Latex based, rapid and easy assay for human leptospirosis in a single test format

Evaluation of the diagnostic potential of recombinant leptospiral OMP A-like protein (Loa22) and transmembrane (OmpL37) protein in latex agglutination test for serodiagnosis of leptospirosis in animals

Leptospirosis is a re-emerging zoonotic disease of animals and humans caused by pathogenic Leptospira, which has major public health concerns. The study is aimed to express the recombinant outer membrane protein (OMP) A-like protein (rLoa22) and transmembrane (rOmpL37) protein of Leptospira interrogans serovar Hardjo in the Escherichia coli and their evaluation as a diagnostic antigen in the latex agglutination test (LAT) to detect anti-leptospiral antibodies in the sera of animals. The Loa22 and OmpL37 genes lacking signal peptide coding sequences were individually amplified (522 and 963 bp), by polymerase chain reaction, and directionally cloned into a pETite N-His Kan vector for expression. The expressed purified proteins were characterized by sodium dodecyl sulphate-polyacrylamide gel electrophoresis and immunoblot, which confirmed leptospiral specific reactive protein with a molecular weight of ~19 and 36 kDa, respectively. The sensitized latex beads coated with these OM proteins separately were evaluated in LAT using cattle sera of microscopic agglutination test (MAT) confirmed positive (n = 53) and negative (n = 52) cases of leptospirosis. The rLoa22 LAT and rOmpL37 LAT revealed the relative diagnostic sensitivity of 94·34 and 96·23%, diagnostic specificity of 92·31 and 96·15% and accuracy of 93·33 and 96·19%, with the excellent agreement of Cohen's kappa value of 0·87 and 0·92, respectively. After extensive evaluation, this rapid recombinant protein-based field diagnostic test can be applied as a screening test for the detection of anti-leptospiral antibodies in the sera of animals in the field conditions.

Evaluation of recombinant leptospiral surface antigen (Lsa27) lipoprotein for serodiagnosis of human leptospirosis by latex agglutination test

PURPOSE

Leptospirosis has wide clinical presentations often mimicking other illnesses, thus rapid and simple diagnostics will have facilitated the initial patient management and therapy compared to other inaccessible and laborious tests/assays.

METHOD

In this study, the sensitized latex beads coated with purified recombinant outer membrane (OM)-leptospiral surface antigen (Lsa27) lipoprotein of pathogenic Leptospira was evaluated as a diagnostic antigen in latex agglutination test (LAT) for the detection of anti-leptospiral antibodies in the human sera. The prepared rLsa27 latex beads were evaluated with the confirmed microscopic agglutination test (MAT) reactive (at 1:50) Leptospira-specific positive (n = 42) and non-reactive negative (n = 80) sera from human cases suspected of leptospirosis with the history of pyrexia of unknown origin.

RESULT

The results revealed the relative diagnostic sensitivity of 90.48 % (confidence interval (CI) at 95 % : 77.4-97.3 %) and diagnostic specificity of 91.35 % (CI at 95 %: 82.8-96.4 %), with an accuracy of 90.98 % (CI at 95 %: 84.44-95.41 %), and the kappa value of 0.8036 ± 0.056 SE (CI at 95 %: 0.69-0.91) with a substantial agreement against gold standard serological MAT.

CONCLUSION

The findings suggest that the rLsa27 protein-based LAT can be useful as a simple rapid screening diagnostic test for the detection of anti-leptospiral antibodies in the sera of humans. This rapid test can be complemented by other confirmatory diagnostics for the early detection of Leptospira antibodies which may in turn help in the prompt treatment and mitigates the public health problem at primary health care level.

Expression of Recombinant Leptospiral Surface Lipoprotein-Lsa27 in E. coli and Its Evaluation for Serodiagnosis of Bovine Leptospirosis by Latex Agglutination Test

