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Item The effects of rain and flooding on leptospirosis incidence in sheep and cattle in New Zealand(Taylor and Francis Group on behalf of the New Zealand Veterinary Association, 2025-08-12) Sadler E; Vallee E; Watts J; Wada MAims To describe the spatio-temporal patterns of leptospirosis case counts in sheep and cattle in New Zealand, and to assess their association with climate variables indicative of flooding and surface runoff. As livestock are a major reservoir of Leptospira spp. and an important source of zoonotic transmission, understanding these patterns is critical for informing livestock and public health interventions in the context of climate change. Methods Confirmed cases of bovine and ovine leptospirosis from January 2011 to December 2023 were extracted from the Ministry for Primary Industries’ Animal Health Surveillance programme. Climate data was sourced from the National Institute of Water and Atmospheric Research. Using the χ2 test and Poisson regression models, the association between district-level case counts and four climate indices were examined: seasonal mean rainfall, seasonal frequency of extreme rainfall, seasonal mean soil moisture, and seasonal frequency of estimated surface runoff. Results Findings indicated an average of 13 confirmed cases for sheep annually, with notable surges in 2017 (34 cases) and 2023 (36 cases), aligning with extreme climate events. Poisson regression models for sheep leptospirosis identified significant associations with extreme rainfall (incidence risk ratio (IRR) = 5.03; 95% CI = 1.18–21.45), mean rainfall (IRR = 1.25; 95% CI = 1.15–1.36), surface runoff (IRR = 1.09; 95% CI = 1.04–1.15), and soil moisture (IRR = 1.03; 95% CI = 1.02–1.03). Cattle leptospirosis was positively associated with surface runoff (IRR = 1.06; 95% CI = 1.02–1.10) and soil moisture (IRR = 1.01; 95% CI = 1.00–1.01). Associations with extreme rainfall (IRR = 1.46; 95% CI = 0.49–4.31) and mean rainfall (IRR = 1.07; 95% CI = 1.00–1.14) were not statistically significant. Conclusions The outcomes of this study provide new evidence linking extreme rainfall, surface runoff, and other climate variables with increased leptospirosis case counts in sheep, with less pronounced but notable associations in cattle. These findings highlight the vulnerability of livestock to climate-driven disease pressures and suggest that future extreme weather events may increase the risk of leptospirosis outbreaks. This has important implications for targeted vaccination, surveillance, and public health preparedness in flood-prone rural regions of New Zealand.Item Case-control study of leptospirosis in Aotearoa New Zealand reveals behavioural, occupational, and environmental risk factors(Cambridge University Press, 2025-06-02) Nisa S; Ortolani E; Vallée E; Marshall J; Collins-Emerson J; Yeung P; Prinsen G; Wright J; Quin T; Fayaz A; Littlejohn S; Baker MG; Douwes J; Benschop J; Hahné SLeptospirosis in NZ has historically been associated with male workers in livestock industries; however, the disease epidemiology is changing. This study identified risk factors amid these shifts. Participants (95 cases:300 controls) were recruited nationwide between 22 July 2019 and 31 January 2022, and controls were frequency-matched by sex (90% male) and rurality (65% rural). Multivariable logistic regression models, adjusted for sex, rurality, age, and season - with one model additionally including occupational sector - identified risk factors including contact with dairy cattle (aOR 2.5; CI: 1.0-6.0), activities with beef cattle (aOR 3.0; 95% CI: 1.1-8.2), cleaning urine/faeces from yard surfaces (aOR 3.9; 95% CI: 1.5-10.3), uncovered cuts/scratches (aOR 4.6; 95% CI: 1.9-11.7), evidence of rodents (aOR 2.2; 95% CI: 1.0-5.0), and work water supply from multiple sources - especially creeks/streams (aOR 7.8; 95% CI: 1.5-45.1) or roof-collected rainwater (aOR 6.6; 95% CI: 1.4-33.7). When adjusted for occupational sector, risk factors remained significant except for contact with dairy cattle, and slaughter without gloves emerged as a risk (aOR 3.3; 95% CI: 0.9-12.9). This study highlights novel behavioural factors, such as uncovered cuts and inconsistent glove use, alongside environmental risks from rodents and natural water sources.Item Leptospirosis, melioidosis, and rickettsioses in the vicious circle of neglect.