Listeriosis is of greatest clinical significance in ruminants,
but monogastrics can also be affected. (See the report of septicemia
in a foal in the references.)
Infection usually occurs via ingestion of the organism from
feed/environment. It can also enter through the nasal mucosa,
conjunctiva and wounds.
Clinical presentations in animals include:
- encephalitis ("circling disease")
- This is the most common form of listeriosis in cattle, sheep
and goats.
- signs include circling, facial paralysis, nystagmus, dysphagia,
head pressing and blindness.
- high mortality
- abortion
- Replication across the placenta >>> aspiration and
infection of the fetus >>> abortion.
- septicemia
- much more common in neonates than adults
- mastitis
- There may be prolonged shedding in the milk and this can
be an important source for infection of humans.
- The 2002 USDA NAHMS study found that 6.5% of farms tested
had L. monocytogenes present in their bulk tanks when
sampled.
