A sandwich enzyme immunoassay for bovine interferon-γ and its use for the detection of tuberculosis in cattle

An in vitro cellular assay for bovine tuberculosis has recently been developed. This assay detects gamma-interferon released in response to specific antigen in a whole blood culture system. The bio-assay previously described for the detection of bovine gamma-interferon (IFN-gamma) has now been replaced with a sandwich enzyme immunoassay (EIA) which utilises two monoclonal antibodies to bovine IFN-gamma. The EIA detects less than 25pg/ml of recombinant bovine IFN-gamma and is specific for biologically active bovine IFN-gamma; and does not detect bovine alpha or beta interferon. IFN-gamma from sheep, goat and buffalo, but not from pig, deer or man, are also recognised by the EIA. The bovine IFN-gamma EIA when used in conjunction with the whole blood culture system has resulted in a simple, rapid and sensitive in vitro assay for specific cell mediated immune responsiveness to M. bovis infection in cattle.     

Detection of Mycobacterium avium subsp. paratuberculosis in skeletal muscle and blood of ewes from a sheep farm in New Zealand

Abstract

AIM: To determine whether viable Mycobacterium avium subsp. paratuberculosis (Map) is present in skeletal muscle and blood in ewes with and without Johne's disease confirmed histologically.

METHODS: A total of 51 mixed-aged ewes in poor body condition from a farm with a history of clinical Johne's disease were culled and examined at necropsy. BACTEC radiometric culture was performed on samples of skeletal muscle from the biceps femoris, mononuclear cells in peripheral blood (hereafter referred to as blood), and ileum. Histological sections and Ziehl-Neelsen (ZN)-stained impression smears of terminal ileum and mesenteric lymph nodes were examined. Ewes were defined as having confirmed Johne's disease if there was histopathological evidence typical of the disease within the ileum and adjacent lymph nodes.

RESULTS: Eighteen of 21 (86%) ewes with confirmed clinical Johne's disease were culture-positive for Map from sites peripheral to the alimentary tract, comprising 15 from skeletal muscle and 13 from blood. Five of 30 (17%) ewes that did not have Johne's disease were culture-positive, with four from skeletal muscle and one from blood. The likelihood that ewes with confirmed Johne's disease had systemic Map infection compared with ewes without was determined as OR=30 (95% CI=6.3–142.0; p<0.001).

CONCLUSION: The prevalence of Map infection of skeletal muscle and blood in ewes with confirmed Johne's disease was 71% and 62% respectively, and in unaffected ewes was 13% for muscle and 3% for blood.

CLINICAL RELEVANCE: Skeletal muscle and blood are potential sources of exposure of humans to Map, and the risk appears higher from sheep with Johne's disease.     

Evidence for extreme climatic warmth from late cretaceous arctic vertebrates

A Late Cretaceous (92 to 86 million years ago) vertebrate assemblage from the high Canadian Arctic (Axel Heiberg Island) implies that polar climates were warm (mean annual temperature exceeding 14 degreesC) rather than near freezing. The assemblage includes large (2.4 meters long) champsosaurs, which are extinct crocodilelike reptiles. Magmatism at six large igneous provinces at this time suggests that volcanic carbon dioxide emissions helped cause the global warmth.     

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%).     

Efficiency of inspection procedures for the detection of tuberculous lesions in cattle

The sensitivity of the abattoir inspection procedure introduced for Australian export beef in 1976 was compared to a detailed necropsy procedure for the detection of tuberculous lesions in cattle. In a sample of cattle that were reactors to the tuberculin test, abattoir inspection failed to detect an estimated 47% of cattle with lesions. The detailed necropsy examination of cattle with lesions of tuberculosis identified 21 sites of infection compared with 13 to 18 in cattle examined by routine meat inspection procedures. Of the lesions detected during detailed necropsy, 15.9% did not involve the thoracic cavity or the medial retropharyngeal lymph nodes. The failure to detect lesions during abattoir inspection has its greatest significance in an animal with a single lesion. If the 245 cattle found with single lesions during detailed necropsy had been examined by abattoir inspection using the 1976 or the 1986 procedures, 0.8 and 8.9%, respectively, of these animals would not have been detected because the diseased tissues would not have been examined. If meat inspection is to provide an effective means of monitoring the level of bovine tuberculosis during the final stages of eradication, a procedure no less sensitive than that introduced in 1976 should be used.