.