Foal-Specific Foci of Sepsis
In adult horses the umbilicus has atrophied as have the umbilical arteries, vein, and urachus. In foals, however, normal regression takes up to two weeks after birth (Whitcomb 2013). Until then the structures receive blood flow, although limited, and are exposed to the external environment at birth. This opening to the extracorporeal environment provides a good site for a nidus of infection to develop. In addition, ill foals can develop a patent urachus, in which a previously closed urachus reopens, providing another site for bacteria to enter the body (Knottenbelt et al 2004). Hematogenous spread of bacteria into the umbilical vessels can lead to abscessation of the vessels or the liver. Another area of foal-specific disease localization is the joints and physes, as foals are predisposed to developing septic arthritis and epiphysitis compared to adult horses. This is due to the anatomy of the blood vessels in the subchondral bone of both the physis and the epiphysis which allows septic emboli to lodge therein (Knottenbelt et al 2004). Clinical signs of septic arthritis / epiphysitis are lameness, joint or leg swelling, and pain on palpation of the area. Finally, there is an increased incidence of bacterial meningitis in foals compared to adults secondary to sepsis (Knottenbelt et al 2004). This most likely occurs due to septic invasion into the central nervous system in cases with systemic sepsis as the bacterial causes are the same types of bacteria associated with neonatal sepsis. Clinical signs of meningitis include lethargy, recumbency, fever, cervical pain, and seizures.