EVIDENCE of infectivity in the bone marrow of cattle infected with the agent of bovine spongiform encephalopathy (BSE) is limited to a single report of transmission to wild-type mice from ...experimentally orally exposed cattle at the end of the incubation period ( Wells and others 1999 ). The protocol for assay of selected tissues from the initial oral exposure study by the intracerebral inoculation of cattle ( Wells and others 1996 , Wells and others 1998 ) has been described by Wells and others (2005) , but briefly, groups of five Holstein-Friesian calves from herds free of clinical BSE and with a history of no exposure to meat and bone meal were each injected at age four to six months with 1·0 ml of a 10 per cent tissue homogenate in saline solution.
The continuous monitoring of bovine spongiform encephalopathy (BSE) cases is an integral component of European research and surveillance programmes, to ensure that any changes in the presentation of ...transmissible spongiform encephalopathies (TSE) in cattle can be detected and defined. Monitoring is generally limited to the brainstem at the level of the obex, for reasons of practicality, safety and cost. Demonstration of disease-specific prion protein (PrP(d)) by immunohistochemistry is currently the most widely used confirmatory tool for both active and passive surveillance. This study assessed PrP(d) immunostaining in the brainstems (obex) of cattle with BSE in the UK and Italy. Immunoreactivity 'profiles' were created for each case based on the nature of the immunostaining, its relative intensity and precise neuroanatomical location. This study compares the obex immunostaining patterns of Italian cases (only active surveillance) and two UK groups (both active and passive surveillance). The neuroanatomical distribution and relative intensity of PrP(d) was highly reproducible in all cases. The overall staining intensity varied widely but was generally stronger in the active than in the passive surveillance populations. The conclusion to be drawn from this comparative study is that the pattern of immunopathology in these routine screening samples for BSE diagnosis and surveillance is the same in the UK and Italy, whether or not the animal was displaying typical, or indeed any, clinical signs at the time of sampling. This indicates that the current confirmatory diagnostic strategy remains appropriate for active surveillance applications.
This paper considers the problem of direction-of-arrival (DOA) estimation for multiple uncorrelated plane waves incident on so-called `fully augmentable' sparse linear arrays. In situations where a ...decision is made on the number of existing signal sources (m) prior to the estimation stage, we investigate the conditions under which DOA estimation accuracy is effective (in the maximum-likelihood sense). In the case where m is less than the number of antenna sensors (M), a new approach called `MUSIC-maximum-entropy equalization' is proposed to improve DOA estimation performance in the `preasymptotic region' of finite sample size (N) and signal-to-noise ratio. A full-sized positive definite (p.d.) Toeplitz matrix is constructed from the MxM direct data covariance matrix, and then, alternating projections are applied to find a p.d. Toeplitz matrix with m-variate signal eigensubspace (`signal subspace truncation'). When m greater than or equal to M, Cramer-Rao bound analysis suggests that the minimal useful sample size N is rather large, even for arbitrarily strong signals. It is demonstrated that the well-known direct augmentation approach (DAA) cannot approach the accuracy of the corresponding Cramer-Rao bound, even asymptotically (as N arrow right infinity ) and, therefore, needs to he improved. We present a new estimation method whereby signal subspace truncation of the DAA augmented matrix is used for initialization and is followed by a local maximum-likelihood optimization routine. The accuracy of this method is demonstrated to be asymptotically optimal for the various superior scenarios (m greater than or equal to M) presented.
Sections of the medulla oblongata from the brains of sheep were examined for prion protein (PrP) by immunohistochemistry. On the basis of the morphology and neuroanatomical distribution of the ...deposits, distinct disease-associated patterns of PrP deposition were identified in scrapie-affected sheep, suggesting at least four distinct phenotypes of scrapie. In addition, clearly defined patterns of PrP deposition, readily distinguished from the disease-associated PrP deposits, were identified in some normal sheep from scrapie-free flocks. In five sheep, believed to be preclinically affected by scrapie, PrP deposition of a disease-specific type but of restricted distribution was identified, demonstrating the sensitivity of the technique for the diagnosis of scrapie. The neuroanatomical distribution of these early PrP deposits suggest that the route of entry of the scrapie agent into the brain is via parasympathetic motor neurons in the vagus nerve which innervate the gastrointestinal tract.
