Failure to transmit scrapie infection by transferring preimplantation embryos from naturally infected donor sheep

The objective of the study was to examine whether or not the preimplantation embryo can act as a carrier of classic scrapie infection. The study was carried out on quarantined premises with sheep of highly susceptible scrapie genotypes. Uninfected embryos, collected from New Zealand-derived Suffolk ewes, were surgically transferred into recipient ewes that were also of New Zealand origin. Seventeen negative control lambs were born on the study premises from these embryo transfers. Thirty-nine experimental lambs were from embryos collected from naturally infected donor ewes. The experimental lambs were also born on the study premises after their surgical transfer into recipient ewes of New Zealand origin. These embryos had been collected from donor ewes in a scrapie-infected flock where the ewes were clinically sick with scrapie or developed clinical scrapie after embryo collection. All lambs were confirmed as scrapie susceptible of the ARQ/ARQ genotype. Twenty-eight experimental animals survived to the end point of the study at 5 yr of age with a mean survival of 1579 d. In the negative control group, 12 of 17 sheep survived to 5 yr of age with a mean survival of 1508 d. Postmortem examinations were carried out on all animals derived by embryo transfer, and in none was histologic or immunohistochemical evidence of scrapie found. In contrast, in the originating flock the majority of scrapie cases occurred in ARQ/ARQ genotyped animals where a 56% mortality from scrapie had been recorded in animals of this genotype. Thus, the study provides no evidence for transmission of scrapie and reinforces published evidence that vertical transmission of scrapie may be circumvented by embryo transfer procedures.

150 THE ROLE OF THE PRE-IMPLANTATION EMBRYO IN THE VERTICAL TRANSMISSION OF NATURAL SCRAPIE INFECTION IN SHEEP

The objective of this study was to examine whether or not the pre-implantation embryo can act as a carrier of scrapie. The study was carried out on quarantined premises with sheep of highly susceptible scrapie genotypes. Fifty-seven lambs were produced from embryos collected from donor ewes. These donor ewes were in a scrapie-infected flock and became clinically sick with scrapie or developed clinical scrapie after embryo collection. Fifty of the generated lambs were confirmed as having scrapie-susceptible genotypes with 48 animals identified as ARQ/ARQ and 2 as ARQ/ARH. The respective mean and median ages for the 57 scrapie-susceptible experimental offspring in the study were 1565 and 1826 days. Forty-one of these animals survived to the end point of the study at 5 years of age. In a negative control group the mean and median ages at death for the 17 sheep were 1500 and 1826 days, respectively, and 12 survived to 5 years of age. Post-mortem examinations were carried out on all animals derived by embryo transfer and in none was histological or immunohistochemical evidence of scrapie found. In contrast, in the originating infected flock the majority of scrapie cases occurred in ARQ/ARQ genotyped animals with 56% mortality from scrapie in animals of this genotype. Thus, the study provides no evidence for transmission of scrapie and reinforces published evidence that vertical transmission of scrapie may be circumvented by embryo transfer procedures. This study was commissioned and financially supported by Defra. Amongst the many involved in the study the authors particularly wish to acknowledge Jon Hunton, James Mylne, Tony Wrathall and Chris Lewis. Keith Chalmers Watson is thanked for his interest and for the land rental that made the work feasible.

Evaluation of a survey approach to estimating the prevalence of cattle carrying antimicrobial-resistant Escherichia coli

A random survey of farms in the Highlands and Islands of Scotland provides estimated of the prevalence of calves, finishers and cows carrying ampicillin, apramycin and/or nalidixic acid resistant Escherichia coli. While the survey provides information on the geographical variation in risk, the results are of limited value for interpreting causality.

Modelling the epidemiology and transmission of Verocytotoxin-producing Escherichia coli serogroups O26 and O103 in two different calf cohorts

Mathematical models are constructed to investigate the population dynamics of Verocytotoxin-producing Escherichia coli (VTEC) serogroups O26 and O103 in two different calf cohorts. We compare the epidemiological characteristics of these two serogroups within the same calf cohort as well as the same serogroups between the two calf cohorts. The sources of infection are quantified for both calf cohort studies. VTEC serogroups O26 and O103 mainly differ in the rate at which calves acquire infection from sources other than infected calves, while infected calves typically remain infectious for less than 1 week regardless of the serogroups. Fewer than 20% of VTEC-positive samples are the result of calf-to-calf transmission. PFGE typing data are available for VTEC-positive samples to further subdivide the serogroup data in one of the two calf cohort studies. For serogroup O26 but not O103, there is evidence for unequal environmental exposure to infection with different PFGE types.

