Heart rate variability analysis in sheep affected by transmissible spongiform encephalopathies

<p>Abstract</p> <p>Background</p> <p>The function of the autonomic nervous system can be assessed by determining heart rate variability (HRV), which is impaired in some brainstem diseases in humans. Transmissible spongiform encephalopathies (TSEs) in sheep are diseases characterised by accumulation of disease-associated prion protein in the brainstem, including nuclei of the parasympathetic nervous system. This study was undertaken to assess whether analysis of HRV can be used as an aid in the diagnosis of TSEs in clinically affected, naturally or experimentally infected sheep.</p> <p>Findings</p> <p>When HRV indices were compared between 41 clinical TSE cases (18 sheep infected with scrapie and 23 sheep infected with bovine spongiform encephalopathy), 11 control sheep and six sheep reported as scrapie suspects or dosed with BSE brain homogenate, which were not confirmed as TSE cases by postmortem tests, no significant differences were found between the groups. Median heart rate was significantly different but only when sheep were grouped by gender: it was higher in female TSE cases than in control sheep and higher in female than castrated male ovine classical BSE cases.</p> <p>Conclusions</p> <p>HRV analysis was not useful as a diagnostic aid for TSEs of sheep.</p

Time and frequency domain analysis of heart rate variability in cattle affected by bovine spongiform encephalopathy

<p>Abstract</p> <p>Background</p> <p>Heart rate variability (HRV) analysis is a method to assess the function of the autonomic nervous system. Brainstem nuclei that influence HRV are affected by vacuolar changes and accumulation of disease-associated prion protein (PrP^d) in bovine spongiform encephalopathy (BSE) resulting in clinical signs suggestive of an increased parasympathetic tone. It was hypothesised that BSE in cattle causes changes in the autonomic nervous system; this was tested by comparing HRV indices derived from 1048 electrocardiograms, which were recorded from 51 naturally or experimentally infected cattle with BSE confirmed by postmortem tests, 321 clinical suspect cases or cattle inoculated with potentially infectious tissue without disease confirmation and 78 BSE-free control cattle.</p> <p>Findings</p> <p>Statistically significant differences were found for low or high frequency power, their normalised values and ratio when the last recording prior to cull or repeated recordings were compared but only between male and female cattle of the three groups and not between groups of the same gender, even though BSE cases of each gender appeared to be more nervous during the recording. The same findings were made for heart rate, deviation from the mean RR interval and vasovagal tonus index when repeated recordings were compared. BSE cases with severe vacuolar changes in the parasympathetic nucleus of the vagus nerve had a significantly lower low:high frequency power ratio but not a lower heart rate than BSE cases with mild vacuolation, whereas severity of vacuolar changes in the solitary tract nucleus or intensity of PrP^daccumulation in both nuclei did not appear to have any affect on either index. Abnormalities in the electrocardiogram were detected in 3% of the recordings irrespective of the BSE status; sinus arrhythmia was present in 93% of the remaining recordings.</p> <p>Conclusions</p> <p>HRV analysis was not useful to distinguish BSE-positive from BSE-negative cattle grouped by gender, and HRV indices appeared to be mainly influenced by gender. There is agreement with earlier studies that vacuolar changes in the brainstem may be associated with an increased parasympathetic tone in BSE and that abnormalities in an electrocardiogram can be detected in cattle without evidence of heart disease.</p

Classical Scrapie Did Not Re-occur in Goats After Cleaning and Disinfection of the Farm Premises

