Stefan Alenius

Principles for eradication of bovine viral diarrhoea virus (BVDV) infections in cattle populations.

Systematic eradication of BVDV without vaccination started in Scandinavia in 1993. In principle, the schemes include; (1) identification of non-infected and infected herds using different combinations of serological herd tests such as bulk milk tests and spot tests (sample of animals in a certain age), (2) monitoring/certification of non-infected herds by repeated sampling, applying one of the above-mentioned methods and (3) virus clearance in infected herds aimed at removing persistently infected (PI) animals in a cost- and time-efficient manner. In the virus clearance protocol described, an initial test is performed on all animals with subsequent follow-up of calves born as well as of dams seronegative in the initial test. It is generally recommended to perform an initial antibody test on all samples. This should be done not only to screen for seronegative animals on which virus isolation should be attempted (i.e. possible PI animals), but more in order to identify non-immune animals in reproductive age, that is, the key animals in herd-level persistence of infection. In Sweden, a common finding has been self-clearance, where the infection ceases without any other intervention than controlled introduction of new animals. Other epidemiological observations concern the course of events following virus introduction. Important risk factors for spreading BVDV are discussed, where livestock trade is perceived as the most central to control. Live vaccines, imported semen and embryos constitute special hazards, since they may act as vehicles for the introduction of new BVDV strains. The importance of making farmers aware of herd biosecurity and their own responsibility for it is stressed, and in order to maintain a favourable situation after a scheme has been concluded, effort must be put into establishing such a persisting attitude in the farming community.

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

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

Acute phase proteins as indicators of calf herd health.

Abstract The potential for using acute phase proteins (APPs) in the assessment of herd health was studied by examining the levels of serum haptoglobin, serum amyloid A (SAA) and plasma fibrinogen in relation to clinical findings and leukocyte counts in calves. Two groups of calves from conventional dairy farms were studied. The animals were examined 10 times during the first six weeks after introduction into a new environment. Haptoglobin, SAA and fibrinogen were analysed and weight gain, disease symptoms and treatments were recorded. Analysis of antibodies against viral infections was performed. An acute phase reaction (APR) score was established at each sampling by combining the APP results and total leukocyte counts. The health status differed between the two groups, although no manipulation of health had been performed, except that the group with a higher incidence of disease had a concurrent experimental infection with lungworm as part of another study. In the group with a higher incidence of disease, the mean weight gain was significantly lower, and the number of sampling days with elevated serum concentrations of APPs, and the mean maximum concentrations of haptoglobin and fibrinogen were significantly higher compared to the healthier group. The APR score was significantly higher at days 4 and 8 of the study in the group with a higher incidence of disease. The results indicate that measurement of APPs could be a useful tool for evaluation of health in calf herds.

Dynamics of virus infections involved in the bovine respiratory disease complex in Swedish dairy herds

Abstract The dynamics of bovine respiratory syncytial virus (BRSV), bovine parainfluenza virus 3 (PIV-3), bovine corona virus (BCoV) and bovine viral diarrhoea virus (BVDV) infections were studied in 118 dairy herds in south western Sweden. By using serology on paired samples from three ∼7 vs. ∼15-month-old calves per herd, the propagation of infections was investigated over about a 1-year period. The results implied that at least 74% of calves had experienced one or more of the monitored infections at the age of ∼7 months (Sample 1, Spring); 30%, 48%, 34% and 8% were seropositive to BRSV, PIV-3, BCoV and BVDV, respectively. Seroconversions to BRSV, PIV-3, BCoV and BVDV occurred in 26%, 38%, 50% and 3% of seronegative animals and 63% had antibodies against two or more infections at ∼15 months (Sample 2). In total, 90–97% of animals that were seropositive in Sample 1 remained positive in Sample 2. A significant association was found between BVDV and BCoV (P =0.01). Moreover, a significantly higher proportion of herds in which no calves had a recorded history of respiratory disease (n =15) were classified as negative to all four infections monitored when compared to herds in which disease was observed (P =0.0002). This study showed a high infection burden in young animals and effective spread of BRSV, PIV-3 and BCoV in one area of Sweden. BVDV infections were restricted to a few herds, reflecting the effect of a voluntary control program against BVDV in Sweden.

Effects of infection with bovine virus diarrhoea virus on health and reproductive performance in 213 dairy herds in one county in Sweden

Abstract Bulk tank milk samples, collected twice with a 1 year interval, from 213 Swedish dairy herds with no vaccination programme against bovine virus diarrhoea virus (BVDV), were tested for antibodies to BVDV using an indirect enzyme-linked immunosorbent assay. The herds were classified into four different BVDV groupings based on changes in the estimated prevalence of BVDV antibody-positive cows in the herds. The estimated mean prevalences of BVDV antibody-positive cows were maintained as > 80% in 58 (27.2%) and as

Bovine herpesvirus type 1 (BHV-1) and bovine viral diarrhoea virus (BVDV) infections in dairy herds: self clearance and the detection of seroconversions against a new atypical pestivirus.

The epidemiology of bovine herpesvirus type 1 (BHV-1) and bovine viral diarrhoea virus (BVDV) was studied in a population of small dairy herds that had not been vaccinated. Bulk tank milk samples of 186 herds in Thailand were collected four times between 2002 and 2004. Serum samples from individual animals in 11 herds were also taken on three occasions. The prevalence of BHV-1 in the 186 herds was 61% in 2002, decreasing to 48% in 2004 and for BVDV was 91% in 2002, decreasing to 72% in 2004. A BVDV antigen-positive calf was found in one of the 11 herds, and animals in this herd and three other herds seroconverted to a recently described atypical BVDV strain (HoBi). This study showed a significantly decreasing prevalence for both BHV-1 and BVDV due to a self-clearance process. Further studies are needed to find out how the atypical BVDV strain entered the cattle population.

