[{"data":1,"prerenderedAt":-1},["ShallowReactive",2],{"$fxLN3MUwXCdr5RPjwZYIDpOj8CHyjOmngWTgoKXPtZbg":3,"$fr0tztCp0lr7jxPBgxRu6dJx3SiQm-lP0GSCIZnnht7w":32,"$f3Ft0rKFJHppdzE-vuveecxx1BUcg9iOlMLtyzf_MJDg":115},[4,8,12,16,20,24,28],{"title":5,"slug":6,"path":7},"About Microbeonline.com","about-microbeonline-com","\u002Fabout-microbeonline-com\u002F",{"title":9,"slug":10,"path":11},"About Me","about-me","\u002Fabout-microbeonline-com\u002Fabout-me\u002F",{"title":13,"slug":14,"path":15},"Advertise with Us","advertise-us","\u002Fadvertise-us\u002F",{"title":17,"slug":18,"path":19},"Privacy Policy","privacy-policy","\u002Fprivacy-policy\u002F",{"title":21,"slug":22,"path":23},"Abbreviations","abbreviations","\u002Fabbreviations\u002F",{"title":25,"slug":26,"path":27},"Microbes","microbes","\u002Fmicrobes\u002F",{"title":29,"slug":30,"path":31},"Books","recommended-books","\u002Frecommended-books\u002F",{"type":33,"data":34},"blog",{"slug":35,"title":36,"description":36,"seoTitle":37,"seoDescription":37,"author":38,"createdDate":39,"lastUpdatedDate":40,"draft":41,"category":42,"image":37,"body":43,"faq":44,"tags":45,"related":47},"leptospira-interrogans-characteristics-pathogenesis-and-lab-diagnosis","Leptospira interrogans: Characteristics, Pathogenesis, Lab Diagnosis",null,"Acharya Tankeshwar","2020-10-02","2026-07-05",false,"bacteriology","*Leptospira interrogans* is a member of the class **Spirochaetes** order **Spirochaetales** and the family **Leptospiraceae**. There are two species of Leptospira; *Leptospira interrogans* are the pathogenic species and are the causative agents of leptospirosis or Weil’s disease, whereas *L. biflexa* is saprophytic.\n\n![](https:\u002F\u002Fassets.microbeonline.com\u002Fblogs\u002FA-scanning-electron-microscopy-image-of-Leptospira-interrogans-The-outer-image-is-the.png)\\## Morphological Characteristics\n\n- **Tightly coiled fine spirochete**:\n\n*L. interrogans* have a size of 6-12 μm in length x 0.1 μm in width, allowing them to pass through filters used to sterilize the culture medium. They are tightly and regularly coiled, with **characteristic hooked ends (hence the species name interrogans resembling interrogation or question mark)**.Spirals have a wavelength (interval between spirals) of 0.5μm and amplitude of 0.1μm. They possess a **single endoflagellum** attached to the pole and are highly motile, exhibiting spinning and translational movements.\n\n- **Not Stained with dyes**\n\nThey cannot be seen under the light microscope due to their thinness (**leptos, meaning fine or thin**). They do not take up ordinary stains but may be observed by dark ground or phase-contrast microscope or stained by silver impregnation method and by immunofluorescence.\n\n- **Antigenically complex**: Divided into serogroups which were further divided into serovars. On the basis of agglutination testing with specific antisera against the surface LPS antigens, *Leptospira* is divided into:\n\n*Leptospira interrrogans*: Comprises 250 serogroups, consisting of over 250 serovars. *L. biflexa:* 65 serovars arranged in 38 serogroups.\n\n## Pathogenesis\n\n- **Source:** Although more than 100 animals can be infected, important sources of infection are rats, dogs, cattle, and pigs. Even asymptomatic animals can transmit the infection via urine *(persistent colonization of renal tubules of carrier animals.)*\n\n![](https:\u002F\u002Fassets.microbeonline.com\u002Fblogs\u002FAnimals-Transmitting-leptospirosis.jpg)\\- **Transmission:**\n\n**Zoonotic**: A person may acquire leptospirosis if he\u002Fshe comes in contact with the urine of infected animals (or other body fluids, except saliva) such as dogs, pigs, and cattle directly or through contaminated food water, or soils.  Abrasions or cuts in the skin increase the chances of infection. It is an **occupational hazard** for many people who work outdoors or with animals, such as farmers, slaughterhouse workers, veterinarians, and animal caretakers. Leptospirosis has also been associated with swimming, kayaking, and rafting in contaminated lakes and rivers. Person-to-person transmission is rare.