The emergence of Leptospira borgpetersenii serovar Arborea in Queensland, Australia, 2001 to 2013

Background

Leptospirosis is an emerging infectious disease, with increasing frequency and severity of outbreaks, changing epidemiology of populations at risk, and the emergence of new serovars. Environmental drivers of disease transmission include flooding, urbanisation, poor sanitation, changes in land use and agricultural practices, and socioeconomic factors. In Queensland, human infection with Leptosira borgpetersenii serovar Arborea was first reported in 2001. This study aims to report the emergence of serovar Arborea in Queensland from 2001 to 2013, and investigate potential risk factors for infection and drivers of emergence.

Methods

Data on laboratory-confirmed cases of human leptospirosis in Queensland were obtained from the enhanced surveillance system at the WHO/FAO/OIE Collaborating Centre for Reference and Research on Leptospirosis in Brisbane, Australia. The changing epidemiology of serovar Arborea from 2001 to 2003 was described with respect to case numbers, proportion of leptospirosis cases attributed to the serovar, and geographic distribution. Differences in risk factors for the most common serovars were compared.

Results

During this period, 1289 cases of leptospirosis were reported, including 233 cases attributed to serovar Arborea. Risk factors for infection include male gender (91 % of cases), occupation, and recreational exposure. Most common occupations recorded were banana workers (28.4 %), meat workers (7.2 %), dairy farmers (5.8 %), graziers/stockmen (5.5 %), ‘other agricultural/rural workers’ (16.4 %), and tourists or tourism operators (4.6 %). Time trend analysis showed that while non-Arborea cases decreased over the study period, Arborea cases increased by 3.4 cases per year. The proportion of annual cases attributed to Arborea peaked at 49 % in 2011 after unprecedented flooding in Queensland. Mapping of cases by residential location showed expansion of the geographic range of serovar Arborea, concentrating mostly around Brisbane, Cairns and Innisfail. Serovars varied significantly between ages and occupational groups, and serovar Arborea was most strongly associated with ‘other agricultural/rural workers’.

Conclusions

Leptospira borgpetersenii serovar Arborea has been emerging in Queensland since 2001, with increase in case numbers, the proportion of leptospirosis infections attributed to the serovar, as well as expansion of its geographic distribution. Reasons for this emergence are unknown, but climatic factors and environmental change are likely to have played important roles.

Electronic supplementary material

The online version of this article (doi:10.1186/s12879-015-0982-0) contains supplementary material, which is available to authorized users.

The role of leptospirosis reference laboratories

The general goal of reference centres is to support the community, from diagnostic laboratories to research institutions, in the execution of their work by providing reference strains and reagents and giving instructions and recommendations to individual colleagues and national and international organisations on a wide variety of issues. There are different levels of reference centres, from local to international, with an increasing package of tasks and responsibilities. Local reference centres might limit activities to diagnostic confirmation by applying standard testing, while international reference centres cover a wider range of activities from design, validation and harmonisation of diagnostic and reference technologies to international monitoring associated with recommendations on the global burden and distribution of leptospirosis and its prevention and control to national and international health decision makers. This chapter focusses on four major pillars constituting reference tasks in addition to the obvious provision of reference substances, i.e. Research and training, Diagnosis, Identification of Leptospira and Surveillance. Due to financial and organisational constraints, reference centres are restricted in their capacity for basic research and consequently focus on applied research into various aspects of leptospirosis. They offer training, either individually or groupwise, that might vary from standard technologies to novel sophisticated methodologies, depending on the need and requests of the trainee. Most reference centres are involved in the confirmation of preliminary diagnosis obtained at peripheral levels, such as local hospitals and health centres, while other major activities involve the design and validation of diagnostics, their international harmonisation and quality assurance. Identification of causative Leptospira strains (or serovars) is key to the identification of infection sources and is critical for surveillance. Hence, reference centres also focus on the development, application and provision of methods that are required for unambiguous characterisation of new and recognised Leptospira strains and the maintenance of the integrity of strain collections. In line with their central role, reference centres are frequently associated with local, national and/or international surveillance activities linked to an advisory role and the production of guidelines. Such surveillance activities usually comprise collation of morbidity and mortality data, signalling of outbreaks and the investigation of infection sources and risks.

Neutrophil counts in leptospirosis patients infected with different serovars

In leptospirosis patients, haematological abnormalities have been reported. The aim of this study was to determine if neutrophil counts were different between patients known to be infected with a range of leptospiral serovars. The study retrospectively compared the neutrophil counts from the first blood samples taken from 210 leptospirosis patients at first presentation to a Queensland Health hospital. Significant differences (p <0.001) were observed in neutrophil counts across the 11 different infecting serovars. These findings suggest that neutrophil counts may be useful in the development of an algorithm determining the infecting serovar in suspected leptospirosis patients. Further studies are required to delineate host cytokine responses which may suggest the underlying aetiology of the observed differences in neutrophil counts. Such studies would also provide valuable therapeutic insights into treating the disease.

Molecular confirmation of co-infection by pathogenic Leptospira spp. and Orientia tsutsugamushi in patients with acute febrile illness in Thailand

Leptospirosis and scrub typhus are major causes of acute febrile illness in rural Asia, where co-infection is reported to occur based on serologic evidence. We re-examined whether co-infection occurs by using a molecular approach. A duplex real-time polymerase chain reaction was developed that targeted a specific 16S ribosomal RNA gene of pathogenic Leptospira spp. and Orientia tsutsugamushi. Of 82 patients with an acute febrile illness who had dual infection on the basis of serologic tests, 5 (6%) had polymerase chain reaction results positive for both pathogens. We conclude that dual infection occurs, but that serologic tests may overestimate the frequency of co-infections.

A single multilocus sequence typing (MLST) scheme for seven pathogenic Leptospira species

Background

The available Leptospira multilocus sequence typing (MLST) scheme supported by a MLST website is limited to L. interrogans and L. kirschneri. Our aim was to broaden the utility of this scheme to incorporate a total of seven pathogenic species.

Methodology and Findings

We modified the existing scheme by replacing one of the seven MLST loci (fadD was changed to caiB), as the former gene did not appear to be present in some pathogenic species. Comparison of the original and modified schemes using data for L. interrogans and L. kirschneri demonstrated that the discriminatory power of the two schemes was not significantly different. The modified scheme was used to further characterize 325 isolates (L. alexanderi [n = 5], L. borgpetersenii [n = 34], L. interrogans [n = 222], L. kirschneri [n = 29], L. noguchii [n = 9], L. santarosai [n = 10], and L. weilii [n = 16]). Phylogenetic analysis using concatenated sequences of the 7 loci demonstrated that each species corresponded to a discrete clade, and that no strains were misclassified at the species level. Comparison between genotype and serovar was possible for 254 isolates. Of the 31 sequence types (STs) represented by at least two isolates, 18 STs included isolates assigned to two or three different serovars. Conversely, 14 serovars were identified that contained between 2 to 10 different STs. New observations were made on the global phylogeography of Leptospira spp., and the utility of MLST in making associations between human disease and specific maintenance hosts was demonstrated.

Conclusion

The new MLST scheme, supported by an updated MLST website, allows the characterization and species assignment of isolates of the seven major pathogenic species associated with leptospirosis.