The expressed recombinant leptospiral surface adhesion lipoprotein (Lsa27) of pathogenic Leptospira in E. coli was evaluated for the detection of Leptospira antibodies in cattle sera by latex agglutination test (LAT). The Lsa27 lacking signal peptide coding gene sequences from L. interrogans serovar Pomona was amplified (~ 660 bp) by PCR and the amplicon was cloned into pETiteN-HisKan vector. The expressed recombinant Lsa27 histidine-tagged fusion protein (rLsa27) was Ni-NTA affinity purified under denaturation followed by renaturation methods. The purified rLsa27 was characterized by SDS-PAGE and immunoblot, which confirmed the leptospiral protein with a MW of ~ 25 kDa. Further, the prepared sensitized latex beads coated with rLsa27 were evaluated as a diagnostic antigen for detection of pathogenic Leptospira antibodies by using known microscopic agglutination test (MAT) positive (n = 74) and negative (n = 62) sera for Leptospira antibodies in LAT, which revealed the relative diagnostic sensitivity of 91.89% and specificity of 87.10% against the gold standard serological test, MAT. Furthermore, on evaluation of developed rLsa27 LAT using serum samples from cattle associated with the history of abortions and reproductive disorder (n = 309), the relative sensitivity of 96.15%, and specificity of 89.11% were observed. Therefore, this rapid field test using the rLsa27 is first of its kind and it could be used as a screening test for the detection of Leptospira antibodies or it can be complemented by other diagnostics for the diagnosis /surveillance of bovine leptospirosis.

IgM ELISA for leptospirosis diagnosis: a systematic review and meta-analysis

Abstract A systematic review with meta-analysis was performed to estimate the accuracy of IgM ELISA for Leptospirosis diagnosis. A search of Medline, Lilacs, Embase, Cochrane Central Register of Controlled Trials and Grey literature (Google Scholar and British Library) was conducted. The medical subject headings (MeSHs) and the words “leptospirosis”, “human leptospirosis” and “IgM ELISA” were used. Fifty-two studies were analyzed, which included 10,775 samples. The pooled sensitivity of all the studies was 86% (CI 95%, 85%-87%) and specificity was 90% (CI 95%, 89%-91%). In studies of the acute phase, the sensitivity and specificity were 84% (CI 95%, 82%-85%) and 91% (CI 95%, 90%-91%), respectively. In conclusion, IgM ELISA is sensitive for use as an initial screen for leptospiral infections.

Diagnosis of toxoplasmosis in pregnancy. Evaluation of latex–protein complexes by immnunoagglutination

The aim of this work was to obtain a reagent based on latex particles for ruling out acute toxoplasmosis in pregnant women by immunoagglutination (IA). Latex–protein complexes (LPC) were previously synthesized coupling the recombinant protein ofToxoplasma gondiiP22Ag and the homogenate of the parasite to latex particles with different size, chemical functionality and charge density. LPC were tested in IA assays against a panel of 72 pregnant women serum samples. Results were analysed through receiver operating characteristic curves, determining area under the curve (AUC), sensitivity, specificity positive and negative predictive values (PPV and NPV, respectively). It was observed that the antigenicity of proteins was not affected during sensitization by either physical adsorption or covalent coupling. The best results in the sense of maximizing discrimination of low avidity sera from chronic ones were observed for the IA test based on latex particles with carboxyl functionality and the recombinant P22Ag, obtaining an AUC of 0·94, a sensitivity of 100% and a NPV of 100%. In this way, the proposed test could be useful for the toxoplasmosis diagnosis in pregnant women, with the advantages of being cheap, rapid and easy to be implemented.

Liposome-Enhanced Lateral-Flow Assays for Clinical Analyses

Clinical and environmental analyses frequently necessitate rapid, simple, and inexpensive point-of-care or field tests. These semiquantitative tests may be later followed up by confirmatory laboratory-based assays, but provide an initial scenario assessment important for resource mobilization and threat confinement. Lateral-flow assays (LFAs) and dip-stick assays, which are typically antibody-based and yield a visually detectable signal, provide an assay format suiting these applications extremely well. Signal generation is commonly obtained through the use of colloidal gold or latex beads, which yield a colored band either directly proportional or inversely proportional to the concentration of the analyte of interest. Here, dye-encapsulating liposomes as a highly visible alternative are discussed. The semiquantitative LFA biosensor described in this chapter relies on a sandwich immunoassay for the detection of myoglobin in whole blood. After an acute myocardial infarction (AMI) event, several cardiac markers are released into the blood, the most common of which are troponin, creatine kinase MB, C-reactive protein, and myoglobin. Due to its early release, myoglobin has value as an indicator of a recent heart attack amongst conditions which present with similar symptoms and its lack of elevation can effectively rule out a heart attack (Brogan et al., Ann Emerg Med 24:665-671, 1994). The assay described within relies on sandwich complex formation between a membrane immobilized capture monoclonal antibody against myoglobin, a detector biotinylated monoclonal antibody against a different epitope on myoglobin, and streptavidin-conjugated visible dye (sulforhodamine B)-encapsulating liposomes to allow for signal generation.

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.

