Infectious Diseases: Borrelia and Tuberculosis

Borrelia

• Causes Lyme disease and relapsing fever in humans.
• Lyme disease is caused by Borrelia burgdorferi.
  • Transmitted by ticks, specifically hard ticks of the genus Ixodes.
  • Characterized by an expanding red "bull's-eye" rash at the infection site.
• Relapsing fever is caused by different Borrelia species.
  • Louse-borne relapsing fever is caused by Borrelia recurrentis and transmitted by human body lice.
  • Tick-borne relapsing fever is caused by various Borrelia species and transmitted by soft ticks.
  • Characterized by recurring episodes of septicemia and fever due to the body's repeated efforts to remove the spirochetes.

Tuberculosis

• Infection characterized by granulomatous inflammation, forming tubercles.
• Primarily affects the lungs but can involve any organ or tissue.
• Primary TB: Initial infection, usually doesn't progress to active TB in most cases.
• Post-primary/secondary TB: Dormant bacilli reactivate and develop into active TB.
• Active TB: TB bacilli multiply, leading to signs and symptoms of the disease.
• Latent TB: Bacilli are dormant, no symptoms or signs are seen.
  • Can be detected by TST and IFN-g release assay.
  • Some patients' chest X-rays may show evidence of primary infection.

Mycobacterium leprae

• Humans are the primary reservoir, with armadillos being the only other known host.
• Bacteria cannot grow in cell-free culture.
• Has low virulence.
• Transmission occurs through direct contact with lesions or nasal secretions, and inhalation of respiratory droplets. Requires long-term exposure.
• Causes leprosy:
  • Tuberculoid leprosy: Non-progressive form with a strong cell-mediated immune response, low infectivity.
  • Lepromatous leprosy: More virulent form with a weak cell-mediated immune response, high infectivity.

Chlamydia trachomatis

• Has a limited host range, primarily infecting humans.
• Enters the body through abrasions and lacerations.
• Infects the conjunctiva and various mucous membranes.
• Clinical manifestations result from cell destruction and inflammation.

Chlamydia trachomatis: Diseases

• Sexually transmitted diseases:
  • Asymptomatic infection is common, especially in women.
  • Reinfection can cause pelvic inflammatory disease.
  • Most frequent cause of infection-related sterility.
  • Lymphogranuloma venereum: Initial genital lesion followed by bubo formation.
  • Nongonococcal urethritis, Proctitis: Can also cause these infections.
• Ocular diseases:
  • Transmitted through direct contact with infected secretions or indirect contact with contaminated objects.
  • Trachoma: Endemic in developing countries, a leading cause of preventable blindness.
  • Adult inclusion conjunctivitis: Usually seen in sexually active adolescents/adults with genital infection. Can be transmitted through autoinoculation.
• Infections of the newborn:
  • Transmitted from mother to infant during birth.

Mycoplasmas

• Smallest free-living microbes.
• Lack cell walls but have sterols in their cytoplasmic membranes.
• Require various growth factors from a host or laboratory media.
• Can colonize mucous membranes of the respiratory and urinary tracts in humans.

Mycoplasma pneumoniae

• Attaches to epithelial cells lining the human respiratory tract.
• Transmission occurs through respiratory droplets.
• Causes primary atypical pneumonia.
  • Early symptoms are atypical of other types of pneumonia.
  • Often mild, not requiring hospitalization (also known as walking pneumonia).
  • Common in children aged 5-15.

Other Mycoplasmas

• M. hominis, M. genitalium, and Ureaplasma urealyticum are associated with human diseases.
  • Often colonize the urinary and genital tracts.
• M. genitalium and U. urealyticum can cause non-gonococcal urethritis.
• M. hominis can cause pelvic inflammatory disease (PID) in women.
• Abstinence and safe sex practices help prevent the spread of these organisms.