Serum antibody levels to Taenia saginata in cattle grazed on Scottish pastures

The serum antibody levels to Taenia saginata of three groups of cattle were assessed by an enzyme-linked immunosorbent assay (ELISA). The first group of cattle were from four farms which had a confirmed T saginata cysticercosis outbreak, all of which had cattle classed as infected by ELISA. The second group were from four farms where sewage sludge had been applied to pasture subsequently grazed by the cattle. One of these farms had cattle classed as infected by ELISA. The control cattle, which were all classed as uninfected by ELISA, came from five farms whose pasture had not been treated with sewage sludge. In a wider survey, involving sera from 47 additional farms, the majority could not be distinguished from the control farms in the earlier survey. However, samples from three of the farms had a similar number of positives to two of the known infected farms in the initial survey. Since the ELISA assay may indicate infected herds, farms such as these warrant further investigation.     

Factors affecting the natural transmission of bovine leukaemia virus infection in Queensland dairy herds

Natural transmission of bovine leukaemia virus (BLV) infection in south-eastern Queensland dairy herds was slow in 2 herds with a low to moderate (13 to 22%) prevalence of infection. Infection spread much more rapidly in a herd that had a higher prevalence (42%) when first tested. In a 13 month study of this herd, the cumulative incidence of infection was 24%. In one herd new infections were confined almost entirely to calves of uninfected dams. Following the end of feeding bulk milk to calves, a common practice in dairy herds, no more calves in this herd became infected. In laboratory experiments, neither prolonged housing of susceptible calves with infected cattle, consumption of drinking water contaminated with infected blood, nor inoculation of sheep with saliva from infected cattle resulted in transmission of BLV infection. Sheep were infected by subcutaneous inoculation of a suspension of purified lymphocytes from an infected heifer. The minimum infective dose was 10(3) lymphocytes, equivalent to the number of lymphocytes in approximately 0.1 microliter blood. Thus, procedures involving the transfer of a very small volume of blood from animal-to-animal have the potential to transmit infection.     

Serodiagnosis of bovine cysticercosis by detecting live Taenia saginata cysts using a monoclonal antibody-based antigen-ELISA

An ante mortem antigen-ELISA-based diagnosis of Taenia saginata cysticercosis was studied in artificially (n = 24) and naturally (n = 25) infected cattle with the objective of further validating the assay as a field diagnostic test. Based on total dissection as the definitive method of validity, the assay minimally detected 14 live cysticerci in artificially infected calves and 2 in naturally infected steers. In natural infections, the minimum number of live cysticerci consistently detected by Ag-ELISA was 5 while in artificial infections it was above 14. However, other animals with 12 and 17 live cysticerci in artificially infected calves, and 1 and 2 live cysticerci in naturally infected steers, escaped detection for unknown reasons. Animals harbouring dead cysticerci gave negative reactions in the assay as was the case in non-infected experimental control calves. There was a statistically significant positive linear correlation between Ag-ELISA optical density values and burdens of live cysticerci as obtained by total dissection of both artificially infected calves (r = 0.798, n = 24; P < 0.05) and naturally infected steers (r = 0.631, n = 25; P < 0.05). These results clearly show the potential effectiveness of ante mortem monoclonal antibody-based antigen detection ELISA in the diagnosis of bovine cysticercosis in cattle. Its value lies in the diagnosis of infection in cattle as a screening test in a herd, rather than as a diagnostic test at the individual level, due to false positive and negative reactions. In a herd of heavily infected cattle, the assay may, however, provide for individual diagnosis. Nevertheless, more work is recommended to increase its sensitivity so as to be able to diagnose light infections consistently in the field.     

