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

Chlamydia species are obligate intracellular Gram negative bacteria with ribosomes, DNA and RNA and an outer membrane containing lipopolysaccharides (LPS). The peptidoglycan cell wall is resistant to lysozymes.

These bacteria only grow in the presence of living eukaryotic cells as they are unable to synthesise ATP therefore requiring intermediates from host cells. There are 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

The 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