Reckettsia dr.ihsan alsaimary

Rickettsia
Professor Dr. Ihsan Edan Alsaimary

General Characteristics
 Small obligate intracellular coccobacilli
 Gram negative (poorly), better stained with
Giemsa (Blue)
 Have cell membrane, bigger than virus but
smaller than bacteria
 Have DNA and RNA
 Have an ATP transport system that allows them to
use host ATP
 Arthropod reservoirs and vectors ( e.g., ticks,
mites, lice or fleas).
 Sensitive to antibiotics

Structure:
Similar with Gram negative bacteria
Cell membrane: outer membrane
peptidoglycan
lipopolysaccharide (LPS)
Microcapsule and polysaccharide
Two antigenically distinct groups:
 LPS: heat-stable, cross-reactive with somatic antigens
of non-motile Proteus species (Weil-Felix test)
 Outer membrane protein: heat-unstable, species-specific

six genera in this class cause human
diseases:
Rickettsia
Bartonella
Coxiella (does NOT cause skin rash)
Ehrlichia
Orientia
Anaplasma

Diseases Caused by the Rickettsia

Pathogenic Mechanism
Materials：
Mechanism：
Local lymph or micro blood vessels
Endothelial cells, micro blood vessels
in whole body
Fever, rash, headache, etc
(1st bacteremia)
(2nd bacteremia)
Endothelial cells, micro blood vessels
Endotoxin and Phospholipase A
Bites or faeces of arthropod
Targets:

Pathogenesis
 Rickettsia (also Ehrlichia) is unstable and die
quickly outside host cells.
 Coxiella highly resistant to desiccation, remain
viable in environment for months to years.
 Rickettsia replicate in endothelial cells, cause cell
damage and blood leakage, skin rash, microthrombi,
hemorrhage.
 Hypovolemia, hypoproteinemia, reduced perfusion,
organ failure.

Immunity
 Cellular immunity is important, and humoral
immunity is helpful.
 Persons become immune to further infection
following recovery from the disease.

Diagnosis and Prevention
 Microscopy
 Serological Test (Weil-Felix reaction, ELISA, IF,
PCR)
 Breaking the infection chain ( controlling and
killing the intermediate hosts and reservoir
hosts)
 Inactivated vaccine has protective effect
 Chloromycetin, tetracycline are helpful for
therapy, sulphonamides are not administered
(increasing the penetrating of the vessel).

 Diagnosis/serological tests
 Direct detection of Rickettsia in tissues (Giemsa
stain or direct fluorescent antibody test) Weil-
Felix reaction – in certain rickettsial infections
(typhus group) antibodies are formed that will
agglutinate OX strains of Proteus vulgaris.
 This is used as a presumptive evidence of typhus
group infection, however, the test is not very
sensitive or specific and many false positives occur.
 Agglutination or complement fixation tests
using specific Rickettsial antigens are better
serological diagnostic tests.

Virulence factors
Rickettsial sp.
Induced phagocytosis
Recruitment of actin for intracellular
spread
Coxiella burnetti
Is resistant to lysosomal enzymes

Coxiella burnetii
 Biologically and genomically distinct from
Rickettsia; more closely related to Legionella
and Francisella.
 Obligate intracellular pathogen
 Multiply in phagolysosome

Coxiella Burnetii
 Q fever（query fever ）
 Self-limiting flu-like syndrome with high
fever (40℃)
 Primary reservoirs are wild (cattle, sheep,
goat etc.)
 Non-cross reactive antigen with non-motile
Proteus (Weil-Felix reaction negative)
 Live in macrophages of vertebrate host

Q fever
 Most infections are mild or asymptomatic
 Acute disease:
 Pneumonia - high fever, severe headache, chill,
resemble “atypical pneumonia”
 Granulomatous hepatitis, hepatosplenomegaly,
 Chronic disease: subacute endocarditis with
long incubation period and poor prognosis

Pathogenesis
 Target tissue is the lung, proliferate in
phagolysosomes of infected cells, then disseminate
to other organs
 Undergo antigenic variation (cell wall LPS):
phase I antigen: LPS with a complex carbohydrate,
can block antibody binding; infectious form
phase II antigen: modified LPS, expose surface
proteins to antibody, less infectious form
 Formation of immune complex: cause of signs and
symptoms

Diagnosis
Serologic tests (IFA, ELISA, CF)
 Acute Q fever: IgM and IgG are
developed against phase II antigen.
 Chronic Q fever: antibodies against both
phase I and II antigens are elicited.
(phase I antigen: weak antigenic)

T/P/C:
 Doxycycline for prolonged period
 Vaccine is available (single dose
with no booster immunization for
uninfected people)

Spotted fever
 Have a restricted geographic distribution; Rocky
mountain spotted fever (RMSF) is the prototype of
the group, caused by R. rickettsii.
 Organisms are maintained in hard ticks (wood
tick and dog tick) by transovarian transmission.
 Transmitted to humans by ticks (need 24-48h to
establish infection).
 High fever, chills, headache, skin rash (>90%,
extremities to trunk)
 GI symptoms, respiratory failure, encephalitis,
renal failure.

 Diagnosis is urgent, because the prognosis
depends on the duration of illness. (identify
key clinical signs – rash)
 Culture: tissue culture or embryonated eggs
(danger for personals )
 Microscopy: Giemsa stain; FA for biopsy
tissue specimens (rapid and specific)
 Serology: migration inhibitory factor test
(MIF), measure MIF(monocyte/macrophage
inhibitory factor.
 Molecular diagnosis: PCR, not species-
specific

Prevention/Control:
 Tetracyclines (e.g., doxycycline)
 No vaccine
 Prevent tick bites (can survive for as
long as 4 years without feeding)

Brill-Zinsser Disease
A recrudescent form of
epidemic typhus arising years
after the initial attack.

Diagnosis:
MIF test
T/P/C:
Tetracyclines, Chloramphenicol
Louse-control
Formaldehyde-inactivated vaccine

Bartonella Henselae
 Cat scratch disease (CSD)
 Weil-Felix reaction negative
 Infection by cats or dogs
 “Parinaud” Eye-Lymph node syndrome
The eye looks red, irritated, and painful,
similar to conjunctivitis.

Ehrlichia and Anaplasma
 Intracellular bacteria that
lodge in phagosomes of
mononuclear and
granulocytic phagocytes, but
not RBC.
 multiply in phagosomes =
morulae
Grow cycle: three stages -
elementary body, initial body,
morula

Clinical disease
Human monocytic ehrlichiosis
 E. chaffeensis : infect blood monocytes and
mononuclear phagocytes in tissues and organs
 Vector - Lone Star tick
 Reservoir - white-tailed deer, domestic dogs
Ehrlichia inclusions (peripheral blood
smear, Wright-Giemsa)

T/P/C:
 Diagnosis is urgent. Prompt
treatment with doxycycline
 No vaccine
 Avoid tick-infested areas

Reckettsia dr.ihsan alsaimary

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Reckettsia dr.ihsan alsaimary