Minder BSE en scrapie

De dierziekte BSE is gevaarlijk voor de mens. Onderzoekers van het Central Veterinary Institute (CVI) hebben daarom snelle diagnostische tests ontwikkeld en ingezet bij rundvee, schapen en geiten. Ook hebben ze ervoor gezorgd dat schapen minder vatbaar zijn voor de verwante prionziekte scrapie

TSE pathogenesis in cattle and sheep

Many studies have been undertaken in rodents to study the pathogenesis of transmissible spongiform encephalopathies (TSE). Only a few studies have focused on the pathogenesis of bovine spongiform encephalopathy (BSE) and scrapie in their natural hosts. In this review, we summarize the most recent insights into the pathogenesis of BSE and scrapie starting from the initial uptake of TSE agents and crossing of the gut epithelium. Following replication in the gut-associated lymphoid tissues (GALT), TSE agents spread to the enteric nervous system (ENS) of the gut. Infection is then carried through the efferent fibers of the post-ganglionic neurons of the parasympathetic and sympathetic nervous system to the pre-ganglionic neurons in the medulla oblongata of the brain and the thoracic segments of the spinal cord. The differences between the pathogenesis of BSE in cattle and scrapie in sheep are discussed as well as the possible existence of additional pathogenetic routes

Risicobeoordeling schapenscheren en schapenwol voor mens en dier in de Nederlandse wolproductieketen

Het doel van dit onderzoek is een risicobeoordeling van de microbiologische risico's voor mens en dier van het schapenscheren, transport en het bewerken van schapenwol in de wolproductieketen in Nederland, inclusief de opties voor eventueel noodzakelijke risicoreducerende maatregelen. De VWA wilde de volgende vragen beantwoord hebben: 1. Welke microbiologische gevaren vormen in Nederland een risico voor infectie van en verspreiding onder mensen en dieren naar aanleiding van directe en indirecte contacten met het product wol in de wolproductieketen? 2. Kunt u deze microbiologische risico's in prioritaire volgorde plaatsen (kwalitatieve of indien mogelijk semikwantitatieve risicobeoordeling)? 3. Als er risico's aanwezig zijn, die op basis van een expertmening niet verwaarloosbaar klein zijn, welke risicoreducerende maatregelen kunnen mogelijk worden toegepast in de productieketen en op welk moment

Transmission and quantification of verocytotoxin-producing Escherichia coli O157 in dairy cattle and calves

Data from a field study of 14 months duration in a naturally colonized dairy herd and data from an experiment with calves were used to quantify transmission of verocytotoxin-producing Escherichia coli (VTEC O157) in cattle. For the latter, two groups of 10 calves were randomly assigned and put out in one of two pastures. From each group, five animals were experimentally inoculated with 109 c.f.u. O157 VTEC and, considered infectious, put back in their group. Each of the susceptible contact calves became positive within 6 days of being reunited. The estimate of the basic reproduction ratio (R0) in the experiment was 7·3 (95% CI 3·92¿11·5), indicating that each infectious calf will infect seven other calves on average during an assumed infectious period of 28 days in a fully susceptible population. The R0 among dairy cows appeared to be about 10 times lower (0·70, 95% CI 0·48¿1·04). After the transmission experiment, six contact-infected animals that were shedding continuously during the experiment were housed in a tie stall during winter. After 40 days, all six tested negative for O157 VTEC. In June, after a period of 34 weeks in which the heifers remained negative, they were put out in a clean and isolated pasture to observe whether they started shedding again. On each pasture that was infected with O157 VTEC during the transmission experiment the previous summer, newly purchased susceptible calves were placed. None of the heifers or calves started shedding during 14 weeks, indicating that both the heifers and the previously contaminated pasture did not function as reservoir of O157 VTE

Selection and optimization of proteolytically stable llama single-domain antibody fragments for oral immunotherapy

We previously demonstrated that oral application of the recombinant single-domain antibody fragment (VHH) clone K609, directed against Escherichia coli F4 fimbriae, reduced E. coli-induced diarrhoea in piglets, but only at high VHH doses. We have now shown that a large portion of the orally applied K609 VHH is proteolytically degraded in the stomach. Stringent selection for proteolytic stability identified seven VHHs with 7- to 138-fold increased stability after in vitro incubation in gastric fluid. By DNA shuffling we obtained four clones with a further 1.5- to 3-fold increased in vitro stability. These VHHs differed by at most ten amino acid residues from each other and K609 that were scattered over the VHH sequence and did not overlap with predicted protease cleavage sites. The most stable clone, K922, retained 41% activity after incubation in gastric fluid and 90% in jejunal fluid. Oral application of K922 to piglets confirmed its improved proteolytic stability. In addition, K922 bound to F4 fimbriae with higher affinity and inhibited fimbrial adhesion at lower VHH concentrations. K922 is thus a promising candidate for prevention of piglet diarrhoea. Furthermore, our findings could guide selection and improvement by genetic engineering of other recombinant antibody fragments for oral use

Sharp decline in scrapie prevalence in the Netherlands after breeding for resistance: Are we close to achieving eradication?

