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.     

The seroprevalence of Actinobacillus pleuropneumoniae in Swiss pig breeding herds--a study with the ApxIV ELISA

At the end of the national eradication program for Enzootic Pneumonia (EP) and Porcine Actinobacillosis (APP) in Switzerland (2003), A. pleuropneumoniae serotype 2 is considered to have been eradicated. There is no current information about the distribution of the other serotypes available. The ApxIV ELISA detects antibodies against all serotypes of A. pleuropneumoniae, without cross-reaction with other bacterial species. The aim of this study was to achieve actual data concerning the seroprevalence of A. pleuropneumoniae in breeding-herds and to validate the ApxIV ELISA under field conditions, especially for the diagnosis of latently infected breeding-herds without clinical signs, and to achieve more information about the role of herd book farms for the spread of the infectious agent. A total of 2068 serum samples from 96 pig herds in Switzerland were examinated. Over half of the examinated herd book farms showed positive results in this ELISA. 93% of the breeding herds were positive. On single animal level sensitivity was 96% and specifity 100%. Herd sensitivity ranged between 67% and 99%. Herd specifity was 100%. The results show that the ApxIV ELISA is a valuable tool for the detection of latently infected herds.     

Eradication of Mycoplasma hyopneumoniae from infected swine herds joining the LSO 2000 health class

The study was conducted in order to determine if eradication of swine enzootic pneumoniae (SEP) had succeeded with different variants of partial depopulation during the eradication programme on swine farrowing farms joining a health class, LSO 2000. The farms in the health class need to be free from swine enzootic pneumoniae, swine dysentery, sarcoptic mange and atrophic rhinitis. Twenty-one eradication attempts for M. hyopneumoniae were carried out using different variants based on separating adult animals for 2 weeks from infected young pigs which were not returned to the herd. The infected young pigs were kept in the same building (variant 1) in 4 herds and on the same compound (variant 2) as disease-free pigs in 12 herds. The infected young pigs were finally all sold. In 5 herds only adult animals were present during the eradication (variant 3). The eradication attempt succeeded in 81% and failed or remained uncertain in 19% of the herds. The result was confirmed with 1) frequent clinical follow-up of the health status in the herds (both the farrowing and the finishing units) joining the LSO 2000 health class 2) milk and/or blood serology. Possible causes of the failure of the eradication attempt were described: a short distance between infected and uninfected animals, the time period between diagnosis of SEP and initiation of the programme, the age of the youngest animal kept on the farm, the period of time when animals with different status were reared close to each other, the medications used, the cleaning of the facilities during the programme and the season. Further, a good cooperation between the farmer, the local veterinarian and the animal health service of the slaughterhouse was an essential part of the initiation and the follow-up of the programme. The secondary aim of the study was to collect information about the expenses during the programme. Only 57% of the farmers gave some estimates for the expenses on their farms. For variants 1, 2 and 3 the expenses were 879, 1110 and 1274 FIM per sow (1 USD = 5.5 FIM), respectively (p > 0.1).     

Herd-level diagnosis for Salmonella enterica subsp. enterica serovar Dublin infection in bovine dairy herds

Herd-level sensitivities of bacteriological and serological methods were compared in 79 bovine dairy herds, recently infected with Salmonella enterica subsp. enterica serovar Dublin. All farms experienced clinical signs of salmonellosis for the first time and had no history of vaccination against salmonellosis. At the start of the study, infection with serovar Dublin was confirmed with at least one positive bacteriologic culture for serovar Dublin from a clinical case (gold standard for herd infection).Bacteriological culture was done on samples of dung-pits, drinking water, bulk-milk filters, and faeces of animals with current or earlier clinical signs of salmonellosis. Blood samples of all animals and bulk-milk samples were tested using an ELISA.Herd-level sensitivity (HSe) of culture of dung-pits, drinking water, bulk-milk filters, and faeces of animals with current or earlier signs of salmonellosis was 45, 5, 7, and 38%, respectively. HSe for serology of all animals was 100%. If blood samples of all calves 4-6 months old were examined, at least one calf was seropositive on 91% of the infected farms. If serology was performed on samples of animals with current or earlier signs of salmonellosis, at least one animal was seropositive on 80% of the infected farms. HSe for bulk-milk samples was 54%. However, if clinical signs of salmonellosis were observed only in lactating animals, sensitivity of bulk-milk serology was 79%.Interesting combinations of methods were the combination of serology of bulk milk with either serology of animals with current or earlier signs of salmonellosis (HSe=91%), or serology of all calves of 4-6 months old (HSe=99%).     

