A Case of Bovine Spongiform Encephalopathy in Denmark

Bovine spongiform encephalopathy (BSE), a transmissible spongiform encephalopathy in cattle, was first described in England by Wells et al. (1987). The infection occurs mainly due to digestion of feedstuffs containing ruminant derived protein in form of meat and bone meal contaminated with a scrapie-like agent (Wilesmith et al. 1991). Later, cases of BSE were diagnosed in the Republic of Ireland, Oman, France, and Switzerland (Marinovic & Senn 1991). This report describes the first case of BSE in Denmark.     

Sporadic Creutzfeldt-Jakob disease in the United Kingdom: analysis of epidemiological surveillance data for 1970-96.

OBJECTIVE: To identify changes in the occurrence of Creutzfeldt-Jakob disease that might be related to the epidemic of bovine spongiform encephalopathy. DESIGN: Epidemiological surveillance of the United Kingdom population for Creutzfeldt-Jakob disease based on (a) referral of suspected cases by neurologists, neuropathologists, and neurophysiologists and (b) death certificates. SETTING: England and Wales during 1970-84, and whole of the United Kingdom during 1985-96. SUBJECTS: All 662 patients identified as sporadic cases of Creutzfeldt-Jakob disease. MAIN OUTCOME MEASURES: Age distribution of patients, age specific time trends of disease, occupational exposure to cattle, potential exposure to causative agent of bovine spongiform encephalopathy. RESULTS: During 1970-96 there was an increase in the number of sporadic cases of Creutzfeldt-Jakob disease recorded yearly in England and Wales. The greatest increase was among people aged over 70. There was a statistically significant excess of cases among dairy farm workers and their spouses and among people at increased risk of contact with live cattle infected with bovine spongiform encephalopathy. During 1994-6 there were six deaths from sporadic Creutzfeldt-Jakob disease in the United Kingdom in patients aged under 30. CONCLUSIONS: The increase in the incidence of sporadic Creutzfeldt-Jakob disease and the high incidence in dairy farmers in the United Kingdom may be unrelated to bovine spongiform encephalopathy. The most striking change in the pattern of Creutzfeldt-Jakob disease in the United Kingdom after the epidemic of bovine spongiform encephalopathy is provided by the incidence in a group of exceptionally young patients with a consistent and unusual neuropathological profile. The outcome of mouse transmission studies and the future incidence of the disease in the United Kingdom and elsewhere, will be important in judging whether the agent causing bovine spongiform encephalopathy has infected humans.     

The spread of prions through the body in naturally acquired transmissible spongiform encephalopathies

Transmissible spongiform encephalopathies are fatal neurodegenerative diseases that are caused by unconventional pathogens and affect the central nervous system of animals and humans. Several different forms of these diseases result from natural infection (i.e. exposure to transmissible spongiform encephalopathy agents or prions, present in the natural environment of the respective host). This holds true also for scrapie in sheep, bovine spongiform encephalopathy in cattle, chronic wasting disease in elk and deer, or variant Creutzfeldt-Jakob disease in humans, all of which are assumed to originate predominantly from peroral prion infection. This article intends to provide an overview of the current state of knowledge on the spread of scrapie, chronic wasting disease, bovine spongiform encephalopathy and variant Creutzfeldt-Jakob disease agents through the body in naturally affected hosts, and in model animals experimentally challenged via the alimentary tract. Special attention is given to the tissue components and spreading pathways involved in the key stages of prion routing through the body, such as intestinal uptake, neuroinvasion of nerves and the central nervous system, and centrifugal spread from the brain and spinal cord to peripheral sites (e.g. sensory ganglia or muscles). The elucidation of the pathways and mechanisms by which prions invade a host and spread through the organism can contribute to efficient infection control strategies and the improvement of transmissible spongiform encephalopathy diagnostics. It may also help to identify prophylactic or therapeutic approaches that would impede naturally acquired transmissible spongiform encephalopathy infections.     

