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    Biosecurity and exotic disease surveillance in the New Zealand pig industry : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy at Massey University, New Zealand
    (Massey University, 2013) Neumann, Eric James
    The New Zealand commercial pig industry is modern and highly productive. The industry is free from many of the important infectious diseases present in much of the rest of the world. However, alongside the commercial industry are a large number of non-commercial pig holdings operated with minimal attention to biosecurity. The extent to which the activities in the non-commercial sector might negatively impact the commercial sector was unknown therefore a series of projects was undertaken to explore the likelihood of an exotic disease occurring. A risk assessment was undertaken to determine the likelihood porcine reproductive and respiratory syndrome (PRRS) virus would be introduced into New Zealand through imported fresh pork. The study estimated that at least 4.3 pig herds per year were likely to become infected with PRRS and that 36% of these incursions would spread to additional herds. It was recognized that the data describing the interactions between commercial and non-commercial pigs could be improved so a prospective study was undertaken to collect information about the movements of pigs and genetic material between farms. To assist in development of a national surveillance programme, two additional studies were then initiated. First, a study was conducted to determine the effect of blood sample mishandling on the performance of ELISA assays and second, a retrospective analysis of data from a national abattoir-based lesion recording system (PigCheck) was conducted. These studies were done with the realization that future surveillance activities would need to incorporate creative means of generating high-quality surveillance data, from various surveillance components, using both laboratory- and field-based staff. Investment Logic Mapping was then used to assist the industry in establishing a biosecurity and surveillance strategy. A single strategy ‘improve surveillance’ was identified as the key area for biosecurity investment. In response to this finding, modelling of potential surveillance activities was completed and a surveillance programme was proposed costing approximately $0.50 per pig annually. The work presented in this thesis demonstrates the New Zealand pig industry is susceptible to introduction of an exotic disease and that the population of non-commercial pigs must be considered when developing biosecurity, and disease readiness or response plans for the commercial industry. The described studies show that a cost effective national disease surveillance programme can be implemented through use of a combination of existing and newly developed sources of surveillance information.
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    Epidemiology of porcine rotaviral infections : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Veterinary Virology at Massey University
    (Massey University, 1988) Fu, Zhen Fang
    The epidemiology of porcine group A rotavirus was studied in commercial herds of pigs in New Zealand. A commercial enzyme-linked immunosorbent assay (ELISA) kit (Dakopatts, Copenhagen) was found to be highly sensitive (100%) and specific (96.8%) for the detection of group A rotavirus in pig faeces when compared to electron microscopy (EM). A highly sensitive and specific ELISA test for the measurement of antibody against group A rotavirus in pigs was also developed. Of 521 faecal samples collected from Massey University Piggery in a cross-sectional survey, 47 (9%) were positive for group A rotavirus by the ELISA test. Only sucking (19.3%) and weaner (14.4%) pigs were shedding rotavirus. Rotavirus was not detected in the faeces of fattener pigs (over two months old) or adult pigs including sows and boars. Three cohort studies revealed that all pigs became infected with group A rotavirus before they were 40 days of age and shed the virus for an average of eight days. Some of the piglets shed rotavirus a second time approximately 10 days after the first period of shedding. All piglets ceased to shed the virus by two months of age. Rotaviral shedding was associated with the occurrence of milk scours in sucking piglets. Diarrhoea in weaner pigs (post-weaning diarrhoea, PWD) was more closely associated with the presence of haemolytic E.coli than with rotavirus in faeces. Infection with group A rotavirus was transmitted from piglet to piglet and from litter to litter. In one cohort of 50 piglets from five litters, shedding of rotavirus was first detected in one litter, then in the second litter two days later, and finally in other litters of piglets. Over a period of 16 days, all piglets in the five litters were infected. Group A rotavirus was also detected in dust, faeces and effluent collected from the