Chlamydia Species - General Characteristics

Introduction

Chlamydia species include host adapted and non-host adapted species varying in virulence for different hosts. They can casue various diseases, including respiratory, enteric, pleural and reproductive diseases in animals and humans; specific conditions include conjunctivitis, arthritis, abortion, urethritis, enteritis, pneumonia, encephalomyelitis. Disease manifestation varies from subclinical to severe systemic infections - intestinal infections are often subclinical and persistent.Human infections are commonly acquired from infected birds with psittacosis or ornithosis, causing respiratory infections in the handler.

Bacterial Characteristics

• Obligate intracellular bacteria
• Gram negative bacteria with outer membrane, LPS, ribosomes, DNA and RNA
• Peptidoglycan cell wall resistant to lysozyme
• Only grow in presence of living eukaryotic cells
• Unable to synthesis ATP therefore require intermediates from host cells
• Not stained by Gram stain
• Two morphological forms
  • Elementary body, the infective extracellular form, which is small, metabolically inert and osmotically stable; surrounded by cytoplasmic membrane, outer membrane with LPS, but no peptidoglycan
  • Retiuculate body: larger, metabolically active, osmotically fragile
• Elementary body survives in the environment for several days

Pathogenesis and pathogenicity

• Elementary body enters host epithelial cells by receptor-mediated endocytosis
• Transformation into larger reticulate body within endosome; known as an inclusion
• Reticulate body divides by binary fission to form many new chlamydia cells
• Reticulate bodies mature and condense to form elementary bodies
• Elementary bodies released from dying host cells after about 72 hours to infect other cells
• Persistent infections can occur if replication delayed by environmental conditions such as presence of interferon gamma
• Many infections subclinical due to intracellular existence of chlamydia preventing inflammatory reactions
• Chronic infections may fail to induce an immune response, or may repeatedly stimulate the immune system, causing a delayed hypersensitivity reaction and tissue damage
• Prolonged faecal shedding of organisms
• Clinical infections occur in non-natural host species
• CLinical signs depend on route of infection and degree of exposure

Diagnosis

• Direct microscopy of smears and tissues e.g. organs from aborted foetuses, liver/spleen from avian cases
• Kosters (modified Ziehl-Neelsen) stain of placental smears shows small red rods
• Blue inclusions in cytoplasm of Giemsa-stained cells
• Methylene blue stain with darkfield microscopy
• Fluorescent antibody stain
• Antigen detection kits for diagnosis from swabs
• ELISA to detect Chlamydophila LPS
• Isolation in embryonated eggs and McCoy cells as well as animal tissues
• PCR to detect chlamydial DNA
• Serological tests: complement fixation, ELISA, indirect immunofluorescence

• May cause arthritis in sheep and arthritis in cattle

sheep

• Chlamydia sp.
  • Sporadic or outbreaks of lamb polyarthritis
  • High morbidity, low mortality
  • Commonly together with conjunctivitis
  • Most recover but may remain lame

cattle

• • Chlamydia sp.
    • Severe disease in young calves
    • High mortality
    • Can be seen in smears of synovial fluid from swollen joints
    • Oedematous and hyperaemic surrounding tissue
    • Possibly due to intrauterine infection