Rickettsial Family

Prof. Md. Akram Hossain

1Prof. Muhammad Akram Hossain, Ricketssia

� 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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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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Compliments of the CDC

Prof. Muhammad Akram Hossain, Ricketssia 13

Compliments of the CDC

Prof. Muhammad Akram Hossain, Ricketssia 14

Compliments of the CDC

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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

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Treatment, Prevention, and Control

� tetracycline/chloramphenicol�vaccines under study/one=

Prof. Muhammad Akram Hossain, Ricketssia

Q fever�control =

insecticides/cleanliness

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Pathogenesis: Ehrlichia

� Tick bite (deer or dog)� Invasion of white cells: lymphocytes,

neutrophils, monocytes

Prof. Muhammad Akram Hossain, Ricketssia

neutrophils, monocytes� 20% of patients show rash� Lymph nodes up, high fever, headache,

malaise, myalgia� Treat with doxycycline

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