Page 654 - The Veterinary Care of the Horse

Pathophysiology

• The bacterium is inhaled or ingested.
VetBooks.ir • It colonizes the mucosa of the pharynx and tonsils and spreads to the lymph nodes of the

head and upper neck.

• Toxins and enzymes are released which cause severe tissue damage resulting in pain and
abscessation.

• The toxins cause the high temperature, depression and anorexia.

• The bacterium is surrounded by a capsule containing a special protein which prevents it
from being ingested and destroyed by white blood cells.

• Occasionally, the bacterium spreads via the bloodstream to other sites in the body
resulting in ‘bastard strangles’.

Which horses are particularly susceptible?

• The disease is particularly common in situations where groups of young horses are kept

together and new individuals are introduced regularly to the group.
• The resistance of the individuals to infection is decreased by poor management factors

such as inadequate feeding and parasite control measures. Mortality in these situations
can be 5–7%.

• Any factor causing chronic stress will make a population susceptible to strangles and
other diseases.

• Any situation in which many horses are in close proximity with a number moving on and

off the premises, e.g. racing stables, studs and livery yards, facilitates the spread of
disease.

When to call the vet

If you suspect strangles infection, contact your vet immediately. Early diagnosis and prompt
action reduces the risk of a large outbreak occurring.

Diagnosis

Diagnosis is made on the clinical signs. It is confirmed by isolation of Streptococcus equi

from swabs taken from the nasopharynx, guttural pouches or burst abscesses. Blood tests are
not usually necessary. If they are taken they reveal a high total white cell count with a

marked neutrophilia. Plasma fibrinogen, amyloid A and globulins are also likely to be raised.