Entry versus blockade of brain infection following oral or intraperitoneal scrapie administration: role of prion protein expression in peripheral nerves and spleen

Naturally occurring transmissible spongiform encephalopathy (TSE) diseases such as bovine spongiform encephalopathy in cattle are probably transmitted by oral or other peripheral routes of infection. While prion protein (PrP) is required for susceptibility, the mechanism of spread of infection to the brain is not clear. Two prominent possibilities include hematogenous spread by leukocytes and neural spread by axonal transport. In the present experiments, following oral or intraperitoneal infection of transgenic mice with hamster scrapie strain 263K, hamster PrP expression in peripheral nerves was sufficient for successful infection of the brain, and cells of the spleen were not required either as a site of amplification or as transporters of infectivity. The role of tissue-specific PrP expression of foreign PrP in interference with scrapie infection was also studied in these transgenic mice. Peripheral expression of heterologous PrP completely protected the majority of mice from clinical disease after oral or intraperitoneal scrapie infection. Such extensive protection has not been seen in earlier studies on interference, and these results suggested that gene therapy with mutant PrP may be effective in preventing TSE diseases.     

Seroprevalence of Neospora caninum infection in dairy cattle of Southern China

A seroepidemiological survey of Neospora caninum infection in dairy cattle was carried out in China's southern Guangdong Province between July 2009 and March 2010. A total of 370 serum samples of dairy cattle was collected from 5 farms and examined for antibodies to N. caninum by enzyme-linked immunosorbent assay. The overall seroprevalence of N. caninum in dairy cattle was 18.9% (70/370). The seroprevalence of N. caninum in aborting cows (22.7%) was higher than that in nonaborting cows (16.3%), but the difference was not statistically significant (P > 0.05). Five-yr-old dairy cattle had the highest seroprevalence (27.8%), followed by those that were 6-yr-old (20.4%). Dairy cattle with 4 pregnancies had the highest seroprevalence (29.2%). There was no apparent association of N. caninum seropositivity with age or number of pregnancies (P > 0.05). The results of the present survey indicated that the infection with N. caninum is prevalent in dairy cattle of all ages in southern China, which may be one of the causes of bovine abortion. This is the first report of seroprevalence of N. caninum in dairy cattle in southern China.     

Mathematical models of Neospora caninum infection in dairy cattle: transmission and options for control

The transmission and control of Neospora caninum infection in dairy cattle was examined using deterministic and stochastic models. Parameter estimates were derived from recent studies conducted in the UK and from the published literature. Three routes of transmission were considered: maternal vertical transmission with a high probability (0.95), horizontal transmission from infected cattle within the herd, and horizontal transmission from an independent external source. Putative infection via pooled colostrum was used as an example of within-herd horizontal transmission, and the recent finding that the dog is a definitive host of N. caninum supported the inclusion of an external independent source of infection. The predicted amount of horizontal transmission required to maintain infection at levels commonly observed in field studies in the UK and elsewhere, was consistent with that observed in studies of post-natal seroconversion (0.85-9.0 per 100 cow-years). A stochastic version of the model was used to simulate the spread of infection in herds of 100 cattle, with a mean infection prevalence similar to that observed in UK studies (around 20%). The distributions of infected and uninfected cattle corresponded closely to Normal distributions, with S.D.s of 6.3 and 7.0, respectively. Control measures were considered by altering birth, death and horizontal transmission parameters. A policy of annual culling of infected cattle very rapidly reduced the prevalence of infection, and was shown to be the most effective method of control in the short term. Not breeding replacements from infected cattle was also effective in the short term, particularly in herds with a higher turnover of cattle. However, the long-term effectiveness of these measures depended on the amount and source of horizontal infection. If the level of within-herd transmission was above a critical threshold, then a combination of reducing within-herd, and blocking external sources of transmission was required to permanently eliminate infection.     

