New BSE form identified

Researchers in Italy have identified a novel form of bovine spongiform encephalopathy (mad cow disease) in two seemingly healthy cows that could further our understanding of human diseases such as Creutzfeldt-Jakob disease. But others say that the findings reported in the February 17 online PNAS do not necessarily provide insights in human manifestations of the disease. Cristina Casalone and colleagues at the Centro di Referenza Nazionale per le Encefalopatie Animali in Turin report that more than one prion strain may be responsible for bovine spongiform encephalopathy (BSE). The molecular signature of the newly discovered strain, combined with its corresponding brain deposition and disease pathology bear striking similarities to sporadic Creutzfeldt-Jakob disease (sCJD) in humans (PNAS ref). Michael Coulthart, director of the Prion Diseases Program at the National Microbiology Laboratory with Health Canada, cautions against prematurely assuming there is a correlation. “The connection between these novel phenotypes of BSE and something going on in human sCJD is so far unproven.” Transmissible spongiform encephalopathies (TSEs) in humans can be sporadic, acquired, or inherited diseases. Sporadic (or spontaneous) TSE is the most common, occurring in roughly one in a million individuals. Symptoms of sporadic and inherited TSEs do not appear until later in life and are characterized by dementia, loss of coordination, and senility, followed by coma and death. Variant CJD (vCJD) is rare, with just 18 cases reported in the UK in 2003. Tainted meat consumption is believed to be the cause of vCJD, which discriminately strikes young people. Casalone and colleagues identified this new form of mad cow disease identification of two healthy, older cows that tested positive for BSE during compulsory screening, but which lacked evidence of vacuolar lesions—the hallmark of mad cow disease. “Instead, we found amyloid plaques and [prion] distribution quite different from BSE,” said Salvatore Monaco from the G.B. Rossi Polyclinic in Verona, a senior author on the study, in an interview with The Scientist. “The disease shared many similarities with sCJD, and when we compared the molecular features, [of the new strain] we also saw similarities.” In both BSE and vCJD, the disease pathology is characterized by extensive vacuolar destruction and prion distribution, predominately in the brainstem. However, the team noted that the olfactory mucosa was the site of early deposition of this new strain of prion—a distribution also typical of sCJD. They termed this new form of BSE, bovine amyloidotic spongiform encephalopathy (BASE): plaques have never previously been described in BSE. This, in conjunction with a recent report from France of a novel prion phenotype among BSE-positive cattle, questions the long and widely held assumption that a single causative agent is responsible for mad cow disease, according to the Italian group. But unequivocal characterization of prion “strains” is still in its comparative infancy. “The question of strain variation is a little more mysterious [for prions] compared with bacteria or viruses, because they have a genome,” said Coulthart. “With prions, there is abundant scientific evidence that strain phenomenon exists, but nobody knows the physical basis for it.” Monaco plans to attempt to provide evidence supporting a link between this new form of mad cow disease and sCJD by performing transmission studies in which transgenic mice are infected with material from an sCJD-infected brain or an infected cow brain. Both Monaco and Coulthart suggest that these findings from France and Italy also raise the possibility that these recent cases may, in fact, be spontaneous forms of mad cow disease without an infectious origin. In their paper, Calvatore et al. suggest that spontaneous disease may account for the age differences seen between cattle with “classic” BSE and the two older cows with this new mad cow disease, who appeared otherwise healthy. Monaco speculated that there may be another possibility; mad cow disease may be caused by several different strains.

New BSE form identified

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