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Item Changing epidemiology of Leptospirosis in New Zealand, with a focus on the novel strain of Leptospira borgpetersenii : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Veterinary Science at Massey University, Palmerston North, New Zealand(Massey University, 2024-12-25) Sokolova, MarynaIn New Zealand, leptospirosis has been a common disease in dairy cattle since the 1940s. Six pathogenic Leptospira serovars from two species have been identified as endemic to New Zealand: Leptospira borgpetersenii serovars (sv.) Hardjobovis (Hardjo), Tarassovi, Ballum, Balcanica, and Leptospira interrogans sv. Pomona and Copenhageni. From these, sv. Pomona and Hardjo are the most commonly reported in cattle, and sv. Ballum, Tarassovi, and Copenhageni are less common. The estimated 99% of the national dairy herd is vaccinated against leptospirosis by vaccines containing antigens to Pomona and Hardjobovis and sometimes vaccines also include Copenhageni antigen. Vaccines for protecting dairy cows against Tarassovi were unavailable in New Zealand before December 2023. Historically, leptospirosis due to Tarassovi infection in New Zealand cattle was considered accidental and clinically unimportant. Serosurveys of apparently healthy cattle in New Zealand showed that over the past fifty years, Tarassovi seroprevalence increased from 6% (50/300) at MAT ≥ 50 to 18% (698/3878) at MAT ≥ 48. More recently, a serology and urine shedding study from 2015- 2016 evaluated the status of 4,000 dairy cows from 200 randomly selected farms, stratified by New Zealand's geographical location and herd size. The study found that on the animal level, 17% of the study animals showed evidence of past infection with Tarassovi, as defined by at least one sample reacting at MAT ≥ 48 for the study's purposes. Moreover, 96% (90/94) of PCR-positive urine samples were sequenced, and 68% (54/80) of those were found to have a novel allele in the sequenced region at the glmU loci. Thus, the use of molecular diagnostic tools, specifically molecular typing targeting a partial region of the glmU gene, allowed New Zealand researchers to identify a novel L. borgpetersenii strain, informally called strain (str.) Pacifica, in the urine of these cows. The 2015-2016 survey reported that dairy cows with Tarassovi titres were associated with urinary shedding, as determined by microscopic agglutination test (MAT) and polymerase chain reaction (PCR) testing, respectively. Because of this association, str. Pacifica is thought to belong to the serogroup Tarassovi. Additionally, the DNA of str. Pacifica has been retrospectively detected in cattle and deer samples dating back as early as 2007. Moreover, the 19-year (1999-2007) average annual incidence of notified human cases of Tarassovi leptospirosis was estimated at 12.59/100,000 in dairy farmers, compared to an overall annual average incidence of 2.01/100,000. These coincidental findings raised public health concerns. Therefore, at least some cases of Tarassovi seropositivity, as identified by MAT and reported before 2021, could partially be attributed to str. Pacifica. To confirm str. Pacifica's serogroup, isolation by culture and complete genetic characterisation of an isolate are required. Since str. Pacifica was only recently detected, its epidemiology, morphology, maintenance, and pathogenicity in the host population, as well as its impact on animal and human health, were not well understood. In this study, we investigated the possibility of isolating str. Pacifica from cow's urine by running a series of laboratory experiments where laboratory-adapted strains were used as a proxy for L. borgpetersenii str. Pacifica in the absence of an isolate to better understand its growth requirements. Laboratory-adapted Leptospira borgpetersenii strains were seeded into different types of media, and Leptospira growth rates were evaluated (Chapter 3). As a result, we ruled out unsuitable media and growth conditions, and this work helped to select the best media and growth conditions for a follow-up field investigation, where freshly collected cow's urine was seeded into selected media. Str. Pacifica was isolated from the urine of a shedding cow using HAN medium at 37°C and 5% CO2. However, this medium failed to sustain str. Pacifica and the culture was lost (Chapter 4). In addition, over the 2020-2021-2022 milking seasons, we collected and tested blood and urine samples from dairy farms, identified as str. Pacifica positive from the 2016 survey. Our results revealed that str. Pacifica was still maintained in the same dairy herds six years after initial detection. Moreover, we reported an estimated prevalence ratio (PR) of 7, indicating that the prevalence of shedders was seven times as high at the beginning than at the end of lactation in primiparous cows (Chapter 4). These findings provide evidence that str. Pacifica is adapted to dairy cows in New Zealand, and the peak shedding in primiparous heifers occurs in early lactation. Since the highest levels of str. Pacifica shedding were detected at the start of the milking season during peak milk production, which also coincides with a relatively short 