New cattle TSE identified

Researchers in Italy have discovered a new transmissible spongiform encephalopathy (TSE) in cattle, according to a recent publication in Proc. Natl Acad. Sci. USA.

The TSEs or prion diseases are progressive neurodegenerative disorders that are associated with the accumulation in the brain of an insoluble, protease-resistant form (PrP^Sc) of the prion protein (PrP^C). Until now, only one TSE — bovine spongiform encephalopathy (BSE) — has been known in cattle, and a single agent, that is, a single strain of PrP^Sc, has been associated with BSE and the equivalent human infection, variant Creutzfeldt–Jakob disease (CJD).

In this study, Casalone et al. analysed the brains of Italian cattle that had tested positive for BSE after routine slaughter. In the eight cattle brains sampled, Western blot analysis revealed that there were two distinct forms of PrP^Sc present — in two of the cattle samples, the molecular mass of both the predominant PrP^Sc glycoform and the protease-resistant fragment were lower than those found in the other six cattle, which showed a typical molecular signature for BSE. In these two cattle, the distribution of PrP^Sc was also altered — the protein accumulated within the olfactory bulb and thalamus, rather then in the brainstem as with BSE PrP^Sc. Additionally, PrP-immunopositive plaques, a feature not found in typical BSE, were detected in the brains of these two animals.

Casalone et al. propose that this pathology represents a new form of cattle TSE that they have named bovine amyloidotic spongiform encephalopathy, or BASE. Somewhat ominously, Casalone et al. report that the neuropathology, and PrP^Sc distribution and glycotype that are characteristic of BASE are very similar to that associated with a particular subtype of sporadic CJD. As the two cattle in which BASE was present were healthy at the time of slaughter it is possible that BASE could be a sporadic cattle TSE. Until more research is completed, however, the authors urge caution in assessing any link between the two conditions in different species.