Author: Catriona Wootton, Dermatologist, UK, 2017. DermNet NZ Editor in Chief: A/Prof Amanda Oakley, Dermatologist, Hamilton, New Zealand. December 2017.
Rickettsia are small, obligate intracellular, Gram negative bacteria that spend part of their life cycle in an arthropod host (tick, flea, body louse or mite). Humans are infected with the rickettsial organism either via a bite or contact with faeces from an infected arthropod. The disease that develops depends upon the specific bacterium transmitted. Many different bacterial species are classified within the rickettsial group and a variety of different clinical manifestations are seen which vary greatly in terms of severity. The majority of rickettsial diseases result in a rash and some will also result in a cutaneous eschar, aiding diagnosis.
Spotted fever group rickettsial disease, or the rickettsial spotted fevers, include:
As the rickettsial diseases are transmitted via arthropods, humans at risk of infection are those who come into contact with the specific arthropod vectors. The rickettsial spotted fevers are transmitted by ticks, mites and fleas, depending on the species.
Some of the most common rickettsial spotted fevers are listed below but many others exist. There are at least 14 species transmitted by ticks, 1 by mites and 1 by fleas.
The classical triad of symptoms in all rickettsial diseases is:
The severity of the rickettsial spotted fevers varies considerably. The complications seen include:
Diagnosis is spotted fever group rickettsial disease is based on the clinical presentation and risk factors for exposure to ticks or mites. Laboratory confirmation can be difficult and includes:
The differential diagnosis includes any disease causing rash, fever and headache.
The differential diagnosis for an eschar includes:
Rickettsial spotted fevers can be treated successfully with tetracycline antibiotics, especially doxycycline. Chloramphenicol is the second-line treatment option.
No vaccines exist for rickettsial infections.
Rickettsial infections can be prevented by taking measures to reduce exposure to ticks and mites.
The outcome very much depends on the type of spotted fever. RMSF is a serious and potentially life-threatening disease. The possible sequelae from RMSF include amputation due to necrosis, hearing loss, paralysis and mental disability.
The other spotted fevers are generally much milder and in some cases patients may be asymptomatic.
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