BSE inoculation to prion diseases-resistant sheep reveals tricky silent carriers

The possible transmission of bovine spongiform encephalopathy (BSE) agent to sheep contributed to select genetically sheep considered as resistant to prion diseases i.e., with PrP ARR/ARR genotype. Here, we report the infection of two PrP ARR/ARR genotype sheep using the cattle BSE agent inoculated by peripheral routes. Disease-associated prion protein (PrP(d)) was detected in the brain for one case (at 2191 days post-infection (dpi)) and only in the nervous enteric system for the other one (at 673dpi). The electrophoretic pattern of PrP(d) from the obex region in this BSE challenged sheep was shown to be closer from that found in naturally scrapie-affected sheep with regard to the apparent molecular mass of the unglycosylated PrP(d). Importantly, the absence of any clinical symptoms up to 6 years following experimental challenge suggests that silent carriers of the BSE agent may exist among ARR homozygous sheep.     

Comparison of abnormal prion protein glycoform patterns from transmissible spongiform encephalopathy agent-infected deer,elk, sheep,and cattle

Analysis of abnormal prion protein glycoform patterns from chronic wasting disease (CWD)-affected deer and elk, scrapie-affected sheep and cattle, and cattle with bovine spongiform encephalopathy failed to identify patterns capable of reliably distinguishing these transmissible spongiform encephalopathy diseases. However, PrP-res patterns sometimes differed among individual animals, suggesting infection by different or multiple CWD strains in some species.     

Assessment of the risk posed by bovine spongiform encephalopathy in cattle in Great Britain and the impact of potential changes to current control measures

We extended an existing back-calculation model to analyse data on reported clinical cases of bovine spongiform encephalopathy (BSE), data from random testing of healthy animals slaughtered in abattoirs and testing data from animals reported as sick or dying on the farm. Extensive analysis of demographic data was also undertaken. We estimated past and current BSE infection prevalences in the cattle population and the degree of case under-ascertainment resulting from excess mortality in cattle near to disease onset. Ongoing levels of human exposure to BSE infectivity were also estimated, together with the effect on these of a range of possible exposure-reduction strategies that might replace the current rule banning tissue from cattle over 30 months (OTM) of age from the human food supply. While any policy change that allows a wider age range of animals into the human food supply will increase levels of human exposure to infectivity, the risk posed by such increases is small by comparison with historical exposure levels. Making the pessimistic assumption that there will be 5000 deaths during the variant Creutzfeldt-Jakob disease (vCJD) epidemic in total, our analysis indicates that replacement of the OTM rule with testing would result in 0.04 additional vCJD deaths over the next 60 years. However, there is substantial (more than 40-fold) uncertainty surrounding this estimate, the sources of which are discussed.     

Implications of BSE infection screening data for the scale of the British BSE epidemic and current European infection levels

The incidence of confirmed clinical cases of bovine spongiform encephalopathy (BSE) in Great Britain continues to decline, but the recent discovery of cases in previously unaffected countries (including Israel, Japan, Poland, Slovenia and Spain) has heightened concerns that BSE transmission was more intense and widespread than previously thought. We use back-calculation methods to undertake an integrated analysis of data on infection prevalence in apparently healthy cattle and the incidence of confirmed clinical disease. The results indicate substantial underascertainment of clinical cases over the course of the British epidemic, and consequently that two- to fourfold more animals were infected than previously estimated. Upper bounds on the predicted size of the new variant Creutzfeldt-Jakob Disease (vCJD) epidemic are unaffected, as the prediction methods employed fit to observed vCJD mortality data, and are not sensitive to estimates of the absolute magnitude of past human exposure to BSE-infected cattle, only to relative changes in exposure through time. We also estimate the per-head incidence of infection in cattle born between 1993 and 1997 in other European Union countries, using data on the testing of apparently healthy cattle slaughtered for consumption. Infection incidence for cattle born after mid-1996 was highest in Greece, Italy and Belgium, with Spain and The Netherlands having intermediate levels, and estimates for Great Britain, Germany and France being comparably low.     

Feed-borne transmission and case clustering of BSE

An unresolved issue in the epidemiology of bovine spongiform encephalopathy (BSE) in the UK is what precisely determines the degree to which cases of disease in cattle are clustered within herds throughout the course of the epidemic. This paper presents an analysis of feed-borne transmission at the herd level and tests various models of case-clustering mechanisms, associated with heterogeneity in exposure to infectious feed, against observed epidemic pattern. We use an age-structured metapopulation framework in which the recycling of animal tissue between herds via feed producers is explicitly described. We explore two alternative assumptions for the scaling with herd size of the within-herd risk of exposure of an animal to infectious material. We find that whereas exposure heterogeneity caused by variation in feed and offal processing methods and by variation in per-animal feed uptake can explain the pattern of case clustering seen in the BSE epidemic, exposure heterogeneity due to the aggregation of infectivity within feed cannot.     