Previous studies dealing with direction-of-arrival (DOA) estimation for uncorrelated planes waves incident on nonuniform M-sensor arrays assumed that the number of signal sources m was known or had ...already been estimated. In the "conventional" case (m < M), traditional detection techniques such as Akaike's information criterion (AIC) and minimum description length (MDL) that are based on the equality of several smallest eigenvalues in the covariance matrix may be applied, although we demonstrate that these results can be misleading for nonuniform arrays. In the "superior" case (m greater than or equal to M), these standard techniques are not applicable. We introduce a new approach to the detection problem for "fully augmentable" arrays (whose set of intersensor differences is complete). We show that the well-known direct augmentation approach applied to the sample covariance matrix is not a solution by itself since the resulting Toeplitz matrix is generally not positive definite for realistic sample volumes. We propose a transformation of this augmented matrix into a positive definite Toeplitz matrix T sub( mu ) with the proper number of equal minimum eigenvalues that are appropriate for the candidate number of sources mu . Comparison of the results of these best-fit transformations over the permissible range of candidates then allows us to select the most likely number of sources m using traditional criteria and yields uniquely defined DOA's. Simulation results demonstrate the high performance of this method. Since detection techniques for superior scenarios have not been previously described in the literature, we compare our method with the standard AIC and MDL techniques in a conventional case with similar Cramer-Rao bound (CRB) and find that it has a similar detection performance.
Pandemic influenza A(H1N1)pdm09 virus has retained its ability to infect swine whilst developing the ability to transmit effectively between humans, thus making the pig a valuable model for studying ...disease pathogenesis in both species. Lung lesions in pigs caused by infection with influenza A viruses vary in both their severity and distribution with individual lung lobes exhibiting lesions at different stages of infection pathogenic development and disease resolution. Consequently, investigating interactions between the virus and host and their implications for disease pathogenesis can be complicated. Studies were undertaken to investigate the discrete expression of pro‐ and anti‐inflammatory mediators during lung lesion formation in pigs during infection with influenza A(H1N1)pdm09 (A/Hamburg/05/09) virus. Laser capture microdissection was used to identify and select lung lobules containing lesions at different stages of development. Dissected samples were analysed using quantitative RT‐PCR to assess pro‐ and anti‐inflammatory cytokine mRNA transcripts. Differential expression of the immune mediators IL‐8, IL‐10 and IFN‐γ was observed depending upon the lesion stage assessed. Upregulation of IFN‐γ, IL‐8 and IL‐10 mRNA was observed in stage 2 lesions, whereas decreased mRNA expression was observed in stage 3 lesions, with IL‐8 actively downregulated when compared with controls in both stage 3 and stage 4 lesions. This study highlighted the value of using laser capture microdissection to isolate specific tissue regions and investigate subtle differences in cytokine mRNA expression during lesion development in pigs infected with influenza A(H1N1)pdm09.
Tissues from sequential-kill time course studies of bovine spongiform encephalopathy (BSE) were examined to define PrP immunohistochemical labeling forms and map disease-specific labeling over the ...disease course after oral exposure to the BSE agent at two dose levels. Study was confined to brainstem, spinal cord, and certain peripheral nervous system ganglia—tissues implicated in pathogenesis and diagnosis or disease control strategies. Disease-specific labeling in the brainstem in 39 of 220 test animals showed the forms and patterns observed in natural disease and invariably preceded spongiform changes. A precise temporal pattern of increase in labeling was not apparent, but labeling was generally most widespread in clinical cases, and it always involved neuroanatomic locations in the medulla oblongata. In two cases, sparse labeling was confined to one or more neuroanatomic nuclei of the medulla oblongata. When involved, the spinal cord was affected at all levels, providing no indication of temporal spread within the cord axis or relative to the brainstem. Where minimal PrP labeling occurred in the thoracic spinal cord, it was consistent with initial involvement of general visceral efferent neurons. Labeling of ganglia involved only sensory ganglia and only when PrP was present in the brainstem and spinal cord. These experimental transmissions mimicked the neuropathologic findings in BSE-C field cases, independent of dose of agent or stage of disease. The model supports current diagnostic sampling approaches and control measures for the removal and destruction of nervous system tissues in slaughtered cattle.