\n\n> 3R’s: The three important epidemiological determinants for leptospirosis include exposure to rodents, rainfall, and rice field.\n\n- **Risk factors:**\n\nLower socioeconomic status Urban and rural slum areas Rainfall and floods Occupational exposure to animal urine, e.g., rice field workers and farmers.\n\n- Global distribution: Worldwide, the highest burden of the disease has a reported in urban slums of Brazil, India, and Thailand.\n\n## Signs and Symptoms\n\nLeptospirosis can use many symptoms, some of which may be mistaken for other diseases such as dengue fever and other [viral hemorrhagic diseases](\u002Fviral-hemorrhagic-fever\u002F). It can lead to kidney damage, meningitis, liver failure, respiratory distress, and even death if left untreated.\n\nLeptospirosis is often misdiagnosed as aseptic meningitis, influenza, dengue, hepatic disease, or pyrexia of unknown origin. Therefore, diagnosis is based on laboratory tests rather than clinical symptoms alone, but these tests are not always available, especially in developing countries.\n\n**There are two phases of Infections:**\n\n1. The acute or bacteremic\u002Fsepticemic phase\n2. Immune phase: Aseptic meningitis\n\n**First Phase: Acute or bacteremic\u002Fsepticemic phase**\n\n- Entry via mucous membranes of the eyes, nose, or mouth or through skin abrasion\n- Vascular damage: Spirochetes can be found in the walls of capillaries, medium, and large-sized vessels. The exact mechanism of vascular damage is not clear.\n- Penetration and invasion of tissues are due to active motility and release of hyaluronidase.\n- Invade bloodstream and hematogenous spread multiple sites of the body: producing fever, dysfunction of the liver (jaundice), kidneys (uremia), lungs (hemorrhage) central nervous system (aseptic meningitis)\n\n**Second Phase (Immune Phase)**\n\nAfter seroconversion, Spirochetes disappear from the blood, but they may colonize in the kidney: *Leptospira*becomes adherent to the proximal tubular brush border and is excreted in the urine.\n\n#### Clinical Manifestations\n\nIncubation period: 5-14 days\n\n**Two distinct clinical syndromes:**\n\n- Mild anicteric febrile illness: 90% of patients. Biphasic in nature; septicemic phase followed by immune phase.\n- Weil’s disease (hepato-renal-hemorrhagic syndrome)\n\n##### Weil’s Syndrome\n\n- a severe form of the leptospirosis infection (icteric) which occurs in approximately 10% of patients\n- jaundice and significant liver damage\n- kidney and\u002For vascular dysfunction\n- lethal pulmonary hemorrhages\n- Typical biphasic course may not be present.\n- death is up to 10% of cases\n\n## Laboratory Diagnosis\n\nLeptospirosis is usually diagnosed in the laboratory by detecting antibodies, by culturing the bacteria from **blood, CSF, urine,** or tissues, or by demonstrating the presence of leptospires in tissues using [antibodies](\u002Fimmunoglobulin-structure\u002F) labeled with fluorescent markers.\n\nDetecting *L. interrogans* in a clinical specimen (urine, blood, or CSF) by immunofluorescence, impregnation stains such as Fontana stain, modified Steiner technique, or by using dark-ground microscopy or phase-contrast microscopy is a commonly used microscopic method. Other methods include [polymerase chain reaction (PCR)](\u002Fpolymerase-chain-reaction-pcr-steps-types-applications\u002F) and immunostaining.