After an outbreak of classical scrapie in a dairy goat herd with over 1,800 goats, all goats in the herd were culled in 2008, cleaning and disinfection of the premises was implemented, and restocking with goats took place ~4 months after depopulation. Ten years later the new herd population is over 3,000 goats. This study was carried out to determine whether the measures were effective to prevent re-occurrence of scrapie to the 1% prevalence level seen when scrapie was first detected on this farm. A total of 280 goats with a minimum age of 18 months, which were predominantly at the end of their productive life, were euthanized, and brain and retropharyngeal lymph node examined by immunohistochemistry for disease-associated prion protein. Genotyping was done in all euthanized goats and live male goats used or intended for breeding to determine prion protein gene polymorphisms associated with resistance to classical scrapie. None of the goats presented with disease-associated prion protein in the examined tissues, and 34 (12.2%) carried the K222 allele associated with resistance. This allele was also found in four breeding male goats. The study results suggested that classical scrapie was not re-introduced on this goat farm through mass restocking or inadequate cleaning and disinfection procedures. Further scrapie surveillance of goats on this farm is desirable to confirm absence of disease. Breeding with male goats carrying the K222 allele should be encouraged to increase the scrapie-resistant population

Objects in contact with classical scrapie sheep act as a reservoir for scrapie transmission

Classical scrapie is an environmentally transmissible prion disease of sheep and goats. Prions can persist and remain potentially infectious in the environment for many years and thus pose a risk of infecting animals after re-stocking. In vitro studies using serial protein misfolding cyclic amplification (sPMCA) have suggested that objects on a scrapie- affected sheep farm could contribute to disease transmission. This in vivo study aimed to determine the role of field furniture (water troughs, feeding troughs, fencing, and other objects that sheep may rub against) used by a scrapie-infected sheep flock as a vector for disease transmission to scrapie-free lambs with the prion protein genotype VRQ/VRQ, which is associated with high susceptibility to classical scrapie. When the field furniture was placed in clean accommodation, sheep became infected when exposed to either a water trough (four out of five) or to objects used for rubbing (four out of seven). This field furniture had been used by the scrapie-infected flock 8 weeks earlier and had previously been shown to harbor scrapie prions by sPMCA. Sheep also became infected (20 out of 23) through exposure to contaminated field furniture placed within pasture not used by scrapie-infected sheep for 40 months, even though swabs from this furniture tested negative by PMCA. This infection rate decreased (1 out of 12) on the same paddock after replacement with clean field furniture. Twelve grazing sheep exposed to field furniture not in contact with scrapie-infected sheep for 18 months remained scrapie free. The findings of this study highlight the role of field furniture used by scrapie-infected sheep to act as a reservoir for disease re-introduction although infectivity declines considerably if the field furniture has not been in contact with scrapie-infected sheep for several months. PMCA may not be as sensitive as VRQ/VRQ sheep to test for environmental contamination

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

<p>Abstract</p> <p>Background</p> <p>The majority of atypical bovine spongiform encephalopathy (BSE) cases so far identified worldwide have been detected by active surveillance. Consequently the volume and quality of material available for detailed characterisation is very limiting. Here we report on a small transmission study of both atypical forms, H- and L-type BSE, in cattle to provide tissue for test evaluation and research, and to generate clinical, molecular and pathological data in a standardised way to enable more robust comparison of the two variants with particular reference to those aspects most relevant to case ascertainment and confirmatory diagnosis within existing regulated surveillance programmes.</p> <p>Results</p> <p>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.</p> <p>Conclusions</p> <p>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.</p

Experimental transmission of atypical scrapie to sheep

<p>Abstract</p> <p>Background</p> <p>Active surveillance for transmissible spongiform encephalopathies in small ruminants has been an EU regulatory requirement since 2002. A number of European countries have subsequently reported cases of atypical scrapie, similar to previously published cases from Norway, which have pathological and molecular features distinct from classical scrapie. Most cases have occurred singly in flocks, associated with genotypes considered to be more resistant to classical disease. Experimental transmissibility of such isolates has been reported in certain ovinised transgenic mice, but has not previously been reported in the natural host. Information on the transmissibility of this agent is vital to ensuring that disease control measures are effective and proportionate.</p> <p>Results</p> <p>This report presents the successful experimental transmission, in 378 days, of atypical scrapie to a recipient sheep of homologous genotype with preservation of the pathological and molecular characteristics of the donor. This isolate also transmitted to ovinised transgenic mice (Tg338) with a murine phenotype indistinguishable from that of Nor 98.</p> <p>Conclusion</p> <p>This result strengthens the opinion that these cases result from a distinct strain of scrapie agent, which is potentially transmissible in the natural host under field conditions.</p