Sensitivity of an immunomagnetic-separation-based test for detecting Escherichia coli O26 in bovine feces

The sensitivity of a test for cattle shedding Escherichia coli serogroup O26 was estimated using several fecal pats artificially inoculated at a range of concentrations with different E. coli O26 strains. The test involves the enrichment of fecal microflora in buffered peptone water, the selective concentration of E. coli O26 using antibody-coated immunomagnetic-separation beads, the identification of E. coli colonies on Chromocult tryptone bile X-glucuronide agar, and confirmation of the serogroup with E. coli serogroup O26-specific antisera using slide agglutination. The effective dose of E. coli O26 for an 80% test sensitivity (ED(80)) was 1.0 x 10(4) CFU g(-1) feces (95% confidence interval, 4.7 x 10(3) to 2.4 x 10(4)). Differences in test sensitivity between different E. coli O26 strains and fecal pats were also observed. Individual estimates of ED(80) for each strain and fecal pat combination ranged from 4.2 x 10(2) to 4.8 x 10(5) CFU g(-1). These results suggest that the test is useful for identifying individuals shedding a large number of E. coli O26 organisms or, if an appropriate number of individuals in a herd are sampled, for identifying affected herds. The study also provides a benchmark estimate of sensitivity that can be used to compare alternative tests for E. coli O26 and a methodological approach that can be applied to tests for other pathogenic members of the Enterobacteriaceae and other sample types.

Heterogeneous shedding of Escherichia coli O157 in cattle and its implications for control

Identification of the relative importance of within- and between-host variability in infectiousness and the impact of these heterogeneities on the transmission dynamics of infectious agents can enable efficient targeting of control measures. Cattle, a major reservoir host for the zoonotic pathogen Escherichia coli O157, are known to exhibit a high degree of heterogeneity in bacterial shedding densities. By relating bacterial count to infectiousness and fitting dynamic epidemiological models to prevalence data from a cross-sectional survey of cattle farms in Scotland, we identify a robust pattern: approximately 80% of the transmission arises from the 20% most infectious individuals. We examine potential control options under a range of assumptions about within- and between-host variability in infection dynamics. Our results show that the within-herd basic reproduction ratio, R(0), could be reduced to <1 with targeted measures aimed at preventing infection in the 5% of individuals with the highest overall infectiousness. Alternatively, interventions such as vaccination or the use of probiotics that aim to reduce bacterial carriage could produce dramatic reductions in R(0) by preventing carriage at concentrations corresponding to the top few percent of the observed range of counts. We conclude that a greater understanding of the cause of the heterogeneity in bacterial carriage could lead to highly efficient control measures to reduce the prevalence of E. coli O157.

Prevalence and virulence factors of Escherichia coli serogroups O26, O103, O111, and O145 shed by cattle in Scotland

A national survey was conducted to determine the prevalence of Escherichia coli O26, O103, O111, and O145 in feces of Scottish cattle. In total, 6,086 fecal pats from 338 farms were tested. The weighted mean percentages of farms on which shedding was detected were 23% for E. coli O26, 22% for E. coli O103, and 10% for E. coli O145. The weighted mean prevalences in fecal pats were 4.6% for E. coli O26, 2.7% for E. coli O103, and 0.7% for E. coli O145. No E. coli O111 was detected. Farms with cattle shedding E. coli serogroup O26, O103, or O145 were widely dispersed across Scotland and were identified most often in summer and autumn. However, on individual farms, fecal shedding of E. coli O26, O103, or O145 was frequently undetectable or the numbers of pats testing positive were small. For serogroup O26 or O103 there was clustering of positive pats within management groups, and the presence of an animal shedding one of these serogroups was a positive predictor for shedding by others, suggesting local transmission of infection. Carriage of vtx was rare in E. coli O103 and O145 isolates, but 49.0% of E. coli O26 isolates possessed vtx, invariably vtx1 alone or vtx1 and vtx2 together. The carriage of eae and ehxA genes was highly associated in all three serogroups. Among E. coli serogroup O26 isolates, 28.9% carried vtx, eae, and ehxA-a profile consistent with E. coli O26 strains known to cause human disease.

Modelling the epidemiology of Verocytotoxin-producing Escherichia coli serogroups in young calves

We investigate the epidemiology of 12 Verocytotoxin-producing Escherichia coli (VTEC) serogroups observed in a calf cohort on a Scottish beef farm. Fitting mathematical models to the observed time-course of infections reveals that there is significant calf-to-calf transmission of VTEC. Our models suggest that 40% of all detected infections are from calf-to-calf transmission and 60% from other sources. Variation in the rates at which infected animals recover from infection by different VTEC serogroups appears to be important. Two thirds of the observed VTEC serogroups are lost from infected calves within 1 day of infection, while the rest persist for more than 3 days. Our study has demonstrated that VTEC are transmissible between calves and are typically lost from infected animals in less than 1 week. We suggest that future field studies may wish to adopt a tighter sampling frame in order to detect all circulating VTEC serogroups in similar animal populations.

