Evaluation of ovine herpesvirus type 2 infections, as detected by competitive inhibition ELISA and polymerase chain reaction assay, in dairy cattle without clinical signs of malignant catarrhal fever

OBJECTIVE: To monitor ovine herpesvirus type 2 (OvHV-2) infection status and the association between OvHV-2 infection and development of clinical signs of malignant catarrhal fever (MCF) in cattle. DESIGN: Longitudinal study. ANIMALS: 30 mature adult cows and 18 cattle submitted for necropsy. PROCEDURE: Blood and milk samples were collected at monthly intervals from 30 adult cows for 20 consecutive months. Nasal and ocular swab specimens were also collected during months 9 through 20. Polymerase chain reaction (PCR) assay for detection of OvHV-2 was performed on blood, milk, nasal swab, and ocular swab specimens. Competitive inhibition ELISA (CI-ELISA) for detection of antibodies against MCF viruses was performed on serum samples obtained prior to study initiation and monthly during the last 12 months. Tissues obtained from herdmates without clinical signs of MCF that were submitted for necropsy were analyzed for OvHV-2 DNA via PCR assay for possible sites of latency. RESULTS: Initially, 8 of 30 cows had positive CI-ELISA results. Seroconversion was detected in 4 cows. Ovine herpesvirus type 2 DNA was intermittently detected in blood, milk, nasal secretions, or ocular secretions from 17 of 30 cows. Twenty-one cows had positive CI-ELISA or PCR assay results. No cattle in the study developed clinical signs of MCF. Results of PCR assays performed on tissue samples from 2 of 18 animals submitted for necropsy were positive for OvHV-2. CONCLUSIONS AND CLINICAL RELEVANCE; OvHV-2 infection can occur in cattle without concurrent development of clinical MCF. Ovine herpesvirus type 2 DNA was detected intermittently, suggesting fluctuating viral DNA loads or reinfection in subclinical cattle. A definitive site of latency was not identified from tissues obtained during necropsy.     

ATLes: the strategic application of Web-based technology to address learning objectives and enhance classroom discussion in a veterinary pathology course

A case-based program called ATLes (Adaptive Teaching and Learning Environments) was designed for use in a systemic pathology course and implemented over a four-year period. Second-year veterinary students working in small collaborative learning groups used the program prior to their weekly pathology laboratory. The goals of ATLes were to better address specific learning objectives in the course (notably the appreciation of pathophysiology), to solve previously identified problems associated with information overload and information sorting that commonly occur as part of discovery-based processes, and to enhance classroom discussion. The program was also designed to model and allow students to practice the problem-oriented approach to clinical cases, thereby enabling them to study pathology in a relevant clinical context. Features included opportunities for students to obtain additional information on the case by requesting specific laboratory tests and/or diagnostic procedures. However, students were also required to justify their diagnostic plans and to provide mechanistic analyses. The use of ATLes met most of these objectives. Student acceptance was high, and students favorably reviewed the online 'Content Links' that made useful information more readily accessible and level appropriate. Students came to the lab better prepared to engage in an in-depth and high-quality discussion and were better able to connect clinical problems to underlying changes in tissue (lesions). However, many students indicated that the required time on task prior to lab might have been excessive relative to what they thought they learned. The classroom discussion, although improved, was not elevated to the expected level-most likely reflecting other missing elements of the learning environment, including the existing student culture and the students' current discussion skills. This article briefly discusses the lessons learned from ATLes and how similar case-based exercises might be combined with other approaches to enhance and enliven classroom discussions in the veterinary curriculum.     

Lawsonia intracellularis proliferative enteropathy in a weanling foal in Australia

A 6-month-old Quarter Horse weanling filly was presented with lethargy, weight loss, inappetance, mild diarrhoea, marked ventral oedema and severe panhypoproteinaemia. Serum antibody titres for Lawsonia intracellularis were very high but PCR to detect faecal shedding of the organism was negative. Proliferative enteropathy due to L. intracellularis infection was diagnosed. After treatment for 4 weeks with oral erythromycin and rifampicin the filly made a complete recovery.     

