Rickettsial Infection Clinical Presentation

Updated: Jun 14, 2016
  • Author: Mobeen H Rathore, MD, CPE, FAAP, FIDSA; Chief Editor: Russell W Steele, MD  more...
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Early signs and symptoms of these infections are notoriously nonspecific and may mimic benign viral illnesses, making the diagnosis more difficult. Certain features that aid in making the early diagnosis of rickettsial diseases include (1) a history of tick bite or exposure, (2) recent travel to endemic areas, and (3) similar illness in family members, coworkers, or family pets (especially dogs).

Rocky Mountain spotted fever (RMSF)  [23]

  • Fever, headache, rash, confusion, and myalgia are cardinal features.

  • Onset may be gradual or abrupt, beginning approximately 1 week (range, 2-14 d) following a bite from an infected tick. As many as 40% of patients may be unaware of the tick bite, which is usually painless and may go unnoticed or be easily forgotten.

  • Headache is usually persistent, intense, and intractable.

  • Patients may appear toxic, and this usually progresses to mental confusion and delirium.

  • GI symptoms (eg, abdominal pain and diarrhea) commonly occur during early stages of illness.

  • Conjunctival injection may also be seen.

Rickettsialpox  [4]

  • After an incubation period of 9-14 days, a red papule develops at the site of the mite bite. The papule subsequently develops an eschar. The appearance of the latter roughly coincides with the appearance of fever.

  • Irregular fluctuating fever (38-41°C) occurs and lasts for less than a week. Fever is accompanied by headache, chills, rigors, profuse sweating, myalgias, and occasionally by rhinorrhea, cough, sore throat, nausea, vomiting, and abdominal pain.

Boutonneuse fever

See the list below:

  • Incubation period is usually 6 days (ranges from 1-16 d).

  • An eschar or cutaneous necrosis caused by rickettsial vasculitis at the tick-bite site of inoculation, known as tache noire ("black spot"), is pathognomonic. However, it may not be seen in 14-40% of cases. This lesion heals slowly over 10-20 days without leaving a scar.

  • The disease has an acute onset with high fever (above 39°C), headache, malaise and arthromyalgias. Headaches are less frequent in children. [10] Unusual presentations, such as acute pancreatitis, have also been described. [21]

  • African tick bite fever is similar but has a more timid presentation. It differs from other similar rickettsioses in that it produces a painful lymphadenopathy, multiple eschars, nuchal myalgia, and, occasionally, a sparse vesicular rash. [1, 24]

Louse-borne (epidemic) typhus

See the list below:

  • The illness has an abrupt onset occurring 1-2 weeks following the bite of an infected louse.

  • Patients develop fever, intractable headache, and rash. The rash appears on days 4-7 of illness and spreads from the trunk to the extremities, sparing the face, palms, and soles. The lesions progress from macules to maculopapules to petechiae.

  • Conjunctival injection, rales, and delirium commonly occur.

Brill-Zinsser disease (relapsing louse-borne typhus)

Presentation is analogous to primary louse-borne epidemic typhus but is milder.

Murine (endemic or flea-borne) typhus  [14]

  • Murine typhus is similar to louse-borne typhus but tends to have a milder and shorter course.

  • Fever is less pronounced and remittent, headache is less severe, and rash is less extensive. The latter may be absent in approximately 50% of patients.

Tsutsugamushi disease (ie, scrub typhus)  [14]

  • The incubation period is approximately 1-2 weeks.

  • In fewer than half of patients, the site of the mite bite develops a necrotic eschar with enlargement of regional lymph nodes similar to rickettsialpox.

  • Inquiring about history of travel to the Southwest Pacific or Southeast Asia, where patients almost exclusively contract this disease is also helpful.

Q fever  [25, 5]

  • Primary infection is usually asymptomatic. Adults and men are more likely to have symptomatic infection compared with children and women, respectively.

  • Incubation period ranges from 2-6 weeks.