(PLOS, 2025-01-23) Tshokey T; Ko AI; Currie BJ; Munoz-Zanzi C; Goarant C; Paris DH; Dance DAB; Limmathurotsakul D; Birnie E; Bertherat E; Gongal G; Benschop J; Savelkoel J; Stenos J; Saraswati K; Robinson MT; Day NPJ; Graves SR; Belmain SR; Blacksell SD; Wiersinga WJ; Stevenson BThe global priorities in the field of infectious diseases are constantly changing. While emerging viral infections have regularly dominated public health attention, which has only intensified after the COVID-19 pandemic, numerous bacterial diseases have previously caused, and continue to cause, significant morbidity and mortality-deserving equal attention. Three potentially life-threatening endemic bacterial diseases (leptospirosis, melioidosis, and rickettsioses) are a huge public health concern especially in low- and middle-income countries. Despite their continued threat, these diseases do not receive proportionate attention from global health organizations and are not even included on the WHO list of neglected tropical diseases (NTDs). This, in turn, has led to a vicious circle of neglect with continued, yet conceivably preventable, hospitalizations and deaths each year especially in the vulnerable population. This is a call from a group of multi-institutional experts on the urgent need to directly address the circle of neglect and raise support in terms of funding, research, surveillance, diagnostics, and therapeutics to alleviate the burden of these 3 diseases.Item Molecular typing of Leptospira spp. in farmed and wild mammals reveals new host-serovar associations in New Zealand.(Taylor and Francis Group, 2024-01-01) Wilkinson DA; Edwards M; Shum C; Moinet M; Anderson NE; Benschop J; Nisa SAIMS: To apply molecular typing to DNA isolated from historical samples to determine Leptospira spp. infecting farmed and wild mammals in New Zealand. MATERIALS AND METHODS: DNA samples used in this study were extracted from urine, serum or kidney samples (or Leptospira spp. cultures isolated from them) collected between 2007 and 2017 from a range of domestic and wildlife mammalian species as part of different research projects at Massey University. Samples were included in the study if they met one of three criteria: samples that tested positive with a lipL32 PCR for pathogenic Leptospira; samples that tested negative by lipL32 PCR but were recorded as positive to PCR for pathogenic Leptospira in the previous studies; or samples that were PCR-negative in all studies but were from animals with positive agglutination titres against serogroup Tarassovi. DNA samples were typed using PCR that targeted either the glmU or gyrB genetic loci. The resulting amplicons were sequenced and typed relative to reference sequences. RESULTS: We identified several associations between mammalian hosts and Leptospira strains/serovars that had not been previously reported in New Zealand. Leptospira borgpetersenii strain Pacifica was found in farmed red deer (Cervus elaphus) samples, L. borgpetersenii serovars Balcanica and Ballum were found in wild red deer samples, Leptospira interrogans serovar Copenhageni was found in stoats (Mustela erminea) and brushtail possums (Trichosurus vulpecula), and L. borgpetersenii was found in a ferret (Mustela putorius furo). Furthermore, we reconfirmed previously described associations including dairy cattle with L. interrogans serovars Copenhageni and Pomona and L. borgpetersenii serovars Ballum, Hardjo type bovis and strain Pacifica, sheep with L. interrogans serovar Pomona and L. borgpetersenii serovar Hardjo type bovis, brushtail possum with L. borgpetersenii serovar Balcanica, farmed deer with L. borgpetersenii serovar Hardjo type bovis and hedgehogs (Erinaceus europaeus) with L. borgpetersenii serovar Ballum. CONCLUSIONS: This study provides an updated summary of host-Leptospira associations in New Zealand and highlights the importance of molecular typing. Furthermore, strain Pacifica, which was first identified as Tarassovi using serological methods in dairy cattle in 2016, has circulated in animal communities since at least 2007 but remained undetected as serology is unable to distinguish the different genotypes. CLINICAL RELEVANCE: To date, leptospirosis in New Zealand has been diagnosed with serological typing, which is deficient in typing all strains in circulation. Molecular methods are necessary to accurately type strains of Leptospira spp. infecting mammals in New Zealand.