Chlamydia and Chlamydophila species

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Chlamydophila psittaci involved in feline rhinotracheitis together with herpes virus 1 C.psittaci more frequently infects the conjunctival epithelium -> chronic conjunctivitis, see feline chlamydiosis

• May cause arthritis in sheep and arthritis in cattle

Overview

• Host adapted and non-host adapted species varying in virulence for different hosts
• Different species cause specific diseases in particular hosts
• Repsiratory, enteric, pleural and reproductive diseases in animals and humans
• Intestinal infections often subclinical and persistent

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
• Grow in embyonated eggs and McCoy cells as well as animal tissues
• Not stained by Gram stain
• Kosters (modified Ziehl-Neelson, small red rods) or fluorescent antibody stain required for detection
• Blue inclusions in cytoplasm of Giemsa-stained cels
• Antigen detection kits for diagnosis from swabs
• 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
• 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

Chlamydophila psittaci

• Causes notifiable psittacosis in birds

Chlamydophila abortus

• Ovine enzootic abortion
• Contagious ovine abortion in late pregnancy
• Infection via ingestion or inhalation causes a bacteraemia
• Bacteria localise in placenta and cause placentitis, leading to abortion
• Abortion rates may reach 30%
• Fertility not impaired
• Survival of elementary bodies in faeces and wild birds are a source of infection from one lambing season to the next
• Ewes may be carriers for several years
• Venereal transmission from infected rams
• Some immunity develops after infection, protecting ewes from subsequent disease
• Vaccines prevent infection but will not clear infection from persistently-infected animals
• Vaccination of ewe lambs

Chlamydophila felis

• Host adapted species in cats
• Feline interstitial pneumonia and conjunctivitis
• Diagnosis by antigen detection in ocular/nasal secretions - ELISA, PCR, Kosters, fluorescent antibody test
• Vaccine