Herd-level risk factors of bovine tuberculosis in England and Wales after the 2001 foot-and-mouth disease epidemic.

OBJECTIVES: We present the results of a 2005 case-control study of bovine tuberculosis (bTB) breakdowns in English and Welsh herds. The herd management, farming practices, and environmental factors of 401 matched pairs of case and control herds were investigated to provide a picture of herd-level risk factors in areas of varying bTB incidence. METHODS: A global conditional logistic regression model, with region-specific variants, was used to compare case herds that had experienced a confirmed bTB breakdown to contemporaneous control herds matched on region, herd type, herd size, and parish testing interval. RESULTS: Contacts with cattle from contiguous herds and sourcing cattle from herds with a recent history of bTB were associated with an increased risk in both the global and regional analyses. Operating a farm over several premises, providing cattle feed inside the housing, and the presence of badgers were also identified as significantly associated with an increased bTB risk. CONCLUSIONS: Steps taken to minimize cattle contacts with neighboring herds and altering trading practices could have the potential to reduce the size of the bTB epidemic. In principle, limiting the interactions between cattle and wildlife may also be useful; however this study did not highlight any specific measures to implement.

The prevalence, distribution and severity of detectable pathological lesions in badgers naturally infected with Mycobacterium bovis.

The Randomized Badger Culling Trial (RBCT) began in 1998 to determine the impact of badger culling in controlling bovine tuberculosis in cattle. A total of 1166 badgers (14% of total) proactively culled during the RBCT were found to be tuberculous, offering a unique opportunity to study the pathology caused by Mycobacterium bovis in a large sample of badgers. Of these, 39% of adults (approximately 6% of all adults culled) had visible lesions (detectable at necropsy) of bovine tuberculosis; cubs had a lower prevalence of infection (9%) but a higher percentage of tuberculous cubs (55.5%) had visible lesions. Only approximately 1% of adult badgers had extensive, severe pathology. Tuberculous badgers with recorded bite wounds (approximately 5%) had a higher prevalence of visible lesions and a different distribution of lesions, suggesting transmission via bite wounds. However, the predominance of lesions in the respiratory tract indicates that most transmission occurs by the respiratory route.

Herd-level risk factors associated with tuberculosis breakdowns among cattle herds in England before the 2001 foot-and-mouth disease epidemic.

A case-control study of the factors associated with the risk of a bovine tuberculosis (TB) breakdown in cattle herds was undertaken within the randomized badger culling trial (RBCT). TB breakdowns occurring prior to the 2001 foot-and-mouth disease epidemic in three RBCT triplets were eligible to be cases; controls were selected from the same RBCT area. Data from 151 case farms and 117 control farms were analysed using logistic regression. The strongest factors associated with an increased TB risk were movement of cattle onto the farm from markets or farm sales, operating a farm over multiple premises and the use of either covered yard or 'other' housing types. Spreading artificial fertilizers or farmyard manure on grazing land were both associated with decreased risk. These first case-control results from the RBCT will be followed by similar analyses as more data become available.

Bovine tuberculosis: towards a future control strategy.

The Independent Scientific Group on Cattle TB was appointed by the Government in 1998 to implement and develop the research recommendations of the 1997 Krebs report on bovine tuberculosis in cattle and badgers. In this article, members of the group discuss the approach they are adopting in attempting to ensure that future control strategies are scientifically based. In a second article, to be published in next week's Veterinary Record, the group will consider the extent to which efforts to control the disease in cattle may be constrained by limitations in current testing procedures.

Pathogenesis and diagnosis of infections with Mycobacterium bovis in cattle. Independent Scientific Group on Cattle TB.

In last week's Veterinary Record, members of the Independent Scientific Group on Cattle TB discussed the approach they are adopting in attempting to develop sustainable strategies for controlling bovine tuberculosis in cattle (VR, February 19, pp 207-210). In this second, complementary article, they consider the extent to which efforts to control the disease may be constrained by limitations in current testing procedures.

Effect of vaccination against Aujeszky's disease compared with test and slaughter programme: epidemiological and economical evaluations.

In January 1990, a 6-year program was initiated to eliminate endemic Aujeszky's Disease virus (ADV) infection from the pig herds in an area of Northern Germany, bordering Southern Denmark, with intensive pig farming. In the first 3 years of the campaign, an intensive compulsory vaccination program, with glycoprotein I (gI)-deleted vaccines, of all pigs in the area was employed. Beginning in June 1990 and for the first 3 years of the project, approximately 200 herds randomly selected from all herds in the area, were serologically tested each quarter. In each farrow-to-feeder (FAFE), feeder-to-finish (FEFI) and farrow-to-finish (FAFI) herd, 20 female breeding pigs, 20 finishing pigs (> or = 50 kgs liveweight) and 10 female breeding pigs and 10 finishing pigs, respectively, were blood sampled. The sera were tested by the Herd-Check Anti-PRV(S) ELISA test (IDDEX Inc., ME). Sera positive to this test were examined by the HerdCheck Anti-ADV gI-ELISA test (IDDEX Inc., ME). Data on potentially confounding management factors were collected through a pilot-tested questionnaire, administered to farmers by 2 veterinarians who blood sampled the pigs. For fattening herds (FEFI and fattening sections of FAFI herds), the association between the odds of > or = 1 gI+ finishing pigs and the time between initiation of the program in the area and sampling date (a surrogate for the effect of the program) was modelled using ordinary logistic regression. The association between the odds of gI+ females in seropositive (> or = gI+ females) FAFE and FAFI herds and time since initiation of the program was investigated with logistic-binomial regression models. Results of the study show that the longer the period from the beginning of compulsory vaccination to the date the herd was sampled the lower the odds of gI+ fattening herds and gI+ female breeding pigs in herds of the area. The beneficial effect of mass vaccination on the reduction of ADV spread was accounted for by this relationship. For fattening herds this relationship appeared curvilinear, with the reduction in the log-odds being more rapid in the 1st year of the program. This non-linear pattern indicates that for the elimination of the risk of ADV-infection from fattening herds of the area, the mass vaccination program should be complemented with additional measures such as test-and-slaughter of infected breeding pigs. A computerized economical model to estimate the effects of ADV-infection at the herd and area level has been developed. The analytical structure consists of a basic epidemiological model linked to an economic estimation framework. The economic model predictions allow priorities to be given to alternative control strategies. Mass vaccination of all pigs in regions with endemically infected herds followed by test-and-removal of seropositive animals is the most cost-effective way to control the spread of ADV within the swine population. Other possible control strategies such as intensive vaccination or complete test-and-removal all had higher overall costs, either because of the less efficient production, or because of the high costs of straight test-and-removal.