Leptospirosis is a common zoonotic disease worldwide. Genotyping of the causative organisms provides important insights into disease transmission and informs preventive strategies and vaccine development. Multilocus sequence typing (MLST) is the most widespread genotyping methodology for bacterial pathogens, but the Leptospira scheme supported by a public MLST database is currently only applicable to L. interrogans and L. kirschneri. The purpose of this study was to extend the scheme to a total of seven pathogenic Leptospira species. This was achieved through the development of a modified scheme in which one of the seven MLST loci was replaced, together with newly designed primers for the remaining 6 loci. Comparison of the original and modified scheme demonstrated that they were very similar, hence sequence type (ST) assignments were largely carried over to the modified scheme. Phylogenetic trees reconstructed from concatenated sequences of the seven loci of the modified scheme demonstrated perfect classification of isolates into seven pathogenic species, which resided in clearly distinct phylogenetic clusters. Congruence was low between STs and serovars. The MLST scheme was used to gain new insights into the population genetic structure of Leptospira species associated with clinical disease and maintenance hosts in Asia.

Fool's gold: Why imperfect reference tests are undermining the evaluation of novel diagnostics: a reevaluation of 5 diagnostic tests for leptospirosis

BACKGROUND

We observed that some patients with clinical leptospirosis supported by positive results of rapid tests were negative for leptospirosis on the basis of our diagnostic gold standard, which involves isolation of Leptospira species from blood culture and/or a positive result of a microscopic agglutination test (MAT). We hypothesized that our reference standard was imperfect and used statistical modeling to investigate this hypothesis.

METHODS

Data for 1652 patients with suspected leptospirosis recruited during three observational studies and one randomized control trial that described the application of culture, MAT, immunofluorescence assay (IFA), lateral flow (LF) and/or PCR targeting the 16S rRNA gene were reevaluated using Bayesian latent class models and random-effects meta-analysis.

RESULTS

The estimated sensitivities of culture alone, MAT alone, and culture plus MAT (for which the result was considered positive if one or both tests had a positive result) were 10.5% (95% credible interval [CrI], 2.7%-27.5%), 49.8% (95% CrI, 37.6%-60.8%), and 55.5% (95% CrI, 42.9%-67.7%), respectively. These low sensitivities were present across all 4 studies. The estimated specificity of MAT alone (and of culture plus MAT) was 98.8% (95% CrI, 92.8%-100.0%). The estimated sensitivities and specificities of PCR (52.7% [95% CrI, 45.2%-60.6%] and 97.2% [95% CrI, 92.0%-99.8%], respectively), lateral flow test (85.6% [95% CrI, 77.5%-93.2%] and 96.2% [95% CrI, 87.7%-99.8%], respectively), and immunofluorescence assay (45.5% [95% CrI, 33.3%-60.9%] and 96.8% [95% CrI, 92.8%-99.8%], respectively) were considerably different from estimates in which culture plus MAT was considered a perfect gold standard test.

CONCLUSIONS

Our findings show that culture plus MAT is an imperfect gold standard against which to compare alterative tests for the diagnosis of leptospirosis. Rapid point-of-care tests for this infection would bring an important improvement in patient care, but their future evaluation will require careful consideration of the reference test(s) used and the inclusion of appropriate statistical models.

Leptospirosis in American Samoa--estimating and mapping risk using environmental data

Background

The recent emergence of leptospirosis has been linked to many environmental drivers of disease transmission. Accurate epidemiological data are lacking because of under-diagnosis, poor laboratory capacity, and inadequate surveillance. Predictive risk maps have been produced for many diseases to identify high-risk areas for infection and guide allocation of public health resources, and are particularly useful where disease surveillance is poor. To date, no predictive risk maps have been produced for leptospirosis. The objectives of this study were to estimate leptospirosis seroprevalence at geographic locations based on environmental factors, produce a predictive disease risk map for American Samoa, and assess the accuracy of the maps in predicting infection risk.

Methodology and Principal Findings

Data on seroprevalence and risk factors were obtained from a recent study of leptospirosis in American Samoa. Data on environmental variables were obtained from local sources, and included rainfall, altitude, vegetation, soil type, and location of backyard piggeries. Multivariable logistic regression was performed to investigate associations between seropositivity and risk factors. Using the multivariable models, seroprevalence at geographic locations was predicted based on environmental variables. Goodness of fit of models was measured using area under the curve of the receiver operating characteristic, and the percentage of cases correctly classified as seropositive. Environmental predictors of seroprevalence included living below median altitude of a village, in agricultural areas, on clay soil, and higher density of piggeries above the house. Models had acceptable goodness of fit, and correctly classified ∼84% of cases.

Conclusions and Significance

Environmental variables could be used to identify high-risk areas for leptospirosis. Environmental monitoring could potentially be a valuable strategy for leptospirosis control, and allow us to move from disease surveillance to environmental health hazard surveillance as a more cost-effective tool for directing public health interventions.

Leptospirosis is the most common bacterial infection transmitted from animals to humans. Infected animals excrete the bacteria in their urine, and humans can become infected through contact with animals or a contaminated environment such as water and soil. Environmental factors are important in determining the risk of human infection, and differ between ecological settings. The wide range of risk factors include high rainfall and flooding; poor sanitation and hygiene; urbanisation and overcrowding; contact with animals (including rodents, livestock, pets, and wildlife); outdoor recreation and ecotourism; and environmental degradation. Predictive risk maps have been produced for many infectious diseases to identify high-risk areas for transmission and guide allocation of public health resources. Maps are particularly useful where disease surveillance and epidemiological data are poor. The objectives of this study were to estimate leptospirosis seroprevalence at geographic locations based on environmental factors, produce a predictive disease risk map for American Samoa, and assess the accuracy of the maps in predicting infection risk. This study demonstrated the value of geographic information systems and disease mapping for identifying environmental risk factors for leptospirosis, and enhancing our understanding of disease transmission. Similar principles could be used to investigate the epidemiology of leptospirosis in other areas.

Leptospirosis in American Samoa 2010: epidemiology, environmental drivers, and the management of emergence

Leptospirosis has recently been reported as an emerging disease worldwide, and a seroprevalence study was undertaken in American Samoa to better understand the drivers of transmission. Antibodies indicative of previous exposure to leptospirosis were found in 15.5% of 807 participants, predominantly against three serovars that were not previously known to occur in American Samoa. Questionnaires and geographic information systems data were used to assess behavioral factors and environmental determinants of disease transmission, and logistic regression was used to identify factors associated with infection. Many statistically significant factors were consistent with previous studies, but we also showed a significant association with living at lower altitudes (odds ratio [OR] = 1.53, 95% confidence interval [CI]: 1.03-2.28), and having higher numbers of piggeries around the home (OR = 2.63, 95% CI: 1.52-4.40). Our findings support a multifaceted approach to combating the emergence of leptospirosis, including modification of individual behavior, but importantly also managing the evolving environmental drivers of risk.

Emergence of new leptospiral serovars in American Samoa - ascertainment or ecological change?

Background

Leptospirosis has recently been discussed as an emerging infectious disease in many contexts, including changes in environmental drivers of disease transmission and the emergence of serovars. In this paper, we report the epidemiology of leptospiral serovars from our study of human leptospirosis in American Samoa in 2010, present evidence of recent serovar emergence, and discuss the potential epidemiological and ecological implications of our findings.

Methods

Serovar epidemiology from our leptospirosis seroprevalence study in 2010 was compared to findings from a study in 2004. The variation in geographic distribution of the three most common serovars was explored by mapping sero-positive participants to their place of residence using geographic information systems. The relationship between serovar distribution and ecological zones was examined using geo-referenced data on vegetation type and population distribution.

Results

Human leptospirosis seroprevalence in American Samoa was 15.5% in 2010, with serological evidence that infection was caused by three predominant serovars (Hebdomadis, LT 751, and LT 1163). These serovars differed from those identified in an earlier study in 2004, and were not previously known to occur in American Samoa. In 2010, serovars also differed in geographic distribution, with variations in seroprevalence between islands and different ecological zones within the main island.