Leptospirosis in humans

Leptospirosis is a widespread and potentially fatal zoonosis that is endemic in many tropical regions and causes large epidemics after heavy rainfall and flooding. Infection results from direct or indirect exposure to infected reservoir host animals that carry the pathogen in their renal tubules and shed pathogenic leptospires in their urine. Although many wild and domestic animals can serve as reservoir hosts, the brown rat (Rattus norvegicus) is the most important source of human infections. Individuals living in urban slum environments characterized by inadequate sanitation and poor housing are at high risk of rat exposure and leptospirosis. The global burden of leptospirosis is expected to rise with demographic shifts that favor increases in the number of urban poor in tropical regions subject to worsening storms and urban flooding due to climate change. Data emerging from prospective surveillance studies suggest that most human leptospiral infections in endemic areas are mild or asymptomatic. Development of more severe outcomes likely depends on three factors: epidemiological conditions, host susceptibility, and pathogen virulence (Fig. 1). Mortality increases with age, particularly in patients older than 60 years of age. High levels of bacteremia are associated with poor clinical outcomes and, based on animal model and in vitro studies, are related in part to poor recognition of leptospiral LPS by human TLR4. Patients with severe leptospirosis experience a cytokine storm characterized by high levels of IL-6, TNF-alpha, and IL-10. Patients with the HLA DQ6 allele are at higher risk of disease, suggesting a role for lymphocyte stimulation by a leptospiral superantigen. Leptospirosis typically presents as a nonspecific, acute febrile illness characterized by fever, myalgia, and headache and may be confused with other entities such as influenza and dengue fever. Newer diagnostic methods facilitate early diagnosis and antibiotic treatment. Patients progressing to multisystem organ failure have widespread hematogenous dissemination of pathogens. Nonoliguric (high output) renal dysfunction should be supported with fluids and electrolytes. When oliguric renal failure occurs, prompt initiation of dialysis can be life saving. Elevated bilirubin levels are due to hepatocellular damage and disruption of intercellular junctions between hepatocytes, resulting in leaking of bilirubin out of bile caniliculi. Hemorrhagic complications are common and are associated with coagulation abnormalities. Severe pulmonary hemorrhage syndrome due to extensive alveolar hemorrhage has a fatality rate of >50 %. Readers are referred to earlier, excellent summaries related to this subject (Adler and de la Peña-Moctezuma 2010; Bharti et al. 2003; Hartskeerl et al. 2011; Ko et al. 2009; Levett 2001; McBride et al. 2005).

Rapid serological assays for leptospirosis are of limited value in southern Vietnam

Leptospirosis, although ubiquitous and potentially lethal, is often not diagnosed. The seroprevalence of anti-Leptospira antibodies and the utility of two rapid tests for the serodiagnosis of the disease were studied in Binh Thuan, an area in southern Vietnam with favourable conditions for Leptospira. In an initial survey, blood samples from 44 patients with undifferentiated fever and 83 healthy subjects were each examined for anti- Leptospira antibodies using three tests: an ELISA; a latex card-agglutination test (Dri Dot); and a lateral-flow assay (LeptoTek Lateral Flow). In the ELISA, samples from 35% of the healthy subjects and 40% of the febrile patients were found to have titres of anti- Leptospira IgM of at least 1:80. Only one of the 13 patients checked again, in ELISA, 3 weeks later, showed the marked increase in IgM titre that is indicative of acute leptospirosis. In the initial survey, although the positive results of the lateral-flow assay, applied to whole blood and serum, showed a good agreement with those of the ELISA (kappa = 0.743), the results of the lateral-flow assay were often indeterminate. The card-agglutination test was more specific. The overall agreement between the results of the rapid tests and those of the ELISA was generally poor. When the samples classified as 'indeterminate' in the lateral-flow assay were considered positive, the maximum kappa-value for this assay applied to whole blood was only 0.512. In conclusion, it appears that high seroprevalences of anti- Leptospira IgM and low incidences of acute leptospirosis limit the diagnostic value of the rapid tests that were investigated. The lateral-flow assay is not specific enough. The card-agglutination test is possibly better but, because of the low incidence, its sensitivity could not be evaluated adequately in the present study.

