Obligate intracellular bacteria Chlamydia Rickettsiae Ehrlichia

1. Sum 07
Obligate intracellular bacteria
1. Chlamydia
2. Rickettsiae
3. Ehrlichia

2. Sum 07
Chlamydia : Basics
• Two genera with three important species
– Chlamydia
• C. trachomatis
– Chlamydophila
• C. psittaci
• C. pneumoniae (TWAR)

3. Sum 07
Species Serotype Disease in humans
C.Trachomatis
A,B,C Trachoma
D-K Cervicitis
Urethritis
Proctitis
Conjunctivitis
Pneumonia (in
neonates)
L1,L2,L3 LGV

4. Sum 07
Trachoma
• Trachoma is the most common cause of
potentially preventable blindness in the world
• Endemic in Middle East, North Africa, India
• Transmitted eye-to-eye via droplet nuclei,
contaminated hands, flies
• Serotypes A,B and C
• Begins as follicular conjunctivitis inflammation
of conjunctiva 
• Scarring causes eyelids to turn in 
• Corneal abrasion, ulceration, and pannus
formation (blood vessels invade cornea) 
• Blindness

5. Sum 07
Trachoma
Thickened
Eyelashes turned in and cells infiltrated into cornea as inflammation
Conjunctivitis

6. Sum 07
Chlamydia trachomatis
• Most common cause of STD in USA.
• Often asymptomatic
– 80% of infected women are asymtomatic
– 25% of infected men are asymptomatic
• In males:
– Responsible for 50% of nonspecific urethritis
– Patients present with
• Dysuria (painful urination) and a
• Thin watery discharge containing
• Numerous neutrophils but no bacteria (on
Gram staining)
– “neutrophils without bacteria”

7. Sum 07
Thin watery discharge
associated
with C. trachomatic
urethritis

8. Sum 07
Chlamydia vs. Gonorrhea

9. Sum 07
Chlamydia trachomatis
• In females:
– PID
– Urethritis and cervicitis
– Cervical involvement is the source of
conjunctivitis in newborns
• (most common cause of ophthalmia
neonatorum)

10. Sum 07
Chlamydia trachomatis
• In newborns:
– Conjunctivitis (ophthalmia neonatorum).
• Conjunctivitis in newborns:
– Ist 24-48 hrs after birth  chemical
conjunctivitis
– 2-5 days ; bilateral  N.gonorrhoea
– 2-5 days ; unilateral  Staph aureus
– After 5-7 days ; bilateral  Chlamydia
trachomatis (MCC of ophthalmia
neonatorum)

11. Sum 07
Interstitial pneumonia caused by Chlamydia
trachomatis
• Occurs in 10-20% of newborns who pass
through an infected birth canal.
• Patients present with:
– Rhinitis followed by “staccato” cough –
very short and sharp
– Tachypnea
– Conjunctivitis
– Eosinophilia on peripheral blood

12. Sum 07
Lymphogranuloma venereum (LGV)
• Sexually transmitted chronic ulcerative disease
• Caused by C.trachomatis serotypes L1, L2, and
L3.
• Primary lesion : papule or an ulcer on the genital
mucosa or nearby skin.
• Infection of the draining lymphnodes occurs
causing swollen, tender lymphadenopathy.
• Inguinal lymphadenopathy
– usually unilateral
– groove sign due to enlargement of both the
femoral and inguinal nodes.
• Dissemination to rectum  proctitis.
• Abscess may form in the LN  may rupture.

13. Sum 07
Lymphogranuloma venereum
Unilaterally enlarged LN,
note groove sign
Groove Sign

14. Sum 07
Other Chlamydia
• C . psittaci  ornithosis or psittacosis
– A zoonosis due to inhalation of C. psittaci
from psittacine bird (parrots, paraketes)
– Infection results in interstitial pneumonia
• C.pneumoniae  interstitial pneumonia

15. Sum 07
Rickettsial diseases

16. Sum 07
Rickettsiae
• Are small , obligate intracellular parasites.
• All transmitted to humans by arthropods
(except: Coxiella burnetii :air-borne)
• All have vertebrate reservoirs (except epidemic
typhus)
• Replicate in cytoplasm of endothelial cells.
• Injure endothelial cells  hemorrhagic vasculitis
 petechial rash.
• Typical clinical symptoms of rickettsial infection:
– fever, headache and rash.