Phenotypic and functional characterisation of follicle-associated epithelium of rectal lymphoid tissue

Lymphoid follicles cluster in the terminal rectum of various animal species and of man and hence this site may be important in the development of immune responses to pathogens. For the induction of immune responses at mucosal sites, interplay is required between various cell types performing functions ranging from antigen-sampling cells via antigen-presenting cells to antigen-specific lymphocytes. Therefore, we have characterised the cell populations and relevant functioning of follicle-associated epithelium (FAE) and associated follicles in the terminal portion of rectum in cattle as a representative mammal. Immunohistochemical studies of this region identified immune cell subsets (CD4+, CD8+, WC 1+gammadelta, CD2+, CD 21+ and CD 40+ cells) characteristic of an immune-inductive site. Examination of FAE identified a subset of cells with structural and functional features of antigen-sampling M-cells. Cells of the FAE and adjacent follicle-associated crypts expressed vimentin and a subset of these cells internalised microparticles, a further attribute of M-cells. The FAE cells were phenotypically heterogeneous and therefore the function and phenotype of these cell subsets requires further characterisation, particularly with respect to their potentially important role in the interaction of hosts with pathogens and the development of immune responses.

Distribution of Escherichia coli O157 in bovine fecal pats and its impact on estimates of the prevalence of fecal shedding

The distribution of Escherichia coli O157 in bovine feces was examined by testing multiple samples from fecal pats and determining the density of E. coli O157 in immunomagnetic separation (IMS)-positive fecal samples. The density of E. coli O157 in bovine feces was highly variable, differing by as much as 76,800 CFU g(-1) between samples from the same fecal pat. The density in most positive samples was <100 CFU g(-1), the limit of reliable detection by IMS. Testing only one 1-g sample of feces per pat with IMS may result in a sensitivity of detection as low as 20 to 50%. It is therefore probable that most surveys have greatly underestimated the prevalence of E. coli O157 shedding in cattle and the proportion of farms with shedding cattle. The sensitivity of the detection of E. coli O157 in bovine feces can be as much as doubled by testing two 1-g samples per pat rather than one 1-g sample.

Transfer of antibiotic resistance between commensal and pathogenic members of the Enterobacteriaceae under ileal conditions

AIM

To determine the rate of antibiotic resistance transmission between commensal and pathogenic representatives of the Enterobacteriaceae.

METHODS AND RESULTS

Through the use of a validated in vitro simulation of the porcine ileum, the transmission of antibiotic resistance was detected between commensal Escherichia coli, E. coli O157 and Salmonella spp. Countable transconjugant populations arose readily and, in one example, proved capable of indefinite persistence.

CONCLUSIONS

Genetic material conferring antibiotic resistance is readily transmissible between members of the Enterobacteriaceae under ileal conditions. Recipient phenotype influences the persistence of multi-resistant transconjugants.

SIGNIFICANCE AND IMPACT OF THE STUDY

The observation that the conjugal transmission of antibiotic resistance is commonplace under ileal conditions impacts primarily on the risk of food contamination by multi-resistant bacteria. The establishment of a multi-resistant transconjugant population as a dominant member of the microflora maintains a genetic reservoir of antimicrobial resistance.

Influence of tetracycline exposure on tetracycline resistance and the carriage of tetracycline resistance genes within commensal Escherichia coli populations

AIMS

To assess the influence of incremental tetracycline exposure on the genetic basis of tetracycline resistance within faecal Escherichia coli.

METHODS AND RESULTS

Through the adoption of a novel combination of multiple breakpoint selection, phenotypic characterization and the application of a polymerase chain reaction based gene identification system it proved possible to monitor the influence of antibiotic exposure on resistance gene possession. Using tetracycline as a case study a clear hierarchy was revealed between tet genes, strongly influenced by host antimicrobial exposure history.

CONCLUSIONS

The antimicrobial exposure regime under which an animal is produced affects both the identity and magnitude of resistance gene possession of a selected bacterial population within its enteric microflora. Among the ramifications associated with such resistance gene selection is the degree of resistance conferred and the carriage of linked resistance determinants. This selection is applied by exposure to antibiotic concentrations well below recognized minimum inhibitory tetracycline concentration breakpoints widely adopted to characterize bacterial 'susceptibility'.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study confirms the ability of minimal antibiotic exposure to select for the continued persistence of resistance genes within the enteric microflora. It is clearly demonstrated that different antimicrobial regimes select for different resistance genes, the implications of which are discussed.