Dynamics of bovine herpesvirus type 1 infection in Estonian dairy herds with and without a control programme

Bovine herpesvirus type 1 (BHV-1) is an important bovine pathogen, exacerbating poor health and the productivity of cattle. The aims of this study were to detect the efficacy of vaccination programmes in lowering the seroprevalence of BHV-1 gE within the dairy herd and to follow the dynamics of the infection in non-vaccinated herds with uninfected heifers. A two-year longitudinal study was carried out on seven herds that were vaccinated, and in five herds with uninfected heifers without applying a control programme. After the start of the vaccination programme, calves born remained free from the virus. However, in one herd, 7 per cent (95 per cent CI 2 to 18) of these animals showed antibodies to BHV-1 two years after the first vaccination. A decline in BHV-1 antibody prevalence was found in vaccinating herds. Among the five herds not under the control programme, one experienced active virus spread, although one herd experienced self-clearance of the virus. In the herds with high BHV-1 prevalence, vaccinating all cattle from three months of age twice a year with a commercial inactivated marker vaccine efficiently protected offspring from becoming infected, and lowered the prevalence of BHV-1 within the herd. A small proportion of herds may experience self-clearance of the virus.     

Detection of calves persistently infected with bovine pestivirus in a sample of dairy calves in south-eastern Queensland

Objective To determine the proportion and incidence of calves persistently infected with bovine pestivirus in calves (n = 1521) supplied to the Tick Fever Research Centre and to assess the test regime to detect calves persistently infected with bovine pestivirus.
Design Calves, 1 to 6 weeks old, selected for use in the production of the tick fever vaccine were collected from 21 properties in 56 separate groups between October 1990 and December 1996. Each group was examined for the presence of calves persistently infected with bovine pestivirus.
Procedure All calves were routinely tested for antibody to bovine pestivirus and bovine pestivirus antigen using a serum neutralisation test and an antigen-capture ELISA, respectively. Pooled lymphocyte samples from calves were also monitored for bovine pestivirus by inoculation of sheep. Whole herd testing was carried out in eight herds, using a serum neutralisation test as a screen test followed by an antigen-capture ELISA of cattle with a serum neutralisation test titre of less than 32.
Results Fourteen of the 1521 calves tested (0.9%), were detected as persistently infected and the incidence ranged from 0.0 to 3.0 % per year over 6 years. Persistently infected calves were found in 13 of the 59 groups and originated from 7 of the 21 herds used. In whole herd testing on the properties of origin, cattle persistently infected with bovine pestivirus were detected in four of the eight herds tested
Conclusions The proportion of calves persistently infected with bovine pestivirus is similar to that in other countries and indicates that bovine pestivirus could be a significant cause of economic loss in Australian cattle herds. In detecting calves persistently infected with bovine pestivirus, the combination of sheep inoculation, paired antigen-capture ELISA and serum neutralisation tests appeared to be highly sensitive and specific.     

Mycoplasma bovis-free breeding of cattle]

On a cattle farm latently infected by M. bovis, field studies aiming at the formation of a mycoplasma free herd, were carried out with a group of newborn female calves. These calves were strictly separated from their dams and any other cattle immediately after parturition. Intensive investigations for mycoplasmas were made over 30 months (mycoplasma isolation from nasal swabs, antibody detection by means of indirect hemagglutination test and ELISA technique). M. bovis could never be isolated from the samples. Also, there were no antibodies to M. bovis. In some animals antibody titers to M. bovis occurred after having contact with cattle infected with M. bovis. The results demonstrate a practicable way to establish cattle herds free from M. bovis infection.     

Sensitivity of test strategies used in the Voluntary Johne's Disease Herd Status Program for detection of Mycobacterium paratuberculosis infection in dairy cattle herds

