Chlamydia Species - General Characteristics

Host adapted and non-host adapted species varying in virulence for different hosts
Species cause specific diseases in particular hosts
Respiratory, 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

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

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

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

sheep

Chlamydia sp.
- Sporadic or outbreaks of lamb polyarthritis
- High morbidity, low mortality
- Commonly together with conjunctivitis
- Most recover but may remain lame

cattle

Contents