\n\n![ - (a) Growth from blood in EMJH semisolid mediaLeptospirais forming subsurface colonies in the tube on the left and no growth in the tube on the right; (b) dark field microscopy image of the culture showing spirochetes with morphology compatible with Leptospira; (c) Conventional PCR targeting lipL32 gene  (Image source: Christopher Ryan Larson)](https:\u002F\u002Fassets.microbeonline.com\u002Fblogs\u002Fa-Growth-from-blood-in-EMJH-semisolid-media-Leptospira-is-forming-subsurface-colonies.png)Figure: (a) Growth from blood in EMJH semisolid media Leptospirosis forming subsurface colonies in the tube on the left and no growth in the tube on the right; (b) dark field microscopy image of the culture showing spirochetes with morphology compatible with Leptospira; (c) Conventional PCR targeting lipL32 gene  (Image source: Christopher Ryan Larson)\n\n### Microscopy and Staining\n\n![ - 1998 Rob WeyantThis scanning electron micrograph (SEM) depicts a number ofLeptospira sp.bacteria atop a 0.1. µm polycarbonate filter.](https:\u002F\u002Fassets.microbeonline.com\u002Fblogs\u002FLEPTOSPIRA-Electron-micrograph.jpg)Figure: 1998 Rob WeyantThis scanning electron micrograph (SEM) depicts a number ofLeptospira sp.bacteria atop a 0.1. µm polycarbonate filter.\n\nDemonstrating leptospires in the fluids using **Dark-Field Microscopy** is often described as a proper diagnostic method, but its significance is doubtful.  Serum protein and fibrin strands, and other cell debris in blood resemble leptospires, while the concentration of organisms in the urine of humans and animals is frequently too low to be detectable by this method. Care and great experience are therefore necessary to avoid mistaking artifacts for leptospires.\n\nLeptospires are **corkscrew-shaped bacteria** that differ from other spirochaetes by the presence of end hooks. They are too thin to be visible under an ordinary microscope. All leptospires look-alike with minor differences, so morphology does not help differentiate between pathogenic and saprophytic leptospires or the various pathogenic leptospires.\n\n![ - Leptospiral microscopic agglutination test with live antigen using dark field microscopy](https:\u002F\u002Fassets.microbeonline.com\u002Fblogs\u002FLeptospiral-microscopic-agglutination-test-with-live-antigen-using-dark-field-microscopy.png)Figure: Leptospiral microscopic agglutination test with live antigen using dark field microscopy\n\n### Culture\n\nThe culture of *Leptospira* is a problematic and relatively insensitive process; it is laborious and can take up to three months. In the acute phase, which lasts for about ten days, the leptospires can often be cultured from blood or cerebrospinal fluid (CSF). When a specific antibody response is detected (at approx. ten days), leptospires disappear from the blood. During the second phase, which may last up to several months, bacteriuria is often intermittent.\n\nLeptospires grow in a variety of cultural media. Media with 14% (v\u002Fv) rabbit serum, such as **Fletcher’s or EMJH (Ellinghausen, McCullough, Johnson, Harris) medium**, is used for the isolation. Their growth is relatively slow, with a doubling time of about 6–8 hours at best. Incubation is done at 28-30°C for about 13 weeks, with culture examined every third day by darkfield microscopy.  In the dark field microscopy, leptospires are observed as thin, coiled, rapidly moving microorganisms.\n\n### Antibody detection\n\nAntibodies may be detected in the blood within 5–7 days of symptom onset. Evidence of seroconversion between acute and convalescent-phase serum specimens confirms the diagnosis of leptospirosis, which can be demonstrated by a microscopic agglutination test (MAT).\n\n#### Microscopic Agglutination Test (MAT)\n\nMAT is a gold standard method for diagnosing leptospirosis, but it may only be available in reference laboratories. MAT has high sensitivity and detects serovar-specific antibodies.  Seroconversion with a 4-fold or larger rise in titer between acute- and convalescent-phase serum specimens obtained two weeks, or more apart confirms the diagnosis. A single elevated MAT titer in a patient with a compatible febrile illness and suspected exposure suggests acute leptospirosis.\n\n**Major disadvantages of Microscopic Agglutination Test (MAT)**\n\n1. In the endemic regions, there may be a substantial proportion of the population with elevated titers of MAT.\n2. The performance of MAT is restricted to laboratories capable of maintaining strains for the preparation of live antigens.