Download Question Bank –lecture six Rickettsia Chlamydia Q1 Write on the

Question Bank –lecture six Rickettsia Chlamydia
Q1 Write on the following :
a. Obligate Intracellular Pathogen.
1. Rickettsia
2. Chlamydia
b. Rickettsia.
Rickettsia - Virus-like bacteria Infect cells lining the capillaries (intracellular). Transmitted by
insects (arthropods). Defective bacteria - leaky plasma membranes, very small 0.3-1.0
micrometers. Ex. Rocky Mountain Spotted Fever, typhus, Q fever.
c. Chlamydia
Chlamydia - “virus-like” (intracellular) Spread from one human to the next. Very small: 0.20.7 micrometers. Defective bacteria - can’t make their own ATP. Complicated reproductive
cycle. Diseases: blindness, urethritis, and pneumonia.
d. Mycoplasma Mycoplasma Sometimes form long strands that resemble fungi in microscopic
appearance.
No cell walls - instead contains sterols.
Ameboid locomotion - disease: “walking” pneumonia
The smallest bacteria - 0.2 micrometers
e.
General Characteristics of Rickettsia:
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Intracellular, gram negative organism
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Requires host to replicate and survive
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Cause febrile illness through the bite of an arthropod
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Patient often presents with a rash
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Posses a cell wall
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f. Enumerate genera of Family Rickettsiaceae.
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Zoonotic infection
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Human microbial pathogens ~61% zoonotic
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Rickettsia are arthropod-borne infections
Spotted Fever Group
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Rickettsia rickettsii – Rocky Mountain spotted fever; rodent, tick
Typhus Group
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Rickettsia typhi – Endemic typhus; rodent, flea
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Rickettsia prowazekii – Epidemic typhus; mammal, louse
g. Compare between bacteria, virus ,mycoplasma chlamydia and rickettsia
h. Rickettsia Lab daignosi:
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i.
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Giemsa, or Immunofluorescence assay (IFA) - direct detection MO in tissue
Weil-Felix reaction – Nonspecific test
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Rickettsial antibody agglutinate Proteus vulgaris
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Presumptive evidence of typhus group infection
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Not very sensitive or specific, many false positives
Agglutination or Complement Fixation (CF) assay - use specific Rickettsial antigen,
test for infection and antibody.
Rickettsial Virulence Factors
Induced phagocytosis, intracelluular growth – protected from host immune
clearance
Replicates in endothelial cells – cell damage, vasculitis
Recruitment of actin - intracellular spread
l. Cell to cell spreading by Rickettsia rickettsii
m. Rickettsial Infection and Disease .
n. R. typhi : Endemic Typhus Fever.
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typhus” “fever”
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Disease worldwide in warm, humid areas (Gulf states, So Cal.; S. America, Africa,
Asia, Australia, Europe)
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Murine typhus - rat primary reservoir, transmitted to human by rat flea
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Disease occurs sporadically
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Clinically same, but less severe than epidemic typhus
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Restricted to chest, abdomen; generally uncomplicated, lasts <3 weeks
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Low fatality
0. R. prowazekii : Epidemic Typhus Fever.
1.
2.
3.
4.
Disease C & S Americas, Africa; less common USA
Human, squirrel primary reservoir
Transmitted by louse; bites, defecates in wound
At risk - people living in crowded, unsanitary conditions; often war, famine, natural
disaster
5. Complications - myocarditis, CNS dysfunction
6. Mortality high untreated cases, up to 20%
7. Brill-Zinsser disease - individual may harbor MO, latent infection with occasional
relapses
s. Rickettsia: Treatment and Prevention
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RMSF
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Doxycycline drug of choice
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Avoid ticks, wear protective clothing, use insect repellents, insecticides
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In infested areas, check and remove ticks immediately
Typhus Fever
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Doxycycline effective
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Improve personal hygiene and living conditions, reduce lice by insecticides,
control rodent population
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Inactivated vaccine for epidemic typhus
t. laboratory Diagnosis of Rickettsial Disease.
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Immunohistochemical detection
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Serological tests
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PCR
u. Family Chlamydiaceae genera.
