EAFL is commonly associated with bacterial infection of the inner placental sac (amnion), umbilical cord, and the foetus. Many different bacteria have been isolated with the most common isolates being bacteria that are normally present in the environment and that do not normally cause disease in horses.
It is not easy to diagnose EAFL. There are many causes of abortion and pregnancy loss in mares. Many of the changes that are seen on post mortem of EAFL cases (foetus and placental tissue) are fairly non-specific. Diagnosis therefore requires a complete post mortem examination of foetus and expelled placenta including gross examination and collection of samples for histology, bacteriology and virology. Other known causes of abortion need to be ruled out and a combination of typical changes seen in EAFL cases must be detected. Case definitions for confirmed and suspect cases have been published in the Australian Veterinary Journal (Todhunter et al 2009).
It is almost certain that many cases of EAFL are not diagnosed because a post mortem may not be done after a mare has aborted, or because only a limited post mortem may be done for example to rule out specific conditions such as equine herpes virus abortion (EHV). In these cases it is usually very difficult to be confident that EAFL may have been the cause.