Download 5_Rickettsiae, Orienta, Coxiaella and Ehrlichia

ZaidKhalid MBBS220
Rickettsiae, Orienta, Coxiaella, Bartonella and Ehrlichia
Rickettsiae
General Characteristics
1. Small gram negative coccobacilli
2. Best stained by Giemsa, particularly in infected cells
3. Cell wall contains lipopolysaccharide
a. At least 2 large proteins in the outer membrane
b. Peptidoglycan
4. Can only be grown in living host cells
a. Embryonated egg
b. Cell cultures
Epidemiology and Pathogenesis
1. It has animal reservoir
a. Insect vectors
i. Prominent component of
their life cycles
2. It infects vascular endothelium
a. After a bite from anthropod
vector
3. Vasculitis, primary pathologic
lesion
a. Multiplication of rickettsiae
at the endothelium
4. Focal areas of endothelial
proliferation and perivascular
infiltration
a. Leads to thrombosis
b. Leakage of RBC into the
surrounding tissues
c. Which account for
i. Rash
ii. Petechial lesion
5. Vascular lesions occur
throughout the body
a. Causing systemic
manifestation of the disease
6. Infection characterised by
a. Fever
b. Headache with widespread
focal lesions
c. Rash is the most prominent
5. Outside host cell, rickettsiae
a. Ceases metabolic activity
b. Leaks in
i. Proteins
ii. Nucleic acid
iii. Essential small molecules
c. Thus making it
i. Rapid loss of infectivity
ii. Cause penetration of a new host cell requires energy
6. Rickettsiae needs to borrow some host cell essential
molecules for
a. Adequate growth
b. Making it fragile in the environment
Lab Diagnosis
1. Culturing of rickettsiae is
a. Dangerous
b. Difficult
2. Only be done in Reference Lab
3. Serological tests are the primary
means of diagnosis
4. It includes
a. Weil-Felix test
i. Serum of pts infected by
typhus agglutinate with certain
Proteus sp.
ii. This test is lacked of
1. Sensitivity
2. Specificity
b. Indirect fluorescent antibody
(IFA)
c. Immunoperoxidase test
Treatment
DOC – early treatment
1. Tetracycline
2. Chloramphenicol
Antibiotics don’t kill the
bacteria, only supress its
growth
Recovery depends solely
on pts immune response
ZaidKhalid MBBS220
Coxiella
Coxiella burnetti
General Characteristics
1. Small intracellular bacteria
a. Stained poorly by Gram stain
b. Best with Giemsa stain
2. Replicates in phagolysosome of infected cells
3. Able to undergo antigenic variation
a. Expression of cell wall lipopolysaccharide antigen
4. Have affinity to reticuloendothelial system
5. Resistant to drying
a. Able to produce infection thru respiratory route
Virulence Factor
1. Categorised in two phases
a. Phase I antigen (infectious form)
i. Blocks antibody reaction with
surface proteins
b. Phase II antigen
i. Exposing the surface proteins to
antibodies
ii. Producing a less infectious form
2. Antibody reaction is useful in the
determination of
a. Acute infection
b. Chronic infection
3. Acute disease
a. Characterised by antibodies to
the exposed phase II antigen
4. Chronic disease
a. High antibody titers against Phase
I and Phase II antigens are
detected in patients
Clinical Disease
1.