  • Acute Q fever infection usually has an abrupt onset, with fever, intractable headache, chills, myalgia, cough, and chest pain. The three clinical presentations more commonly observed are flulike illness, pneumonia, and hepatitis.

  • Rash is absent in over 90% of cases.

  • Chronic Q fever infection is less common (1-5%). It may be manifested as endocarditis, chronic or relapsing multifocal osteomyelitis, chronic hepatitis, chronic vascular infection, endocarditis, pericarditis, or myocarditis. [26] The infection may be insidious, developing months to years following the acute infection.

  • Humans contract the disease by inhaling contaminated aerosols when they come in contact with infected animals or materials contaminated by them. Workers who handle livestock (eg, cattle, sheep, goats), especially at the time of slaughter or parturition, are at an increased risk of infection. Human infection also occurs after ingestion of contaminated raw milk. [5]

Tickborne lymphadenopathy (TIBOLA) and Dermacentor -borne-necrosis-eschar-lymphadenopathy (DEBONEL)  [1]

  • An eschar associated with painful cervical lymphadenopathy appears 1 week after a tick bite to the occipital scalp.

  • Fever and rash are seldom present.

  • Patients may develop persistent asthenia and alopecia at the site of the eschar.




See the list below:

  • Fever reaches 40-41°C and, more commonly, has a persistent pattern rather than an oscillating one. [23, 4]

  • Rash starts on the second or third day of the illness. It usually appears peripherally on the wrists and ankles and spreads to involve the extremities and trunk. Rarely, the rash may be evanescent or localized to a particular region of the body. [27]

  • Typically, the lesions are small (1-5 mm), blanching, erythematous macules that may progress to maculopapules and petechiae.

  • Skin necrosis is rare. In as many as 20% of cases, patients may not develop a rash (spotless RMSF), but this should not delay institution of proper therapy based on historical and clinical data.

  • Signs of meningoencephalitis and coma may follow delirium.

  • Meningismus may accompany the disease but is not necessarily associated with abnormal cerebrospinal fluid (CSF) findings (eg, minor elevation of CSF lymphocyte count). Other neurologic findings may include cortical blindness, seizures, central deafness, ataxia, paralysis, and cranial palsies.

  • Cardiac involvement frequently occurs. Adequate monitoring and workup are necessary to exclude arrhythmias and congestive cardiac failure.

  • Pulmonary manifestations may range from atelectasis to infiltrates or pulmonary edema.

  • Myalgia is a common feature and usually manifests as thigh or calf tenderness.

  • Retinal disease (i.e., edema, papilledema, cotton wool exudates, hemorrhages, retinal artery occlusion) occurs more commonly than uveitis or iritis.

  • Enlargement of the liver or spleen is infrequent.


See the list below:

  • Regional lymph nodes at the area of the primary eschar typically become enlarged.

  • A macular rash develops within several days of the onset of fever. The lesions then develop into vesicular maculopapules over a few days. The rash is distributed on the face, neck, trunk, and extremities and easily may be confused with the rash of varicella, especially in adult patients (hence, the name). In addition to the exanthem, the disease also may involve the mucus membranes, causing an enanthem. The pox usually heals within 2-3 weeks without scarring.

  • In addition to the exanthem, the disease also may involve the mucus membranes, causing an enanthem.

Boutonneuse fever

See the list below:

  • Generalized myalgia occurs, and even myositis can be demonstrated.

  • Eschars can be often found in the trunk, arms and legs of cases. In young children they are frequently found on the scalp in a retroauricular area.

  • A rash appears on days 3-5 after the fever onset. It spreads from the extremities to the trunk, neck, palms, and soles within 36 hours. It usually spares the face. [10]

  • The lesions progress from macular to maculopapular and may persist for 2-3 weeks.

  • Atypical cutaneous findings may occur in a few patients and 1-4% of cases never develop a rash.