Conclusions

Our findings might indicate artefactual emergence (where serovars were long established but previously undetected), but we believe the evidence is more in favour of true emergence (a result of ecological change). Possibilities include changes in interactions between humans and the environment; introduction of serovars through transport of animals; evolution in distribution and/or abundance of animal reservoirs; and environmental changes that favour transmission of particular serovars.

Future research should explore the impact of ecological change on leptospirosis transmission dynamics and serovar emergence, and investigate how such new knowledge might better target environmental monitoring for disease control at a public health level.

Bats as a source of emerging zoonotic diseases – the interface with wildlife Leptospirosis – importance of a One Health approach

The term leptospirosis represents a spectrum of human and veterinary diseases caused by pathogenic serovars of the spirochaete genus Leptospira. It is of global significance as a cause of human mortality and morbidity, and of disease in domestic and production animals and in wildlife. A One Health approach to leptospirosis control is essential because human infection almost invariably results either from direct animal exposure or from exposure to environments contaminated by infected animals. The relationships between human and veterinary leptospirosis are illustrated by Australian experience. A major factor limiting control of the disease is poor communication and cooperation between those working from medical and veterinary perspectives. Leptospira shows great antigenic and genetic diversity, and so international leptospirosis reference laboratories are a vital but fragile resource. There is a compelling need to maximise cooperation between all professions with an interest in leptospirosis, to create outcomes, to communicate with governments and to ensure essential resources.

Comparison of two multilocus sequence based genotyping schemes for Leptospira species

BACKGROUND

Several sequence based genotyping schemes have been developed for Leptospira spp. The objective of this study was to genotype a collection of clinical and reference isolates using the two most commonly used schemes and compare and contrast the results.

METHODS AND FINDINGS

A total of 48 isolates consisting of L. interrogans (n = 40) and L. kirschneri (n = 8) were typed by the 7 locus MLST scheme described by Thaipadungpanit et al., and the 6 locus genotyping scheme described by Ahmed et al., (termed 7L and 6L, respectively). Two L. interrogans isolates were not typed using 6L because of a deletion of three nucleotides in lipL32. The remaining 46 isolates were resolved into 21 sequence types (STs) by 7L, and 30 genotypes by 6L. Overall nucleotide diversity (based on concatenated sequence) was 3.6% and 2.3% for 7L and 6L, respectively. The D value (discriminatory ability) of 7L and 6L were comparable, i.e. 92.0 (95% CI 87.5-96.5) vs. 93.5 (95% CI 88.6-98.4). The dN/dS ratios calculated for each locus indicated that none were under positive selection. Neighbor joining trees were reconstructed based on the concatenated sequences for each scheme. Both trees showed two distinct groups corresponding to L. interrogans and L. kirschneri, and both identified two clones containing 10 and 7 clinical isolates, respectively. There were six instances in which 6L split single STs as defined by 7L into closely related clusters. We noted two discrepancies between the trees in which the genetic relatedness between two pairs of strains were more closely related by 7L than by 6L.

CONCLUSIONS

This genetic analysis indicates that the two schemes are comparable. We discuss their practical advantages and disadvantages.

Serosurvey of leptospirosis and investigation of a possible novel serovar Arborea in farmed deer in New Zealand

AIM

To investigate the prevalence of Leptospira spp. and possible novel serovar Arborea infection in farmed deer in New Zealand.

METHODS

In September 2006, five serum samples from a serum bank from each of 70 farms sampled for a previous national prevalence survey were forwarded to the World Health Organisation/Food and Agriculture Organisation/World Organisation for Animal Health (WHO/FAO/OIE) reference laboratory for leptospirosis in Brisbane, Australia, to test for reactivity to a reference panel of 23 serovars, most believed to be exotic to New Zealand, using the microscopic agglutination test (MAT). Eleven farms were seropositive for Arborea, a serovar novel to New Zealand. In July 2007, 126 additional banked serum samples from nine of those 11 farms (n=8-20/farm) were sent to the reference laboratory for similar serology. Two farms in the Southland region were considered positive for serovar Arborea. Tissue from deer kidneys (n=43) from these two farms collected at a deer slaughter premises (DSP) was cultured in November 2007 and November 2008. Sera from those deer were also sent to the laboratory in Brisbane.

RESULTS

From the initial 350 sera, 96 (27.4%) and 19 (5.4%) samples were positive for Leptospira borgpetersenii serovar Hardjo-bovis and Leptospira interrogans serovar Pomona respectively. There were cross-reactions between serovar Hardjo-bovis with serovars Medanensis and Szwajizak. Serological evidence of serovars Tarassovi, Grippotyphosa, Celledoni, Australis, Zanoni, Robinsoni, Canicola, Kremastos, Bulgarica, Cynopteri, Ballum, Bataviae, Djasiman, Javanica, Panama, Shermani and Topaz was negative or sporadic, generally with titres of 1:50 and therefore likely non-specific. Fourteen (4.0%) samples from 11 farms were positive for serovar Arborea, justifying further investigation. The prevalence of serovar Arborea was 15% and 30% on two farms, from the 126 samples. None of 43 kidney and serum samples collected subsequently from those two farms were positive by culture or serology for serovar Arborea.

CONCLUSIONS

While there were samples serologically positive for serovar Arborea in deer, attempts to isolate the organism were unsuccessful. The sample size for the follow-up investigation was insufficient to validate the presence or absence of infection, so further study should be undertaken to verify the status of this serovar of Leptospira spp. in New Zealand, in both deer and other livestock species.

Accuracy of loop-mediated isothermal amplification for diagnosis of human leptospirosis in Thailand

There is a lack of diagnostic tests for leptospirosis in technology-restricted settings. We developed loop-mediated isothermal amplification (LAMP) specific for the 16S ribosomal RNA gene (rrs) of pathogenic and intermediate group Leptospira species. The lower limit of detection was 10 genomic equivalents/reaction, and analytical specificity was high; we observed positive reactions for pathogenic/intermediate groups and negative reactions for non-pathogenic Leptospira species and other bacterial species. We evaluated this assay in Thailand by using a case–control study of 133 patients with laboratory-proven leptospirosis and 133 patients with other febrile illnesses. Using admission blood, we found that the rrs LAMP showed positive results in 58 of 133 cases (diagnostic sensitivity = 43.6, 95% confidence interval [CI] = 35.0–52.5) and in 22 of 133 controls (diagnostic specificity = 83.5, 95% CI = 76.0–89.3). Sensitivity was high for 39 patients who were culture positive for Leptospira spp. (84.6, 95% CI = 69.5–94.1). The rrs LAMP can provide an admission diagnosis in approximately half of patients with leptospirosis, but its clinical utility is reduced by a lower specificity.

Diagnostic accuracy of real-time PCR assays targeting 16S rRNA and lipL32 genes for human leptospirosis in Thailand: a case-control study

Background

Rapid PCR-based tests for the diagnosis of leptospirosis can provide information that contributes towards early patient management, but these have not been adopted in Thailand. Here, we compare the diagnostic sensitivity and specificity of two real-time PCR assays targeting rrs or lipL32 for the diagnosis of leptospirosis in northeast Thailand.

