Aspects of bovine herpesvirus-1 infection in dairy and beef herds in the Republic of Ireland

Background

Infection with bovine herpesvirus-1 (BHV-1) causes a wide range of disease manifestations, including respiratory disease and abortion, with world-wide distribution. The primary objective of the present study was to describe aspects of BHV-1 infection and control on Irish farms, including herd-level seroprevalence (based on pooled sera) and vaccine usage.

Methods

The characteristics of a diagnostic indirect BHV-1 antibody ELISA test when used on serum pools were evaluated using laboratory replicates for use in the seroprevalence study. The output from this indirect ELISA was expressed as a percentage positivity (PP) value. A proposed cut off (PCO) PP was applied in a cross-sectional study of a stratified random sample of 1,175 Irish dairy and beef cattle herds in 2009, using serum pools, to estimate herd seroprevalence. The study was observational, based primarily on the analysis of existing samples, and only aggregated results were reported. For these reasons, ethical approval was not required. Bulk milk samples from a subset of 111 dairy herds were analysed using the same ELISA. Information regarding vaccine usage was determined in a telephone survey.

Results

A PCO PP of 7.88% was determined to give 97.1% sensitivity and 100% specificity relative to the use of the ELISA on individual sera giving maximization of the prevalence independent Youden''s index, on receiver operating characteristics analysis of replicate results. The herd-level BHV-1 seroprevalence was 74.9% (95% CI - 69.9%-79.8%), with no significant difference between dairy and beef herds. 95.5% agreement in herd classification was found between bulk milk and serum pools. Only 1.8 percent of farmers used BHV-1 marker vaccine, 80% of which was live while 75% of vaccinated herds were dairy.A significant association was found between herd size (quartiles) and seroprevalence (quartiles).

Conclusions

The results from this study indicate BHV-1 infection is endemic, although BHV-1 vaccines are rarely used, in the cattle population in Ireland.     

Quantifying badger exposure and the risk of bovine tuberculosis for cattle herds in county Kilkenny, Ireland

The objectives of the study were to quantify the levels of badger exposure for cattle and to test the hypothesis that increased badger exposure does not increase the risk of bovine tuberculosis (BTB) in a herd. Information that became available from the targeted removal of badgers over the study period, and from a badger-removal project in county Kilkenny, during 1996-1999 was used. The specific location of cattle within each farm, and the length of time that cattle spent in each farm field during the grazing season, and in the barnyard during winter, was used to build an exposure coefficient to quantify the amount of badger exposure that cattle encountered either on pasture or in the barn. The study design was a matched case-control study in which the control herds were selected using incidence density sampling. During the 4-year study period, 543 badgers were removed and of these 96 badgers were classified as tuberculosis positive; 96 BTB herd breakdowns occurred. There was a significant association between case herds and having a higher badger sett exposure coefficient during 1996-1998. No significant association between case herds and having a higher exposure coefficient based on the number of badgers, or the number of tuberculous badgers, during September 1997-December 1999 was found.     

Targeted badger removal and the subsequent risk of bovine tuberculosis in cattle herds in county Laois, Ireland

We investigated the impact of targeted removal of badgers on the subsequent bovine tuberculosis (BTB) risk in cattle herds in county Laois, Ireland. The study period was 1989-2005. For each of 122 targeted badger-removal licenses (permit to remove badgers in the proximity of cattle herds undergoing a serious BTB episode), the herd number (index herd) for which the license was given was obtained. The herds in the proximity of the index herd were identified from another database. The main "exposure" in our study was the geographical location of herds relative to the area in which targeted badger removal was conducted. We categorized herds into five different exposure groups: herds were classified as non-exposed and denoted as group 0 (reference group) if they were located 500 m or more from the edge of any parcel of land of the index herd; group 1, was the index herds, group 2 the immediate (contiguous) neighbors of the index herd, group 3 herds were not immediate neighbors but within 150 m and group 4 herds were between 150 m and 500 m distance from the edge of any parcel of land of the index herd, respectively. We conducted a survival analysis (allowing multiple failures per herd) to compare the hazard of having a BTB episode in any of the four groups of exposed herds vs. the hazard in herds in the reference group. We controlled for other known risk factors as well taking into account a temporal component. Our analysis showed that the hazard ratio for the index herds (group 1) were non-significantly increased, indicating that there was no difference in the hazard of failing a BTB test (after the targeted badger removal was conducted) between index herds and reference herds. For the rest of the herds farther away from badger removal activities the hazards were lower than herds in areas not under badger removal. The hazard in the reference group decreased over the study period.     

