Harrison’s Manual of Medicine 19th edition provides 600+ internal medicine topics in a rapid-access format. Download Harrison’s App to iPhone, iPad, and Android smartphone and tablet. Explore these free sample topics:
-- The first section of this topic is shown below --
Microbiology and Epidemiology
Borrelia burgdorferi, the causative agent of Lyme disease, is a fastidious microaerophilic spirochete. The human infection Lyme borreliosis is caused primarily by three pathogenic genospecies: B. burgdorferi sensu stricto (hereafter referred to as B. burgdorferi), Borrelia garinii, and Borrelia afzelii.
- B. burgdorferi is the sole cause of Lyme borreliosis in the United States; all three genospecies are found in Europe, and the latter two species occur in Asia.
- Lyme disease is the most common vector-borne illness in the United States, with ~300,000 cases each year.
- Ixodes ticks transmit the disease.
- I. scapularis, which also transmits babesiosis and anaplasmosis, is found in northeastern and midwestern states; I. pacificus is found in western states.
- The white-footed mouse is the preferred host for larval and nymphal I. scapularis. Adult ticks prefer the white-tailed deer as host.
- Nymphal ticks transmit the disease to humans during the early summer months after feeding for ≥24 h.