Abstract
Members of the order Rickettsiales are small, obligately intracellular, Gram-negative bacteria that reside within an arthropod host (tick, flea, louse, or mite) during part of their life cycle. At least 25 bacterial species belonging to six genera ( Rickettsia, Orientia, Ehrlichia , Anaplasma, Neorickettsia, and Neoehrlichia ) in this order as well as the related Coxiella genus in the order Legionellales are known agents of human diseases. Typical symptoms include fever, headache, and myalgias. The cutaneous manifestations vary from nearly always present rashes and/or eschars in some spotted fevers and typhus to rare skin eruptions in other conditions. Clinical recognition of the characteristic cutaneous findings and early initiation of empiric antimicrobial treatment with doxycycline is paramount, especially for life-threatening Rocky Mountain spotted fever and other severe rickettsioses.
Keywords
rickettsiosis, Rocky Mountain spotted fever, African tick bite fever, spotted fever group rickettsiae, rickettsialpox, typhus, scrub typhus, human monocytic ehrlichiosis, human granulocytic anaplasmosis, Q fever
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Rickettsiae are small, obligately intracellular, Gram-negative bacteria that reside within an arthropod host (tick, flea, louse, or mite) during part of their life cycle
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The arthropod vector transmits the rickettsiae in its saliva or feces during feeding
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The major vertebrate target cells of Rickettsia (endothelium), Orientia (endothelium), Ehrlichia (monocytes or neutrophils), Anaplasma (neutrophils), and Coxiella (macrophages) determine to a large degree the pathogenesis of the disease
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In most spotted fever rickettsioses and scrub typhus, an eschar at the site of the vector’s inoculation of organisms is an important physical sign
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A rash is the diagnostically critical clinical manifestation of Rocky Mountain spotted fever, other spotted fevers, murine typhus, and louse-borne typhus
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One of the most common rickettsial diseases in travelers is African tick bite fever
Introduction
Members of the order Rickettsiales are small, obligately intracellular, Gram-negative bacteria that reside within an arthropod host for at least part of their life cycle . At least 25 bacterial species belonging to six genera ( Rickettsia, Orientia, Ehrlichia , Anaplasma, Neorickettsia, and Neoehrlichia ) as well as the related Coxiella genus in the order Legionellales are known agents of human diseases ( Table 76.1 ). Cutaneous manifestations vary from nearly always present in some spotted fevers and typhus to rare in others, such as human granulocytic anaplasmosis and Q fever ( Table 76.2 ). Clinical recognition of a rash is frequently the event that leads to appropriate antimicrobial treatment for life-threatening Rocky Mountain spotted fever (RMSF) and other rickettsioses.
| EPIDEMIOLOGY OF RICKETTSIAL AND RELATED INFECTIONS | |||
|---|---|---|---|
| Agent | Disease | Transmission | Geographic distribution |
| Rickettsia rickettsii | Rocky Mountain spotted fever, Brazilian spotted fever | Bite of tick: | |
| Dermacentor variabilis ( Fig. 76.1 ) | Eastern two-thirds and Pacific Coast of US | ||
| D. andersoni | Rocky Mountain states | ||
| Rhipicephalus sanguineus | Southwestern US; northern Mexico; Brazil | ||
| Amblyomma cajennense, A. aureolatum, A. imitator, A. sculptum | Mexico; Central and South America | ||
| Rickettsia akari | Rickettsialpox | Bite of mouse mite : | |
| Liponyssoides sanguineus | North America; Eurasia | ||
| Rickettsia conorii (4 subspecies) | Boutonneuse fever (Mediterranean spotted fever), Indian and Israeli tick typhus, Astrakhan spotted fever | Bite of tick : | |
| Rhipicephalus sanguineus | Southern Europe; Africa; western and southern Asia | ||
| Rh. pumilio | Southern Russia | ||
| Rickettsia sibirica | North Asian and Siberian tick typhus, lymphangitis-associated rickettsiosis | Bite of tick : | |