OBJECTIVE: To evaluate sensitivities at the herd level of test strategies used in the Voluntary Johne's Disease Herd Status Program (VJDHSP) and alternative test strategies for detecting dairy cattle herds infected with Mycobacterium paratuberculosis. DESIGN: Nonrandom cross-sectional study. SAMPLE POPULATION: 64 dairy herds from Pennsylvania, Minnesota, Colorado, Ohio, and Wisconsin. Fifty-six herds had at least 1 cow shedding M. paratuberculosis in feces; the other 8 herds were free from paratuberculosis. PROCEDURE: For all adult cows in each herd, serum samples were tested for antibodies to M. paratuberculosis with an ELISA, and fecal samples were submitted for bacterial culture for M. paratuberculosis. Sensitivities at the herd level (probability of detecting infected herd) of various testing strategies were then evaluated. RESULTS: Sensitivity at the herd level of the testing strategy used in level 1 of the VJDHSP (use of the ELISA to test samples from 30 cows followed by confirmatory bacterial culture of feces from cows with positive ELISA result) ranged from 33 to 84% for infected herds, depending on percentage of cows in the herd with positive bacterial culture results. If follow-up bacterial culture was not used to confirm positive ELISA results, sensitivity ranged from 70 to 93%, but probability of identifying uninfected herds as infected was 89%. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that the testing strategy used in the VJDHSP will fail to identify as infected most dairy herds with a low prevalence of paratuberculosis. A higher percentage of infected herds was detected if follow-up bacterial culture was not used, but this test strategy was associated with a high probability of misclassifying uninfected herds.     

Field validation of a commercial blocking ELISA to differentiate antibody to transmissible gastroenteritis virus (TGEV) and porcine respiratory coronavirus and to identify TGEV-infected swine herds.

A commercially available blocking ELISA was analyzed for its ability to identify antibodies to porcine coronaviruses (transmissible gastroenteritis virus [TGEV] or porcine respiratory coronavirus [PRCV]), to differentiate antibodies to TGEV and PRCV, and to identify TGEV-infected herds. Nine sera from uninfected pigs, 34 sera from 16 pigs experimentally infected with TGEV, and sera from 10 pigs experimentally infected with PRCV were evaluated using both the TGEV/PRCV blocking ELISA and a virus neutralization (VN) assay. The ELISA was not consistently effective in identifying pigs experimentally infected with TGEV until 21 days postinfection. Sera from 100 commercial swine herds (1,783 sera; median 15 per herd) were similarly evaluated using both tests. Thirty of these commercial herds had a clinical history of TGEV infection and a positive TGEV fluorescent antibody test recorded at necropsy within the last 35 months, while 70 herds had no history of clinical TGEV infection. The blocking ELISA and the VN showed good agreement (kappa 0.84) for the detection of porcine coronavirus antibody (TGEV or PRCV). The sensitivity (0.933) of the ELISA to identify TGEV-infected herds was good when considered on a herd basis. The ELISA was also highly specific (0.943) for the detection of TGEV-infected herds when the test results were evaluated on a herd basis. When sera from specific age groups were compared, the ELISA identified a greater proportion (0.83) of pigs in herds with TGEV antibody when suckling piglets were used. In repeatability experiments, the ELISA gave consistent results when the same sera were evaluated on different days (kappa 0.889) and when sera were evaluated before and after heating (kappa 0.888). The blocking ELISA was determined to be useful for herd monitoring programs and could be used alone without parallel use of the VN assay for the assessment of large swine populations for the detection of TGEV-infected herds.     

Evaluation of an antigenic fraction of Taenia hydatigena metacestode cyst fluid for immunodiagnosis of bovine cysticercosis

An antigenic fraction (ThFAS) isolated from Taenia hydatigena metacestode cyst fluid was used in an ELISA to detect antibodies to T saginata in experimentally and naturally infected cattle. In 10 calves given 1,000 to 100,000 T saginata eggs (20% to 60% viability), IgG and IgM antibodies were detected in all the calves by post-inoculation week 3. Immunoglobulin G antibody values remained increased until calves were slaughtered at post-inoculation weeks 13 to 26. Six naturally infected calves (determined by postmortem examination) were considered positive, using the ELISA. Shared antigens were demonstrated between ThFAS and T saginata and T crassiceps; there were no shared antigens between ThFAS and Haemonchus contortus or Fasciola hepatica. Specific lectin binding to ThFAS indicated the presence of glycoconjugates. Immunoblot analysis indicated that a low molecular weight polypeptide (10,000 Mr) bears the immunodiagnostic antigen.     