3-month mating period, the associations between str. Pacifica and milk production and reproductive performance of milking cows were also investigated using herd test data and serological and PCR test results of the 2016 survey. Statistical models, including linear, logistic, and generalised mixed models with fixed and random effects, as well as a shared frailty survival model, were used to evaluate the associations between str. Pacifica positivity and reproduction (Chapter 5) and milk reproduction (Chapter 6) in dairy cows. Results of the statistical analysis of the association between str. Pacifica positivity and reproduction (Chapter 5) of dairy herds showed that str. Pacifica delayed the time from calving to conception (HR = 0.84; 95%: CI 0.74-0.96), although there was no effect on the pregnancy rate (Chapter 5). An analysis of milk production data did not reveal any associations with str. Pacifica at either animal or herd level (Chapter 6). The absence of clinical signs and the lack of association with milk production and reproduction at both the animal and herd levels provides further evidence towards str. Pacifica being well adapted to dairy cows. Therefore, evidence from this thesis suggests that dairy cattle are the maintenance host for str. Pacifica in New Zealand. It is also important to note that str. Pacifica shedders can infect people, especially dairy farmers, milkers, and farm workers who are in regular contact with str. Pacifica-shedding animals. Therefore, the prevention of str. Pacifica transmission via vaccination or the use of appropriate personal protective gear should be prioritised.Item Leptospirosis in dairy herds : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy at Massey University, School of Veterinary Science, Massey University, Palmerston North, New Zealand(Massey University, 2019) Yupiana, YuniThe introduction and adoption of Leptospira vaccination in most New Zealand dairy herds in the 1980s was associated with a substantial reduction of the incidence of notified human leptospirosis cases in the population and notably among dairy farm workers. However, 80% of cases notified from 1999 to 2016 with a “farmer-type” occupation were dairy farmers, hence this occupational group continues to be at risk for leptospirosis. Failure to vaccinate dairy herds can have serious public health consequences. An example is described in an opportunistic case study, chapter 3 of this thesis. Within the space of three months in early 2015, three workers from a dairy farm with an unvaccinated dairy herd were hospitalised with leptospirosis caused by serovars Hardjo and Pomona. In young and adult dairy cattle from this farm, Hardjo, Pomona, Copenhageni, Ballum and Tarassovi serovars were all detected serologically. While two of the diseased workers recovered, one remains affected four years after the event being unable to return to work. These circumstances – the continuation of dairy workers among notified human cases and the potentially serious consequences from failure to vaccinate or to achieve effective immunity – have raised concerns about the effectiveness of the long–term vaccination programme in dairy herds. The concerns were further substantiated by an opportunistic pilot study (2011) that found evidence of Leptospira shedding in vaccinated dairy cattle. Therefore, a large cross-sectional study of New Zealand dairy farms was conducted involving 200 dairy farms and 4,000 cows. Farms were randomly selected from the national database and blood and urine was collected from 20 cows per herd. Non- response (30%) was investigated by personal interview which indicated that selection bias (e.g. by selecting only farmers with vaccinated herds) was minimal, if not absent. Shedding was indicated by a positive qPCR at cow-level and by one or more shedders per herd at herd-level. A serological response was considered positive when titres of the microscopic agglutination test (MAT) were at or above 48. Overall shedding rates were 2.4% at cow- and 26.5% at herd-level. Seropositivity to Hardjo, Pomona and, when trivalent vaccines were used, Copenhageni, was most likely a response to vaccination. None of the vaccinal serovars were associated with urine shedding. However, there was a strong linear association at the cow-level between increasing MAT titres to Tarassovi and the likelihood of shedding. Serological evidence for exposure to Tarassovi was observed in 17% of cows and 74% of the herds. Few cows (1%) and 16% herds were sero-positive to Copenhageni when not vaccinated against this serovar which, however, was not associated with cow-level shedding. Similarly, the rodent-related serovar Ballum was not associated with shedding; with positive titres observed in 3% of cows and 38% of herds. Studies in the 1970s and 1980s found little serological evidence of Tarassovi, so we conclude that this serovar has emerged, became endemic and is now probably causing most of the shedding in the dairy cattle population. Considering published evidence that a large proportion of notified cases in dairy farmers were Tarassovi, there is strong corroborative evidence that this serovar poses a public health risk for workers on dairy farms. Our survey