Rickettsia rickettsii: Difference between revisions

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Rickettsia rickettsii
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* Causes '''Rocky Mountain spotted fever (RMSF)'''
*Causes '''Rocky Mountain spotted fever (RMSF)'''


== Background ==
==Background==
=== Microbiology ===
===Microbiology===
* Obligate intracellular bacteria
* Structurally Gram-negative, but difficult to stain
** Needs Gimenez method or acridine orange stain
* Contain lipopolysaccharide (LPS) as well as OmpA and OmpB autotransporters


*Obligate intracellular bacterium
=== Life Cycle ===
*Structurally [[Stain::Gram-negative]], but difficult to stain
* Transmitted by ticks
**Needs Gimenez method or acridine orange stain
** ''[[Vector::Dermacentor variabilis]]'' (American dog tick) in the eastern two-thirds of the US
*Contain lipopolysaccharide (LPS) as well as OmpA and OmpB autotransporters
** ''[[Vector::Dermacentor andersoni]]'' (Rocky Mountain wood tick) in the western states
** ''[[Vector::Rhipicephalus sanguineus]]'' in Mexico and Arizona
** ''[[Vector::Amblyomma cajennense]]'' and ''Amblyomma aureolatum'' in South America
** ''[[Vector::Amblyomma imitator]]'' in Mexico
* Has a deleterious effect on ticks
* Transmitted trans-stadially (stage to stage) and trans-ovarially in ticks, as well as horizontally through vertebrate hosts
* Only the adult ticks feed on humans, during prolonged feeding of 1 to 2 weeks
** Injects salivary glands at 6 to 10 hours
** Can also be infected during tick temoval, when it is crushed between the fingers
* As few as a single bacillus can cause disease


=== Pathophysiology ===
===Life Cycle===
* From cutaneous innoculation, bacilli spread via lymphatics and small blood vessels to the larger blood vessels
* There, the OmpA, OmpB, Sca1, and Sca2 proteins induce phagocytosis by vascular endothelial cells
* From there, they replicate and spread to adjacent cells


*Transmitted by ticks
=== Epidemiology ===
**''[[Vector::Dermacentor variabilis]]'' (American dog tick) in the eastern two-thirds of the US
* Wide global distribution
**''[[Vector::Dermacentor andersoni]]'' (Rocky Mountain wood tick) in the western states
** Most cases in the US are in the south Atlantic and south-central regions
**''[[Vector::Rhipicephalus sanguineus]]'' in Mexico and Arizona
*** Highly endemic in North Carolina
**''[[Vector::Amblyomma cajennense]]'' and ''[[Vector::Amblyomma aureolatum]]'' in South America
** Also occurs in Argentina, Brazil, Colombia, Panama, Costa Rica, and Mexico
**''[[Vector::Amblyomma imitator]]'' in Mexico
* Most cases occur in late spring and summer
*Has a deleterious effect on ticks
* Higher with occupational tick exposures
*Transmitted trans-stadially (stage to stage) and trans-ovarially in ticks, as well as horizontally through vertebrate hosts
* Other spotted fever species include ''R. conorii'' (Europe, Africa, and South Asia), ''R. sibirica'' (eastern Russia and Asia), ''R. africae'' (sub-Saharan African and West Indies), ''R. parkeri'' (North and South America), and ''R. slovaca'' (Europe), as well as ''R. felis'' (worldwide)
**Trans-ovarial transmission uncommon for ''D. variabilis''
*Only the adult ticks feed on humans, during prolonged feeding of 1 to 2 weeks
**Injects salivary glands at 6 to 10 hours
**Can also be infected during tick removal, when it is crushed between the fingers
*As few as a single bacillus can cause disease


===Pathophysiology===
== Clinical Manifestations ==
* Incubation period of [[Usual incubation period::2 to 14 days]]
* Most common presenting symptoms are high fever, headache, and myalgias
* Rash starts after a few days, on the wrists and ankles and spreading inward
* GI symptoms are common: nausea/vomiting and abdominal pain, sometimes diarrhea
* Can see papilledema from retinal vasculitis without elevated intracerebral pressure
* Can also have conjunctivitis, lymphadenopathy, stupor, edema, meningismus, hepatosplenomegaly, pneumonitis, myocarditis, gangrene
** Neurologic involvement has a poor prognosis
* Often have increased AST and thombocytopenia (from consumption), occasionally anemia, hyponatremia, hypoalbuminemia, and AKI
** Normal or low WBCs
* Death occurs within 7 to 15 days without appropriate treatment
** Mortality is high without treatment (30%) and still elevated if treated early (1-5%)


