Massey Documents by Type

Permanent URI for this communityhttps://mro.massey.ac.nz/handle/10179/294

Browse

Subject: search.filters.subject.Bovine viral diarrhea

Search Results

Now showing 1 - 4 of 4
  • Thumbnail Image
    Item
    Development and validation of a field deployable test for the diagnosis of high-priority infectious animal diseases in New Zealand : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Veterinary Science at Massey University, Manawatu, Palmerston North, New Zealand
    (Massey University, 2024-03-15) Bueno, Rudolfo
    In the event of infectious disease incursions, rapid and accurate diagnosis is essential for ensuring appropriate and prompt control measures are put in place to minimise further transmission. Foot and mouth disease (FMD) is one example of an exotic disease that could severely affect New Zealand’s livestock industries if introduced to this country. Pen-side testing can help by providing a rapid confirmation of a provisional diagnosis without the delays and risks associated with sending samples to a diagnostic laboratory. The aim of the work presented in this thesis was to develop and validate a field deployable diagnostic test system for prompt and accurate detection of FMD virus (FMDV). In addition, the test can be used to simultaneously detect two other viruses that would be expected to be on the differential diagnosis list: bovine viral diarrhoea type 1 (BVDV-1) and type 2 (BVDV-2). Chapter 1 comprises a brief literature review of FMDV infections in susceptible species, followed by a review of the current and emerging trends in field deployable diagnostics as applicable to animal diseases. In Chapter 2, a multi-criteria scoring and ranking model for identifying the best test platform for development of the deployable field test is presented. The general flow of the method consisted of defining the requirements for the ideal test platform, identifying, and shortlisting potential candidate systems, describing the criteria for evaluation, and scoring the candidate platforms against the criteria by a panel of recruited experts. This participatory and collective opinion provided a basis for selecting T-COR 8™ (Tetracore®) as the best overall fit-for-purpose. In Chapter 3, several easy techniques for processing clinical samples compatible with the selected test platform were examined. These protocols were applied to test panels comprising serial dilutions of BVDV-1 or equine rhinitis A virus (ERAV) in serum or oral swab samples. The latter was used as a proxy for FMDV. The protocols were compared to a reference extraction method based on the observed detection limit, as judged by quantification cycle (Cq) values generated in virus-specific reverse transcription quantitative polymerase chain reaction (RT-qPCR) assays. The complexity of sample manipulation and time required were also considered. Dilution of the sample with phosphate-buffered saline (PBS), with or without a pre-heating step, was chosen as the most suitable method for integration in the pen-side PCR testing. Development of the field assay’s controls is described in Chapter 4. These included a synthetic positive control transcript (R3+) that could be safely used with assays aimed at the detection of several pathogens associated with development of vesicular disease in cattle. The universal control transcript also incorporated an exogenous internal control (IC) target, which was designed to be used with a phage based (Qβ) internal control (IC) system. Optimization of a Qβ IC assay for use in the pen-side multiplex RT-qPCR (mRT-qPCR) is also included in this Chapter. In Chapter 5, development, and optimisation of mRT-qPCR for the differential detection of FMDV, BVDV-1 and BVDV-2, including detection of a Qβ as exogenous IC, is presented. The optimised mRT-qPCR showed linearity over five 10-fold dilutions of R3+ transcript, good efficiency, and low intra-and inter-assay variability. The mRT-qPCR was highly specific for the detection of representative FMDV serotypes and was also able to simultaneously detect BVDV-1 and BVDV-2 isolates. The assay did not react with other viruses that can produce vesicular lesions, nor did it react with unrelated bovine pathogens endemic in New Zealand. Multiplexing the four primer- and probe sets did not affect the performance and analytical sensitivity of the assay for the detection of individual components when compared to the respective singleplex assays. The diagnostic performance of the optimised mRT-qPCR for detecting FMDV, BVDV-1 and BVDV-2 is presented in Chapters 6 and 7. Diagnostic specificity was evaluated using sera and oral swabs from New Zealand cattle. Diagnostic sensitivity for FMDV detection was assessed using mock oral swabs from outbreak samples in two endemic countries (Lao PDR and Myanmar). The robustness of the field PCR was evaluated at three field locations with varied environmental conditions (New Zealand, Lao PDR, and Myanmar). Overall, the diagnostic specificity (DSp) of the field mRT-qPCR for three target viruses (FMDV, BVDV-1 and BVDV-2) was close to 100%, which was similar to the performance of respective reference PCRs. Although the diagnostic sensitivity (DSe) of the FMDV component was comparable to that obtained with the reference method, care must be taken in interpreting the result since FMD positive samples used for evaluation of the sensitivity of the mRT-qPCR were not sourced from New Zealand