Clinical findings in two cases of atypical scrapie in sheep: a case report

BACKGROUND: Atypical scrapie is a recently recognised form of transmissible spongiform encephalopathy of sheep that differs from classical scrapie in its neuropathological and biochemical features. Most cases are detected in apparently healthy sheep and information on the clinical presentation is limited. CASE PRESENTATION: This report describes the clinical findings in two sheep notified as scrapie suspects and confirmed as atypical scrapie cases by immunohistochemistry and Western immunoblotting. Although both sheep displayed signs suggestive of a cerebellar dysfunction there was considerable variation in the individual clinical signs, which were similar to classical scrapie. CONCLUSION: Any sheep presenting with neurological gait deficits should be assessed more closely for other behavioural, neurological and physical signs associated with scrapie and their presence should lead to the suspicion of scrapie

Assessing the aggregated probability of entry of a novel prion disease agent into the United Kingdom

In 2018 prion disease was detected in camels at an abattoir in Algeria for the first time. The emergence of prion disease in this species made it prudent to assess the probability of entry of the pathogen into the United Kingdom (UK) from this region. Potentially contaminated products were identified as evidenced by other prion diseases. The aggregated probability of entry of the pathogen was estimated as very high and high for legal milk and cheese imports respectively and very high, high and high for illegal meat, milk and cheese products respectively. This aggregated probability represents a qualitative assessment of the probability of one or more entry events per year into the UK; it gives no indication of the number of entry events per year. The uncertainty associated with these estimates was high due to the unknown variation in prevalence of infection in camels and an uncertain number and type of illegal products entering the UK. Potential public health implications of this pathogen are unknown although there is currently no evidence of zoonotic transmission of prion diseases other than bovine spongiform encephalopathy to humans

Estimating the impact on food and edible materials of changing scrapie control measures : the scrapie control model

Multiple controls established during the bovine spongiform encephalopathy (BSE) epidemic were not solely applied to BSE in cattle, but were implemented for scrapie in sheep and goats due to concerns over the occurrence of BSE in sheep. In the absence of BSE in sheep being observed, control measures for prion diseases are now being evaluated to ensure they remain proportionate to risk. This risk assessment, aims to estimate, by use of stochastic simulation, the impact of reducing controls for Specified Risk Materials (SRM) from sheep at abattoir. Three scenarios have been included: 1) current list of SRM; 2) brain and spinal cord of adult sheep; and 3) the brain of adult sheep. Results indicate the total amount of infectivity passing through British abattoirs is highest for atypical scrapie with nearly 3,500,000 Ovine Oral (OO) ID50 per year. The majority of this infectivity enters Category 1 waste for incineration, with only 13,000 OO ID50 per year within edible products. Under Scenario 2, an additional 4,000 OO ID50 per year would be classified as edible products from the lifting of restrictions on the distal ileum of adult sheep. However, if SRM removal was limited to brain, an additional 110,000 OO ID50 per year would be permitted into edible products with the lifting of restrictions on the spinal cord of adult sheep. For classical scrapie, there is a mean estimate of infectivity of 30,000 OO ID50 per year at abattoir. This is lower than for atypical scrapie due to the lower occurrence of this disease in Britain. However, more infectivity is destined to reach the food chain as the disease is peripherally distributed in the carcase. The highest contributor to the total amount of infectivity consumed per year is the intestines (duodenum and jejunum). If SRM removal is limited to the brain and spinal cord of sheep over 12 months of age, there is an approximate mean increase from 19,000 to 21,000 OO ID50 per year diverted to edible products. If the SRM list is restricted to brain only, this increases to over 23,000 OO ID50 per year. For the potential of sheep-BSE, there is a very low estimate of 29 OO ID50 per year in total from carcases entering abattoir, due to the potential very rare occurrence of this disease. Given changes in SRM regulations there is a change of an additional 4 OO ID50 per year being diverted to edible products