Methods/Principal Findings

A case-control study of 266 patients (133 cases of leptospirosis and 133 controls) was constructed to evaluate the diagnostic sensitivity and specificity (DSe & DSp) of both PCR assays. The median duration of illness prior to admission of cases was 4 days (IQR 2–5 days; range 1–12 days). DSe and DSp were determined using positive culture and/or microscopic agglutination test (MAT) as the gold standard. The DSe was higher for the rrs assay than the lipL32 assay (56%, (95% CI 47–64%) versus 43%, (95% CI 34–52%), p<0.001). No cases were positive for the lipL32 assay alone. There was borderline evidence to suggest that the DSp of the rrs assay was lower than the lipL32 assay (90% (95% CI 83–94%) versus 93%, (95%CI 88–97%), p = 0.06). Nine controls gave positive reactions for both assays and 5 controls gave a positive reaction for the rrs assay alone. The DSe of the rrs and lipL32 assays were high in the subgroup of 39 patients who were culture positive for Leptospira spp. (95% and 87%, respectively, p = 0.25).

Conclusions/Significance

Early detection of Leptospira using PCR is possible for more than half of patients presenting with leptospirosis and could contribute to individual patient care.

The role of fruit bats in the transmission of pathogenic leptospires in Australia

Although antileptospiral antibodies and leptospiral DNA have been detected in Australian fruit bats, the role of such bats as infectious hosts for the leptospires found in rodents and humans remains unconfirmed. A cohort-design, replicated survey was recently conducted in Far North Queensland, Australia, to determine if the abundance and leptospiral status of rodents were affected by association with colonies of fruit bats (Pteropus conspicillatus spp.) via rodent contact with potentially infectious fruit-bat urine. In each of four study areas, a 'colony site' that included a fruit-bat colony and the land within 1500 m of the colony was compared with a 'control site' that held no fruit-bat colonies and was >2000 m from the nearest edge of the colony site. Rodents were surveyed, for a total of 2400 trap-nights, over six sampling sessions between September 2007 and September 2008. A low abundance of rodents but a high carriage of leptospires in the rodents present were found to be associated with proximity to a fruit-bat colony. For example, means of 0·4 and 2·3 fawn-footed melomys (Melomys cervinipes) were collected/100 trap-nights at sites with and without fruit-bat colonies, respectively (P<0·001), but the corresponding prevalences of leptospiral carriage were 100% and 3·6% (P<0·001). Such trends were consistent across all of the sampling sessions but not across all of the sampling sites. Leptospires were not isolated from fruit bats by culture, and the role of such bats in the transmission of leptospires to rodents cannot be confirmed. The data collected do, however, indicate the existence of a potential pathway for transmission of leptospires from fruit bats to rodents, via rodent contact with infectious fruit-bat urine. Fruit bats may possibly be involved in the ecology of leptospires (including emergent serovars), as disseminators of pathogens to rodent populations. Stringent quantitative risk analysis of the present and similar data, to explore their implications in terms of disease prevalence and wildlife population dynamics, is recommended.

High-resolution melt-curve analysis of random amplified polymorphic DNA (RAPD-HRM) for the characterisation of pathogenic leptospires: intra-serovar divergence, inter-serovar convergence, and evidence of attenuation in Leptospira reference collections

High-resolution melt-curve analysis of random amplified polymorphic DNA (RAPD-HRM) is a novel technology that has emerged as a possible method to characterise leptospires to serovar level. RAPD-HRM has recently been used to measure intra-serovar convergence between strains of the same serovar as well as inter-serovar divergence between strains of different serovars. The results indicate that intra-serovar heterogeneity and inter-serovar homogeneity may limit the application of RAPD-HRM in routine diagnostics. They also indicate that genetic attenuation of aged, high-passage-number isolates could undermine the use of RAPD-HRM or any other molecular technology. Such genetic attenuation may account for a general decrease seen in titres of rabbit hyperimmune antibodies over time. Before RAPD-HRM can be further advanced as a routine diagnostic tool, strains more representative of the wild-type serovars of a given region need to be identified. Further, RAPD-HRM analysis of reference strains indicates that the routine renewal of reference collections, with new isolates, may be needed to maintain the genetic integrity of the collections.

Molecular epidemiology of Leptospira borgpetersenii serovar Arborea, Queensland, Australia, 1998-2005

Leptospira borgpetersenii serovar Arborea is an emerging cause of leptospirosis in Australia. It was not previously recognized as an endemic serovar before the 1990s, but at that point, human infections with the serovar increased significantly. Using fluorescent-amplified fragment-length polymorphism (FAFLP) molecular typing, human and rodent isolates were compared genetically. Typing revealed 11 unique profiles among the 23 isolates examined; however, there was no clonality revealed between the human and rodent isolates. There was clonality among rodent isolates from geographically related areas. This study highlights the utility of Leptospira culture combined with FAFLP for the examination of the epidemiology of this disease.

Climate change, flooding, urbanisation and leptospirosis: fuelling the fire?

Flooding and heavy rainfall have been associated with numerous outbreaks of leptospirosis around the world. With global climate change, extreme weather events such as cyclones and floods are expected to occur with increasing frequency and greater intensity and may potentially result in an upsurge in the disease incidence as well as the magnitude of leptospirosis outbreaks. In this paper, we examine mechanisms by which climate change can affect various ecological factors that are likely to drive an increase in the overall incidence as well as the frequency of outbreaks of leptospirosis. We will discuss the geographical areas that are most likely to be at risk of an increase in leptospirosis disease burden owing to the coexistence of climate change hazard risk, environmental drivers of leptospirosis outbreaks, local socioeconomic circumstances, and social and demographic trends. To reduce this disease burden, enhanced surveillance and further research is required to understand the environmental drivers of infection, to build capacity in emergency response and to promote community adaptation to a changing climate.

High-resolution melt-curve analysis of random-amplified-polymorphic-DNA markers, for the characterisation of pathogenic Leptospira

A new test for pathogenic Leptospira isolates, based on RAPD-PCR and high-resolution melt (HRM) analysis (which measures the melting temperature of amplicons in real time, using a fluorescent DNA-binding dye), has recently been developed. A characteristic profile of the amplicons can be used to define serovars or detect genotypes. Ten serovars, of leptospires from the species Leptospira interrogans (serovars Australis, Robinsoni, Hardjo, Pomona, Zanoni, Copenhageni and Szwajizak), L. borgpetersenii (serovar Arborea), L. kirschneri (serovar Cynopteri) and L. weilii (serovar Celledoni), were typed against 13 previously published RAPD primers, using a real-time cycler (the Corbett Life Science RotorGene 6000) and the optimised reagents from a commercial kit (Quantace SensiMix). RAPD-HRM at specific temperatures generated defining amplicon melt profiles for each of the tested serovars. These profiles were evaluated as difference-curve graphs generated using the RotorGene software package, with a cut-off of at least 8 'U' (plus or minus). The results demonstrated that RAPD-HRM can be used to measure serovar diversity and establish identity, with a high degree of stability. The characterisation of Leptospira serotypes using a DNA-based methodology is now possible. As an objective and relatively inexpensive and rapid method of serovar identification, at least for cultured isolates, RAPD-HRM assays show convincing potential.

Haematological and clinical-chemistry markers in patients presenting with leptospirosis: a comparison of the findings from uncomplicated cases with those seen in the severe disease

In a retrospective study, the laboratory findings from the first blood samples taken following hospital presentation in patients with uncomplicated leptospirosis have been compared with the corresponding data for patients admitted, to a high-dependency medical ward or intensive-care unit, with severe leptospirosis. The aim was to identify those laboratory markers that differentiate the two clinical groups upon initial presentation. Marked differences were observed, in some of the haematological and clinical-chemistry markers, between the patients with severe leptospirosis and those with the uncomplicated disease. Statistically significant differences were found in haemoglobin concentrations, haematocrits, counts of erythrocytes, leucocytes, neutrophils and platelets, and serum concentrations of creatinine, urea, protein and albumin. These markers may therefore be useful in the assessment and early detection of disease severity in patients with suspected leptospirosis. Investigations into the use of albumin treatments, which might significantly improve the clinical care of patients with acute leptospirosis, appear to be justified.