cattle. The mRT-qPCR also had high DSe for detecting BVDV-1 infected cattle when the BVDV RNA levels expected to be present in clinical samples from either persistently infected (PI) or transiently infected animals were considered. Pre-heating of samples increased the sensitivity of the BVDV-1 component of the assay. Further validation using additional FMDV-positive and negative clinical specimens should be attempted in the future. Overall, the work presented in this thesis resulted in the development of a simple, extraction-free pen-side PCR test that can be deployed around New Zealand for rapid and reliable detection of FMDV in the event of a suspected incursion. Future work to enhance its use would involve exploration of other methods of preparing samples so that the test can be utilised in screening sub-clinical FMDV infections during post-outbreak surveillance.
  • Thumbnail Image
    Item
    Establishment of optimal control strategies to eliminate bovine viral diarrhoea in New Zealand : a thesis submitted in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Veterinary Epidemiology at Massey University, Manawatu, New Zealand
    (Massey University, 2020) Han, Jun-Hee
    Although there has been a noticeable reduction in the prevalence of bovine viral diarrhoea virus (BVDV) in New Zealand over the past decade, it is well recognised that New Zealand will need a systematic compulsory programme to eliminate BVDV. The aims of this thesis were to address the knowledge gaps around the epidemiology and economics of BVDV to explore the cost-effectiveness of different national BVDV control frameworks. First, the risk factors for BVDV infection were explored using data collected from cattle herds across the country. A Bayesian network analysis revealed that animal contacts between neighbouring farms significantly increased the risk of herds being seropositive for BVDV. The second study used data collected from New Zealand commercial beef farms to estimate the transmission rate of BVDV from extensively grazed persistently infected (PI) animals. Using an approximate Bayesian computation method, the BVDV transmission rate was estimated at 0.11 per PI animal per day, which was lower than previously derived estimates for dairy herds and intensively farmed beef herds. For the third study, BVDV simulation models were developed for New Zealand dairy and beef farms to estimate the economic impacts of BVDV outbreak and to identify the most cost-effective control strategies at an individual farm level. The direct losses due to BVDV outbreak were estimated as NZ$ 22.22 per dairy cow per year and NZ$ 41.19 per beef cow per year. Annual testing to cull identified PI calves and annual vaccination were economically beneficial to control a BVDV outbreak for a dairy and beef breeding farm, respectively. In the fourth study, BVDV transmission was simulated at a national scale with the models, predicting that BVDV could be successfully and economically controlled by requiring dairy farms to double fence boundaries and perform either annual calf testing or herd-level screening test and requiring beef farms to conduct annual vaccination. Overall, the findings from the thesis highlight that BVDV elimination is both technically feasible and cost-efficient in New Zealand. The outputs of this thesis can be used to facilitate discussion with farmers and stakeholders about the benefits and feasibility of national BVDV elimination in New Zealand.
  • Thumbnail Image
    Item
    Epidemiology of BVD in New Zealand dairy herds : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Veterinary Epidemiology at Massey University, Manawatu, New Zealand
    (Massey University, 2016) Weir, Andrew Muir
    The objective of this thesis was to determine the prevalence and incidence of bovine viral diarrhoea (BVD) virus at cow and herd level, define risk factors for new infection and to quantify the impact at cow level of seroconversion during the seasonal breeding programme under the seasonal calving, pasture grazed systems in New Zealand. A questionnaire and bulk tank milk (BTM) BVD PCR and antibody ELISA test was completed for 402 New Zealand dairy herds, and repeated in the subsequent lactation. North Island herds had a high turnover rate with 67% of virus positive herds clearing infection each lactation and being replaced with newly infected herds, while the larger South Island herds rarely cleared infection naturally (14% per lactation) and maintained a higher prevalence (32% compared to 8.5% for North Island herds). Transmission pathways associated with bulk tank BVD status were purchasing cows, neighbour's stock, and stock movements off-farm. The other factors associated with bulk tank BVD status were herd size, herd BVD vaccination, and herd ownership structure. In 10 BTM PCR positive herds, all lactating cows (n=3,793) were tested for BVD antibody at the start of the seasonal breeding programme (planned start of mating; PSM), and again 125 days later, to identify cows that seroconverted during the observation period. Improved cutoff values were derived for the IDEXX milk antibody ELISA. There were few (3.8%) susceptible lactating cows at PSM in herds with a lactating persistently infected cow (PI), but most of these susceptible cows (82%) seroconverted. This required 4.6 contacts per PI each day. There were more susceptible (31%), and a smaller proportion of susceptible cows seroconverted (32%) in herds without