Enzyme-linked immunosorbent assay to diagnose human leptospirosis: a meta-analysis of the published literature

We report an evaluation of the accuracy of ELISA for the detection of Leptospira-specific antibodies in humans. Eighty-eight studies published in 35 articles met all inclusion criteria and were submitted to meta-analysis. Pooled sensitivity and specificity were 0·779 (95% CI 0·770-0·789) and 0·913 (95% CI 0·908-0·917), respectively, and the area under the curve was 0·964. Heterogeneity across studies was statistically significant, but none of the sources of heterogeneity (disease stage, antigen used, antibody detected) could fully explain this finding. Although the convalescent stage of disease was significantly associated with higher diagnostic accuracy, IgM ELISA was the best choice, regardless of the stage of disease. Negative ELISAs (IgG or IgM) applied in the acute phase do not rule out leptospirosis due to the possibility of false-negative results. In this case it is advisable to request a second blood sample or to apply a direct method for leptospiral DNA.

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.

Development of transcriptional fusions to assess Leptospira interrogans promoter activity

Background

Leptospirosis is a zoonotic infectious disease that affects both humans and animals. The existing genetic tools for Leptospira spp. have improved our understanding of the biology of this spirochete as well as the interaction of pathogenic leptospires with the mammalian host. However, new tools are necessary to provide novel and useful information to the field.

Methodology and Principal Findings

A series of promoter-probe vectors carrying a reporter gene encoding green fluorescent protein (GFP) were constructed for use in L. biflexa. They were tested by constructing transcriptional fusions between the lipL41, Leptospiral Immunoglobulin-like A (ligA) and Sphingomielynase 2 (sph2) promoters from L. interrogans and the reporter gene. ligA and sph2 promoters were the most active, in comparison to the lipL41 promoter and the non-induced controls. The results obtained are in agreement with LigA expression from the L. interrogans Fiocruz L1-130 strain.

Conclusions

The novel vectors facilitated the in vitro evaluation of L. interrogans promoter activity under defined growth conditions which simulate the mammalian host environment. The fluorescence and rt-PCR data obtained closely reflected transcriptional regulation of the promoters, thus demonstrating the suitability of these vectors for assessing promoter activity in L. biflexa.

Liposome-enhanced lateral-flow assays for the sandwich-hybridization detection of RNA

Clinical and environmental analyses frequently necessitate rapid, simple, and inexpensive point-of-care or field tests. These semiquantitative tests may be later followed up by confirmatory laboratory-based assays, but can provide an initial scenario assessment important for resource mobilization and threat confinement. Lateral-flow assays (LFAs) and dip-stick assays, which are typically antibody-based and yield a visually detectable signal, provide an assay format suiting these applications extremely well. Signal generation is commonly obtained through the use of colloidal gold or latex beads, which yield a colored band either directly proportional or inversely proportional to the concentration of the analyte of interest. Here, dye-encapsulating liposomes as an alternative are discussed. The LFA biosensors described in this chapter rely on the sandwich-hybridization of a nucleic acid sequence-based amplified (NASBA) mRNA target between a membrane immobilized capture probe and a visible dye (sulforhodamine B)-encapsulating liposome conjugated reporter probe. Although the methodology of this chapter is focused on LFAs for the detection of RNA through sandwich hybridization, the information within can be readily adapted for sandwich and competitive immunoassays. Included are an introduction and application notes toward this end. These include notes ranging from the detection of nonamplified RNA and single-stranded DNA, conjugation protocols for antibodies and other proteins to liposomes, and universal assay formats.

Laboratory evaluation of a simple and rapid latex agglutination assay for the serodiagnosis of typhoid fever

A latex agglutination assay for the serodiagnosis of typhoid fever was evaluated on samples collected from patients with clinical suspicion of typhoid fever in South Sulawesi, Indonesia, where the disease is endemic. The latex assay is very easy to use, gives a rapid result and may be used as a point-of-care diagnostic test. For acute phase samples collected on average 6 days after the onset of illness, the sensitivity is 42.5% for culture-confirmed patients with typhoid fever and the specificity is 96.9%. The sensitivity improved with the duration of illness from 30.8% for samples collected during the first 4-5 days of illness to 45.5% for samples collected between days 7 and 9, and to 84.6% for the samples collected more than 9 days after the onset of illness. Testing of follow-up samples may further improve sensitivity by demonstrating seroconversion.

