Author: Dr Marie Hartley, Staff Writer, 2009.
Relapsing fever is caused by a group of bacteria called Borrelia. Borrelia are transmitted to humans by two vectors: ticks (of the genus Ornithodoros) and lice. Louse-borne relapsing fever will not be discussed further in this section.
Various species of Borrelia predominate in different geographic locations. Each Borrelia species are identified closely with their tick vector and they share parallel names. For example Borrelia hermsii are transmitted by Ornithodoros hermsii ticks. The ticks' hosts are wild rodents or other mammals.
Tick-borne relapsing fever (TBRF) is endemic in many countries. In developed countries humans acquire infection by contact with the ticks in caves, when crawling under houses in endemic areas, or in remote log cabins. There are approximately 25 cases of TBRF in the United States each year. In developing countries the ticks live in thatched roofs and mud walls and floors of houses. The incidence of TBRF can be more than 6% in parts of Africa.
TBRF is characterised by relapsing (i.e. recurring) episodes of fever, often accompanied by other symptoms. The symptoms of TBRF begin abruptly around 2 to 10 days after the tick bite. The patient experiences around 3 to 6 days of fever, headache, muscle and joint pain, shaking chills, and abdominal pain. The first fever episode ends in ‘crisis’, which consists of a markedly high temperature, raised heart rate, and raised blood pressure. After 10 to 30 minutes temperature and blood pressure fall dramatically, and the patient sweats profusely.
Following this the patient is symptom-free for around one week, before a recurrence of the fever and other symptoms. The patient experiences an average of three recurrent episodes throughout the course of the illness, although up to 10 recurrences can occur in patients who are untreated.
Other clinical features that may be present include: enlarged liver and spleen, jaundice, respiratory symptoms, and central nervous system involvement.
Long-term complications occasionally occur including: iritis (inflammation of the iris of the eye), depression, and heart failure. In an estimated 2% to 5% of patients the disease is fatal.
Rash occurs in up to 50% of patients, depending on the particular species of Borrelia involved. A variety of skin lesions have been associated with TBRF:
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