History
The incubation period for Rocky Mountain spotted fever (RMSF) is 2-14 days after the tick bite. A history of tick bite is present in only two thirds of cases.
Symptoms can begin gradually or abruptly. Fever, headache, rash, myalgia, and mental confusion are the major clinical manifestations.
The patient's body temperature usually exceeds 38.8°C (101.8°F). Headache is the most common neurologic manifestation. In older children and adults, the headache may be intractable and may be ongoing day and night. Young children may not complain of headache.
Nausea, vomiting, and abdominal pain may occur. Conjunctival hyperemia and photophobia may be observed.
Rash
The rash of Rocky Mountain spotted fever is an important pathognomonic feature of the disease and is present in 80-90% of patients. Rash begins as blanching maculopapular lesions. These lesions become petechial or purpuric in approximately one half of patients, accounting for the disease’s former name of black measles. [9]
The rash first appears peripherally on the wrists and ankles. It spreads centripetally over the next 2-3 days. Involvement of the palms and soles is an important diagnostic feature.
In most patients, rash usually appears by the second or third day. However, it may be delayed until the sixth day.
Early recognition of the blanching macular eruption is vital, because the classic petechial rash does not typically appear until 6 days or so after the initial symptoms become apparent.
Physical Examination
Body temperature exceeds 38.8°C (101.8°F). The patient may have a toxic appearance. The characteristic skin rash is present in 80-90% of infected individuals. Hepatomegaly and splenomegaly are present in approximately 33% of patients. Signs of meningoencephalitis include restlessness, irritability, mental confusion, and delirium.
Meningismus may occur. Findings may include neck stiffness, photophobia, a positive Kernig sign (pain on knee extension when the hip is flexed to 90°), and a positive Brudzinski sign (knee and hip flexion when the neck is flexed).
Ataxia may be present. Spastic paralysis may occur. Sixth nerve palsy may be observed. Muscle tenderness is a common feature.
Complications
Complications may include the following:
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Meningitis
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Renal failure
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Pulmonary involvement
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Liver impairment with development of jaundice
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Splenomegaly
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Myocarditis
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Thrombocytopenia
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Geographic distribution of Rocky Mountain spotted fever incidence in 2010, cases per million: Courtesy of the US Centers for Disease Control and Prevention.
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Annual incidence (per million persons) for Spotted Fever Rickettsiosis (SFR) in the United States, 2017. Courtesy of the CDC.
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Under a magnification of 98X, this scanning electron microscopic (SEM) image depicts the dorsal view of the head region from an American dog tick, Dermacentor variabilis, magnified 98X. D. variabilis is a known carrier of Rocky Mountain Spotted Fever (RMSF) caused by the bacterium, Rickettsia rickettsii. Courtesy of the Public Health Image Library (PHIL), CDC, photo credit Janice Haney Carr.
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Rocky Mountain Spotted Fever (RMSF) rash in a child. It appears day 3-5 of illness, begins in ankles and wrists, and typically involves palms and soles. In early stages it is macular and later it is petechial. Courtesy of the Morbidity and Mortality Weekly Report (MMWR), CDC.
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Tick identification. (i) American dog tick (Dermacentor variabilis), ii) Rocky Mountain wood tick (Dermacentor andersoni), and, iii) brown dog tick (Rhipicephalus sanguineus) iv) Lone star tick (Amblyomma americanum). Courtesy of the CDC.
Tables
Organism |
Disease or Presentation |
Geographic Location |
Rickettsia rickettsii |
Rocky Mountain spotted fever |
North, Central and South America |
Rickettsia akari |
Rickettsialpox |
Worldwide |
Rickettsia conorii |
Mediterranean spotted fever, boutonneuse fever, Israeli spotted fever, Astrakhan fever, Indian tick typhus |
Europe, Asia, Africa, India, Israel, Sicily, Russia |
Rickettsia sibirica |
Siberian tick typhus, North Asian tick typhus |
Siberia, People's Republic of China, Mongolia, Europe |
Rickettsia australis |
Queensland tick typhus |
Australia |
Rickettsia honei |
Flinders Island spotted fever, Thai tick typhus |
Australia, South Eastern Asia |
Rickettsia africae |
African tick-bite fever |
Sub Saharan Africa, Caribbean |
Rickettsia japonica |
Japanese or Oriental spotted fever |
Japan |
Rickettsia felis |
Cat flea rickettsiosis, flea borne typhus |
Worldwide |
Rickettsia slovaca |
Necrosis, erythema, lymphadenopathy |
Europe |
Rickettsia heilongjaiangensis |
Mild spotted fever |
China, Asian region of Russia |
Rickettsia parkeri |
Mild spotted fever |
US |
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