Rickettsiaceae
Rickettsia, Orientia, Ehrlichia
and Coxiella
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Aerobic,gram-negative bacilli (stain poorly)
Obligate intracellular(cytoplasm of eucaryotic
cells)
Originally classified in a single family
Distinct, unrelated genera according to their
analysis of DNA sequences
Very small (originally thought to be viruses)
Humans are accidental hosts (animals and
arthropods are reservoirs, and arthropods are
vectors (ticks, mites, lice and fleas)
Rickettsia, Orientia, Ehrlichia
and Coxiella
Best seen by Giemsa and Gimenez
 All are strict intracellular parasites:
 Enter by phagocytosis
 Binary fission is slow (9-12 hours)
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Rickettsia, Orientia, Ehrlichia
and Coxiella
Why obligate intracellular ? An energy
parasite: uses host cell ATP
 Outside the host cell unstable
 Coxiella resistant to desiccation
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Rickettsiae
Spotted fever group(Benekli ateş): at least 17
rickettsiae
R. rickettsii
R.conorii,R. akari
 Typhus group:
R.prowazekii
R.typhi
*Bacteria replicate in endothelial cells , leakage
from blood vessels
*Hypovolemia and hypoproteinemia
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Rickettsiae
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are maintained in reservoir hosts, primarily
rodents and their arthropod vectors (e.g.,
ticks, mites, fleas)
Rickettsiae
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The distribution of rickettsial diseases is
determined by the distribution of the arthropod
host/vector.
Most infections with tick vectors (e.g., spotted
fevers) have a restricted geographic distribution,
whereas rickettsial infections with other vectors
such as lice (R. prowazekii), fleas (Rickettsia
typhi), and mites (Rickettsia akari, Orientia
tsutsugamushi) have worldwide distribution.
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© 2005 Elsevier
Rickettsiae
R. rickettsii: Rocky Mountain spotted fever(Kayalık
dağlar benekli humması)
Vector: hard ticks (West hemisphere)
Reservoir: ticks and wild rodents
Transmission: adult ticks
More than 90% infection occur from April to
October
Transmission requires prolonged contact (24-48
hours)
Rickettsiae
R. rickettsii: Rocky Mountain spotted fever
Incubation 2-14 days after tick bite which may be
painless and may not be remembered.
Fever, chills,headache, myalgias
Rash: macular to petechial, initially involves the
extremities then spread to the trunk
Complications: gastrointestinal symtoms,
respiratory failure, encephalitis and renal failure
Rickettsia rickettsii
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Laboratory diagnosis:Microscopy and culture not
useful.
Serology:
Weil-Felix: agglutination test using Proteus
antigens-insensitive and nonspesific
Rickettsia-spesific antibodies by
Immunofluorescent assay (IFA)
Antibody response: 2-3 weeks
Direct detection of antigen in biopsy specimens
by IFA or NAT(Nucleic acid amplification
techniques).
Rickettsia rickettsii
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Treatment Prevention and Control:
Tetracycline(Doxycycline), chloramphenicol,
fluoroquinolone(ciprofloxacin)
Delay in treatment:morbidity and mortality is
high(20%)
No vaccine
Avoidance of tick-infested areas, insect
repellents, prompt removeal of attached ticks
Ticks survive as long as 4 years without feeding.
Other spotted fever Rickettsiae
R. akari: rickettsialpox
 USA, Soviet Union,Korea
 Rodents are resorvoirs, vectors:mouse
ectoparasites(mites)
 Usually mild
 Papulovesicular
 Doxycycline or chloramphenicol
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Rickettsia prowazekii
Epidemic typus(Lekeli humma,klasik tifüs)
 Louse-borne typus
 Vector: Pediculus humanus (human body
louse)
 Reservoir:humans
 Epidemic typhus: in crowded unsanitary
conditions such as wars, natural diasters.
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Rickettsia prowazekii
Epidemic typus
 2-30 days incubation
 Nonspesific symptoms then high fever
headache, arthralgia, anorexia
 Some with petechial or macular rash
 Mortality may be as hig as 66% with
myocarditis and CNS dysfunction
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Rickettsia prowazekii
Recrudescent disease (Brill-Zinsser
disease):can occur in people years after
their initial infection.
 MIF is used for diagnosis
 Tetracycline and chloramphenicol
 Effective louse control measures
 Formaldehyde-inactivated vaccine in high
risk populations
 R. quintana:louse-born
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Rickettsia typhi
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Endemic typhus
Worlwide distribution
Reservoir: wild rodents
Vector: flea
Incubation:7-14 days the course usually
uncomplicated
IFA
Tetracycline, doxycycline or chloramphenicol
Rodent reservoir control should be directed
Orientia tsutsugamushi
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Scrub typhus(çalılık humması,Japon benekli
humması)Asia, Japan
Vector: mites (chiggers, red mites)
Reservoir:mites, wild rodents
Incubation:6-18 days
Maculopapular rash, headache,fever, myalgias
Tetracycline, doxycycline or chloramphenicol
Ehrlichia
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Ehrlichiosis
Vector and reservoir: ticks
Sennetsu fever:E. senetsu:raw fish with ehrlishia
infected flukes :restricted to Japan
Three stages: elementary bodies, initial body
and morula
Giemsa stain of peripheral blood: intracellular
organism
Serology, probes
Doxycycline
Coxiella burnetii
Q fever
 Worlwide
 No vector, by inhalation
 Reservoir: cattle,sheep,goats and cats
 Acute or chronic (mortality high)
 More closely related to Legionella and
Francisella
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Coxiella burnetii
Stable to environmental conditions
 Survive in soil for years
 Excreted also by milk
 Atypical pneumonia
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Coxiella burnetii
Can be cultered(not commonly used)
 Serology
 Amplification techniques
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