This paper addresses the problem of ambiguities in direction of arrival (DOA) estimation for nonuniform (sparse) linear arrays. Usually, DOA estimation ambiguities are associated with linear ...dependence among the points on the antenna array manifold, that is, the steering vectors degenerate so that each may be expressed as a linear combination of the others. Most nonuniform array geometries, including the so-called "minimum redundancy" arrays, admit such manifold ambiguities. While the standard subspace algorithms such as MUSIC fail to provide unambiguous DOA estimates under these conditions, we demonstrate that this failure does not necessarily imply that consistent and asymptotically effective DOA estimates do not exist. We demonstrate that in most cases involving uncorrelated Gaussian sources, manifold ambiguity does not necessarily imply nonidentifiability; most importantly, we introduce algorithms designed to resolve manifold ambiguity. We also show that for situations where the number of sources exceeds the number of array sensors, a new class of locally nonidentifiable scenario exists.
The maximum likelihood ratio (LR) lower bound analysis introduced in our previous papers is applied to support the detection-estimation of multiple Gaussian spread (distributed, scattered) sources. ...Since angular spreading eliminates any "noise eigensubspace" from the spatial covariance matrix, traditional detection techniques based on the equality of noise-subspace eigenvalues are not applicable here. Brute-force "focusing", which is based on the Schur-Hadamard inverse, is shown to be inefficient. Our technique is based on generalized likelihood-ratio test (GLRT) principles and involves LR maximization over the set of admissible covariance matrix models. The introduced technique yields results that statistically exceed the LR generated by the exact covariance matrix, which is used as the lower bound. High optimization efficiency drives high detection-estimation performance that, nevertheless, breaks down under certain threshold conditions. It is demonstrated that this breakdown phenomenon is not curable within the maximum likelihood (ML) paradigm since these highly erroneous solutions are still "better" than the true covariance matrix (as measured by the LR).
European regulations for the control of bovine spongiform encephalopathy (BSE) decree destruction of the intestines from slaughtered cattle, therefore producers have been obliged to import beef ...casings from countries with a negligible BSE risk. This study applies immunohistochemical and biochemical approaches to investigate the occurrence and distribution of disease-associated prion protein (PrP(Sc)) in the duodenum, jejunum and ileum of cattle orally exposed to a 1 g or 100 g dose of a titrated BSE brainstem homogenate. Samples were derived from animals at various times post exposure. Lymphoid follicles were counted and the frequency of affected follicles recorded. No PrP(Sc) was detected in the duodenum or jejunum of animals exposed to a 1 g dose or in the duodenum of animals receiving a 100 g dose. PrP(Sc) was detected in the lymphoid tissue of the ileum of 1/98 (1.0%) animals receiving the 1 g dose and in the jejunum and ileum of 8/58 (13.8%) and 45/99 (45.5%), respectively, of animals receiving the 100 g dose. The frequency of PrP(Sc)- positive follicles was less than 1.5% per case and biochemical tests appeared less sensitive than immunohistochemistry. The probability of detecting lymphoid follicles in the ileum declined with age and for the 100 g exposure the proportion of positive follicles increased, while the proportion of positive animals decreased with age. Detection of PrP(Sc) in intestinal neural tissue was rare. The results suggest that the jejunum and duodenum of BSE-infected cattle contain considerably less BSE infectivity than the ileum, irrespective of exposure dose. In animals receiving the low exposure dose, as in most natural cases of BSE, the rarity of PrP(Sc) detection compared with high-dose exposure, suggests a very low BSE risk from food products containing the jejunum and duodenum of cattle slaughtered for human consumption.