The microscopic agglutination test (MAT) is an unreliable predictor of infecting Leptospira serovar in Thailand

A prospective study in Thailand identified 106 patients with culture-proven leptospirosis. The accuracy of the microscopic agglutination test (MAT) in predicting the infecting serovar was evaluated in 78/106 (74%) patients with a diagnostic titer. MAT correctly determined the infecting serovar in 26 cases (33%), indicating that this assay is a poor predictor of infecting serovar in our setting.

Leptospirosis in the Asia Pacific region

Background

Leptospirosis is a worldwide zoonotic infection that has been recognized for decades, but the problem of the disease has not been fully addressed, particularly in resource-poor, developing countries, where the major burden of the disease occurs. This paper presents an overview of the current situation of leptospirosis in the region. It describes the current trends in the epidemiology of leptospirosis, the existing surveillance systems, and presents the existing prevention and control programs in the Asia Pacific region.

Methods

Data on leptospirosis in each member country were sought from official national organizations, international public health organizations, online articles and the scientific literature. Papers were reviewed and relevant data were extracted.

Results

Leptospirosis is highly prevalent in the Asia Pacific region. Infections in developed countries arise mainly from occupational exposure, travel to endemic areas, recreational activities, or importation of domestic and wild animals, whereas outbreaks in developing countries are most frequently related to normal daily activities, over-crowding, poor sanitation and climatic conditions.

Conclusion

In the Asia Pacific region, predominantly in developing countries, leptospirosis is largely a water-borne disease. Unless interventions to minimize exposure are aggressively implemented, the current global climate change will further aggravate the extent of the disease problem. Although trends indicate successful control of leptospirosis in some areas, there is no clear evidence that the disease has decreased in the last decade. The efficiency of surveillance systems and data collection varies significantly among the countries and areas within the region, leading to incomplete information in some instances. Thus, an accurate reflection of the true burden of the disease remains unknown.

Reclassification of Leptospira meyeri serovar Perameles to Leptospira interrogans serovar Perameles through serological and molecular analysis: evidence of a need for changes to current procedures in Leptospira taxonomy

It has been recognized that there is heterogeneity among Leptospira isolates in culture collections worldwide, causing confounding results for researchers utilizing these organisms; one such culture is Leptospira meyeri serovar Perameles. The serovar reference strain Bandicoot 343 was previously identified to the species level by DNA-DNA hybridization; however, subsequent published studies demonstrated results that contradicted the initial speciation. In this study, initial serological testing was performed with isolates from the culture collections of the Centers for Disease Control (CDC), Atlanta, USA (strain Lepto0214), and the WHO/FAO/OIE Collaborating Centre for Reference and Research on Leptospirosis, Brisbane, Australia (strain Bandicoot 343), and the original serovar Perameles hyperimmune antiserum produced in 1964. The results indicated that strain Lepto0214 was not serologically reactive to the antiserum. However, further investigations revealed an alternative serovar Perameles strain held in the CDC collection (Lepto0213) that yielded titres against the antiserum. 16S rRNA gene sequencing of the three strains revealed that Lepto0214 had significant sequence similarity with previously sequenced L. meyeri strains; however, strains Lepto0213 and Bandicoot 343 had significant similarity with Leptospira interrogans strains. 16S rRNA gene sequencing results were confirmed by pulsed-field gel electrophoresis; Lepto0214 had a pattern similar to that of L. meyeri serovar Hardjo strain Went 5, and the pattern differed significantly from those of Lepto0213 and Bandicoot 343. This research provides evidence for the reclassification of serovar Perameles from L. meyeri to L. interrogans. This reclassification highlights a need for changes to how reference Leptospira serovars are identified, disseminated and stored, with the aim of reducing heterogeneity of reference strains between culture collections.

Leptospira kmetyi sp. nov., isolated from an environmental source in Malaysia

A single Leptospira strain (designated Bejo-Iso9(T)) was isolated from a soil sample taken in Johor, Malaysia. The isolate showed motility and morphology typical of the genus Leptospira under dark-field microscopy. Cells were found to be 10-13 microm in length and 0.2 microm in diameter, with a wavelength of 0.5 microm and an amplitude of approximately 0.2 microm. Phenotypically, strain Bejo-Iso9(T) grew in Ellinghausen-McCullough-Johnson-Harris medium at 13, 30 and 37 degrees C, and also in the presence of 8-azaguanine. Serologically, strain Bejo-Iso9(T) produced titres towards several members of the Tarassovi serogroup, but was found to be serologically unique by cross-agglutinin absorption test and thus represented a novel serovar. The proposed name for this serovar is Malaysia. Phylogenetic analysis of 16S rRNA gene sequences placed this novel strain within the radiation of the genus Leptospira, with sequence similarities within the range 90.4-99.5% with respect to recognized Leptospira species. DNA-DNA hybridization against the three most closely related Leptospira species was used to confirm the results of the 16S rRNA gene sequence analysis. The G+C content of the genome of strain Bejo-Iso9(T) was 36.2 mol%. On the basis of phenotypic, serological and phylogenetic data, strain Bejo-Iso9(T) represents a novel species of the genus Leptospira, for which the name Leptospira kmetyi sp. nov. is proposed. The type strain is Bejo-Iso9(T) (=WHO LT1101(T)=KIT Bejo-Iso9(T)).

Lymphopenia is observed regularly in the acute (leptospiraemic) phase but not the immune phase of leptospirosis

Lymphocyte counts in patients with leptospirosis have been shown to be variable. This study retrospectively compared lymphocyte counts from the first blood samples taken following hospital presentation in patients with leptospirosis who were either (i) IgM non-reactive, (ii) IgM reactive and microscopic agglutination test (MAT) non-reactive or (iii) IgM and MAT reactive in an effort to determine whether differences in lymphocyte counts are observed in the acute and immune phase of leptospirosis. Statistical differences in lymphocyte counts were observed between the three groups. In conclusion, this study has shown that the phase of leptospiral infection may affect patient lymphocyte counts.

Leptospira weilii serovar Topaz, a new member of the Tarassovi serogroup isolated from a bovine source in Queensland, Australia

This paper reports on a Leptospira isolate of bovine origin and its identification as belonging to a previously unknown serovar, for which the name Topaz is proposed. The isolate (94-79970/3) was cultured from bovine urine from a north Queensland dairy farm in Australia. Strain 94-79970/3 grew at 30 degrees C in Ellinghausen McCullough Johnson Harris (EMJH) medium but failed to grow at 13 degrees C in EMJH medium or in the presence of 8-azaguanine. Serologically, strain 94-79970/3 produced titres against the Leptospira borgpetersenii serovar Tarassovi, the reference strain for the Tarassovi serogroup; however, no significant titres to any other serovars within the serogroup were obtained. Using 16S rRNA and DNA gyrase subunit B gene analysis, strain 94-79970/3 was identified as a member of the species Leptospira weilii. We propose that the serovar be named Topaz, after the location where the original isolate was obtained. The reference strain for this serovar is 94-79970/3 (=KIT 94-79970/3=LT722).