farrowing and weaner houses, and from a weaner house which had not been used for three months. Rotavirus was not detected in any of the sows (11) during the period of investigation. Neither was rotavirus detected in fattener pigs (from two months of age to the time of slaughter), nor in the environments where old pigs (fattener and sow houses) were housed. It was not therefore possible to confirm that adult pigs, especially sows, act as carriers for rotaviral infection of young piglets as has been suggested by other workers. All the piglets acquired maternal antirotaviral antibody from their dams and the levels of antibody in piglets' sera were comparable to those in the colostrum of their dams. The maternally-derived antibody was also detected in piglets' faeces. Antibody in sera and in faeces declined rapidly after birth. Rotaviral shedding commenced in each of the cohorts when the geometric mean ELISA antibody titre fell below 1/1600 (equivalent to serum neutralizing antibody titre of 1/8 to 1/16). However, this correlation between antibody titres and protection was not observed in individual litters. In each of the cohorts studied, rotaviral shedding was usually detected initially in one or two piglets of a litter. The infection then spread to other piglets within the same litter and, finally, to piglets of other litters in the same group. Onset of rotaviral infection in particular litters was related to their location in the farrowing unit rather than to the levels of antibody. The shedding pattern of group A rotavirus was studied further in another five New Zealand piggeries and was found to be similar to that observed at the Massey University Piggery. Faecal samples from these piggeries were analyzed by polyacrylamide gel electrophoresis (PAGE) and no common electrophoretype of group A rotavirus was found in these piggeries. More than one electrophoretype of group A rotavirus was detected in three of these piggeries. Faecal samples collected from Massey University Piggery were also analyzed by PAGE and it was found that rotaviruses detected during the first two years of the present investigation had identical electrophoretypes, but one isolate detected in the third year had a distinctively different pattern. Non-group A rotaviruses were also detected for the first time in New Zealand. Nine samples had an electrophoretic pattern similar to that of group C rotavirus and one was similar to that of group B rotavirus. One of the samples containing group C rotavirus was from two litters of piglets with diarrhoea at two to four days of age. In one of these piggeries, five electrophoretypes of rotaviruses representing three groups were detected. These observations indicate that rotaviral infections are important causes of milk scours in piglets, and are probably significant in exacerbating PWD. The epidemiology of rotaviral infections is complicated by a number of factors. These include the continuous transmission of virus from pig to pig and from litter to litter, the survival of the virus in the piggery environment, the incomplete protection afforded by maternally-derived antibody, and the simultaneous circulation of different strains and different groups of rotavirus in one piggery.
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    The epidemiological investigation of pig diseases : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy at Massey University
    (Massey University, 1995) Wongnarkpet, Sirichai
    A series of epidemiological studies was carried out to identify methods of improving productivity of New Zealand and Thai pig herds. Disease surveillance at slaughter of 2,807 finisher pigs from 3 piggeries in the North Island of New Zealand was conducted over a 13 month period. This was used to establish and apply procedures suited to New Zealand conditions, for monitoring the subclinical status of 8 production-limiting diseases and 1 zoonotic disease. Enzootic pneumonia, sarcoptic mange and oesophagogastric ulcer were the most commonly observed lesions. Seasonal patterns were found for enzootic pneumonia, pleurisy and ascariasis lesions. Seasonal effects were found to be associated in part with temperature variation. The effectiveness of simultaneous administration of commercial Mycoplasma hyopneumoniae and Actinobacillus pleuropneumoniae vaccines was assessed in 380 pigs from an indoor commercial piggery. These vaccines produced significant improvement of growth rate during the high risk period for clinical pneumonia, and increased slaughter weight. Enzootic pneumonia lesions were significantly reduced by more than 50%, but pleurisy and pleuropneumonia lesions were not significantly reduced. No evidence of synergy between the vaccines in influencing lesion severity for pleuropneumonia was detected. A longitudinal study of thirty cohort pigs was conducted within the vaccination trial, to describe the epidemiological pattern of subclinical A. pleuropneumoniae infection of healthy pigs. A. pleuropneumoniae