[{"data":1,"prerenderedAt":-1},["ShallowReactive",2],{"$fxLN3MUwXCdr5RPjwZYIDpOj8CHyjOmngWTgoKXPtZbg":3,"$f10LwthqWS10GIsravNEEMKYy0xKB7udRx1sjjlloJGU":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},"relapsing-fever-etiology-diagnosis","Borrelia species: Properties, Pathogenesis, Lab Diagnosis",null,"Acharya Tankeshwar","2022-04-10","2026-07-05",false,"bacteriology","Relapsing fever is a bacterial infection characterized by **recurrent episodes of fever** and nonspecific symptoms following exposure to insect vector-carrying *Borrelia* species.\n\n![](https:\u002F\u002Fassets.microbeonline.com\u002Fblogs\u002FRelapsing-fever-general-idea.png)There are two main types of relapsing fever:\n\n1. **Epidemic relapsing fever** also known as Louse-borne relapsing fever (LBRF) is caused by *B. recurrentis* and transmitted by a **louse**. LBRF outbreaks most commonly occur in conditions of overcrowding and social disruption. *Note: epidemic typhus is also louse-borne typhus.*\n2. **Endemic** **relapsing fever** also known as Tick-borne relapsing fever (TBRF) is caused by *Borrelia* species other than *B. recurrentis* such as *B. duttoni, B. hermsii*and \\*B. turicatae.It is transmitted by a **tick.**\n\nBorrelia miyamotoi disease (sometimes called hard tick relapsing fever) is another newer type of relapsing fever which is now getting increased attentions.\n\n## Pathogenesis\n\nMode of transmission:\n\n- **Epidemic** relapsing fever: Human-human transmission occurs by the body louse (*Pediculus humanus*).Borreliae are introduced by crushing of the **louse** (e.g. by scratching) leading to deposition of insect’s infected hemolymph containing numerous spirochetes on the abraded skin and mucous membranes.\n- **Endemic** relapsing fever: It is transmitted by bite of an infected **tick** (*Ornithodoros* species).\n\nFrom the inoculated site, *Borrelia* spreads rapidly leading to bacteremia and fever. Host’s immune system tries to eliminate the bacilli from the body.\n\nHowever, the borrelial surface antigens frequently undergo **antigenic variation**. Each time, new antigens are produced which can evade host’s immune system leading to repeated bacteremia and recurrent febrile episodes.\n\n**Difference between Epidemic and Endemic relapsing fever**\n\n| Character | Epidemic relapsing fever (louse-borne) | Endemic relapsing fever (tick-borne) |\n| --- | --- | --- |\n| Agent | B. recurrentis | B. duttoni, B. hermsii |\n| Epidemiology | Epidemic | Usually endemic |\n| Natural host | Humans | Rodents |\n| Vector | Pediculus humanus spp . | Various; Ornithodoros hermsii, O. turicatae, O.parkeri in USA |\n| Distribution | East Africa (Sudan and Ethiopia) | North America, Central Asia, and Africa |\n| Hemorrhage, CNS features | More common | Less common |\n| Treatment | Doxycycline-single-dose | Doxycycline for 1 week. |\n\nBoth epidemic and endemic relapsing fever have similar manifestations although not identical. Incubation period is about 7-8 days.\n\n**Recurrent febrile episodes** lasting for 3-5 days occur intervening with afebrile periods for 7-9 days. Subsequent episodes are shorter\n\n**Non-specific symptoms** may be present like alteration of sensorium, abdominal pain, vomiting and diarrhea.\n\n**Hemorrhages:** Petechiae, epistaxis, and blood-tinged sputum are more likely in epidemic RF.\n\n**Neurologic features** such as meningitis, seizure, focal deficits, paraplegia and psychosis may occur in 10-30% of cases and are more common in epidemic RF.\n\n## Laboratory Diagnosis\n\n![ - Approaches for the diagnosis of Relapsing fever (Image source: Aurélien Fotso Fotso and Michel Drancourt)](https:\u002F\u002Fassets.microbeonline.com\u002Fblogs\u002FDiagnosis-of-Relapsing-Fever.png)Figure: Approaches for the diagnosis of Relapsing fever (Image source: Aurélien Fotso Fotso and Michel Drancourt)\n\n### Microscopy\n\n- Peripheral thick or thin smear-stained by Wright or [Giemsa stain](\u002Fgiemsa-stain-principle-procedure-and-results\u002F)\n- Direct fluorescent antibody test using monoclonal antibody aids in species identification.