The Nematode Heterotylenchus autumnalis and Face Fly Musca autumnalis: A Field Study in Northern California

Helerolylenchus aulumnalis was found in six northern California counties surveyed, and the incitlence of nematode infection of face flies ranged from 4.7 to 43.8%. Intensive studies at a cattle ranch in Yuba County showed that population densities of the host and nematode infections were highest in flies from cow pats receiving full sun. Average host population density was 105.7 puparia per pat, and nematode infection averaged 38.6%. Pats in partial sun averaged 13.5 puparia and 13,1% nematode infection. No face fly was recovered from shaded pats. When data from pats first exposed during day or night were compared, no significant differences in host population density or nematode infection rates were apparent. Uninfected and superinfected flies were more frequent than predicted by a Poisson distribution.Infected and uninfected female flies of all ages captured on white sticky traps appeared to feed with similar frequency upon a creatny substance which was probably acquired from cattle, However, older infected females fed less on blood and more upon dung than older uninfected females. Percent nematode infection and host population densities were highest in spring and early summer, declined to a midsummer low, and then increased slightly. Both dung-reared flies and captured females showed similar trends in abundance anti infection rates. Regression analysis indicated that H. autumnalis may not be regulating face fly population density.     

BSE case associated with prion protein gene mutation

Bovine spongiform encephalopathy (BSE) is a transmissible spongiform encephalopathy (TSE) of cattle and was first detected in 1986 in the United Kingdom. It is the most likely cause of variant Creutzfeldt-Jakob disease (CJD) in humans. The origin of BSE remains an enigma. Here we report an H-type BSE case associated with the novel mutation E211K within the prion protein gene (Prnp). Sequence analysis revealed that the animal with H-type BSE was heterozygous at Prnp nucleotides 631 through 633. An identical pathogenic mutation at the homologous codon position (E200K) in the human Prnp has been described as the most common cause of genetic CJD. This finding represents the first report of a confirmed case of BSE with a potential pathogenic mutation within the bovine Prnp gene. A recent epidemiological study revealed that the K211 allele was not detected in 6062 cattle from commercial beef processing plants and 42 cattle breeds, indicating an extremely low prevalence of the E211K variant (less than 1 in 2000) in cattle.     

Use of deltamethrin 'pour-on' insecticide for the control of cattle trypanosomosis in the presence of high tsetse invasion

A deltamethrin 'pour-on' insecticide was applied monthly to over 2000 cattle exposed to a high challenge of drug-resistant trypanosomes and high tsetse re-invasion pressure in the Ghibe valley, south-west Ethiopia. Blood samples were taken monthly from an average of 760 cattle for determination of PCV and presence of trypanosomes. The area of the valley is approximately 350 km2 and the cattle grazed in roughly four locations covering about a quarter to half of the area. Two years before the trial commenced, Glossina morsitans submorsitans Newstead (Diptera: Glossinidae) began to invade the valley. Despite the use of the pour-on the mean apparent density of G. m. submorsitans continued to rise, and, during the 4 years of tsetse control, was more than three-fold higher than that recorded during the previous 18 months. Over the same period there was little change in the apparent density of Glossina pallidipes Austen (Diptera: Glossinidae). By contrast, the mean monthly prevalence of trypanosome infections in cattle over 36 months of age decreased from 38.3 to 29.0%, the incidence of new infections decreased from 26.6 to 16.0% (a reduction of 40%), and packed cell volume in cattle increased from 21.7 to 24.1%. Evidence of a change in apparent parasite transmission rate was demonstrated by regression of infection incidence in cattle on the logarithm of apparent density of G. m. submorsitans. Before the trial started the regression coefficient was 45.8 +/- 6.3 and this reduced to 9.2 +/- 2.5% incidence per log(e) (flies/trap/day) during the period of tsetse control. It was concluded that this indicated reductions in tsetse numbers in the immediate vicinities of cattle in a way that was not reflected in overall tsetse catches. Nevertheless, the comparatively high levels of trypanosome prevalence that persisted in the cattle demonstrates that, where invasion prevalence is high, treatment of small pockets of cattle will not eradicate tsetse. To achieve more significant reduction in trypanosome prevalence in cattle, integrated methods of control utilizing target barriers in the major routes of invasion will be needed.     

