Chlamydia and Chlamydophila species

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BACTERIA



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 ornithosis, 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
  • Epidemiology:
    • Many wild and domestic birds susceptible
    • Organisms present in respiratory secretions and faeces of infected birds
    • Infection via inhalation or ingestion
    • Subclinical infection common
    • Intermittent shedding for prolonged periods
    • Stress precipitates disease outbreaks
  • Clinical signs:
    • Generalised infection affecting intestinal and respiratory tracts
    • Up to 10 day incubation period
    • Loss of condtion, oculonasal discahrge, diarrhoea and respiratory distress depending on strain
    • Hepatomegaly, airsacculitis and peritonitis
  • Diagnosis: stained smears, immunohistochemistry, ELISA, PCR, isolation, antibody detection by ELISA and complement fixation
  • Treatment: tetracyclines for several weeks
  • Control: quaranteen imported birds and give tetracyclines; good husbandry
  • Involved in feline rhinotracheitis together with herpes virus 1
  • Zoonotic by aerosol infection - can cause systemic disease with pneumonia, meningitis or meningoencephalitis


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 chlamydiosis
  • 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


Chlamydophila pecorum

  • Common inapparent intestinal infection of cattle
  • Conjunctivitis and arthritis
  • Sporadic bovine encephalomyelitis:
    • Usually in cattle under 3 years
    • Fever, incoordination, depression, excessive salivation, diarrhoea
    • Recumbency and opisthotonos before death
    • Up to 50% mortality
    • Vacular damage in brain
    • Serofibrinious peritonitis
    • Treat with high doses tetracyclines and tylosin


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