\n\n**Other serological methods**\n\n1. Microplate IgM ELISA and\n2. IgM dot-ELISA dipstick test\n\n### Molecular Methods\n\nPolymerase Chain Reaction (PCR) assay can be used on clinical samples such as CSF, urine, or blood to detect the presence of leptospiral DNA. It is based upon the amplification of 16S rRNA gene sequences of Leptospira.\n\n#### Advantages and disadvantages of diagnostic tests for the detection of Leptospirosis\n\n| Tests | Advantages | Disadvantages |\n| --- | --- | --- |\n| Dark Field Microscopy | Visualize leptospira | Lack of sensitivity and specificity. 10^4 Leptospires\u002Fml is necessary for one organism\u002Ffield to be visible under DFM. |\n| IgM ELISA | Most widely used | IgM cannot be detected in the early stages of infection and can persist in the blood for years. |\n| Microscopic Agglutination Test (MAT) | Gold Standard | Less sensitive in the early phase of the disease. Labor-intensive and complicated procedure. |\n| Polymerase Chain Reaction (PCR) | Successful in detecting Leptospira DNA in serum and urine samples of patients | Reagents are expensive . It requires a large quantity of DNA but cannot identify the infecting serovar. |\n\n**References and further reading**\n\n- Budihal, S. V., & Perwez, K. (2014). Leptospirosis diagnosis: competancy of various laboratory tests. *Journal of clinical and diagnostic research : JCDR*, *8*(1), 199–202. \u003Chttps:\u002F\u002Fdoi.org\u002F10.7860\u002FJCDR\u002F2014\u002F6593.3950>\n- Ahmad, S. N., Shah, S., & Ahmad, F. M. (2005). Laboratory diagnosis of leptospirosis. *Journal of postgraduate medicine*, *51*(3), 195–200.\n- Dr Terpstra, W. J. (n.d.). *Human leptospirosis: Guidance for diagnosis, surveillance and Control*. World Health Organization. \u003Chttps:\u002F\u002Fwww.who.int\u002Fpublications-detail-redirect\u002Fhuman-leptospirosis-guidance-for-diagnosis-surveillance-and-control>\n- Centers for Disease Control and Prevention. (2023, August 30). *Leptospirosis*. Centers for Disease Control and Prevention. \u003Chttps:\u002F\u002Fwww.cdc.gov\u002Fleptospirosis\u002Findex.html>\n- Global Leptospirosis Environmental Action Network (GLEAN). (n.d.). *Glean*. GLEAN. \u003Chttps:\u002F\u002Fsites.google.com\u002Fsite\u002Fgleanlepto\u002Fhome>",[],[46],"spirochetes",[48,54,60,67,90],{"slug":49,"title":50,"description":50,"seoTitle":37,"seoDescription":37,"author":38,"createdDate":51,"lastUpdatedDate":40,"draft":41,"category":42,"image":37,"faq":52,"tags":53},"relapsing-fever-etiology-diagnosis","Borrelia species: Properties, Pathogenesis, Lab Diagnosis","2022-04-10",[],[46],{"slug":55,"title":56,"description":56,"seoTitle":37,"seoDescription":37,"author":38,"createdDate":57,"lastUpdatedDate":40,"draft":41,"category":42,"image":37,"faq":58,"tags":59},"treponema-pallidum-properties-pathogenesis-and-disease","Treponema pallidum: Properties, Pathogenesis, and Disease","2022-02-22",[],[46],{"slug":61,"title":62,"description":63,"seoTitle":37,"seoDescription":37,"author":38,"createdDate":64,"lastUpdatedDate":40,"draft":41,"category":42,"image":37,"faq":65,"tags":66},"borrrelia-burgdorferi-lyme-disease","Borrelia burgdorferi (Lyme disease): Clinical Features, Diagnosis","Lyme disease is caused by Borrelia burgdorferi and transmitted by Ixodes ticks. Learn the three stages, the bull's-eye rash, laboratory diagnosis, and treatment — with clinical pearls for medical students.","2021-05-21",[],[46],{"slug":68,"title":69,"description":70,"seoTitle":37,"seoDescription":37,"author":38,"createdDate":71,"lastUpdatedDate":72,"draft":41,"category":42,"image":37,"faq":73,"tags":89},"demonstration-of-treponema-pallidum-using-dark-field-microscopy","Demonstration of Treponema pallidum Using Dark-Field Microscopy","The full dark-field procedure for detecting Treponema pallidum in a chancre, the 20-minute window that makes or breaks it, and why oral or rectal samples can give a false positive.","2021-05-07","2026-07-06",[74,77,80,83,86],{"question":75,"answer":76},"Can dark-field microscopy be used on an oral or rectal