Validation of a bulk tank milk antibody ELISA to detect dairy herds likely infected with bovine viral diarrhoea virus in New Zealand

AIMS: To assess the sensitivity and specificity of a bulk tank milk (BTM) antibody enzyme-linked immunosorbent assay (ELISA) to detect likely infection of a dairy herd with bovine viral diarrhoea virus (BVDV). The ELISA was subsequently used to estimate the prevalence of likely infected herds in parts of the North Island of New Zealand. METHODS: BTM samples from 724 randomly selected dairy herds in the Waikato, Bay of Plenty and Northland regions of New Zealand were tested for BVDV antibodies. From this group, 20 herds were again randomly selected from each of the quartiles of the ELISA percentage inhibition (%INH) result. From each participant herd, serum from 15 randomly selected calves aged 6-18 months and 15 cows was collected and tested using an indirect blocking ELISA for BVDV antibodies. RESULTS: Among serum results from calves from 50 herds available for analysis, 34 (68%) herds were classified as likely non-infected (0-3 seropositive among 15 calves) and 16 (32%) as likely infected (5-15 seropositive among 15 calves). Receiver-operator characteristic (ROC) analysis identified an optimal cut-off for BTM of 80%INH associated with 81% sensitivity and 91% specificity for likely herd infection. The prevalence of BVDV antibodies in cows within herds and %INH for BVDV in bulk milk were positively correlated (p<0.01). The association between bulk milk %INH and the prevalence of BVDV antibodies in calves was stronger than the same association in cows. Based on the threshold of 80%INH, the 95% confidence interval (CI) for prevalence of likely infection in the 724 herds in the Waikato, Bay of Plenty and Northland regions of New Zealand was 12-17%. Vaccination against BVDV was not significantly associated with the likely infection status of the herd based on prevalence of BVDV antibodies among calves. CONCLUSION: An ELISA test result for BVDV antibodies in BTM >/=80%INH can be used as a threshold to indicate the presence of likely infection with BVDV in dairy herds in New Zealand, with 81% sensitivity and 91% specificity.     

Experiences in the control of brucellosis in cattle herds in the government district of Hannover

Caused by imported beef cattle new outbreaks of Brucellosis (subtype III) were observed in the government district of Hannover, which was "Brucellosis free" over a long period. With the aim to interrupt the series of infections from herd to herd it seemed to be necessary to introduce a herd screening system including frequent tests. It was not possible to screen the herds by the usual way of blood serum testing because of reasons of practicability and economy. A practicable alternative was the ELISA supported tank investigation. Four of the last six outbreaks were detected by this milk sampling. The other two infected herds were detected by only clinical symptoms because the lactating cows were not infected and had no contacts to the infected separately held heifers. The required test frequency in the dairy cattle herds could only be realized applying an ELISA supported highly sensitive tank milk test method. This method offered the chance of discovering infected herds as soon as possible and prevented greater economical losses and animal health risks. The tank milk screening of the dairy cattle herds to detect antibodies against Brucellosis (and additional EBL and IBR) has now become a standard method to continue the official status "free from..." This is a safer and a more economic alternative to the previous blood sampling of cattle older than two years with a three years interval because this method guarantees a safe information about the serological status of each cow which is now tested at least once a year, depending on the time of dry standing status.(ABSTRACT TRUNCATED AT 250 WORDS)     

Infectivity of bovine leukaemia virus infected cattle: an ELISA for detecting antigens expressed in in vitro cultured lymphocytes.