Q fever
a. Zoonosis
b. Infecting human thru inhalation
rather than anthropod bite
c. Asymptomatic in humans
d. Develops acutely or as a chronic
infection
2. Acute disease
a. Begins 9-20 days after inhalation
b. With abrupt onset of
i. Fever
ii. Chills
iii. Headache
c. No rash
d. Development of
i. Hepatomegaly
ii. Abnormal liver function
e. Complications like (rare)
i. Myocarditis
ii. Pericarditis
iii. Encephalitis
3. Chronic disease
a. Culture-negative endocarditis
Diagnosis
1. High rising titer of
antibody of Q
fever antigen is
detected by
a. Complication
Fixation Test
(CFT)
b. Indirect
Florescent
Antibody test
(IFA)
Treatment
1. DOC of acute infection
a. Tetracycline
2. DOC of chronic
infection
a. Rifampicin
b. Plus
i. Doxycycline
ii. Or Bactrim
ZaidKhalid MBBS220
Orienta
Orienta tsutsugamushi
General Characteristics
1. Formerly known as Rickettsia tsutsugamushi
2. Reservoir is from mite
a. Transmitted transovarian means
Clinical Disease
Scrub typhus
1. Transmitted thru mites
a. Chiggers
b. Red mites
2. Mite larvae (chiggers) deposit the
organism as they feed
3. After 10-12 days of incubation, pts will
develop
a. Severe headache
b. Fever and myalgia
3.
Bartonella
General Characteristics
1.
2.
Treatment
c. Macular to popular rash
4. Typical initial lesion
a. Necrotic eschar at the site of bite on
extremities
b. Develops 50-80% of cases
5. May develop generalised
a. Lymphadenopathy
b. Hepatosplenomegaly
The only rickettsiaceae can be cultured on artificial media
Media is
a. Freshly prepared brain-heart infusion
b. Agar with 5% or 10% of
i. Rabbit
ii. Or horse blood
c. Should be incubated in humid atmosphere for up to 3-4weeks
Types
a. Bartonella quintana
i. Causative agent of trench fever
ii. Worldwide distribution
iii. Named from prominence appearance in the trenches of World War I
iv. Reservoir in human
v. Vector is the body louse
b. Bartonella henselae
i. Causative agent of cat scratch disease
Clinical Disease
Cat scratch disease
1.
2.
Lymphocutaneous disease
Pts has history of
a. Cat scratch
b. Cat exposure
3. 5-120 days of incubation
a. Nodular/indurated swelling appears at the scratch area
b. May discharge few pus
Local draining lymph nodes
a. Enlarge
b. Become tender
c. Suppurating and discharging
5. Disease is self-limiting
a. May last for 3weeks or more
4.
DOC
1. Tetracycline
2. Or chloramphenicol
Treatment
DOC
1. Oral tetracycline
2. Oral erythromycin
These antibiotics may
shorten the course of
illness
ZaidKhalid MBBS220
Ehrlichia
General Characteristics
1. Taxonomically grouped with Rickettsiae
2. It is
a. Obligatory intracellular organism
b. Parasitises the granulocytes
c. Gram negative coccus
d. Multiplies in intracytoplasmic vacuoles of the infected
cells
3. Has tick vectors
4. Tropism for either (polymorph)
a. Monocytes
Clinical Disease
Ehrlichiosis
1. Characterised
(manifestation of infectious
mononucleosis) by
a. Fever
b. Lymphadenopathy
c. Atypical lymphocytosis
2. Consistent symptoms
a. Fever
b. Headache
c. Malaise
d. Myalgia
e. Arthralgia
f. Nausea
3. 30% of cases
a. Patchy erythema
b. Maculopapular rash
c. Petechiae
4. 90% have history of tick
bites
5. Within 48-72 hours, may
present with
a. Lymphopenia
b. Leucopenia
c. Thrombocytopenia
b. Granulocytes
5. Further divided into
a. Ehrlichia chaffeensis
i. Causing human monocytotrophic ehrlichiosis
ii. Primarily found in the South-Eastern USA
b. Ehrlichia sennetsu
i. Similar disease
ii. Found in
1. Western Japan
2. Malaysia
Diagnosis
1. Diagnosis is confirmed by
a. Observing typical morulae in
WBC
b. Indirect florescent antibody test
2. Culture requires variety of tissue
culture lines
3. Reference Lab can perform
a. PCR
b. Culture
Treatment
DOC
1. Tetracycline in the
form of doxycycline
2. Rifampicin is
alternative drug