Diagnosis: case 3

The specialty tests indicate that the foal is suffering from subacute osteomyelitis 
with a resulting joint infection.  The bone infection is subacute since there is no evidence of 
a fever (a fever is seen with more advanced cases) and there is pain on palpation and gait 
abnormalities.  In foals, hematogenous osteomyelitis localizes in the metaphyseal vessels of 
the long bones in the extremities.  The cannon bone, the site of the radiographic lesions in 
this filly, certainly fits this category.  In neonates, the metaphyseal vessels still have 
vascular connections with the epiphyseal vessels, so there is always the possibility that the 
infection will spread from the bone into the adjacent joint space.  There is evidence of that 
process in this filly since the joint culture yielded a pure culture of Klebsiella pneumoniae.  
In humans, a joint infection with this organism usually indicates an underlying problem of 
urosepsis or abdominal sepsis, but there is no indication of these diseases in the filly.  In 
fact, the source of the Klebsiella is unknown, but there is the possibility that the filly 
obtained the bacteria at parturition since Klebsiella can be found in the mareÕs genital tract.  
Sources of hematogenous bacteria infection in foals include the umbilicus, respiratory tract, 
intestinal tract, or the mareÕs uterus.
	It takes 2-3 weeks before radiographic changes are evident with osteomyelitis.  
Since this foal is only 2 weeks old, it is likely that she obtained the infection in utero or 
shortly after birth.  The bacteria cause local abscesses and necrosis.  Bone necrosis is a 
result of the hostile conditions of decreased pH and pO2.  Abscess formation increases the 
local pressure, exacerbating the necrosis.  A hallmark of chronic osteomyelitis is sequestra 
(dead bone fragments) with the growth of the abscesses to the skin (cloaca).