  • Cervical adenopathy may be found in 33-75% of affected children.

  • Patients with African tick–bite fever usually have a lower incidence of rash. It is usually vesicular and sparser than in Boutonneuse fever. Also, multiple eschars and prominent regional lymphadenopathy are present. [24]

  • Other manifestations and complications are similar to those seen in patients with RMSF.

Louse-borne (epidemic) typhus  [14]

  • A rash appears on days 4-7 of illness and spreads from the trunk to the extremities, sparing the face, palms, and soles. Initially the rash may be concentrated in the axilla.

  • The lesions progress from macules to maculopapules to petechiae.

  • Uncommonly, complications such as gangrene, pericarditis, myocarditis, pleural effusion, and pneumonia may occur.

  • In severe cases, meningoencephalitis and delirium with fatal cardiac and renal failure may ensue.

Brill-Zinsser disease (ie, relapsing louse-borne typhus)

This is analogous to primary louse-borne epidemic typhus. The rash is usually milder and resolves faster.

Murine (endemic or flea-borne) typhus

See the list below:

  • It is similar to louse-borne typhus but tends to have a milder and shorter course.

  • The rash is less extensive. Unlike RMSF, the rash usually spreads from the trunk to the extremities.

Tsutsugamushi disease (ie, scrub typhus)

See the list below:

  • Unlike in other rickettsial diseases, generalized lymphadenopathy is a common feature (80%) of scrub typhus. It develops concomitantly with other manifestations, such as fever, headache, and rash. [14]

  • The rash, which occurs 1-3 weeks following exposure to the vector, is frequently truncal and has a short duration. In 50% of cases, patients have an inoculation eschar.

  • Hepatosplenomegaly, ocular pain, and conjunctival injection are relatively common.

  • Other less common manifestations include deafness, tinnitus, myocarditis, atypical pneumonia, and adult respiratory distress syndrome.

Q fever  [25]

  • Pneumonitis occurs in more than half of patients. Cough is usually nonproductive and physical findings may not be pronounced.

  • Radiography may reveal a wide variety of pathologic findings, ranging from multiple segmental opacities to pleural effusion, lobar consolidation, or linear atelectasis.

  • Hepatitis presents with a fever and silent elevation of liver enzymes (transaminases). Hepatosplenomegaly may be present. [5]

  • Chronic Q fever infection must be excluded in patients with multifocal osteomyelitis, especially if a history of exposure to farm animals is noted. [26]




This disease is caused by R rickettsii. [1, 6]

Tick vectors of RMSF include the Rocky Mountain wood tick (Dermacentor andersoni) in the Western United States and Canada; the American dog tick (Dermacentor variabilis) in the Eastern United States, along the US Pacific coast, and in the central United States; and the Lone Star tick (Amblyomma americanum) in some southern areas. [3] Examples of the ticks are shown in the images below.

This photo shows the relative sizes of the adult f This photo shows the relative sizes of the adult forms of Ixodes scapularis (right) and Dermacentor variabilis (left). These ticks are shown next to a common match for scale. I scapularis is also referred to as Ixodes dammini. Photo by Darlyne Murawski; reproduced with permission.
This photo is of an adult female, Amblyomma americ This photo is of an adult female, Amblyomma americanum, and a nymphal form of the same species (shown next to a common match for scale). Photo by Darlyne Murawski; reproduced with permission.

From 2002-2004, cases of RMSF reported from rural Arizona by Demma and colleagues were attributed to exposure to the common brown dog tick (Rhipicephalussanguineus). [28] This represents a change from the typical vectors for this disease.

Expansions in tick populations can introduce rickettsial agents to new geographic areas and previously unrecognized rickettsiae -vector-human host relationships continue to evolve and be described. [29] Research from Germany identified a possible role for migratory birds in the distribution of emerging tick-borne pathogens including Rickettsiae. [30]

Rickettsiae multiply within ticks and pass to the next generation transovarially.