administered a questionnaire about vaccination practices and putative risk factors. All but one of the farmers had regular vaccination programmes for calves, heifers and cows using mostly bivalent (80%, 69%, 68% of farms, respectively) and some trivalent vaccines (20%, 31%, 32% of farms, respectively). Regardless of the almost universal practice of Leptospira vaccination in dairy cattle, fewer than 40% famers conformed with Best Practice Guidelines (2012) developed and propagated by the New Zealand Veterinary Association. A further objective was a risk factor analysis (Chapter 6). One cow-level (age) and three herd-level (presence of sheep or dogs, herd size) factors were significantly associated with the risk of shedding. As 93% of the potential factors evaluated were at herd level, and with only 200 herds included in the study, and the shedding rate being relatively low, the statistical power might have been too low to identify other herd-level determinants related to the management and environment of the farms. Nevertheless, a linear negative effect of age suggested that young cows were more likely to shed Leptospira than adult cows, and therefore increase the risk of infection for dairy workers. Evidence from this thesis suggests that current Leptospira vaccination practices are effective for preventing the exposure of farm workers against the serovars most commonly incorporated in vaccines (Hardjo and Pomona), and the less common serovar Copenhageni. Thus, continuation with vaccination is supported. The public health risk arising from Tarassovi that has emerged, and evidence here that this serovar is widely present in the dairy cattle population, justifies raised awareness, the adoption of protection measures additional to vaccination, further research into the epidemiology of Tarassovi and an evaluation of the justification for its inclusion into vaccines. Dairy workers are advised to take extra care and precautions when milking and handling cows, especially first calving heifers irrespective of their vaccination status.Item Molecular and eco-epidemiology of Leptospira borgpetersenii serovar Ballum in wild invasive mammals in a farming environment 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, Palmerston North, New Zealand(Massey University, 2020) MOINET, MarieLeptospirosis is an important zoonosis in New Zealand where it has historically been associated with livestock. Formerly negligible in human cases notified, Leptospira borgpetersenii serovar Ballum—associated with rodents and hedgehogs (Erinaceus europaeus)—is now preponderant. The role of wild introduced mammals in the epidemiology of leptospirosis has been overlooked in New Zealand but remains a critical question. In this thesis, we determined the prevalence of Leptospira serovars, renal colonisation and seroprevalence in wild mammals and sympatric livestock. During a cross-sectional and a longitudinal survey, house mice (Mus musculus), ship rats (Rattus rattus) and hedgehogs were trapped in farms with a history of leptospirosis to collect sera and kidneys. Urine and sera from livestock (dairy or beef cattle, sheep) and dogs were also collected on the same farms. Sera were tested by microagglutination test to identify serovars/serogroups that circulate in wildlife for comparison with those circulating in livestock. Urine and kidney samples were used to determine prevalence by qPCR, to isolate circulating leptospires by culture and subject them to whole genome sequencing, in order to determine their phylogenetic relationships and compare them to other sequences locally, nationally and internationally. Capture-mark recapture (CMR) methods were used to investigate the population dynamics of mice naturally infected with Ballum. Finally, the level of lesions and bacterial load in kidneys were assessed visually by histopathology and put in perspective with other results to investigate reservoir dynamics. Direct or indirect presence of Ballum was found in all wild and domestic species investigated. Overall apparent prevalence in mice, rats and hedgehogs was respectively 46%, 95% CI [39, 52%], 44% [26, 62%] and 27% [11, 50%]. It varied greatly between seasons in mice, with a spring peak (83 to 86%) and minimum in autumn (31 to 37%). Mice densities reached up to 56 mice/ha and varied seasonally in the opposite way, resulting in a relatively constant density of infected mice, ranging 3-8 infected mice/ha. An extremely low rate of mutations hindered the investigation of transmission pathways using genomics. However, despite little or no lesions in all species, the bacterial load was markedly higher in mice, suggesting rats and hedgehogs are secondary hosts. Control strategies to mitigate exposure to Leptospira in NZ should include wild mammals, and especially mice.Item Modelling infectious diseases in multiple species : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Applied Mathematics at Massey University, Albany, New Zealand(Massey University, 2019) Babylon, AndreaLeptospirosis is an infectious disease caused by bacteria in the genus Leptospira and is considered as the disease of interest in this thesis. It is the highest occurring occupational disease in New Zealand