Spotted fever group rickettsial disease

Author: Catriona Wootton, Dermatologist, UK, 2017. DermNet NZ Editor in Chief: A/Prof Amanda Oakley, Dermatologist, Hamilton, New Zealand. December 2017.


What are the rickettsial diseases?

Rickettsia are small, obligate intracellular, Gram negative bacteria that spend part of their life cycle in an arthropod host (tickfleabody 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.

What is spotted fever group rickettsial disease?

Spotted fever group rickettsial disease, or the rickettsial spotted fevers, include:

Ricketssial spotted fever

Who gets rickettsial spotted fevers?

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. 

Classification and causes of rickettsial spotted fevers

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. 

Rocky Mountain spotted fever (RMSF)

  • Distribution: USA, Canada, Mexico, South America
  • Also known as Sao Paulo typhus, American spotted (or tick) fever, lone star spotted fever, Columbian spotted fever 
  • Bacteria: Rickettsia rickettsii
  • Vector: tick (Dermacentor spp., Rhipicephalus sanguineus, Amblyomma spp.)
  • Hosts: rodents, canines
  • Severity: moderate to severe
  • Rash: widespread maculopapular becoming petechial and purpuric with areas of necrosis
  • Features: abdominal pain, myalgia, necrosis
  • Seasonality: May–September most common
  • Complications: multisystem involvement, encephalitis, renal failure, amputation secondary to necrosis, hearing loss, nerve damage
  • Mortality risk: significant (up to 30%)

African tick typhus

  • Distribution: Sub-Saharan Africa, West Indies
  • Bacteria: Rickettsia africae
  • Vector: tick (Amblyomma spp.)
  • Hosts: cattle
  • Severity: asymptomatic or mild typically
  • Rash: maculopapular or vesicular
  • Unusual features: eschars are often multiple, clusters of people affected at the same time
  • Seasonality: November–April most common
  • Complications: prolonged fever, reactive arthritis
  • Mortality risk: very low 

Boutonneuse fever 

  • Distribution: Southern Europe, Africa, Southern Russia, Southern Asia
  • Also known as Mediterranean spotted (or tick) fever
  • Bacteria: Rickettsia conorii
  • Vector: tick (Rhipicephalus sanguineus)
  • Hosts:  canines, rodents
  • Severity: mild
  • Rash: macular then maculopapular rash
  • Seasonality: May–September most common
  • Mortality risk: low 

Rickettsialpox

  • Distribution: USA, South Africa, Balkan states, Ukraine (mainly urban locations)
  • Also known as Kew Gardens spotted fever, and vesicular rickettsiosis
  • Bacteria: Rickettsia akari
  • Vector: House mouse mite (Liponyssoides sanguineus)
  • Hosts: rodents
  • Severity: asymptomatic or mild typically
  • Rash: sparse papulovesicular rash
  • Unusual features: central nervous system features have been reported, such as stiff neck, photophobia
  • Seasonality: often occurs after extermination of infected rodents as the mites seek new hosts
  • Mortality risk: very low

Flea-borne spotted fever

  • Distribution: worldwide
  • Bacteria: Rickettsia felis
  • Vector: cat fleas (Ctenocephalides felis)
  • Hosts: felines, canines, rodents
  • Severity: probably mild
  • Rash: generalised maculopapular rash
  • Unusual features: emergent disease (only discovered in last 20 years), cases poorly characterised and under-appreciated currently
  • Mortality risk: probably low

What are the clinical features of rickettsial spotted fevers?

The classical triad of symptoms in all rickettsial diseases is:

  • Fever
  • Severe headache
  • Myalgia (muscle pain).

Rash

  • Typically develops 3–6 days after the onset of illness
  • Often starts on the limbs spreading to the trunk
  • Palm and sole involvement may occur
  • Typically maculopapular but may be vesicular
  • Petechiae can occur and may lead to areas of necrosis
  • A cutaneous eschar may be seen at the site of the tick or mite bite in some of the rickettisal diseases, typically 4–10 days after inoculation. 

What are the complications of rickettsial spotted fevers?

The severity of the rickettsial spotted fevers varies considerably. The complications seen include:

  • Abdominal pain
  • Necrosis which can lead to amputation
  • Inflammation of the lungs
  • Hypotension
  • Acute renal failure
  • Acute respiratory failure
  • Neurological damage
  • Shock and multisystem failure
  • Encephalitis (inflammation of the brain).

How are rickettsial spotted fevers diagnosed?

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:

  • Serology
  • Polymerase chain reaction (PCR)
  • Cell culture

What is the differential diagnosis for rickettsial spotted fevers?

The differential diagnosis includes any disease causing rash, fever and headache.

The differential diagnosis for an eschar includes:

What is the treatment for rickettsial spotted fevers?

Rickettsial spotted fevers can be treated successfully with tetracycline antibiotics, especially doxycycline. Chloramphenicol is the second-line treatment option.

Prevention of rickettsial spotted fevers

No vaccines exist for rickettsial infections. 

Rickettsial infections can be prevented by taking measures to reduce exposure to ticks and mites.

  • Applying an effective insect repellent, such as DEET
  • Wearing long trousers, shoes and socks in tick habitats
  • Regularly checking pets for ticks
  • Reducing domestic rodent populations

What is the outcome of rickettsial spotted fevers?

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.

 

Related Information

References 

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  • Brown LD & Macaluso KR. Rickettsia felis, an emerging flea-borne rickettsiosis. Curr Trop Med Rep 2016; 3: 27-39. DOI: 10.1007/s40475-016-0070-6. PubMed Central.
  • Crespo P, Seixas D, Marques N, Oliveira J, da Cunha S & Meliço-Silvestre A. Mediterranean spotted fever: case series of 24 years (1989-2012). SpringerPlus 2015; 4: 272. DOI: 10.1186/s40064-015-1042-3. PubMed Central.
  • Chikeka I & Dumler JS. Neglected bacterial zoonoses. Clin Microbiol Infect 2015; 21(5): 404-15. DOI: 10.1016/j.cmi.2015.04.022. Journal.
  • Parola P, Paddock CD, Socolovschi C, et al. Update on tick-borne rickettsioses around the world: A geographic approach. Clin Microbiol Rev 2013; 26(4): 657-702. DOI: 10.1128/CMR.00032-13. PubMed Central.

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