Rickettsiae

Question 1

What are bacteriological features of Rickettsiae?

Answer 1

•	Gram negative bacteria
•	Obligate intracellular pathogens 
–	I.E. NEED LIVING CELLS TO SURVIVE 
–	IF YOU WANT TO CULTURE THEM NEED LIVING CELLS TOO!	
–	Arthropod vector
–	Peptidoglycan cell wall
The overall group includes the genera 
–	Rickettsiae 
–	Orientia

Question 2

What is the host range of Rickettsiae?

Answer 2

• Wide host range: different species are associated with various insects, birds and mammals

Question 3

How can Rickettsiae spread?

Answer 3

• SPREAD: Transmitted from a vertebrate host by an insect, e.g., body louse, rat flea, tick, mite

Question 4

What is the epidemiology of Rickettsiae?

Answer 4

The “spotted fever” group of rickettsial diseases are mainly confined to the Americas (e.g., Rocky Mountain Spotted Fever) and the Far East

In Continental Europe particularly in times of war, rickettsial infections, especially “epidemic typhus” may occur (unsanitary conditions, famine, evacuation into emergency camps)

Question 5

What is the clinical presentation of Rickettsiae?

Answer 5

• Multiply at the site of inoculation from which they disseminate throughout the body –with localisation in the endothelial cells of small blood vessels
• Clinically all present with fever, headache, and intense myalgias, often in association with rash and organ involvement
• GI symptoms common
• RMSF – overall mortality 4% (even with treatment)
• Epidemic typhus – 20% - 50% mortality (untreated)
Tropism for endothelial cells that line blood vessels - in Rocky Mountain Spotted fever- localise to the vascular smooth muscle cells.
Rickettsiae microorganisms appear to exert their pathologic effects by adhering to and then invading the endothelial lining of the vasculature within the various organs affected.
(UNLIKE CHLAMYDIA)

Question 6

What is the diagnosis of Rickettsiae?

Answer 6

• Serology

– 4 fold rise in titres

Question 7

What is the treatment of Rickettsiae?

Answer 7

– Doxycycline

Question 8

What’s you diagnosis? 20 year old hill walker:
Just back from holidays in US
Spent the holiday walking and camping in forests – cant remember if he got any bites
Has a petechial rash that began on his ankles and wrists and then spread to the trunk.

Answer 8

RMSF