and the country has one of the highest (per capita) incidences of human leptospirosis in the world. Transmission commonly occurs by contact with infectious animals, or materials contaminated by them. The disease is the cause of great financial losses to the country due to both the medical cost of treating infectious individuals, as well as due to production losses in the farming industry. As such, studying the dynamics of infection and possible control measures for the disease in animals, which also minimises exposure to humans, is an important area of research. This thesis aims to develop New Zealand specific models demonstrating the dynamics of leptospirosis infection within and between multiple host species, specifically rats and sheep, thus contributing towards an understanding of not only how ecological exchanges between different host populations influence the spreading of the disease, but also how the incidence of leptospirosis may be diminished. This is achieved with the use of compartmental SI type models of increasing complexity, with simpler models used as building blocks in constructing the more advanced systems. The models presented involving only rats consider an age structure within the population, with different behaviours and infection risks associated with each age class. Models involving only sheep focus on the periodic forcing implemented on the host population by the farmer, and also include an age structure, albeit a somewhat simpler one than the one in the rat models. The seasonal forcing on the livestock population results in a cyclical system which is displayed using limit cycle diagrams. This behaviour is mirrored in the model considering both host species in concert. Each model presents a variety of results, including bifurcation diagrams and quasi-basic reproduction numbers which display the behaviour of the system. The effect of varying various parameter values on the system is explored, and how these may change in relation to climate change is discussed. Parameter values used in numerical results demonstrating analytical ones are New Zealand specific and the model is used to predict conditions under which the infection will persist in the population.Item Epidemiology of canine leptospirosis in New Zealand : a thesis presented in fulfilment of the requirements for the degree of Master of Veterinary Science at Massey University, Palmerston North, New Zealand(Massey University, 2015) Harland, Alison LynneLeptospirosis is a disease of worldwide significance affecting dogs, livestock, and humans. It can be a severe clinical or subclinical disease, either of which contribute to shedding of leptospires in the environment. This work includes a detailed literature review of leptospirosis, the disease, and its prevention and epidemiology as it pertains to dogs worldwide and in New Zealand where the epidemiology is unique. Original work includes a nationwide sero-prevalence survey quantifying the risk of exposure for serovars Copenhageni, Hardjo and Pomona for New Zealand dogs. An additional survey of South Island farm dogs investigates the prevalence of exposure to and urinary shedding of leptospires in dogs exposed to livestock with a high prevalence of infection. This is the first study to investigate shedding of leptospires in dog urine in New Zealand, and challenges a long held perception that dogs may only serve as a maintenance host for serovar Canicola. Conclusions: Urinary shedding of Leptospira spp. was demonstrated in more than 12 (95% C.I: 5-24) % of New Zealand farm dogs. It is speculated that these dogs may be serving as maintenance hosts for a number of serovars in addition to Canicola, and may contribute to the maintenance of this disease in a farm environment, and affected dogs may be a zoonotic risk. Urinary shedding of leptospires can occur in dogs with low or negative MAT titres. Exposure to serovar Copenhageni is common for New Zealand dogs, and farm working dogs appear to be at risk for exposure to serovar Hardjo. Serovar Pomona causes severe clinical disease in dogs in New Zealand. Veterinarians investigating clinical cases suspicious for leptospirosis should consider MAT testing for Pomona and Hardjo in addition to Copenhageni, and concurrent PCR testing on blood and/or urine may expedite a diagnosis. Completion of convalescent serology and culture of urine from suspected cases is strongly encouraged. There is a need for a vaccine to protect dogs at risk of infection with serovar Pomona, and consideration should be given to also including serovar Hardjo in the vaccine. Further work is needed to determine the prevalence and duration of urine shedding by dogs nationwide, with culture confirmation and identification of the serovars isolated.Item Leptospirosis diagnostics and exposure at the human and animal interface in New Zealand : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Veterinary Clinical Science at Massey University, Manawatu, New Zealand(Massey University, 2014) Fang, FangThe studies presented in this thesis investigate key questions about leptospirosis diagnostics in animals and humans in New Zealand (NZ): how do different diagnostic tests perform on various specimens