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.

Potential use of vaccination in cattle or badgers to control bovine tuberculosis.

The application of regular herd testing to identify and remove infected animals has proved to be a highly successful method of controlling bovine tuberculosis (TB) in many parts of the world. However, in some countries, notably the United Kingdom, Ireland and New Zealand, the disease has continued to pose a significant problem, despite intensive herd testing. Persistence of disease in these countries is associated with the presence of wildlife reservoirs of infection. Attempts to control bovine TB by culling of wildlife have been, at best, only partially successful and have proved difficult to sustain. This has led to considering of vaccination either of wildlife or cattle as a potential control measure. However, there are a number of obstacles that need to be overcome before vaccination can be considered a practical option. Vaccine efficacy, methods used for vaccine delivery in wildlife, potential interference of vaccination with diagnostic tests for cattle and appropriate design of field trials are among the issues that need to be addressed.

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.

Altered immune response to proteins fed after neonatal exposure of piglets to the antigen.

The weaning of piglets onto soya proteins at 3 weeks old normally results in an active response to the fed protein, as determined by the appearance of serum IgG antisoya antibody. This system thus allows the effects of manipulation on the response to a fed protein to be studied. In animals previously given 1 g of soya protein at birth, the magnitude of the antibody response to soya fed at 3 weeks was decreased, although similar amounts of the fed protein could be detected in serum. In addition, the relative affinity of the dominant interaction between antigen and antibody was reduced in these piglets by almost an order of magnitude. By comparison, the ability of piglets given soya at birth to respond to injected soya was not significantly reduced. These results indicate that the regulation of responses to fed and systemic antigens is largely separate. Very early oral exposure to antigen may affect the ability of neonatal animals to mount immune responses to, specifically, fed proteins while leaving the response to systemic antigen largely intact.

Maturation of cellular defence in the respiratory tract of young calves.

The maturation of respiratory tract defence was investigated in a longitudinal study of calves during the first 100 days of life. From day 7, the proportions of the cell types identified in bronchoalveolar lavage (BAL) fluid were similar to those found in adults, with a predominance of alveolar macrophages over polymorphonuclear neutrophils (PMNs) and lymphocytes. Functionally, bactericidal activity of BAL cells was defective and for the first 21 days they supported intracellular bacterial growth. At 24 hours of life, the movement of peripheral blood neutrophils to a chemotactic source was poor, but this increased rapidly during the first week of life. Like BAL cells, peripheral blood PMNs supported intracellular bacterial growth for the first two weeks of life. These studies suggest that cellular defence mechanisms may be compromised during the first week of life.

Specific immunological unresponsiveness following active primary responses to proteins in the weaning diet of piglets.

Young piglets weaned onto soya diets frequently develop diarrhoea which may have a dietary and/or immunological component. Piglets abruptly weaned onto soya at 3 weeks of age developed levels of serum IgG anti-soya antibodies almost comparable to those induced by injection with soya protein in adjuvant at 7 weeks. In the piglets primed by feeding, no significant further increase in antibody occurred after subsequent systemic injection. In contrast, secondary responses were observed in age-matched animals, previously primed by injection, and primary responses were obtained in previously naive piglets. The results demonstrate the development of specific unresponsiveness to soya proteins in neonates fed soya, despite the occurrence of an initial vigorous immune response to the fed protein.

Use of a direct enzyme-linked antiglobulin test for laboratory diagnosis of immune-mediated hemolytic anemia in dogs.

Detection of autoantibody, complement, or both bound to RBC is an essential requirement for unequivocal diagnosis of immune-mediated hemolytic anemia in dogs. An enzyme-linked antiglobulin test was adapted for laboratory diagnosis of this disease. The refinement and routine use of this assay have allowed further observation of the pathogenesis of the disease process. In particular, degree of hemolysis can be related to the degree of RBC sensitization associated with primary immune-mediated hemolytic anemia, and this correlation is highest for IgG autoantibody. Results indicate that autoantibody isotype might have an important role in the hemolytic process.

Dietary antigen handling by mother and offspring.

Sows were fed ovalbumin (OvA) as a novel protein antigen either throughout gestation and lactation (G + L) or during lactation only (L). This resulted in a significant uptake of OvA into blood, colostrum and milk along with a specific IgG response. In piglets from the G + L group, OvA and antibodies to OvA were detected in serum after ingestion of colostrum. In a large proportion of these piglets OvA was still detected at 3 weeks of age. In the L group a significant proportion of the piglets responded to OvA whilst still suckling their mother. At 3 weeks of age all piglets were weaned onto an egg-based diet. A similar uptake of OvA was seen in all piglets but there was no response to OvA in the G + L piglets. In piglets from sows fed only during lactation, however, a rapid IgG anti-OvA response and signs of diarrhoea were seen. The results suggest that factors of immunological importance are passed over from mother to offspring and it is proposed that immunological experience of dietary antigens by the mother is important for a 'safe' tolerance induction in her offspring.

Investigation into factors influencing performance of the canine antiglobulin test.

