The syndrome of relapsing fever consists of two clinical entities: epidemic relapsing fever caused by Borrelia recurrentis (LBRF) and transmitted by the human body louse and endemic relapsing fever caused by Borrelia spp. (TBRF) and transmitted by arthropods (Table 1). A. Epidemiology. 1. Louse-borne epidemic relapsing fever (LBRF).
Lyme disease is a tick-borne illness caused by the spirochete B burgdorferi. Lyme disease can be divided into early disease (stage 1, EM), disseminated infection (stage 2), and late disease (stage 3, persistent infection). The first stage involves the skin, followed by stages 2 and 3, which often affect the skin, joints, CNS, and heart.
The term syphilis was first used in 1530 by the Italian physician Girolamo Fracastoro in his epic poem Syphilis Sive Morbus Gallicus. Much has been learned since then about this sexually transmitted disease caused by T pallidum.
Tertiary disease, usually seen 5-20 years after initial infection, traditionally includes cardiovascular syphilis, late benign (or gummatous) syphilis, and neurosyphilis (see Box 1). Fewer organisms are found in lesions during this stage. The incidence of cardiovascular involvement is probably underestimated, although clinically significant disease eventually develops in ~ 10% of all untreated patients.
The secondary stage of syphilis occasionally overlaps with the primary phase but usually begins ~ 6 weeks after resolution of the chancre; however, it can develop as late as 6 months after infection (see Box 1). Most patients have some degree of skin or mucocutaneous involvement. A faint and evanescent macular rash of the trunk and abdomen known as roseola syphilitica is sometimes seen initially.
The lesions of primary syphilis appear at the site of inoculation after an incubation period that is inversely proportional to the number of infecting organisms, usually 3 weeks (Box 1). The chancre is an ulcerative lesion that varies in size from several millimeters to 2 cm.
Originally thought to be fungi due to their hyphae-like appearance, they are now recognized as bacteria based on their cell wall components, reproduction by fission without sporulation or budding, inhibition by antibacterial agents, and molecular phylogenetic analysis. The actinomycete chromosomes contain a high content of guanosine and cytosine.
Disease occurs when mechanical insult disrupts the mucosal barrier or organisms gain access to privileged sites. For example, actinomycosis commonly occurs after dental procedures, trauma, surgery, or aspiration. Actinomyces israelii causes the majority of human disease owing to this genus, but other species, including Actinomyces naeslundii, Actinomyces viscosus, Actinomyces enksonii, Actinomyces odontolyticus, and Actinomyces meyeri have also been implicated. Actinomycosis is threefold more common in men than women.
Nocardia spp. are strictly aerobic, ubiquitous soil-dwelling organisms that are largely responsible for the decomposition of organic plant material. Infection usually occurs via inhalation of these organisms in airborne dust particles, leading to pulmonary disease.
The increasingly relative importance of the atypical mycobacteria, many of which are ubiquitous in the environment, was recognized with the decline in tuberculous disease. Generally, atypical mycobacteria are unusual causes of disease in patients who are immunocompetent but can in immunocompromised hosts such as AIDS and cancer patients.