Topic 1: Introduction to Rickettsia and Chlamydia

Question 1

• List the key differences between the rickettsia and chlamydia
Site of multiplication

Answer 1

Rickettsia: Cytoplasm of cell

Chlamydia: Cytoplasm of cell

Question 2

• List the key differences between the rickettsia and chlamydia
Mode of replication

Answer 2

Rickettsia: Fission with cross-wall formation daughter cells with infectivity of parent cell
Generation time ~ 18 hrs.

Chlamydia: They have a defined developmental cycle. Infectious elementary body (small infectious form) infects call forms larger reticulate body (that is non-infectious), which divides by fission and is ultimately reorganised to form small progeny elementary bodies.
Generation time ~ 30 hrs.

Question 3

• List the key differences between the rickettsia and chlamydia
Size

Answer 3

Rickettsia: Size 250 x 600 nm or longer

Chlamydia: Infectious elementary bodies 250 – 350nm diameter.
Non-infectious reticulate body 600 – 1000 nm diameter.

Question 4

• List the key differences between the rickettsia and chlamydia
Dependence on host cell for energy requirements

Answer 4

Rickettsia: Limited dependence on host cell Chlamydia: Extreme dependence on host

Question 5

• List the key differences between the rickettsia and chlamydia
Susceptibility to antibiotics affecting 70S ribosome function

Answer 5

Rickettsia: Yes, preferably tetracycline

Chlamydia:
Tetracyclines: yes
Streptomycin: no (bus does prevent absorption to cell)

Question 6

• List the key differences between the rickettsia and chlamydia
Biological vectors

Answer 6

Rickettsia: Transmitted by arthropods and arthropods are natural host

Chlamydia: Arthropods are not involved in transmission

Question 7

• List the key differences between the rickettsia and chlamydia
Antigenic characteristics

Answer 7

Rickettsia:
No cross-reaction with chlamydia
No common antigen – species within the same genus often do cross-react antigenically

Chlamydia:
No cross-reaction with rickettsia
The species share common LPS antigens.

Question 8

2. Describe the mode of transmission of the rickettsia and how it differs from chlamydia
   Rickettsia

Answer 8

• Multiplies in arthropods such as:
  • Insects: lice and fleas
  • Arachnids: ticks and mites
• Infection occurs through bites
• Special relationship to the Rickettsiales to the blood-forming organs, circulatory system and leucocytes
• Facilitates transfer by biting arthropods

Question 9

2. Describe the mode of transmission of the rickettsia and how it differs from chlamydia
   Chlamydia

Answer 9

• Low pathogenicity except when animals are stressed
• Diseases produced can run chronic courses
• Individuals infected for prolonged periods
• Commonly found in:
  • Birds
  • Humans
  • Koalas
  • Rumen (sheep & cows)
  • Cats

Question 10

3. List the two families within the Rickettsiales and explain how the difference in affinity for cells leads to disease expression
   Order: RICKETTSIALES
   Family: Rickettsiaceae

Answer 10

• Affinity for lymphoreticular endothelia or leucocytic cells that results in:
  • Lymphoreticular hyperplasia (rapid growth proliferation of normal cells that resemble lymph tissue.
  • Signs of vascular damage such as haemorrhages or effusion (occurs without an external blow or sudden movement and is related to an inherent or natural defect in the wall of the artery)
• Common names for these diseases are:
  • Spotted
  • Petechial (pinpoint, round spots that appear on the skin as a result of bleeding)

Question 11

3. List the two families within the Rickettsiales and explain how the difference in affinity for cells leads to disease expression
   Order: RICKETTSIALES
   Family: Anaplasmataceae

Answer 11

• Affinity for RBC
• Associated with damage to RBC resulting in:
  • Anaemia
  • Haemogloburina

Question 12

4. Be able to explain the clinical signs and distribution of cattle tick fever
   Anaplasma marginale (cattle tick fever)
   • Clinical Signs

Answer 12

• Mild fever
• Anaemia
• Jaundice
• Can take months to recover
• Can be transmitted by:
  • Castration
  • Spay
  • Multiple use of same instruments/needles

Question 13

4. Be able to explain the clinical signs and distribution of cattle tick fever
   Anaplasma marginale (cattle tick fever)
   • Distribution

Answer 13

• Northern areas of Australia
  • Kimberly’s
  • Northern Territory
  • Queensland (coastal regions)

Question 14

5. List the chlamydial species endemic to Australia

Answer 14

• Chlamydophila pneumoniae

• Chlamydophila psittaci
- For Aves species:
• Turkeys (ornithine species): omithosis
• Birds (Psittacine species): psittacosis

•	Chlamydophila pecorum
-	Seen in:
•	Pigs
•	Koalas
•	Rumen (sheep & cattle)

• Chlamydophila felis
- Seen in
• Cats

Question 15

6. Describe the main chlamydial diseases seen in Australia including avian chlamydiosis (and zoonotic aspects) and the diseases caused by C. pecorum
   • Chlamydophila pneumoniae

Answer 15

– Widespread in koalas but not a significant cause of disease.
– Occasional respiratory disease manifest by rhinitis, coughing,
– Sneezing, serous nasal discharge.

Question 16

6. Describe the main chlamydial diseases seen in Australia including avian chlamydiosis (and zoonotic aspects) and the diseases caused by C. pecorum
   • Chlamydophila psittaci

Answer 16

• For Aves species:
  • Turkeys (ornithine species): omithosis
  • Birds (Psittacine species): psittacosis
• C. psittaci seems to have only low pathogenicity and a feature of infections is that clinical disease is often precipitated by stress.
• C. psittaci is zoonotic and considerable care should be taken when handling animals suspected of having a chlamydial disease.
• The principal method of transmission of chlamydia is through direct contact of susceptible animals with infected animals or fomites.
• Inhalation of aerosols containing dried faecal or nasal excrement is also possible.

Question 17

6. Describe the main chlamydial diseases seen in Australia including avian chlamydiosis (and zoonotic aspects) and the diseases caused by C. pecorum
   • Chlamydophila pecorum

Answer 17

• Seen in:
  • Pigs
  • Koalas
  • Rumen (sheep & cattle - sporadic bovine encephalomyelitis (SBE))
• Cause of polyarthritis in sheep/lambs (systemic infection of sheep with localisation of organisms in serous membranes)
• Also linked to sporadic and small outbreaks of ovine abortions
• Clinical signs can include fever, in appetence, depression and death but can be vague.
• Calves become uncoordinated and stagger, circle, or fall over objects
• Morbidity rates are most commonly <25%, but can reach 50%.
• The mortality rate can approach 30% and is highest in calves
• Lesions are not limited to the brain; vascular damage can be seen in several organs.

Question 18

6. Describe the main chlamydial diseases seen in Australia including avian chlamydiosis (and zoonotic aspects) and the diseases caused by C. pecorum
   • Chlamydophila felis

Answer 18

• Seen in
  • Cats
• In cats, the incubation period after exposure to an infected cat ranges from 3 to 10 days. Signs can include serous to mucopurulent conjunctivitis, nasal discharge, and sneezing
• Although the disease in cats has been referred to as feline pneumonitis, chlamydiae rarely cause pneumonia in cats.
• Transmission occurs as a result of direct, close contact between cats, because the organism survives poorly in the environment.
• Chlamydial conjunctivitis in cats should be differentiated from conjunctivitis caused by feline herpes virus 1 and feline calicivirus
• Vaccines are available