PRNP gene variation in Pakistani cattle and buffaloes

Bovine spongiform encephalopathy (BSE) is a neurodegenerative prion protein misfolding disorder of cattle. BSE is of two types, classical BSE and atypical BSE which in turn is of two types, H-type BSE and L-type BSE. Both H-type BSE and L-type BSE are primarily sporadic prion disorders. However, one case of H-type BSE has recently been associated with E211K polymorphism in the prion protein gene (PRNP). Two polymorphisms in the bovine PRNP are also associated with susceptibility to classical BSE: a 23 bp insertion/deletion (indel) in the PRNP promoter region and a 12 bp indel in the first intron. No information regarding BSE susceptibility in Pakistani cattle is available. The present study aimed at achieving this information. A total of 236 cattle from 7 breeds and 281 buffaloes from 5 breeds were screened for E211K polymorphism and 23 bp and 12 bp indels employing triplex PCR. The E211K polymorphism was not detected in any of the animals studied. The 23 bp insertion allele was underrepresented in studied cattle breeds while the 12 bp insertion allele was overrepresented. Both 23 bp and 12 bp insertion alleles were overrepresented in studied buffalo breeds. Almost 90% of alleles were insertion alleles across all studied buffalo breeds. The average frequency of 23 bp and 12 bp insertion alleles across all studied cattle breeds was found to be 0.1822 and 0.9407, respectively. There were significant differences between Pakistani and worldwide cattle in terms of allele, genotype and haplotype frequencies of 23 bp and 12 bp indels. The higher observed frequency of 12 bp insertion allele suggests that Pakistani cattle are relatively more resistant to classical BSE than European cattle. However, the key risk factor for classical BSE is the dietary exposure of cattle to contaminated feedstuffs.     

The epidemiology of fasciolosis in the inter-Andean valley of Cajamarca, Peru

Fasciolosis is recognised as a major problem in dairy cattle in parts of Peru. A longitudinal study of dairy cattle in Cajamarca, Peru was used to determine the annual pattern of infection with Fasciola hepatica. After a gradual increase from January, peak egg production occurred in August/September and then dropped rapidly. Indirect indicators of infection, eosinophil counts and serum liver-enzyme activities, indicated that the major period of new infection in cattle occurred from December to May each year. Examination of snails demonstrated that, although there was no clear annual cycle in snail abundance, the majority of snails infected with cercariae were found between January and March. Climatological data indicated that there was sufficient moisture for development of the parasite during a limited period each year, coinciding with the period of maximum abundance of cercaria-infected snails, but that irrigation could substantially alter the amount of water available. Infections in tracer-calves decreased from December to September, with little or no infection occurring between June and August, but suggesting that there could be significant infection prior to December. Thus a defined annual cycle of infection was observed, where cattle acquired infection from December to May and this infection matured to produce peak egg counts in August/September which were then available to infect the intermediate host for the next cycle of infection.     