was first isolated at 4 weeks of age from one vaccinated pig. The incidence of A. pleuropneumoniae infection reached a maximum of 54% and 40% at 11 weeks of age in vaccinated and control pigs. No evidence was found to support the hypothesis that infection with M. hyopneumoniae increases susceptibility to A. pleuropneumoniae infection. Pig production data from 16 Thai and 18 New Zealand pig herds for 1991, and from 14 Thai and 16 New Zealand herds for 1992 were analysed to define opportunities for improving productivity in temperate and tropical environments. In Thailand, potential areas for improving productivity are particularly through increasing total litter size and improved management of breeding procedures. In New Zealand, potential areas for improvement are particularly reduction of stillbirths and pre-weaning mortality, and reduction of sow mortality. A new method of graphical presentation of important productivity parameters was used to clearly demonstrate differences in performance between the two countries. PigFIX, a fertility investigation expert system linked to a computer-based herd recording system, was developed to provide diagnostic guidance on likely causes of fertility problems and offer guidance on possible corrective action. A novel approach was used in developing the method by which PigFIX assessed reproductive performance. Graphical and text-based reports were developed to show the user what conclusions had been drawn in the analysis. PigFIX was shown in verification studies on six herds to produce conclusions which agreed with a human expert on identification of major reproductive problems.
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    Systems for the prevention and control of infectious diseases in pigs : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy at Massey University
    (Massey University, 1998) Stärk, Katharina D. C.; Stärk, Katharina D. C.
    An expert system (RestiMATE) was designed that assists veterinary practitioners in assessing the respiratory health status of a pig farm. RestiMATE uses classification rules to identify patterns of environmental risk factors for respiratory diseases and to select optimal management interventions to control and prevent respiratory diseases. The classification rules are based on expert interviews and on empirical data collected in New Zealand. Recursive partitioning and neural network techniques have been applied for rule induction. These methods were compared with logistic regression and appeared to be similarly efficient in terms of classification while providing additional insight into the structure of a data set. Non-parametric analytical methods appear to be particularly suitable when analysing complex data sets and for exploratory data analysis. EpiMAN-SF is an advanced decision-support system designed to manage and analyse data accumulated during an African swine fever or classical swine fever emergency. EpiMAN-SF offers state-of-the-art technology for managing data related to a swine fever epidemic, including laboratory results. An expert system was developed to support rapid classification of contacts between pig farms in terms of the risk of virus transmission. These classifications are used to set priorities in visiting farms for laboratory investigations. The validation of the expert system showed that its evaluation was more consistent and generally more risk-averse than that of human experts. A stochastic simulation model was developed to investigate the spread of swine fever infection within a farm and a second model (INTERSPREAD-SF) was designed to forecast the dynamics of the epidemic within a region and to evaluate control strategies. INTERSPREAD-SF has been validated using real outbreak data from Germany and was shown to be capable of realistically replicating the behaviour of classical swine fever. However, more research is needed to complete our knowledge about the detailed epidemiological processes during a swine fever epidemic. A prerequisite for efficient disease control in pig populations is reliable animal identification. A series of trials was conducted in order to compare electronic ear tags and implantable identification chips with visual ear tags. It was shown that the difficulties with respect to implants are loss rates of up to 18.1% within 4 weeks after implantation while electronic ear tags were lost or damaged by processing at the abattoir in up to 23.4% of pigs. Infectious aerosols were reviewed as an additional aspect of the causative network of infectious diseases in pigs. An air sampling system based on air filtration was developed and applied in combination with polymerase chain reaction assays. Using this technique, Mycoplasma hyopneumoniae, the major causative agent of enzootic pneumonia was isolated from air samples for the first time. However, the attempt to isolate classical swine fever virus from the air was unsuccessful, probably due to technical difficulties.