Relapsing Fever



Relapsing Fever


Barbara W. Stechenberg



Relapsing fever is a vector-borne, spirochetal infection characterized by recurring febrile episodes of a remitting nature. It is caused by several species of Borrelia. Borrelia are loosely coiled spirochetes that easily stain with Wright or Giemsa stain, allowing diagnosis to be established by examination of the blood smear. They also can be grown on artificial media. The organism undergoes spontaneous antigenic variation in vivo and in vitro. Different antigenic variants result in repeated episodes of dense spirochetemia and account for the cyclic nature of the disease. With each remission, antibodies are produced to a specific strain, which then is immobilized and removed from the circulation.


EPIDEMIOLOGY

Louse-borne epidemic relapsing fever is caused by Borrelia recurrentis. Lice become infected by feeding on spirochetemic humans. Transmission to humans takes place when the bite wound is contaminated with the infectious hemolymph of the louse as it is crushed or wounded. This form of relapsing fever no longer is found in the United States, but it occurs in Africa and South America, particularly in areas of crowding, cold weather, and poor hygiene.

Endemic relapsing fever is transmitted by ticks of the genus Ornithodoros. B. hermsii and B. turicatae are the most common species in North America, but many species are implicated worldwide. After the tick becomes engorged on an infected host, Borrelia invade all tissues, and the tick remains capable of transmitting infection for years. These ticks occur in many areas of the world; in the United States, they are seen primarily in forested mountain areas of the western states, particularly in areas or dwellings with large rodent nests. The bite of these ticks is painless, and the ticks feed for short periods (10 to 30 minutes), often at night.

Jul 24, 2016 | Posted by in ORTHOPEDIC | Comments Off on Relapsing Fever

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