Genus Ricksttsia.

Question 1

Classification

Answer 1

Family: Rickettsiaceae

Genus: Rickettsia

Typhus group

( 3 species)

Spotted fever group

SPECIES

R.rickettsii —> Rocky Mountain spotted fever (focus)

R.akari —> Rickettsial pox

Question 2

Rickettsia rickettsii

Answer 2

Rickettsia rickettsii

• Dermacentor ticks are both the vector and main reservoir
• transmission via tick bite

Question 3

Morphology

Answer 3

• gram negative rod

- pleomorphic

Question 4

Growth characteristics

Answer 4

• aerobic
• obligate intracellular parasite
• Fastidious: CoA and NAD+ needed for growth —> provided by the host

Question 5

Antigenic structure

Answer 5

Dominant outer membrane proteins:

• OMP A
• OMP B

Alkali stable polysaccharide

Shares antigens with proteus

• antigens cross react with OX strains of Proteus vulgaris (Weil-Felix reaction)

Question 6

Virulence factor

Answer 6

No toxins or virulence factors are known

Question 7

Disease

Answer 7

Rocky Mountain spotted fever

> rash does not start immediately —> incubation period of 2 days to 2 weeks
rash of different ages
rash progresses from the extremities —> spreads centrally

• fever
• headache
• myalgia

Question 8

Microbiological diagnosis

Answer 8

• antibody detection in serologic tests such as ELISA
• Weil-Felix test is no longer used
• Stain and culture are rarely performed

Question 9

Treatment and prevention

Answer 9

• tetracycline

Prevention

No vaccine

> protective clothing and prompt removal of ticks