The quantitative measurement of antimicrobial resistance in Escherichia coli at the meta-population level (meta-population analysis)

AIMS

To define a method that describes antimicrobial resistance of meta-populations of bacteria in both a quantitative and biologically meaningful way.

METHODS AND RESULTS

Using spiral plating and colony counting technology we obtained, from animal faecal samples, the density of Escherichia coli that grow at different concentrations of antibiotic. A mathematical description of this dose-response curve fitted the data well. The parameters of this model have biological meaning and the model allowed subtle differences between meta-populations to be detected.

CONCLUSIONS

This method, termed MPA (meta-population analysis), is practical and provides a useful quantitative description of antimicrobial resistance in a bacterial meta-population.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study shows that resistance can be defined quantitatively. The method may be used in many epidemiological and clinical studies of antimicrobial resistance in animals and humans.

What is antibiotic resistance and how can we measure it?

Antibiotic resistance is being found with increasing frequency in both pathogenic and commensal bacteria of humans and animals. Quantifying resistance within and between bacterial and host populations presents scientists with complex challenges in terms of laboratory methodologies and sampling design. Here, we discuss, from an epidemiological perspective, how antibiotic resistance can be defined and measured and the limitations of current approaches.

Emissions of methyl halides and methane from rice paddies

Methyl halide gases are important sources of atmospheric inorganic halogen compounds, which in turn are central reactants in many stratospheric and tropospheric chemical processes. By observing emissions of methyl chloride, methyl bromide, and methyl iodide from flooded California rice fields, we estimate the impact of rice agriculture on the atmospheric budgets of these gases. Factors influencing methyl halide emissions are stage of rice growth, soil organic content, halide concentrations, and field-water management. Extrapolating our data implies that about 1 percent of atmospheric methyl bromide and 5 percent of methyl iodide arise from rice fields worldwide. Unplanted flooded fields emit as much methyl chloride as planted, flooded rice fields.

The use of dummy data points when fitting bacterial growth curves

We consider the problem of fitting mathematical models for bacterial growth and decline to experimental data. Using models which represent the phases of the growth and decline cycle in a piecewise manner, we describe how least-squares fitting can lead to potentially misleading parameter estimates. We show how these difficulties can be overcome by extending a data set to include hypothetical observations (dummy data points) which reflect biological beliefs, and the resulting stabilization of parameter estimates is analysed mathematically. The techniques are illustrated using real and simulated data sets.

Characterisation of Listeria ivanovii isolates from the UK using pulsed-field gel electrophoresis

Forty-three Listeria ivanovii isolates were collected in the UK between 1991 and 1997 from: 35 animal infections; two human infections; five foods; and one environmental source. A further two type strains of L. ivanovii (subsp. ivanovii and subsp. londoniensis) were obtained from a culture collection. These bacteria were characterised by conventional phenotypic methods and by pulsed-field gel electrophoresis (PFGE) using ApaI and SmaI. Forty-two of the isolates from the UK were identified as L. ivanovii subsp. ivanovii and the remaining culture as L. ivanovii subsp. londoniensis. Six and four PFGE profiles were obtained using ApaI and SmaI digestion respectively; six composite profiles were obtained combining the results for both enzymes. The PFGE profile of the UK L. ivanovii subsp. londoniensis (isolated from processed shrimps) was similar to the type strain of this subspecies and differed from all of the L. ivanovii subsp. ivanovii tested. The majority of isolates (38 out of 45) belonged to one profile showing that the UK population of this bacterium is much less genetically diverse than similar studies have shown for Listeria monocytogenes.

Specific PCR primers from the 16S-23S rRNA spacer region for the rapid detection and identification of Actinobacillus seminis

Actinobacillus seminis is a common cause of ovine epididymitis and ram infertility. The ability to detect and identify this organism promptly is important commercially for the quality control of ram semen samples. Actinobacillus seminis is a fastidious and slow-growing bacterium and primary isolation and presumptive identification can be difficult and time-consuming. In this study, two ribosomal operons, termed rrnA and rrnB, have been characterized in the A. seminis genome, and these contain one and two tRNAs, respectively, in the spacer region between the 16S and 23S rRNA genes. Species-specific primers for A. seminis were developed from the sequence of the spacer region of rrnB for the identification and detection of A. seminis by PCR. The PCR assay was specific for A. seminis and gave no amplification products with phenotypically similar organisms such as Histophilus ovis. Storage solution used to preserve semen for long-term storage was found to inhibit the PCR. Therefore, for diagnostic purposes, the assay would best be performed after primary isolation or perhaps on fresh semen prior to storage if obvious contamination is indicated.