Risk of bovine tuberculosis for cattle sold out from herds during 2005 in Ireland

A retrospective cohort study was conducted to determine the risk of bovine tuberculosis (TB) among animals sold out from herds that were free to trade animals during the year 2005 according to their bovine TB testing history during the year 2005. The present study sample comprised of 338,960 animals, of which 124,360 animals were sold out from herds that were restricted from trading at some stage during 2005 (bovine TB 'exposed') and 214,600 animals that were sold from herds which did not have their trading status withdrawn in 2005 (bovine TB 'non-exposed'). The overall risk of a diagnosis of bovine TB during the two-year period after the animals were sold out was 0.69 per cent. The odds of bovine TB were 1.91 higher for animals sold out from bovine TB 'exposed' herds compared with animals sold out from bovine TB 'non-exposed' herds (OR 95 per cent CI: 1.76 to 2.07, P<0.0001). Ten per cent of animals identified during field surveillance with bovine TB did so less than two months after being sold out in 2005, and similarly, 10 per cent of the animals classified as bovine TB positive by finding a bovine TB lesion at slaughter did so within 25 days (or less) of being sold out in 2005.     

Geographical association between the genotype of bovine tuberculosis in found dead badgers and in cattle herds

In a survey, 457 badgers that had been found dead in Wales were postmortem-examined, and samples were examined by histology and by extended culture (for up to 12 weeks). Mycobacterium bovis was cultured from 55 badgers (12.0 per cent), and the histology typical of M bovis infection was seen in a further six (1.3 per cent). The prevalence in badgers in each of 10 geographical areas varied between 0 and 26 per cent (P<0.001), and was associated with the incidence of confirmed M bovis infection in cattle herds in the same areas (P<0.01). In northern Wales, bTB was rare in both hosts. An infected badger was 12.3 times more likely to be within 5 km of a confirmed cattle bTB breakdown than an uninfected badger. The M bovis isolates from badgers belonged to one of four genotypes defined by spoligotype and variable number tandem repeat type. These genotypes were also found in 290 concurrent confirmed herd breakdowns, and tended to be similar to the genotypes in badgers in the same geographical areas. When badgers and cattle no more than 30 km apart were compared, the genotype diversity was greater in cattle than in badgers (P=0.016), suggesting that the movement of cattle plays a greater part in the spatial distribution of M bovis than the movement of badgers.     

A case-control study on the association of selected risk factors with the occurrence of bovine tuberculosis in the Republic of Ireland

We did a case-control study on the association between the occurrence of bovine tuberculosis in herds in the East Offaly area and a number of possible risk factors: herd size, the purchasing of cattle, the herd history, the status of contiguous herds, distance to the nearest badger sett, and animal factors such as age, breed and animal type. The characteristics of 100 herds that had a confirmed outbreak of tuberculosis at a herd test in 1988 were compared with those from an equal number of herds that passed at least one tuberculin test during that year. The study base consisted of 1379 herds mainly from the eastern part of County Offaly. The data were analysed at both herd and animal levels. Factors that were associated with an increased risk of tuberculosis breakdowns at the herd level were (i) the total number of animals in the herd and (ii) the restriction of a contiguous herd for tuberculosis within a period of 6 months prior to or following the herd under study. A number of factors were associated with an animal having an increased risk of failing a tuberculin test. After adjusting for all other variables in the model, cows, heifers and bullocks were 10.3, 14.8 and 8.0 times, respectively, more likely to fail a tuberculin test than calves. Cattle that had teen purchased since the previous herd test were less likely to fail a tuberculin test compared with cattle that had been present at the time of the preceding herd test.     

Distribution and environmental risk factors for paratuberculosis in dairy cattle herds in Michigan.