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 Occupational leptospirosis in New Zealand : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy at Massey University, Institute of Veterinary, Animal and Biomedical Sciences, Palmerston North, New Zealand(Massey University, 2016) Sanhueza Frigolett, Juan ManuelAlthough a decreasing trend of human notifications was observed from 2001 to 2014 (Chapter 1), the incidence of human leptospirosis in New Zealand continues to be higher than in other high-income countries and affecting predominately people occupationally exposed to livestock (i.e. abattoir workers and farmers). Additionally, evidence suggests that leptospirosis may have a higher detrimental effect on production in deer compared with beef cattle or sheep. It was also observed that vaccination against Leptospira of not previously infected animals reduce the risk of urinary shedding of leptospires after challenge, and that there is limited evidence supporting or disproving that maternally derived antibodies interfere with the effect of vaccination when animals are vaccinated at a young age. When sero-positivity was defined as a serum microscopic agglutination test (MAT) titre of ≥48, 6.6% of farmers (Chapter 2) and 5.1% of veterinarians (Chapter 3) were sero-positive to at least one of five Leptospira serovars (Hardjo-bovis, Pomona, Copenhageni, Ballum, Tarassovi). Veterinarians had a higher risk of being seropositive when they slaughtered cattle or pigs at home or worked in a mixed animal practice. Assisting calving of cattle or deer, farming deer alone or in combination with cattle and/or sheep, flat terrain on farm, and abundance of wild deer on farm, increased Leptospira sero-positivity of farmers. Apart from vaccinating farmed livestock, increased awareness of such risk factors and the use of protective equipment may reduce the human leptospirosis incidence in these occupational groups. Similar to earlier observations in abattoir workers, Leptospira sero-prevalence of farmers and veterinarians was associated with the recall of influenza-like illness of sampled individuals. Using the estimated incidence of influenza-like illness attributable to Leptospira infection (population attributable risk) of veterinarians (0.05%), farmers (1.3%) and abattoir workers (2.7%), we quantified the burden of human leptospirosis in terms of disability-adjusted life years (DALYs) and economic cost of infection; the latter including the cost of vaccination, which is primarily used in dairy cattle (Chapter 4). Annual DALYs were estimated to be 0.43 per 100,000 people in New Zealand, and 16.76 per 100,000 people when only considering the occupationally-exposed population (abattoir workers, farmers, veterinarians). This ranks leptospirosis in New Zealand’s high-risk population similar to worldwide estimates of DALYs for rabies and dengue. The total annual cost of leptospirosis due to human disease (i.e. treatment and absence from work); production loss in deer, beef cattle, and sheep; and the cost for vaccinating them was estimated to be NZ$25.36 million. One third of this total was attributed to vaccination of dairy cattle. The annual cost of human treatment and workplace absence due to severe and mild leptospirosis was NZ$4.49 million. Total lost production cost was NZ$11.31 million, half of which was attributable to reproductive and growth reduction in deer. No estimates are currently available from any other country for the public health burden and the overall economic loss including farmed livestock for this disease. Since vaccination of livestock is currently regarded as the most effective means of preventing human exposure, the literature on the efficacy of Leptospira vaccines for preventing urinary shedding was systematically reviewed (Chapter 5). The metaanalysis of vaccination trial results, using articles with sufficiently detailed data, resulted in a pooled vaccine efficacy estimate of 82% when shedding was assessed by culture. The findings of this thesis contribute towards a better understanding of the public health burden, economic cost, infection sources for humans, and the efficacy of vaccination for reducing the risk of Leptospira urinary shedding in domestic livestockItem 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 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 Occupational exposure to pathogenic Leptospira from sheep carcasses in a New Zealand abattoir : a dissertation presented in partial fulfilment of the requirements for the degree of Masters in Veterinary Studies at Massey University, Palmerston North, New