Leptospira wolffii sp. nov., isolated from a human with suspected leptospirosis in Thailand

A single Leptospira strain (designated Khorat-H2(T)) was isolated from the urine of an adult male patient with suspected leptospirosis from the province of Nakornrachasima, Thailand. The isolate showed typical Leptospira motility and morphology under dark-field microscopy. Cells were 10-13 mum long and 0.2 mum in diameter, with a wavelength of 0.5 mum and an amplitude of approximately 0.3 mum. Phenotypically, strain Khorat-H2(T) did not grow at 13 degrees C but grew at 30 and 37 degrees C and in the presence of 8-azaguanine. Serological identification using the microscopic agglutination test revealed that strain Khorat-H2(T) had no cross-reaction with any recognized Leptospira serogroups. Phylogenetic analysis of the 16S rRNA gene sequence placed the novel strain within the radiation of the genus Leptospira, with sequence similarities of 88.1-97.7 % to recognized Leptospira species. DNA-DNA hybridization against the type strains of the three most closely related Leptospira species was used to confirm the results of the 16S rRNA sequence analysis. The G+C content of strain Khorat-H2(T) was 41.8 mol%. On the basis of phenotypic, serological and phylogenetic data, strain Khorat-H2(T) represents a novel species of the genus Leptospira, for which the name Leptospira wolffii sp. nov. is proposed. The type strain is Khorat-H2(T) (=WHO LT1686(T) =KIT Khorat-H2(T)).

A dominant clone of Leptospira interrogans associated with an outbreak of human leptospirosis in Thailand

BACKGROUND

A sustained outbreak of leptospirosis occurred in northeast Thailand between 1999 and 2003, the basis for which was unknown.

METHODS AND FINDINGS

A prospective study was conducted between 2000 and 2005 to identify patients with leptospirosis presenting to Udon Thani Hospital in northeast Thailand, and to isolate the causative organisms from blood. A multilocus sequence typing scheme was developed to genotype these pathogenic Leptospira. Additional typing was performed for Leptospira isolated from human cases in other Thai provinces over the same period, and from rodents captured in the northeast during 2004. Sequence types (STs) were compared with those of Leptospira drawn from a reference collection. Twelve STs were identified among 101 isolates from patients in Udon Thani. One of these (ST34) accounted for 77 (76%) of isolates. ST34 was Leptospira interrogans, serovar Autumnalis. 86% of human Leptospira isolates from Udon Thani corresponded to ST34 in 2000/2001, but this figure fell to 56% by 2005 as the outbreak waned (p = 0.01). ST34 represented 17/24 (71%) of human isolates from other Thai provinces, and 7/8 (88%) rodent isolates. By contrast, 59 STs were found among 76 reference strains, indicating a much more diverse population genetic structure; ST34 was not identified in this collection.

CONCLUSIONS

Development of an MLST scheme for Leptospira interrogans revealed that a single ecologically successful pathogenic clone of L. interrogans predominated in the rodent population, and was associated with a sustained outbreak of human leptospirosis in Thailand.

Leptospirosis serology in the common brushtail possum (Trichosurus vulpecula) from urban Sydney, Australia

The common brushtail possum (Trichosurus vulpecula) is indeed a common marsupial in major cities of Australia. This species is known to be susceptible to leptospirosis and often lives in close contact with humans, raising concerns about the potential for transmission of this disease in urban areas. A total of 192 brushtail possum blood samples were collected from 136 individuals in suburban areas of metropolitan Sydney from November 2002 to November 2004. Sera were screened against a reference panel of 21 Leptospira spp. using the microscopic agglutination test. Leptospiral antibodies were detected in 9.6% (13/136) of tested brushtail possums and represented two serovars; antibodies to Leptospira interrogans serovar Hardjo were most frequently identified (11/136). A representative of the exotic sero-group Ballum, most likely serovar Arborea, was found in two of 136 brushtail possums. Exposure to leptospirosis seemed to be associated with age, as older animals had a higher incidence, but there was no distinction in relation to gender. Antibody prevalence varied between the different sampling sites and seropositive animals were clustered and restricted to a few sites. These data support the possible role of brushtail possums as a maintenance host for Leptospira spp. in urban environments and also identified them as a previously unknown and potential source of serovar Arborea.

Epidemiology of Leptospira weilii serovar Topaz infections in Australia

Leptospirosis is a zoonotic disease with a worldwide distribution. Leptospira weilii serovar (sv.) Topaz is a newly described serovar first isolated in the far north of Queensland, Australia. The epidemiology of L. weilii sv. Topaz infections in Australia was characterised through the use of surveillance questionnaires and molecular studies. There have been 24 human and 2 animal (bovine and bandicoot) L. weilii sv. Topaz infections diagnosed since 1991. The majority of these infections have occurred in Far North Queensland, with the remaining infections occurring in South East Queensland and in Western Australia. The majority of patients with L. weilii sv. Topaz infections presented with classical leptospirosis symptoms including; fever, headaches, sweats, chills and myalgia. The occupations of human cases of L. weilii sv. Topaz infection included banana farming, dairy and beef cattle production and tourist related activities. Fluorescent amplified fragment length polymorphism (FAFLP) was performed on 15 L. weilii sv. Topaz isolates including 2 animal isolates. Clustering analysis grouped the 15 isolates into 5 main clades with 13 unique FAFLP profiles. A high level of relatedness was demonstrated between 2 animal and 2 human isolates.

Clinical diagnosis and geographic distribution of leptospirosis, Thailand

We defined the positive predictive accuracy of a hospital-based clinical diagnosis of leptospirosis in 9 provinces across Thailand. Of 700 suspected cases, 143 (20%) were confirmed by laboratory testing. Accuracy of clinical diagnosis varied from 0% to 50% between the provinces and was highest during the rainy season. Most confirmed cases occurred in the north and northeast regions of the country.

Molecular typing of Leptospira spp. based on putative O-antigen polymerase gene (wzy), the benefit over 16S rRNA gene sequence

Molecular typing of leptospiral strains based on variation within putative O-antigen polymerase gene (wzy) was determined among reference strains and those isolated from patients. Using the PCR primers designed from the flanking gene of wzy derived from Leptospira interrogans serovar Copenhageni, all L. interrogans serovars as well as human and rodent leptospiral isolates from Thailand could be amplified. The size of PCR product ranged from 1 to 1.5 kb. The limitation of these primer pairs was the inability to amplify those strains whose sequences differ in the region of the primers, these included Leptospira biflexa (serovar Patoc), Leptospira borgpetersenii (serovar Tarassovi) and Leptospira kirschneri (serovar Bim, Bulgarica, Butembo). Notably, amplification was not limited to L. interrogans as demonstrated by the amplification of some strains from L. kirschneri, Leptospira meyeri, Leptospira noguchii, Leptospira santarosai, L. borgpetersenii and Leptospira weilii. The phylogenetic tree of wzy sequence, inferred by posterior probability of the Bayesian, enabled the categorization of leptospiral serovars into seven genetically related group, of which its differentiation power was better than that of the more highly conserved 16S rRNA gene, which is used extensively for genotyping.

Optimization of culture of Leptospira from humans with leptospirosis

A prospective study of 989 patients with acute febrile illness was performed in northeast Thailand to define the yield of Leptospira from four different types of blood sample. Based on a comparison of the yields from whole blood, surface plasma, deposit from spun plasma, and clotted blood samples from 80 patients with culture-proven leptospirosis, we suggest a sampling strategy in which culture is performed using whole blood and deposit from spun plasma.

The epidemiology of leptospirosis and the emergence of Leptospira borgpetersenii serovar Arborea in Queensland, Australia, 1998-2004

Leptospirosis is one of the most commonly encountered zoonoses in both Australia and the rest of the world. The incidence of leptospirosis in Queensland over the 7-year study period (1998-2004) was 3.1/100000 population. Enhanced surveillance questionnaires were used to collect patient data and facilitate an epidemiological investigation of leptospirosis in Queensland. Farming occupations comprised the majority of occupational exposure cases, however, recreational exposure accounted for 18% of the 883 cases. Rainfall and the presence of animal hosts had the most influence on the incidence of leptospirosis. Several trends in serovar numbers over this period are noted, in particular the emergence of L. borgpetersenii serovar Arborea, which accounted for 22% of all leptospirosis cases in Australia and 68% of South-East Queensland cases in 2004. Assessment of epidemiological trends in leptospirosis is important to obtain directed public health intervention and outcomes in the reduction of leptospirosis cases.