OBJECTIVE: To determine prevalence of paratuberculosis among dairy cattle herds and to identify associated soil-related risk factors. SAMPLE POPULATION: Serum and soil samples for 121 Michigan dairy herds. PROCEDURE: Blood samples were collected from cows at each farm and tested for Mycobacterium paratuberculosis, using an antibody ELISA. Soil samples were collected from pastures and exercise lots; pH and available iron content were determined. A questionnaire was administered to collect data regarding farm management practices and productivity. RESULTS: 55% of the herds tested had > or = 2 M paratuberculosis-positive cattle. Adjusting sample prevalence for distribution of herd size strata yielded a statewide herd prevalence of 54%. Of 3,886 cattle tested, 267 had positive results. Prevalence of test-positive cattle was 6.9%. For every part per million (ppm) increase in soil iron content, there was a 1.4% increase in the risk of a herd being test-positive. An increase in soil pH of 0.1 was associated with a 5% decrease and an increase in soil iron content of 10 ppm was associated with a 4% increase in the number of test-positive cattle. Application of lime to pasture areas was associated with a herd being only 10% as likely to be paratuberculosis positive and with a 72% reduction in number of test-positive cattle. CONCLUSIONS AND CLINICAL RELEVANCE: Prevalence of paratuberculosis-positive dairy herds in Michigan (54%) was greater than expected, but prevalence of paratuberculosis-positive cattle (6.9%) was within anticipated values. These prevalences were associated positively with acidic soil and increased soil iron content. Application of lime to pasture areas was associated with reduced risk of paratuberculosis.     

Bovine tuberculosis and milk production in infected dairy herds in Ireland

This study describes the relationship between bovine tuberculosis (TB) and milk yield in TB-infected dairy herds in Ireland. The study had two objectives: to determine whether cows detected as TB reactors (and thus subject to immediate slaughter) were likely to be the higher milk-producing cows, and to determine whether subclinical TB infection was associated with reduced milk production at or around the time of disclosure (detection). All Irish dairy herds restricted from trading between the 1^st June 2004 and the 31^st May 2005 as a result of two or more TB reactors by the Single Intradermal Comparative Tuberculin Test (SICTT) were considered for study. The data consisted of 419 herds. Data were collected on all TB reactors and a random sample of 5 non-reactor cows in these herds: a data set of 4340 cows (2342 TB reactors and 1998 non-reactors). Previous milk data for the cows were taken into consideration and thus all lactations on a cow were analysed together with the years of lactations. There was an inherent hierarchical structure in the data, with lactations nested within cows and cows within herds and thus a linear mixed model with two random effects was used to describe the data. The results of this study showed that for all lactations and years under investigation, milk yield was significantly lower for TB reactor cows, with differences ranging from 120 kg (2003, lactation 3) to 573 kg (2001, lactation 1), when compared to the non-reactor cows.     

The impact of badger removal on the control of tuberculosis in cattle herds in Ireland

In Ireland, the herd prevalence of bovine tuberculosis has remained stable for several decades, and in common with several other countries, progress towards eradication has stalled. There is evidence in support of the potential role of infected badgers (Meles meles, a protected species) in bovine tuberculosis in Ireland and Britain. However, this evidence on its own has not been sufficient to prove disease causation. Field trials are likely to offer the best opportunity to define this role. Building on the earlier East Offaly project, our objectives were to assess the impact of badger removal on the control of tuberculosis in cattle herds in Ireland.

The study was conducted from September 1997 to August 2002 in matched removal and reference areas (average area of 245.1 km²) in four counties: Cork, Donegal, Kilkenny and Monaghan. Badger removal was intensive and proactive throughout the study period in the removal areas, but reactive (in response to severe tuberculosis outbreaks in cattle) in the reference areas. Removal intensity in the removal and reference areas during the first 2 years of the study averaged 0.57 and 0.07 badgers/km²/year, respectively.

The outcome of interest was restriction of cattle herds due to confirmed tuberculosis, where tuberculous lesions were detected in one or more animals. Data were analysed using logistic regression (modelling the probability of a confirmed herd restriction) and survival analysis (modelling time to a confirmed herd restriction).

During the study period, there was a significant difference between the removal and reference areas in all four counties in both the probability of and the time to a confirmed herd restriction due to tuberculosis. In the final year of the study, the odds of a confirmed herd restriction in the removal (as compared to the reference areas) were 0.25 in Cork, 0.04 in Donegal, 0.26 in Kilkenny and 0.43 in Monaghan. Further, the hazard ratios (removal over reference) ranged from 0.4 to 0.04 (a 60–96% decrease in the rate at which herds were becoming the subject of a confirmed restriction).     

Vertical transmission of bovine leukemia virus and bovine immunodeficiency virus in dairy cattle herds.

