MICROBIOLOGY

• Lyme disease: see separate module for Borellia burgdorferi sensu latu.
• Epidemic, louse-borne relapsing fever (LBRF): person-person transmission of Borrelia species such as B. recurrentis (like typhus) by human body louse (Pediculus humanus).
  • Worldwide infection (ex. S’ Pacific)
  • B. recurrentis only causes epidemic louse-borne RF.
  • Spirochete, helical 5-40µm long with 3-10 spirals (see Fig 1).
• Sporadic endemic, tick-borne relapsing fever (TBRF): tick-borne (Ornithodoros, soft ticks) reservoirs include rodents and small animals.
  • Species:
    
    • >15 Borrelia spp. cause endemic tick-borne RF.
  • TBRF vectors and Borrelia spp.:
    • In North America, all cases of TBRF have been associated w/ 2 spp. of soft ticks: O. hermsii and O. turicatae [Fig 2].
      • These soft ticks do not attach for long but bite and feed on blood like chiggers or bedbugs, feeding at night.
        • Bites are not painful; sometimes, crusted blood can be seen on the skin.
        • Usually live in nests of chipmunks, squirrels and small mammals.
    • The three main agents of TBRF in the U.S. are B. hermsii, B. parkeri, and B. turicatae.
      
      • Microscopic inspection cannot distinguish bacterial spp.
        • B. hermsii can be identified by a monoclonal antibody, and most Borrelia spp. can be sorted by PCR analysis using genome species-specific markers. However, neither of these is routinely available in most commercial laboratories.
    • Borrelia duttoni, transmitted by the Ornithodoros moubata tick vectors, is a cause of TBRF in Tanzania and other parts of Africa.
      • It tends to be more severe than usual TBRF.
• Borrelia miyamotoi: recently described human pathogen tick-transmitted (Ixodes) and may cause a febrile illness similar to human granulocytic anaplasmosis and meningoencephalitis[18].
  
  • It may cause febrile illness of nonspecific nature. Still, a report from Russia described some with erythema migrans, but unclear if due to Lyme disease co-infection (with B. burgdorferisensu latu)[21].
    • Easily confused with HGA, HME, or acute Lyme disease without a rash.
      • Presentations may appear to mimic bacterial sepsis with fever, elevated LFTs and thrombocytopenia.
  • Cases are seen in Europe and U.S.
    • The same distribution as Lyme disease as it appears to spread in the U.S. by Ixodes scapularis.
      • Descriptions in New England, mid-Atlantic and upper Midwest states
  • Subclinical infections are likely as up to 5-10% seropositive in some New England communities.
• Borrelia mayonii (described in 2016): a member of B. burgdorferi sensu latu with a high blood spirochetemic load, unlike Lyme disease. Also transmitted by Ixodes ticks.
  
  • The few patients reported were all from MN and WI only.
  • Febrile illness that may be severe enough to prompt hospitalization
    • Rash: ranges from erythema migrans-like to diffuse maculopapular
    • Arthritis
    • Neurologic