Identification of pathogenic Leptospira species by conventional or real-time PCR and sequencing of the DNA gyrase subunit B encoding gene

Background

Leptospira is the causative genus of the disease, leptospirosis. Species identification of pathogenic Leptospira in the past was generally performed by either DNA-DNA hybridisation or 16s rRNA gene sequencing. Both methods have inherent disadvantages such as the need for radio-labelled isotopes or significant homology between species. A conventional and real-time PCR amplification and sequencing method was developed for an alternate gene target: DNA gyrase subunit B (gyrB). Phylogenetic comparisons were undertaken between pathogenic Leptospira 16srRNA and gyrB genes using clustering and minimum evolution analysis. In addition 50 unidentified Leptospira isolates were characterised by gyrB sequencing and compared with conventional 16s rRNA sequencing.

Results

A conventional and real-time PCR methodology was developed and optimised for the amplification of the gyrB from pathogenic Leptospira species. Non pathogenic and opportunistic Leptospira species such as L. fainei and L. broomi were not amplified. The gyrB gene shows greater nucleotide divergence (3.5% to 16.1%) than the 16s rRNA gene (0.1% to 1.4%). Minimum evolution analysis reveals that the gyrB has a different evolution topology for L. kirschneri and L. interrogans. When the two genes were compared for the identification of the 50 unknown isolates there was 100% agreement in the results.

Conclusion

This research has successfully developed a methodology for the identification of pathogenic Leptospira using an alternate gene to 16s rRNA. The gyrB encoding gene shows higher nucleotide/evolutionary divergence allowing for superior identification and also the potential for the development of DNA probe based identification.

Flying foxes as carriers of pathogenic Leptospira species

Recent serologic studies have identified flying foxes (Pteropus spp.) as carriers of leptospirosis; however, little is known about the role of flying foxes as carriers of pathogenic Leptospira spp. To determine if Australian Pteropus spp. are carriers of pathogenic Leptospira spp., TaqMan real-time polymerase chain reaction (PCR) was used to detect leptospiral DNA in kidney and urine specimens from four species of flying fox, including the spectacled flying fox (Pteropus conspicillatus), black flying fox (Pteropus alecto), grey-headed flying fox (Pteropus poliocephalus), and little red flying fox (Pteropus scapulatus). Of the 173 kidney samples tested, 19 (11%) were positive for leptospiral DNA. Positive individuals were detected in all four species; significant differences in prevalence were not detected between species, between species within the same geographic area, or between geographically separated samples from the same species. Of the 46 urine samples tested, 18 (39%) tested positive by PCR, confirming that flying foxes shed leptospires into the environment. The detection of leptospiral DNA in the kidneys and urine of flying foxes suggests that flying foxes are carriers of pathogenic Leptospira spp. No evidence collected in the present study, however, suggests that flying foxes pose a significant risk of leptospirosis to the wider community or that humans who are in regular, close contact with flying foxes are at risk for leptospirosis.

Development of a Multiple-Locus Variable Number of Tandem Repeat Analysis (MLVA) for Leptospira interrogans and its application to Leptospira interrogans serovar Australis isolates from Far North Queensland, Australia

Background

Leptospirosis is a zoonotic disease caused by the genus, Leptospira. Leptospira interrogans is the most common genomospecies implicated in the disease. Epidemiological investigations are needed to distinguish outbreak situations or to trace reservoirs of the organisms. Current methodologies used for typing Leptospira have significant drawbacks. The development of an easy to perform yet high resolution method is needed for this organism.

Methods

In this study we have searched the available genomic sequence of L. interrogans serovar Copenhageni strain Fiocruz L1-130 for the presence of tandem repeats [1]. These repeats were evaluated against reference strains for diversity. Six loci were selected to create a Multiple Locus Variable Number of Tandem Repeats (VNTR) Analysis (MLVA) to explore the genetic diversity within L. interrogans serovar Australis clinical isolates from Far North Queensland.

Results

The 39 reference strains used for the development of the method displayed 39 distinct patterns. Diversity Indexes for the loci varied between 0.80 and 0.93 and the number of repeat units at each locus varied between less than one to 52 repeats. When the MLVA was applied to serovar Australis isolates three large clusters were distinguishable, each comprising various hosts including Rattus species, human and canines.

Conclusion

The MLVA described in this report, was easy to perform, analyse and was reproducible. The loci selected had high diversity allowing discrimination between serovars and also between strains within a serovar. This method provides a starting point on which improvements to the method and comparisons to other techniques can be made.

A quantitative PCR (TaqMan) assay for pathogenic Leptospira spp

BACKGROUND

Leptospirosis is an emerging infectious disease. The differential diagnosis of leptospirosis is difficult due to the varied and often "flu like" symptoms which may result in a missed or delayed diagnosis. There are over 230 known serovars in the genus Leptospira. Confirmatory serological diagnosis of leptospirosis is usually made using the microscopic agglutination test (MAT) which relies on the use of live cultures as the source of antigen, often performed using a panel of antigens representative of local serovars. Other techniques, such as the enzyme linked immunosorbent assay (ELISA) and slide agglutination test (SAT), can detect different classes of antibody but may be subject to false positive reactions and require confirmation of these results by the MAT.

METHODS

The polymerase chain reaction (PCR) has been used to detect a large number of microorganisms, including those of clinical significance. The sensitivity of PCR often precludes the need for isolation and culture, thus making it ideal for the rapid detection of organisms involved in acute infections. We employed real-time (quantitative) PCR using TaqMan chemistry to detect leptospires in clinical and environmental samples.

RESULTS AND CONCLUSIONS

The PCR assay can be applied to either blood or urine samples and does not rely on the isolation and culture of the organism. Capability exists for automation and high throughput testing in a clinical laboratory. It is specific for Leptospira and may discriminate pathogenic and non-pathogenic species. The limit of detection is as low as two cells.

Leptospiral antibodies in flying foxes in Australia

The sera of 271 pteropid bats (or flying foxes) collected from Queensland, New South Wales, Western Australia, and the Northern Territory were screened against a reference panel of 21 Leptospira spp. using the microscopic agglutination test (MAT). Sera were collected from December 1997 through August 1999. The MAT panel represented those serovars previously isolated in Australia, as well as exotic serovars found in neighboring countries. Leptospiral antibodies were detected in 75 (28%) of the sera and represented seven serovars, one of which, L. interrogans serovar cynopteri has been regarded as exotic to Australia. Sixty sera were reactive to one serovar, 12 sera were reactive to two serovars, and three sera were reactive to three serovars. The L. kirschneri serovar australis was most frequently identified (60.2%). The findings suggest a previously unrecognized role of pteropid bats in the natural history of leptospirosis. The potential exists for establishment of infection in new host species, the transmission of new serovars to known host species, and for changes in virulence of leptospires as a result of passage through these species.

Prevalence of antibodies of Leptospira serovars in beef cattle in central Queensland

OBJECTIVE

To obtain up-to-date data on the prevalence of antibodies to Leptospira serovars in central Queensland beef herds preliminary to assessing their role in bovine subfertility and the role of cattle as a zoonotic reservoir.

DESIGN

Sera from 2857 female cattle in 68 central Queensland beef herds were tested for antibodies to 14 Leptospira serovars using the microscopic agglutination test. Vaccination use and age of cattle were collected to enable the calculation of crude and age-stratified seroprevalences.