Vertical transmission of bovine leukemia virus (BLV) and bovine immunodeficiency virus (BIV) was investigated in five dairy cattle herds in Hokkaido, where 36.1 and 17.0% of cattle were BLV and BIV seropositive, respectively, and 9.9% of dams were co-infected with both BIV and BLV. Twenty six cases of offspring born from dams infected with only BLV (17 cases) or with both BIV and BLV (9 cases) were examined for the presence of BLV and BIV before and after colostrum feeding by polymerase chain reaction (PCR) and syncytium assay. After birth, all calves were separated immediately from their dams. The offspring born from BLV-positive dams were BLV-negative before colostrum feeding, suggesting that no transplacental transmission had occurred. Thereafter, these offspring were fed colostrum or milk from their dams, but still remained BLV-negative. The other offspring born from BLV-positive dams were fed with BLV-negative colostrum, or with pasteurized BLV-positive colostrum. All these calves remained negative for BLV infection, suggesting that in utero transmission of BLV is negligible. In the case of offspring born from dams co-infected with BLV and BIV, calves were BIV-positive before colostrum feeding at 1 day after the birth, indicating in utero transmission of BIV. After colostrum feeding from their dams, newborn calves became BLV-positive. In addition, one calf was BLV-positive even before colostrum feeding. These results suggest that BIV can be transmitted to offspring in utero, and that BLV can be transmitted through colostrum or milk if dams are infected with both BIV and BLV.     

Prevalence of pathogens causing subclinical mastitis in 15 dairy herds in the Republic of Ireland

: Milk samples from 285 cows in 15 dairy herds were collected for bacteriological analysis. Cows were selected on the basis of a somatic cell count (SCC) exceeding 200,000 cells per ml at the three most recent milk recordings prior to sampling. Staphylococcus aureus and Streptococcus uberis were the predominant isolates accounting for 21% (n = 61) and 19% (n = 53) of isolates, respectively. Streptococcus uberis was more frequently isolated from split-calving herds than from spring-calving herds and this difference was statistically significant (P < 0.005). Herds with suboptimal housing had a significantly greater prevalence of S. uberis than did herds where housing was adequate (P < 0.005). The isolation rates for S. aureus was significantly greater in herds where parlour hygiene was suboptimal (P < 0.05).     

Prevalence of bovine tuberculosis in pastoral cattle herds in the Oromia region,southern Ethiopia

A cross-sectional study of bovine tuberculosis (BTB) was conducted in pastoral cattle herds in southern Ethiopia, from February to August 2008 using the comparative intradermal tuberculin test. The prevalence of BTB and the risk factors for having positive reactor herds were assessed in four pastoral associations in two districts of southern Ethiopia, namely Goro-Dola with 242 cattle in 16 herds and Liben with 231 cattle in 15 herds. A herd was considered positive if there was at least one reactor animal in a herd. The test results were interpreted based on the Office Internationale des Epizooties recommended 4-mm and a recently suggested 2-mm cut-off. The apparent individual animal prevalence of tuberculin reactors was 5.5% (95% confidence interval (CI), 4.0–8.0%) and 7.0% (95% CI, 5.0–10.0%), whereas the true prevalence estimate was 4.4% (95% CI, 0.8–8.0%) and 6.1% (95% CI, 2.6–9.5%), when using the 4-mm and the 2-mm cut-offs, respectively. The overall herd apparent prevalence of tuberculin reactor animals was 41.9% (95% CI, 24.9–60.9%) and 48.4% (95% CI, 30.2–66.9%) with the 4-mm and 2-mm cut-offs, respectively. A positive tuberculin test was associated with the age of animals and the main drinking water sources during dry seasons. In order to investigate the public health risks and the epidemiological importance of BTB in the area, we recommend to include other livestock species (camels and goats) as well as humans in future studies.     

Pathologic findings and association of Mycobacterium bovis infection with the bovine NRAMP1 gene in cattle from herds with naturally occurring tuberculosis

