Chlamydia and Chlamydophila species
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
Chlamydophila pecorum
- Neurological disease
- Common intestinal infection of cattle
- 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
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