Occurrence of infectious upper respiratory tract disease and response to vaccination in horses on six sentinel premises in northern Colorado

REASONS FOR PERFORMING STUDY: Horses vaccinated against common agents of infectious upper respiratory disease (IURD) may not have detectable serum antibody and may not be protected from clinical disease. OBJECTIVES: The objectives of this study were to 1) investigate the serological response of horses to vaccination against influenza virus (H3N8 and H7N7) and equine herpesviruses (EHV) in a field setting and 2) evaluate associations among vaccination status, serum antibody concentrations, and occurrences of IURD in monitored horses. METHODS: In this study, horses on 6 Colorado premises were vaccinated parenterally against influenza virus and EHV, and serological response evaluated. Horses were monitored, and biological samples collected from individuals with clinical IURD and control horses. RESULTS: Of 173 horses, 61 (35.3%), 21 (12.1%) and 4 (2.3%) seroconverted in response to vaccination against EHV, influenza virus H7N7 and influenza virus H3N8, respectively. CONCLUSIONS: Outbreaks of IURD in study horses were associated with influenza virus H3N8 and Streptococcus equi infection, and serological response to vaccination with conventional products was poor. POTENTIAL RELEVANCE: These results confirm that horses may not respond with detectable serological responses to conventional vaccination against common respiratory viruses and, therefore, suggest that alternate methods of protecting horses against common respiratory viruses should be sought.     

Inhibition of egg development by phosphine in the cosmopolitan pest of stored products Liposcelis bostrychophila (Psocoptera: Liposcelididae)

Phosphine-induced delay in development of eggs was investigated as a mechanism of resistance to this fumigant in Liposcelis bostrychophila Badonnel. One-day-old eggs of a susceptible and a strongly resistant strain of L bostrychophila were exposed to a range of phosphine concentrations for 6days at 30 (+/- 1) degrees C and 70 (+/- 2)% RH. Delay in mean hatching period occurred in both susceptible and resistant eggs, although it was more pronounced in the latter. A maximum delay of 2.65 days was recorded for eggs of the susceptible strain at 0.01 mg litre(-1) (the highest concentration at which eggs survived) and 13.39 days for the resistant strain at 1 mg litre(-1) (the highest concentration tested). Delay in egg development time was positively correlated with increasing phosphine concentration. Our results reveal that the most successful strategy to control resistant L bostrychophila is to apply relatively low concentrations of phosphine for extended exposure times (eg 0.05 mg litre(-1) for 16 days) that allow all eggs to hatch to the much less tolerant nymph stage.     

A multilaboratory evaluation of a commercial enzyme-linked immunosorbent assay test for the detection of antibodies against Mycobacterium avium subsp. paratuberculosis in cattle.

Five laboratories participated in a study to evaluate sources of variation in results from an enzyme-linked immunosorbent assay (ELISA) for antibodies against Mycobacterium avium subsp. paratuberculosis. Each laboratory repeatedly tested duplicates of a negative, positive (P), and high-positive (HP) serum sample, which were supplied by the United States Department of Agriculture: Animal and Plant Health Inspection Service: Veterinary Services, National Veterinary Services Laboratories, Ames, IA, on all 96-well microtiter plates when routinely testing other samples for M. avium subsp. paratuberculosis antibodies. These 3 sera were aliquoted and sent to the 5 participating laboratories. This study focused on variation in test results because of assay reagents and laboratory techniques and did not account for biologic variability associated with the time course of infection in cattle. Overall, results from 868 microtiter plates were used in the study. For each sample a sample-to-positive (S/P) ratio was calculated according to the manufacturer's directions. The S/ P ratio for the P sample ranged from 0.06 to 1.039 (mean = 0.466 and 0.484 for wells 1 and 2, respectively) and those for the HP sample ranged from 2.446 to 8.727 (mean = 4.027 and 3.980 for wells 1 and 2, respectively). The majority of the variation in S/P ratio for the P sample was attributed to kit lot (37.5%), followed by random (unexplained) error (27.0%), laboratory (18.3%), and kit lot by laboratory (11.9%). By eliminating plates in which the separation between negative and positive control ODs was less than 0.4, the proportion of variation attributed to laboratory was reduced markedly. These results confirm that there is variability in M. avium subsp. paratuberculosis ELISA results and that several sources contribute to the observed variability. The study gives a relative estimate of the contribution of various sources to the overall variability observed in the M. avium subsp. paratuberculosis ELISA results with kit lot being a primary contributor. Similar data for other ELISA tests for antibodies to M. avium subsp. paratuberculosis or other antigens also should be developed.     

