Experimental infection of sheep and goats with transmissible mink encephalopathy virus.

In a study to learn more about the pathogenicity of transmissible mink encephalopathy virus for the natural hosts of scrapie, 20 Cheviot sheep and 19 dairy goats were inoculated intracerebrally with the Idaho strain of the virus. Five sheep and nine goats became affected with a progressive neurological disease. The incubation period in the sheep varied from 45 to 80 months (mean, 65 months) and in the goats from 31 to 40 months (mean, 35 months). Except for degeneration of the cerebral cortex (neocortex), the disease was indistinguishable clinically and neurohistologically from scrapie. During two more passages of the virus in goats, the incubation period was shortened to 12 to 15 months, the morbidity rate rose to 100% (6/6 dairy goats and 3/3 African pygmy goats), and the cortical lesion became constant and more pronounced. By the intracerebral inoculation of pastel mink, transmissible mink encephalopathy virus was detected in the brains of several affected sheep and goats but not in extraneural sites (lymphoid tissues and intestine), except for a trace amount in the proximal colon of one goat. Even after two passages in goats, the virus remained nonpathogenic for the laboratory mouse. Despite the essential likeness of the experimental disease and scrapie, the common identity of their causal viruses remains to be determined. Even so, the results of this study are still compatible with the view that transmissible mink encephalopathy virus almost certainly is scrapie virus whose biological properties became altered by chance passage in mink, a carnivore and an aberrant host.     

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.     

Molecular architecture of the "stressosome," a signal integration and transduction hub

A commonly used strategy by microorganisms to survive multiple stresses involves a signal transduction cascade that increases the expression of stress-responsive genes. Stress signals can be integrated by a multiprotein signaling hub that responds to various signals to effect a single outcome. We obtained a medium-resolution cryo-electron microscopy reconstruction of the 1.8-megadalton "stressosome" from Bacillus subtilis. Fitting known crystal structures of components into this reconstruction gave a pseudoatomic structure, which had a virus capsid-like core with sensory extensions. We suggest that the different sensory extensions respond to different signals, whereas the conserved domains in the core integrate the varied signals. The architecture of the stressosome provides the potential for cooperativity, suggesting that the response could be tuned dependent on the magnitude of chemophysical insult.