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

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

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

Ovine enzootic abortion
Especially in intensive systems
Ewe lambs may acquire infection at birth, and abort in their first pregnancy
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
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
Also abortion in cattle, goats and pigs

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

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