A simple ELISA is described for quantifying expression of bovine leukaemia virus (BLV) antigens in short-term cultures of peripheral blood lymphocytes (PBL) isolated from infected cattle. The PBL-ELISA demonstrated that antigen expression levels in infected cattle could vary by more than 50-fold. Inoculation of sheep with dilutions of lymphocytes from two BLV-infected cattle, differentiated in the PBL-ELISA by 50 to 100-fold, suggested that antigen expression levels were correlated with infectivity. Haematological data indicated that increased antigen expression in PBL cultures was associated with an increased number of circulating B-lymphocytes, irrespective of whether or not an animal had lymphocytosis. This supported the hypothesis that BLV-infected cattle that are PBL-ELISA positive are more infectious and may present a greater risk of transmitting the disease. The applicability of the PBL-ELISA to a field situation was assessed with 98 BLV-infected cattle from three commercial dairy herds with infection prevalences of 11%, 23% and 47%. Similar percentages (49%, 50% and 52%) of PBL-ELISA positive cattle were identified among those infected cattle available for testing in the three herds. An additional 22 infected cattle from an experimental herd were tested to assess the stability of antigen expression levels over an 8 month period. Fewer (27%) of these cattle were identified as PBL-ELISA positive and antigen expression levels were generally lower than those observed in the commercial herds. Antigen expression levels in the experimental herd remained stable over the period of the study. The potential of the PBL-ELISA to assist in BLV eradication programs by identifying those seropositive cattle with the greatest potential to transmit infection is discussed.     

Validation of a bulk tank milk antibody ELISA to detect dairy herds likely infected with bovine viral diarrhoea virus in New Zealand

AIMS: To assess the sensitivity and specificity of a bulk tank milk (BTM) antibody enzyme-linked immunosorbent assay (ELISA) to detect likely infection of a dairy herd with bovine vi- ral diarrhoea virus (BVDV). The ELISA was subsequently used to estimate the prevalence of likely infected herds in parts of the North Island of New Zealand.

METHODS: BTM samples from 724 randomly selected dairy herds in the Waikato, Bay of Plenty and Northland regions of New Zealand were tested for BVDV antibodies. From this group, 20 herds were again randomly selected from each of the quartiles of the ELISA percentage inhibition (%INH) result. From each participant herd, serum from 15 randomly selected calves aged 6–18 months and 15 cows was collected and tested using an indirect blocking ELISA for BVDV antibodies.

RESULTS: Among serum results from calves from 50 herds available for analysis, 34 (68%) herds were classified as likely non-infected (0-3 seropositive among 15 calves) and 16 (32%) as likely infected (5–15 seropositive among 15 calves). Receiver- operator characteristic (ROC) analysis identified an optimal cut-off for BTM of 80%INH associated with 81% sensitivity and 91% specificity for likely herd infection. The prevalence of BVDV antibodies in cows within herds and %INH for BVDV in bulk milk were positively correlated (p<0.01). The association between bulk milk %INH and the prevalence of BVDV antibodies in calves was stronger than the same association in cows. Based on the threshold of 80%INH, the 95% confidence interval (CI) for prevalence of likely infection in the 724 herds in the Waikato, Bay of Plenty and Northland regions of New Zealand was 12–17%. Vaccination against BVDV was not significantly associated with the likely infection status of the herd based on prevalence of BVDV antibodies among calves.

CONCLUSION: An ELISA test result for BVDV antibodies in BTM ≥80%INH can be used as a threshold to indicate the presence of likely infection with BVDV in dairy herds in New Zealand, with 81% sensitivity and 91% specificity.     

Serodiagnosis of Salmonella dublin infection in Danish dairy herds using O-antigen based enzyme-linked immunosorbent assay.