Zealand(Massey University, 2007) Dorjee, SitharThis research was undertaken in response to a rising trend in the incidence of notified human leptospirosis cases, particularly in meat workers, between 2000 and 2005 in New Zealand. Meat workers constituted the highest proportion (65% during 2004) of notified leptospirosis cases. Sheep either alone or in combination with other animals constituted the second most important animal contact source of human infection (after cattle). Further justification of this research was due to the fact that a number of cases were reported from meat workers employed in sheep-only abattoirs and concerns were raised that sheep may be a significant source of human infection. A longitudinal study was undertaken to determine the serological and cultural prevalence of two of the most commonly diagnosed serovars, Leptospira borgpetersenii serovar Hardjobovis and Leptospira interrogans serovar Pomona. Lines of sheep and individual sheep were systematically randomly sampled at a sheep-only abattoir in Feilding from May 2004 to June 2005. In addition, an assessment of the risk of occupational exposure of meat workers to carcasses shedding live leptospires was carried out using a stochastic model. The association between white-spotted kidney lesions and the serological and cultural prevalence of leptospirosis in sheep was determined along with the diagnostic value of these lesions to predict serological and culture status at the line and individual carcass levels. The study showed that the prevalence of lines with sheep seropositive to one or both serovars was 44% (95% CI 35–54), corresponding to 45% (95% CI 35–55) of farms. This indicates that nearly half the sampled farms had been exposed to infection previously. The overall individual serological prevalence in the sample of 15,855 sheep processed was 6% (95% CI 5–7). Lambs born in the 2003–2004 season had a significantly higher serological prevalence to one or both serovars at the line and individual animal levels compared with lambs born in the 2004–2005 season, suggesting a strong seasonal effect. The serological prevalence of Hardjobovis was significantly higher than Pomona at the line and individual animal levels. The overall isolation rates of live leptospires from seropositive kidneys of Hardjobovis and Pomona were 22% and 17% respectively, and 1% from seronegative carcasses. From a purposively selected line (suspected of being from a farm with active leptospirosis) all 13 kidneys of seropositive carcasses were culture positive indicating a high risk of exposure of meat workers to leptospires in such a situation. Kidneys from seropositive carcasses were significantly more likely to return culture positive compared with kidneys from seronegative carcasses. The assessment of daily risk of exposure of meat workers indicated moderate risk for eviscerators and meat inspectors ranging from 3–11 (95% CI 0–22) and 6–18 (95% CI 1–34) carcasses potentially shedding live leptospires respectively, and a high risk for offal-handlers that ranged from 18–54 (95% CI 7–91) shedding carcasses. The results from the third study showed that the prevalence of white spotted kidneys was 16% and 91% at the individual sheep and line levels, respectively. Carcasses with white spotted kidneys were 5.2 times (95% CI 3.9–7.1) more likely to test seropositive to one or both serovars, but lesions were poor predictors of serological status as judged by test sensitivity and positive predictive values. Furthermore, a positive linear association between white-spot kidney lesion scores and seropositivity to either or both serovars was evident. Consideration of lesion status of lines rather than for individual animals resulted in higher test sensitivity but still suffered from a low positive predictive value. Leptospires were isolated from 5% (95% CI 4–8) kidneys that were cultured. There was no statistically significant association between white spotted kidney lesion scores and culture test results in the survey data; however, a significant linear positive association was evident when culture data from a purposively sampled farm was merged with the survey data. We conclude that the processing of sheep in sheep-only abattoirs constitutes a definite exposure risk of meat workers to leptospirosis and that exposure risks ranged from moderate to high degrees depending on type of duties performed on the slaughter room floor. Furthermore, since grossly visible white-spotted kidney lesions