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
• Species cause specific diseases in particular hosts
• Repsiratory, enteric, pleural and reproductive diseases in animals and humans
• Conjunctivitis, arthritis, abortion, urethritis, enteritis, pneumonia, encephalomyelitis
• Manifestation varies from subclinical to severe systemic infections
• Intestinal infections often subclinical and persistent
• Human infections usualy acquired from infected birds, causing psittacosis or ornthosis, causing respiratory infections

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

Chlamydophila psittaci

• Causes notifiable psittacosis in birds

Chlamydophila abortus

• Ovine enzootic abortion
• Especially in intensive systems
• Ewe lambs may acquire infection at birth and abort in their first pregnancy
• Pathogenesis:
  • Infection via ingestion or inhalation causes a bacteraemia
  • Bacteria localise in placenta and cause placentitis, leading to late abortion or premature weak lambs
  • Necrosis of cotyledons and oedema of adjacent tissue, as well as dirty pink uterine discharge
  • Aborted lambs well preserved
  • Large numbers of chlamydiae shed in placenta and uterine discharges; survive in environment for several days
  • Abortion rates may reach 30% in susceptible flock
  • Ewes infected late in pregnancy may not abort, but may abort during the next pregnancy
  • No other clinical signs in aborting ewes
  • Fertility not impaired
• Transmission:
  • 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
• Vaccination:
  • Live attenuated vaccines prior to breeding or inactivated vaccines during pregnancy
  • Vaccines prevent infection but will not clear infection from persistently-infected animals
  • Vaccination of ewe lambs prior to breeding
• Treatment: long-acting oxytetracyclines during an outbreak to protect in-contact pregnant ewes
• Control: isolate aborted ewes; destroy placentas, thorough cleaning
• Also abortion in cattle, goats and pigs
• Serious infection in pregnant women

Chlamydophila felis

• Host adapted species in cats
• Feline conjunctivitis, rhinitis and rarely interstitial pneumonia
• Epidemiology
  • Up to 10% cats infected
  • Infection via contact with conjunctival or nasal secretions
  • Infection may persist with prolonged shedding and clinical relapses
  • Stress of parturition and lactation may cause shedding of organisms leading to transmission to offspring
• Clinical signs:
  • Incubation period 5 days
  • Conjunctival congestion, clear ocular discharge, blepharospasm
  • May have sneezing and nasal discharge
  • Resolves within a few weeks, or causes persistent infection
• Diagnosis:
  • Intracytoplasmic inclusions in stained conjunctival smears
  • Antigen detection in ocular/nasal secretions - ELISA, PCR, Kosters, fluorescent antibody test
• Modified live vaccines reduce clinical signs but do not prevent infection or shedding

Diagnosis

• Direct microscopy of smears and tissues e.g. organs from aborted foetuses, liver/spleen from avian cases
• Kosters (modified Ziehl-Neelson) 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 embyonated eggs and McCoy cells as well as animal tissues
• PCR to detect chlamydial DNA
• Serological tests: complement fixation, ELISA, indirect immunofluorescence