Bacteria

SPIROCHETES

Classification of Spirochetes
Human pathogens belong to following 3 genera: Treponema Leptospira Borrelia Others (saprophytes) are found in water, sewage and in mouth & genital tracts of humans.

Treponema

Main treponemes are: T. pallidum - Syphilis:Venereal (sexual) disease T. pertenue - Yaws Non venereal T. carateum - Pinta disease All three species are morphologically identical

Characteristics of T.pallidum

Elongated, motile (endoflagella- axial filament), spiral bacteria with tapering ends seen under Dark Ground Microscope by staining with silver saltsCulture – Do not grow on artificial media.Virulent strains can be maintained in rabbit testis by serial passages e.g. Nichol’s strain – used for diagnosis & researchReiter’s strain – nonpathogenic strain cultivated for diagnosis.

Characteristics of T.pallidum

T pallidum may remain motile for 3–6 days at 25°C. In whole blood or plasma stored at 4°C, organisms remain viable for at least 24 hoursVery delicate, easily killed by drying or heating at 42C for an hr.Antigenicity –has hyaluronidase Induce Ab asNon specific - Reagin Ab (cardiolipin extracted from normal mammalian )Specific – Trponemal Ab, immobilizing and killing live motile T pallidum and fixing complement

Syphilis

Sexually transmitted disease.Entry through minute abrasions on mucosa or skin.Incubation period - about a month (2–10 weeks ).Infectivity is maximum during first 2 years of disease – primary & secondary stages

Stages of syphilis

Primary syphilis – hard chancre on genitals: painless, avascular, circumscribed, indurated & ulcerated lesion; covered with a thick glairy exudate rich in spirochetesHeals spontaneously in 10-40 days


Stages of syphilis
Secondary syphilis – Most infectious stage 2–10 weeks the "secondary" lesions appear after 1 lesion heals.Pt is asymptomatic but widespread dissemination occurs via bloodMaculopapular skin rashes on the body, mucous patches in the oropharyngeal area & condylomata at mucocutaneous junctions

Stages of syphilis

Latent syphilis – quiescent stage which follows secondary stageTertiary syphilis – develop after years, characterized by the development of: granulomatous lesions (gummas) in skin, bones, and liverLate tertiary or quaternary syphilis –cardiovascular lesions like aneurysm, aortitis neurosyphilis : tabes dorsalis or general paralysis of insane

Congenital syphilis

Mother to the fetus through the placenta beginning in the 10th to 15th weeks of gestationinfected fetuses die, and miscarriages result; others are stillborn at term.Clinical features – keratitis, saddle shaped nose, Hutchinsons teeth, 8th nerve deafness.The reagin titer in the blood of the child rises with active infection but falls with time if antibody was passively transmitted from the mother. In congenital infection, the child makes IgM antitreponemal antibody.

Saddle shaped nose

Hutchinsons teeth

Laboratory Diagnosis

Specimens include tissue fluid expressed from early surface lesions for demonstration of spirochetes; blood serum for serologic tests. Dark-Field Examination The exudate is examined under oil immersion with dark-field illumination for typical motile spirochetes. Immunofluorescence Tissue fluid or exudate is fixed, stained with a fluorescein-labeled antitreponeme serum, and examined by means of immunofluorescence microscopy for typical fluorescent spirochetes.

Nontreponemal tests

Test for reagin Ab using cardiolipin Ag. VDRL (Venereal Disease Research Laboratory) test RPR (Rapid Plasma Reagin) test used as screening tests for syphilis. Reagin is a mixture of IgM and IgG antibodies reactive with the cardiolipin-cholesterol-lecithin complex. false positive reactions are seen in Influenza, carditis and connective tissue diseases

Treponemal antibody tests

Measure Ab against T pallidum antigens. The tests are confirmatory for positive result from a nontreponemal test, include: T pallidum hemagglutination (TPHA) T pallidum immobilization (TPI) test Treponemal antibody tests using the EIA for T pallidum Fluorescent treponemal antibody absorbed (FTA-ABS) test


Immunity &Treatment
A person with active or latent syphilis appears to be resistant to superinfection with T pallidum. If early syphilis is treated adequately the individual again becomes fully susceptible Penicillin is the drug of choice 2nd line- Erythromycin, Tetra/ Doxycycline Neurosyphilis - Ceftriaxone

Borrelia

Are arthropod transmitted Spirochetes and they cause Relapsing fever – two types:a. Epidemic – is caused by B. recurrentis and is transmitted by human lice. This is a more severe form of the disease than the endemic form.b. Endemic – is caused by many Borrelia species and is transmitted by ticks

Borrelia

Relapsing fever
IP (12-15) days after.Abrupt onset of fever, headache, and myalgia for 4-10 days.Ab are formed and the number of organisms decrease → afebrile period → The fever then relapses because of antigenic variation « Ab are no longer effective and the organism numbers increase. Blood specimens are obtained during the rise in fever, for smears and animal inoculation.

B.vincenti

Normal mouth commensalMay give rise to ulcerative gingivostomatitis or oropharyngitis (Vincent’s angina) during malnutrition or viral infectionsB. vincenti always associated with fusiform bacilli – fusospirochetosisDiagnosis – gram staining of exudatesTreatment – Penicillin

B.burgdorferi

Causes Lyme disease, transmitted by ticksCharacteristic rash – erythema chronicum migrans, may have (fever, headache, nausea, vomiting, myalgia, and fatigue). If untreated → arthritis (acute or chronic), and cardiac or neurologic complications due to immune complexes.B burgdorferi DNA detected by the polymerase chain reaction.

Leptospira

Pathogenic L. interrogans → Weil’s disease or leptospirosisisNon pathogenic free living L. biflexaVery thin, delicate spirochetes with hooked endsThey are actively motile, seen by dark-field microscope.Leptospirae can survive for weeks in water(alkaline pH)


Weil’s disease Leptospires in water contaminated by the urine of rats; enters the body through cuts or abrasions on the skin or through intact mucosa of mouth, nose or conjunctivaIncubation period – about 10 days (2 to 20)Mild fever to severe or fatal illness with hepatorenal damage1- Blood – 1st week only- and Urine – 2nd week of disease-for microscopic examination and cultureThe diagnosis is confirmed serologically. Agglutinating antibodies first appear by the end of 1st week & increase till 4th week of disease