Chlamydia trachomatis – STD, eye infection
Chlamydophila pneumoniae – pneumonia
Chlamydophilia psittaci – pneunomia (psittacosis); birds, humans
z. Chlamydia Characteristics
Obligate intracellular parasite
Cell wall similar G(-) bacilli, lack peptidoglycan
Energy parasites, use ATP of host cell
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Unique growth cycle because they are deficient in independent energy metabolism
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Replication involves elementary body (EB) and reticulate body (RB)
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EB’s are infectious and non-metabolically acitve
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RB’s are noninfectious and metabolically active
y. Chlamydia: Life Cycle – Elementary Body (EB)
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Circular, infectious form; 300-400 nm
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Metabolically inactive
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Resistant to harsh environments
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0 hour - EB binds to host cell, induced phagocytosis
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Outer membrane of EB prevents lysosome fusion, survives in phagosome
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8 hours - EB reorganizes into Reticulate Body (RB)
x. Chlamydia: Life Cycle – Reticulate Body (RB)
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Noninfectious form, larger, less dense, 800-1000 nm
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Metabolically active
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8-30 hours
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Synthesize new materials
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Multiply by binary division
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Form inclusion body
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Reorganize, condense into EB
35-40 hours - cell lyses, releases EB, begins cycle again
Q2 Explain briefly the following :
a. Chlamydia: Lab ID.
Stain tissue
a. Giemsa stain
b. Direct fluorescent antibody (DFA)
c. ELISA
d. Less sensitive
b. Cell culture
a. More sensitive method
b. Grow MO in tissue culture, stain infected cells
c. DNA amplification test
a. Recently developed
b. Specific, sensitive
c. Now routine test of choice
c. Chlamydia: Virulence Factors
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Intracellular replication – protected from host immune defense
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Prevent fusion of phagolysome – evades phagocytic killing
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Repeated infections by C. trachoma result in cell pathology
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Serotypes A-K and L1, L2, L3 - serotype identifies strain’s clinical manifestation
d. Chlamydia pneumoniae
Important respiratory pathogen (acute respiratory disease, pneumonia, and
pharyngitis)
Common (50% of adults have antibodies)
College age students most susceptible
Implicated in asthma
Risk factor for Guillain-Barre’ syndrome
• Reinfection common
• Biphasic clinical picture
– Prolonged sore throat and hoarseness, followed by flu-like lower respiratory
symptoms
– Pneumonia and bronchitis
e.
Chlamydia trachomatis
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Most commonly sexually transmitted bacterial pathogen in U.S.
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Only HPV is a more commonly sexually transmitted disease
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Major cause of sterility in U.S.
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May be transmitted to newborns during delivery
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Other sites of infection
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Trachoma – infection of the conjunctiva, resulting in scarring and blindness
(Mostly in India and Egypt)
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Lymphogranuloma venereum
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f.
Results in conjunctivitis
Infects lymph nodes
Chlamydia psittaci
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Causes psittacosis (parrot fever)
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Identification based on history of close contact with birds and serologic evaluation
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parrot” “parrot fever”
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Naturally infects avian species
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Mild to severe respiratory infections
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Human infection by contact infected bird
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Infection - subclinical to fatal pneumonia
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Commonly causes atypical pneumonia with fever, chills, dry cough, headache, sore
throat, nausea, and vomiting
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h. Chlamydia trachomatis: Trachoma
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“rough” “trachoma” granulations on conjunctiva
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Serotypes A-C
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Single, greatest cause blindness developing countries
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Infections mainly children (reservoir), infected first three months life
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Transmission eye-to-eye, direct contact (droplet, hand, clothing, fly)
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Chronic infection, reinfection common
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Conjunctival scarring, corneal vascularization
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Scars contract, upper lid turn in so eyelashes cause corneal abrasions
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Leads to secondary bacterial infections, blindness
i.
l.
Chlamydia: Treatment and Prevention
Genital tract infection and conjunctivitis:
Adult - azithromycin or doxycycline, prompt treatment of patients and partners
Newborn – erythromycin
Public Health education
Trachoma:
Need prompt treatment, prevent reinfection
Systemic tetracycline, erythromycin; long term therapy necessary
Improve living, sanitary conditions
Difficult to prevent endemic disease in developing countries due to lack of
resources, medical care
Laboratory Diagnosis.
If cultured, must be in cells
Direct microscopic examination to find EB’s
visualized with fluorescein-conjugated antibodies
Enzyme immunoassay
Nucleic acid probes with and without amplification (PCR)
Serologic tests are method of choice for detection (Four-fold rise in titer)
m. Why is penicillin ineffective against Chlamydia? What antibiotic can be used to treat
this patient?
n.
Describe the growth cycle of Chlamydia. What structural features make the EBs
and RBs well suited for their environment?
o. Describe the differences among the three species in the family Chlamydiaceae
that cause human disease.