collected at different stages of infection; how well do tests from a commercial and a research laboratory agree; how do serological test results and urine/kidney quantitative real-time PCR (qPCR) results compare; and what is the utility of PCRs on blood from acute human cases? Additional studies investigate occupational risk at the human-animal interface. In trials where the animals were challenged with Leptospira borgpetersenii serovar Hardjobovis (Hardjobovis) and/or Leptospira interrogans serovar Pomona (Pomona), sequential samples were taken from sheep and cattle to evaluate diagnostic tests at various known times post-infection. Although no statistically significant differences were found, results suggested that during the early stage of a Pomona infection in sheep, qPCR on serum had the highest sensitivity for detecting leptospires in blood, followed by blood culture and qPCR on whole blood. In sheep infected under carefully controlled experimental conditions, culture tended to have higher sensitivity for detecting leptospires (either Hardjobovis or Pomona) in urine than qPCR; whereas in cattle with Hardjobovis infection, higher sensitivity was apparent using qPCR. Sensitivity was similar in culture and qPCR for detecting leptospires in kidney from sheep with either Hardjobovis or Pomona infections. There was low sensitivity and specificity of dark field microscopy for both urine and kidney samples, thus questioning the usefulness of this technique in veterinary settings. A cross-sectional study was carried out at a NZ sheep and cattle abattoir to investigate the seroprevalence (by microscopic agglutination test (MAT)), shedding rate (by urine qPCR), and renal colonisation rate (by kidney qPCR) of slaughtered animals. Urine, kidney and blood samples were collected from carcasses of 399 sheep and 146 cattle. The animal-level seroprevalence found in sheep (57%, predominately lambs) and cattle (73%, predominately ≤18 months old) was substantially higher than in previous studies; these and the recorded shedding rate (27%) and renal colonisation rate (27%) raised occupational health concerns that meat workers from this abattoir may be at risk of exposure to leptospires during their daily work routine. iv Samples from this abattoir study were used to investigate the inter-laboratory test agreements between a research (HLRL) and a commercial veterinary diagnostic laboratory (GV), and test agreements (HLRL) between specimens for leptospirosis diagnosis. Urine qPCR results on from the two laboratories had almost perfect agreement (kappa = 0.93). The MAT agreement between these two laboratories was higher for Hardjobovis (kappa = 0.94) than Pomona (kappa = 0.53). This serovar-dependent difference suggested that the different MAT results may be more likely due to the different source of antigen cultures (especially serovar Pomona) used in two laboratories than observer variation. These inter-laboratory comparisons can assist researchers and diagnosticians in understanding the sometimes discrepant test results received. Within HLRL, almost perfect agreement (kappa = 0.84) between qPCR results on urine and kidney suggested that the qPCR on these two specimens can be used interchangeably. The comparisons between MAT and qPCR on both kidney and urine, suggested that except from Hardjobovis-seropositivity in sheep, Pomona-seropositivity in sheep and seropositivity of both Hardjobovis and Pomona in cattle was not considered to be predictive for indicating shedding/renal colonisation at individual animal level. A pilot panel of isolates from 18 sheep and five cattle kidney cultures demonstrated the utility of a multi-locus sequence typing scheme for genotyping Leptospira spp. field isolates from sheep and cattle in NZ. The sequence results provided sufficient genetic variability to assign the isolates to two distinct species, those being L. borgpetersenii and L. interrogans. Two dominant serovars (Hardjobovis and Kenniwicki) were identified. Identical sequences found in Hardjobovis isolates from sheep and cattle provided evidence for inter-species transmission of Leptospira spp. Aiming to establish the best diagnostic test or combination of tests for the early diagnosis of human leptospirosis, suspect leptospirosis patients were recruited via rural general practitioners (GP), hospital doctors and phlebotomists within the Waikato District Health Board area. For each recruited patient (n = 14), blood culture, MAT (on acute and convalescent serum), and whole blood/serum PCRs (by three laboratories) were performed. Although it is difficult to make conclusions based on findings from 14 patients recruited from one region, this is the first attempt to compare different diagnostic tests for acute leptospirosis cases in NZ. The information of clinical v symptoms, demographics, and exposure to risk factors can contribute to the GPs‟ suspicion of future leptospirosis cases. A cross-sectional study was conducted to determine the seroprevalence and quantify putative risk factors for both intra- and extra-curricular exposure to leptospirosis among undergraduate veterinary students at Massey University, NZ. All participating students (n = 302) were MAT negative