Antiglobulin (Coombs') reagents were assessed for their ability to detect immunoglobulin and complement attached to red cells. Polyspecific and monospecific reagents were prepared using a number of immunisation protocols. Performance of these antisera against control red cells was compared, in a direct Coombs' test, with samples from cases of canine autoimmune haemolytic anaemia (AIHA). A combined reagent containing two monospecific antisera (anti-IgG + anti-C3) gave optimum results. Positive control red cells were required to standardise canine Coombs' reagents for the laboratory diagnosis of AIHA. The optimum incubation temperature for the canine Coombs' test was shown to be 37 degrees C.

The effect of parenteral immunisation on antibody production in the pig colon.

Local and systemic antibody production was studied in pigs to compare responses to live and killed bacterial antigen and purified protein antigen, with and without prior mucosal stimulation. Recovery from challenge with live bacteria and intramuscular injection with killed bacteria gave rise to similar high levels of serum IgG antibody, but the ratio of specific IgA to IgG in the colon was significantly higher after infection than following vaccination with killed bacteria. Vaccination with a protein antigen gave rise to serum and local antibody production. Prior feeding of the antigen had a tolerising effect on the serum antibody response, but production of IgG and IgA antibody by the colon was not suppressed.

Antibody production by the pig colon during infection with Treponema hyodysenteriae.

When 47 pigs were dosed orally with cultures of Treponema hyodysenteriae, 44 (94 per cent) developed swine dysentery. Of those which recovered and were rechallenged, nine of 21 (43 per cent) showed clinical signs, as did one of 10 (10 per cent) challenged on a third occasion. Clinical disease was associated with development of specific IgG, IgA and IgM antibodies in serum and the local production of IgA in gut mucosal tissues. The appearance of antibody was not directly related to protection but rather indicated either prolonged exposure (in the case of serum IgG) or recent exposure to T hyodysenteriae (for secretory IgA). Infection also resulted in the appearance of IgG and IgA memory cells in gut-associated lymphoid tissue. However, these studies indicated that humoral immunity alone is not responsible for the onset of a protective response to T hyodysenteriae in the colon.

Circulating lymphocytes, neutrophils and immune complexes in pigs after feeding.

There are reports in the literature claiming that pigs experience a lymphopenia after feeding. This is not observed in other species. We set out to investigate this phenomenon because of the unusual route of lymphocyte recirculation in pigs. for it suggested that this might be a specific response to dietary antigens. We were unable to confirm this phenomenon. A lymphopenia was observed in both test and control groups as a non-specific response to restraint and blood sampling. In contrast, feeding was associated with a significant neutrophilia (mean 58%, P less than 0.002). There were no increases in circulating IgA, IgG or IgM immune complexes after feeding but IgG immune complexes remained at a higher level than in the control group.

Adjuvant effect of cholera toxin on the mucosal immune response to soluble proteins. Differences between mouse strains and protein antigens.

We examined the effect of orally administered cholera toxin (CT) on the immune response to keyhole limpet haemocyanin (KLH) and ovalbumin (OVA) in high (C57Bl/6 H2b), medium (CBA H2k), and low (BALB/c H2d) responder I-A haplotypes to CT. Mice were fed OVA or KLH on three occasions at 10-day intervals and the effect of simultaneous feeding of CT determined. Isotype-specific antibody levels were assayed in serum samples collected 7 days after the last immunization. Antibody was also measured in the supernatant of gut explant cultures incubated at either 4 or 37 degrees C. Increased antibody levels in cultures kept at 37 degrees C indicated release of local intracellular antibody. Cholera toxin exerted an adjuvant effect on the mucosal response of all three strains to KLH and OVA. Overall, the responses to CT and the second protein were not correlated; we interpret these findings to indicate that while CT had an effect on the mucosal immune system which enhances the immune response to itself and other protein antigens, the final outcome of the response to the second antigen is dependent on differences in the ability of the strains to process, recognize, and respond to a particular antigen.

Regulation of phagolysosome pH in bovine and human neutrophils: the role of NADPH oxidase activity and an Na+/H+ antiporter.

Fluorescein-labelled Staphylococcus aureus were used to follow changes in phagolysosome (PL) pH of bovine and human neutrophils following phagocytosis. Under aerobic conditions there was an alkalinisation of the PL followed by a slow decline. Under anaerobic conditions no alkalinisation of the PL was seen, and pharmacological inhibition of the NADPH oxidase with diphenyleneiodonium (DPI) resulted in a rapid acidification of the PL following phagocytosis. The inclusion of amiloride, an inhibitor of Na+/H+ antiporter activity, produced a more rapid alkalinisation phase following phagocytosis under aerobic conditions and reduced, but did not abolish, the acidification phases seen under anaerobic conditions or following treatment of neutrophils with DPI. The results suggest that PL pH is influenced by NADPH oxidase activity and to a lesser extent by a Na+/H+ antiporter. The antibacterial effectiveness of neutrophil granule proteins may be affected under conditions that influence the functioning of these two systems.