Chlamydia, Rickettsia, Mycoplasm & Similar

Chapter 20: Chlamydia, Rickettsia, Mycoplasma & Similar Organisms

General Information

  • Copyright: Jones & Bartlett Learning, LLC, an Ascend Learning Company. www.jblearning.com
  • Note: Exam focused on parasitology, not microbiology.

Chlamydiaceae Family

  • Definition:
    • Obligate intracellular parasites originally believed to be viruses.
  • Characteristics:
    • Gram-negative type cell wall.
    • Contains DNA, RNA, & prokaryotic ribosomes.
    • Can synthesize proteins, lipids, and nucleic acids.
    • Cannot produce ATP; requires a host to multiply by binary fission.
  • Genera:
    • Chlamydia
    • Chlamydophila
  • Species causing human infections:
    • Chlamydia trachomatis
    • Chlamydophila psittaci
    • Chlamydophila pneumoniae

Chlamydiae Life Cycle

  • Inclusion Dependent Life Cycle:
    • Inclusions:
    • Elementary Body (EB): Infective inclusion that binds to host cells, taken to phagosome, reorganizes.
    • Reticulate Body (RB): Metabolically active but not infective; multiplies (BF) 18-24 hours post-infection; reorganizes into many EBs, can be seen on staining.
    • Released upon cell rupture.

Diseases Caused by Chlamydia trachomatis

  • Diseases:
    • Lymphogranuloma venereum (LGV)
    • Endemic trachoma
    • Nongonococcal urethritis
    • Infant pneumonitis
  • Host Cells Affected:
    • Epithelial cells of mucous membranes (cervix, endocervix, respiratory tract, conjunctiva).
  • Biovars:
    • Trachoma
    • Lymphogranuloma venereum (LGV)
  • Serovars:
    • Based on major outer membrane protein (MOMP) and associated specific infections.
  • Differences:
    • Biovars: Differ physiologically or biochemically from other strains in a species.
    • Serovars: Have antigenic differences from other strains in a species.

Chlamydia trachomatis: Serovars & Diseases

  • Trachoma:
    • Leading cause of preventable blindness worldwide.
    • Transmission: Direct contact with secretions or contaminated fomites.
    • Pathogenesis: Irritation leads to scarring; inward eyelid resulting in lash irritation.
    • Associated Serovars: A, B, Ba, C.
  • Lymphogranuloma venereum (LGV):
    • STD endemic in Africa, Asia, and South America.
    • Symptoms: Small painless ulcer that may heal spontaneously, followed by acute lymphadenitis of inguinal nodes (high fever, chills, pain, headache).
    • Possible dissemination to cause arthritis, pneumonia, meningitis, or granulomatous proctitis.
    • No long-term immunity; recurrent scarring may develop.
    • Associated Serotypes: L1, L2a, L2B, L3.
  • Nongonococcal urethritis & cervicitis:
    • Most prevalent STI in the US (2018: 1.76 million cases, 2.9% increase from 2017).
    • Transmission: Through hands, hot tubs, pools, and makeup.
    • Symptoms: Purulent infection without blindness or asymptomatic, especially in young women (<25 y.o).
    • Complications: May serve as a reservoir for PID, ectopic pregnancy, infertility; associated with BV & high-risk HPV infections.
    • Neonatal conjunctivitis or pneumonitis – Associated Serovars: D, E, F, G, H, I, J, K.

Diagnostic Methods for Chlamydia trachomatis

  • Specimen Collection:
    • Conjunctival, urethral, cervical, or rectal scrapings/swabs using Dacron or rayon swabs (to avoid toxicity, as cotton swabs are toxic).
  • Identification Methods:
    • Molecular methods such as Nucleic Acid Amplification Tests (NAAT or PCR):
    • High sensitivity and specificity; good detection with small loads.
    • Types: Endocervical swabs, urethral swabs, urine. Use first-void urine in asymptomatic individuals.
    • Routine exam recommended annually.
    • Serological methods for antibody detection: Limited usefulness due to high carrier rates.
  • Other Identification Methods:
    • Chlamydial antigen using Direct Fluorescent Antibody (DFA) techniques.
    • Use fluorescein-labeled isothiocyanate bound MOMP or LPS.
    • Cytological methods requiring scraping of epithelial cells; monoclonal Abs improve specificity.
    • Cell culture used to be the gold standard; required complex procedures and was time-consuming.

Treatment of Chlamydia trachomatis

  • Medications:
    • Treatment includes Macrolides or Fluoroquinolones.
    • Routine susceptibility testing is not performed due to impracticality in routine labs; performed traditionally in cell culture.

Parrot Fever: Chlamydophila psittaci

  • Disease Name: Psittacosis or Ornithosis (Parrot fever).
  • Epidemiology:
    • Rare in the US (50 cases per year); affects psittacine birds.
  • Transmission: Inhalation of contaminated aerosols or fomites.
  • Symptoms:
    • May be subclinical & mild to severe pneumonia, often mild to moderate.
    • May disseminate to the reticuloendothelial system (lymph nodes, liver, spleen).
  • Diagnosis:
    • Requires patient history; diagnosis made through Micro-immunofluorescence serological testing (looking for a four-fold increase in titer or single titer > 1:32).

Chlamydophila pneumoniae

  • Infections:
    • Range from mild to severe respiratory tract infections; attributed to about 10-15% of community-acquired pneumonia in the US (about 250K cases per year).
  • Transmission: Direct human contact.
  • Identification:
    • Using Nucleic Acid Amplification (PCR).
    • Serologic testing, particularly micro-immunofluorescence. IgM > 1:32, IgG > 512 or 4X increase.