PCR methods and plasmid profile analysis for characterisation of Histophilus ovis strains

The value of polymerase chain reaction (PCR)-based DNA fingerprinting and plasmid profile analysis for differentiation of Histophilus ovis isolates was assessed. Nineteen isolates of H. ovis were typed by PCR-ribotyping, repetitive extragenic palindromic element (REP)-PCR and enterobacterial repetitive intergenic consensus (ERIC)-PCR. These methods distinguished five types by PCR-ribotyping, 11 types by REP-PCR and seven types by ERIC-PCR. The ribotyping method produced a relatively simple pattern and a small number of distinct types and was useful for differentiation of H. ovis from the phenotypically similar organism, Haemophilus somnus. REP- and ERIC-PCR both produced complex banding patterns, but increased the discrimination between strains. Plasmids were found in 12 of the 19 isolates and there were four different plasmid profiles. A combination of the PCR methods and plasmid profile analysis provided a high resolution typing method for H. ovis.

PCR methods for rapid identification and characterization of Actinobacillus seminis strains

Twenty-four isolates of Actinobacillus seminis were typed by PCR ribotyping, repetitive extragenic palindromic element (REP)-based PCR, and enterobacterial repetitive intergenic consensus (ERIC)-based PCR. Five types were distinguished by REP-PCR, and nine types were distinguished by ERIC-PCR. PCR ribotyping produced the simplest pattern and could be useful for identification of A. seminis and for its differentiation from related species. REP- and ERIC-PCR could be used for strain differentiation in epidemiological studies of A. seminis.

Comparison of five tests for the detection of antibodies against chlamydial (enzootic) abortion of ewes

Five tests for antibodies against chlamydial (enzootic) abortion of ewes were compared using 255 sera from experimentally (group 1) or naturally (group 2) infected animals, flocks free of the disease (group 3) and individual animals testing positively by the complement fixation test but from flocks with no evidence of chlamydial abortion (group 4). Sera from five specific pathogen-free lambs vaccinated with two different subtypes of Chlamydia pecorum were also included (group 5). All tests used some form of processed culture of C psitiaci as antigen. Specificities, established with group 3 and 4 sera, ranged between 96 per cent (ELISA using lipopolysaccharide antigen) and 59 per cent (Immunocomb). Reactions with group 5 sera suggested that the cause of false positive results in the field might be cross-reactive antibodies against the arthritogenic subtype of C pecorum. Sensitivities, established with groups 1 and 2 sera, ranged between 81 per cent (Immunocomb) and 51 per cent (ELISA using solubilised protein antigen). The minimum sample sizes required to be 95 per cent certain of detecting at least five seropositives in two infected flocks (combined data) were 15 to 48, dependent on the test applied. The Western blot test, applied to a proportion of samples, yielded no false positives with group 3 sera but 31.7 per cent with group 4 sera. Thus, none of the tests in this comparison emerged as sufficiently satisfactory in all respects, suggesting that further improvements in chlamydial serology must come through the use of non-native antigens or in the form of a competitive ELISA.

Antimicrobial resistance of Salmonella enterica typhimurium DT104 isolates and investigation of strains with transferable apramycin resistance

An examination of salmonella isolates collected by the Scottish Agricultural College Veterinary Services Division from April 1994 to May 1995 was conducted to determine the extent to which Salmonella enterica serotype Typhimurium phage type 104 (DT104) occurred and to investigate the antimicrobial resistance patterns of isolates. Typhimurium DT104 was the predominant salmonella and was isolated from nine species of animal. All isolates of this phage type possessed resistance to at least one antimicrobial and 98% of the isolates were resistant to multiple antimicrobials with R-type ACTSp the predominant resistance pattern. Various other resistance patterns were identified and transferable resistance to the veterinary aminoglycoside antimicrobial apramycin was demonstrated in three strains. A retrospective study for gentamicin resistance in isolates from the Scottish Salmonella Reference Laboratory collection revealed a human isolate of Typhimurium DT104 resistant to gentamicin but sensitive to apramycin and a bovine isolate with apramycin and gentamicin resistance.