Usefulness of two enzyme-linked immunosorbent assays (ELISA) for screening of dairy herds for antibodies to lipopolysaccharide (LPS) of Salmonella dublin (O:1,9,12) was investigated. Sera (3097) were collected from 40 dairy herds located in three areas of Denmark with different prevalence of salmonellosis: ten salmonellosis-free herds from the island of Samsø where there is no history of salmonellosis, ten salmonellosis-free herds from the island of Sealand where outbreaks are infrequent, and 20 salmonella infected herds from Jutland where salmonellosis is enzootic. The samples were analyzed for antibodies to S. dublin LPS using an indirect (O:9,12) and a blocking (O:9) ELISA. Using herd history of salmonellosis, herd location and clinical state of the herds as reference, the herd sensitivity and herd specificity of the tests were 100% and 100% in the indirect ELISA and 95% and 100% in the blocking ELISA, respectively. A significant correlation was found between the two tests (rs = 0.46, p < 0.001). However, the indirect ELISA detected more seropositive animals than the blocking ELISA (17% vs. 7%, respectively). In calves from Sealand, level of background reaction was significantly lower (p < 0.001) compared to the heifers and the cows. The percentages of seropositive calves in both tests were higher (p < 0.01) in comparison to cows (19 vs. 8 in indirect ELISA, and 14 vs. 6 in blocking ELISA, respectively). Results of the study indicated that it is possible to apply LPS ELISA in serological screening for salmonellosis.     

Further evaluation of an indirect enzyme-linked immunosorbent assay for the diagnosis of bovine tuberculosis

The sensitivity and specificity of an ELISA for the detection of bovine IgG anti-Mycobacterium bovis antibodies were 73.6% and 94.1%, respectively, as determined in 53 bacteriologically confirmed tuberculous cattle and 101 healthy cattle from a tuberculosis-free area. In addition, the results of ELISA and tuberculin tests in 149 cattle were compared with those of subsequent necropsy studies. Both tests failed to detect 2 animals with tuberculous lesions and positive culture; 3/12 cattle with M. bovis isolation and no lesions, and 2/7 with atypical mycobacterial infection reacted to tuberculin, but none had antibodies; in 128 cattle with neither lesions nor mycobacterial isolation, 6 were tuberculin reactors and 7 others had antibodies. Negative results were obtained by ELISA in 21/22 paratuberculous cattle. Antibodies were not detected in 88.9% to 96.4% of 697 cattle from two tuberculin negative herds of an endemic area. In a herd with proved M. bovis infection, distribution of seropositive animals in tuberculin and non-tuberculin reactors was similar. Antibody responses to cutaneous tuberculin stimuli were observed in 4 experimentally infected cattle, but only in 2/10 healthy controls after repeated PPD stimuli. Nine controls which had either received a single tuberculin dose or none showed no increase in antibody levels. The low sensitivity of this ELISA limits its usefulness as a diagnostic tool for bovine tuberculosis eradication campaigns. However, it could be helpful in epidemiological surveillance if its efficiency to identify infected herds is demonstrated.     

Evaluation of an O antigen enzyme-linked immunosorbent assay for screening of milk samples for Salmonella dublin infection in dairy herds.

Levels of antibodies to the O antigens (O:1,9,12) of Salmonella dublin were tested in 1355 serum, 1143 cow milk and 160 bulk milk samples from dairy herds using an enzyme-linked immunosorbent assay (ELISA). In order to define the background reaction, milk samples from all lactating cows and serum samples from 9 animals were collected in each of 20 salmonellosis-free herds located on the island of Bornholm, where cattle salmonellosis has not been reported. Similar samples were collected from all stalled animals in 10 herds with recent (< 6 months) outbreaks of salmonellosis located in Jutland, where salmonella infection is enzootic. Using herd history of salmonellosis, herd location and clinical status of the herds as criteria, the optimal cutoff in the milk ELISA was determined as being at least 5% of the samples having optical density > 0.5, resulting in herd sensitivity of 1.0 and herd specificity of 0.95. While none of the sera in the herds from Bornholm was ELISA positive, 2 herds had a few reactors in the milk ELISA. Using the same cutoff, all but 1 bulk milk sample from 150 herds on Bornholm was ELISA-negative, and all 10 salmonellosis-positive herds from Jutland were ELISA-positive. A significant correlation was found between ELISA reactions in milk and in serum of cows (34% and 32% respectively, rs = 0.69, P < 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)     