| Dermacentor nuttallii, D. silvarum, Haemaphysalis concinna, Hyalomma asiaticum , other species | Eurasia and Africa | ||
| Rickettsia heilongjiangensis | Far Eastern spotted fever | Bite of tick: | |
| Haemaphysalis species, D. silvarum | Eastern Russia, China, Thailand, Japan | ||
| Rickettsia australis | Queensland tick typhus | Bite of tick : | |
| Ixodes holocyclus | Eastern Australia | ||
| Rickettsia honei | Flinders Island spotted fever | Bite of tick : | |
| Bothriocroton hydrosauri , other species | Australia and Nepal (Flinders Island is located between Tasmania and mainland Australia) | ||
| Rickettsia japonica | Japanese spotted fever | Bite of tick : | |
| vector status not established for ticks that carry the agent ( Haemaphysalis flava, H. longicornis, Ixodes ovatus, Dermacentor taiwanensis ) | Japan and eastern Asia | ||
| Rickettsia massiliae | Rickettsia massiliae rickettsiosis | Bite of tick: | |
| Rhipicephalus species | Europe, South America, Africa | ||
| Rickettsia felis | Flea-borne spotted fever | By flea: | |
| e.g. Ctenocephalides felis | Worldwide | ||
| Rickettsia africae | African tick bite fever | Bite of tick: | |
| Amblyomma hebraeum | Southern Africa | ||
| A. variegatum | Central, eastern, and western Africa; Caribbean islands | ||
| Rickettsia parkeri | Rickettsia parkeri rickettsiosis (maculatum disease, American tick bite fever) | Bite of tick: | |
| Amblyomma maculatum, A. americanum | North America | ||
| A. triste, A. tigrinum | South America | ||
| Rickettsia species 364D | Rickettsia species 364D rickettsiosis | Bite of tick: | |
| Dermacentor occidentalis | California | ||
| Rickettsia aeschlimannii | Rickettsia aeschlimannii infection | Bite of tick : | |
| Hyalomma marginatum | Africa | ||
| Rickettsia slovaca, Rickettsia raoultii, or Candidatus Rickettsia rioja | Tick-borne lymphadenopathy, Dermacentor-borne necrosis and lymphadenopathy (DEBONEL) | Bite of tick (usually on the scalp): | |
| Dermacentor marginatus, D. reticularis | Europe | ||
| Rickettsia prowazekii | Epidemic louse-borne typhus | Feces of human body louse ( Pediculus humanus var. corporis ) | South America; Africa; Eurasia |
| Brill–Zinsser disease | None (recrudescence of latent infection) | ||
| Flying squirrel typhus | Contact with flying squirrel ( Glaucomys volans ) and its fleas and lice | North America | |
| Rickettsia typhi | Murine (endemic) typhus | Feces of fleas : | |
| Xenopsylla cheopis | Worldwide | ||
| Ctenocephalides felis | North America | ||
| Orientia tsutsugamushi | Scrub typhus | Bite of larval trombiculid mites : | |
| L. deliense, L. fletcheri, L. scutellare, L. arenicola | Southern and eastern Asia; islands of the southwestern Pacific and Indian Oceans; northern Australia | ||
| e.g. L. pallidum | Japan; Korea; Russian Far East | ||
| e.g. L. scutellare | China; Malaysia | ||
| e.g. L. deliense, L. fletcheri, L. arenicola | Tropical regions | ||
| Ehrlichia chaffeensis | Human monocytic ehrlichiosis | Bite of tick : | |
| Amblyomma americanum ( Fig. 76.1 ), Dermacentor variabilis | Southeastern and South Central US | ||
| Ehrlichia muris -like (EML) agent | EML agent ehrlichiosis | Bite of tick: | |
| Ixodes scapularis | Upper midwestern US | ||
| Ehrlichia ewingii | Ehrlichia ewingii ehrlichiosis | Bite of tick: | |
| Amblyomma americanum | Southeastern and South Central US | ||
| Anaplasma phagocytophilum | Human granulocytic anaplasmosis | Bite of tick: | |
| Ixodes scapularis ( Fig. 76.1 ) | Northern US | ||
| I. pacificus | Far western US | ||
| I. ricinus, I. persulcatus | Eurasia | ||
| Candidatus Neoehrlichia mikurensis | Candidatus Neoehrlichia mikurensis infection * | Bite of tick: | |
| Ixodes ricinus | Europe | ||
| Ixodes persulcatus | East Asia | ||
| Neorickettsia sennetsu | Sennetsu fever § | Ingestion of infected trematode-infested raw fish or fish paste | East Asia |
| Coxiella burnetii | Q fever | Aerosol of infected products of parturition of ruminants (e.g. sheep, cattle, goats), cats, and other animals ** | Worldwide |
* Febrile illness described primarily in immunocompromised patients with a hematologic malignancy or autoimmune disease.