*From cutaneous inoculation, bacilli spread via lymphatics and small blood vessels to the larger blood vessels
=== Rash ===
*There, the OmpA, OmpB, Sca1, and Sca2 proteins induce phagocytosis by vascular endothelial cells
* Begins as small (1–5 mm in diameter), blanching, pink macules on the ankles, wrists, or forearms that subsequently spread to the arms, legs, and trunk
*From there, they replicate and spread to adjacent cells
** Often involves the palms and soles
** Usually spares the face
* Classic spotted or generalized petechial rash, including involvement of the palms and soles, usually appears by day 5 or 6
* Rash may not occur in black patients and elderly patients


=== Other spotted fevers ===
===Epidemiology===
* Typically less severe disease course
* Often have eschar at tick bite site


*Wide global distribution
== Differential Diagnosis ==
**Most cases in the US are in the south Atlantic and south-central regions
* Typhoid fever, measles, rubella, respiratory tract infection, gastroenteritis, acute surgical abdomen, enteroviral infection, meningococcemia, disseminated gonococcal infection, secondary syphilis, leptospirosis, immune complex vasculitis, immune thrombocytopenic purpura, thrombotic thrombocytopenic purpura, infectious mononucleosis, drug reaction, ehrlichiosis, anaplasmosis, and other rickettsial diseases
***Highly endemic in North Carolina
* Other spotted fevers
**Also occurs in Argentina, Brazil, Colombia, Panama, Costa Rica, and Mexico
*Most cases occur in late spring and summer
*Higher with occupational tick exposures
*Other spotted fever species include ''R. conorii'' (Europe, Africa, and South Asia), ''R. sibirica'' (eastern Russia and Asia), ''R. africae'' (sub-Saharan African and West Indies), ''R. parkeri'' (North and South America), and ''R. slovaca'' (Europe), as well as ''R. felis'' (worldwide)


==Clinical Manifestations==
== Diagnosis ==
* Microscopy and Culture
** Can be isolated from blood, though it's not commonly done
* Serology
** Enables retrospective diagnosis, since antibodies are only detectable in convalescent phase
** Indirect immunofluorescence and enzymes immunoassay
*** Titre of 1:64 is diagnostic, but does not distinguish between spotted fevers
*** Takes 7 to 10 days for IgM
*** Usually wait 2 to 3 weeks after onset for convalescent
* Molecular Testing
** PCR possible but not sensitive


*Incubation period of [[Usual incubation period::2 to 14 days]]
== Management ==
*Most common presenting symptoms are high [[fever]], [[headache]], and [[myalgias]]
* Supportive management, with aggressive fluid resuscitation
*[[Rash]] starts after a few days, on the wrists and ankles and spreading inward as well as outward to include [[Rashes involving palms and soles|palms and soles]]
* Antimicrobials
*GI symptoms are common: [[nausea]]/[[vomiting]] and [[abdominal pain]], sometimes [[diarrhea]]
** [[Is treated by::Doxycycline]] 100 mg po bid
*Can see [[papilledema]] from retinal vasculitis without raised intracerebral pressure
** [[Is treated by::Tetracycline]] 25-50 mg/kg/day or [[Is treated by::chloramphenicol]] 50-75 mg/kg/day divided qid
*Can also have [[conjunctivitis]], [[lymphadenopathy]], [[stupor]], [[edema]], [[meningismus]], [[hepatosplenomegaly]], [[pneumonitis]], [[myocarditis]], [[gangrene]]
** Duration is 7 days and at least 2 days afebrile
**Neurologic involvement has a poor prognosis
** Can use [[doxycycline]] in children <8 years for the durations required to treat [[rickettioses]]
*Often have increased AST and [[thombocytopenia]] (from consumption), occasionally [[anemia]], [[hyponatremia]], [[hypoalbuminemia]], and [[AKI]]
**Normal or low WBCs
*Death occurs within 7 to 15 days without appropriate treatment
**Mortality is high without treatment (30%) and still elevated if treated early (1-5%)

===Rash===

*Begins as small (1–5 mm in diameter), blanching, pink macules on the ankles, wrists, or forearms that subsequently spread to the arms, legs, and trunk
**Often involves the palms and soles
**Usually spares the face
*Classic spotted or generalized petechial rash, including involvement of the palms and soles, usually appears by day 5 or 6
*Rash may not occur in black patients and elderly patients

===Comparison to Other Spotted Fevers===

*Others typically less severe disease course
*Others often have eschar at tick bite site