RESULTS

The most commonly detected antibodies were to serovars hardjo (15.8% crude seroprevalence), tarassovi (13.9%), pomona (4.0%) and szwajizak (2.2%). Vaccinates were omitted from the hardjo and pomona seroprevalence data. The seroprevalence for hardjo and pomona tended to increase with age of the animals.

CONCLUSION

These results are broadly similar to those of previous serological surveys. The data suggest that serovars other than hardjo, pomona and tarassovi, are unlikely to have a significant role in bovine subfertility and that cattle are unlikely to be a source of human infection with them in central Queensland.

Reservoir hosts of Leptospira inadai in India

Isolation of Leptospira from the kidneys of Rattus rattus wroughtoni hinton, Rattus rattus rufescens, Bandicota bengalensis and Bandicota indica was attempted in Bangalore in southern India. In total, 296 spirochaetes were isolated from 1,348 kidney cultures (an isolation rate of 22%). A batch of fifty-six isolates from India was identified, based on serological and polymerase chain reaction analysis, of which twenty-three isolates were identified as L. inadai by the World Health Organization/Food and Agriculture Organization Collaborating Centre for Reference and Research on Leptospirosis, in Brisbane. This is the first record of isolation of L. inadai from rodents. The preponderance of L. inadai in four different species of rodents suggests that these animals could be the natural reservoir hosts of L. inadai, and raises a critical question as to the likely impact of this species of Leptospira on the renal carrier status of other Leptospira pathogenic to humans and animals in this part of India. Virulence studies conducted at the University of Trieste in Italy, revealed that isolates of L. inadai from India were moderately or totally serum resistant when subjected to a serum killing test. To establish the possible seroprevalence of this species in the population, the inclusion of L. inadai in the battery of leptospiral antigens used for sero-epidemiological studies is recommended.

Lai-like leptospira from the Andaman Islands

BACKGROUND & OBJECTIVES

Leptospirosis has been an important public health problem in the Andaman Islands since 1988. As information about the exact etiological agent is not available, the present study was undertaken to isolate and identify Leptospira from human patients.

METHODS

An isolate coded AF61 was recovered from the blood of a patient clinically suspected to have leptospirosis, with fever, headache and body aches as the main symptoms. The isolation was done using Ellinghausen-McCullough-Johnson-Harris (EMJH) medium following standard procedure. The isolate was identified using microscopic agglutination test (MAT) with 'groupsera', cross agglutination absorption test (CAAT) and monoclonal antibodies.

RESULTS

Agglutination tests with rabbit antisera revealed that the isolate belonged to the serogroup icterohaemorrhagiae. The CAAT results showed that it was closely related to the serovar lai. Analysis of AF61 with monoclonal antibodies confirms our observation with CAAT that it is closely related to the reference strain Lai serovar lai.

INTERPRETATION & CONCLUSIONS

Serovar lai, has been associated with pulmonary haemorrhage in China and Korea. However, the strain AF61 was not isolated from a patient with pulmonary symptoms. Further studies are needed to understand the possible relationship between serovars and clinical patterns and the distribution of serovar lai and lai-like strains in Asia.

Leptospira autumnalis isolated from a human case from Avadi, India, and the serovar's predominance in local rat and bandicoot populations

Leptospira were successfully isolated from the urine of an Indian patient who had been clinically diagnosed as having leptospirosis. In an attempt to determine the source of this infection, 28 rats (Rattus rattus) and 58 bandicoots (Bandicota bengalensis) living in the vicinity of the patient's home in Avadi, a suburban area of the city of Chennai (Madras), India, were then investigated. Each animal was checked for infection by microscopical examination of fresh and stained urine, serological analysis of serum, and the culture of urine and kidney samples. Direct, dark-field, observation of fresh urine samples and examination of urine samples after Fontana's silver staining were found to be the least sensitive of the tests used. The results of the serological microscopic agglutination test (MAT) indicated that four (14.3%) of the rats and nine (16.1%) of the bandicoots had significant agglutinins, predominantly for the serogroups icterohaemorrhagiae and autumnalis. Leptospira were isolated from at least one culture of samples from one rat and each of four bandicoots. Each of these rodent isolates and the human isolate were typed as Leptospira interrogans serovar autumnalis.

Identification of Leptospira biflexa by real-time homogeneous detection of rapid cycle PCR product

Sequence analysis of 16S rRNA genes extracted from nucleic acids databases enabled the identification of a Leptospira biflexa (L. biflexa) signature sequence, against which a reverse primer designated L613, was designed. This primer, when used in conjunction with a universal bacterial specific forward primer designated Fd1, enabled the development of a LightCycler-based PCR protocol in which fluorescence emission due to binding of SYBR Green I dye to amplified products could be detected and monitored. A melting temperature (Tm), determined from the melting curve of the amplified product immediately following the termination of thermal cycling, confirmed that the product was that of L. biflexa. Agarose gel electrophoresis therefore was not necessary for identification of PCR products. The PCR protocol was very rapid, and consisted of 30 cycles with a duration of 20 s for each cycle with the monitoring of the melting curve requiring an additional 3 min. The whole protocol was completed in less than 20 min. The PCR protocol was also specific and enabled the identification of 18 strains of L. biflexa, whilst excluding 14 strains of L. interrogans and Leptonema illini. Two examples of its utility in improving work flow of a Leptospira reference laboratory are presented in this article. The use of a simple boiling method for extraction of DNA from all the members of the Leptospiraceae family DNA further simplifies the procedure and makes its use conducive to diagnostic laboratories.

Leptospira interrogans antibodies in feral pigs from New South Wales

The sera of 195 hunter-killed feral pigs (Sus scrofa), collected in New South Wales (Australia) from April to November 1995, were screened against a reference panel of 14 Leptospira interrogans serovars using a microscopic agglutination test (MAT). The panel represented those serovars previously isolated from wild and domestic mammals in mainland Australia. Antileptospiral agglutinins were detected in 20% of the sera tested and included nine L. interrogans serovars. The majority of serological reactors (63%) were to L. interrogans serovar pomona. Sera from 26% of immunoreactors cross reacted with antigens from one or more serovars. No differences were noted in the prevalence of L. interrogans antibodies between the sexes, or between pigs from areas of low and high rainfall. The implications of leptospirosis in feral pigs on the transmission of leptospires to wildlife, livestock, and humans are discussed.

Real-time homogeneous assay of rapid cycle polymerase chain reaction product for identification of Leptonema illini

Partial 16S rDNA sequences of eight Leptospira-like field isolates that reacted weakly or not at all to microscope agglutination test were found to be similar to the 16S rDNA sequence of the nonpathogen Leptonema illini-type strain 3055. Comparison of these sequences with those of Leptospira 16S rDNA sequences revealed a Leptonema species signature sequence for which a forward amplification primer was designed. This primer was used in conjunction with a bacterial-specific 16S rDNA universal reverse primer for developing a LightCycler-based rapid PCR protocol in which fluorescence emission due to the binding of SYBR green I dye to the amplified products was continuously monitored. A melting temperature (T(m)) determined from the melting curve of the amplified product immediately after PCR confirmed that the product was of Leptonema. The protocol for 24 samples consisting of 30 PCR cycles and melting curve acquisitions required 30 min to complete and agarose gel electrophoresis of the PCR products was not necessary. The method was specific as PCR products were detected from the seven Leptonema reference strains and the eight field isolates that had been previously verified as Leptonema by 16S rDNA sequencing, but not from the two representative strains from each of the eight Leptospira genospecies tested.