a lactating PI. Seroconversion was associated with 13% longer PSM to conception (3.2 days), 4% lower pregnancy rate, 6% lower conception to AI, and $11.97 (1.9 times) greater cost of clinical disease. The average cost per transient infection was $91.08. These results contributed to voluntary BVD control efforts in New Zealand and will be essential for developing a comprehensive cost-benefit model to estimate the average total cost of BVD, and assessing the benefit of various control strategies. Keywords: Bovine Viral Diarrhoea; BVD; BVDV; virus; diarrhea; pestivirus; Flaviviridae; veterinary; epidemiology; New Zealand; dairy; prevalence; incidence; herd; cow; reproduction; disease; transient infection; immune suppression; PI; PCR; ELISA; antibody; milk; economic; cost; seasonal; pasture-based; observational study; longitudinal; cross-section; risk factor; risk; probability; proportion; rate; mastitis; lactation; seroconversion; regression; generalised estimating equation; GEE; Hurdle model; accelerated failure time; AFT; questionnaire; survey; sharemilker; cow behaviour; herd management; model
  • Thumbnail Image
    Item
    Bovine pestivirus disease : an investigation of a severe outbreak of bovine viral diarrhoea virus infection in calves in New Zealand : a thesis presented in partial fulfilment of the requirements for the degree of Master of Veterinary Studies in Infectious Diseases at Massey University, Palmerston North, New Zealand
    (Massey University, 2000) Anderson, Peter D
    An outbreak of bovine pestivirus disease, in which there was high mortality (37%) in 102 calves, was investigated. It was postulated that the severity of the outbreak may have been due to the presence of a highly virulent strain of bovine viral diarrhoea virus. Nine calves from the field outbreak were transported to Massey University for detailed clinical, post-mortem and laboratory examination. Samples were also submitted from a further three animals on the farm. The results of immunological and virological studies indicated that seven calves had acute bovine viral diarrhoea virus infection and five calves had mucosal disease. Although the mucosal disease cases showed more severe clinical signs, lesions were widespread in both groups. A non-cytopathic bovine viral diarrhoea virus isolate from one calf was used as the challenge virus in a transmission experiment designed to investigate the pathogenicity of this strain. The 11 calves used in this experiment comprised of four unvaccinated, challenged calves, four vaccinated calves (two challenged, two in-contact), two unvaccinated, in-contact calves and a control (neither vaccinated nor in-contact). The experiment took place over a month, allowing multiple clinical examinations and sampling procedures to be carried out before necropsy. The challenge virus caused mild disease, with lesions similar to those reported in experiments in which Type 1 bovine viral diarrhoea virus isolates were used. Following experimental challenge, virus was not recovered from the calves, but a serological diagnosis of bovine viral diarrhoea virus infection was made by demonstrating a greater than fourfold rise in titre of bovine viral diarrhoea virus antibody in all challenged calves. There were only minor changes in haematological indices in challenged calves. The six challenged calves showed two distinctive lesions in intestinal sections. These were crypt necrosis (of glands of Lieburkuhn) and cryptal prolapse (herniation of crypts into the submucosal site of Peyer's patches depleted of lymphocytes). In the disease outbreak, these lesions were only observed in the mucosal disease cases. Focal haemorrhages at sites of lymphocytic nodules were found in the nasal cavity of all challenged and vaccinated calves in the transmission experiment, but not in the unvaccinated, in-contact calves or the control calf. These lesions have not been reported in natural infections. Vaccination was only partially protective, and there was evidence of spread of bovine viral diarrhoea virus infection to one vaccinated, in-contact calf. Scoring of histological lesions allowed a measurement of the effect of vaccination. There was a 60% reduction in the total histological lesion score in the four vaccinated calves (two challenged, two in-contact) when compared with the four unvaccinated, challenged animals. It was concluded that the high mortality seen in the calves in the field outbreak was due to mucosal disease, and that this was consequential to a high infection rate in the dams during pregancy at a time when the foetuses were at risk of becoming persistently infected (45-125 days of gestation). The pathological "fingerprint" for bovine viral diarrhoea virus infection was found to be the concomitant finding of three lesions at necropsy. Firstly, erosive lesions in the squamous epithelium of the upper alimentary tract. Secondly, catarrhal enteritis, with the distinctive and characteristic microscopic lesions of crypt necrosis and cryptal prolapse. Thirdly, lymphoid tissue lesions, especially lymph node enlargement, lymphoid depletion and inflammation of Peyer's patches. Despite the difficulties in pathotyping the challenge virus in the transmission experiment, there was little evidence that it was a Type 2 strain. Genetic typing of this virus, by sequencing of polymerase chain reaction products, would be useful in determining its place in the phylogeny of bovine pestiviruses.