Identification of a novel potential antigen for early-phase serodiagnosis of leptospirosis

This study examined four genes encoding for predicted membrane proteins selected from the genome sequences of Leptospira interrogans. Genes were cloned and the proteins expressed in E. coli. Immunoblotting analysis of the recombinants with sera from early and convalescent phases of a leptospirosis patient showed that two proteins, namely Lp29 and Lp49, were reactive with serum from both phases of the illness. These data were further confirmed in enzyme-linked immunosorbent assay using sera from both phases of seventeen confirmed leptospirosis specimens, suggesting that these proteins are presented to the host immune system during infection. In the early phase, anti-Lp29 IgM was detected in all sera when microscopic agglutination tests (MAT), the reference method for diagnosis of leptospirosis, were negative. The gene encoding Lp49 is conserved among five tested leptospiral pathogenic serovars, while Lp29 is present in serovars that are predominant in urban settings. These recombinant antigens might be valuable for serodiagnosis of both phases of leptospirosis.

Rapid latex agglutination test for the serodiagnosis of human brucellosis

We developed and evaluated a user-friendly latex agglutination assay for the serodiagnosis of human brucellosis. The assay was obtained by coating colored latex beads with Brucella lipopolysaccharides and drying of the activated beads onto white agglutination cards. Individual cards were sealed in a protective foil to secure stability of the dried reagent and to obtain a test in a single assay format. The latex agglutination assay is simply performed by suspending the dried latex reagent in a drop of serum and looking for macroscopic agglutination of the latex beads by visual inspection. Results are obtained within 30 s after mixing the sample with the test reagent. The sensitivity of the assay was determined to be 89.1% (95% confidence interval [CI], 76-96) for the initial serum samples collected from patients with culture-confirmed brucellosis and the specificity is 98.2% (95% CI, 96-99). The assay is ideal for use as a field test in remote areas and as point-of-care test in hospitals and health care centers that lack the expertise and facilities to perform the more demanding classic serologic tests.

Evaluation of the EIE-IgM-Leptospirose assay for the serodiagnosis of leptospirosis

Access to low-cost, effective diagnosis for leptospirosis is urgently needed in developing countries. The EIE-IgM-Leptospirose, a kit produced for public health laboratories in Brazil, was shown to have a sensitivity of 76% (77 of 102 patients) and 100% (102 of 102 patients) during acute and convalescent-phase leptospirosis, respectively, and a specificity of 93-100% (total healthy and patient control subjects evaluated, 486). These findings indicate that the assay will be useful for diagnosis of this emerging infectious disease in Brazil and other developing countries.

Rapid diagnostic tests for dengue and leptospirosis: antibody detection is insensitive at presentation

OBJECTIVE

To determine the performance of rapid diagnostic tests for dengue and leptospirosis that rely on detecting antibodies that may not be produced when patients present for medical treatment.

METHODS

We prospectively enrolled 723 patients with undifferentiated febrile illness presenting to rural hospitals in northern and northeastern Thailand over a 1-year period. We evaluated rapid antibody detection diagnostic tests for dengue and leptospirosis on these patients.

RESULTS

Sensitivity of the tests was low at the acute visit (7.6-21.5%). Sensitivity at the convalescent visit ranged from 25.8% to 81.5% and was significantly higher than at the acute visit for all tests (chi(2), P < 0.001).

CONCLUSIONS

Low sensitivity of the rapid tests at presentation suggests that their utility in the acute phase of dengue and leptospirosis is limited.

Leptospira immunoglobulin-like proteins as a serodiagnostic marker for acute leptospirosis

There is an urgent need for improved diagnosis of leptospirosis, an emerging infectious disease which imparts a large disease burden in developing countries. We evaluated the use of Leptospira immunoglobulin (Ig)-like (Lig) proteins as a serodiagnostic marker for leptospirosis. Lig proteins have bacterial immunoglobulin-like (Big) tandem repeat domains, a moiety found in virulence factors in other pathogens. Sera from patients identified during urban outbreaks in Brazil reacted strongly with immunoblots of a recombinant fragment comprised of the second to sixth Big domains of LigB from L. interrogans serovar Copenhageni, the principal agent for transmission in this setting. Furthermore, the sera recognized an analogous LigB fragment derived from L. kirschneri serovar Grippotyphosa, a pathogenic serovar which is not endemic to the study area. The immunoblot assay detected anti-LigB IgM antibodies in sera from 92% (95% confidence interval, 85 to 96%) of patients during acute-phase leptospirosis. The assay had a sensitivity of 81% for sera from patients with less than 7 days of illness. Anti-LigB antibodies were found in sera from 57% of the patients who did not have detectable anti-whole-Leptospira responses as detected by IgM enzyme-linked immunosorbent assay and microagglutination test. The specificities of the assay were 93 to 100% and 90 to 97% among sera from healthy individuals and patients with diseases that have clinical presentations that overlap with those of leptospirosis, respectively. These findings indicate that the antibody response to this putative virulence determinant is a sensitive and specific marker for acute infection. The use of this marker may aid the prompt and timely diagnosis required to reduce the high mortality associated with severe forms of the disease.