A review of Listeria monocytogenes and listeriosis

Following the initial isolation and description in 1926 Listeria monocytogenes has been shown to be of world-wide prevalence and is associated with serious disease in a wide variety of animals, including man. Our knowledge of this bacterial pathogen and the various forms of listeriosis that it causes has until recently been extremely limited, but recent advances in taxonomy, isolation methods, bacterial typing, molecular biology and cell biology have extended our knowledge. It is an exquisitely adaptable environmental bacterium capable of existing both as an animal pathogen and plant saprophyte with a powerful array of regulated virulence factors. Most cases of listeriosis arise from the ingestion of contaminated food and in the UK the disease is particularly common in ruminants fed on silage. Although a number of forms of listeriosis are easily recognized, such as encephalitis, abortion and septicaemia, the epidemiological aspects and pathogenesis of infection in ruminants remain poorly understood. The invasion of peripheral nerve cells and rapid entry into the brain is postulated as a unique characteristic of its virulence, but relevant and practical disease models are still required to investigate this phenomenon. This review offers an up to date introduction to the organism with a description of virulence determinants, typing systems and a detailed account of listeriosis in animals. Experimental and field papers are reviewed and further sections deal with the diagnosis, treatment and control of listeriosis in animals. A final part gives an overview of listeriosis in man.

Comparison of the absorbed ELISA and agar gel immunodiffusion test with clinicopathological findings in ovine clinical paratuberculosis

Thirty-two sheep with clinical paratuberculosis and 43 normal, healthy control animals were tested for serum antibodies to Mycobacterium avium subspecies paratuberculosis with the absorbed enzyme-linked immunosorbent assay (ELISA) and agar gel immunodiffusion (AGID) test. All the sheep were necropsied and the diseased cases were categorised as having either multibacillary ('lepromatous') or paucibacillary ('tuberculoid') intestinal lesions. The ELISA and AGID test were highly sensitive when testing the multibacillary group (86.4 per cent and 100 per cent, respectively) but the sensitivity of the tests in the paucibacillary group was significantly lower (10 to 50 per cent and 30 per cent, respectively). These findings were related to the ELISA optical density readings, with the multibacillary samples having values significantly greater than those of the paucibacillary and control groups, and the optical density values appearing to correlate with the numbers of mycobacteria present in the intestinal lesions. These results indicate both the usefulness of serological testing in the diagnosis of the multibacillary form of paratuberculosis and the difficulty in identifying animals with the paucibacillary form of the disease.

Voltage dependency of light-evoked on-off transient amacrine cell responses in carp retina

The voltage dependency of the ON and the OFF components of transient amacrine cell responses was studied using two-electrode voltage-clamp and current-clamp techniques in the isolated retina of the carp. The two independent approaches gave similar data. When cells were voltage clamped near their resting potentials, both response components were associated with transient inward currents. Hyperpolarization increased response size (current or voltage) whilst depolarization decreased it. Response reversal, or a tendency for it, occurred at membrane potentials significantly more positive than the resting level with some quantitative variability. These data support the view that the ON-OFF depolarizations represent basically excitatory postsynaptic potentials and that the transience of the responses cannot mainly be due to any voltage-dependent conductance.

Concurrent bovine viral diarrhoea virus and Salmonella typhimurium DT104 infection in a group of pregnant dairy heifers

Two days after being imported into the United Kingdom one of a group of 30 pregnant dairy heifers showed clinical signs of bovine viral diarrhoea virus (BVDV) infection and subsequently died. Before it died the heifer was BVDV antigen-positive and antibody-negative. The gross post mortem findings were suggestive of mucosal disease but in addition to noncytopathic BVD virus, Salmonella typhimurium DT104 was cultured from tissues and gut contents. The other heifers were screened for S typhimurium by culturing faeces, and serology showed that 13 (45 per cent) of the group seroconverted to BVDV in the three weeks between samplings and the remainder were seropositive, indicating previous exposure. During this period four heifers showed clinical signs of acute BVDV infection but recovered uneventfully. Four animals (14 per cent) were positive for S typhimurium DT104 on faecal culture, and three of these excretors concurrently seroconverted to BVDV. Of the 29 heifers remaining in the group, one aborted in late gestation, 26 bore live calves and two delivered stillborn calves. Pre-colostral blood samples from the calves showed that their dams' pre-existing antibody titres correlated well with in utero fetal protection. In non-immune dams, exposure to BVDV between 69 and 120 days of gestation led to the birth of live persistently viraemic calves. Infection between 120 and 140 days of gestation led to the birth of live calves with evidence of congenital damage to the central nervous system, and infection later than 140 days of gestation led to the birth of live, normal calves with high pre-colostral antibody titres to BVDV. One calf which sucked colostrum was antibody and virus antigen-positive when sampled at 12 hours old but regular blood sampling failed to detect viraemia again until the calf was seven weeks old when it became persistently viraemic.