Rickettsiae are transmitted to a vertebrate host through saliva while a tick is feeding. It usually takes several hours of attachment and feeding before the rickettsiae are transmitted to the host. The risk of exposure to a tick carrying R rickettsii is low. Generally, about 1-3% of the tick population carries R rickettsii, even in areas where most human cases are reported.

Recognized or potential tick-borne spotted fever group rickettsial pathogens in the United States, other than R rickettsii include R akari, Rickettsia felis, Rickettsia parkeri, Rickettsia amblyomii, Rickettsia rhipicephali, and various unnamed serotypes (eg, Tillmook, 364-D). [31]


It is caused by R akari, a member of the spotted fever group of Rickettsiae.

The disease is distinguishable from other rickettsial infections by the presence of an eschar at the site of the mouse mite (Liponyssoides sanguineus) bite, a vesiculopustular eruption, and the absence of Weil-Felix agglutinins.

The house mouse (Mus musculus) is the natural host of the mite transmitting rickettsialpox in the United States. Other rodents have been associated with the disease in other parts of the world. [6]

Boutonneuse fever

This disease is a tick-borne infection caused by various subspecies of Rickettsia conorii complex (R conorii conorii is the cause of Mediterranean spotted fever; R conorii israelensis is the cause of Israeli spotted fever; R conorii caspica is the cause of Astrakhan spotted fever; and R conorii indica is the cause of Indian tick typhus) , Rickettsia africae (the cause of African tick–bite fever) , or R slovaca, which are obligate intracellular organisms transmitted to humans by various ticks, depending on the geographical location. [10]

Contact with dogs carrying infected ticks appears to be the important risk factor for human infection.

Louse-borne (epidemic) typhus

This disease is caused by R prowazekii.

It is transmitted to humans by lice (ie, Pediculus humanus). Humans are the primary reservoir for R prowazekii.

Brill-Zinsser disease (ie, relapsing louse-borne typhus)

The rickettsial cause is the same but is related to the reactivation of the organism from a poorly defined latent state.

Murine (endemic or flea-borne) typhus

This disease is primarily caused by R typhi (Rickettsia mooseri) and R felis, which share a large antigenic moiety with R prowazekii.

It is transmitted from rat-to-rat by a rat flea (X cheopis) and accidentally to humans by the feces of infected fleas.

The cat flea (C felis) can also transmit the disease. [19]

Tsutsugamushi disease (ie, scrub typhus)

This disease is caused by O tsutsugamushi, which has a remarkable antigenic heterogeneity.

It is transmitted to humans by the larval form of trombiculid mites (ie, chiggers) that live and breed in the soil and scrub vegetation. The mite is both the reservoir and the vector that passes the bacteria transovarially. Rodents are also reservoirs. Humans are accidentally infected.

Q fever

The name derives from "Query Fever," given in 1935 following an outbreak of febrile illness in an abattoir in Australia. The disease is caused by C burnetii, a short, Gram negative, strictly intracellular bacterium.

Originally classified in the order Rickettsiales, C burnetii has since been placed (with Legionella and Francisella) into the gamma subdivision of the Proteobacteria on the basis of sequences of the 16SrDNA encoding genes. [5]

Unlike human rickettsial infections, it is a zoonosis transmitted from diseased animals to humans by the aerosol route or ingestion of raw milk.

Animals commonly infected include domestic livestock, especially cattle, sheep, and goats, as well as rodents, marsupials (in Australia), and cats (in Canada).

Ticks play a very minor role, if any, in transmission of the disease to humans; however, they transmit the disease to rodents and domestic animals.

C burnetii is a resilient organism that remains latent in infected hosts (eg, domestic livestock) until it is activated by a physiologic stressor, such as parturition. It then multiplies and contaminates the animals' surroundings, where it remains a potential source of infection for months. It is considered by the Center for Disease Control and Prevention (CDC) a potential agent of bioterrorism (class B). [6, 5]