Post on 14-Apr-2018
� Howard Taylor Ricketts (1871-1910)was an American pathologist afterwhom the Rickettsiaceae family andthe Rickettsiales are named.
� In the earlier part of his career,Ricketts undertook research at
Prof. Muhammad Akram Hossain, Ricketssia
Ricketts undertook research atNorthwestern University onblastomycosis and later at theUniversity of Chicago on and RockyMountain spotted fever
� In 1909, Ricketts became interested intyphus due to an outbreak in MexicoCity and the apparent similarity of thedisease to spotted fever. Somewhatironically, days after isolating theorganism that he believed causedtyphus, he himself died of thedisease.
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Charles Jules Henry Nicolle(September 21, 1866 Rouen -February 28, 1936) was a Frenchbacteriologist who received theNobel Prize in Medicine for his
Prof. Muhammad Akram Hossain, Ricketssia
Nobel Prize in Medicine for hisidentification of lice as thetransmitter of epidemic typhus in1903.
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� Henrique da Rocha Lima(1879–1956) was a Brazilianphysician, pathologist andinfectologist.
� Working in Germany, he discoveredRickettsia prowazekii, thepathogen of epidemic typhus.
Prof. Muhammad Akram Hossain, Ricketssia
pathogen of epidemic typhus.� He named it Rickettsia prowazeki,
after Howard Taylor Ricketts(1871)-1910) and German zoologistProwazek, who both died of this
disease.
� In 2007, a new strain of Gram-negative bacteria was named afterRocha Lima, Bartonellarochalimae
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Frank Macfarlane Burnet, Australianbiologist.
He was a pioneer in the application ofecological principles to viral diseases.
He proposed two concepts in immunology –acquired immunological tolerance and the
Prof. Muhammad Akram Hossain, Ricketssia
acquired immunological tolerance and theclonal selection theory of antibodyproduction
In the later stages of his life he lectured andwrote extensively about problems of humanbiology and human affairs, ageing and cancer.He was a Foundation Fellow and, from 1965 to1969, President of the Australian Academy ofScience.
Coxiella burnetti is named after him.Frank Macfarlane Burnet5
� 3 genera - obligate intracellular parasites:� Rickettsia
Prof. Muhammad Akram Hossain, Ricketssia
� Rickettsia� Coxiella� Ehrlichia
� Not an intracellular parasite� Rochalimaea (transferred to Bartonella)
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General Characteristics
� Resemble bacteria/grow only in living cells (NOT viruses)
� Parasites of arthropods = lice, fleas,
Prof. Muhammad Akram Hossain, Ricketssia
� Parasites of arthropods = lice, fleas, ticks, mites - infect humans via bite
� Similar in size and shape - nonmotile coccobacillary forms
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Pathogenesis: Rickettsia� Arthropod bite � Invade endothelial cells/vascular� Destroy endothelial cells
Prof. Muhammad Akram Hossain, Ricketssia
� Destroy endothelial cells� Inflammatory cells
accumulate/blood leakage: rash� Released organisms reinfect
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Signs of Infection
� Fever, chills� Severe headache
4th-6th day later = skin rash =
Prof. Muhammad Akram Hossain, Ricketssia
� 4th-6th day later = skin rash = lasts throughout course of disease
� EXCEPTION: Q-fever = no rash
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Important Clinical Diseases
� Typhus Group
�Rickettsia prowazekii = Epidemic typhus
Prof. Muhammad Akram Hossain, Ricketssia
Epidemic typhus–body louse = bite/feces–fever/severe headache–skin rash = trunk to extremities
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Important Clinical Diseases
� Spotted Fever Group� Rickettsia rickettsii = Rocky Mountain
spotted fever
Prof. Muhammad Akram Hossain, Ricketssia
spotted fever
–tick bite–fever/severe headache–skin rash = wrists and ankles to
trunk/palms of hands, soles of feet
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Important Clinical Diseases
� Scrub Typhus Group�Rickettsia tsutsugamushi =
Scrub typhus
Prof. Muhammad Akram Hossain, Ricketssia
Scrub typhus–mite bite–fever/severe headache–skin rash = covers body/eschar
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Important Clinical Diseases
� Q-Fever Group
�Coxiella burnetii - Q fever–inhale contaminated aerosol;
Prof. Muhammad Akram Hossain, Ricketssia
–inhale contaminated aerosol; resist dessication = up to 3 years outside host
–intermittent fever/pneumonia–NO skin rash
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Important Clinical Diseases
� Scrub Typhus Group�Rickettsia tsutsugamushi =
Scrub typhus
Prof. Muhammad Akram Hossain, Ricketssia
Scrub typhus–mite bite–fever/severe headache–skin rash = covers body/eschar
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Important Clinical Diseases
� Q-Fever Group
�Coxiella burnetii - Q fever–inhale contaminated aerosol;
Prof. Muhammad Akram Hossain, Ricketssia
–inhale contaminated aerosol; resist dessication = up to 3 years outside host
–intermittent fever/pneumonia–NO skin rash
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Important Clinical Diseases
� Trench Fever Group - transferred to Bartonella
�Rochalimaea quintana - Trench
Prof. Muhammad Akram Hossain, Ricketssia
�Rochalimaea quintana - Trench fever–body louse bite/feces–fever/headache/mild symptoms–skin rash - global
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Diagnosis of Rickettsial Diseases
� Rise in serum antibody/often do not develop in early stages
Prof. Muhammad Akram Hossain, Ricketssia 21
Treatment, Prevention, and Control
� tetracycline/chloramphenicol�vaccines under study/one=
Prof. Muhammad Akram Hossain, Ricketssia
Q fever�control =
insecticides/cleanliness
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