Sulphur-induced polioencephalomalacia in lambs

An outbreak of polioencephalomalacia affected 16 of 46 Swaledale lambs and five of 25 Scottish blackface lambs 15 to 32 days after they were introduced to an ad libitum concentrate ration containing 0.43 per cent sulphur. The clinical signs were acute and included depression central blindness and head-pressing, but no hyperaesthesia, nystagmus, dorsiflexion of the neck or opisthotonos were observed. Treatment of the affected lambs with vitamin B1, dexamethasone and antibiotics was associated with a prolonged recovery period, though no further cases were identified after vitamin B1 had been given parenterally to all the lambs at risk.

Prevalence of Actinobacillus seminis in the semen of rams in the United Kingdom

A survey was conducted to establish the prevalence of Actinobacillus seminis in ovine semen and the possible importance of the organism as a cause of ram infertility. A seminis was isolated from three of 16 infertile rams and the infected animals had lesions of the genital tract and produced poor quality semen. A seminis was also isolated from two of 96 fertile rams used as donors of semen for artificial insemination programmes. The strains of A seminis could be identified on the basis of their API ZYM profiles. The results suggest that in the United Kingdom A seminis should be considered as a common cause of infertility in rams.

Development and evaluation of an indirect ELISA to detect antibodies to abortion strains of Chlamydia psittaci in sheep sera

A novel indirect enzyme-linked immunosorbent assay (ELISA) for antibodies against abortion strains of Chlamydia psittaci (C. psittaci) has been developed. The antigen used was chlamydial elementary bodies treated sequentially with N-lauroyl sarcosine and n-octyl-beta-D-glucopyranoside and finally solubilized with N-lauroyl sarcosine and dithiothreitol. Treating the antigen with sodium periodate after coating of the plates increased the specificity for antibodies to abortion strains. The test was evaluated initially with sera from experimentally infected sheep and an uninfected control group. These sheep were monitored for lambing performance and infection status. When used in conjunction with the indirect micro-immunofluorescence test (MIF), the ELISA was able to identify as negative all twenty-five sera from ewes that had no typical placental lesions and identified as positive twenty of twenty-one sera from infected ewes that had either typical placental lesions or had been found positive by isolation of chlamydia in cell culture. The combination of ELISA and MIF was also able to discriminate correctly groups of sera from six flocks with a history of infection from four known uninfected flocks.

Primary cutaneous listeriosis in adults: an occupational disease of veterinarians and farmers

Seventeen cases of cutaneous listeriosis in adults are reviewed. The condition appeared as papular or pustular lesions on the arms or hands, and was most often acquired as an occupational hazard from infected animals. The cases were all mild and were resolved successfully. However, listeric infections are potentially fatal, and as the initial cause of the lesion may be unknown, it is recommended that veterinarians and farmers should have suspect lesions examined microbiologically.

Serological evidence implicating Neospora species as a cause of abortion in British cattle

By means of an immunofluorescence antibody test (IFAT), using in vitro cultured parasites as antigen, antibodies to Neospora species at titres > or = 1/1280 were found in 11 of 120 Scottish cattle that had recently aborted but in only one of 97 cattle from herds in which there had been no recent abortions (P < 0.01). The specificity of the antibodies was confirmed by the lack of cross reactivity between samples with high titres to Neospora and toxoplasma antigen in a direct agglutination test, and by the absence of reactivity at > or = 1/640 in the IFAT of convalescent sera from cattle infected experimentally with Toxoplasma gondii, Sarcocystis cruzi, Eimeria bovis, E alabamensis, Cryptosporidium parvum and Babesia divergens. These results demonstrate that Neospora species infection occurs commonly in aborting cattle in Britain, and that the IFAT may be a useful tool for investigating the infection.

Characterization by Multilocus Enzyme Electrophoresis of Listeria monocytogenes Isolates Involved in Ovine Listeriosis Outbreaks in Scotland from 1989 to 1991

Initial results from a study of five small ovine listeriosis outbreaks in Scotland in 1989 to 1991 are presented. Forty-eight isolates including three from silage were typed at 10 polymorphic enzyme loci by using multilocus enzyme electrophoresis resulting in the identification of 12 electrophoretic types. Phylogenetic analysis partitioned the 12 electrophoretic types into two statistically distinct divisions distinguishing 1/2a serotypes from non-1/2a serotypes.

False-negative morphine-augmented cholescintigraphy in a patient with gangrenous cholecystitis

Intravenous morphine sulfate is commonly used to shorten study time and has been reported not to lower the specificity of hepatobiliary imaging. Although the false-negative rate is low, caution has to be taken in interpreting morphine-enhanced cholescintigraphy. The report presents a false-negative study in a patient with acute gangrenous cholecystitis.