\n- Dark ground microscope (low sensitivity).\n- Quantitative buffy coat (QBC) analysis is an alternative method with higher sensitivity.\n- It is poorly gram-negative\n\n### Microscopy and Staining\n\nDetection of the spirochetes in the blood of the patient during the febrile illness. In contrast to other spirochetes the relapsing fever borreliae are well stained by acid aniline dyes, such as Wright’s or Giemsa’s stains.\n\nThe borrelial spirochetes are thin, undulant, or overtly spiral organisms that are most visible when they are located between RBCs. Thick and thin films should be made as for malaria, because in some cases spirochetes will be detected only by examination of the thick film.\n\n### Culture\n\nDuring the afebrile period, microscopy fails to detect *Borrelia*; hence, the confirmation is made by isolation of Borrelia from blood. Animal pathogenicity testing can be done by intraperitoneal inoculation into white mice.\n\n### Serology\n\nELISA and [IFA (indirect fluorescence assay)](\u002Findirect-fluorescent-antibody-ifa-test\u002F) are available to detect serum antibodies. A fourfold rise in antibody titer between acute and convalescent serum samples or with a single convalescent serum sample that is reactive. However, false-positive results may occur in other spirochete infections.\n\nAn IFA titer of 1:128 to 1:256 or higher is considered positive. However, only a few reference laboratories perform serology for the diagnosis of this infection because the borreliae need to be cultivated to use in an indirect IFA.\n\n**GIpQ assay**: It is the most reliable serological method. It is an immunoblot assay detecting antibody against the recombinant GlpQ antigen (glycerophosphodiester phosphodiesterase).\n\n### Molecular methods\n\n[Multiplex Real-time PCR](\u002Fmultiplex-pcr-principle-applications-and-limitations\u002F) has been developed targeting 16SrRNA, flagellar B protein *(flaB*), gyrase B (gyrB) and GlpQ genes to identify the various species of *Borrelia*.\n\n**References and further readings**\n\n- Fotso, Aurélien & Drancourt, Michel. (2015).[Laboratory Diagnosis of Tick-Borne African Relapsing Fevers: Latest Developments](https:\u002F\u002Fwww.researchgate.net\u002Fpublication\u002F283684389_Laboratory_Diagnosis_of_Tick-Borne_African_Relapsing_Fevers_Latest_Developments\u002Fcitations). Frontiers in Public Health. 3. 10.3389\u002Ffpubh.2015.00254.\n- [Color Atlas and Textbook of Diagnostic Microbiology](https:\u002F\u002Famzn.to\u002F2vRkUvk), Koneman, 5th edition",[],[46],"spirochetes",[48,54,61,84,90],{"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},"treponema-pallidum-properties-pathogenesis-and-disease","Treponema pallidum: Properties, Pathogenesis, and Disease","2022-02-22",[],[46],{"slug":55,"title":56,"description":57,"seoTitle":37,"seoDescription":37,"author":38,"createdDate":58,"lastUpdatedDate":40,"draft":41,"category":42,"image":37,"faq":59,"tags":60},"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":62,"title":63,"description":64,"seoTitle":37,"seoDescription":37,"author":38,"createdDate":65,"lastUpdatedDate":66,"draft":41,"category":42,"image":37,"faq":67,"tags":83},"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",[68,71,74,77,80],{"question":69,"answer":70},"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":72,"answer":73},"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":75,"answer":76},"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":78,"answer":79},"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":81,"answer":82},"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":85,"title":86,"description":86,"seoTitle":37,"seoDescription":37,"author":38,"createdDate":87,"lastUpdatedDate":40,"draft":41,"category":42,"image":37,"faq":88,"tags":89},"leptospira-interrogans-characteristics-pathogenesis-and-lab-diagnosis","Leptospira interrogans: Characteristics, Pathogenesis, Lab Diagnosis","2020-10-02",[],[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",9,{"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]