§ Mononucleosis-like syndrome characterized by fever, malaise, and generalized lymphadenopathy.
** Less common means of transmission include ingestion of contaminated dairy products and tick bites (e.g. Dermacentor spp.).
| DERMATOLOGIC MANIFESTATIONS OF RICKETTSIAL INFECTIONS | ||||
|---|---|---|---|---|
| Disease | Rash incidence (%) | Appearance of rash after onset of illness | Characteristics | Eschar (%) |
| Rocky Mountain spotted fever, Brazilian spotted fever | 90 | 3–5 days | Early macules, later papules; petechiae in 50% of patients; retiform purpura in severe disease | <1 |
| Rickettsialpox | 100 | 2–3 days | Early macules and papules; later papulovesicles and crusts | 90 |
| Boutonneuse fever and related conditions | 95 | 3–5 days | Early macules, later papules | 50 |
| North Asian tick typhus and related conditions | 100 | 4–5 days | Macules and papules | 75 |
| Far Eastern spotted fever | 90 | 3–4 days | Macules and papules | 90 |
| Queensland tick typhus | 90 | 2–6 days | Macules, papules, and vesicles | 75 |
| Flinders Island spotted fever | 85 | A few days | Early macules and papules, later (in some patients) petechiae | 50 |
| Japanese spotted fever | 100 | A few days | Early macules, later (in some patients) petechiae | 90 |
| Rickettsia massiliae rickettsiosis | 75 | Not reported | Macules and papules | 100 |
| Flea-borne spotted fever | 80 | A few days | Macules and papules; occasionally pustules | 15–20 |
| African tick bite fever | 50 | 2–5 days | Generally relatively few lesions; macules, often vesicles | 90, often multiple |
| Rickettsia parkeri rickettsiosis | 80 | 2–4 days | Macules, papules, often vesicles | 100 |
| Rickettsia species 364D rickettsiosis | 15 | Not reported | Macules in region of eschar (one patient) | 100 |
| R. aeschlimannii infection | 50 | Not known | Macules and papules | 100 |
| Tick-borne lymphadenopathy | 5 | Not reported | Macules and papules | 100 |
| Epidemic louse-borne typhus | 50–100 | 4–5 days | Early macules, later papules; petechiae | None |
| Brill–Zinsser disease | 50 | 4–6 days | Macules and papules | None |
| Flying squirrel typhus | 65 | 2–8 days | Macules and papules | None |
| Murine (endemic) typhus | 80 | 5 days | Early macules, later papules | None |
| Scrub typhus | 50 | 4–6 days | Early macules, later papules | 60–90 |
| Human monocytic ehrlichiosis | 40 | Median, 5 days | Macules, papules, occasionally petechiae | None |
| Ehrlichia muris -like agent ehrlichiosis | 10 | Not reported | Not reported | None |
| Human granulocytic anaplasmosis | ≤5 | Not reported | Erythematous rash on neck/chest; petechiae or purpura | None |
| Candidatus Neoehrlichia mikurensis infection | Rare | Not reported | Erythematous macules, erythema nodosum | None |
| Sennetsu fever | Rare | Not reported | Diffuse erythema, petechiae | None |
| Q fever | Rare | Associated with chronic infection | Macules, papules, palpable purpura; rarely erythema nodosum | None |
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