lesion to diagnose syphilis?","No. Both the mouth and rectal mucosa normally carry commensal spirochetes, such as Treponema denticola in the oral cavity, that are morphologically and behaviorally indistinguishable from Treponema pallidum under dark-field examination. A positive result from these sites risks a false-positive diagnosis; specimens from oral or rectal lesions should instead be tested by a pathogen-specific method or serology.",{"question":78,"answer":79},"Why must the dark-field specimen be examined within 20 minutes of collection?","Motility is often essential to correctly identifying Treponema pallidum, and the organism loses motility quickly once outside the host. A delayed examination can produce a false-negative result even if the organism was present in the original specimen.",{"question":81,"answer":82},"What does \"Treponemas resembling T. pallidum observed\" mean, exactly?","This reporting language reflects that the identification is based on characteristic morphology (a tightly wound, corkscrew shape) and motility (rotation, flexion, and snapping movements), not a pathogen-specific molecular or antigen-based marker. This is also why the technique isn't reliable on specimen sites with look-alike commensal organisms.",{"question":84,"answer":85},"How sensitive is dark-field microscopy for diagnosing syphilis?","Approximately 80% in primary syphilis, but sensitivity declines as the infection progresses into later stages and can be further reduced if the patient has already applied topical antibiotics to the lesion.",{"question":87,"answer":88},"What size is Treponema pallidum, and how does that compare to a red blood cell?","It measures roughly 6 to 14 μm in length, slightly longer than the diameter of a typical erythrocyte, which serves as a useful visual size reference during dark-field examination.",[46],{"slug":91,"title":92,"description":93,"seoTitle":37,"seoDescription":37,"author":94,"createdDate":95,"lastUpdatedDate":96,"draft":41,"category":42,"image":37,"faq":97,"tags":113},"dark-field-microscopy","Dark-field Microscopy: Principle and Uses","How dark-field microscopy makes spirochetes like Treponema pallidum visible without staining, by detecting scattered light rather than resolving fine detail.","Nisha Rijal","2020-04-21","2026-07-21",[98,101,104,107,110],{"question":99,"answer":100},"Why is dark-field microscopy used to diagnose primary syphilis instead of a routine stain?","Treponema pallidum does not stain well with routine methods and is difficult to see by bright-field microscopy. Dark-field microscopy shows the organism as a bright, motile, corkscrew-shaped structure against a completely dark background, using its live motility as the identifying feature.",{"question":102,"answer":103},"Does dark-field microscopy improve resolution compared to bright-field microscopy?","No. The fundamental resolving power of the microscope, roughly 0.2 μm, stays the same. Dark-field microscopy instead improves contrast and the ability to detect structures at or below that resolving limit by showing only the light they scatter, rather than trying to resolve their fine detail directly.",{"question":105,"answer":106},"Why can spirochetes like Treponema pallidum be seen with dark-field microscopy but not bright-field?","Spirochetes are roughly 0.1 to 0.18 μm wide, thinner than the light microscope's ~0.2 μm resolving limit, so bright-field microscopy cannot resolve them. Dark-field microscopy detects the light they scatter instead, making them visible as bright, moving threads against a dark background even though their fine structure still can't be resolved.",{"question":108,"answer":109},"What are the main limitations of dark-field microscopy?","The specimen must be living, unstained, and examined very quickly since motility is often essential for identification. Strong illumination can damage the sample, dust particles can be mistaken for organisms, and thick preparations reduce contrast and accuracy.",{"question":111,"answer":112},"Is