Antibodies against bovine herpesvirus (BHV) 5 may be differentiated from antibodies against BHV1 in a BHV1 glycoprotein E blocking ELISA

We examined whether antibodies against bovine herpesvirus (BHV) 5 cross-react with BHV1 antigens and whether they could interfere with BHV1 eradication programmes. Six calves were experimentally infected with different doses of BHV5 strain N569; homologous antibodies were first detectable on day 11 post infection; they cross-reacted in a BHV1 virus neutralisation test, in a BHV1-glycoprotein (g)-B blocking ELISA and in a BHV1-gE ELISA, but not in a BHV1-gE blocking ELISA. This study indicates that, in ongoing BHV1 eradication programmes, based on vaccines that lack gE, BHV5 infections may not lead to false-positive serological reactions in case cattle are tested for BHV1-gE antibodies by the BHV1-gE blocking ELISA; antibodies against BHV5 may be differentiated from antibodies against BHV1. The BHV1-gE blocking ELISA may, therefore, offer opportunities for the serological differentiation between BHV1 and BHV5 infections.     

Experiences with the eradication of the bovine herpes virus 1 in Lower Saxony

In this paper first the general cascade of animal disease eradication from the voluntary control programme up to culling of infected animals is described. Afterwards the development of the eradication of Bovine Herpes Virus in Lower Saxony is illustrated. Obvious the number of farms which are not eradicating decreases since the testing on BHV1 is obligate in Germany. In 2004 60% of the cattle holdings were free from BHV1. At least the measures which will be taken in Lower Saxony to increase the success of eradication are explained.     

Use of an enzyme-linked immunosorbent assay in a bovine brucellosis eradication program

An enzyme-linked immunosorbent assay (ELISA) was developed and was compared with the complement fixation test (CFT) in a bovine brucellosis eradication program. The ELISA detected significantly more reactors than the CFT in both strain 19 vaccinated infected herds (1.79% versus 1.14%) and non-vaccinated infected herds (4.2% versus 3.59%) but not in either vaccinated or non-vaccinated brucella-free herds. The specificity for both tests in brucella-free herds was greater than 0.998. The specificity and sensitivity of the ELISA were compared with those of 3 other tests (the Rose Bengal test; the indirect haemolysis test [IHLT] and the CFT) on serum from 151 animals cultured at slaughter. The calculated specificity of the ELISA in this infected group was lower than for both the CFT and the IHLT (0.58 versus 0.67 versus 0.75). The sensitivity however was much greater (1.0 versus 0.73 versus 0.71). The value of the ELISA when used in an eradication program is discussed.     

Laboratory decision-making during the classical swine fever epidemic of 1997-1998 in The Netherlands

The National Reference Laboratory for classical swine fever (CSF) virus in the Netherlands examined more than two million samples for CSF virus or serum antibody during the CSF epizootic of 1997–1998. The immense amount of samples and the prevalence of border disease (BD) virus and bovine viral diarrhoea (BVD) virus infections in Dutch pig herds necessitated the diagnostic efforts of the laboratory to be focused on generating CSF specific test results throughout the eradication campaign.