for each serovar (Hardjobovis, Pomona, and Ballum), using a cut-point of ≥ 48. This study demonstrated that these veterinary students were at low risk of contracting leptospirosis, despite frequent exposure to potential sources of infection (e.g. animal urine within and outside veterinary curriculum, home slaughtering, hunting, and outdoor activities involving fresh water). The similar frequency of exposure to the non-work putative risky activities (hunting and home slaughtering) reported in veterinary students as previously reported in meat workers, added strength to the finding that non-work activities are less important risk factors compared to within-work activities.Item The serological and cultural prevalence in sheep of leptospiral infection in the North Island of New Zealand : a thesis presented in partial fulfilment (30%) of the requirements for the degree of Master of Philosophy in Veterinary Pathology and Public Health at Massey University, New Zealand(Massey University, 1981) Bahaman, Abdul RaniA survey of sheep from the North Island of New Zealand was conducted for leptospiral infection. The results of the serological examination showed 20.5 percent of the sheep had titres ( ≥1:48) to Hebdomadis serogroup, 3.8 percent to serovar pomona, 2.6 percent to serovar tarassovi, 2.3 percent to serovar copenhageni and 2.7 percent to serovar ballum. No titres of 1:48 or greater were detected to serovar australis. It was shown that a minimum dilution of 1:24 resulted in many non-specific or cross-reaction. A minimum dilution of 1:48 was more accurate for detecting the serological prevalence of agglutinins to leptospires in ovine sera. In the cultural survey, serovar hardjo was isolated from three animals in one group of sheep. It was considered that the Hebdomadis titres were more likely to represent previous infection with hardjo than with balcanica. Based on the serological and cultural examinations from the general survey and a study farm, a pattern of infection was recorded. The serological prevalence and the geometric mean titre (GMT) of different age groups of sheep from different farms and the lack of success on obtaining further isolates of hardjo indicated that sheep are not the maintenance host for this serovar in New Zealand. Although infection of sheep by serovar hardjo is not uncommon, it is a sporadic occurrence and endemic infection is unlikely to occur. Preliminary investigations on the use of radioimmunoassay in detecting leptospires or leptospiral antigens in urine are presented.Item Feline leptospiral infection : with particular emphasis on Leptospira interrogans servor ballum : a thesis presented in partial fulfilment of the requirements for the degree of Master of Philosophy in Veterinary Pathology and Public Health at Massey University(Massey University, 1979) Shophet, RashelFollowing a review of the literature this thesis attempts to study the susceptibility of the cat to different leptospiral serovars. Particular studies were conducted to investigate the pathogenicity, development of the carrier state and the serological response of the cat infected by the oral and intraperitoneal route with Leptospira interrogans serotype balluw. To investigate the hazard of the cat as a carrier and to simulate the field situation of prey-predator chain as a likely source of infection cats were fed infected mice. A serological survey was also conducted to determine the most commonly occurring leptospiral infection in the cat.Item Leptospirosis in humans and pastoral livestock in New Zealand : a thesis presented in partial fulfilment of the requirements for the doctoral degree of Doctor of Philosophy at Massey University(Massey University, 2013) Dreyfus, AnouThis PhD investigated leptospirosis in humans and pastoral livestock in New Zealand (NZ). A longitudinal ‘abattoir study’, in which blood from workers (n=592) from sheep (n=4), deer (n=2) and beef (n=2) slaughtering abattoirs was tested by the microscopic agglutination test (MAT), revealed that 10-31%, 17-19% and 5% of workers respectively, had antibodies against Leptospira interrogans sv Pomona (Pomona) and/or L. borgpetersenii sv Hardjobovis (Hardjobovis). While the annual infection risk for meat workers of sheep plants was 11.1%, it was 0% in workers processing deer and 1.2% in those processing beef cattle. Sixty workers had a history of probable leptospirosis while working in abattoirs between 1962 and 2010 and three sheep abattoir workers within the one year study period. In sheep abattoirs, new infection with Hardjobovis or Pomona measured by serology was associated with a two-fold higher risk of ‘flu-like’ illness, and an average of four days absence from work. The average annual risk of experiencing flu-like symptoms due to infection with Leptospira measured by serology was 2.7%. The under-ascertainment of officially notified cases with leptospirosis in the last five years was estimated at between 16 and 56 times. Work position was the strongest risk factor for sero-positivity with Pomona and/or Hardjobovis in sheep and deer abattoir workers. The prevalence and new infection risk was highest in workers at the beginning of the slaughter board and the use of personal