Rickettsiaceae Family

  • Genera: Rickettsia and Orientia.
  • Characteristics:
    • Small, pleiomorphic, non-motile, Gram-negative, obligate intracellular bacteria.
    • Cannot survive outside of a host or vector.
    • Multiply by binary fission and contain RNA & DNA.
  • Humans are considered accidental hosts.
    • Infect many mammals and birds; transmitted mainly by arthropod vectors: lice, fleas, mites, and ticks.

Rickettsial Diseases

  • Cycle Characteristics:
    • Disease transmission typically occurs through the bite of an infected vector, incubating for 3-14 days.
    • Bacteria attach to host endothelial cell surface receptors of blood vessels, resulting in phagocytosis, multiplication, and release, leading to vascular lesions.
  • Symptoms to Diagnose:
    • History of fever, headache, a spreading maculopapular rash that generally starts at the ankles and wrists affecting the brain, heart, lungs, with possible conjunctivitis and mild respiratory distress.

Specific Rickettsia Species and Diseases

  • Spotted Fever Group:
    • R. rickettsii: Rocky Mountain spotted fever - most common in the US (2000 cases/year).
    • Vectors: Hard ticks (Dermacentor variabilis, D. andersoni).
    • Pathogenesis includes escaping the phagosome and multiplying in cytoplasm causing vasculitis.
    • R. akari: Rickettsial pox, biphasic with a mouse mite vector; endemic to regions like Korea, Ukraine, and Eastern US.
    • R. conorii: Boutonneuse fever (Mediterranean spotted fever) with endemic occurrences.
Typhus Group
  • R. prowazekii:
    • Causes epidemic typhus with facial rash but no eschar; vector is the human body louse.
    • Invasion via gut lining where feces enter the skin.
  • Sporadic Typhus: Infected squirrel fleas serve as vectors.
  • R. typhi: Causes endemic (murine) typhus, noted in warm, humid climates with less severe symptoms compared to RMSF.
  • Orientia tsutsugamushi: Scrub typhus, primarily sourced from rat reservoirs; favors East Asia, Australia, and Japan.

Diagnosis of Rickettsia

  • Clinical Signs and Patient History:
    • Triad: fever, headache, characteristic rash.
  • Diagnostics:
    • Immunohistochemistry with labeled antibodies.
    • Conventional and real-time PCR.
    • Tissue cultures.
    • Serological identification in convalescent specimens.

Anaplasmataceae: Ehrlichiosis & Anaplasmosis

  • Genera: Ehrlichia and Anaplasma.
  • Structures:
    • Contains two forms: Dense elementary body (EB) and reticulate body (RB); can form morulae (clusters).
  • Diagnosis:
    • Patient history, morulae observed in host cells.
    • Direct antigen testing from liver, spleen, or bone marrow.

Anaplasmataceae: Diseases

  • Ehrlichiosis:
    • E. chaffeensis: Causes Human Monocytic Ehrlichiosis (HME).
    • Common in southeastern, south-central, and mid-Atlantic regions of the US.
  • Vector: Amblyomma americanum (Lone Star Tick); reservoir includes deer, dogs, and humans.
  • Symptoms: Headache, fever, malaise; may cause leukopenia, thrombocytopenia, elevated liver enzymes.
  • Differentiation:
    • E. ewingii: Granulocytic ehrilichiosis which mainly invades neutrophils.
  • Anaplasma:
    • Anaplasma phagocytophilum: Causes Human granulocytic anaplasmosis resembling HME.

Q Fever: Coxiella

  • C. burnetii: Q fever (query).
  • Symptoms: Non-specific flu-like symptoms; may spread to heart, liver, lungs; slow chronic form has a high mortality rate.
    • Previously classified as Rickettsia; it is tick-borne but can also grow in cell-free media and survives environmental exposure.
  • Transmission: Aerosolization, ingestion from infected animals (cats, dogs, cattle, sheep).

Mycoplasmataceae Family

  • Genera: Mycoplasma and Ureaplasma.
  • Characteristics:
    • Smallest free-living organisms, pleiomorphic without a cell wall, making them resistant to antibiotics targeting cell wall synthesis.
    • Capable of independent replication and growth on artificial media.
  • Pathogenic Species:
    • M. pneumoniae: Causes primary atypical pneumonia.
    • M. hominis, M. genitalium, and U. urealyticum: Associated with urogenital tract infections.

Mycoplasma pneumoniae: Primary Atypical Pneumonia

  • Commonly referred to as: Eaton Agent.
  • Infections:
    • Can cause chest colds, symptoms include nonproductive cough and respiratory infection in children.
  • Transmission: Direct contact; environments such as schools, dorms, LTCs, hospitals are conducive, particularly during fall and winter.
  • Complications: Possible hemolytic anemia, rash, meningitis, temporary arthritis.
  • Treatment: Antibiotics such as Erythromycin or Tetracycline (ß-lactams ineffective due to absence of cell wall).

Urogenital Mycoplasma Infections

  • Affecting Mycoplasma hominis, M. genitalium, and Ureaplasma urealyticum.
  • Infections: Can cause asymptomatic colonization or lead to Nongonococcal urethritis.
  • Diagnostic Methods:
    • Culture, serology, and swabs from relevant sites (amniotic fluid, discharge specimens).

Diagnostics for Mycoplasma pneumoniae

  • Serology: Initial testing before PCR, detecting IgG and IgM.
  • PCR: Oropharyngeal, nasal swabs, sputum.
  • Cultures: Challenging to grow, using diphasic liquid medium supplemented with yeast and horse blood at 37°C for 4 weeks in CO2.
  • Historical Aspect: Cold agglutinins are nonspecific antibodies found in approximately 50% of infected individuals; they agglutinate Type O red blood cells at low temperatures. Axtensions include a 4x increase in antibody titer or >1:128 indicates infection.