Changes

*Especially in intensive systems

*Especially in intensive systems

*Ewe lambs may acquire infection at birth and abort in their first pregnancy

*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

**Infection via ingestion or inhalation causes a bacteraemia

*Necrosis of cotyledons and oedema of adjacent tissue, as well as dirty pink uterine discharge

**Bacteria localise in placenta and cause placentitis, leading to late abortion or premature weak lambs

*Aborted lambs well preserved

**Necrosis of cotyledons and oedema of adjacent tissue, as well as dirty pink uterine discharge

*Large numbers of chlamydiae shed in placenta and uterine discharges; survive in environment for several days

**Aborted lambs well preserved

*Abortion rates may reach 30% in susceptible flock

**Large numbers of chlamydiae shed in placenta and uterine discharges; survive in environment for several days

*Ewes infected late in pregnancy may not abort, but may abort during the next pregnancy

**Abortion rates may reach 30% in susceptible flock

*No other clinical signs in aborting ewes

**Ewes infected late in pregnancy may not abort, but may abort during the next pregnancy

*Fertility not impaired

**No other clinical signs in aborting ewes

*Survival of elementary bodies in faeces and wild birds are a source of infection from one lambing season to the next

**Fertility not impaired

*Ewes may be carriers for several years

*Venereal transmission from infected rams

**Survival of elementary bodies in faeces and wild birds are a source of infection from one lambing season to the next

*Some immunity develops after infection, protecting ewes from subsequent disease

**Ewes may be carriers for several years

*Live attenuated vaccines prior to breeding or inactivated vaccines during pregnancy

**Venereal transmission from infected rams

*Vaccines prevent infection but will not clear infection from persistently-infected animals

**Some immunity develops after infection, protecting ewes from subsequent disease

*Vaccination of ewe lambs prior to breeding

**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

*Treatment: long-acting oxytetracyclines during an outbreak to protect in-contact pregnant ewes

*Control: isolate aborted ewes; destroy placentas, thorough cleaning

*Control: isolate aborted ewes; destroy placentas, thorough cleaning