Detection of 82% of the 429 outbreaks was achieved through the combined use of a direct immunofluorescence and peroxidase assay (FAT/IPA) with samples (tonsils) collected from clinically-suspected pigs. This suggests that in the majority of the outbreaks, the pigs had clinical signs that were recognised by the farmer and/or veterinarians, indicating the presence of CSF virus in a pig herd. A positive diagnosis of 74% of all the tissue samples (tonsils) collected at infected pig holdings was established by FAT. More than 140,000 heparinised blood samples were examined by virus isolation, resulting in the detection of 4.5% of the infected herds. CSF virus was isolated in approximately 29% of all the blood samples collected from pigs at infected or suspected farms.

Several serological surveys — each done within a different framework — led to the detection of 13.5% of the total number of outbreaks. The detection of CSF virus antibody in serum was carried out by semi-automated blocking ELISA. Approximately 28.5% of the sera which reacted in the ELISA were classified as CSF virus-neutralising antibody positive and 26.5% as positive for other pestiviruses following the virus neutralisation test (VNT).

We concluded that two of the CSF laboratory diagnostic methods described were determinative in the eradication campaign: first, the FAT for the screening of diseased pigs; and second, the ELISA and VNT when millions of predominantly healthy pigs needed to be screened for the presence of CSF serum antibody. Decision-making on the basis of results generated by either method can, however, be seriously hindered when samples are examined from pig herds with a high prevalence of non-CSF pestiviruses.     

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.     

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.     

Longitudinal study of hepatitis E virus infection in Spanish farrow-to-finish swine herds

Hepatitis E is a zoonotic disease and is highly prevalent in European swine livestock. There is a need to compare the infection dynamics of hepatitis E virus (HEV) between herds with the same production system and determine the percentage of animals that could arrive infected at slaughter age. Therefore, a longitudinal study was performed in six Spanish farrow-to-finish affected farms. Twenty piglets per farm were monitored from nursery to slaughter. RT-PCR and serology techniques were applied to analyze longitudinally collected sera and/or faecal samples. Liver and bile samples were also taken at the abattoir. Anti-HEV IgM were firstly detected at 7 weeks of age in 5 farms whereas at 13 weeks of age in 1 farm (farm 2). At slaughter age 50–100% of pigs had seroconverted to anti-HEV IgG in the former 5 farms whereas in the other herd only 5% of pigs were IgG seropositive (farm 2). Six out of 96 livers and 5 out of 80 biles analyzed were HEV positive at the abattoir (total percentage of infected animals: 11.5%). All these positive animals had already seroconverted except 2 pigs of farm 2. Hence, pigs can be seronegative at slaughter age being infected during the latest fattening period. Manipulation of HEV-infected livers or other organs from pigs could be considered a possible route of transmission in Spanish abattoirs. This study represents the first longitudinal survey on swine HEV infection dynamics conducted in different herds.     

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.     

Bovine virus diarrhoea (BVD) control programme in an area in the Rome province (Italy)

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.     

Evaluating control strategies for outbreaks in BHV1-free areas using stochastic and spatial simulation

Several countries within the EU have successfully eradicated bovine herpesvirus type I (BHV1), while others are still making efforts to eradicate the virus. Reintroduction of the virus into BHV1-free areas can lead to major outbreaks - thereby causing severe economic losses. To give decision-makers more insight into the risk and economic consequences of BHV1 reintroduction and into the effectiveness of various control strategies, we developed the simulation model InterIBR. InterIBR is a dynamic model that takes into account risk and uncertainty and the geographic location of individual farms. Simulation of a BHV1-outbreak in the Netherlands starts with introduction of the virus on a predefined farm type, after which both within-farm and between-farm transmission are simulated. Monitoring and control measures are implemented to simulate detection of the infection and subsequent control. Economic consequences included in this study are related to losses due to infection and costs of control. In the simulated basic control strategy, dairy farms are monitored by monthly bulk-milk tests and miscellaneous farms are monitored by half-yearly serological tests. After detection, movement-control measures apply, animal contacts are traced and neighbour farms are put on surveillance. Given current assumptions on transmission dynamics, we conclude that a strategy with either rapid removal or vaccination of infected cattle does not reduce the number of infected farms compared to this basic strategy - but will cost more to control. Farm type with first introduction of BHV1 has a considerable impact on the expected number of secondarily infected farms and total costs. To limit the number of infected farms and total costs due to outbreaks, we suggest intensifying the monitoring program on farms with a high frequency of cattle trade, and monthly bulk-milk testing on dairy farms.     