Introduction. In the Netherlands an ambitious scrapie control program was started at the national level in 1998, based on genetic selection of animals for breeding. From 2002 onwards EU regulations required intensive active scrapie surveillance as well as certain control measures in affected flocks. Materials and Methods. Here we use standard statistical methods as well as mathematical modeling to analyze (1) data on genotype frequencies and scrapie prevalence in the Dutch sheep population obtained from both surveillance and affected flocks; (2) data on PrP genotype frequencies in a random sample of flocks; (3) postal survey results on between-flock differences in breeding strategy and flock management. Results and Conclusions. Analyzing the data (1) we find that the breeding program has produced a steady increase in the level of genetic scrapie resistance in the Dutch sheep population. We also found that a few years later this was followed by a sharp decline in the prevalence of classical scrapie in tested animals. Notably, the estimated classical scrapie prevalence level per head of susceptible genotype declined significantly as well. This indicates that selective breeding has a disproportionate effect on infection prevalence, reminiscent of the well-known population effect of vaccination against a transmissible disease. The overall recent decline in classical scrapie prevalence in Dutch sheep suggests that eradication of the disease in The Netherlands may be within reach. However, a subset of farms may still continue to act as a core group for scrapie transmission for some time, as we show by analyzing between-flock heterogeneities using the data (2) and (3). In addition, genetic resistance levels may decline again in future as participation to the selective breeding program has recently become voluntary

Q fever in pregnant Goats: PAthogenesis and excretion of Coxiella burnetii

Coxiella burnetii is an intracellular bacterial pathogen that causes Q fever. Infected pregnant goats are a major source of human infection. However, the tissue dissemination and excretion pathway of the pathogen in goats are still poorly understood. To better understand Q fever pathogenesis, we inoculated groups of pregnant goats via the intranasal route with a recent Dutch outbreak C. burnetii isolate. Tissue dissemination and excretion of the pathogen were followed for up to 95 days after parturition. Goats were successfully infected via the intranasal route. PCR and immunohistochemistry showed strong tropism of C. burnetii towards the placenta at two to four weeks after inoculation. Bacterial replication seemed to occur predominantly in the trophoblasts of the placenta and not in other organs of goats and kids. The amount of C. burnetii DNA in the organs of goats and kids increased towards parturition. After parturition it decreased to undetectable levels: after 81 days post-parturition in goats and after 28 days post-parturition in kids. Infected goats gave birth to live or dead kids. High numbers of C. burnetii were excreted during abortion, but also during parturition of liveborn kids. C. burnetii was not detected in faeces or vaginal mucus before parturition. Our results are the first to demonstrate that pregnant goats can be infected via the intranasal route. C. burnetii has a strong tropism for the trophoblasts of the placenta and is not excreted before parturition; pathogen excretion occurs during birth of dead as well as healthy animals. Besides abortions, normal deliveries in C. burnetii-infected goats should be considered as a major zoonotic risk for Q fever in humans

Prion-type dependent deposition of PRNP allelic products in heterozygous sheep

Susceptibility or resistance to prion infection in humans and animals depends on single prion protein (PrP) amino acid substitutions in the host, but the agent's modulating role has not been well investigated. Compared to disease incubation times in wild-type homozygous ARQ/ARQ (where each triplet represents the amino acids at codons 136, 154, and 171, respectively) sheep, scrapie susceptibility is reduced to near resistance in ARR/ARR animals while it is strongly enhanced in VRQ/VRQ carriers. Heterozygous ARR/VRQ animals exhibit delayed incubation periods. In bovine spongiform encephalopathy (BSE) infection, the polymorphism effect is quite different although the ARR allotype remains the least susceptible. In this study, PrP allotype composition in protease-resistant prion protein (PrPres) from brain of heterozygous ARR/ VRQ scrapie-infected sheep was compared with that of BSE-infected sheep with a similar genotype. A triplex Western blotting technique was used to estimate the two allotype PrP fractions in PrPres material from BSE-infected ARR/VRQ sheep. PrPres in BSE contained equimolar amounts of VRQ- and ARR-PrP, which contrasts with the excess (>95%) VRQPrP fraction found in PrP in scrapie. This is evidence that transmissible spongiform encephalopathy (TSE) agent properties alone, perhaps structural aspects of prions (such as PrP amino acid sequence variants and PrP conformational state), determine the polymorphic dependence of the PrPres accumulation process in prion formation as well as the disease-associated phenotypic expressions in the host.</p

Prions

The report 'Zoonoses and Zoonotic Agents in Humans, Food, Animals and Feed in The Netherlands 2003 - 2006' is based on data that is reported annually to the European Commission, in accordance with the Directive 2003/99/EC on the monitoring of zoonoses and zoonotic agents. They are supplemented with data from Dutch surveillance, monitoring and control programmes and relevant research projects concerning zoonoses and zoonotic agents by the different institutions that have contributed to the preparation of this report. The report also includes information on recent research on the antibiotic resistance of micro-organisms derived from human and animal material. Specific documentation and reports regarding the described programmes and research projects are available from the authors mentioned in the editorial list. The extended dataset on antimicrobial resistance and trends in the Netherlands has been published recently as a report: Maran 2003, 2004 and 2005