Campylobacter spp. in Irish Feedlot Cattle: A Longitudinal Study Involving Pre‐harvest and Harvest Phases of the Food Chain

The aim of this study was to investigate faecal shedding and transmission of Campylobacter spp. in cohorts of cattle within a feedlot, to assess subsequent contamination of carcasses with this pathogen and to identify risk factors associated with faecal shedding of Campylobacter spp. A cohort of 133 heifers housed in four adjacent pens was examined over a five and a half month period, from entering the feedlot to slaughter. A parallel investigation of individual rectal faecal samples and pen environmental samples were taken at monthly intervals from November to February. The entire outer and inner surfaces of a carcass side of each animal were swabbed immediately following slaughter. Campylobacter spp. were isolated from 322 (54%) of the 600 rectal faecal samples. Campylobacter jejuni and C. coli accounted for 69 and 29.7% of the isolate recovered, respectively. A total of 159 environmental samples were examined, of these Campylobacter spp. was isolated from 46 samples (29%). Campylobacter jejuni and C. coli accounted for 35 and 59% of these isolates, respectively. Campylobacter spp. was not isolated from any of the dressed carcasses. Logistic regression indicated prevalence of Campylobacter spp. faecal shedding within pens was positively correlated to the pen, the month of sampling and the Campylobacter spp. contamination status of the pen dividing bars and the water trough surface. Campylobacter spp. should be considered as a pathogen shed in the faeces of a substantial proportion of feedlot cattle. However, with good hygienic practice during harvest, a very low level of this pathogen can be achieved on dressed carcasses.     

Actinobacillus pleuropneumoniae serotype 1 carrying the defined aroA mutation is fully avirulent in the pig

The aroA gene from Actinobacillus pleuropneumoniae serotype 1 reference strain 4074 was isolated and sequenced. The gene complemented the aroA mutation in Escherichia coli AB2829. A kanamycin resistance cassette was inserted into the aroA gene and the mutant gene was reintroduced into A. pleuropneumoniae by allelic replacement. Intratracheal infection of susceptible pigs with A. pleuropneumoniae aroA caused no signs of respiratory disease or lung lesions in any of the animals at a dose 10(4) times the dose reliably known to induce acute pleuropneumonia; all animals infected with the unaltered control strain developed acute disease. The aroA mutant was rapidly eliminated from the lungs and tonsil of infected animals. The mutant may represent a safely attenuated strain for use in live bacterial vaccination or the delivery of antigen by the intranasal route. However, the residence time of the mutant in the respiratory tract of the pig may be too short for it to be useful in generating a protective immune response.     

Relationship between milk urea concentration and the fertility of dairy cows

The relationship between milk urea concentration and the fertility of dairy cows was examined in two studies. The first examined the relationship between bulk milk urea concentration and overall herd fertility, using data collected from 250 herds in the UK. There was no relationship either between bulk milk urea concentration and fertility, or between changes in bulk milk urea concentration and fertility. The second study compared the relationship between the milk urea concentration five days after service, and the fertility of individual cows on 11 UK dairy farms. There was no significant difference between the milk urea concentration of the cows that became pregnant and those that did not.