Leptospirosis in the tropics and in travelers

Leptospirosis, caused by spirochetes of the genus Leptospira, has increasingly been recognized to affect travelers and residents in tropical settings. A zoonotic disease, leptospirosis is transmitted to humans through environmental surface waters contaminated by the urine of chronically infected mammals. Outcome of infection varies, ranging from acute febrile illness (including self-resolving undifferentiated fever) to aseptic meningitis to a fulminant syndrome of jaundice, oliguric renal failure, pulmonary hemorrhage, and refractory shock. Hospitalized cases have mortality rates as high as 25%. A recent clinical trial showed that third-generation cephalosporin is as effective as doxycycline and penicillin in the treatment of acute disease. Doxycycline is effective in preventing leptospirosis in travelers. No protective vaccine is currently available.

Leptospirosis

PURPOSE OF REVIEW

Leptospirosis, a spirochaetal zoonotic disease, has been recognized as an important emerging infectious disease in the last 10 years. This review addresses the issues in the epidemiology, diagnosis and clinical management which confront public health responses, and highlights the progress made towards understanding the Leptospira genome, biology and pathogenesis.

RECENT FINDINGS

Leptospirosis has spread from its traditional rural base to become the cause of epidemics in poor urban slum communities in developing countries. Mortality from severe disease forms, Weil's disease and severe pulmonary haemorrhage syndrome, is high (>10% and >50%, respectively) even when optimal treatment is provided. Moreover, the overall disease burden is underestimated, since leptospirosis is a significant cause of undifferentiated fever and frequently not recognized. Barriers to addressing this problem have been the lack of an adequate diagnostic test and effective control measures. China and Brazil, countries in which leptospirosis is a major health problem, have completed the sequence of the Leptospira interrogans genome. Together with new genetic tools and proteomics, new insights have been made into the biology of Leptospira and the mechanisms used to adapt to host and external environments. Surface-exposed proteins and putative virulence determinants have been identified which may serve as sub-unit vaccine candidates.

SUMMARY

Major progress has been made in the basic research of leptospirosis. Future challenges will be to translate these advances into public health measures for developing countries. Yet the most effective responses may be interventions that directly address the determinants of poverty, such as poor sanitation, which are often responsible for transmission.

Enzyme-linked immunosorbent assay for the detection of canine Leptospira antibodies using recombinant OmpL1 protein

OmpL1 is a 31-kDa outer membrane protein characterized in 1993 and known to be expressed only in pathogenic Leptospira spp. Recombinant OmpL1 (GST-rOmpL1) was expressed for use as an ELISA antigen for the detection of anti-Leptospira antibodies. In immunoblot analysis, the protein reacted with sera of dogs infected with three different serotypes of Leptospira interrogans, while did not react with sera of dogs both uninfected negative controls and infected with Borrelia burgdorferi, which is closely related to Leptospira spp. Moreover, in ELISA using GST-rOmpL1, the optical density (O.D.) values from the positive controls were very high (1.125 +/- 0.549). In contrast, the O.D. values from clinically healthy dogs and dogs with diseases other than leptospirosis were very low (0.109 +/- 0.046 and 0.089 +/- 0.046, respectively). These data suggest that the detection of anti-Leptospira antibodies by ELISA using the GST-rOmpL1 protein can be applied for diagnosis of canine leptospirosis.

Evaluation of the clinical utility of a rapid blood test for human leptospirosis

A rapid assay device for the detection of Leptospira-specific immunoglobulin M (IgM) antibodies was applied on whole blood samples collected from a group of consecutive patients admitted with clinical suspicion of leptospirosis to a district hospital in Kerala, India. The hospital is located in an area that is endemic for leptospirosis. The results of the rapid assay showed an agreement of 94.3% with those of an IgM ELISA routinely used for the serodiagnosis of leptospirosis. The rapid assay was simply performed by the addition of 10 microL blood to the sample well of a plastic assay device followed by the addition of 130 microL sample fluid. The assay was read after 10 min by visual inspection and was scored positive when staining of the antigen line in the test zone was observed. The assay utilizes stabilised components and can be stored without the need for refrigeration. These characteristics make the assay ideal in areas where the disease is common and where laboratory support is not routinely available.