Experimental H-type and L-type bovine spongiform encephalopathy in cattle: observation of two clinical syndromes and diagnostic challenges

Two groups of four cattle, intracerebrally inoculated with L-type or H-type BSE, all presented with a nervous disease form with some similarities to classical BSE, which progressed to a more dull form in one animal from each group. Difficulty rising was a consistent feature of both disease forms and not seen in two BSE-free, non-inoculated cattle that served as controls. The pathology and molecular characteristics were distinct from classical BSE, and broadly consistent with published data, but with some variation in the pathological characteristics. Both atypical BSE types were readily detectable as BSE by current confirmatory methods using the medulla brain region at the obex, but making a clear diagnostic distinction between the forms was not consistently straightforward in this brain region. Cerebellum proved a more reliable sample for discrimination when using immunohistochemistry.The prominent feature of difficulty rising in atypical BSE cases may explain the detection of naturally occurring cases in emergency slaughter cattle and fallen stock. Current confirmatory diagnostic methods are effective for the detection of such atypical cases, but consistently and correctly identifying the variant forms may require modifications to the sampling regimes and methods that are currently in use.After bovine spongiform encephalopathy (BSE) was first described as a novel neurological disease in cattle in the United Kingdom (UK) more than 20 years ago [1], subsequent research indicated that it was caused by a single agent based on the clinical [2], pathological [3], molecular [4,5] and biological [6] phenotype. Experimental inoculation of cattle with agents found in transmissible spongiform encephalopathies (TSEs) of other species, such as scrapie [7-9] or chronic wasting disease [10], produced a neurological disease, but in each case the disease was different phenotypically from BSE. The introduction of active surveillance in various countries has resulted in the detectio