dark-field microscopy used routinely in diagnostic laboratories?","Not routinely. It requires a special condenser setup, a fresh, living specimen examined immediately, and a trained microscopist, which limits its use to specific point-of-care situations like suspected primary syphilis rather than general diagnostic panels.",[114,46],"microscopy",[116,122,129,134,138,142,147,152,156,160],{"slug":117,"name":38,"description":118,"image":119,"body":120,"postCount":121},"acharya-tankeshwar","Editor-in-chief","https:\u002F\u002Fassets.microbeonline.com\u002Fauthors\u002Ftankeshwar-acharya-author-microbeonline.jpg","***Tankeshwar Acharya, MSc (Medical Microbiology)***\n\n*Tankeshwar Acharya is an Assistant Professor in the Department of Microbiology at Patan Academy of Health Sciences (PAHS), Nepal, where he has been teaching and practicing clinical microbiology for over 14 years. He is the founder of Microbe Online, one of the leading free microbiology education resources on the web, covering bacteriology, mycology, parasitology, immunology, and clinical laboratory diagnostics written from direct experience in both the classroom and the diagnostic laboratory.*",433,{"slug":123,"name":124,"description":125,"image":126,"body":127,"postCount":128},"ashma-shrestha","Ashma Shrestha","SEO Copywriter and Science Communicator\nKathmandu, Nepal","https:\u002F\u002Fassets.microbeonline.com\u002Fauthors\u002Fashma-shrestha.png","Ashma Shrestha holds a Master of Science in Medical Microbiology from the Institute of Science and Technology (IOST), Tribhuvan University, Nepal, where she developed a strong foundation in virology, molecular biology, and diagnostic microbiology.\n\nShe now works as an SEO Copywriter at Resolution Digital, where she combines her scientific training with research-driven content strategy. She is certified in Google Analytics and Google Business Profile (GBP), and brings a data-informed approach to science communication writing content that is not only accurate but structured to reach and serve the students who need it most.\n\nAt microbeonline, Ashma contributes articles primarily in virology and molecular biology, areas she finds most compelling for their mechanistic depth and their growing clinical relevance. Her writing reflects the same standard the site is built on: factual rigor, clear explanation of the *why* behind microbiology concepts, and content that helps students move from memorization to genuine understanding.\n\nShe is passionate about making complex microbiological concepts accessible without sacrificing accuracy; a skill that sits at the intersection of her scientific training and her professional work in content and SEO.",81,{"slug":130,"name":131,"description":132,"image":37,"body":37,"postCount":133},"sushmita-baniya","Sushmita Baniya","Author \u002F Contributor",32,{"slug":135,"name":136,"description":132,"image":37,"body":37,"postCount":137},"samikshya-acharya","Samikshya Acharya",20,{"slug":139,"name":140,"description":132,"image":37,"body":37,"postCount":141},"alisha-tripathi","Alisha Tripathi",6,{"slug":143,"name":144,"description":145,"image":37,"body":37,"postCount":146},"aastha-shrestha","Aastha Shrestha"," Author \u002F Contributor",10,{"slug":148,"name":149,"description":150,"image":37,"body":37,"postCount":151},"guest-author","Guest Author","Guest Author \u002F Contributor",2,{"slug":153,"name":154,"description":132,"image":37,"body":37,"postCount":155},"srijana-khanal","Srijana Khanal",18,{"slug":157,"name":158,"description":150,"image":37,"body":37,"postCount":159},"dr-poonam-acharya","Dr. Poonam Acharya",1,{"slug":161,"name":94,"description":132,"image":37,"body":162,"postCount":163},"nisha-rijal","**Nisha Rijal** is a microbiologist and quality assurance specialist. She served for nearly 12 years as a microbiologist at the National Public Health Laboratory (NPHL), Nepal's national reference laboratory, and continues to work as a consultant microbiologist in international public health organization. ",51]