protective equipment (PPE) appeared not to reduce the risk of sero-positivity or new infection. The risk factor analysis revealed that the infection risk prevailed in the abattoirs and was not evident for non-work related risk factors, such as hunting, home slaughtering and farming. In a multi-species cross-sectional ‘farm study’ (n=238), 97% of sheep and beef and 76% of deer farms had at least one in 20 animals MAT sero-positive against Hardjobovis and/or Pomona. Overall, 50% of adult sheep, 58% of adult beef and 34% of yearling/adult deer were positive against either serovar. Hardjobovis was more prevalent in all three livestock species than Pomona. The regional prevalence distribution in sheep was different for Hardjobovis and Pomona. Grazing beef with deer reduced the likelihood of positivity against Pomona in beef. Co-grazing with another species did not increase the odds of the within-herd prevalence for deer and sheep of Pomona or Hardjobovis and for beef the within-herd prevalence of Hardjobovis controlling for other farm-level risk factors. The incidence of probable leptospirosis in cattle herds in 2009 was 2.6%, in sheep flocks 0% and in deer herds 1%. Tailing rates of sheep farms were positively correlated with prevalence of Hardjobovis: a 1% increase in prevalence was equivalent to a 0.11 increase in tailing percentages, which is unlikely to be causative since this association lacks biological plausibility. All other reproduction and culling rates of any species were not significantly associated with prevalence.Item Studies on some aspects of the epidemiology of bovine leptospirosis : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Veterinary Pathology and Public Health at Massey University(Massey University, 1978) Hellstrom, John StephenA survey of bovine sera indicated that titres to Leptospira interrogans serovar hardjo were present in 60% of New Zealand cattle; 18% of sera were positive against serovar pomona and 9% against serovar tarassovi. Detailed studies were undertaken in a herd with a high prevalence of hardjo and pomona titres. It was determined that more than 90% of newborn calves acquired titres detectable by the microscopic agglutination test (MAT) after suckling seropositive dams. The magnitude of the titre acquired by a calf was strongly correlated with that of its dam. These titres declined steadily, with a half-life of 15 to 17 days; most calves were seronegative after 100 days of age and all by 190 days of age. Following natural infection cattle developed peak titres ranging from 1:768 to 1:8689 within fourteen days after sero-conversion. Initially these titres fell rapidly, declining on average by 62% in the first year and 89% in the first two years after infection. Thereafter titres declined slowly with a mean loss of 5% of residual titre per year. Chromotographical studies on sera from cattle of various ages and at various stages of infection revealed that both IgM and IgG were involved in MAT response to leptospiral infection. Passively acquired titres in calves were largely attributable to IgG1 antibodies. The MAT response of infected cattle was initially attributable IgM antibodies but IgG1 antibodies were involved within the first week after sero-conversion and became the predominant immunoglobulin within 42 days. In convalescent titres of more than one year's duration IgM antibodies frequently were not involved and, in some animals apparently infected for some years, IgG2 accounted for up to 14% of the MAT response. Prospective cohort studies on groups of calves indicated that most became infected with hardjo at about 12 months of age during the winter and early spring. Analysis of climatic factors indicated that outbreaks of infection were strongly correlated with the level of moisture in the environment rather than rainfall per se. Susceptible calves became infected only following close contact with other leptospiruric cattle; no other wild, feral or domestic animal reservoir of hardjo infection was detected. Leptospiruria was demonstrated to persist for up to 14 months in hardjo-infected cattle. The existence of an endemic cycle was demonstrated in which calves infected during one winter infected younger, susceptible calves in the following winter. Evidence was presented to support an hypothesis that bovine pomona infection is a self-limiting sporadic disease which is attributable to direct or indirect contact with infected pigs. The survival of pomona for six weeks in an acidic soil (pH 5.5) under simulated Manawatu winter conditions and the potential for spread of this serovar from pigs to cattle via the environment was demonstrated. The existence of a period of up to three months after the loss of detectable colostral MAT titres during which calves appear to be refractory to experimental inoculation with hardjo was demonstrated. It was also shown that convalescent hardjo titres are protective against experimental challenge of cattle with that serovar. On the basis of experimental studies it is believed that cattle are susceptible to infection with balcanica and that it is not possible to distinguish between bovine infections with this serovar and hardjo except by cultural techniques.