Comparison between dairy cow disease incidence in data registered by farmers and in data from a disease-recording system based on veterinary reporting

Abstract Sweden has a national disease-recording system based on veterinary reporting. From this system, all cattle-disease records are transferred to the dairy industry cattle database (DDD) where they are used for several purposes including research and dairy-health statistics. Our objective was to evaluate the completeness of this data source by comparing it with disease data registered by dairy farmers. The proportion of veterinary-treated disease events was estimated, by diagnosis. Disease incidence in the DDD was compared, by diagnosis and age, with disease data registered by the farmers. Comparison was made, by diagnosis, for (i) all disease events and (ii) those reported as veterinary-treated. Disease events, defined as “observed deviations in health, from the normal” were recorded by the farmers during January, April, July and October 2004. For the diagnoses calving problems, peripartum disorders, puerperal paresis and retained placenta, incidence proportions (IP) with 95% confidence intervals (CIs) were estimated. For all other disease problems, incidence rates (IR) were used. In total, 177 farmers reported at least 1 month and 148 reported all 4 months. Fifty-four percent of all disease events in the farmers’ data were reported as veterinary-treated. For several of the most common diagnoses, the IRs and IPs for all events were significantly higher in farmers’ data than in the DDD. Examples are, in cows: clinical mastitis, cough, gastro-intestinal disorders and lameness in hoof and limb; and in young stock: cough and gastro-intestinal disorders. For veterinary-treated events only, significant differences with higher IR in the farmers’ data were found in young stock for sporadic cough and sporadic gastro-intestinal disorders. The diagnosis “other disorders” had significantly more events in the DDD than in farmers’ data, i.e. veterinarians tended to choose more unspecific diagnoses than the farmers. This result indicates that the true completeness is likely to be higher than our estimate. We conclude that for the time period studied there was differential under-reporting associated with the diagnosis, the age of the animal and whether the herd was served by a state-employed or private veterinarian.

Validation of a test for dams carrying foetuses persistently infected with bovine viral-diarrhoea virus based on determination of antibody levels in late pregnancy.

Our objective was to estimate, using a generalised linear mixed-model approach, the sensitivity and specificity of an indirect ELISA when used to identify dams pregnant with persistently bovine viral-diarrhoea virus (BVDV)-infected foetuses. Cows that had been tested for antibodies to BVDV with a positive result during their pregnancy and where the offspring had been tested for both antibody and virus were identified by accessing the Swedish BVD database and the official pedigree records. The resulting data set consisted of 2162 cow-calf pairs in 126 herds, of which 281 included virus-positive calves. The sensitivities and specificities at 12 different decision thresholds (corresponding to optical densities (ODs) between 0.5 and 1.6) were estimated using generalised linear mixed models (binomial error, logit link), in which the gold standard (the BVDV status of the calf) was included as a covariate. In each model, the dependent variable was the dichotomous test result at the decision threshold in question. There was a significant positive interaction between the calfs status and gestational stage in all 12 models--indicating that the sensitivity and specificity at any given decision threshold was improved when the the test was performed later in pregnancy. The test should be applied only when samples have been taken in late gestation--not before the seventh month in pregnancy. If applied during the last months of pregnancy, the point estimate of the sensitivity ranges between 0.94 and 1.0 as the decision threshold is moved from 1.0 and downwards to 0.7. Similarly, the specificity ranges between 0.39 and 0.67 as the decision threshold is moved from 0.8 and upwards to 1.1.

Natural infection with bovine virus diarrhoea virus in a dairy herd: A spectrum of symptoms including early reproductive failure and retained placenta

Abstract The consequences of natural infections by bovine virus diarrhoea virus (BVDV) in a dairy herd comprising approximately 60 cows were studied over a 3 year period. The outcome of 39 pregnancies after artificial insemination or natural service during a 4 month period of risk for contracting BVDV was nine abortions, one mummified foetus, one still-birth, three calves that died within 1 week of age, 12 calves persistently infected (PI) with BVDV (11 males and one female) and 13 non-PI calves. Retrospective studies showed that only two of the 13 dams (15.4%) of non-PI calves had been inseminated once, which is a significantly (P < 0.001) lower rate than for 192 other gestations (66.7%) during the 3 year period. The gestational duration of multiparous cows (but not of heifers) was longer (P < 0.01) for five cows with PI calves (mean ± SD 287.6 ± 9.5 days) than for 53 other gestations in 35 cows (280.6 ± 3.8 days). Five of the 12 dams of the PI calves had not expelled the foetal membranes within 2 days after calving, which is a higher (P < 0.001) incidence than the seven cases of retained placenta observed after 198 other calvings. Furthermore, there was a 4.4-fold higher risk (P < 0.01) of treatment for enteritis and/or pneumonia in calves and a 6.0-fold higher risk of calf mortality associated with the introduction of BVDV. The mean heart girth of the PI calves was less (P < 0.05) than that of non-PI calves, at both 80 and 180 days of age.

Therapeutic Effect of Trisodium Phosphonoformate on Cutaneous Herpesvirus Infection in Guinea Pigs

When applied topically, trisodium phosphonoformate (PFA) displayed activity against established cutaneous herpesvirus infections in guinea pigs similar to that exhibited by the closely related phosphonoacetic acid (PAA); however, unlike PAA, PFA was not locally skin irritating. The therapeutic benefits of topical application of PFA were clearly evident when application was delayed for 48 h after virus inoculation, at which time lesions were well developed. The therapeutic effect was dependent on the concentration of PFA and the duration of treatment. PFA exhibited significant activity against established infections when administered intraperitoneally, although it was less effective via this systemic route than when applied topically.