Rickettsia
27 October 2020 22:25
Rickettsiae:
The Rickettsiae are a diverse collection of obligately intracellular Gram-negative bacteria found in
ticks, lice, fleas, mites, chiggers, and mammals. They include the genera Rickettsiae, Ehrlichia,
Orientia, and Coxiella. These zoonotic pathogens cause infections that disseminate in the blood to
many organs.
General Features of Rickettsiae:
• Obligate intracellular pathogens
• Extremely small coccoids or rods (0.3 x 1 to 2micrometre)
• Has no flagella
• Cannot grow on microbiological media, some grow in embryonated eggs or in tissue culture
cells
• Structurally similar to gram negative cells (LPS & peptidoglycan cell walls)
• Multiply by binary fission but only in infected cells
• With the exception of Coxiella all transmitted by arthropod vectors (e.g. ticks, mites, lice,
fleas)
Diseases caused by Rickettsiae
Disease Agent Arthropod Vector
Rocky Mountain spotted fever Rickettsia rickettsii Wood tick
Rickettsial pox Rickettsia akari House mouse mites
Murine typhus Rickettsia typhii Rat flea
Epidemic typhus Rickettsia prowazekii Human body louse
Scrub typhus Orientia tsutsugamushi Chigger mites (mite larva)
Ehrlichiosis Ehrlichia chaffeenis Lone star tick
Q fever Coxiella burnetti None-spread by inhalation
Typhus
○ Caused by Rickettsia prowazekii
○ Arrived in Europe in 1489 via soldiers returning from Cyprus.
○ In 1557-1559 an outbreak in England killed 10% of the population
○ Transmitted by Pediculus humanus corporis (contamination with infected faeces during
feeding)
○ Incubation 7-14 days, high fever 40 degrees Celsius, chills, headache, may lead to coma.
○ Macular eruption (skin disease) 5-6 days after onset.
REMEMBER THE DIFFERENCE: TYPHUS VS TYPHOID (caused by two different bacteria)
Typhus: Cough, headache, joint and muscle pain, nausea, chills, confusion, low blood pressure
(Rickettsia typhi, prowazekii)
Rickettsia Page 1
27 October 2020 22:25
Rickettsiae:
The Rickettsiae are a diverse collection of obligately intracellular Gram-negative bacteria found in
ticks, lice, fleas, mites, chiggers, and mammals. They include the genera Rickettsiae, Ehrlichia,
Orientia, and Coxiella. These zoonotic pathogens cause infections that disseminate in the blood to
many organs.
General Features of Rickettsiae:
• Obligate intracellular pathogens
• Extremely small coccoids or rods (0.3 x 1 to 2micrometre)
• Has no flagella
• Cannot grow on microbiological media, some grow in embryonated eggs or in tissue culture
cells
• Structurally similar to gram negative cells (LPS & peptidoglycan cell walls)
• Multiply by binary fission but only in infected cells
• With the exception of Coxiella all transmitted by arthropod vectors (e.g. ticks, mites, lice,
fleas)
Diseases caused by Rickettsiae
Disease Agent Arthropod Vector
Rocky Mountain spotted fever Rickettsia rickettsii Wood tick
Rickettsial pox Rickettsia akari House mouse mites
Murine typhus Rickettsia typhii Rat flea
Epidemic typhus Rickettsia prowazekii Human body louse
Scrub typhus Orientia tsutsugamushi Chigger mites (mite larva)
Ehrlichiosis Ehrlichia chaffeenis Lone star tick
Q fever Coxiella burnetti None-spread by inhalation
Typhus
○ Caused by Rickettsia prowazekii
○ Arrived in Europe in 1489 via soldiers returning from Cyprus.
○ In 1557-1559 an outbreak in England killed 10% of the population
○ Transmitted by Pediculus humanus corporis (contamination with infected faeces during
feeding)
○ Incubation 7-14 days, high fever 40 degrees Celsius, chills, headache, may lead to coma.
○ Macular eruption (skin disease) 5-6 days after onset.
REMEMBER THE DIFFERENCE: TYPHUS VS TYPHOID (caused by two different bacteria)
Typhus: Cough, headache, joint and muscle pain, nausea, chills, confusion, low blood pressure
(Rickettsia typhi, prowazekii)
Rickettsia Page 1