Sources of Escherichia coli O157 and experiences over the past 15 years in Sheffield, UK

In the first documented outbreak of HC caused by Escherichia coli O157, which occurred in the North-west USA in 1982, there was a strong association between infection and prior consumption of ground beef from a chain of fast food restaurants. Foods of bovine origin, including beef, milk and dairy products, have since been implicated in many outbreaks of infection world-wide. Investigations during the course of outbreaks, or at random, have shown that cattle are a major reservoir of E. coli O157. E. coli O157 was isolated from cattle at slaughter in Sheffield in 1987, this being the first isolation from cattle in the UK. Following a cluster of cases in May/June 1992, an abattoir study showed the organism to be present in 4% of cattle at slaughter and on up to a third of carcasses from rectal swab-positive animals. E. coli O157 was isolated from a food source (unpasteurized milk), for the first time in the UK, in Sheffield in May 1993. During surveillance in 1995-6, E. coli O157 was isolated from 15.7% of cattle, with a monthly prevalence which varied from 5 to 37%. E. coli O157 was also isolated from 2.2% of sheep. During surveillance in 1996, E. coli O157 was isolated from 5.9% of samples of lamb products and from 1.5% of samples of beef products, despite the prevalence in cattle being much higher than in sheep. Work is in progress to try to explain this higher prevalence in lamb products. During 1997 in Sheffield, the only cases of E. coli O157 for which a confirmed source was established were associated with direct animal contact on farm visits. During on-farm investigations of these cases, E. coli O157 was isolated from faecal samples from adult cattle, calves, three different breeds of sheep, two different breeds of pigs, goats and a pony.     

The effect of infection with bovine viral diarrhea virus on the fertility of Swiss dairy cattle

Bovine viral diarrhea virus is a major cattle pathogen with a worldwide distribution. Animals may be infected with BVD virus transiently or persistently. Transient infection leads to protective immunity. Persistent infection is unique because it is associated with an immunotolerance that is specific to the infecting strain of BVD virus. Persistent infection results from viral invasion of fetuses between the second and fourth month of development. Such animals are of prime importance in the epidemiology of BVD because they shed large amounts of virus, and thus serve as a constant source of infection for non-immune animals. Infection of pregnant animals during the first two months of gestation may result in an increased rate of return to estrus. Animals infected in the period of five months to birth may abort or give birth to calves with malformations. The effects of BVD virus on fertility and gestation are well documented from experimental infection. However, much less is known of the extent of losses under field conditions. The main reason for this may be the multitude of other causes of increased return rates and gestation failures. In addition, the incidence of infection with BVD virus may vary over time and depends on management practices. In this study, we investigated the impact of BVD virus on gestation failures under field conditions in a large cattle-breeding area of Switzerland, where no specific measures to control BVD are in effect. Our approach consisted of relating seroconversions to BVD virus with the rate of return to estrus, abortion, and birth of calves with apparent malformations. These parameters of fertility were compared to those of animals immune to BVDV infection due to previous exposure to the virus and animals without seroconversion. Our data show that infection with BVD virus during the first 45 days of gestation did not influence the rate of return to estrus. By contrast, we observed a statistically significant increase in the abortion rate in mid-term gestation (Days 46 to 210) while no such effect was observed in the later stages of gestation. No clinically manifest malformations were observed in the offspring of animals that had seroconverted to BVD virus. In our study population the prevalence of BVDV antibody positive cattle varied only slightly between 78% and 80% over the period of observation. Our data showed that 7% (CI: 2.4-14%) of fetal deaths may be attributable to infection with BVD virus.     

Minimum Effective Dose of Cattle and Sheep BSE for Oral Sheep Infection

The minimum dose required to cause infection of Romney and Suffolk sheep of the ARQ/ARQ or ARQ/ARR prion protein gene genotypes following oral inoculation with Romney or Suffolk a sheep Bovine spongiform encephalopathy (BSE)-derived or cattle BSE-derived agent was investigated using doses ranging from 0.0005g to 5g. ARQ/ARQ sheep which were methionine (M) / threonine (T) heterozygous or T/T homozygous at codon 112 of the Prnp gene, dosed ARQ/ARR sheep and undosed controls did not show any evidence of infection. Within groups of susceptible sheep, the minimum effective oral dose of BSE was found to be 0.05g, with higher attack rates following inoculation with the 5g dose. Surprisingly, this study found no effect of dose on survival time suggesting a possible lack of homogeneity within the inoculum. All clinical BSE cases showed PrP^d accumulation in brain; however, following cattle BSE inoculation, LRS involvement within Romney recipients was found to be significantly lower than within the Suffolk sheep inoculated group which is in agreement with previous reports.