were positively associated with serological and cultural prevalence of disease it would be advisable for meat workers to take extra care when processing lines with a high prevalence of carcasses with these lesions to reduce the risk of infection. This recommendation is made despite the poor predictability of serological and cultural status of these lesions.Item Leptospirosis in free-living animals in New Zealand, with particular reference to the possum (Trichosurus Vulpecula) : 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) Hathaway, Stephen CliveA serological survey of 600 possums (Trichosurus vulpecula) from farmland environments in the southern half of the North Island of New Zealand revealed that titres against leptospires of the Hebdomadis serogroup were present in 52% of sera. Bacteriological studies identified the causative organism as Leptospira interrogans serovar balcanica. This serovar had previously been isolated only in Eastern Europe; from man, cattle and pigs. Isolation of leptospires from kidneys was aided by the use of a system involving whole kidney homogenisation in γ-sterilised plastic bags in a 'Coleworth Stomacher'. Comparison of cultural and serological results demonstrated that, when titres were read at low minimum serum dilutions, the serological prevalence was an accurate indicator of the bacteriological prevalence. Field surveys and experimental studies demonstrated that the possum was a typical maintenance host for balcanica. Experimental infection was easily established and 50% of animals were still leptospiruric one year after infection. Experimental infection with hardjo could not be established, and it is considered that previous reports of endemic hardjo infection in possums in New Zealand could be incorrect. There was a marked difference in the age-specific prevalence of balcanica infection in possum populations, with infection being restricted to sexually-mature animals. Evidence is presented to support the hypothesis that infection becomes established following behavioural changes associated with the onset of sexual maturity. It is suggested that the transmission of balcanica within a population is dependant on direct contact between animals rather than environmental contamination. No correlation could be shown between the prevalence of infection in different populations and the nature of the habitat. A consistent paradoxical reaction to hardjo was found in sera from possums infected with balcanica. Chromatographic studies revealed that this was due to heterologous agglutinating activity of antibodies of the IgM class. Chromatographic studies also indicated that, following infection, the transition of the predominant agglutinating activity in sera from antibodies of the IgM class to antibodies of the IgG class was considerably slower than in eutherian mammals. Balcanica was found to haemolyse red blood cells of several species. An in vitro haemolysin test for the differentiation of balcanica and hardjo isolates is described. Haemolytic activity has not been previously demonstrated in other members of the Hebdomadis serogroup. Investigations of other small free-living mammals revealed that serogroup Ballum infection was endemic in ship rats (Rattus rattus), house mice (Mus musculus) and hedgehogs (Erinaceus enropaeus) in natural and syanthropic biotopes. The Norway rat (Rattus norvegicus) was also shown to be capable of maintaining a focus of Ballum serogroup infection when the population density was high. No leptospires from other than the Ballum serogroup were isolated from the rodents examined. Field evidence suggested that there was no predator-chain transmission of leptospiral infection from rodents to free-living carnivores. -Birds were similarly found to be unimportant in the epidemiology of leptospirosis in the ecosystems studied. The nidality of leptospirosis was investigatad in an intensive farming environment for a period of two years, and well-defined maintenance-host parasite relationships for different serovars were defined in both domestic and free-living species. No cultural and very little serological evidence of interspecies transfer was found, despite the apparent opportunity for transfer of infection. The concept of a maintenance host for a particular leptospiral serovar was investigated using a laboratory mouse model. As a consequence of this investigation and field studies, the characteristics of a maintenance host for a leptospiral serovar are redefined.