Prevalence of Fasciola hepatica in dairy herds in England and Wales measured with an ELISA applied to bulk-tank milk

An ELISA developed to diagnose Fasciola hepatica infection in cattle by detecting serum antibodies was adapted and validated for use with samples of bulk-tank milk. The prevalence of the infection in 61 dairy herds was established by using serum antibody levels or faecal egg counts measured in a proportion of the cows in each herd. The correlation between the results of the ELISA and the herd seroprevalence was 0.83. Using a cut-off value of 27 per cent positive, the bulk-tank ELISA identified herds in which more than 25 per cent of the cows were infected with a diagnostic sensitivity of 96 per cent (95 per cent confidence interval 89 to 100 per cent) and a diagnostic specificity of 80 per cent (95 per cent confidence interval 66 to 94 per cent). By applying the ELISA to 623 herds in England and 445 herds in Wales, the prevalence of F hepatica infection in England was estimated to be 48 per cent (95 per cent confidence interval 46 to 54 per cent), and in Wales 86 per cent (95 per cent confidence interval 84 to 90 per cent).     

A comparison of the enzyme linked immunosorbent assay and the indirect haemagglutination technique applied to sera from cattle experimentally infected with Taenia saginata (Goeze, 1782)

The serological response of 6 calves to experimental oral infection with between 60,000 and 100,000 Taenia saginata eggs at 3–12 months of age was monitored by the enzyme-linked immunosorbent assay (ELISA) and the tanned cell indirect haemagglutination technique (IDH). A serum antibody response was detected by both techniques by 2–3 weeks post infection, rising to a plateau about 4–6 weeks post infection. The serum antibody levels began to decline by about 30 weeks post infection. Two uninfected control cattle gave negative reactions.In addition, the serological response of 5 calves which had received a dose of 10,000 T. saginata eggs at 2–3 days of age and then weekly serial doses of 500 eggs for 12 months thereafter, was compared with a similar group of 5 calves, which had received the single infection of 10,000 eggs at 2–3 days of age only. Calves in both groups developed an antibody response detectable by the ELISA technique whereas those in a group of 5 control calves did not show such a response. When studied individually however there was marked variation in the serum antibody levels of these young cattle, as although some calves gave a relatively strong serological response, others hardly varied from the controls.     

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.     

Investigation of an outbreak of mucosal disease in a beef cattle herd in southwestern Saskatchewan.

This study describes the epidemiological investigation of an outbreak of mucosal disease that occurred on a ranch in southwestern Saskatchewan. Over a six-month period during the fall and winter of 1991-1992, in a herd of 515 beef cattle and 96 bison, 20 yearling cattle from a group of 105 housed in one feedlot pen died from mucosal disease. A further eight yearlings were slaughtered for salvage because they were at risk of dying from mucosal disease. Mucosal disease mortalities were the first observed evidence of fetal infections with bovine viral diarrhea virus in this herd. Animals that died from mucosal disease exhibited signs of ill thrift prior to death. Deaths from mucosal disease were confined to the progeny of one herd of beef cows. Following an outbreak of fetal infection with bovine viral diarrhea virus during 1989-1990, at least 28 (22%) of the 128 calves born from this herd of cows in the spring of 1990 were persistently infected with bovine viral diarrhea virus. However, only one calf born from this herd in 1991, and five calves born from all herds in 1992 were persistently infected. Of the five persistently infected calves born in 1992, three were born to persistently infected replacement heifers born in 1990. These heifers calved without assistance in 1992, but only one of their calves survived past three days of age, and it was persistently infected. In January 1992, 82% of the total herd had reciprocal antibody titers to bovine viral diarrhea virus of > or = 1024 which suggested a high level of herd immunity to bovine viral diarrhea virus.(ABSTRACT TRUNCATED AT 250 WORDS)