Eradication of porcine sarcoptic mange within a health declared production model

The success of a large-scale eradication programme against sarcoptic mange was evaluated in piglet producing herds belonging to the health class LSO 2000. These farms are monitored to be free from sarcoptic mange, swine enzootic pneumoniae, swine dysentery and progressive atrophic rhinitis. The local veterinarians were instructed to eradicate sarcoptic mange from the herds by 2 ivermectin injections 14 days apart or 3 treatments with phoxim pour-on 6 days apart before the farms were able to join the health class. The study consisted of a questionnaire administered to the farmers, farm visits and follow-ups associated with the regular control of the health class. A questionnaire was sent to all of the 379 accepted farrowing farms. Altogether 323 farmers had initiated an eradication programme at least 7 months before the questionnaire was distributed and 96% of them believed that the mange eradication programme had been successful. In most of the successful herds (90%), the local veterinarian had treated the animals by the recommended methods, and the majority of the farmers (88%) had cleaned and sprayed the pens with insecticides on the days of treatment. Three out of the 7 unsuccessful farms had employed methods other than those recommended. Twenty-five herds were randomly selected for an intensified control. The rubbing index was < or = 0.1 in all herds visited, indicating freedom from mange. Sows or gilts, 15-20 animals per farm, were skin scraped and no Sarcoptes scabiei was found. The same animals were blood sampled and serum antibodies to S. scabiei were measured by an indirect ELISA. All except 1 farm had low optical density (OD) values in most of the samples. The owner of that farm had become uncertain about the mange status of the herd and had recently retreated all animals with acaricides. The number of complaints about mange in the finishing units buying health class feeder pigs was low. The study demonstrates that it is possible to run an eradication programme against sarcoptic mange, in which a large number of farmers together with their veterinarians participate. It is possible to eradicate mange not only at the herd but also at the population level. The ELISA test employed proved to be a possible tool to monitor the efficacy of mange-eradication programmes.     

An estimated prevalence of Johne's disease in a subpopulation of Alabama beef cattle.

The objective of this study was to estimate the overall prevalence of animals that were infected with Mycobacterium avium ssp. paratuberculosis in a subpopulation of Alabama beef cattle. This was determined using a commercial enzyme-linked immunosorbent assay (ELISA) for the detection of M. avium ssp. paratuberculosis-specific antibodies in serum. Serum was collected from 79 herds that were participating in the Alabama Brucellosis Certification program. A total of 2,073 beef cattle were randomly tested by selecting 30 animals per herd in herds greater than 30 and selecting all animals in herds 30 and less for testing. It has been estimated that the commercial ELISA test used has a 60% sensitivity and a 97% specificity. Of the 79 herds tested, 29 herds were seronegative, 24 herds had 1-2 positive animals, and 26 herds had 3 or more seropositive animals. The average number of infected animals per positive herd was 3.3. In addition, a calculated minimum of 53.5% of the herds were identified as Johne's positive herds with a 95% confidence level. Of the total number of animals tested, 8.0% (166/2,073) of them were positive by the ELISA. After adjustments for test sensitivity and specificity and the proportion of animals sampled per herd, the true prevalence was calculated to be 8.75%. These data suggest that approximately 50% of the herds are infected with M. avium ssp. Paratuberculosis, and the overall prevalence of infection in Alabama beef cattle is approximately 8%, which correlates with other previously published regional estimates.     