==Differential Diagnosis==

*[[Typhoid fever]], [[measles]], [[rubella]], respiratory tract infection, [[gastroenteritis]], acute surgical abdomen, [[Enterovirus|enteroviral infection]], [[Neisseria meningitidis|meningococcemia]], [[disseminated gonococcal infection]], [[secondary syphilis]], [[leptospirosis]], immune complex [[vasculitis]], immune thrombocytopenic purpura, [[thrombotic thrombocytopenic purpura]], [[infectious mononucleosis]], [[adverse drug reaction]], [[ehrlichiosis]], [[anaplasmosis]], and other [[Rickettsiae|rickettsial diseases]]
*Other [[Spotted fever|spotted fevers]]

==Diagnosis==

*Microscopy and Culture
**Can be isolated from blood, though it's not commonly done
*Serology
**Enables retrospective diagnosis, since antibodies are only detectable in convalescent phase
**Indirect immunofluorescence and enzymes immunoassay
***Titre of 1:64 is diagnostic, but does not distinguish between spotted fevers
***Takes 7 to 10 days for IgM
***Usually wait 2 to 3 weeks after onset for convalescent
*Molecular Testing
**PCR possible but not sensitive

==Management==

*Supportive management, with aggressive fluid resuscitation
*Antimicrobials
**[[Is treated by::Doxycycline]] 100 mg po bid
**[[Is treated by::Tetracycline]] 25-50 mg/kg/day or [[Is treated by::chloramphenicol]] 50-75 mg/kg/day divided qid
**Duration is 7 days and at least 2 days afebrile
**Can use [[doxycycline]] in children <8 years for the durations required to treat [[rickettioses]]


{{DISPLAYTITLE:''Rickettsia rickettsii''}}
{{DISPLAYTITLE:''Rickettsia rickettsii''}}

Revision as of 02:30, 8 August 2020

  • Causes Rocky Mountain spotted fever (RMSF)

Background

Microbiology

  • Obligate intracellular bacterium
  • Structurally Gram-negative, but difficult to stain
    • Needs Gimenez method or acridine orange stain
  • Contain lipopolysaccharide (LPS) as well as OmpA and OmpB autotransporters

Life Cycle

  • Transmitted by ticks
  • Has a deleterious effect on ticks
  • Transmitted trans-stadially (stage to stage) and trans-ovarially in ticks, as well as horizontally through vertebrate hosts
    • Trans-ovarial transmission uncommon for D. variabilis
  • Only the adult ticks feed on humans, during prolonged feeding of 1 to 2 weeks
    • Injects salivary glands at 6 to 10 hours
    • Can also be infected during tick removal, when it is crushed between the fingers
  • As few as a single bacillus can cause disease

Pathophysiology

  • From cutaneous inoculation, bacilli spread via lymphatics and small blood vessels to the larger blood vessels
  • There, the OmpA, OmpB, Sca1, and Sca2 proteins induce phagocytosis by vascular endothelial cells
  • From there, they replicate and spread to adjacent cells

Epidemiology

  • Wide global distribution
    • Most cases in the US are in the south Atlantic and south-central regions
      • Highly endemic in North Carolina
    • Also occurs in Argentina, Brazil, Colombia, Panama, Costa Rica, and Mexico
  • Most cases occur in late spring and summer
  • Higher with occupational tick exposures
  • Other spotted fever species include R. conorii (Europe, Africa, and South Asia), R. sibirica (eastern Russia and Asia), R. africae (sub-Saharan African and West Indies), R. parkeri (North and South America), and R. slovaca (Europe), as well as R. felis (worldwide)

Clinical Manifestations

Rash

  • Begins as small (1–5 mm in diameter), blanching, pink macules on the ankles, wrists, or forearms that subsequently spread to the arms, legs, and trunk
    • Often involves the palms and soles
    • Usually spares the face
  • Classic spotted or generalized petechial rash, including involvement of the palms and soles, usually appears by day 5 or 6
  • Rash may not occur in black patients and elderly patients

Comparison to Other Spotted Fevers

  • Others typically less severe disease course
  • Others often have eschar at tick bite site

Differential Diagnosis

Diagnosis

  • Microscopy and Culture
    • Can be isolated from blood, though it's not commonly done
  • Serology
    • Enables retrospective diagnosis, since antibodies are only detectable in convalescent phase
    • Indirect immunofluorescence and enzymes immunoassay
      • Titre of 1:64 is diagnostic, but does not distinguish between spotted fevers
      • Takes 7 to 10 days for IgM
      • Usually wait 2 to 3 weeks after onset for convalescent
  • Molecular Testing
    • PCR possible but not sensitive

Management

  • Supportive management, with aggressive fluid resuscitation
  • Antimicrobials
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