You are in: eMedicine Specialties > Infectious Diseases > MEDICAL TOPICS RickettsialpoxArticle Last Updated: Apr 11, 2008AUTHOR AND EDITOR INFORMATIONSection 1 of 10
  Author: Julie A Ake, MD, Fellow, Infectious Disease Service, Walter Reed Army Medical Center Coauthor(s): Richard J Scarfone, MD, Associate Professor, Department of Pediatrics, University of Pennsylvania School of Medicine; Attending Physician and Director of Emergency Preparedness, Division of Emergency Medicine, The Children's Hospital of Philadelphia; Timothy J Whitman, DO, Consulting Staff, Department of Infectious Disease, National Naval Medical Center; Chi Hiong U Go, MD, Assistant Professor, Department of Internal Medicine, Texas Tech University Health Science Center at Odessa Editors: Fred A Lopez, MD, Vice-Chair, Department of Internal Medicine, Division of Infectious Diseases, Assistant Professor, Louisiana State University School of Medicine; Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine; Charles V Sanders, MD, Edgar Hull Professor and Chairman, Department of Internal Medicine, Professor of Microbiology, Immunology and Parasitology, Louisiana State University School of Medicine at New Orleans; Medical Director, Medicine Hospital Center, Charity Hospital and Medical Center of Louisiana at New Orleans; Consulting Staff, Ochsner Medical Center; Eleftherios Mylonakis, MD, Clinical and Research Fellow, Department of Internal Medicine, Division of Infectious Diseases, Massachusetts General Hospital; Burke A Cunha, MD, Professor of Medicine, State University of New York School of Medicine at Stony Brook; Chief, Infectious Disease Division, Winthrop-University Hospital Author and Editor Disclosure Synonyms and related keywords: rickettsialpox, gamasid rickettsiosis, vesicular rickettsiosis, Rickettsia akari, R akari, Allodermanyssus sanguineus, A sanguineus, Liponyssoides sanguineus, L sanguineus, Mus musculus, M musculus, spotted-fever group of rickettsiae, papule, maculopapulovesicular exanthema, leukocytosis, leukopenia, lymphadenopathy, chickenpox, boutonneuse fever, hand-foot-and-mouth disease, scrub typhus INTRODUCTIONSection 2 of 10
  BackgroundRickettsialpox is a mild, self-limited, zoonotic febrile illness characterized by eschar formation at the location of a mite bite, followed by the onset of systemic symptoms and a more generalized papulovesicular rash. The causative agent is Rickettsia akari, a member of the spotted-fever group of rickettsiae. PathophysiologyR akari is an obligate intracellular gram-negative coccobacillus. Its vector is the colorless mite Liponyssoides sanguineus (formerly Allodermanyssus sanguineus), which is found on mice (most commonly the house mouse [Mus musculus]) and other rodents. These hosts serve as the reservoir for the disease. A sanguineus will bite humans when murine hosts are scarce. About 7-10 days after the painless bite, a papular skin lesion appears at the bite location and becomes vesicular with a surrounding area of erythema. An eschar forms and slowly heals. About 3-7 days after the initial skin lesion develops, patients may suddenly develop high-grade fever, chills, headaches, and myalgias with subsequent development of a sparse generalized papulovesicular rash. The disease is mild and self-limited and usually persists for about a week. FrequencyUnited StatesRickettsialpox occurs primarily in urban areas, where the density of mites, mice, and humans is high. Huebner et al first isolated and named rickettsialpox in 1946 in New York City.1 Although the prevalence of confirmed cases is very low, several reports suggest the disease is more common than previously thought. Serologic evidence of rickettsialpox exposure was found in 16% of 631 intravenous drug users in inner-city Baltimore, Md, and in 9% of 204 intravenous drug users in Harlem, NY.2, 3 In addition, between 2001 and 2003, the number of clinical samples submitted to the Centers for Disease Control and Prevention (CDC) increased following the anthrax bioterror attack, reflecting an increased awareness of eschar-associated febrile illness.4 Prior to this, these clinical syndromes may have been misdiagnosed, or perhaps the infected persons did not seek medical attention. Consequently, rickettsialpox is widely believed to be an underrecognized and underreported clinical entity. InternationalInternationally, the disease has been described in Mortality/MorbidityRickettsialpox is a benign, self-limited disease. No fatalities have been reported. The incubation period varies from 10-21 days. Rickettsialpox usually resolves within 14-21 days; however, headache and lassitude may persist for another 1-2 weeks. SexRickettsialpox has no sexual predilection. AgeRickettsialpox has no age predilection. It has been reported in patients aged 6 months to 72 years. CLINICALSection 3 of 10
History