Quantification of the transmission of bovine herpesvirus 1 among red deer (Cervus elaphus) under experimental conditions

Bovine herpesvirus 1 (BHV1) is endemically present in a cattle population that lives in a nature reserve in the Netherlands. Red deer (Cervus elaphus), living in the same nature reserve, can come into contact with the BHV1-infected cattle and could then become infected with BHV1. For the eradication of BHV1 in cattle, it is, therefore, important to know whether red deer alone can play a role in the transmission of BHV1. For that reason, we quantified the transmission of BHV1 among farmed red deer under experimental conditions. Two groups of ten animals were formed. In each group, five of these animals were inoculated with BHV1 and the other five served as contact animals. Three inoculated animals in each transmission experiment became infected and none of the contact animals became infected. The one-sided 95% confidence interval for R [0.0-0.94] showed that limited transmission might occur among red deer. Based on these results, we would expect only minor outbreaks of BHV1 to occur in red deer populations. We concluded that BHV1 will probably not survive longer than a few decades (several times the mean deer lifetime) in red deer populations. Consequently, it is not necessary for the eradication of BHV1 in cattle to eradicate BHV1 in red deer populations as well.     

Establishing a pilot bovine viral diarrhoea virus eradication scheme in Somerset

Beginning in April 2006, 41 farms were recruited onto a pilot Bovine viral diarrhoea virus (BVDV) eradication programme across the south of England with the majority of study herds concentrated in Somerset. Each herd was assessed and where relevant cleared of persistently infected (PI) animals. Seven farms dropped out before whole herd screening could be performed. Of the remaining 34 farms, 20 (59 per cent) were classified as infected although two of these were initially misclassified as BVDV-free. Over the course of three years, 61 PIs were identified across 16 of the 20 infected farms. 72 per cent of PIs indentified on the first herd test were below two years of age. PI prevalence ranged from 0.2 to 3.1 per cent of infected herds and was highest in herds that did not vaccinate. By the end of 2009, 24/34 (71 per cent) of study farms were BVDV-free while 10 (29 per cent) remained infected.     

Experiences from the Danish programme for eradication of bovine virus diarrhoea (BVD) 1994-1998 with special reference to legislation and causes of infection

The main experiences from the Danish bovine virus diarrhoea (BVD) eradication programme over 5 years from 1994 to 1999 are presented. The last 3 years of the programme has been strongly supported by legislation. The most important regulations have been blood testing of live animals before movement to other herds, common pastures or exhibitions, and monitoring of all herds at regular intervals for the presence of the infection. Nevertheless, free herds have experienced infection, e.g., 204 dairy herds in 1998. Of herds found to be infected in the period from July 1997 through June 1998 after previously having been registered to be BVD-free, 67 herds were thoroughly investigated. Nineteen herds (28%) were found infected because of purchase of pregnant cows or heifers which delivered persistently infected (PI) calves, and 24 (36%) and two (3%) because of PI animals on neighbouring pastures or in neighbouring farm houses, respectively. In five herds (7%) pregnant heifers had become infected on one and the same common pasture, while in 17 herds (25%) no immediate cause of infection could be demonstrated. Yet, airborne spread from PI herds as a source of infection was suspected in some of these cases. It was furthermore concluded from investigations presented, that antibody-positive AI bulls were a remote but unlikely possibility. Free-living deer in Denmark had to be considered uninfected. Presence of PI-animals in sheep on infected farms has been seen and is paid attention to in individual cases. The results underline the need for legislation to be used in eradication programmes in areas with a high prevalence of infection and to be introduced right from the beginning in order to minimise the risk of infection for free herds.     

Herd-level seroprevalence of swine-influenza virus in Korea

A total of 911 serum samples from 130 herds (an average of nine serum samples per herd) in Korea were examined for antibody to swine H1N1-influenza virus using enzyme-linked immunosorbent assay (ELISA). The list of farms was obtained from the Korean Swine Association, and herds were included from all five of the country’s states. Farms were selected using a random-numbers table for swine within farms and for farms. All serum samples were collected from 22- to 24-week-old finishing pigs between September 2000 and March 2001. By ELISA, 93 out of 130 sampled herds (71.5%) were positive against swine H1N1-influenza virus. Our data suggested that seropositive herds for swine H1N1-influenza virus are distributed diffusely throughout the Republic of Korea.