OBJECTIVE: To determine necropsy and Mycobacterium bovis culture results in cattle from herds with tuberculosis, the role of the bovine NRAMP1 gene in resistance and susceptibility to infection with M bovis, and the association between magnitude of the tuberculous lesions and various types of M bovis isolates. ANIMALS: 61 cattle from herds with tuberculosis in Texas and Mexico. PROCEDURE: 61 cattle were evaluated by necropsy; 59 had positive and 2 had negative caudal fold tuberculin intradermal test (CFT) results. Thirty-three cattle with positive CFT results were genotyped to evaluate polymorphism of the 3' untranslated region of the bovine NRAMP1 gene, using single-stranded conformational analysis, 9 were resistant to M bovis with no tuberculous lesions and negative M bovis culture results, and 24 were susceptible with tuberculous lesions and positive M bovis culture results. Isolates of M bovis were analyzed by restriction fragment length polymorphism (RFLP) on the basis of IS6110 sequences and direct-repeat fingerprinting patterns. RESULTS: 21 (35.6%; 21/59) cattle with positive CFT results had tuberculous lesions or positive culture results; in addition, 1 of 2 cattle with negative CFT results had tuberculous lesions and positive culture results. Tuberculous lesions were most common in the thorax (35/63; 55.5%) and lymphoid tissues of the head (10/63; 15.9%). Tuberculous lesions varied from 1 to 11/animal; 8 of 21 (38.1%) had solitary lesions. Associations were not found between resistance or susceptibility to infection with M bovis and polymorphism in the NRAMP1 gene or between the magnitude of the lesions and various RFLP types of M bovis isolates. CONCLUSIONS AND CLINICAL RELEVANCE: The NRAMP1 gene does not determine resistance and susceptibility to infection with M bovis in cattle.     

Frequency of bluetongue and bovine parvovirus infection in cattle in South Carolina dairy herds

A survey of South Carolina diary cattle in 12 commercial herds was conducted, using serologic testing to determine the frequency and impact on reproduction of bluetongue (BT) and bovine parvovirus (BFV) infections. Results of the study of serum antibodies titers and dairy cattle health records indicated that the majority of the cattle surveyed was adequately protected against the major reproductive tract diseases through vaccination programs. The frequency of reproductive dysfunction was common in vaccinated herds, however. Six of the 12 herds in the survey had cattle which were BT serotest reactors, although total numbers of these reactor cattle were relatively small. Further, reproductive performance of reactor cows indicated that BT was of little consequence and was not associated with reproductive problems. All herds contained BPV serotest reactors and the latter comprised 59.7% of the total number of cows surveyed. The BPV seroreactor cows were commonly associated with the group of reproductive problem cows which experienced higher rates of embryonic mortality and more services per conception than did nonreactor cattle. The results of the survey emphasize the need for continued investigation and efforts to control BT, and especially BPV infection, in dairy cattle.     

Seroprevalence of bovine immunodeficiency virus in dairy and beef cattle herds in Korea.

Infection of bovine immunodeficiency virus (BIV), a lentivirus, is thought to sporadically occur throughout the world, but seroepidemiological surveys concerning the incidence of BIV are limited and have not been undertaken in Korea. A total of 266 sera from different twenty dairy (Holstein) and twenty-six Korean native beef (Hanwoo) farms of the south-western part of Korea was analyzed for the presence of anti-BIV antibodies by Western blotting. Thirty five percent and 33% of dairy and beef cattle, respectively, were BIV-seropositive. By nested polymerase chain reaction, it was confirmed that these seropositive cows had provirus in the peripheral blood mononuclear cells. To demonstrate the correlation with BIV and bovine leukemia virus (BLV) infection, these sera were also analyzed for anti-BLV antibodies by immunodiffusion test, resulting in high prevalence of BLV infection but relatively a few dual infections. We report herein the first serological detection of antibodies to BIV in Korea.     

Prevalence of bovine viral diarrhea virus in dairy cattle herds in eastern China

Tropical Animal Health and Production - Bovine viral diarrhea virus (BVDV) is a worldwide spreading pestivirus affecting cattle and other ruminants; however, there have been few reports on...     

Simulation model of within-herd transmission of bovine tuberculosis in Argentine dairy herds

Transmission of bovine tuberculosis was quantified in three dairy herds located in south Santa Fe Province, Argentina. Using estimates of Mycobacterium bovis transmission (β) and a Reed–Frost simulation model, the prevalence of tuberculosis infection in the study herds over time was investigated. The Reed–Frost model was modified by incorporating randomness in both β and the incubation period () of M. bovis. The mean estimated herd β was 2.2 infective contacts per year and did not differ significantly between the study herds. Modeling as Poisson distributed (mean 24 months) best fit the observed prevalences. Infection was predicted by the model either to spread quickly (<10 years) within a herd and reach a high prevalence (>50%), or to persist at a low prevalence (<5–10%). The model was robust, predictions were realistic and the mean β estimated was consistent with previous studies of bovine tuberculosis.