17. Sum 07
Rocky Mountain Spotted Fever( RMSF)
• Most common rickettsial disease in U.S.
• Common along the East Coast
• Caused by Rickettsia rickettsii.
• Transmitted by hard tick : Dermacentor
andersoni (dog tick)
• Pathogenesis –
– R. rickettsii invade and replicates in endothelial
cells causing Hemorrhage  rash
– Hemorrhage  hypovolemia  reduced perfusion
 organ failure

18. Sum 07
Rocky Mountain Spotted Fever( RMSF)
• Follows tick bite by 2-14 days (avg = 7)
• Onset – fever, chills, headache, myalgias
– Rash develops after 3 days
– Starts on extremities, spreads to trunk
– Palms and soles may be involved (syphilis and
meningococcemia also)
• Three classic diagnostic features of RMSF
– rash, fever and history of tick bite.

19. Sum 07
Rocky Mountain Spotted Fever
• Other clinical features:
– Severe headache, photophobia, pain when
moving eyes
– Conjunctival suffusion and periorbital
edema are important clinical clues
especially if associated with edema/ rash
of hands and feet
• Complications:
– Pulmonary edema  ARDS  cause of
death.

20. Sum 07
Dog tick
Tick embedded in the skin

21. Sum 07
RMSF Rashes

22. Sum 07
Rash of rocky mountain spotted fever on the
hands and forearms.

23. Sum 07
Epidemic Typhus
• Caused by Rickettsia prowazekii
• Transmitted by: human body louse (Pediculus
corporis).
• Occurs in crowded unsanitary conditions, usually
war and natural disasters
• Rickettsiae proliferate at the site of bite 
blood  infect vascular endothelium.
• Patients develop fever, headache and rash
(generalized)
– face, palms, and soles are spared

24. Sum 07
Epidemic Typhus
• Other features include:
– Encephalitis (typhus nodule)
– Gangrene of skin (tips of finger, nose,
earlobes, scrotum , penis etc).

25. Sum 07Human body louse

26. Sum 07
Coxiella burnetii (Q fever)
• The only Rickettsiae transmitted without a
vector.
• Transmission  inhalation
• At risk people:
– Dairy farmers and vets associated with the
birthing process of infected sheep, cattle and
goat.
• Clinical findings:
– High fever, chest pain and myalgias
– Interstitial pneumonia
– Granulomatous hepatitis
– Infective endocarditis

27. Sum 07
Coxiella – The Exceptions
• Airborne rather than arthropod bite
• Proliferate in respiratory tract rather than
endothelium
• Extraordinarily stable in the environment,
unlike the Rickettsiales

28. Sum 07
Ehrlichia – Ehrlichiosis
• Intracellular parasite of granulocytes and
monocytes
• Ehrlichiosis : two forms
1.Human Monocytic Ehrlichiosis (HME)
2.Human Granulocytic Ehrlichiosis (HGE)

29. Sum 07
Ehrlichiosis
• Human monocytic ehrlichiosis:
– Caused by E.chaffeensis
– Vector : lone star tick
– Reservoir – White-tailed deer
• Human granulocytic ehrlichiosis:
– Caused by two species of Ehrlichia
• E.ewingii and E.phagocytophilia
– Vector – Ticks (Ixodes)
– Reservoir – Small mammals
• Clinical disease: Both diseases : resembles RMSF
• Diagnosis: Giemsa stained PS
– Intracellular organisms called morulae

30. Sum 07
Ehrlichiosis (Ehrlichia chaffeenis)
morula within monocyte