Physical
Causes
DIFFERENTIALSSection 4 of 10
Varicella-Zoster Virus
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| Disease | Rash/Eschar | Generalized Rash | Clinical Features | Geography |
| Rickettsialpox secondary to R akari infection | A red papule with a vesicle in the center dries and forms a black eschar with surrounding induration. Multiple eschars are possible. | The papulovesicular rash is usually on the trunk and extremities; the palms, soles, and oral mucosa may also be involved. | The papule precedes the febrile illness and mild systemic symptoms. Regional lymphadenopathy may develop. | See Frequency |
| Chickenpox secondary to varicella zoster infection | The papule turns into a vesicle on an erythematous base and resembles a "dew drop on a rose petal." | The rash begins on the head and progresses to the trunk, arms, and then legs; vesicles are present in all stages. | It is common in children. No black eschar is present. | Worldwide |
| Mediterranean spotted fever secondary to Rickettsia conorii infection | At the site of a tick bite, a single eschar with a red halo forms. | The rash is generalized, involves the palms and soles, and is often maculopapular, occasionally petechial. | Fever, headache, myalgias may develop. The onset is abrupt. The disease may be severe in context of comorbidity. | North Africa, Middle East, Southern Europe |
| African tick bite fever secondary to R africae infection | Single or multiple eschars with regional lymphadenopathy | A scant generalized rash, vesicular or maculopapular, may be present. Conversely, the rash may be absent. | Fever, headache, myalgias, regional lymphadenopathy; associated with reports of subacute neuropathy | Sub-Saharan Africa, Caribbean |
| Human spotted fever secondary to R parkeri infection | Single or multiple eschars develop from erythematous papules. | Scant nonpruritic papules | Fever, headache, myalgias, arthralgias | United States |
| Scrub typhus secondary to Orientia tsutsugamushi infection | A vesicle or black scab appears on an erythematous base at the bite site. | Vesicles are usually on the trunk or extremities. | The rash fades within a few days; pneumonitis is common. | Asia-Pacific rim |
Skin biopsies are not routinely obtained to confirm a diagnosis of rickettsialpox. If collected, biopsy samples show epidermal infiltration by mononuclear cells and necrosis of the dermis and epidermis. Inflammation around blood vessels with thrombi and extravasation of red blood cells may also be observed. Vacuolar degeneration of basal cell layers is consistently present.
Rickettsialpox is a self-limited disease; however, antibiotics hasten defervescence and provide relief of other systemic symptoms. A presumptive diagnosis of rickettsialpox can be made based on high clinical suspicion in the correct geographic context, and empiric antimicrobial therapy can be appropriately prescribed. The treatment of choice is doxycycline 100 mg administered orally twice daily until the patient has clinically recovered for approximately 48 hours. Usually, 5-7 days is sufficient. Supportive and symptomatic therapy may also be provided.
If antibiotics cause no response within 48 hours, seek an alternate diagnosis.
A brief course of a tetracycline antibiotic is recommended. Quinolones may also be considered. Chloramphenicol is an alternate treatment but is not usually recommended because of substantial toxicity.
Empiric antimicrobial therapy must be comprehensive and should cover all likely pathogens in the context of the clinical setting.
| Drug Name | Doxycycline (Bio-Tab, Doryx, Vibramycin, Doxy) |
|---|---|
| Description | Inhibits protein synthesis and, thus, bacterial growth by binding to 30S and possibly 50S ribosomal subunits of susceptible bacteria. |
| Adult Dose | 100-mg PO q12h |
| Pediatric Dose | <8 years: Not recommended >8 years: 2-5 mg/kg/d in 1-2 divided doses for 2-5 d; not to exceed 200 mg/d |
| Contraindications | Documented hypersensitivity; severe hepatic dysfunction |
| Interactions | Bioavailability decreases with antacids containing aluminum, calcium, magnesium, iron, or bismuth subsalicylate; tetracyclines can increase hypoprothrombinemic effects of anticoagulants; tetracyclines can decrease effects of oral contraceptives, causing breakthrough bleeding and increased risk of pregnancy |
| Pregnancy | D - Fetal risk shown in humans; use only if benefits outweigh risk to fetus |
| Precautions | Photosensitivity may occur with prolonged exposure to sunlight or tanning equipment; reduce dose in renal impairment; consider serum level determinations in prolonged therapy; tetracycline use during tooth development (last half of pregnancy through age 8 y) can cause permanent discoloration of teeth; Fanconi-like syndrome may occur with outdated tetracyclines |
Article Last Updated: Apr 11, 2008