Purification of listeriolysin O and development of an immunoassay for diagnosis of listeric infections in sheep

A protein of 58,000-Da molecular mass was purified from the supernatant fluid of a dialysis sac culture of Listeria monocytogenes by cation-exchange chromatography. The purified protein, homogeneous by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and possessing the characteristics of listeriolysin O (LLO), was used to develop an indirect enzyme-linked immunosorbent assay. Anti-LLO antibodies were shown to be consistently produced in sheep after experimental challenge with L. monocytogenes serovar 4b. The assay also successfully detected and measured specific anti-LLO antibodies in the sera of silage-fed sheep among which listeric enteritis and abortions had occurred.

Pyrolysis mass spectrometry of Listeria monocytogenes isolates from sheep

Forty-eight isolates of Listeria monocytogenes from sheep and silage, involved in five small outbreaks of listeriosis, were compared by pyrolysis mass spectrometry (PyMS). The method clustered isolates from single animals, and showed that epidemiologically associated isolates were closely related to each other. PyMS is a simple technique capable of analysing large numbers of samples daily, and its application in veterinary studies should help to elucidate the epidemiology of listeriosis.

Chromaticity of synaptic inputs to H1 horizontal cells in carp retina: analysis by voltage-clamp and spectral adaptation

Cone photoreceptor inputs to H1 horizontal cells (H1 HCs) in carp retina were studied by measuring light-modulated currents (IL) to monochromatic stimuli (460, 533, 688 nm) under a voltage-clamp condition. By using double-barrelled micro-electrodes H1 HCs were voltage-clamped whilst perfusing with dopamine to uncouple the cells. The IL of the H1 HCs driven by each cone input was segregated by selective chromatic adaptation, and differences in the kinetics of the IL of the H1 HCs were revealed. Thus, all together, three types of IL were observed: (1) a 'fast outward' current to the long-wavelength stimulus; (2) a 'slow outward' current to the middle-wavelength stimulus; and (3) a 'delayed inward' current that followed the peak of 'slow outward' current to the short-wavelength stimulus. The reversal potentials of the three currents were estimated to be at least 20 mV more positive than the dark resting potential by extrapolation of the IL-V curve. These observations are consistent with the idea that the H1 HCs receive sign-inverting, conductance decreasing synaptic input(s) from at least one other cone mechanism, in addition to the main conventional EPSP type synaptic input from red-sensitive cones.

Clinical and serum antibody responses to lambs to infection by Listeria monocytogenes

Oral dosing of lambs with 1 x 10(10) colony forming units of Listeria monocytogenes daily for three days produced no clinical signs but protected the animals against bacteraemia following subsequent homologous subcutaneous challenge. Following the subcutaneous injections, comparison with controls revealed significantly lower rectal temperatures and a significant difference in positive blood cultures. In both groups signs of systemic illness were unremarkable. However, two and 10 days after the subcutaneous challenges neurological signs developed in two lambs. L monocytogenes was isolated from the brain of one lamb and histopathological lesions of listeric encephalomyelitis were demonstrated in both. After oral infection antibodies to L monocytogenes whole cell antigen were detectable in serum agglutination tests and by ELISA. Serological responses to flagellin were examined by ELISA and to listeriolysin O by immunoblotting. The responses of the animals to flagellin were weak and inconsistent, but antibodies to listeriolysin O were detectable after both oral and subcutaneous challenge. The subclass of antibody involved in this response was shown to be predominantly IgG1.

Nutritional factors associated with vaginal prolapse in ewes

Serum calcium, magnesium and phosphate values of ewes recently affected by vaginal prolapse were compared with unaffected ewes in four flocks. Subclinical hypocalcaemia was demonstrated in some affected and unaffected ewes in three flocks. Magnesium and phosphate values were normal. In two flocks the body condition of ewes recently affected by vaginal prolapse was variable and reflected the variation in condition found in the flock. In a third flock affected ewes had significantly lower body condition scores than unaffected ewes (P less than 0.001). Analysis of the fourth flock was not possible. Oestrogenic mycotoxins were not detected in any of the feed samples taken from these flocks. The following year the management, nutrition and energy, and the protein and calcium status of ewes in 12 flocks of greyface/mule ewes with a history of a regular high (greater than 3 per cent) or low (less than 1 per cent) prevalence of vaginal prolapse were compared. A high prevalence was not associated with any particular feedstuff. A high or intermediate (1 to 3 per cent) prevalence of vaginal prolapse was found in three of the four flocks managed as a single group and these three flocks were fed on an unrestricted basis. Body condition scoring and beta-hydroxybutyrate estimation confirmed that ewes in these flocks were overfed. The prevalence of vaginal prolapse in the flocks was not related to the serum albumin, calcium or urea of the ewes. Therefore subclinical hypocalcaemia was probably a consequence of vaginal prolapse rather than a cause.