A comparison of the interferon gamma assay with the absorbed ELISA for the diagnosis of Johne''s disease in cattle

Two interferon gamma (IFN-gamma) assays, the IFN-gamma enzyme immunoassay (EIA) and the IFN-gamma bioassay and an absorbed ELISA were used to screen 6 cattle herds for Johne's disease. Each herd had a history of Johne's disease but the majority of infected animals did not show clinical signs. The disease status of the cattle, which were removed from the herds, was confirmed by bacteriological culture of faeces or histopathological examination and culture of tissues collected at necropsy. The sensitivities of the IFN-gamma assays and the absorbed ELISA were determined using test results from infected animals. The sensitivity of the IFN-gamma EIA in detecting subclinical (71.8 to 93.3%) and clinical animals (100%) was not significantly different. However, the IFN-gamma bioassay and the absorbed ELISA were more sensitive in detecting cattle with advanced infections (80%) than those that were subclinically affected (16.7 to 33.3%).     

A case-control study to identify farm factors affecting fertility of dairy herds: multivariate description of factors

Objectives To determine whether a multivariate model could be developed to describe farm factors affecting fertility of dairy herd and to examine the factors that determined better reproductive performance on dairy farms in New South Wales.
Procedure We examined the results of a survey of breeding practices, mating policies, recording systems, timing of mating, heat detection, treatment of metritis and manager demographics of dairy farms using Principal components analysis, logistic regression and the sign test.
Results Eight principal components for heat detection computed using Principal component analyses were included in the multivariate model to reflect primary and secondary heat detection signs used in the breeding decisions of managers. A final model identified three variables: optimum number of days to first service, number of people detecting heats, and age of manager which significantly influenced the risk of being in the high or low reproductive performance groups. A failure to breed at an appropriate time after calving and having more people responsible for heat detection was associated with herds with a prolonged intercalving interval. While the model provided a good fit for the data, it was not highly discriminatory. Examination of 83 management practices affecting fertility using the sign test (P = 0.01) indicated that managers of herds with good reproductive performance employed better management and breeding practices more often than managers of herds with poor reproductive performance.
Conclusions Mating cows sooner after calving and using fewer people to detect oestrus should reduce calving to conception intervals. Veterinarians investigating herd reproductive performance should consider the potential for a number of subtle failures of management to significantly impair fertility rather than limit investigations to a few factors.     

Q fever in pregnant goats: humoral and cellular immune responses

Q fever is a zoonosis caused by the intracellular bacterium Coxiella burnetii. Both humoral and cellular immunity are important in the host defence against intracellular bacteria. Little is known about the immune response to C. burnetii infections in domestic ruminants even though these species are the major source of Q fever in humans. To investigate the goat’s immune response we inoculated groups of pregnant goats via inhalation with a Dutch outbreak isolate of C. burnetii. All animals were successfully infected. Phase 1 and Phase 2 IgM- and IgG-specific antibodies were measured. Cellular immune responses were investigated by interferon-gamma, enzyme-linked immunosorbent spot test (IFN-γ Elispot), lymphocyte proliferation test (LPT) and systemic cytokines. After two weeks post inoculation (wpi), a strong anti-C. burnetii Phase 2 IgM and IgG antibody response was observed while the increase in IgM anti-Phase 1 antibodies was less pronounced. IgG anti-Phase 1 antibodies started to rise at 6 wpi. Cellular immune responses were observed after parturition. Our results demonstrated humoral and cellular immune responses to C. burnetii infection in pregnant goats. Cell-mediated immune responses did not differ enough to distinguish between Coxiella-infected and non-infected pregnant animals, whereas a strong-phase specific antibody response is detected after 2 wpi. This humoral immune response may be useful in the early detection of C. burnetii-infected pregnant goats.     

Seroconversion to avian influenza virus in free-range chickens in the Riverland region of Victoria

Background Since 2005, H5N1 avian influenza (AI) has spread from South-East Asia to over 60 different countries, resulting in the direct death or slaughter of over 250,000,000 poultry. Migratory waterfowl have been implicated in this spread and in Australia there have been numerous isolations of low-pathogenicity AI virus from wild waterfowl and shorebirds. The Department of Human Services, Victoria maintains 10 sentinel free-range chicken flocks in the Riverland at locations that are populated by large numbers of waterfowl known to carry a range of strains of AI. Objective This study analysed historical samples collected in 1991–94 and 2003–06 from the library of serum samples for antibodies against AI to assess the potential for transfer of AI virus from wild waterfowl to free-range poultry. Results Of the 2000 serum samples analysed, 17 were positive for antibodies against AI and 87 were suspect, with a clustering of positive and suspect results in the years 1994, 2003 and 2004. There was also a clustering of positive samples at the site of the Barmah flock. Nine sequential sets of sera from individual chickens with at least one positive result were identified. Analysis of these sequential sets showed that infection was acquired on site but that the antibody response to AI infection was short-lived and was no longer detectable at 8 weeks after the positive finding. Conclusion The surveillance of sentinel chickens is a potential avenue for monitoring the circulation of AI viruses and could provide an early warning system for the commercial poultry industries.